Many people question what the difference is between flared ports and slot ports. There are fairly basic differences between the two, and depending on your situation, one might suit you better than the other. The common purpose of the two ports is that they must be the correct length for the particular subwoofer box to achieve the desired sub box tuning. There are a few differences that may help in your decision between flared and slot ports for your custom subwoofer box.
Showing posts with label Box Building. Show all posts
Showing posts with label Box Building. Show all posts
PORT DESIGN INFORMATION
WHY GO PORTED?
Efficiency is the easiest one word reason for choosing ported over a sealed box. Everything is better with a little efficiency sprinkled on it. Ask any motor builder what they would do to a motor if it were theirs and they'd say turbo charge it! What does turbo charging do for an engine? It raises the efficiency. Why not apply this same thing to your audio system. Making the most out of the air space you have for a subwoofer enclosure, is the first step in raising the efficiency of your system. This means that you will utilize this space in the most efficient manner possible.
Designing a ported a.k.a. vented enclosure will not only give you added output, but can give you more low-frequency extension. This means louder and lower! Since the speaker system is the least efficient part of the whole audio chain, would it not make sense to make it as efficient as possible? Of coarse it does.
MORE SOUND, BETTER BASS
This is why venting is basically free output, and free sound quality. Local shops tell you that a small sealed box is the best way to go? Hit up your local hi-end home audio store and find out how many of those $20,000.00 pairs of speakers are sealed designs. You won't find many. Think efficiency, this will help you clear all of that smoke out of your eyes that most car audio manufacturers have been pumping all along.
HOW DOES A PORT WORK
Think of a box port not as a vent in the terms of a venting path for air to travel into and out of a box, but rather as extra cone area that is propagating acoustic energy from the enclosure to the cabin. The air in a port is fixed; it is trapped within the confines of the port walls. When the cone moves there is a corresponding change to the pressure in the box, that pressure change then causes the trapped air in the port to move either forward or backward. It moves as a solid unit, just like a speaker cone does. When you build a properly vented enclosure, its kind of like a two for one special! Since the port is essentially another woofer!
MORE RADIATING AREA
A passive radiator and a vented port work on the same theory. When a port mass moves back and forth, a pressure wave (sound wave) is sent into the cabin. The larger the port, the larger the radiating area is that creates the pressure. Tuning a port is tuning the mass of the trapped air in the port to the air mass in the box volume.
For all out no holds barred SPL efficiency, rule of thumb is the larger the box, the higher the output. The larger the box, the larger the ports can be for a given frequency tuning range. There is no substitute for cubic inches. Some drivers can achieve high efficiency in moderate sized vented enclosures (3 to 4 cubic feet) but will continue to increase in output with increase in volume and port size. Multiple drivers in such enclosures can yield a frightening amount of output and should be used with caution.
THE RIGHT PORT AREA
Most modeling programs that simulate box responses were written for home audio use. They are not suited for high output systems. The port area defaults are inadequate. The port area must be commensurate with cone area. If the port velocity gets too high, the port no longer functions as a port, you end up with a leaky sealed box, double bad.
Lets say we have a 12 inch speaker in a box, roughly 100 sqin of surface area. Many programs and manufacturer sites will suggest a 4" diameter port for a 12" vented box. A 4" diameter port has about 12 sqin of area. This is about an 8-1 ratio of cone area to port area. If the 12 inch cone moves 0.25", the port must move 2.0". It can handle this, but when the cone is moving 1.0", the port must move 8 inches! Now you've got a leaky sealed box.
You need more port area for a clean sounding, high output system. The perfect port formula is this: 16 sqin of port area per cubic foot of box volume. The port should be 16 inches long. Remember, the port is tuned to the box volume, not the sub(s).
This formula was derived from 1000s of hours of in-car testing and 1000s of installs. It works. It takes into account the need for increasing port area for increasing cone area. When combined with the correct box requirements, you'll end up with the perfect match.
VARIABLE PORT TUNING
The design philosophy of low moving mass, well controlled suspension and strong, linear magnetic systems allow the user many design applications never realized with traditional speakers. The growing popularity of the SPL competitions has led to new engineering requirements for an audio system.The problem lies in the fact that the frequencies where a vehicles peak SPL may occur rarely ever coincide with a tuning frequency that promotes utmost sound quality. The peak SPL frequency is usually somewhat higher that the tuning frequency for sound quality.
The use of a larger than normal port will allow the user to find the cars peak frequency for greatest SPL. Reducing the port opening will lower the box tuning frequency and provide loading to the woofer over a wider bandwidth. This will improve the transient response and impact of the system. The higher tuning frequency redirects the woofers radiating energy into a narrow band which when tuned to coincide with the vehicles peaks can yield dramatic SPL numbers. The focus of attention here should be to tune the system to each application. Although the general box recommendation will yield very satisfying results, competing at the highest levels of SPL or SQ contests, or simply yielding the best possible results are directly related to methodical tuning.
Click Here to Read More..
Efficiency is the easiest one word reason for choosing ported over a sealed box. Everything is better with a little efficiency sprinkled on it. Ask any motor builder what they would do to a motor if it were theirs and they'd say turbo charge it! What does turbo charging do for an engine? It raises the efficiency. Why not apply this same thing to your audio system. Making the most out of the air space you have for a subwoofer enclosure, is the first step in raising the efficiency of your system. This means that you will utilize this space in the most efficient manner possible.
Designing a ported a.k.a. vented enclosure will not only give you added output, but can give you more low-frequency extension. This means louder and lower! Since the speaker system is the least efficient part of the whole audio chain, would it not make sense to make it as efficient as possible? Of coarse it does.
MORE SOUND, BETTER BASS
This is why venting is basically free output, and free sound quality. Local shops tell you that a small sealed box is the best way to go? Hit up your local hi-end home audio store and find out how many of those $20,000.00 pairs of speakers are sealed designs. You won't find many. Think efficiency, this will help you clear all of that smoke out of your eyes that most car audio manufacturers have been pumping all along.
HOW DOES A PORT WORK
Think of a box port not as a vent in the terms of a venting path for air to travel into and out of a box, but rather as extra cone area that is propagating acoustic energy from the enclosure to the cabin. The air in a port is fixed; it is trapped within the confines of the port walls. When the cone moves there is a corresponding change to the pressure in the box, that pressure change then causes the trapped air in the port to move either forward or backward. It moves as a solid unit, just like a speaker cone does. When you build a properly vented enclosure, its kind of like a two for one special! Since the port is essentially another woofer!
MORE RADIATING AREA
A passive radiator and a vented port work on the same theory. When a port mass moves back and forth, a pressure wave (sound wave) is sent into the cabin. The larger the port, the larger the radiating area is that creates the pressure. Tuning a port is tuning the mass of the trapped air in the port to the air mass in the box volume.
For all out no holds barred SPL efficiency, rule of thumb is the larger the box, the higher the output. The larger the box, the larger the ports can be for a given frequency tuning range. There is no substitute for cubic inches. Some drivers can achieve high efficiency in moderate sized vented enclosures (3 to 4 cubic feet) but will continue to increase in output with increase in volume and port size. Multiple drivers in such enclosures can yield a frightening amount of output and should be used with caution.
THE RIGHT PORT AREA
Most modeling programs that simulate box responses were written for home audio use. They are not suited for high output systems. The port area defaults are inadequate. The port area must be commensurate with cone area. If the port velocity gets too high, the port no longer functions as a port, you end up with a leaky sealed box, double bad.
Lets say we have a 12 inch speaker in a box, roughly 100 sqin of surface area. Many programs and manufacturer sites will suggest a 4" diameter port for a 12" vented box. A 4" diameter port has about 12 sqin of area. This is about an 8-1 ratio of cone area to port area. If the 12 inch cone moves 0.25", the port must move 2.0". It can handle this, but when the cone is moving 1.0", the port must move 8 inches! Now you've got a leaky sealed box.
You need more port area for a clean sounding, high output system. The perfect port formula is this: 16 sqin of port area per cubic foot of box volume. The port should be 16 inches long. Remember, the port is tuned to the box volume, not the sub(s).
This formula was derived from 1000s of hours of in-car testing and 1000s of installs. It works. It takes into account the need for increasing port area for increasing cone area. When combined with the correct box requirements, you'll end up with the perfect match.
VARIABLE PORT TUNING
The design philosophy of low moving mass, well controlled suspension and strong, linear magnetic systems allow the user many design applications never realized with traditional speakers. The growing popularity of the SPL competitions has led to new engineering requirements for an audio system.The problem lies in the fact that the frequencies where a vehicles peak SPL may occur rarely ever coincide with a tuning frequency that promotes utmost sound quality. The peak SPL frequency is usually somewhat higher that the tuning frequency for sound quality.
The use of a larger than normal port will allow the user to find the cars peak frequency for greatest SPL. Reducing the port opening will lower the box tuning frequency and provide loading to the woofer over a wider bandwidth. This will improve the transient response and impact of the system. The higher tuning frequency redirects the woofers radiating energy into a narrow band which when tuned to coincide with the vehicles peaks can yield dramatic SPL numbers. The focus of attention here should be to tune the system to each application. Although the general box recommendation will yield very satisfying results, competing at the highest levels of SPL or SQ contests, or simply yielding the best possible results are directly related to methodical tuning.
Calculating Port Size
Calculate Port Size
The box port can be calculated with a simple formula. Box volume in cubic feet X 16 (the amount of port area in square inches per cubic feet of box volume). For example, 3.4 cuft X 16 sqin= 54.5 square inches of port area. Try to stay within 10% of this number.
The port length should be 16 inches deep. This tunes the boxes to about 40 Hz.
How To Make A Slot Port
The easiest and most effective way to build a port is to use a slot shaped port that uses 3 sides of your enclosure as port walls. If the port is located at one end of the box, only one additional piece of wood is required to complete the port. The additional piece of wood should be spaced off the end of the box.
The port area is in square inches, meaning it takes height times width to calculate total area. A port 4 inches high by 4 inches wide would calculate as 4 X 4= 16 square inches.
In our example box, we have an inside height of 14.5 inches. To calculate the slot width that would make a total area of 54.5 square inches, and we use 14.5 inches as the height: divide 54.5 by 14.5= 3.76. Round that figure to nearest ¼ inch, and you get an offset measurement of 3 ¾ inch wide. The slot port would be 3 ¾ inches wide by 14 ½ inches tall.
You don’t have to get too critical about the box and port volume, a good rule of thumb is that if you stay within 5-10% of calculated volumes, there will be very little if any audible effects.
Port Length Obstructions
Some port lengths do not allow for 16-inch port depths without some sort of modification. The rule of thumb is not to let the end of the port get any closer to the back wall than the width of the port. So back to our example, we have an internal box depth of 12.5 inches. We need a 16-inch deep port. We will have to bend the port along the back wall to get the full port length. To calculate where to make the bend, subtract the port width from the inside box depth. 12.5 – 3.75=8.75. We must bend the port at 8.75 inches, then continue the port parallel to the back wall for an additional 7.25 (8.75+7.25=16).
You now have an L shaped port totaling 16 inches in depth.
WHY GO PORTED?
Click Here to Read More..
The box port can be calculated with a simple formula. Box volume in cubic feet X 16 (the amount of port area in square inches per cubic feet of box volume). For example, 3.4 cuft X 16 sqin= 54.5 square inches of port area. Try to stay within 10% of this number.
The port length should be 16 inches deep. This tunes the boxes to about 40 Hz.
How To Make A Slot Port
The easiest and most effective way to build a port is to use a slot shaped port that uses 3 sides of your enclosure as port walls. If the port is located at one end of the box, only one additional piece of wood is required to complete the port. The additional piece of wood should be spaced off the end of the box.
The port area is in square inches, meaning it takes height times width to calculate total area. A port 4 inches high by 4 inches wide would calculate as 4 X 4= 16 square inches.
In our example box, we have an inside height of 14.5 inches. To calculate the slot width that would make a total area of 54.5 square inches, and we use 14.5 inches as the height: divide 54.5 by 14.5= 3.76. Round that figure to nearest ¼ inch, and you get an offset measurement of 3 ¾ inch wide. The slot port would be 3 ¾ inches wide by 14 ½ inches tall.
You don’t have to get too critical about the box and port volume, a good rule of thumb is that if you stay within 5-10% of calculated volumes, there will be very little if any audible effects.
Port Length Obstructions
Some port lengths do not allow for 16-inch port depths without some sort of modification. The rule of thumb is not to let the end of the port get any closer to the back wall than the width of the port. So back to our example, we have an internal box depth of 12.5 inches. We need a 16-inch deep port. We will have to bend the port along the back wall to get the full port length. To calculate where to make the bend, subtract the port width from the inside box depth. 12.5 – 3.75=8.75. We must bend the port at 8.75 inches, then continue the port parallel to the back wall for an additional 7.25 (8.75+7.25=16).
You now have an L shaped port totaling 16 inches in depth.
WHY GO PORTED?
High Output Sub Enclosures
I don’t believe in the tiny sub box theory. If you are looking for tiny sound, get a tiny sub and put it in a tiny box. Be happy. If you are looking for real bass, you need to have a real box.
In order to get true high performance, you have to make the most of the available airspace you have. To do otherwise is wasting your time, energy and money. Don’t try to fit a larger speaker in a box that is better suited for the next size down. The smaller sub in the right space will outperform the larger sub in too small of airspace.
The first step in getting major bass in your vehicle is to allocate the space for your enclosure. If you really want to flex some sheet metal, the old adage applies, “there is no substitute for cubic inches”. The more space you make available, the higher the potential spl.
You don’t have to use a large amount of enclosure space to make a loud system; loud can be done with a single sub. The amount of loud needs to be determined as you figure out what space you plan to give up. Really loud bass, where you have to scream at your passengers, can be done on a single or double woofer setup. Stupid loud bass, where there is no point in trying to communicate in the vehicle, takes more space and bigger/more subs. F@#$ing crazy loud bass, where it is impossible for the car next to you to communicate inside his vehicle, takes even more space, even more subs and a gazillion watts of power.
A few tips on what to pay attention to when determining the box shape:
If you plan to use a rear firing setup in a trunk car, make sure your box doesn’t seal off the trunk from the passenger compartment. You need to leave some space for the waves to pass back into the interior of the car. Either make the box as low as possible so the wave passes over the box and enters the cabin via the seatback and rear deck, or reduce the width of the box so the wave can pass to the side and into the car’s interior. A big, giant box may make your trunk extremely loud, but all you’ll hear is muffled rattle if the box takes up the whole space behind the rear seat and under the rear deck.
If you have a hatchback car, keep the box as far back in the vehicle as possible. Keep the port as far to the rear as possible.
Click Here to Read More..
In order to get true high performance, you have to make the most of the available airspace you have. To do otherwise is wasting your time, energy and money. Don’t try to fit a larger speaker in a box that is better suited for the next size down. The smaller sub in the right space will outperform the larger sub in too small of airspace.
The first step in getting major bass in your vehicle is to allocate the space for your enclosure. If you really want to flex some sheet metal, the old adage applies, “there is no substitute for cubic inches”. The more space you make available, the higher the potential spl.
You don’t have to use a large amount of enclosure space to make a loud system; loud can be done with a single sub. The amount of loud needs to be determined as you figure out what space you plan to give up. Really loud bass, where you have to scream at your passengers, can be done on a single or double woofer setup. Stupid loud bass, where there is no point in trying to communicate in the vehicle, takes more space and bigger/more subs. F@#$ing crazy loud bass, where it is impossible for the car next to you to communicate inside his vehicle, takes even more space, even more subs and a gazillion watts of power.
A few tips on what to pay attention to when determining the box shape:
If you plan to use a rear firing setup in a trunk car, make sure your box doesn’t seal off the trunk from the passenger compartment. You need to leave some space for the waves to pass back into the interior of the car. Either make the box as low as possible so the wave passes over the box and enters the cabin via the seatback and rear deck, or reduce the width of the box so the wave can pass to the side and into the car’s interior. A big, giant box may make your trunk extremely loud, but all you’ll hear is muffled rattle if the box takes up the whole space behind the rear seat and under the rear deck.
If you have a hatchback car, keep the box as far back in the vehicle as possible. Keep the port as far to the rear as possible.
Click Here to Read More..
The Perfect Subwoofer Box
We often hear talk (specially in car audio) about certain boxes being RIGHT for certain woofers. Many folks talk like a given woofer wont even play at all if the box size is not exactly perfect!
What is perfect?
Manufacturers often recommend a certain box for their speakers.
Computer box programs can PICK the box size (or tuning) that works best(?) with the woofer if you input the Thiele/Small parameters.
Is the box size the manufacturer recommends perfect? How can it possibly be perfect when they don't even know what kind of car your installing the box into? We all know the car will change the sound (this is called transfer function)! How can they possibly choose the perfect box size? Many times the speaker manufacturers recommendation is chosen not for perfect sound but for an average that might work well in the average car. Many times they might recommend the box that's easiest to build for beginners or small (since many folks like woofs that work in small boxes) or sealed instead of vented because it is less likely for you to blow your speaker in a small sealed box than a large vented box! (if you blow your speaker (a) they might have to replace it. (b) the company might get a reputation for lousy speakers if they blow a lot) Sure, the manufacturers recommendation will probably sound great! But perfect??? Is the manufacturers recommended box size really right for you?
Is the box size provided by computer programs perfect? Again, how can it be unless they take into account the transfer function of the car??? I don't know of a current popular program that does! Most computer programs will calculate a box for you with the lowest response and with the least ripple. In car audio, this many times IS NOT the best! Sometimes (specially in SPL competitions) the ripple the computer program tries to avoid might actually be an SPL or bass boost! Or for an SQ car, a slight ripple (inaudible, an may likely be made up for by the cars transfer function) might get you much deeper bass... Is the computers recommendation the perfect box? Is the computer programs recommended box right for you?
How bout the difference in CUSTOM made boxes vs PREFAB boxes?
Most real car audio enthusiasts would never consider a PREFAB box, we all know the custom built boxes are far superior sounding... BUT ARE THEY REALLY?
From my experience there is a great amount of BADLY BUILT custom boxes being built! Built so badly in fact that for many cases a prefab box would be miles better!
A prefab box could be better than a badly built custom box! I have heard some darned good systems with prefab boxes and some very poor systems with custom built boxes.. It's important if your gonna pay high dollar for an installer to build you a custom box that the installer be good at building boxes or you might just as well have spent your money on a pre-fab and spent the left over money on something else.
PLUS, since we mentioned installers, how many really have any background in speaker design? Many claim to be experts, but in the real world most installers just build the so called custom boxes with no AUDIO PHYSICS in mind. So for a custom box, its important the installer be not only a carpenter but also an expert at loudspeaker box design... Or a pre-fab box might be the better choice! ;-)
And, in reality, there is no PERFECT box, and to really custom build a box to perform as good as possible in a given vehicle it requires huge stacks of expensive test equipment, lots of woodworking tools and saws, and building, testing then rebuilding and retesting, and rebuilding and retesting again and again and again until no more good is achieved. This is done only by a few crazy competition gurus or a few nutty hobbyists, certainly NOT for the average car audio guy, or even the average installer...
So, I think it would be safe to say most so called perfect boxes are no where near perfect, they can all be improved on. And even if they were perfect, putting them in a car will change them, even the direction the box fires in the car can have an effect!
And it makes me laugh when I hear a fellow say something like " the manufacturer recommends 1.5cu ft for this speaker, it wont work in 1.25cu ft!"
Sure it will!
If that's all the space you have,
build it,
play it,
enjoy it!
There are so many variables involved there is a chance the NON-PERFECT box might even sound better than the so called perfect one! Try it ;-)
Enjoy! Click Here to Read More..
What is perfect?
Manufacturers often recommend a certain box for their speakers.
Computer box programs can PICK the box size (or tuning) that works best(?) with the woofer if you input the Thiele/Small parameters.
Is the box size the manufacturer recommends perfect? How can it possibly be perfect when they don't even know what kind of car your installing the box into? We all know the car will change the sound (this is called transfer function)! How can they possibly choose the perfect box size? Many times the speaker manufacturers recommendation is chosen not for perfect sound but for an average that might work well in the average car. Many times they might recommend the box that's easiest to build for beginners or small (since many folks like woofs that work in small boxes) or sealed instead of vented because it is less likely for you to blow your speaker in a small sealed box than a large vented box! (if you blow your speaker (a) they might have to replace it. (b) the company might get a reputation for lousy speakers if they blow a lot) Sure, the manufacturers recommendation will probably sound great! But perfect??? Is the manufacturers recommended box size really right for you?
Is the box size provided by computer programs perfect? Again, how can it be unless they take into account the transfer function of the car??? I don't know of a current popular program that does! Most computer programs will calculate a box for you with the lowest response and with the least ripple. In car audio, this many times IS NOT the best! Sometimes (specially in SPL competitions) the ripple the computer program tries to avoid might actually be an SPL or bass boost! Or for an SQ car, a slight ripple (inaudible, an may likely be made up for by the cars transfer function) might get you much deeper bass... Is the computers recommendation the perfect box? Is the computer programs recommended box right for you?
How bout the difference in CUSTOM made boxes vs PREFAB boxes?
Most real car audio enthusiasts would never consider a PREFAB box, we all know the custom built boxes are far superior sounding... BUT ARE THEY REALLY?
From my experience there is a great amount of BADLY BUILT custom boxes being built! Built so badly in fact that for many cases a prefab box would be miles better!
A prefab box could be better than a badly built custom box! I have heard some darned good systems with prefab boxes and some very poor systems with custom built boxes.. It's important if your gonna pay high dollar for an installer to build you a custom box that the installer be good at building boxes or you might just as well have spent your money on a pre-fab and spent the left over money on something else.
PLUS, since we mentioned installers, how many really have any background in speaker design? Many claim to be experts, but in the real world most installers just build the so called custom boxes with no AUDIO PHYSICS in mind. So for a custom box, its important the installer be not only a carpenter but also an expert at loudspeaker box design... Or a pre-fab box might be the better choice! ;-)
And, in reality, there is no PERFECT box, and to really custom build a box to perform as good as possible in a given vehicle it requires huge stacks of expensive test equipment, lots of woodworking tools and saws, and building, testing then rebuilding and retesting, and rebuilding and retesting again and again and again until no more good is achieved. This is done only by a few crazy competition gurus or a few nutty hobbyists, certainly NOT for the average car audio guy, or even the average installer...
So, I think it would be safe to say most so called perfect boxes are no where near perfect, they can all be improved on. And even if they were perfect, putting them in a car will change them, even the direction the box fires in the car can have an effect!
And it makes me laugh when I hear a fellow say something like " the manufacturer recommends 1.5cu ft for this speaker, it wont work in 1.25cu ft!"
Sure it will!
If that's all the space you have,
build it,
play it,
enjoy it!
There are so many variables involved there is a chance the NON-PERFECT box might even sound better than the so called perfect one! Try it ;-)
Enjoy! Click Here to Read More..
Mapping the Transfer Function
Putting a speaker in a vehicle (or room for that matter) will make the speaker sound different. This is caused by reflections, absorptions and resonance's that exist in that car. This change is called the transfer function.
All cars have a transfer function, typically the most noticeable change to speakers when placed in a car is MORE BASS. More bass is inherent because the car is like a box, an enclosed space that promotes reinforcing reflections of the bass sounds (because the bass waves are long enough to be reflected and still be close enough to in phase and reinforce)....
But the transfer function is more than just a change in bass, it also can cause major changes in the midrange speakers because of the major glass surfaces for the sound to bounce off of! Or the high frequency sounds from the tweeters can be absorbed into the headliner or car upholstery (intentionally sound absorbent by the car manufacturer to absorb road noise)...
So, we cant easily change the transfer function, but we can map it, and then build our system to take advantage of our cars transfer function.
To map the transfer function you will need a Speaker box, a CD with test tones or an audio test generator or a pink noise generator and a decibel meter. There are several CDs available with test tones, I prefer the tone generator but they are fairly expensive and hard to find an install shop with one, pink noise is OK but pink noise generators are probably just as hard to find as audio generators. And for a decibel meter Radio shack sells one for about $30 that will work. Oh, and a piece of graph paper to write down your results.
First, lets map the speaker box. Take your speaker box outdoors in the back yard and aim it away from the house to minimize reflections, hang the SPL meter or microphone for it a few meters in front of the speaker box. Fire up your test tones and set the volume level where the SPL meter gets a reading on most of your test tones (if the low ones don't register don't worry), but not too loud, we don't want to damage the test speaker! Now without touching the volume control, run your test tones and write down on your graph paper the SPL at each tone. You can even make a graph on the graph paper if you want to.
Your results is the frequency response of your test speaker!
Lets put this box in the car and do the test again and see what changes!
Set the test speaker in a nice location, preferably close to where the real speakers will go later. Hang the microphone in the center of the car near where your ears would be if you were driving, and run through the test tones again, reading the SPL meter and writing down the results on the graph paper.
When you done, subtract the back yard numbers from the in car numbers for each frequency and write down your results. For instance, if you had 90dB at 120Hz in the back yard and 95dB in the car then (95-90=5) write down 120Hz=+5dB, and do this for every frequency you mapped. Some frequencies may have negative numbers, this is OK... When your done, you should have a series of frequencies=numbers something like this: 20=+4, 40=+6, 80=+12, 120=+3, 200=0, 400=-3, 600=-4, and so on...
This is your transfer function, you can now look at any frequency and tell what
your car is going to do to ANY SPEAKER you install.
Simple.... Click Here to Read More..
All cars have a transfer function, typically the most noticeable change to speakers when placed in a car is MORE BASS. More bass is inherent because the car is like a box, an enclosed space that promotes reinforcing reflections of the bass sounds (because the bass waves are long enough to be reflected and still be close enough to in phase and reinforce)....
But the transfer function is more than just a change in bass, it also can cause major changes in the midrange speakers because of the major glass surfaces for the sound to bounce off of! Or the high frequency sounds from the tweeters can be absorbed into the headliner or car upholstery (intentionally sound absorbent by the car manufacturer to absorb road noise)...
So, we cant easily change the transfer function, but we can map it, and then build our system to take advantage of our cars transfer function.
To map the transfer function you will need a Speaker box, a CD with test tones or an audio test generator or a pink noise generator and a decibel meter. There are several CDs available with test tones, I prefer the tone generator but they are fairly expensive and hard to find an install shop with one, pink noise is OK but pink noise generators are probably just as hard to find as audio generators. And for a decibel meter Radio shack sells one for about $30 that will work. Oh, and a piece of graph paper to write down your results.
First, lets map the speaker box. Take your speaker box outdoors in the back yard and aim it away from the house to minimize reflections, hang the SPL meter or microphone for it a few meters in front of the speaker box. Fire up your test tones and set the volume level where the SPL meter gets a reading on most of your test tones (if the low ones don't register don't worry), but not too loud, we don't want to damage the test speaker! Now without touching the volume control, run your test tones and write down on your graph paper the SPL at each tone. You can even make a graph on the graph paper if you want to.
Your results is the frequency response of your test speaker!
Lets put this box in the car and do the test again and see what changes!
Set the test speaker in a nice location, preferably close to where the real speakers will go later. Hang the microphone in the center of the car near where your ears would be if you were driving, and run through the test tones again, reading the SPL meter and writing down the results on the graph paper.
When you done, subtract the back yard numbers from the in car numbers for each frequency and write down your results. For instance, if you had 90dB at 120Hz in the back yard and 95dB in the car then (95-90=5) write down 120Hz=+5dB, and do this for every frequency you mapped. Some frequencies may have negative numbers, this is OK... When your done, you should have a series of frequencies=numbers something like this: 20=+4, 40=+6, 80=+12, 120=+3, 200=0, 400=-3, 600=-4, and so on...
This is your transfer function, you can now look at any frequency and tell what
your car is going to do to ANY SPEAKER you install.
Simple.... Click Here to Read More..
Choosing the Correct Port Tuning
Tuning of a ported subwoofer box is determined by a combination of port area, port length, and net volume of the subwoofer box. Tuning changes the frequency at which the frequency response peaks (is loudest) and can change the way a subwoofer box sounds in your setup. Your tuning choice will be determined by the goal of your system install.
If you're looking to achieve an SPL setup your car (getting as loud as possible), you'll want to tune fairly high. High tuning for SPL is usually somewhere around 45Hz or possibly higher. At this high of tuning, the sound quality will not be very good, but it will be louder than if you were to tune low. A SQ (sound quality) based setup will call for a tuning fairly low - even down around 25Hz. This will also allow you to hit the ultra-low notes with your system. Lower-tuned boxes produce better sound quality, more like a sealed box. The downside to lower tuning is that it flattens the frequency response, which will cause the box to lack the boost around the tuning frequency.
To achieve a good mix between SPL and SQ with a ported box, we have found that it's good to be in the lower 30's for tuning. If you tune up around 35Hz, you'll get a fair amount of SPL out of the box and still have fairly good sound quality. If you tune closer to 30, the box will yield better sound quality but have a little less output than the 35Hz. A range between 30 and 35 Hz is generally good for most general setups.
If you want SPL, tune high. If you want SQ, tune low. If you want somewhere in-between the two, we have found a good tuning is right at 33Hz. This is why we default the port tuning to 33Hz on our customization pages for our ported enclosures. When choosing a ported subwoofer box, the freedom to tune the enclosure is a great way to get your system sounding the way you want it to sound.
Building with Acrylic
Acrylic Sheeting/Plexiglas:
Acrylic sheeting is widely known as Plexiglas©. Plexiglass©, however, is the name given to acrylic sheeting manufactured by Atofina. The same acrylic type sheeting is also known by the names Acrylite©, Lucite© and Perspex©. From this point on, I'll refer to it simply as acrylic.
Before we go any farther... Do not peel the protective coating from the sheet until the last possible moment. Acrylic sheeting is very easy to scratch. It may be even easier to scratch than CDs.
Cutting Acrylic:
There are a couple of different ways to cut acrylic. Since my experience is mainly with thin acrylic sheeting (1/2" or less), that's what I'll cover.
Table/Circular Saw:
For rough cutting acrylic, you can use a table saw or a circular saw with a fine blade. Blades with fine closely spaced teeth (like those used for plywood) will work relatively well. Blades with widely spaced teeth (like the type used for cutting MDF) will cause a lot more chipping. I've used an Oldham B7254760 on a circular saw with good results. When using a hand held circular saw, use a guide to make sure you get a straight cut with minimal chipping. There are blades made specifically for cutting acrylic. If you're going to be cutting a lot of acrylic or are using very expensive (thick) material, you need to invest in a blade specifically designed for cutting plastics and laminates.
Jig Saw or Band Saw:
Jig saws can be used to cut acrylic when you need something other than a straight cut. To reduce the work of cleaning up the cut, use the finest blade that you can find. Blades with reduced depth (like those used for scroll work - shown below) will work best due to less friction and less resistance when turning the blade. You'll have to experiment with cutting speed to see what works best. Too much pressure can cause excessive chipping. Going too slow may cause the acrylic to melt. If the acrylic melts when cutting, use a light lubricating oil. Have someone apply the oil to the blade as you're making the cut. DON'T use an aerosol dispensed oil. The propellant may be flammable and may be ignited by the jig saw motor. I've had good results with the blade shown below.
Router:
A router can be used to cut acrylic for either straight or curved cuts. For curved cuts, you'll want to use a router with a collar and a guide (pattern or jig made with 1/4 inch plywood). You'll want to rough cut the material within ~1/8 of an inch of the desired finished shape. Trying to cut too much acrylic will lead to melting of the material. Again, you'll have to experiment with the speed of the cut. To prevent chipping, make sure the blade is not allowed to break contact with the cut edge. If it does break contact with the material and you push the router blade back into the edge too quickly, the cutter may chip the acrylic. You also must make sure you have a sharp bit (carbide recommended) to prevent melting of the material. Again, you'll have to experiment to see what works best for you.
Score and Break:
Thin acrylic sheets (less than ~1/4") can be cut much like regular glass. Instead of using a hardened wheel to chip a line in the glass, you'll use a scoring tool to cut a deep scratch in it. The cutting edge of the scoring tool looks something like a single tooth of a table saw blade (but much thinner). You apply pressure to the tool and drag it along a straight edge guide (which should be clamped securely in place to prevent it from moving). You need to continue scoring the acrylic until the cut is ~1/8 of the way through the material (it may take 20 passes on 1/4" thick stock). After that's done, you'll have to clamp it down on the edge of a table (or something similar). The edge of the table needs to align with the cut. The edge of the table needs to be perfectly square (a radiused edge on the table won't provide the proper stress along the desired cut line). It needs to be clamped very securely so that it can not flex or move. You'll then apply pressure to the piece that's beyond the edge of the table until it snaps. If it was cut deeply enough, it will break cleanly along the desired line. If it was not cut deeply enough, the cut (on the side opposite the scoring) can be as far outside of the desired cut line as the thickness of the material. The image below shows an inexpensive scoring tool (I think it cost ~$3)
Polishing the Edge of the Cut:
Depending on the quality of the cut and the desired end use, the edge may need to be polished. When using the acrylic as a window on a speaker enclosure or for an amp rack, you'll probably want to polish the edge. To make things easy, use a rubber or foam block and waterproof sandpaper. Since it will be nearly impossible to keep the edge perfectly square, I'll usually round it off. With a foam sanding block, start with rough paper (~180 grit). Wet sand with lots of water until the edge is uniform and relatively smooth. Then change to finer and finer paper until you get a satin finish with 600 grit paper (180, 360 and 600 grit will work fine). Remember to use lots of water.
Flame Polishing:
After the edge is polished to a satin finish, you may want to get it to a glass like finish. To do this, you can use a propane torch. Let me recommend that you practice on a scrap piece first. Using a propane torch, you very quickly pass the torch over the edge. You must move the torch very quickly. If you go too slowly, the acrylic will melt and boil. This will leave bubbles in the surface. This is from heating the acrylic too deeply. You only want to heat the very outermost edge/surface to its melting point. This will allow it to flow into a smooth glossy surface. As long as you're moving very quickly along the acrylic, you're not likely to cause bubbles (even if you're using the hottest part of the flame).
Practicing Flame Polishing:
The material that a CD is made of reacts similarly to that of the acrylic sheeting. If you want to scuff up a CD with some 600 grit paper (and water), you'll be able to remove most of the finer scratches and haze with the torch. Remember... Move VERY quickly along the surface. Allow the CD to cool between passes with the torch (just as you would when polishing acrylic). Don't you use a good CD. Try it with one that will not play. Heating the CD will cause it to cup slightly and it probably won't play anymore. This exercise is only to allow you too see how the process works. Two final suggestions... Don't burn yourself and don't burn your parent's house down.
Drilling Acrylic
Spiral Bit:
Standard spiral drill bits will not work well on acrylic. Their cutting angle is too aggressive which causes it to try to cut too quickly. This will lead to cracking and chipping around the hole. If you want to use a bit that can be used for metal also, try a bit like the one shown in the following photo. You can see that the main cutting edge is flat instead of angled like a normal bit. This causes the material to be cut in a more controlled fashion. If you don't want to spend the money on a new bit, you can grind a regular bit to the same profile.
Forstner Bit:
Forstner bits are very high quality bits that are generally used for woodworking. They make a very clean hole with little or no chipping. When used for drilling acrylic, you may need to use a cutting lubricant. I generally use a '3 in 1' type oil. Apply the oil to the cutting surface prior to drilling and to the drill bit shaft as you're moving through the material. If the bit is used dry, the friction between the sides of the bit and the material will cause the acrylic to melt (very bad). When used with lubricant, the hole will be very clean.
Standard Woodboring Bit:
Some people recommend against using woodboring bits but I've never had a problem with them. One advantage of the wood bit is the long centering point. This point will exit the other side of the material before the cutting edge. This allows you to turn the material over and drill from the other side. Since the cutting edge will not be pushing out as the bit cuts through surface of the material, there will be little or no chipping on either side of the material.
When using any of the different bits for drilling acrylic, you should:
- Go slow. Do not force the bit to cut too quickly.
- Use a drill press. This allows you to have much more control over the cutting speed and assures that you're drilling the hole perfectly perpendicular to the material. You should clamp small pieces down. If the bit grabs the material and spins it, it will cut you. Small pieces don't allow you to get a good enough grip to prevent the piece from spinning with the bit.
- Practice on a piece of scrap material. If you crack a piece of acrylic after you've already polished the edges, you are not going to be happy.
- If the acrylic melts as you drill through it (regardless of rate of rotation/feed), try using a light lubricating oil to reduce friction between the bit and the acrylic.
Fasteners:
When screwing a piece of acrylic down, you'll need to use some type of washer under the screw. Fiber, plastic and rubber washers will work. If you can't find those types of washers, standard metal flat washers will be better than nothing. If you use washers, you're less likely to crack the material if the screw doesn't go in prefectly straight. Predrilling the hole in the wood will help assure that the screw goes in straight. When tightening the screws, do not overtighten (especially when the surface under the acrylic is not hard). If there's a soft gasket under the acrylic, overtightening the screw will cause the material to crack. You should also use pan head screws (those with a flat mating surface under its head). Using bevel or bugle headed (drywall) screws will cause the acrylic to crack
Ported Enclosures
Subwoofer enclosures come in many different models. Consider a ported subwoofer enclosure for all of your needs.
If you are in the market for a subwoofer box you need to know exactly what you are getting before deciding to make a purchase. In other words, you need to know what the subwoofer box is made out of, if it is durable, and what type of quality sound the box is going to provide to you.
Every subwoofer box is different, and it is important to answer these questions before moving forward. If you neglect to do the proper amount of research you may end up disappointed with the performance of your subwoofer box. A lot of people do not know that depending on what type of music you listen to, you will need a particular type of subwoofer enclosure. This information can be found by visiting the internet, or heading to your local car or audio store. But enough of that, what you really need to know is what subwoofer enclosure is the best for your needs. Nobody can answer that question but you, but ported subwoofer enclosures may be the way to go.
Ported subwoofer enclosures do a good job of providing quality sound, but you must realize that it will not be the best sound possible. A sealed subwoofer enclosure will provide you with better sound if that is what you are looking for. Even though ported subwoofer enclosures may not be up to par with the sealed boxes, they definitely deliver better quality than bandpass subwoofer boxes. Generally speaking, ported subwoofer enclosures are not quite the best you can get, but at the same time they are not the worst when it comes to the quality of the sound. Another fact about ported subwoofer enclosures is that they provide a higher output as well as more volume than a sealed subwoofer enclosure. With that being said, ported subwoofer enclosures do not quite offer the level of output and volume that a bandpass subwoofer enclosure can offer.
The main advantage of a ported subwoofer enclosure is strong mid-bass sound. If this is what you are looking for in your music you have found the best enclosure available. Ported subwoofer enclosures are almost always bigger than a standard sealed enclosure. These boxes also provide a round port behind the speaker, hence the name.
As you can probably see, every subwoofer enclosure is different. All of them have their own pros and cons, and personal preference is the only thing that makes one better than the next. If you do the appropriate amount of research, and know what kind of sound you are looking to obtain you will then know which type of enclosure to buy.
Ported subwoofer enclosures have a wide audience because of its ability to make most types of music sound good. They are capable at doing everything good and some things extremely well. The only way to find out if a ported subwoofer enclosure is for you is to hear the quality of the music that it can produce. So go out and find somebody who has one and see for yourself if this set up will benefit you. Click Here to Read More..
If you are in the market for a subwoofer box you need to know exactly what you are getting before deciding to make a purchase. In other words, you need to know what the subwoofer box is made out of, if it is durable, and what type of quality sound the box is going to provide to you.
Every subwoofer box is different, and it is important to answer these questions before moving forward. If you neglect to do the proper amount of research you may end up disappointed with the performance of your subwoofer box. A lot of people do not know that depending on what type of music you listen to, you will need a particular type of subwoofer enclosure. This information can be found by visiting the internet, or heading to your local car or audio store. But enough of that, what you really need to know is what subwoofer enclosure is the best for your needs. Nobody can answer that question but you, but ported subwoofer enclosures may be the way to go.
Ported subwoofer enclosures do a good job of providing quality sound, but you must realize that it will not be the best sound possible. A sealed subwoofer enclosure will provide you with better sound if that is what you are looking for. Even though ported subwoofer enclosures may not be up to par with the sealed boxes, they definitely deliver better quality than bandpass subwoofer boxes. Generally speaking, ported subwoofer enclosures are not quite the best you can get, but at the same time they are not the worst when it comes to the quality of the sound. Another fact about ported subwoofer enclosures is that they provide a higher output as well as more volume than a sealed subwoofer enclosure. With that being said, ported subwoofer enclosures do not quite offer the level of output and volume that a bandpass subwoofer enclosure can offer.
The main advantage of a ported subwoofer enclosure is strong mid-bass sound. If this is what you are looking for in your music you have found the best enclosure available. Ported subwoofer enclosures are almost always bigger than a standard sealed enclosure. These boxes also provide a round port behind the speaker, hence the name.
As you can probably see, every subwoofer enclosure is different. All of them have their own pros and cons, and personal preference is the only thing that makes one better than the next. If you do the appropriate amount of research, and know what kind of sound you are looking to obtain you will then know which type of enclosure to buy.
Ported subwoofer enclosures have a wide audience because of its ability to make most types of music sound good. They are capable at doing everything good and some things extremely well. The only way to find out if a ported subwoofer enclosure is for you is to hear the quality of the music that it can produce. So go out and find somebody who has one and see for yourself if this set up will benefit you. Click Here to Read More..
Sealed Enclosures
Speakers are not the only consideration when looking for superior bass to add to your sound system. The type of box that houses the subwoofer is also a major consideration and there are several different types of enclosures that can be used depending upon the kind of bass you want your subwoofer to produce.
One popular type of box for subwoofers is sealed subwoofer enclosures. Basically, a sealed subwoofer enclosure is a sealed box that is completely and totally airtight that provides a home for the woofer. Sealed subwoofer enclosures provide tight and accurate bass, which is sometimes exactly what is needed for the type of music that demands this type of bass. The listener is obviously the one that needs to make the ultimate decision about what the music will sound best with when it comes to bass, but there are guidelines available to help amateurs determine what will sound best with different types of music. A loud booming bass will not be produced from sealed subwoofer enclosures, so if you are not expecting a flat response or deep bass extension, look into other types of boxes for your speakers.
A significant difference in sealed subwoofer enclosures is found in the amount of power required to correctly run your speakers. Ample power is a must for sealed subwoofer enclosures and the best method is to use an amplifier for the additional power. The amplifier must have ample wattage in order to provide enough power to obtain maximum, optimal performance from the sealed subwoofer enclosure. A proper amplifier can be purchased at any stereo equipment store or online for that matter. The amount of wattage is what is most important so be sure to determine what that number is before going out and shopping for a new amplifier. There are plenty of experts available to assist you with figuring out just how much power is actually required to operate your sealed subwoofer enclosure at optimal levels. These experts work primarily in the higher end stereo shops and are usually very willing to share their knowledge of stereo equipment and all of the components required to operate your stereo with the best sound quality available.
Once you have made the decision that sealed subwoofer enclosures are the way to go for the type of bass you want you then have additional options as far as actually getting a box. Many people are skilled enough and able to build sealed subwoofer enclosures themselves, which is certainly one way to go for the serious stereo enthusiast. However, the majority of people tend to purchase already built sealed subwoofer enclosures from a store or vendor online. The tight accurate bass that this type of box offers is only guaranteed if the box the speaker is put into is constructed correctly without any air able to get in. This can be a challenging feat for people who have not built sealed subwoofer enclosures before, which is why most stereo enthusiasts purchase them from someone else. That way the component is guaranteed to function properly and provide the type of bass that you are looking for. Click Here to Read More..
One popular type of box for subwoofers is sealed subwoofer enclosures. Basically, a sealed subwoofer enclosure is a sealed box that is completely and totally airtight that provides a home for the woofer. Sealed subwoofer enclosures provide tight and accurate bass, which is sometimes exactly what is needed for the type of music that demands this type of bass. The listener is obviously the one that needs to make the ultimate decision about what the music will sound best with when it comes to bass, but there are guidelines available to help amateurs determine what will sound best with different types of music. A loud booming bass will not be produced from sealed subwoofer enclosures, so if you are not expecting a flat response or deep bass extension, look into other types of boxes for your speakers.
A significant difference in sealed subwoofer enclosures is found in the amount of power required to correctly run your speakers. Ample power is a must for sealed subwoofer enclosures and the best method is to use an amplifier for the additional power. The amplifier must have ample wattage in order to provide enough power to obtain maximum, optimal performance from the sealed subwoofer enclosure. A proper amplifier can be purchased at any stereo equipment store or online for that matter. The amount of wattage is what is most important so be sure to determine what that number is before going out and shopping for a new amplifier. There are plenty of experts available to assist you with figuring out just how much power is actually required to operate your sealed subwoofer enclosure at optimal levels. These experts work primarily in the higher end stereo shops and are usually very willing to share their knowledge of stereo equipment and all of the components required to operate your stereo with the best sound quality available.
Once you have made the decision that sealed subwoofer enclosures are the way to go for the type of bass you want you then have additional options as far as actually getting a box. Many people are skilled enough and able to build sealed subwoofer enclosures themselves, which is certainly one way to go for the serious stereo enthusiast. However, the majority of people tend to purchase already built sealed subwoofer enclosures from a store or vendor online. The tight accurate bass that this type of box offers is only guaranteed if the box the speaker is put into is constructed correctly without any air able to get in. This can be a challenging feat for people who have not built sealed subwoofer enclosures before, which is why most stereo enthusiasts purchase them from someone else. That way the component is guaranteed to function properly and provide the type of bass that you are looking for. Click Here to Read More..
Building you own subwoofer box
- Materials
A box has to be very rigid. Most common building materials are 5/8″ or thicker particle board or medium density fiberboard.
If building a box with Plexiglas, do not use anything less that 1/2 inch thick.
A common material used to mold complex shaped boxes is fiberglass, but it is a real pain to work with, and several layers need to be applied for a solid finish.
- Gluing, Sealing
Use glue at all joints (cheapest and most used product is Liquid Nails). Make sure there are no holes. Any leaks will degrade the performance of your subs, not to mention the annoying noise air makes when being pushed out of a small hole.
Let glue cure for at least 24 hours before mounting the woofers. The fumes of some products will eat up rubber and other materials subs are made of.
- Holding Joints Together
Screw joints (use 2″ - 2-1/2″ screws) every four inches or so. Pre-drill about 3/4″ deep, so that screws do not split the wood at the edges, especially when working with particleboard.
- A box for Each Sub?
Even though it is not necessary to have two separate chambers for two subs, it is best to take this approach for two reasons: First, if one of the subs dies, then the volume of the box will be “twice” as big, as seen by the sub that is still working. This could cause problems and even damage the other sub. The second reason is bracing. building a box with a divider in the middle will be much sturdier.
- Making Ports
There are several way to build ports. If a pre-made port is not available, the most common material is PVC tubing. PVC tubing is very rigid, comes in different diameters, and is easily found at any hardware store.
Cut the tubing at the desired length. Consider the volume the port takes up when calculating the box volume. Cut a hole in the box. Make sure the hole is as perfect as possible to minimize gaps between the box and the tube. A couple wood braces can be added for screwing the port top the box. Seal the gaps using plenty of Liquid Nails or similar product.
- Bracing
Boxes that are more than a foot on width or length or height, should be braced (use a piece of wood maybe 3 or 4 inches wide across the box, so that box does not flex). It is a good idea to put wood blocks on the corners for reinforcement. Always consider that blocks, braces, neon lights, etc. inside a box take up space and should be accounted for when calculating internal volume.
- Damping/Filling
It is advisable to put damping material inside a box. Pillow polyfill and fiberglass insulation are common, though polyfill is a lot easier on your skin. This increases subwoofer efficiency by dissipating some energy that affects the sub, particularly the voice coil. Polyfill also “fools” a sub into thinking it is in a bigger box. Play around with different amounts of polyfill until you get the desired results.
- Finishing the Box
Add wood filler to holes and sand the box to make a smooth surface. If you are painting the box, It is a good idea to apply primer under the paint.
It is not necessary to sand the box if you are using carpet or padding under vinyl, since the thickness of the material will cover any small imperfections. The best way to cut carpet or vinyl is with a good quality carpet knife. Blades wear out pretty quickly, so buy a handful. Cut a piece of carpet (or vinyl) big enough to cover the whole box. Apply adhesive to both box and carpet (spray 3M adhesive 77 or 90 works great). Wait about a minute and place the fabric over the wood. For a good fit, stretch the fabric when applying it. The fabric should wrap around and end in a place of the box that will not be seen. Do one side at a time, cutting excess carpet. If possible, add staples to hold the fabric at the ends.
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