In order to make speaker measurements, it is suggested that the speaker is mounted in a baffle. What size is typically used for this? I was thinking of 1' square for each driver. Is that ok?
Also, for open space measurements, how far away from obstructions does the speaker/mic have to be? I can easily do 5' offf the ground and 8' from the nearest wall. Is that sufficient or should I shoot for twice that in one or both directions.
Finally, what do people do to line their boxes? I've heard of roofing felt, black top slurry, etc. I wouldn't mind going fancier if the cost wasn't too high but if I could get something from home depot, that would be the best.
Opps, one more! Where might I find the 1/4" felt that some manufacturers use around their speakers to control baffle modes? I've have it on my Snell's and have seen it on numerous other speakers.
TIA,
Phil
Also, for open space measurements, how far away from obstructions does the speaker/mic have to be? I can easily do 5' offf the ground and 8' from the nearest wall. Is that sufficient or should I shoot for twice that in one or both directions.
Finally, what do people do to line their boxes? I've heard of roofing felt, black top slurry, etc. I wouldn't mind going fancier if the cost wasn't too high but if I could get something from home depot, that would be the best.
Opps, one more! Where might I find the 1/4" felt that some manufacturers use around their speakers to control baffle modes? I've have it on my Snell's and have seen it on numerous other speakers.
TIA,
Phil
Phil O.son said:
From what I've heard, the only lining material they use for gluing to the inside of the boxes are 3/8" or 1/2" industrial felt. I think it is wool based. Filling would be wool fibers, polyfill, fiberglass? or dacron. I dont know which one is best for sure but I have heard that wool is the best for mids.
hope this helps.
Phil, Prash,
If you go to Home Depot or the like, see if they have some heavy fiber mats (like door mats). This is what I used in my subs, but it was 25 years ago before the super hardware store chains.
Another source is the tool supply stores (Production Tool in the Detroit area, but there are many others). They are used for machine mounting pads for damping (Hey! what a concept!
). They will come in various thickness with the thinnest probably being about 1/2". I haven't priced them, but they won't be cheap.
You should be able to find the felt at fabric store, but I haven't seen anything very heavy (maybe 1/8" thick). 2 layers would work for you baffle though. I use 1/4" closed cell foam.
Phil, WRT your first question. Are you measuring frequency response?
Happy Hunting
Rodd Yamashita
If you go to Home Depot or the like, see if they have some heavy fiber mats (like door mats). This is what I used in my subs, but it was 25 years ago before the super hardware store chains.
Another source is the tool supply stores (Production Tool in the Detroit area, but there are many others). They are used for machine mounting pads for damping (Hey! what a concept!
). They will come in various thickness with the thinnest probably being about 1/2". I haven't priced them, but they won't be cheap. You should be able to find the felt at fabric store, but I haven't seen anything very heavy (maybe 1/8" thick). 2 layers would work for you baffle though. I use 1/4" closed cell foam.
Phil, WRT your first question. Are you measuring frequency response?
Happy Hunting
Rodd Yamashita
prash,
I'll check out the fabric and craft outlets and see what's available. Someone must sell it!
Rod,
If you mean floor mats another good source is exercise equipment retailers. They sell rubber mats to go under weight machines, tread mills, etc. Is that the kind of mat you are talking about?
Does this go on in addition to stuffing the box with faber fill?
I am new to speaker building and this is what I think I understand:
1. measure impedance in free air by mounting the speaker on a baffle and doing the measurement. Then mount the speaker on the outside of a closed box about one half VAS in volume. That allows T/S parameter extraction.
2. measure frequency response of driver in free air mounted to a baffle, 1 meter/1 watt as far away from everything as possible. This measures both frequency response and acoustic center.
Have I got this correct?
TIA,
Phil
I'll check out the fabric and craft outlets and see what's available. Someone must sell it!
Rod,
If you mean floor mats another good source is exercise equipment retailers. They sell rubber mats to go under weight machines, tread mills, etc. Is that the kind of mat you are talking about?
Does this go on in addition to stuffing the box with faber fill?
I am new to speaker building and this is what I think I understand:
1. measure impedance in free air by mounting the speaker on a baffle and doing the measurement. Then mount the speaker on the outside of a closed box about one half VAS in volume. That allows T/S parameter extraction.
2. measure frequency response of driver in free air mounted to a baffle, 1 meter/1 watt as far away from everything as possible. This measures both frequency response and acoustic center.
Have I got this correct?
TIA,
Phil
you can also use open cell foam on the walls. I us e 2" egg crate stuff. Then for sealed boxes I use about 2 lb per cu. ft. of glass wool or poly fill.
if you the approx size of box then you can meansure the speaker after building the box.
1. usually volume of box can be estimated from published specs or emperical knowledge (1cu. ft. for a 6," 1.5 for a 8" etc...)
2. usually one tries to use as small a baffle as possible and teh rest of the volume is made up by depth of box
3. if there are restrictions of one dimension the other dimensions have to compensate
the advantage of using approx boxes is that you can measure the speaker taking into account the effect of the boxes.
if you the approx size of box then you can meansure the speaker after building the box.
1. usually volume of box can be estimated from published specs or emperical knowledge (1cu. ft. for a 6," 1.5 for a 8" etc...)
2. usually one tries to use as small a baffle as possible and teh rest of the volume is made up by depth of box
3. if there are restrictions of one dimension the other dimensions have to compensate
the advantage of using approx boxes is that you can measure the speaker taking into account the effect of the boxes.
Phil,
1 and 2 of your last post are fine. The frequency response measurements (with out an anechoic chamber) are going to be effected by any reverberated sound. The trick is to minimize reflected sound. You can place the speaker on its back outside and get good half-space measurements.
The "mats" I spoke of are highly compressed "wool" like fibers. If the nautalus equipment pad are like this, they should work fine. Be carely if they are the neoprene type. You'll get some damping, but in a relitively narrow band. The fiber type be more effective over a much broader band. I also have about 2" of fiberglass bat lining my subs. The heavy fiber mat is glued to the walls, and the fiberglass batting covers the whole inside, stapled at the corners and braces.
The use of fiber fill will depend on the type of enclosure you plan on building. As a general rule, you stuff a closed box and just line a vented or passive radiator box. Take a look at this thread:http://www.diyaudio.com/forums/showthread.php?s=&threadid=5868
Did I miss anything?
Rodd Yamashita
1 and 2 of your last post are fine. The frequency response measurements (with out an anechoic chamber) are going to be effected by any reverberated sound. The trick is to minimize reflected sound. You can place the speaker on its back outside and get good half-space measurements.
The "mats" I spoke of are highly compressed "wool" like fibers. If the nautalus equipment pad are like this, they should work fine. Be carely if they are the neoprene type. You'll get some damping, but in a relitively narrow band. The fiber type be more effective over a much broader band. I also have about 2" of fiberglass bat lining my subs. The heavy fiber mat is glued to the walls, and the fiberglass batting covers the whole inside, stapled at the corners and braces.
The use of fiber fill will depend on the type of enclosure you plan on building. As a general rule, you stuff a closed box and just line a vented or passive radiator box. Take a look at this thread:http://www.diyaudio.com/forums/showthread.php?s=&threadid=5868
Did I miss anything?
Rodd Yamashita
Thanks guys for all the info.
Rod,
If I do the half space on the woofer, then I just subtract 6db for the equivalent full space reading?
I WAS thinking of the neoprene mats but I thought of something even better that I have a ton of. It's carpet underlayment. You can buy it by the linear yard at Home Depot. It is wool with a small amount of rubber binder, (not the cheap foam stuff).
It's what I used under my carpet in the HT do dampen the concrete floor and seems to work well.
So for the mid's I just stuff with poly-fill and for the woofs I either stuff with poly-fill if sealed or line if ported, correct?
Thanks again,
Phil
Rod,
If I do the half space on the woofer, then I just subtract 6db for the equivalent full space reading?
I WAS thinking of the neoprene mats but I thought of something even better that I have a ton of. It's carpet underlayment. You can buy it by the linear yard at Home Depot. It is wool with a small amount of rubber binder, (not the cheap foam stuff).
It's what I used under my carpet in the HT do dampen the concrete floor and seems to work well.
So for the mid's I just stuff with poly-fill and for the woofs I either stuff with poly-fill if sealed or line if ported, correct?
Thanks again,
Phil
Hi Phil,
Your questions cover from box design to to frequency response. Am I to assume you are experimenting with different driver/box setups to zero in on what you want?
The reason I ask is that frequency response in an anechoic chamber is different then in a half space (BTW -6db is correct), and both bare little resemblence to the response in your reverberant listening room. This will be particularly ture in the bass region. So I'll ask this question before we go too far afield.
What is the goal behind your frequency response measurements?
Let us know,
Rodd Yamashita
Your questions cover from box design to to frequency response. Am I to assume you are experimenting with different driver/box setups to zero in on what you want?
The reason I ask is that frequency response in an anechoic chamber is different then in a half space (BTW -6db is correct), and both bare little resemblence to the response in your reverberant listening room. This will be particularly ture in the bass region. So I'll ask this question before we go too far afield.
What is the goal behind your frequency response measurements?
Let us know,
Rodd Yamashita
Rod,
From what I understand, the box, freq response, crossover, etc. all interact. From what I've read in the help file of both Speaker Workshop and Soundeasy the first step is to measure the drivers for T/S parameters, impedance, acoustic center, and frequency response. That will get the data necessary to do a box design.
With Soundeasy, (which I will purchase tomorrow), you can enter the data and actually simulate the box then simulate the crossovers. The more accurate the data, the more accurate the simulations.
Once a box is decided on, then the drivers are mounted and the box is measured to compare with the simulation and possible iteration.
I think what the program wants to see is T/S parameters, free air impedance and free air response so that's my first task. From what I remember, all speakers need to be normalized in output so that the box/crossover design simulation will also be accurate, (hence the 6dB correction factor to normalize to the other drivers measured in free air).
I guess I could just build a box and 'see what happens' but as long as accurate simulation is possible, I would prefer it, (once the data is input, it's much less work than trial and error with power tools )
On the mid, (filler), and tweeter, I can place 2" 6 PCF fiberglass sound deadening panels at the ground and nearest wall reflection points but they aren't really that effective for the woof.
Of course I could get exotic and put the woof and mic on 8' ladders, making the nearest reflection 20' or so.
Thanks,
Phil
P.S. I am an engineer so I understand simulations. From what I've heard, Soundeasy does a very good job and even has methods to output data to allow easy comparison between simulation and actual design. For this reason, I want to be very carefull about getting the initial measurement data right.
From what I understand, the box, freq response, crossover, etc. all interact. From what I've read in the help file of both Speaker Workshop and Soundeasy the first step is to measure the drivers for T/S parameters, impedance, acoustic center, and frequency response. That will get the data necessary to do a box design.
With Soundeasy, (which I will purchase tomorrow), you can enter the data and actually simulate the box then simulate the crossovers. The more accurate the data, the more accurate the simulations.
Once a box is decided on, then the drivers are mounted and the box is measured to compare with the simulation and possible iteration.
I think what the program wants to see is T/S parameters, free air impedance and free air response so that's my first task. From what I remember, all speakers need to be normalized in output so that the box/crossover design simulation will also be accurate, (hence the 6dB correction factor to normalize to the other drivers measured in free air).
I guess I could just build a box and 'see what happens' but as long as accurate simulation is possible, I would prefer it, (once the data is input, it's much less work than trial and error with power tools
)On the mid, (filler), and tweeter, I can place 2" 6 PCF fiberglass sound deadening panels at the ground and nearest wall reflection points but they aren't really that effective for the woof.
Of course I could get exotic and put the woof and mic on 8' ladders, making the nearest reflection 20' or so.
Thanks,
Phil
P.S. I am an engineer so I understand simulations. From what I've heard, Soundeasy does a very good job and even has methods to output data to allow easy comparison between simulation and actual design. For this reason, I want to be very carefull about getting the initial measurement data right.
Phil,
Yes, the T/S parameters are the first step. This will get you through determining the box size for the low frequency performance of the bass driver.
I looked at the Soundeasy site. The software looks pretty comprehensive so lets assume it can do what it says it can do to a level of satisfaction. After you’ve determined the box size for the bass driver you’ll need to take the frequency response measurements as you have indicated.
In each case of the woofer, mid, and tweeter, IMHO, you should build a baffle and take half-space measurements. The baffle size should be large compared to the wavelength of the lowest frequency to be measured. The tweeter can be measured on a vertical baffle if the measurements are made over a non-reflective surface, like grass. The mid baffle may get a bit large so it would be easiest to mount the baffle a few inches off the ground facing upward. The woofer should be place in a box of a known volume on the ground facing upward and let the ground be the baffle.
The reasons for the half-space measurements are:
- You eliminate reflections that will effect your measurements.
- A baffle can be clamped to a mass so the driver is stable.
- You don’t know the shape of your finished baffles. A half-space measurement will give a good frame of reference to extrapolate to.
- The problem with whole-space measurements is that the drivers dimensions will interfere will its whole-space radiation within the drivers frequency range. This is eliminated in half-space measurements
- In the case of the bass drive, the box is an integral part of the frequency response.
This brings us to the real question.
Can Soundeasy accommodate different baffle shapes and room interactions?
These are two very strong influences on the ultimate sound of the system. Soundeasy may have baffle step compensation and maybe some general room placement compensation, but this won’t be enough to make up for all of the possible variations. The ultimate response in your listening room has to be an estimate based on the known properties of the speakers and the measurements you make. It’s not always easy, and your not always going to be right, but that’s what it is to be a DIY’er.
From here, you’ll need to search the web and journals and find what you can on how these two issues are dealt with in different situations. There are a number of threads on this forum that discuss these issues as well. Then you can decide on a box design that right for your situation.
Rodd Yamashita
Yes, the T/S parameters are the first step. This will get you through determining the box size for the low frequency performance of the bass driver.
I looked at the Soundeasy site. The software looks pretty comprehensive so lets assume it can do what it says it can do to a level of satisfaction. After you’ve determined the box size for the bass driver you’ll need to take the frequency response measurements as you have indicated.
In each case of the woofer, mid, and tweeter, IMHO, you should build a baffle and take half-space measurements. The baffle size should be large compared to the wavelength of the lowest frequency to be measured. The tweeter can be measured on a vertical baffle if the measurements are made over a non-reflective surface, like grass. The mid baffle may get a bit large so it would be easiest to mount the baffle a few inches off the ground facing upward. The woofer should be place in a box of a known volume on the ground facing upward and let the ground be the baffle.
The reasons for the half-space measurements are:
- You eliminate reflections that will effect your measurements.
- A baffle can be clamped to a mass so the driver is stable.
- You don’t know the shape of your finished baffles. A half-space measurement will give a good frame of reference to extrapolate to.
- The problem with whole-space measurements is that the drivers dimensions will interfere will its whole-space radiation within the drivers frequency range. This is eliminated in half-space measurements
- In the case of the bass drive, the box is an integral part of the frequency response.
This brings us to the real question.
Can Soundeasy accommodate different baffle shapes and room interactions?
These are two very strong influences on the ultimate sound of the system. Soundeasy may have baffle step compensation and maybe some general room placement compensation, but this won’t be enough to make up for all of the possible variations. The ultimate response in your listening room has to be an estimate based on the known properties of the speakers and the measurements you make. It’s not always easy, and your not always going to be right, but that’s what it is to be a DIY’er.
From here, you’ll need to search the web and journals and find what you can on how these two issues are dealt with in different situations. There are a number of threads on this forum that discuss these issues as well. Then you can decide on a box design that right for your situation.
Rodd Yamashita
I would look at the McMaster catalog website for different types of damping materials. Whenever we are looking for a thingy to make a whatchamadoit in the lab I look there first. They have just about everything and I recently got some different types of soft rubber from them to fabricate a "tissue grip".
http://www.mcmaster.com/
http://www.mcmaster.com/
Speaker workshop.
Phil,
if you have not already done so, I would suggest you look at the 'project' on SW. There is a speaker project there done by an experienced DIYer who has explained the process in detail from start to finish. This has probably been put there by the folks at SW to explain how to use the software to a person who is starting out. By the way, I have a project currently underway which is my first and I found that info very useful. Don't look at the 'help' files in SW all that much, they are not informative.
The link is:
http://www.speakerworkshop.com/SW/Project/Main.htm
Phil,
if you have not already done so, I would suggest you look at the 'project' on SW. There is a speaker project there done by an experienced DIYer who has explained the process in detail from start to finish. This has probably been put there by the folks at SW to explain how to use the software to a person who is starting out. By the way, I have a project currently underway which is my first and I found that info very useful. Don't look at the 'help' files in SW all that much, they are not informative.
The link is:
http://www.speakerworkshop.com/SW/Project/Main.htm
prash,
Duh! I should have looked there in the first place. Thanks for the link. I'll read through it today.
diypole,
Wow, what a site. I'll definitely add that to my favorites. Thanks!
Rod,
I was actually thinking about all half space measurements after I posted. Since they are all equally set up that would give a good starting point. Since I have the sound deadening material I may try the tweeter both ways. If the curves are equivalent, then I know I can count on the data. The same with the mids and the woofs, (this is a learning exercise afterall! )
I have good knowledge of room interactions, having spent 5 years perfecting my theater room. I have the RTA-60 at 0.4 across the entire band and will get that down to .35 when I find the time. I know I need a couple of bass traps built as well but I'm actually good for now.
What I thought about doing is on the second phase, do the box measurements at the correct mounting height and mic, (listener), height with sound deadener on the ground so that the speaker is optimized for it's actual in-use setup.
Of course that may change once I read over the Soundeasy project! For now I am currently bteaking in the woofs and mids and will start reading the Soundeasy site.
Thanks again all!
Phil
Duh! I should have looked there in the first place.
Thanks for the link. I'll read through it today.diypole,
Wow, what a site. I'll definitely add that to my favorites. Thanks!
Rod,
I was actually thinking about all half space measurements after I posted. Since they are all equally set up that would give a good starting point. Since I have the sound deadening material I may try the tweeter both ways. If the curves are equivalent, then I know I can count on the data. The same with the mids and the woofs, (this is a learning exercise afterall!
)I have good knowledge of room interactions, having spent 5 years perfecting my theater room. I have the RTA-60 at 0.4 across the entire band and will get that down to .35 when I find the time. I know I need a couple of bass traps built as well but I'm actually good for now.
What I thought about doing is on the second phase, do the box measurements at the correct mounting height and mic, (listener), height with sound deadener on the ground so that the speaker is optimized for it's actual in-use setup.
Of course that may change once I read over the Soundeasy project! For now I am currently bteaking in the woofs and mids and will start reading the Soundeasy site.
Thanks again all!
Phil
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