I am using Bass Box Pro. Some of the drivers I am using (most) do not have the "acoustic data" as part of the driver library. However, it is possible to import this data if it is in the right format. Having the "acoustic data" allows me to better design the crossovers.
Is there a white paper for the procedure to measure the "acoustic data" for a driver?
Or can someone explain how I go about generating this data for my drivers?
Thanks in advance.
Is there a white paper for the procedure to measure the "acoustic data" for a driver?
Or can someone explain how I go about generating this data for my drivers?
Thanks in advance.
This is a pretty big topic, and there are probably tons of post here and all over the internet on taking acoustic measurements. The bottom line is its complicated - particularly, there will be lots of errors in any measurement, and you need to know what they are. The best measurements are ones you do yourself, because what you do changes the acoustic response. I consider measurements necessary to a successful build, but it takes a lot of time, patience and resources to do them well enough.
But, there may be an easier route. Every reputable manufacturer will post a response curve for their driver. It is supposed to be on an infinite baffle, in an anechoic chamber, but to be honest, there usually lot of issues with any of those graphs. But what I'm trying to say is, you find the manufacturer published data for your driver - you copy the graph into SPLtrace, and then it will give you a .frd file that hopefully Bass Box Pro will import and use. Using their data is definitely a compromise though.
Sorry, I hope that isn't too discouraging!
But, there may be an easier route. Every reputable manufacturer will post a response curve for their driver. It is supposed to be on an infinite baffle, in an anechoic chamber, but to be honest, there usually lot of issues with any of those graphs. But what I'm trying to say is, you find the manufacturer published data for your driver - you copy the graph into SPLtrace, and then it will give you a .frd file that hopefully Bass Box Pro will import and use. Using their data is definitely a compromise though.
Sorry, I hope that isn't too discouraging!
The main problem with almost all datasheet frequency response measurements is that they do not represent anything close to what you will get in a real-life speaker box. Drivers are usually measured on an infinite baffle, making the response smooth, flat and appealing. You will not get that response in a box, far from it. The only manufacturer I know that actually measures their (woofer) drivers in a box is SEAS.
So, there is no meaningful standard?
Is the real data I want the acoustic plot from my own enclosure?
That would make sense, I guess. I would think that I want that dat without the crossover. In other words, just a sweep of the raw driver mounted in the vented box I am using.
The whole process seems to be something like Newton's successive approximation.
There is a common standard, and that is infinite baffle or a defined baffle size (IEC baffle - mostly used with tweeters). Problem is however that the standard itself is useless when considering that most speaker drivers are NOT used in infinite baffle, but rather boxes with variable shape and size. So - which box size should be standard? As you see, this is a problem without a good solution. Its like selling car engines specified for a certain 0-60 mph acceleration time...
So what you want is an acoustic measurement of the driver in your own box. Doing such measurements is a science of its own. Usually we measure on-axis, and we try to exclude the listening room from the measurement, by using certain measurement techniques or doing the measurement outdoors high up from the ground (where there is no reflections) or in an an-achoic chamber....
So what you want is an acoustic measurement of the driver in your own box. Doing such measurements is a science of its own. Usually we measure on-axis, and we try to exclude the listening room from the measurement, by using certain measurement techniques or doing the measurement outdoors high up from the ground (where there is no reflections) or in an an-achoic chamber....
Do you have a PC or notebook?
1. Buy the M-audio mobilepre USB soundcard with pre amp for mic.
2. Buy the Parts Express Dayton measurement Mic (with calibration file)
3. Download HOLMimpulse, its found in this forum. Its free and there is lots of help.
4. Create the Sound card calibration file
5. Measure tweeter, lock in time, measure tweeter again
6. Measure woofer.
7. Gating is automatic in HOLM but you can move the gating around.
8. Export Tweeter/woofer files, import them back into X-over pro.
btw, I should have a HOWTO: measure with HOLM thread this week. Its going to be very, very simple because Im disfunctional when it comes to measuring
1. Buy the M-audio mobilepre USB soundcard with pre amp for mic.
2. Buy the Parts Express Dayton measurement Mic (with calibration file)
3. Download HOLMimpulse, its found in this forum. Its free and there is lots of help.
4. Create the Sound card calibration file
5. Measure tweeter, lock in time, measure tweeter again
6. Measure woofer.
7. Gating is automatic in HOLM but you can move the gating around.
8. Export Tweeter/woofer files, import them back into X-over pro.
btw, I should have a HOWTO: measure with HOLM thread this week. Its going to be very, very simple because Im disfunctional when it comes to measuring
Inside measurements are a real problem for me. I have ceramic tile floors thru out most of the house!
Outside would be better. However, I seriously doubt I can hoist 100+ lbs of cabinet in the air, short of renting a crane, which would be a reflective source.
No chambers of any size in this small town.
I might try a ground-plane measurement, but that still needs to be outside and Florida is typically very breezy, so a calm day is another gating event.
However, all this information is helpful, so I thank you very much for the help.
Do you have a PC or notebook?
1. Buy the M-audio mobilepre USB soundcard with pre amp for mic.
2. Buy the Parts Express Dayton measurement Mic (with calibration file)
3. Download HOLMimpulse, its found in this forum. Its free and there is lots of help.
4. Create the Sound card calibration file
5. Measure tweeter, lock in time, measure tweeter again
6. Measure woofer.
7. Gating is automatic in HOLM but you can move the gating around.
8. Export Tweeter/woofer files, import them back into X-over pro.
btw, I should have a HOWTO: measure with HOLM thread this week. Its going to be very, very simple because Im disfunctional when it comes to measuring
The M-audio MobilePre is just what I need! I had the ART USB DualPre, but I fried it and I wanted something that did both input (with phantom power) and output so that I did not need to rely on the built in sound card. The MobilePre looks perfect!
I think that I have a good handle on the tools needed. I just am lost on the actual procedure for getting raw driver data and importing that into Bass Box Pro.
The end result is that I am trying to get a handle on the design and subsequent tweaking of the crossover for my 3-way. I had Madisound generate a design based on my drivers using LEAP, but the design is somewhat incomplete and I now feel that I want to "own" the design.
The only tool I have for crossover and box design is X-over Pro and Bass Box Pro. That should be sufficient to do the job, but I need to fill in the missing pieces in knowledge and real data to get there.
I have X-over pro too, its nice when the driver data is in it already but it lacks many of the drivers I have.
I have not imported my HOLM measurements into it yet successfully, I tried and I got an error. I was going to figure it out this week.
I sent my HOLM Export wav file off to other DIYers that love building crossovers with SoundEasy or LSpCAD (I downloaded LsPCAD to figure it out myself).
I have not imported my HOLM measurements into it yet successfully, I tried and I got an error. I was going to figure it out this week.
I sent my HOLM Export wav file off to other DIYers that love building crossovers with SoundEasy or LSpCAD (I downloaded LsPCAD to figure it out myself).
I can try that.
I have some cushions and I also have a large hairy dog. Do you think I could use her, too?
On the serious side. Let's assume I raise the cabinet up 4 feet in my room, which is 15 feet by 33 feet and somewhat live due to the floor,walls, and ceiling. Will there be a limit to how low I will be able to realistically measure down in frequency with a gated measurement?
This is what my current room looks like (the dog is not shown):
My Listening Room
The large Dalek-shaped objects are my cabinets.
Opps! I forgot to add ceiling height. It is 8 feet at the low end and it rises to about 12 feet at the peak above where the cabinets are now sitting.
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Driver Parameter for Enclosure design
I've skimmed though what's been said here quite quickly, so forgive me if I've missed the point.
From my experience, the most useful parameters for loudspeaker enclosure design, are the "Thiele Small" parameters.
If you don't know what these are, please do some research. It's very usefull stuff.
Unfortunately a lot of driver manufacturers do not provide Thiele Small parameters for their drivers. And for a long time I just had to avoid using these.
But measurements can be made fairly easily.
Check this link for a 'how to':
T-S Parameter Calculator
for some design tips check here too:
Audio Speaker Design Calculators - KBapps.com
I've skimmed though what's been said here quite quickly, so forgive me if I've missed the point.
From my experience, the most useful parameters for loudspeaker enclosure design, are the "Thiele Small" parameters.
If you don't know what these are, please do some research. It's very usefull stuff.
Unfortunately a lot of driver manufacturers do not provide Thiele Small parameters for their drivers. And for a long time I just had to avoid using these.
But measurements can be made fairly easily.
Check this link for a 'how to':
T-S Parameter Calculator
for some design tips check here too:
Audio Speaker Design Calculators - KBapps.com
Equipment Needed
Don't be discouraged by their list of equipment.
You can use software for the sine-wave generator and the frequency meter. The hardware you're discussing will be fine for that.
Then you just need an AC millivolt-meter, and a couple of resistors.
Also, when you add weight to the cone, try to stick it on with something (old chewing gum, maybe) so that it does not vibrate.
-You'll know what I'm talking about if you follow the procedure.
Don't be discouraged by their list of equipment.
You can use software for the sine-wave generator and the frequency meter. The hardware you're discussing will be fine for that.
Then you just need an AC millivolt-meter, and a couple of resistors.
Also, when you add weight to the cone, try to stick it on with something (old chewing gum, maybe) so that it does not vibrate.
-You'll know what I'm talking about if you follow the procedure.
Thanks for joining in. I am familiar with the T/S parameters and have Dickason's book The Loudspeaker Design Cookbook, which is the resource I used for getting the T/S parameters. Right now I am using the published parameters by the manufacture, but will be doing my own measurements shortly.
Where it all falls apart for me is understanding how to capture the acoustic data (as Bass Box Pro calls it) for the raw drivers. Obviously, there is much more than simply sweeping frequencies and understanding the technique for doing this is as important to me as understanding what I am supposed to measure. I am not sure I fully understand either.
That is my knowledge gap. Once I close that I can get back to mucking up my crossover network, which will result in more questions, I am sure.
Pretty good in the equipment category. I need to get my ECM8000 calibrated and pick up an M-Audio MoblePre USB sometime soon. I am an electrical engineer by trade, so I not only have some of the tools I need, I have some familiarity with them, too, which helps.
Most of my knowledge is in software and digital hardware. Nevertheless, there may be a lot to learn, but it is all learnable in time (and money).
TS parameters are fine for woofers (Great for model subwoofers) but IMO they are almost useless for tweeters.
Measuring real impedance (bass box pro does this no?) and getting the impulse response (HOLMimpulse) is key to building crossovers.
Can you build crossovers from TS parameters?
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