How Do I Measuring Driver 'Acoustic Data'

[Loren42]

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.

[cuibono]

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!

[Loren42]

Originally Posted by cuibono

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!

Not at all. It actually makes a lot of sense.

[StigErik]

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.

[Loren42]

Originally Posted by StigErik

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.

[StigErik]

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....

[doug20]

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

[Loren42]

Originally Posted by StigErik

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....

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.

[Loren42]

Originally Posted by doug20

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.

[doug20]

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).