Measuring Loudspeakers

[geoffwarner1]

I just picked up my Behringer ECM8000, M-Audio AudioBuddy, TrueRTA and SMAART.

Now I just need help measuring my Titans and Dr200s.

First off, I will be measuring these speakers outside of my warehouse in the center of a 200 foot parking lot.

I can set everything up, I just need to know the following:

1. How do I position the microphone towards the speaker?
2. Which should I use...TrueRTA or SMAART?
3. Do I use QuickSweep or what to actually make the sound signal?

Thanks for your help!

-Geoff

[WB]

Usually the sub is measured half space, so both the sub and the mic are placed on the ground. The mic about a 1/2" off the ground actually.

The mid/top cabinet is usually measured full space, or a combination of half space and full space, with the separation being the baffle step. I just use full space and ignore the lower frequencies.

[Bill Fitzmaurice]

The mid/top cabinet is usually measured full space, or a combination of half space and full space, with the separation being the baffle step. I just use full space and ignore the lower frequencies.

To get a standard half-space result below the baffle step you measure ground plane, above the baffle step measure on-axis, with the cab at least 1 wavelength above the ground. If you measure ground plane above the baffle step the result is quarter-space.

[bgavin]

I use the equivalent mic, the Edirol UA-25 interface, and TrueRTA. My Dell laptop is the test platform, and QSC PLX amps provide the juice.

Always be sure to download the latest TRTA. I own the Level 4 version, and it has been fraught with data integrity bugs since I bought it. I have no idea if it is anywhere close to providing repeatable results yet.

The calibration of your hardware with TRTA is absolutely mandatory.
Here is a calibration tutorial

I use 100 Hz as my anchor point.
In conjunction with two Radio Shack SPL meters and a Fluke DVM, I set 2.83v at the device under test while providing a 100 Hz sine wave. I use the TRTA default settings for loudness.
The point I have to make here is "consistency". Document EVERYTHING you do regarding a test.
Turn on the TRTA listening engine.
Use the RS meters to measure the 100 Hz tone at the same position as the measurement mic.
Click the peak at 100 Hz.
Calibrate the TRTA SPL level to what the RS meters provide.

Ground plane measurements are the choice for subs.
As noted above, place the mic as close to the ground as you can get without touching.
Use the "chirp" sweep in TRTA to generate your test tone. Take several samples until you get one that is representative of your DUT.

These measurements become faulty above a few hundred Hz. Bill can elaborate more on this.
Lift the DUT to 6 feet off the ground, retest.
Ignore the lows, capture the highs.
Combine the two charts.

These are the 10,000 foot view steps. Details are left to the reader to figure out.

[geoffwarner1]

Makes sense, now the only thing im not clear on is what sound file to use for testing subs.

QuickSweep goes too high in the freq.range.

-Geoff

[bgavin]

You cannot hurt the sub under test, so use the full range chirp. You simply ignore the data above 100 Hz, or the crossover point.