Speaker measurement tools

[bfish]

What?s the likelihood that measurements might be contaminated by a mic preamp, like this one that is designed to ?add warmth to condenser microphones? ?
BEHRINGER: MIC100

I?ve been trying to figure out what?s causing some mysterious 2 millisec / 70cm / 28 inch resonances in my measurements. I?m pretty sure they?re not from room reflections.

Is it necessary to have a mic preamp between a condenser mic (ECM8000) and a sound card (Echo Indigo I/O), or would a plain 48-volt phantom power supply be enough ?

http://img819.imageshack.us/img819/2...03millisec.png

http://img444.imageshack.us/img444/4...isecnormal.png

For the mic pre, it depends on whether the "tube warmth" is mere marketing blather, or real. If it's real, the pre will add harmonics that will invalidate your measurements. To find out, download the benchmark software I linked above, and run the tests with your pre in the loop.

Check the soundcard input level (dBu) spec to see if you need the preamp or not.

Your 28" 2nd impulse is a bit harder. Try moving the mic back. Does the impulse change accordingly?

[Panomaniac]

If you don't care to do the homework before buying your gear, you can join the guys that buy some crap, plug it in, run some tests, then splatter the web with their "scientific data", or at the least can't figure out why their results are unexplainable. Otherwise, read on...

That's pretty offensive.

The M-Audio cards are fine for the hobbyist and can rival much more expensive equipment if used with care. The softwares mentioned here and elsewhere all contain calibration routines for the DAC/ADC loop. I include my mic preamp in that loop. I also use RightMark.

With a modest amount of modern equipment and some practice, good measurements are possible. Most of it comes down to measurement technique, not the equipment. Most hobbyist are not looking for laboratory results, they just want decent tools. Those tools can be had for about $300.

Buying a table saw does not mean you know how to use one. But it's a start. And your chances of getting straight, repeatable cuts is a lot greater than with a handsaw.

[bfish]

...The softwares mentioned here and elsewhere all contain calibration routines for the DAC/ADC loop. I include my mic preamp in that loop. I also use RightMark.

Then you shouldn't be offended.

[bfish]

...Fortunately, there's a simple and freeware option for detailed souncard benchmarking called RightMark Audio Analyser...

Thought I'd elaborate to show the parameters that the free version of RMAA provides. Here's a sample of RMAA data from my card (integral preamp, included in the loop);

[bfish]

... Most hobbyist are not looking for laboratory results, they just want decent tools...

I respectfully disagree. I think they want lab results at bargain prices and there's nothing wrong with that. It's actually doable if do your homework before you buy. That was my point. I learned this the hard way, going thru 3 different setups before I was satisfied.

Whether building speakers from scratch or upgrading and tweaking, DIYers are seeking to get that last bit of performance that simple economics preclude in most production systems. If that last bit of perfomance is shaving a 3dB peak at x frequency, you need the tools to reveal that detail accurately.

[Panomaniac]

Well the equipment might be able to do lab quality results on the cheap, but learning to use it is another matter. Skills take time. And guidance is not unwelcome.

[bfish]

Well the equipment might be able to do lab quality results on the cheap, but learning to use it is another matter...

I completely agree, but learning to use it wasn't the OP's question.

[Panomaniac]

That's why it's another matter.

[sba2]

Bfish,
Thanks for all the good info.

I narrowed the problem down to an interaction between HOLMimpulse and my sound card, an Echo Indigo I/O. Only when a soundcard calibration is used does the caca at 2 msec appear on the IR plot. I don?t know why though?there was no problem when I tried REW (room eq wizard) using a soundcard cal.

Originally I was so focused on the FR plots that I neglected IR ones. I really wish I had magnified and examined the IRs much earlier, before making a multitude of measurements. Now I?ll have to re-measure everything. I tried erasing the soundcard calibrations from my data files, as well as un-checking the calibration box in HOLM, but had no luck. Once the soundcard file is enabled, it seems to become an integral part of the measurements.

Next on the agenda is running some tests using RMAA (thanks again, bfish).

********************

today--

HOLM, measurement of the speaker -- caca at 2 msec still there.


HOLM, measurement of something different (JBL) -- caca at 2 msec still there.


Abandoned HOLM


Installed REW (room eq wizard) & made soundcard calibration.


REW, measurement of the speaker -- caca at 2msec not there
http://img185.imageshack.us/img185/5976/rewb.png


HOLM, restarted, cleared everything, & reset default settings


HOLM, measurement of the speaker, without soundcard calibration -- caca at 2 msec not there
http://img155.imageshack.us/img155/1361/holmwo.png


HOLM, made soundcard calibration
http://img710.imageshack.us/img710/3449/loop.png


HOLM, re-measurement of the speaker with soundcard cal -- caca at 2 msec back again.
http://img294.imageshack.us/img294/1223/holmwith.png

*********************

Echo Indigo I/O soundcard: CardBus-format soundcard for PCs and Macs with two-channel analog inputs and outputs on stereo 1/8" connectors, 128x-oversampling A/D and D/A converters, 24-bit data resolution maintained throughout signal path, onboard 24-bit Motorola DSP for mixing and monitoring, and headphone amp with volume control. Sample rates supported: 32kHz, 44.1kHz, 48kHz, 88.2kHz, 96kHz. Supports full-duplex two-channel in, two-channel out operation. CardBus slot required. Analog input: Frequency response: 10Hz-20kHz, ?0.5dB. Dynamic range: >109dB (A-weighted). THD+noise, 1kHz sinewave at -3dBFS: <0.0014% (A-weighted). Crosstalk, 1kHz sinewave at -3dBFS: <0.0005% (A-weighted). Nominal input level: -10dBV (316mV). Maximum input level: +7.2dBu (1.775V). Input impedance: 10k ohms. Analog output: Frequency response: 10Hz-20kHz, ?0.5dB. Dynamic range: >109dB (A-weighted). THD+noise, 1kHz sinewave at -3dBFS: <0.0013% (A-weighted). Nominal output level: -10dBV (316mV). Maximum output level: +6.3dBu (1.6V).

[bfish]

Glad you found the problem. Unfortunatly I have no experience with HOLM, so I can't help figure out how to fix it.

I noticed your card has stereo mini connectors, which brings back some nightmares I had long ago with an SB Extigy with stereo jacks. The common-to-both-channels neutral pin wasn't grounded, nor was the output neutral common to the input neutral. The details of the problems that caused were too many problems ago for me to remember, all I remember was it was unusable for some testing purposes, so I gave it to a friend's kid to play MP3s through. Might not be a problem with yours, but if it keeps anyone from using an Extigy for measurements, the time it took to type was worth it. (FWIW, the clue that led me to the solution was an unexplainably high degree of stereo crosstalk noted by RMAA).

Another past problem I've had that may only be good for general info...

...Any audio apps on your PC may interfere with your measurement app. Some media players can be very controlling when it comes to your sound card settings. Any add-ins you might have like DFX etc might run on anything sent to your card. Took me several hours to figure out a reverb module I had as an audio addin was causing the crap readings I got. I thought that would only run when I told it to, but that wasn't the case. Had to uninstall it.

While my current setup was close to plug-n-test, I've never had a 100% plug-n-test experience. Oh, sure I could run sweeps, but they weren't right until I fixed whatever it took to get all my cal routines and benchmarking to satisfaction.