Measuring speaker output

[bumpy]

I have looked into this a little and have settled on the Minidsp microphone (approx £100) and REW software (free). The microphone plugs directly into the USB port of a computer so no need for additional boxes.

But, one question still troubles me "what is the microphone listening to?" cant be the sound of silence :)

[Macca]

You'll be wanting to use pink noise for testing, not Simon & Garfunkel ;)

[bumpy]

So can you just burn a pink noise track onto a CD and pay that on your system?

[Macca]

I don't see why not.

[fatmarley]

https://www.minidsp.com/applications/acoustic-measurements/umik-1-setup-with-rew

[bumpy]

All looks good except they are mainly out of stock due to Covid and where they are still in stock the sellers have bumped up the price. I will wait it out.

[Mr. C]

For a basic speaker meas you can use a DMM, so at least you know the channels are balanced.

Otherwise a couple of you chaps could club together to purchase an audio RTA have seen them for around the £600 mark. This would give a suite of meas that would be helpful.

Ideally Rub and Buzz but that tends to be on the more expensive test equipment.

[grog]

i've got access to all sorts of kit through work, AudioPrecision, SoundCheck, etc.. and at home i use REW, it's pretty much perfect for home use and free.
you can use a half decent soundcard to output the signal, pink noise, sine sweep etc, i use a Emu 0204 i picked up for peanuts.
for acoustic measurements something like the mic you mention will be good, i use a similar style Earthworks mic (direct to USB) , but this is a bit overkill for most home use.
for measuring amplifers, per amps etc, i use RMAA which is free also! i use the same soundcard and get very good results.
there is a good article here https://audioxpress.com/article/practical-test-measurement-sound-cards-for-data-acquisition-in-audio-measurements-part-3
parts 1-7 are linked only from the part 1 page for some reason, but the article covers a lot of good stuff for home measurements,

and i'd highly recommend a cheap mic stand, as even small changes in position can show a surprising change in measured response

[bumpy]

I did try experimenting with the microphone in my iPad and free software, but there is lots of low bass signal showing which is not present in reality. It seems to be listening to the room acoustics or to itself (internal goings on within the ipad).

[fatmarley]

If you want to measure the speakers without including the room, you need to gate the reflections out of the measurement.

This calculator will show how low down in frequency you can measure before reflections will interfere with the results. The further you move your speakers away from boundaries, the lower in frequency you can measure (obviously outside, high off the ground is best).

https://mehlau.net/audio/floorbounce/

[Macca]

Can you post the measurements you have taken Chris?

[AJSki2fly]

I have looked into this a little and have settled on the Minidsp microphone (approx £100) and REW software (free). The microphone plugs directly into the USB port of a computer so no need for additional boxes.

But, one question still troubles me "what is the microphone listening to?" cant be the sound of silence :)

Not sure if you have got the MiniDsp yet or not as you mentioned you were going to wait. If you are doing the measurement on a MacBook the built in microphone is actually quite good and you could measure the speakers using this with REW, REW just defaults to the built in Mic. Alternatively if you have a simple webcam, you can use this as it will have a built in microphone, these are also usually quite good and can be surprisingly sensitive.

It would at least give you an idea for now.

[sailor]

In addition to REW and also very good is : http://www.holmacoustics.com/holmimpulse.php and its free too. Favoured by Earl Geddes.

I am happy with Omnimic V2 but it ain't free. Comes with a special CD with different signals that you can play from your computer or CD Player through your DUT. Uses burst tones for freq. response and will also provide CSD's and spectrograms. A bass decay function can identify room modes and helps with proper subwoofer placement. Excellent if using a DBA

The wavelet spectrograms are great for comparing the performance of various horns and waveguides.

A waterfall plot (CSD) gives RT60 of the whole system including room, clearly indicating where the biggest room problems lie. The desireable RT60 for the average room is around 400ms. This is the time it takes for the sound to decay by 60 dB. You can then introduce bass traps and absorption panels and compare results. This feature is essential for optimising the speaker and room system and has a dramatic effect. This is a very underrated and often overlooked approach to great sound. No power or speaker cable at any price can totally transform your system in the same way. None of this is difficult to DIY.

About $300 and for a little more get an extra CD and cable which allows you to measure the T&S and electroacoustic parameters in less than a second.