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Old 27th October 2005, 11:09 AM   #1
Emiel is offline Emiel  Europe
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Default How to measure frequency response with PC?

Hi all,

I recently finished my first pair of DIY speakers, but I think I'm expiriencing some in-room resonances in the lower frequencies. I'd like to measure the frequency response using my PC and change the active filter to compensate.
This question has probably been asked several times before, but searching the forum for an our or two was not very helpful.

My PC has an onboard soundcard with a microphone connection. What microphone shoul I use and what software is to be recommended? And how should it al be set up? Any other things to keep in mind?
Any tips on frequency measurement are welcome!!

Hope you guys can answer my questions!!

Kind regards, Emiel
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Old 27th October 2005, 11:39 AM   #2
SY is offline SY  United States
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Search "Speaker Workshop." You'll be amazed.
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Old 27th October 2005, 11:47 AM   #3
Emiel is offline Emiel  Europe
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Thanks, I am amazed !

I searched for 'frequency measurement' but got all kinds of irrelevant results.

Thanks!
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Old 27th October 2005, 09:29 PM   #4
Jorge is offline Jorge  Brazil
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Just make sure you plce an attenuator (L-pad like, 10k to 1k would be fine) in the PC audio card input.

Othrwise, there's a big risk of frying the card...
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Old 27th October 2005, 11:06 PM   #5
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You need a measurement mic and a mic preamp. The measurement mic will need a power source which is provided by the mic preamp. Your sound card won't have this.

A popular mic is Behringer's ECM8000. Any basic mic preamp with phantom power will do.

Next you need software.
Something basic would be TrueRTA $70-100. It can show you the most obvious problems you might be having and is easy to use.

Something more advanced would be:
- SpeakerWorkshop (free)
- SoundEasy
- Lspcad
- Clio
- Laud
- others that I'm sure I missed.

Aside from SpeakerWorkshop, the above start around $200 and go up from there. Essentially, they are for designing and measuring loudspeakers.

If you can handle SpeakerWorkshop's learning curve, it's definitely the most cost effective route.
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Old 27th October 2005, 11:28 PM   #6
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Room EQ Wizard is an awesome freeware program that will measure your room response and suggest parametric filters to correct it. For low frequencies only, the Radio Shack SPL meter is the cheapest mic/preamp combo (I think they ship internationally) and the Room EQ Wizard can apply the C-weighting correction curve it needs.
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Old 3rd November 2005, 07:51 AM   #7
Emiel is offline Emiel  Europe
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Thanks for all your replies!

I can use a friend's Shure 16A microphone (http://www.shure.com/pdf/discontinued/16a.pdf) and a small Soundcraft mixing console.
The stated frequence range of the Shure 16A is 50Hz to 15kHz, so I doubt it is fit for my purpose, because the room resonances probably will be below 50Hz.
Any comments?

Kind regards,

Emiel
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Old 3rd November 2005, 04:31 PM   #8
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If you had calibration data for that mic you could probably use it for some things but you really want to use a mic that is designed for measuring frequency response.

You can build one for not a lot of money using a Panasonic capsule. Linkwitz details how to use the Panasonic capsule and even modify it for better performance. That would be the budget method but more time consuming.

Or you can go the Behringer ECM8000 route which retails for 58 euro in your neck of the woods.
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Old 3rd November 2005, 05:09 PM   #9
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Here is a good kit made for this purpose. Click on the microphone preamp link.

http://www.highefficiencyloudspeakers.com/
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