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How to measure frequency response of a speaker at home

crabman.me

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Re: How to measure frequency response of a speaker at home

#31

Post by lanthade »

Oh my. I mean, if this guy is happy with his results then more power to him. However, this write up is a textbook case of the blind leading the blind. I don’t even know where to begin. The classic smiley faced EQ, equating spectograph with transfer function, no discussion of phase or any other time domain considerations. It reminds me of when I was 17 and thought I knew everything about computers. Then I went to college and learned how little it was that I actually knew. The author’s knowledge is me when I was 17. I however own thousands of dollars of measurement mics, audio interfaces, and software, and have experience built on decades of pro audio work using those tools and honing my craft.

It’s not my desire to slam the author but it’s also important that people don’t take this correct methodology.

Re: How to measure frequency response of a speaker at home

#32

Post by lanthade »

dietr1ch wrote: post #12
cluckindan wrote: post #3

You need a calibrated measurement microphone to do this for real. Otherwise the microphone’s frequency response will skew the results.

And how do you calibrate a microphone? With a calibrated speaker? :P I'm guessing that there must be a way to either cancel out skews and work around this, but I guess it's just easier to start with a calibrated microphone

Generally speaking “you” do not calibrate a measurement mic. I’m restricting the discussion to measurement mics because that’s pertinent to the OP and because mics have all sorts of frequency responses designed into them on purpose.

Measurement mics (the professionally targeted kind) can with some models be purchased from the manufacturer with a calibration file that can be used by various audio measurement software packages. There are also places that will calibrate your mics for you. In the end what this really means is just figuring out the frequency response characteristics of a given mic relative to a known source. This could just be a case of “we match it to this mic over here.” As long as all the mics someone is using are calibrated to the same standard then it’s less important that they’re perfectly flat in frequency response. I have some really good mics but the bulk of my measurement mics are inexpensive and not calibrated. They work fine though because they all measure close enough to the same that once you figure in all the external parts of a system (the room for instance) the mics minor variations become insignificant. The important thing is that I can put 8 mics around a room and pull reliable data to tune the room and make it sound musical. At the end of the day all the measurement stuff is just there to help you scientifically quantify why a room doesn’t sound right and then you can fix it. Like the last room I tuned that had 2 blown HF drivers and the polarity flipped on some LF drivers. The ears easily said there was a problem. The tools told me right away what they were. Sure I could have found them without the tools and by tweaking settings till everything was right, but the proper tools (and knowing how to use them) makes a huge difference.

Re: How to measure frequency response of a speaker at home

#33

Post by zihotki »

garyfirestorm wrote: post #16
cluckindan wrote: post #3

You need a calibrated measurement microphone to do this for real. Otherwise the microphone’s frequency response will skew the results.

Not just that but the FRF calculation is slightly complex. You need to take into account windowing function, amplitude correction factor, sampling rate and block size of each measurement and %overlap… leakage is a very important thing in signal processing and spectral analysis. Also you need an anechoic environment to capture this, because you would be also capturing room reflections and characteristics of room acous…

Well, you don't need an anechoic environment for that. Just use a time window. Signal will be captured by mic before any reflection arrives. You won't be able to measure lows well, though. But ~300-20k Hz is fine.

Re: How to measure frequency response of a speaker at home

#34

Post by IAmGraydon »

>I eyeballed the two (red) plots and I think they look more or less identical. So I guess there is actually no difference in sound and I just imagined it.

LOL. Why is this even on the front page? He measured it with a phone's mic, then he goes on to "eyeball" the results, which are clearly different even to the eye. He then declares them the same. From top to bottom, everything is wrong with this.

Re: How to measure frequency response of a speaker at home

#36

Post by aljgz »

lanthade wrote: post #31

Oh my. I mean, if this guy is happy with his results then more power to him. However, this write up is a textbook case of the blind leading the blind. I don’t even know where to begin. The classic smiley faced EQ, equating spectograph with transfer function, no discussion of phase or any other time domain considerations. It reminds me of when I was 17 and thought I knew everything about computers. Then I went to coll…

`When disagreeing, please reply to the argument instead of calling names. "That is idiotic; 1 + 1 is 2, not 3" can be shortened to "1 + 1 is 2, not 3".`

`Please don't fulminate. Please don't sneer, including at the rest of the community.`

As a curious person with a degree in Electrical Engineering, and one in Computer Science, very interested in quality audio, etc, I know what you mean.

But please, don't be the person who kills curiousity. This person was curious, did some experiments, and posted the result. If you have time, write some of the major ways that such a measurement is inadequate. If not, link to some resources.

`Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something.`

Re: How to measure frequency response of a speaker at home

#37

Post by niobe »

cluckindan wrote: post #3

You need a calibrated measurement microphone to do this for real. Otherwise the microphone’s frequency response will skew the results.

True, but of the same importance, the speaker cannot be measured independently of the room in a home setup. You need an anechoic chamber, or at least a large and very quiet space. Even a decent size living room will alter the measurements considerably and of course materials matter too.

I have spent a lot of time measuring rooms and you can't underestimate how they can mess with frequencies, but it's also true that good speakers sound pretty good in almost any room, and bad ones will sound bad.

Re: How to measure frequency response of a speaker at home

#38

Post by lanthade »

aljgz wrote: post #36
lanthade wrote: post #31

Oh my. I mean, if this guy is happy with his results then more power to him. However, this write up is a textbook case of the blind leading the blind. I don’t even know where to begin. The classic smiley faced EQ, equating spectograph with transfer function, no discussion of phase or any other time domain considerations. It reminds me of when I was 17 and thought I knew everything about computers. Then I went to coll…

`When disagreeing, please reply to the argument instead of calling names. "That is idiotic; 1 + 1 is 2, not 3" can be shortened to "1 + 1 is 2, not 3".` `Please don't fulminate. Please don't sneer, including at the rest of the community.` As a curious person with a degree in Electrical Engineering, and one in Computer Science, very interested in quality audio, etc, I know what you mean. But please, don't be the perso…

I find it interesting that you chose to respond to my comment like this as opposed to others which are more egregious on the issues you bring up.

That aside though, I did mention a number of issues with the write up. Anyone interested is welcome to dig into them and come back with questions if they desire. This is not however an introductory level topic and I elected to not try to thumb tap out a distillation of a very advanced and multi-faceted topic here.

I would not expect someone with graduate level qualifications and years of experience in software development to try to distill their work down to my level either.

Re: How to measure frequency response of a speaker at home

#39

Post by mikewarot »

cluckindan wrote: post #3

You need a calibrated measurement microphone to do this for real. Otherwise the microphone’s frequency response will skew the results.

For actual speakers, you could use a second of the same type of speaker as a microphone, and assume the losses are similar, do a slow sine sweep through, and just divide all the dB values in half.

Obviously this will only work if there's a passive crossover network, and nothing active in the speakers.

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