Just had an idea..
We send out a flat gated signal to test FR at whatever axis. Then get a speaker as flat as possible. What about after that, sending an entire song, and then comparing the original input to the output. I wonder what kind of details this could show? Thermal compression comes to mind off the top. seeing how well the speaker can track the wave. Might shine a light on terms such as "fast"
I guess it would have to be outside or in an anechoic chamber.
Is this a thing?
We send out a flat gated signal to test FR at whatever axis. Then get a speaker as flat as possible. What about after that, sending an entire song, and then comparing the original input to the output. I wonder what kind of details this could show? Thermal compression comes to mind off the top. seeing how well the speaker can track the wave. Might shine a light on terms such as "fast"
I guess it would have to be outside or in an anechoic chamber.
Is this a thing?
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You don't have to use traditional test signals to measure audio gear if you have sufficiently advanced analysis tools at hand.
https://ccrma.stanford.edu/realsimple/imp_meas/imp_meas.pdf
The above document mentions the use of Octave, which is freeware or shareware.
http://www.kar.fi/KARAudio/Publications/publications/semsl96.pdf
Transfer Function | Studio Six Digital
Measuring Transfer-Functions and Impulse Responses - Springer
https://www.rationalacoustics.com/files/Getting_Started_with_SmaartLive.pdf
Basically, a system that has non-ideal frequency response, phase response or amplitude response will alter the signal stistically. FR and phase alterations can be determined by dividing the FFT of the output signal by that of the input signal. Alterations of the amplitude distribution can be determined using standard statistical measures and this can give insights to nonlinear distortion.
The time distribution of various frequencies and amplitudes in the test signal whether synthetic signal or music will affect the accuracy of the analysis. Just common sense - if a signal has very little content in a given range, the statistics for that range will be sparse and noisy.
Yes, it's a thing. Meyer's Sound was the first company I knew to do this. Their reasons were a little different though. They wanted to be able to adjust large professional installations in auditoriums in real-time. The idea was to use music as the test signal, and adjust for the effects the audience's bodies would have on the FR in the room. It's not a very nice thing to run test signals while your in the middle of a concert, or any time you have an audience waiting.
Another use of this approach was to measure how the delay and FR for fill-in speakers melded with the stage speakers. You want the sound to appear to be coming from the stage, but you want listeners in the back to get as high a quality of sound as those close up. The speed of sound in air changes with barometric pressure and temperature, so is hard to model, but easy to measure with this approach. Meyers is able to monitor and apply adjustments as the room heats up so that the close fill speakers mesh perfectly with the stage at all times is a very advanced feature. It's probably all automated now. Others may also apply these ideas, Meyer's is just the one I know who does this.
As for "fast" you don't need the Meyer's approach in a home. There are several versions of plots which will show you what you need to know about the details of delayed energy storage of a speaker and the room. I do believe they use some sort of time-gating, usually related to number of cycles.
If you want a lot of details at your listening location, start from the drivers and work your way towards your seat. First, get drivers without ringing. Then measure the entire speaker at 3' to check for cabinet resonances. Then it's about the room. Bass notes in an untreated apartment can linger for almost a second. Mid to Treble can reflect off surfaces and smear or harden the image.
Also, use your ears!
Sit 1' away from your speakers and listen to the details. That's as good as you can get. Notice how as you move away from the speakers that detail disappears, even when you adjust the volume level up. That loss of detail is the real enemy. Most speakers sound much better than their listeners will ever know. Also, sadly, most speakers will show compression without having to worry about thermal effects. Do 1-2' measurements at 70, 90 and 100 DB and you'll see the FR change. No reason to heat them up yet.
High tech Pro companies like Meyers and JBL do sweat the thermal compression problems though.
Best,
Erik
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