Only because the distortion energy is dispersed throughout the displayed response. The measurement processing and means of display do make make the distortion evident, but that does not mean the driver's output changes very little with power output - or indeed with power input, as not even they are necessarily the same either due to changes apparent in the driver impedance.
There is a thread here somewhere that discussed it, having trouble finding it
Thank's, yes, edited. It is hard to find the info. What was soundbloke on about? 
Sorry, I don't get the relevance? The comment was about changes in the frequency response due to volume level
Yes it was. And those changes are measurable, just that normally they are lost in the processing that yields the "frequency response". Not seeing them in an FFT-based plot is a limitation of the analysis, not an indication that the frequency response is unchanging with power input and/or power output.
It might be better to leave the "frequency response" for an approximation to the linear component of a driver output and seek a more appropriate measure to characterize its distortion.
And "power compression" is rather vague too because of the thermal masses involved - something that is irrelevant to audibility in a single driver, but not so when that driver is part of a multi-way loudspeaker.
i agree, got any measurements that confirm the whole "response doesn't vary with volume" thing to look at... i'm still in the early collection phase and sorting out measurement errors that could be leading me astray but there does appear to be something happening with response vis a vis volume.
power compression is something i've witnessed coming from a PA background and to me is more of a overall spl issue rather than response variation.
just my
power compression is something i've witnessed coming from a PA background and to me is more of a overall spl issue rather than response variation.
just my
Are you talking about single channel FFT-based measurements (RTA) ?
Or dual channel measurements (transfer function of mag and phase) ?
I ask because I would think dual channel would show any frequency changes with drive level changes, fairly easily ....
Personally, I have a hard time gleaning much from RTA's, in comparison to transfers.
power compression is something i've witnessed coming from a PA background and to me is more of a overall spl issue rather than response variation.
just my
Have you seen Meyer's new test signal for testing power compression?
M-Noise
It's pretty cool...pink noise with an increasing crest factor, as freq increases.
It's supposed to replicate the crest factors found in music better than the constant crest in traditional pink.
I'm looking forward to trying it out for SPL compression, at both the driver and system level. Soon as it gets warm outside.
Wish there was a way to use the M-Noise to measure distortion vs drive levels...
CEA2010 is the best for distortion I've found so far...for subs at least...
REW sine sweeps for the rest...THD definitely rises before compression kicks in, on the speakers/drivers I've tested.....
Neither. The FFT assumes linearity and its application to measuring and analysing non-linearity therefore appears somewhat flawed.
Check those measurements out at hificompass.com, where few if any shows variation on freq response due to drive levels. Measurements at soundstage.com shows small variations too. But subwoofers at sub frequencies can show signs and as can thermal issues
There was this interesting thread, and there are 2 posts that have measurements that I did.
Frequency graphs of speakers....
Frequency graphs of speakers....
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Well, there are not drivers ailates but already implemented in a piece of furniture but serves as an example.
Flat frequency with negative slope is important to enjoy. Dispersion and others parameters too.
Like the distortion.
NRC Measurements: Elac Uni-Fi Slim FS U5 Loudspeakers
SoundStageNetwork.com | SoundStage.com - NRC Measurements: Elac Uni-Fi Slim FS U5 Loudspeakers
Total Harmonic Distortion + Noise
More expensive:
NRC Measurements: KEF Reference 1 Loudspeakers
SoundStageNetwork.com | SoundStage.com - NRC Measurements: KEF Reference 1 Loudspeakers
Total Harmonic Distortion + Noise
The difference is very obvious.
Flat frequency with negative slope is important to enjoy. Dispersion and others parameters too.
Like the distortion.
NRC Measurements: Elac Uni-Fi Slim FS U5 Loudspeakers
SoundStageNetwork.com | SoundStage.com - NRC Measurements: Elac Uni-Fi Slim FS U5 Loudspeakers
Total Harmonic Distortion + Noise
More expensive:
NRC Measurements: KEF Reference 1 Loudspeakers
SoundStageNetwork.com | SoundStage.com - NRC Measurements: KEF Reference 1 Loudspeakers
Total Harmonic Distortion + Noise
The difference is very obvious.
In the Audiophile world, PMC twenty.24 is usually very praised.
NRC Measurements: PMC twenty.24 Loudspeakers
SoundStageNetwork.com | SoundStage.com - NRC Measurements: PMC twenty.24 Loudspeakers
Total Harmonic Distortion + Noise
NRC Measurements: PMC twenty.24 Loudspeakers
SoundStageNetwork.com | SoundStage.com - NRC Measurements: PMC twenty.24 Loudspeakers
Total Harmonic Distortion + Noise
Hi, need help understanding what you're saying...
Because my understanding is that FFT is about the mathematical decomposition of a waveform into a set of sine waves, that sum together to reform the waveform...
And that FFT doesn't care about the source of the waveform,
or whether we would term the waveform 'linear' or 'nonlinear'.....
So I can't picture what you mean by "FFT assumes linearity".....???
Or what you mean by "analyzing non-linearity appears somewhat flawed"?
I guess i should ask what do you mean by linear and non-linear?
Thx
The non-linearity describes the distortion components that are harmonics of the fundamental of which the frequency response graphs. In such a measure, the distortion will be dispersed throughout the range of measure and so be practically indiscernible. Such a frequency response measure is therefore unlikely to tell you anything useful when looking at loudspeaker non-linearity.
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