Is nonlinear distortion of (small) speakers unimportant??

[QMuse]

Yes, groundplane is very accurate in the low frequencies. It's in the high frequencies that accuracy falls away as a result of cancellation between the groundplane reflection and the direct sound hitting the microphone. But for a typical measurement mic this won't occur until well into the 1000s of Hz, as I mentioned

And I never said that stepped sine was inferior to log sweeps for groundplane measurements. I think that was SIY discussing that, in the context of in-room measurements (not groundplane), where stepped sine measurements fail to remove the contribution of the room.

Ok, so how do you measure 110cm floostander which has port almost 1m from the woofers? Do you put it sideways on the floor? What is the measurement distance and how exatly is mic positioned relative to the speaker?

And how do you handle linear distortion because of reflections which mic will measure at that position? I hope this is not done at open space because I thought we were discussing in-room measurement..

 

[andreasmaaan]

I hope this is not done at open space because I thought we were discussing in-room measurement..

Sorry, it wasn't my understanding that the discussion was restricted to in-room measurement. Yes, groundplane has to be done outside, away from any reflective surfaces other than the ground.

But anyway, to answer your specific questions:

Ok, so how do you measure 110cm floostander which has port almost 1m from the woofers?

The distance between the woofer and the port is not very relevant. It's the relative distances from each to the mic that matter. These are usually not very significant compared to the measurement distance. However, it could be a problem for a very deep box with the woofer at the front and the port at the back.

Do you put it sideways on the floor?

It would be best to elevate the speaker on a low stand so that there is a gap between the speaker and the ground. The speaker could be either on its side or upright, tilted so that the mic is on the design axis (or whatever axis you are trying to measure). If you place the speaker sideways directly on the ground, the effective width of the baffle will be doubled, leading to a degree of inaccuracy in the measurements.

What is the measurement distance and how exatly is mic positioned relative to the speaker?

This depends on the dimensions of the speaker and the intended listening distance. The same rules apply as for gated "far-field" measurements.

 

[pma]

This was a setup to make a listening test, and yes a DBT as well. Please do not ask the result, it was like a night and day. The small speaker is unable to make any bass in the room and is brittle, sharp and sounds like a washtub or kettle or a kitchen radio in a direct comparison.

I think that in-room response tells the story about tonality, plus there is a high distortion added.

 

[QMuse]

Sorry, it wasn't my understanding that the discussion was restricted to in-room measurement. Yes, groundplane has to be done outside, away from any reflective surfaces other than the ground.

But anyway, to answer your specific questions:



The distance between the woofer and the port is not very relevant. It's the relative distances from each to the mic that matter. These are usually not very significant compared to the measurement distance. However, it could be a problem for a very deep box with the woofer at the front and the port at the back.



It would be best to elevate the speaker on a low stand so that there is a gap between the speaker and the ground. The speaker could be either on its side or upright, tilted so that the mic is on the design axis (or whatever axis you are trying to measure). If you place the speaker sideways directly on the ground, the effective width of the baffle will be doubled, leading to a degree of inaccuracy in the measurements.



This depends on the dimensions of the speaker and the intended listening distance. The same rules apply as for gated "far-field" measurements.

Ok, that was a misunderstanding as I thought you were about to perform groud floor measurement in the room, hence my questions.

 

[AnalogSteph]

Control 1s are small, rugged, inexpensive and make quite a racket for their size. As a product they are no doubt a win. I don't know anyone who would consider them "serious HiFi" though.

This comparison may serve as a reminder that small yet good loudspeakers are not just dropping out of the sky. For a given SPL, what you are lacking in surface area (there's more than a factor of 2 in Sd between 6.5" and 4") you have to make up for in excursion - so you need long-throw woofers with a suitably constant B*l product to match. Not cheap. You also have to make tradeoffs when it comes to the choice of voice coil formers - Al formers are inexpensive and help getting rid of heat, which is important as going deep at a small size comes with low sensitivity, but cause extra electrical nonlinearity due to eddy currents, the bad kind resulting in plenty of IMD. Kapton formers are more linear but less good at the whole cooling business and more expensive.

The good folks at Neumann probably didn't choose the crappiest 4" woofer they could find for their KH80 DSP model, but compare level handling to the bigger KH120, and it is obvious what kind of a difference a 5-1/4" long-throw job makes.
We are seeing a limit of 90-95 dB in the 60-200 Hz region for the former (at 3% no less, 1% is lower by up to 10 dB) while the latter manages to maintain 100 dB almost down to 100 Hz at 1% level and 80 Hz at 3%.
100 Hz at 90 dB gives -30 dB THD (dominant H2) in the KH80, probably still a hair better than the Control 1 Pro woofer, while the KH120 is down to -40 dB, quickly dropping into the -50s above that.
A >10 dB difference in the "bass handling" spec further confirms these findings.

That's clearly not just driver size alone. I suspect that the demand for really good 4" mid-woofers may be small enough that they are just too expensive for speaker manufacturers' tastes. Besides, I can easily find 5-1/4" sub drivers with absurdly long throw (and low sensitivity), while xmax in the 4" class seems limited to a fraction of that. It seems likely that things could be pushed a little further here, but I guess most people's reasoning at this point seems to be why bother when you can make something a little bigger and get substantially more in return. We might still see it happen though. Right now, this size is just outside the sweet spot for mid-woofers and perhaps a better fit for midrange duties.

 

[Jon AA]

Does anybody have the inside info (they don't publish it) on what THX uses for their criteria in output vs distortion testing? I know, the THX brand has been watered down in recent decades, even becoming something of a joke on some things, but from what I've heard their THX Certified Ultra rating (3000 cu ft room, listening distance of 12 feet) for loudspeakers is actually pretty difficult to achieve. Generally speakers that have it can play pretty darn loudly, pretty darn cleanly.