What are the frequency limits of a WiiM?

[QuarryHunslet]

What about a pipe organ 16Hz stop? Useless? I understand there are a handful of organs with an 8Hz stop. Why?

I presume you mean 32’, and 64’ stops respectively.

 

[harkpabst]

I disagree with your contention they are not "reproducing anything"

Maybe just because I didn't make my point clear.

I do NOT believe this cone movement is autonomous, uncontrolled excursion. The woofers are doing exactly as they are 'commanded' by the amplifier & source components.

And I didn't suggest that there was any uncontrolled excursion. The cones are really following the electrical input signal ... to a degree. There's no excess movement.

But they still cannot reproduce sound pressure, they are just moving around a tiny bit of air. There's a massive mismatch of acoustical impedance, thus there's pretty much no output. The frequency response of a reflex enclosure (sealed enclosure) roughly drops by 24 dB/Oct (12 dB/Oct) below approx. the tuning frequency.

This is nothing else but linear distortion! The cones are still following the input signal, but the SPL output doesn't follow the input voltage in a linear way.

True--below some point it ceases to be music. Maybe at that point it becomes entertainment. Should our systems filter everything below 20Hz? What about a pipe organ 16Hz stop? Useless? I understand there are a handful of organs with an 8Hz stop. Why?

If you want to reproduce the full frequency range of a church organ at your home you won't be able to do that with your existing speakers. No church organ covers the octave below 16 Hz. Occasionally people claim that some organs have been built to emit a "7 Hz tone resonating with the human body". I wouldn't even say there's anecdotal evidence for that, just anecdotes.

This recording "might" be a fluke, an error. It might be deliberate. I think the larger point is should our systems be capable of reproducing everything on disk (or file)? Apparently none of the many engineers involved with the various products in my stereo system felt the need to cut off the infrasonic frequencies, even tho much of my gear dates back to the vinyl age.

The fact that your system doesn't have any rumble filter (passive speakers don't have one for simple technical reasons) is no proof that Hi-Fi systems should be able to reproduce sound below 20 Hz though. Even less in a strictly non-linear matter. Many systems had and have switchable subsonic filters. The term "subsonic" when taken literally gives another pretty clear hint, btw.

Fact is, nobody can hear 3 Hz. Period. Many speakers (read: home theatre subwoofers) attempting to reproduce 20 Hz will only do that with ridiculously high non-linear distortion of 10%, 20% or even more. That means, they will also reproduce 2nd and 3rd harmonics (40 Hz, 60 Hz) at such a high level, that these will mostly mask the original 20 Hz tone. The sensitivity of our hearing decreases massively towards lower frequencies.

At a loudness of 80 phone a 20 Hz sine signal must be ~13 dB higher in level than a 40 Hz sine to sound equally loud. At 40 phone the 20 Hz signal must be at least 20 dB louder. That's massive! See:

Equal-loudness contour - Wikipedia

en.m.wikipedia.org

Now let's do the math: Let's assume we have a sub that can produce 20 Hz at 40 phone with 10% 2nd order distortion, then 40 Hz is reproduced exactly 20 dB lower than 20 Hz. Both tones would appear to be of exactly the same loudness to our hearing!

The biggest problem is yet to come:
Even if your speaker cannot generate any meaningful SPL at 3 Hz and even though we couldn't hear it even if it could, the large excursion of the voice coil creates high amounts of non-linear distortion in higher frequencies. Pretty much all relevant parameters of a woofer like force factor BL or voice coil inductance appear to be pretty non-linear with voice coil excursion (plus there's usually increasing hysteresis with higher excursion). The additional current through the voice coil will unnecessarily heat up the motor system. All these effects will modulate the wanted signal.

There's probably no other company that did as much research on speaker distortion as Purifi. Here are two of their blog posts further illustrating the issues (and how Purifi tackle them, of course).

Doppler distortion vs IMD?

purifi-audio.com

Some Speaker Problems That Needed Solving

purifi-audio.com

 

[guy48065]

That's quite a response!
And not necessary.
I never said I want to *hear* 3hz--I'm just glad my system, which is mostly old & nothing special, can reproduce it (there's that word again).

In my OP I merely said I had never *seen* woofer excursion so low-f and I thought it was a cool visual effect.

 

[harkpabst]

We can absolutely agree on the term "effect".