The ultimate small speaker - final design peer review thread

[SME]

15 hours ago, peniku8 said:

I mean, theoretically the entire cab acts as passive radiator, which means it amplifies frequencies. It does that well once those frequencies excite a panel resonance, which will then likely result mostly in harmonic distortion. I 'd guess that this kind of distortion has its own complexities, since, for example, a 3rd order resonance at 333Hz will excite 1khz, which will have a complex directionality emanating from a speaker side wall the size of a few square feet, so it might actually be challenging capturing this behavior reliably with a single microphone, especially if the mic is on-axis, which will probably not pick up many resonances coming from the side panels. Mounting multiple Piezos to the cab might yield good results. Piezos are pretty cheap and I happen to have a dozen (drum triggers). I might do some testing in that regard when I have absolutely nothing better to do at some point in the future 😅

Distortion matters in two ways.  First, the flexing of the panels might involve enough "excursion" to be nonlinear, which would *generate new distortion*.  Second, the panel resonances may *amplify existing distortion* produced by the driver inconsistently across frequencies.  These are actually very different mechanisms.  For example, light stuffing may address the problem of amplification by absorbing the higher harmonics before they can leak out, but it might not be thick enough to control energy build-up at the fundamental frequency of the panel where "excursion" is greatest.

And yes, things get more interesting with directional effects, so if using distortion measurements to assess cabinet resonance problems, you'd probably need to do sweeps from at least a few different angles.  I admit it's not a big priority for me either.  I worried about it a lot with my first speakers because some other (cheap) speakers I owned had a buzzing panel resonance.  I think the panel must have been vibrating against a plastic part.  The problem area was narrow in frequency, but it was nasty when triggered.  I could reliably hear it even in fairly quiet sine sweeps.  OTOH, I've never noticed any untold sound from the cabinets that I built, even with pretty loud sweeps.  I largely stopped worrying about it.

[peniku8]

6 hours ago, kipman725 said:

Also does anyone know of a 35mm pole stand that could lift a large 30kg speaker high and stable? something more substantial than the usual tripod stands and with a crank for lifting.

I've worked with the Doughty T55510 and it's good, but expensive. Maybe the cheaper Adam Hall SWU 400 T would fit your needs as well. You'd have to make a mounting plate with a 25mm Spigot where the speaker can rest on, but there are also VESA mounting plates with the same spigot, which might work in your case.

[lowerFE]

13 hours ago, kipman725 said:

Hi @lowerFE,

First time I have seen this thread.  I'm quite interested in your measurement methods, when you perform the ground plane measurement do you perform baffle simulations of both the elongated and normal size baffle and then find the difference for your compensation factor?

Also does anyone know of a 35mm pole stand that could lift a large 30kg speaker high and stable? something more substantial than the usual tripod stands and with a crank for lifting.

Yes I did compensate for the mirror image effect with the exact same technique you mentioned.

In the end I settled with ground plane measurements for bass + midrange in order to get the resolution needed in the lower frequencies, and then quasi anechoic gated measurements for HF. The quasi anechoic measurements get really tedious as one would have to compensate for the fact that if you rotate the speaker on a turntable, the axis of rotation is different from the baffle. Because of that the angles and distances are different and it's a lot of work to compensate. Without the correction the speaker appears to have a lot more directivity than it actually does. 

Another trick, wrapping the mic in Roxul or some damping material really smooths out the >10KHz measurements as tiny reflections coming from the mic stand and mic clip causes bumps in the >10KHz response. However, doing that causes the mic to appear to have a much larger body than it really does, and it causes diffraction effects <10KHz. So two measurements, one with no roxul and with roxul, and a splice is needed in order to get accurate measurements across the board.