What makes an apropriate driver for an aperiodic enclosure?

[swak]

The Dynaco A25 and the WD25T use seas drivers on this type of enclosure. What kinds of woofers are appropriate for this kind of use (Qt, VAS, Qm, etc)? Is there a way to simulate aperiodic loadings?

[PeteMcK]

I think Qt is the thing to look at. Most High Qt drvers model best in closed boxes (or open baffle), low Q in vented, so I guess aperiodic would be those drivers that are somewhere in-between, and annoyingly won't model well in either (Probably used as an attempt to get more lows out of highish Q drivers that give a low-midbass hump but don't go low enough below that), Qt of say .5 and up???? (just a WAG)

[planet10]

Aperiodic boxes are one of the areas of speaker design still dominated by guess & by golly.

I have typically used higher Q drivers, but my mentor in aperiodic design successfully used a driver with Q <0,2.

dave

[head_unit]

Aperiodic Speaker Enclosure Design
puts it well:
"An Aperiodic Speaker Enclosure is essentially a poorly sealed box (i.e. leaky)..."
Dick Small (yes, of Thiele-Small fame) said that resistance in a vent was never better than a proper vented box. Please note I'm paraphrasing, that's not exactly how he said it but that was his point. On the other hand, he was speaking theoretically with the implicit assumption that you had perfectly suitable drivers available for every enclosure under consideration. Sometimes if you already have a driver, then you have to make the enclosure suit it.

Loudspeaker Design Cookbook by Vance Dickason uses a lot of measurement and modeling to show the Variovent equates to stuffing a sealed box. (Although at very low frequencies it is just leak really).

After umpteen years as a speaker designer, I'd put aperiodic in the novelty category. Meaning, it's not any better and not magical, but you can try it and see if you like it. But like transmission lines, it's not easy to model so you have to trust to luck a bit.

[Bill F.]

In my way of thinking, it's not very useful to limit the definition of aperiodic alignments to typical monkey coffins with flow-resistive vents. Aperiodic behavior can be usefully created in other types of alignments, too, like a NaO-style U-baffle, a transmission line, or even by stuffing a reflex port.

Taking the U-baffle for example, one could use high stuffing density behind a high-Q driver to aperiodically lower its Qm and its bass peak to a desired point.

[swak]

Thanks to all that have replied so far. I found this blog which brings up some interesting points: Designing Aperiodic Enclosures

I believe planet10 (dave) has contributed there too.

My idea with an aperiodic enclosure is based on treads in this forum from some years ago where Kuei Yang Wang brought up some points I consider very interesting. An aperiodic design can lower the impedance peak at drivers resonance. I remember some posts were I read the aperiodic loading works best with the resistive vent right on the drivers back, sort of what like Eckmiller in Germany did before WW2, as I believe. What I thought is that if that peak in impedance can be tamed with the aperiodic loading, one might be able to use a current amplifier even down to resonance frequency. According to Hawksford, this could dramatically lower distortions and compression (paper available online on his homepage). N. Pass has also played with current amplifiers and has posted encouraging results.

While I am not claiming this type of configuration to be better than others, I find it a very nice experiment. I am building the WD25T which uses aperiodic loading, but porting to a second sealed enclosure. I think it could be a good way to start experimenting with aperiodic loading.

[planet10]

I find the one size fits all idea of things like the variovents somewhat of a simplification & limiting of the tech.

A good example of aperiodic loading (in a TL in this case) is Joe Rasmussen's last speaker.

dave

[planet10]

Originally Posted by swak

Thanks to all that have replied so far. I found this blog which brings up some interesting points: Designing Aperiodic Enclosures

I believe planet10 (dave) has contributed there too.

I don't even see even any indirect contribution of mine there. I do see some flailing around.

Aperiodic in its simpliest sense is without periods. This in the end applies to the suppression of the impedance peaks (or i should say maybe, we don't know what happens real low because the chart is cutoff).

Any box with a hole in it will have a saddle shaped impedance response at the bottom. An aperiodic enclosure suppresses both of these peaks (as interesting as looking at the impedance curve is to look at the 1st derivative of this curve. A classic TL will suppress the lower peak entirely and most of the upper peak. It is aperiodic. I say that my miniOnkens push a vented box towasrds aperiodic -- this can be seen in a ower impedance peak that is greatly, if not completely, reduced.

So one can look at an enclosure and decide if it is aperiodic by looking at the impedance curve. There are a number of routes to this. Joe's (and many clssic) TLs, Perkins PR2, ETM describes "aperic boxes where a sealed box has been stuffed full of damping. One could also have a sealed aperiodic enclosure simply be using a driver of suitably low mechanical Q (very hard to find, but as the benefits of current amps are explored, we may see some). Anyone measure the impedance curve of Dyna A25.A35, A50?

I found the impedance curve for the World Design A25 clone... it is only aperiodic in that the lower impedance peak does seem to be fully suppressed

dave

[FE3T]

Originally Posted by PeteMcK

so I guess aperiodic would be those drivers that are somewhere in-between, and annoyingly won't model well in either

I do vaguely remember reading somewhere that the further you go away from 0,35 (higher or lower) the more errors you will get in a computerized simulation,
Is this correct or pure BS?

[ScottG]

I think this all depends on your application:

Cardioid radiation pattern?

Resistive Impedance?

Lower freq. response near the average in a smaller box than a sealed enclosure?


If you look over Kimmo Sauristo's site, you'll see several designed with the intent of a Cardiod response. The most interesting thing (to me) is his subjective responses to each design.

Joe has the "The Linear Current Loudspeaker" focused on a resistive impedance.. Gary Pimm also achieved this in a sub-woofer design.

The last, "smaller enclosure with more bass", has been the primary emphasis for the design, and as Small regarded (as expressed by Head Unit) - if that's the emphasis look to a bass reflex design.