audio-talk

izzy wizzy wrote: ↑Tue Feb 16, 2021 3:23 pm May I ask where you found this info on aperiodic loading? Is it a sim of some kind?

Well....way back in 1976, when I was doing my final A Level Engineering science I was working on the design of loudspeaker enclosures and the aperiodic design came up from my research into the 1960s designs of Dynaco and their A-25 system. There had also been an article by Edward Jordan, later of Jordan Watts fame, in an ancient Wireless world, belonging to Mr Jepson, our teacher. It was from 1956 or 57, I think. The maths in this was pretty scary as he was using electrical AC theory stuff to electrically simulate various speaker enclosure aspects including something for a Goodmans Axiom something or other, can’t remember the model.

I looked at at the size of a Dynaco, and the plans for a DIY leaky box, using Goodmans drivers and found that the ratio of vent area to cabinet volume appeared to be roughly 8 sq in per cubic foot.
I’ve seen 10 sq in per cubic foot somewhere else, and decided to go down the middle, for no scientific reason, so I ended up with 27 sq in of vent area for my 3 cu ft cabs.

Sorry I can’t be any more helpful. I didn’t develop the aperiodic research any further for the A level as I had to pare down the sprawling project to get it handed in to the examiners. It all seems to be an empirical process even today. There don’t seem to be any hard and fast rules.

However the 9sq in vent area per cubic foot of cabinet seems to work very nicely.
Scott may have the Jordan article but it was very technical and scared the 18 year old crap out of me. For my two penn’orth, there’s no need to get that OCD. The 9 sq in per cubic foot ratio seems perfectly adequate.

For what its worth, the pragmatic way is just to sim a sealed box to give a system Q of 1 with your chosen driver. Build to the box volume given by the sim, then use the ratio to set your vent area from that.

Thanks Steve

Looks like we're playing my song from post 16 of this thread.

Most 'aperiodic' boxes aren't strictly speaking aperiodic (i.e. 'without period'); it's a misnomer for 'leaky sealed box' or 'resistively vented box'. The majority don't employ much in the way of tight engineering since they tend to be used to lower the effective Q through a pressure-bleed of an acoustically under-sized enclosure like Steve's (that's meant in the technical sense of having a system Q > Butterworth, not a pejorative) & aren't necessarily aiming for a very tightly controlled alignment. So the old ROTs you mention Steve are as good as most ways; you just slice holes or high-aspect ratio slots into a box of desired volume & cover with damping. There are more specific alignments, but they tend to get quite involved & it's rare that they offer much in the way of outright benefits. Another way is to model them as a vented box & increase the vent damping in the sim to a very high level. Acoustic / mechanical solution to acoustic problems; they're a good way of cleaning up the LF a bit if a high sealed box Q is causing a bit of excess around system resonance. If they help damp the LF impedance peak a bit, that's a bonus too, although you really need an aperiodic TL to do that thoroughly.

Hi Scott,
Yes I seem to have cottoned on a bit late in the day to what you were saying very early in the thread. I’d been messing about for 12 months, went with the leaky box thing, then discovered you’d mentioned aperiodic, fecking 2 and a lot years ago.

I’ve found the Jordan article Mr Jepson pointed me at all those years ago, on Dave Dlugos’ Planet10 site. Funny how things work out.
http://p10hifi.net/TLS/downloads/TedJordanAperiodic.pdf
The maths is only algebra, most of the time, but it scared me crapless then, not so much now, but I'm older but no wiser.

So, 9 sq" per cubic foot, mine are 4.7 cubic feet, so id want to chisel a hole of 42.3 sq".
So a slot 14" x 3"

A fairly big hole

Yep, that’d do it. Then damp the hole with wadding and finish with the wool felt I gave you.

May I make a couple of suggestions here (been there many times).

Try to avoid cutting large holes if you can. With a large CSA and relatively conventional cross section you will run the risk of the damping material quite literally (and audibly) beating against the cabinet wall. If you want to take this approach & don't want to buy Scan's convenient resistive vents https://www.madisoundspeakerstore.com/f ... -vent-ssv/ is to use the metal grills from PC fans. One inside, one outside; pack space tightly with damping material, be it fibreglass, open-cell foam, rockwool or whatever.

Alternative: slice a full-length slot / slots up the back (or whatever face of the box floats your boat) and cover internally with a thick layer of damping. The high aspect ratio significantly reduces the potential for the damping to move, and you also get frictional losses, increasing the effect. A version of this is to drill multiple small holes in a desired panel, again covering the inside with damping.

Other alternative: use a regular vent. Keep it relatively short (about 50mm) and pack it tightly with damping.

In all these cases, it's a slight juggling act between using sufficient & using too much damping material. At very high packing densities the damping material will become more or less a solid, negating the point of using it, so you'll need to experiment a bit.

The object here is ultimately to bleed off pressure & lower the system Q, i.e. improving the damping at the bottom end; that's typically the main purpose behind this -it allows you to ~mimic a lower Q alignment in an acoustically undersized box.

Klipsch Heresy IV: Fanes: Who needs legs anyway? Sorted!

Hello everyone, my name is Mirko and I am from Solingen Germany.

First of all: My English is not very good, so please excuse mistakes in writing, I use a translation program.

I have been building loudspeakers for 35 years and full range loudspeakers for 20 years. I arrived at the B200 from Visaton and I must say that it is a very good driver. But I want to build a second pair of full-range speakers. I bought a pair of Fane 12-250TC some time ago. These run in 51litre closed cabinets. They have a wonderful sound:

But I would like to have a bit more bass and am thinking of building enclosures exactly like the ones discussed here. I have drawn the speakers in CAD, and I would like to ask the topic creator to check the drawing if I have understood everything correctly. Is it allowed to publish my drawing here? This could also help other people who want to build these speakers.

Thank you for allowing me to be a member of this great forum.

Welcome - nice to have another speaker-builder on the forum !

If you put the drawing up, I’m sure we can have a look at it.

Here is the drawing.


I am sure that I have taken over the dimensions of the housing correctly. But I don't know if the dimensions of the aperiodic holes are correct.

IslandPink wrote: ↑Sat Nov 12, 2022 6:20 pm Welcome - nice to have another speaker-builder on the forum !

Thank you. I hope to be able to contribute productively here.

Fozzibaermopped wrote: ↑Sat Nov 12, 2022 7:12 pm Here is the drawing.


I am sure that I have taken over the dimensions of the housing correctly. But I don't know if the dimensions of the aperiodic holes are correct.

Looks OK to me. It is easy enough to experiment with the slot resistances once you have built the boxes. In fact, you will probably have to do that anyway in order to tailor the low end to your room.