Aperiodic Project With Existing Parts

Like many people here, I have some leftover parts from my car audio days, including two 12" woofers. At the time of my infliction I was a reader of Richard Clark and David Navone's Autosound 2000 newsletter. They eventually began selling parts for projects modeled after their multi-winning Buick Grand National. After some discussion with them, I purchased their Membrain resistive panels which included the ANN "Aperiodic Normalization Network" to help modify the circuit. (In my vehicle at the time: wow.)

Of course now I want to DIY a pair of cabinets for home subs using the same parts.

I know that the original design included specifications saying the box should be as small as possible, with the "membrain" directly behind the woofer. The woofer is technically inside the vehicle and the membrain is open to the trunk area. The description also mentioned to keep the back wave from the membrain (further will read as membrane) from getting into the car interior and affecting the front wave from the woofer.

FFWD to today and I'm reading about open baffle speakers and open baffle woofers. I'm wondering how effective a woofer would be if the rear panel of a speaker box were moved forward to be within an inch of the woofer, had the membrane mounted to it, then letting the membrane see the rest of the box (to eliminate at least some back wave) and leave it open.

I've seen mention of WinISD around these parts so I'll test that software to see if it can even render what I'm thinking.

The membrane and the ANN were custom made for each speaker back in the day so I've no doubt they will work together well. I'm just curious if creating an open-baffle aperiodic woofer with a five-sided box is worth the effort.

Am I missing something? (likely!)
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Sounds like a good plan, except that an OB in room is not an IB in a car, so in room Q is usually targeted to be ≥ 0.7. The stuffing of the rear chamber is a good idea IMO wih or without the damping membrane. For the price of a little efficiency one can have much greater bass extension through a virtual baffle size increase.

All that aside, I've done Q modification but never to a Q of 0.2 with EQ. I don't see why it wouldn't work but passive critically damped works well enough for me.

Good luck with the experiment!
There was a Speaker Builder article years ago where they replaced the back of a cabinet with layers of fiberglass insulation board to achieve something similar. Can't remember much else about it at the moment, but can probably dig it up if no one else remembers the article.


Joined 2003
Not really, but in the '50s this was sometimes done using the 6" thick? near red shade of FB insulation for between ceiling, floor joists, ditto for 'packing' lossy sealed cabs where the components were loosely covered with cheesecloth.
For some reason, part of the title randomly came to me earlier today. It was in AudioXpress, January 2002, "The Infinite Box Concept, Pt 1"


While looking for that, also ran across the Hartley Boffle. No idea how well it worked, but it was a thing.
"Hartley designed and sold his 'Boffle' speaker, which was apparently the first attempt to remove the effects of the rear bass radiation from speaker cones. The design was a box containing a series of spaced baffles behind the main driver. The baffles were wooden frames with felt carpet underlay stretched across them. Each baffle had a different sized hole cut in it - the first being just behind the driver had a diameter a little smaller than the driver diameter. The second and third were reduced successively in diameter down to 3 inches. The fourth & fifth baffles had progressively larger holes in them & the final one didn't have a hole."

And a thread discussing dual chamber aperiodic enclosures:
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You should provide some info about "Membrain" , I had to search about it. This is the article, if someone else is interested

As I understand, its a flow resistor placed close to drivers cone to lower its Q. Almost same thing was used earlier in Sonab OA-5 speaker. A metal mesh basket filled with fiberglass attached behind driver.

Sonab is vented, while "Membrain" is a closed system which use a car trunk as box. The back wave should be separated from listening space, so I think the best way is to make a closed box (to serve as car trunk).
Hartley "Boffle" is interesting suggestion but back wave elimination is less effective under 100Hz.
Also "Membrain" active equalisation (ANN) is optimized for cars, much smaller listening space than average listening rooms, so response will probably be different.
I think its worth the experiment.
Thanks for all the discussion, everyone. I appreciate it.

Davor D, that's the article I have a PDF of here. Funny how it is still online. Thanks for posting a link. The concept from Autosound 2000 is similar to your description, but the actual box is the small enclosure behind the woofer. The aperiodic vent allows the woofer to see the "right" size enclosure (the trunk provides this) at any frequency or resistance, so to speak. I do agree that separating the front wave from the back wave is an important piece of the puzzle.

My initial idea was to build a dual-chamber box, as you suggested, but that is still likely a rather large box. In other home speakers which use an aperiodic design, don't the vents "vent" to the outside anyway? I think I need to find my old Autosound 2000 Tech Briefs and scan the article again. I have more questions than I expected!

The Hartley Boffle...crazy interesting.

Sounds like a good plan, except that an OB in room is not an IB in a car, so in room Q is usually targeted to be ≥ 0.7.

Excellent. Good point, and it gives me something to think about as I delve into this project.
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Also "Membrain" active equalisation (ANN) is optimized for cars, much smaller listening space than average listening rooms, so response will probably be different.
I think its worth the experiment.

I was digging through Autosound 2000 Tech Briefs and ran across this:
"...The ANN (Aperiodic Normalization Network) is required for each acoustic MemBrain system. This active stereo circuitry uses a completely isolated supply and will provide the necessary response compensation and filtering requirements for your specified speaker."

So actually it is built based on specific speaker parameters. This is good news for me.

If I find the original MemBrain articles I'll scan them and post them up.
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Have not found the original article yet, but was interested to find a mention that there were two types of aperiodic membranes available. One style went over the front of the woofer and allowed the back side to be free air in a trunk, and the second membrane style was for behind a woofer. These two types were referred to as first order for the front of the woofer design, and second order for the behind the woofer design.