Perfectionist Audio Subwoofer - has anyone heard one?

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Has anyone out there 'heard' anything about this sub other than from the instruction manual at ? There are a few links to this manual, but I can't find any other info out there regarding this sub.

From the figures quoted in the manual and a DIY price of $US300, why would anyone build anything else??

FREQUENCY RESPONSE (4 pi measurement): 10 Hz to 240 Hz +/- .8 dB
EFFICIENCY: l watt R.M.S. = 95 dB SPL
64 watts R.M.S. = 113 dB SPL
MAXIMUM SOUND PRESSURE LEVEL: 113 dB SPL @ 1 meter on axis

And I guess if you want more than 113dB then you'd have to build 2. Seriously, is this TL an old 'April Fool' joke or does it actually work?
I happen to own a pair of KEF "Concerto" speakers, which I built from a kit way back in 1975. The woofers are the classic B-139 oval shaped speakers.

At the time, the company I bought the kit from offered me pages of different box construction plans, including a couple of transmission line boxes, and, radical for its day, a separate box for the woofers. I built the standard 3 way box, but I can remember the (what we now call) subwoofer design. It was a tapered box about seven feet long, with a B-139 facing out of one end, and at the other a narrow slot about two inches wide.

The idea was to build two of these boxes, and have them lying on the floor in an unobtrusive location. For those who didn't want a couple of seven foot long boxed laying around, there were also plans to build the boxes with a fold in them. From memory (and my memory is pretty good) that folded design I saw twenty five years ago, is what they're pushing on that site.

BTW, the plans I saw boasted a lower frequency of twenty Hertz, not the ten Hertz claimed on the website you've found.

If this uses the B139 there must be some type of error. Now back
in the 70's I built a design by I. M. Fried that was much like this
speaker. It was 14" x 25" x 48" I may be wrong about the 14" it
might have been 15 or 16". This did have good output down to
14hz or so in my appartment. But the b139 is only 84db/watt if I
remember and TL loading usualy cost you a db or 2.

By the way The Audio Amerture had a similar but larger designe
using a 24" Hartley. The box was 2' x 4' x 8' I think it had good
output down to 8hz.

I've used the KEF B-139 in both transmission lines and sealed enclosures and can report that it works well for either. From about 40-50Hz (sealed--add an octave on the low side if it's in a TL) on up to perhaps 150 or 200Hz they are probably competitive with the best drivers today. The edge that newer drivers have is the ability to go somewhat higher, although I doubt any can match the B-139 for rigidity, which translates into less cone breakup, hence lower distortion. The drivers that go lower have larger Xmax, but in its day, it was considered pretty good in that department, too.
Sadly, they were discontinued. (Doesn't bother me much, I've got a small herd of them wandering around...)
If you can find some cheap, latch onto them--they're excellent drivers. Nearly as good was the Dalesford 10" which was often used in the same transmission line designs (just had to change the mounting). I've only got one of those on hand--the other died when a crossover (solid state) fried and passed DC. Now, whoever heard of a crossover dying? Yes, it happens--just not very often.
Speaking of Fried...anybody got the schematic for the Model "C" crossover?

Thank you for your input on this. I have heard (a while back now) the Concerto's and I wondered if the oval speaker in that was the 139 or not.

So it looks like the specs are a *little* optimistic. It still looks reasonable to fill in an octave and a half below a pair of C88's or 89's from Theil&Partner.
Was it a bargain?

Just bought a pair of Kef Concerto's today for £20 from a car-boot-sale. Don't know what that's called elsewhere, it's a field full of people selling their junk. Most is real cr@p!
The "vendor" assured me they worked well :rolleyes: . Well, I handed over the cash, bought them home, and have been listening for an hour in my workshop, and they sound fine to me! :)

I used to have a pair of these 25 years ago. Funny; I feel I remember them now.:cool: They're quite a lot louder than the current workshop speakers (AE Aegis model 1).
I have SERIOUS problems with this statement:


Less than .9% from 10 Hz to 240 Hz @ 95 dB SPL"

That has to be the average taken from the 10 Hz to 240 Hz passband.

To me you have 2 VERY misleading representations here:

1. That the output (95 db here) is similar regardless of freq. (i.e. suggesting a reasonably "flat" response from 10 Hz to 240 Hz.)

2. That distortion is less than .9 percent at lower freq.s in that 10 Hz to 240 Hz at 95db.

In other words while it may be less than .9 percent at say 100 Hz at 95db, what is both the response and distortion like at around 20 Hz? If its less than 5 percent (2nd order) at 20 Hz at 95 db I'd be astonished - even then THAT would be excellent when compared to most designs.
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