Horns and Triodes...?

Yea, I'd love to build a pair of the Voight Pipes myself, and was seriously considering it there for a bit. Tom was kind enough to send me some pointers, I'd picked out the Lowthers I wanted to put in them, and I was on the hairy edge of pulling the trigger. Even had a cabinet-maker friend of mine lined up and we were just trying to figure out what variety of solid hardwood to make'em out of and brainstorming about how to sex them up a bit and turn the basic design into something really special and unique. (Well, actually, he spent most of the time making fun of me for my stereo addiction...). Then reality set in. I too live in a one bedroom appartment, fifth floor walk-up, no less. Moreover, going from Thiels (and equipment to drive the hungry mothers) to horns is no small endevour (especially up and down five flights...). Someday, when I have room for a second system, I'll go the horn route. In the meantime, I suppose I can always impose and listen to someone else's, once they arrive....

As for the friend, his wife is very discerning regarding what finds a home in the living room and what doesn't. When she could not only tolerate but actually liked the Abbeys, there was really no question that they were it. Don't matter how good something might sound, if you can't bring it home, won't do you much good.

I tried the Norwegian (the originals, as per Tom) pipes and wasn't thrilled -- with EX-4's.
HOWEVER, what is spectacular: front loaded (tactrix horn) PM-4's driven by "good-bandwidth" 300B (i.e. using big Tango OPT) + an open baffle (sub)woof system.
The tactrix cuts mechanically @120Hz; the woofs x-over 4th order, passive, preceding woofer amp.

And, Tom (Twl) I also experienced PM4's on flat, open baffle with back damping and the same tactrix @ 120Hz. Special construction to support the PM4's.
Sound? Oh well... let me not waste server space with superlatives.

Unsurprisingly, measured response @ 1 m on axis was +3/-2 db to +19kHz. In room response was ~+/-8db which is outstanding in my book.

Now all that's left is money for two PM4's. Better still 4 or 6 to cover mutlichannel needs...

I'm rambling -- Mezmo, sorry.

Greg, that sounds very interesting. Do I take you to mean that there was no enclosure behind the Lowthers, but a tractrix horn in front? If so, that is quite unusual. What subs did you find that were fast enough to blend well with the Lowthers?

Greg, I have the same question as TWL, how do you front load a Lowther? I can figure backloaded horn, but front loaded? Do you have pictures of this beast, a plan or a link? Furthermore, without these schematics or some illustrations, I am curious to figure out how does it cut "mechanically" at 120hz....the subs, everything, you have described is wrecking my brain and now, I am totally obsessed. If you can give me some "fix" I appreciated.

Paul

Hi Tom, Paul- Geez, I don't have the exact measurements handy and no pics yet (I'm a bit of a wet rag -- sorry).

The whole construction is on an open baffle:
The Lowther is wearing the wooden phase-plug.
The tractrix's flare frequency was calculated for 120Hz; mouth diametre just under 1m; throat is just larger than the Lowther's cone+suspension; horn's length under ~1m; presently (and cheapo-ly) the horn is made out of cardboard & I don't remember how many-sided it is (12 probably).

We plan on using suitably treated (i.e. "good-looking") plywood strips for the final, WAF approved, version...

The back of the cone is damped -- good point Tom. In fact, we tried it open baffle (hmmm), covered the lowther with some material (admittedly better), finally made a small rectangular box, damped the spider, no box damping (best - amazingly!). The point is we were getting interfering reflections from the Lowther's back on the open baffle scheme (we *were* close to the back wall, after all -- about 1m away only)

Now to the subwoof. Quite simply, there were 15" Beyma 400's lying around. With a total q in the upper 0,2's, these were unlikely candidates... but then, they were immediately and freely available for the experiment. Xmax looked OK at ~7mm.

We attached these to the baffle (~65cm width) -- one per side. We attached two 50cm sides to the baffle -- more for structural reasons than anything else and to simulate an H woof (open baffle).

Amazingly, this Beyma/Lowther combo works! The beyma is perhaps not the most versatile transducer around but "speed"/(phase) discrepancies are not subjectively perceptible. The B's BL factor of ~22 and a reasonable mms (just over 100gr, if I remember) probably help here.

However, marrying the dba's (horn w/ the woof) was not that easy.

Putting this together:
We matched ("equalised") the Beyma/P-L combo's db level at ~60 Hz to the horn's ~130Hz (the beymas were losing ~7db @60Hz vs 120Hz) & "flattened" it with the low-pass.

As you expect, the 300B drives the lowthers x-overless. Subwoof: we are taking output from the 300B, feeding that into a passive low-pass, then into an old 400W/Ch Phase Linear (P-L; for the young, that's an old manufacturer:)) which drives the Beyma coils directly. Strangely, the passive filter sounds better than an active one we tried.

Final task: align acoustic centres (i.e., bring the woofs forward). This will have to wait until we finalise the woofer units. If finances allow, the supravox 400-EXC with the electromagnet field coil. Makes for a very versatile driver (basically, one can adjust vas & qes->qts). Also, at $7-800 apop, it's an expensive driver.
Is dreaming allowed? TWO Supravox 400 per side in a W config...

A final point-- my personal contribution to this construction is practically nill; I just insisted on trying open-baffle and supported (enthousiastically) front-loading the Lowthers. This friend calculated the exponential (tractrix) horn by himself! That's when he was oblivious to the fact that there are spreadsheets around and that the horn he was working on answers to the name "tractrix"... the fact that he is a PhD in maths & has 25yrs diy experience helped, I suppose...

Cheers!