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BetsyK Simple TL

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I've been talking about this box for a few months, and I finally completed some graphics. This is a folded TL/TQWT that I modeled in Horn Response. I have built a couple of pairs, and they sound great! They started as a project for my brother and sister-in-law who needed moderately sized enclosures. I like this box over vented boxes due to the intrinsic bracing and midbass gain. I have used them against a wall and in corners. You could make the terminus front facing, but I'd make it as pictured as long as you can get them an inch from the wall. Of course, you could also make them side facing.

I have them stuffed with a pound and a half of polyfill per box. I have it concentrated towards the top, and tapering down to stop just above the folds. The brace is arbitrary. You could leave it out, or you could do something more substantial. The drawing assumes 3/4" material. I used "Arauco" ply, which is an almost entirely void free pine that costs less than $25 a sheet.

This is my favorite reasonably sized box for the BetsyK's. I hope you'll ask questions and try them!

Paul
Wild Burro Audio Labs - DIY Full Range Speakers
 

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Oops! I was just pondering the drawing I posted, and it occurred to me that I screwed up badly. As you can see, the box doesn't have sides. That was intentional, and it is assumed that 3/4" sides cover the whole thing. However, the width of the cabinet with sides is 12"! I show the "guts" as being 12" wide, but they are really 10.5". A finished cabinet would be 12"w x 13d" x 44"h, not 13.5" wide as the drawing would seem to indicate.

Part of the design goal was to make very efficient use of both floor space and materials. So, you can get a pair of cabinets out of a sheet and a half of ply (many places sell half sheets). I get all the front, back and sides out of one piece. First, I cut two 44" pieces of the 8' length (allowing you to cut off the edges if they are damaged or not square). The, I cut each of those into two 10.5" (fronts and backs) and 13" (sides) panels. That allows you an extra inch for kerf (I use a thick plywood blade). So, you waste very, very little of the entire sheet and the grain goes up and down on your speaker. Then, I cut strips out of the other half panel for tops, bottoms and braces.

hope that makes sense,

Paul
Wild Burro Audio Labs - DIY Full Range Speakers
 
Vaguely what I had in mind. Probably won't stick religously to
the original 3rd K12 cab I was unsucessfully trying to sketch.
There are measurement discrepancies I've yet to resolve. I'm
just gonna wing it... In Styrofoam, of course...

Yes, I'm aware this cab is scale for 12, and BetsyK is an 8.
But we already know these two like each other, except for
the eyelet thing. Effect of foam is the only real gamble...
Aruco definately where I'd go next if the Foam don't cut it.
 

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That transmission line cabinet doesn't look like it will be very effective as a resonator, because there is a possible path that a pressure wave could take through the enclosure that would almost be a straight line, due to the way the folding is done, and the fluid flow (airflow) will naturally try to follow the path of least resistance, so the line will behave like it is much shorter than what was probably modeled in Hornresp. The pieces that make up the TL labyrinth look more like reflectors than flow guides. I anticipate this design will need lots of stuffing to perform optimally.
 
Betsy simple TL, really?

I think the posted graphic from Paul is more correctly a labyrinth. It reminds me of Lynn Olsen's Ariel in that it uses "offset" bracing or shelves to create it.

I would suggest considering the Demetri MLTQ from Planet10. I built a pair used with 8" FR drivers. It is very good, although a little large. In my case the FR still needs help from a decent tweeter. I have some Silverflute YAG 20-1/Dayton PT2C planar type tweeters that I'll add to them (simply mounted on top of the cabinets) or some Eminence 1-1/2" silk tweeters.
 
I am a novice when it comes to DIY speaker building, but i recently got a pair of Betsy-K drivers in an exchange deal.
I put them in an old Snell K/II enclosure (18 x 11 x 9 inch dimensions = 30 liters) just to mount them in something, and bypassed the tweeter and crossover which are still in the cabinet. I connected them to my 40W class A amp, and have let them play modest volume music for about 50 hours.
It sounds terrible, with an aggressive midrange which seem elevated compared to the rest of the freq range.
Do they need a notch filter or something to get an even freq.response? Is it not possible to use such an enclosure? Do they need longer burn-in?

I realize, having browsed through some of the forum articles about the BetsyK's, that they are mostly used in enormous horn-loaded enclosures, but that is out of the question for my part.

I do like the design of these BetsyK Simple TL by Paul / pjanda1 here in this thread, and have the means to build them. But i am still curious if they _could_ sound OK in the 30 liter Snell K II cabinets, as my original intention was to use these in my living room as TV-speakers.

But, if that is not possible, i will make the Simple TL build, and have them as an extra set of speakers in my music-listening-room.

Thank you for any help and insights,

Regards, Oyvind, Norway
 
No 'hands on' experience with this driver, but plenty with its genre, so yes, a RLC network is one way to deal with its HF 'shout', though due to its rising on axis response, just toeing them in as required is often sufficient, but it may roll off the extreme HF too much if you still have youthful hearing.

Aiming the left one at the far right seating and right one at the far left is a good place to start.

Doing the 'full-range' driver $0.98 'tweak' can help too. This is inlaying a foam 'ring' or stuffing it with polyfil between the whizzer and diaphragm. Some folks have had some luck just using an elastic hair band [or two] or a 'scrunchie’: Scrunchie - Wikipedia, the free encyclopedia

I often knead the starch out of the whizzer and if I overdo it, then stiffen it back up some by applying shellac or similar while others coat them with Dammar or similar. Some folks just cut them off and add a [super] tweeter, so adapting the existing XO may be an option if the tweeters are still good.

These dimensions are outside [o.d.], but inside [i.d.] is what counts for determining box loading, so will have a somewhat smaller net volume [Vb], maybe as little as 19 L.

Regardless, since it’s sealed, using an HT’s 80 Hz XO should work fine once the speakers and LFE channel are level matched.

If you want to run them full range though, a much larger vented cab will be required.

GM
 

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