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Finished the Thirty-Threes (finally!)


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Finally got around to finishing these. I had bought them on CL about 2 years ago and... well, you know  Here's the thread from when I first bought them:

Thanks to Andy and Steve for providing info. And Greg, who provided the Owner's Manual that is now in the Library. In that thread, Steve F reported:

High Fidelity magazine tested it in August 1970, and described it as "…a modified air-suspension type in which an auxiliary, but acoustically damped, opening on the front baffle helps increase the stiffness of the air mass within the enclosure." It was originally $100 ea. In High Fidelity's 1975 Test Reports compendium, it's listed as $110 ea.

At 23 5/8 x 12 ¾ x 10 5/16 inches, it was just slightly smaller than the AR-2ax/5 enclosures, and a fair amount smaller than the Large Advent. It was a 10" 2-way, crossing over at 1500 Hz, with a 3-position HF level control.

High Fidelity's test results show very commendable response curves, especially the front hemispheric and omnidirectional curves. Their comments were that "..it had a full-bodied, well-balanced, transparent quality that—by comparison to former KLH speakers, seems to put the performers a bit 'more in the room.' "

It's noteworthy, however, that its bass harmonic distortion measurements were markedly worse than the 2ax. At 80 Hz and 100dB SPL, the 33 had 4.5% THD. At 300 Hz and 100 dB SPL, it showed 8.2% THD. For the 2ax, the figures are 1.7% and 1.34% respectively. Even the AR-6—considerably smaller and less expensive than the KLH 33—had significantly less bass distortion: 4.2% and 1.5%.

These have been described as the ported version of the Model Six--same woofer and tweeter, but with a port for extended lows. And they look like the little brother to the Model Fives: Very nice cabinets with the same beveled, solid front frame (also like the Original Large Advents) and the same grille cloth. Like most KLH speakers there were two layers. These had gold synthetic (?) cloth over black.

The woofer cones have a "hot cross buns" pattern of what looks like epoxy glue on the woofers. I've seen this on early AR 2ax woofers and some others. Might this be to stiffen or increase the mass of the cone?

When I bought them from the original owners they were in nice condition, but the finish was very dull, lifeless and had an almost opaque, orange cast(see photo). I did not know about Howard's Restor-a-Finish at the time and that's all they really needed, but I sanded them lightly and applied some Watco Oil. This past week I took them out, used Howard's and then a couple of coats of Minwax Antique Oil. They are a little glossy--Antique Oil is similar to Tung Oil--but I like the ressult. I "may" use a little extra fine steel wool and then wax them.

The crossovers were rebuilt by replacing the electrolytics with new mylar caps. I've gained more confidence in the past 2 years thanks to CSP members (especially Roy and John). Those black and red Callins caps HAD TO GO!!!

The original grille cloth was removed for some experimenting, so I replaced it with Irish Linen. Much more acoustically transparent, I think, than the original double layer, even with a Scotchguard treatment. I did not reinforce the 1/8" Masonite, as I had originally planned. Instead just glued the cloth with Aleene's Tacky Glue. Great stuff! No staples needed. Also used Aleene's to reattach the metal logos.

Speaking of logos. As Andy pointed out, there were "two sizes offered...smaller for models for 22,24,31 etc. and the larger size for models 23, 5, 6, 33 and any other model with a 10 inch woofer, so the 33's would have the larger size badge." Unfortunately, I used my larger stick-on KLH plates on another pair of speakers. Oh well. The smaller ones don't look bad.

So how do they sound? Initial impression is "very good but a little dry." My very unscientific test was to hook up one of these along with one AR2ax and set the AR amp to "Mono." The two speakers seem to be about equal in efficiency--one did not seem any louder

The AR2ax is the "permanent" pair of speakers and if you buy the idea that caps have to break in, the ARs are well broken in while the KLHs are virgins.

On a couple of CDs and a WQXR broadcast, these were the 1st impressions:

On Proprius's "Jazz at the Pawnshop" the Thirty-Threes seemed to do a better job on the vibraphone.
Vocals on "The Christians" (that's a rock group btw--not gospel) the vocals were about even between the KLH and AR, with the KLH just a bit drier.
A recording of Bach piano music on the FM broadcast was pretty close.

But on the other discs, the AR was the clear winner. Fuller, more lush, easier to listen to:
Roy Orbison's vocals on "The Travelling Willburys"
The big bass drums on "Blue Man Group"
The Hammond B3 organ on the Christians (also put on some Joey DeFrancesco and the organ sounds better thru the ARs)
Female vocals: Carly Simon. Just a little warmer thru the ARs.

So: After this very brief listen, the Thirty-Threes are real nice classic speakers but not nice enough to make me give up my AR2ax's. I don't have an AR bias--my absolute favorite speakers in my collection are the KLH Model Twelves (but then, I don't have any AR 3a's--yet).

Ironically, KLH departed from the Acoustic Suspension design in these speakers to get more bass, but the ARs with about the same cabinet size and the same nominal woofer size do the job better. You can read the manual for the Thirty-Three and KLH's explanation of the "Controlled Acoustic Compliance" system here:

As I said--this was a very brief audition, and the caps may not have had a chance to set. But the ARs are staying and the Thirty-Threes will be put up for sale at the local electronics shop (I gotta pare down the size of the speaker collection).
Comments are welcome.







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  • 4 years later...
  • 4 years later...

Hi Arnold and welcome to the CSP!

I'm sorry but I went through my notes and I don't have any record of the cap values. Sorry. Best bet is just open them up and see what's inside. then replace them with modern caps of the same values. There may be some 2-part caps in there: one body with 2 red leads and one black lead. Just replace those with 2 separate caps. Carli caps from Madisound are always a good choice.

Looking at the photo of my crossover, it's not exactly the way I'd do it today but it looks like they may be 2uF, 3uF and 8uF but that's just a guess. See what's in there.


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Arnold -

And the 2μF and 3μF caps (if that's what they are) are wired as if they're replacing a 2-part cap.  But, as -Kent says, the originals should be marked with both the values in microfarads (μF or MFD) and polarity, probably N.P. for non-polarity.  The second of the two photos below are of a 2-part cap similar to the one you're likely to find.



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  • 2 weeks later...

I traced the crossover and found it is similar to KLH 17 except a choke (value unknown) is added in series with the woofer and a 4ohm resistor inserted between the HF network and tweeter, padding the tweeter down to the woofer level (attenuated as a function of the inductor) making the crossover point a bit lower. The interesting thing is that, in theory, one could bypass the choke and 4ohm resistor to arrive at a transfer function identical to model 17. Since the two models (17 and 33) share the same drivers (except for doping on 33's woofer) high probability exists that the modified 33 (basically a 17 in a bigger box - 30 v 20 liter) will sound similar to the stock 17 with the added benefit of deeper bass. Model 33 has a bass half loudness point of about 45hz (similar to KLH 6) vs 55hz for model 17. See my post on audiokarma:


KLH33 crossover.JPG

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