KLH Model Thirty-Three speaker

[Norman Nicolai]

I purchased a set of KLH Model 33 speakers a few days ago off Craigslist for about $25. The cabinets are in rough shape and need a complete refinishing, the tweeters do not work, but the woofers are firing and look to be in great shape. I’m hoping/betting that the tweeters are not working because of bad caps. I’ll know more in a few days when I open them up. The woofers are supposedly the same as the Model 17, and the tweeters the same as Model’s 6 and 17. Oh, and did I mention that the 33’s are not acoustic suspension but are a ported design?

I’m assuming that because of the ported design, these are post Henry, part of the Singer KLH legacy.

If I can get the tweeters to work, and only if I can get the tweeters to work, I’m toying with the idea of restoring them. Otherwise, I’ll just keep the woofers and cabinets as spare parts. I’m figuring that the two woofers alone were probably worth the 25 bucks that I paid for them.

A part of me wants to restore them, but a larger part of me says that if I restore them, I’ll probably be disappointed in the sound, and given the 33’s reputation, I would not be able to recoup much above the $25 purchase price. So why bother with all that restoration labor and replacement capacitor expense? If the tweeters work, I could always sell one tweeter and one woofer to more than recoup my expenses, and keep the working drivers as spares for my existing Model 17 and Model 6 speakers. 

Anyone have any advice or first hand experience with the Model Thirty-Three? It would be nice to have an informed opinion about how they are supposed to sound before I make my decision. 
 

 

[Norman Nicolai]

Just found a closed discussion on this dire started by JKent on the KLH 33 going back about 15 years. His conclusion affirms the idea that the 33’s are nothing special. At the same time it kind of made me curious about they would sound with new caps.

Here’s another question about the KLH 33’s: Since the cabinet is ported and not air tight, do I still have to seal the woofers with Roy C’s special sauce?

[JKent]

Ah. Finally found the thread: 

I no longer have these. They're like "baby Model Fives" and my photos reminded me how important it is to strip and refinish them! Before was dull and lifeless, after refinishing the wood looked beautiful. They also look a lot like the OLAs. Dynaco A-25 or AR-4x.

I don't know what to say about resealing the woofer surrounds. It's an "aperiodic" design so you're right--not airtight. Maybe Roy could advise you on this.

Don't put too much stock in my subjective listening. I compared them to AR-2ax's and preferred the ARs. I did not have KLH Fives on hand at the time, nor AR-3a's. Those would not have been fair comparisons. aybe a better comparison would be the OLA, MFWIW High Fidelity wrote of the Thirty-Three "..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."

YMMV

Edited April 14, 2023 by JKent

[Norman Nicolai]

 

3 hours ago, JKent said:

Ah. Finally found the thread: 

I no longer have these. They're like "baby Model Fives" and my photos reminded me how important it is to strip and refinish them! Before was dull and lifeless, after refinishing the wood looked beautiful.

I don't know what to say about resealing the woofer surrounds. It's an "aperiodic" design so you're right--not airtight. Maybe Roy could advise you on this.

DOn't put too much stock in my subjective listening. I compared them to AR-2ax's and preferred the ARs. I did not have KLH Fives on hand at the time, nor AR-3a's. FWIW High Fidelity wrote of the Thirty-Three "..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."

YMMV

Kent, I found your thread on a Google search with a link to CSP!

Still haven’t opened them up to check the tweeter functionality. If the tweeters are good, I may go ahead and re-cap them, if only to satisfy my curiosity on what they actually sound like. If I like the sound, I’ll take the next step on refinishing the cabinets. 

My basement is getting crowded again with speakers everywhere. And I have my eye on a pair of KLH Model Fives, to boot. I’ve always been intimidated by the crossover rebuild on the Fives. Time to take the next step…

 

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[JKent]

Don’t be intimidated. The Fives aren’t that bad, it’s just those double caps that can be confusing. I’ve done a lot and am happy to help. 

[jessiAV]

Norman, my Model 10's are also a ported design like your Thirty-threes, and have woofers that visually look identical to my Model Seventeens. Both measure about 8 ohms DCR as well, but pushing on the woofer cone is much easier on the Seventeens. Maybe Roy can give us more insights about these models?

   Here is a photo of the Model Tens:

[dxho]

Unique picture! Have not encountered this before. The one on the right appears to have 
the early style glued-in drivers, a la Model One, Two, Three, Four, and Six. These were
apparently built as KLH was shifting to removable speakers. The Seventeen came later
and never used the glued drivers, but it looks like cabinets were the same size.

I would like to also see the rear (terminal plates and serial numbers).

[jessiAV]

Actually, it's just a confusing photo. Both speakers are identical, although the right one is fitted with a fiberboard frame for a yet-to-be-installed grill cloth. Sorry for unintentionally leading you astray with a lower-rez image. You are right, the cabinets are almost the same dimensions as the Seventeens (about 1/4 inch higher).

   Anyway, the woofer surrounds feel noticeably stiffer as compared to my 1965 Seventeens. I will start a new thread about these soon as there is too little information online.

 Norman, maybe let me know if you decide to sell the tweeters?

 

[dxho]

Got it

[RoyC]

On 4/12/2023 at 7:05 PM, JKent said:

I don't know what to say about resealing the woofer surrounds. It's an "aperiodic" design so you're right--not airtight. Maybe Roy could advise you on this.

An aperiodic design allows a specific amount of air to move through a tuned, restrictive "vent" or valve in the cabinet. It is meant to allow the woofer cone to move a bit more freely than it would in an acoustic suspension cabinet. Its intended attributes are to enhance bass response at lower volumes, yet provide much of the cone control of an acoustic suspension speaker at higher volumes. Obviously the woofer and its cabinet have to be designed to work together to prevent bass response aberrations and to provide adequate power handling capability.

It's anyone's guess how finely tuned the KLH 33 and 10 (which seems to be more of an actual ported design?) were, but it would make sense that the woofer surrounds of these models would need to be relatively well sealed to allow the vent/port to do the job properly. Btw, the most famous aperiodic speaker is the Dynaco A25, the woofer of which has a rubber surround.

I don't have enough experience with these models to make any subjective comments about them.

Roy

[Norman Nicolai]

Back to square one...Both tweeters are dead. I get nothing out of of them. Nada. Nothing if hooked up to a speaker cable, and no movement of the cone at all when hooked up to a 1.5V D cell.

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There is however a little bit of a surprise on the inside of the cabinet. From my recent readings, "Aperiodic" systems are supposed to be between an air suspension and ducted system. There is supposed to be some kind of valve or baffle that allows movement of air from inside and outside the cabinet, but it is more restricted than in a ducted port system. Attached are a couple of photos of the port on the Model 33. There is nothing restricting or controlling the airflow in the front or the back of the ducted tube. No baffle or air valve. At this point, I would think the 33's are a just a ported speaker, not an "aperiodic" system where the airflow is restricted and the woofer travels less than a ported system. Unless someone has fooled around on the inside of these speakers and removed something from both cabinets, these are just a ported speaker. BTW, the photo of the inside of the port is a somewhat distorted image. Although it looks like the tube runs all the way to the back of the cabinet, in reality, it ends about 2-3 inches from the back of the cabinet, giving the port somewhat free airflow without restriction from the back of the cabinet.

 

I still haven't decided what I'm going to do, although having gone this far, I'm tempted to look for a pair of used KLH tweeters and complete the project. (In for a dime...)

 

Has anyone ever experimented on replacement tweeters for KLH designs, somewhat like substituting the HiVi tweeters on the AR-2ax? 

 

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[jessiAV]

  For some reason, your pictures at gmail don't seem to open for me.

  Like your Thirty-Threes, the Ten's port is open.  It's six inches deep and ends just about 1 1/2 inches from the rear panel.

 You tweeters may be repairable with very careful 'surgery'. I will try to write you via CSP's mail with details.

[JKent]

Ditto that. Pictures don’t show up. 

[Norman Nicolai]

Let’s try this again…

 

[Martin]

Had a pair of 33s a very long time ago and liked them, so let me offer encouragement to complete your project. Whether or not they were truly aperiodic, it seemed like they were KLH's market response to the highly successful Dynaco A25.  

[RoyC]

15 hours ago, Norman Nicolai said:

Let’s try this again…

Norman...your photo shows your 33's to be a ported speaker, not aperiodic, in which certain low frequencies are emitted from the port.

[JKent]

KLH called it Controlled Acoustic Compliance. I think the port is stuffed with fiberglass but can’t really rely on memory 😉

[RoyC]

6 hours ago, JKent said:

KLH called it Controlled Acoustic Compliance. I think the port is stuffed with fiberglass but can’t really rely on memory 😉

Yeah, which means the woofer moves more freely than it would in a sealed cabinet. This is obviously not a finely tuned design.

[Norman Nicolai]

For what it’s worth, the ports in my newly purchased 33’s are patently open and not stuffed with fiberglass or anything else. Something may hav been removed by a previous owner, but I’m not seeing any signs of previous work.

[jessiAV]

There is a screen covering Norman's tuned port, but otherwise the vent appears nearly identical to the Ten's.

[RoyC]

These are straight forward ported designs, where tubes of specific dimensions are used to pass certain bass frequencies.

All of the aperiodic designs I have seen do not have have a tube as part of its construction. Perhaps the most sophisticated example of an aperiodic vent was manufactured by Dynaudio:  https://site.diy-loudspeakers.com/images/datasheets/loudspeakers/dynaudio/VARIOVENT/DYNAUDIO_VARIOVENT.pdf

Roy

[JKent]

Sorry if I got things off track with my aperiodic comment. I had those speakers years ago, and only long enough to refurbish them. I think this is what got me confused: 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." 

[Norman Nicolai]

I found two working tweeters from a Model 17 and decided to use them in the Model 33 rebuild. I was about 90% finishing rebuilding the crossover with new caps and some new resistors when I put a bit too much pressure on the wires and two of the connectors to the rotary switch broke off. (ouch!) I’ve been working without a schematic, just imitating the connections on the other untouched, unrestored crossover, so I don’t even know what kind of rotary switch it is.

1. Does anyone have a schematic for the Model 33?

2. Anyone know what exact kind of switch it is and what I could use as a replacement?

3. I am not optimistic about finding a replacement switch, so at this point, I would be willing to forego the switch and have the crossover set to a single “normal” position, but without a crossover schematic, I don’t know how to do that and where to begin.

Any ideas?

Photos of untouched and partially rebuilt crossover:

[Norman Nicolai]

More photos attached.

The switch was absolutely filthy and corroded, so I applied a great deal of D5 to it and cleaned gently before working on it. I was afraid to disassemble it entirely because of the lack of a schematic, so the cleaning was only partially successful. 

[Norman Nicolai]

As a non-engineer, this is my best attempt at a crossover schematic for the Model 33: