Model 33 speakers?

[JKent]

Can anyone tell me about these? I bought a pair today. Thought they were 3-way acoustic suspension, but turns out they're 2-way ported. I checked the Library and see they were advertised as "the best $100 speakers" in '71 (each or the pair?). They have 10" Woofers, 2.5" Tweeters, 8ohm impedence.

I like the real walnut--no vinyl. The 3-position level controls seem OK. Do these need cleaning like the pots on the AR? I will probably replace the grille cloth with new linen, like my AR speakers. The fiberboard the cloth is mounted to is only 1/8" and pretty flimsy, so I'll probably reinforce it to stiffen and allow the use of 1/4" staples.

Any comments, info or suggestions? These are my first real KLH speakers--not quite "classic" era I guess, but seem nice. Have not listened to them yet.

[Andy]

They were $100 each, and are a bit unusual in the KLH lineup being of ported design. The only other speakers from the early years which were ported were models 10, 24,15 & 19 from the 1963-66 era. The model 33 was about at the end of the classic KLH era, early 70's.

[JKent]

Thanks for the info Andy. I think this was probably $25 well spent (of course, I'm running out of room, with a pair of AR 4's and 3 Allison 4's in various stages of restoration, and the AR 4's and 2's I'm using, and the growing stack of KLH 21 radios and 18 tuners..... It's a disease I think)

[JKent]

Oh--another question: What about the xovers? I replaced the caps in my ARs. Do the KLHs typically need new caps too?

[Andy]

Many folks do replace the caps to assure the best sound. My KLH model 23's and model 20's have original caps and still sound great, so I've left them for now.

Your model 33's should be a fairly low production model, not seen as often as other models....serial numbers below 25,000 ? The competition in hifi speakers was intense by the 70's and even KLH was loosing sales.

[JKent]

right you are-- SN 022000 and 022006. I'm hoping these are not the speakers with epoxied-in woofers, so I should be able to remove the woofers to access the xover and replace the caps. I'm also assuming the value(s) will be marked. Always open to suggestions.

[Andy]

Don't worry, KLH gave up on those epoxied in drivers about 1965. Just be careful with the speaker screws, sometimes the theaded holes are a bit fragile.

If I remember correctly, the model 33 has a beveled edge like the model 5, and like some early Advents. Sounds like you found a decent speaker, worth putting a litle work into being they were about the end of the line for quality KLH speakers from the Cambridge era. By 1975-76 the products really took a dive, example would be the model 56...two way system still using the earier drivers, but placed in a flimsy lighter cabinet wrapped in vinyl.... I recently found a pair and was surprized to see the KLH label, pretty sub-standard. I dropped them at the Salvation Army !

[JKent]

I did open one up to look at the xover. I'm NOT an electronics tech, and the xover looked a little more complex than the Ars I've rebuilt--there were cylindrical thingies and rectangular thingies wired together. Think I'll leave tose alone.

The cabinets are in good condition--just real dull looking. I've refinished several speakers and radios, so I know I can make these look great.

The grille cloth was "OK". One snag, a litle loose, 30 years' dust & dirt accumulation. These will require a bit more attention. As you probably know, they used 2 layers--the outer burlap-type cloth and an inner black. I tried removing the cloth from one speaker and soaking it in cold water and oxyclean. Shrank a little. I plan to look for a suitable replacement. The cloth is more of a "gold" color as opposed to the "oatmeal" color of my ARs. It also has more of a sheen, but I may use the oatmeal color linen on these. One unforseen glitch is the fact that the cloth is fastened to 1/8" fiberboard. My 1/4" staples will go right through! And it's pretty flimsy. I think I'll fasten strips of 1'8" Masonite around the edges to stiffen it and give something for my staples to grab. Will have to also build up the areas where the velcro is attached.

Here's a photo

[Steve F]

An interesting speaker.

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 [sic] 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%.

The KLH 33 was, by all accounts, a fine speaker in its day. But the Classic AR speakers had bass performance that continues to amaze, even today. No “for its time” qualifier needs to be applied to the bass performance—both in terms of accurate frequency response and freedom from distortion—of the original AR speakers.

Steve F.

[tysontom]

>An interesting speaker.

>

>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 [sic] 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%.

>

>The KLH 33 was, by all accounts, a fine speaker in its day.

>But the Classic AR speakers had bass performance that

>continues to amaze, even today. No “for its time” qualifier

>needs to be applied to the bass performance—both in terms of

>accurate frequency response and freedom from distortion—of the

>original AR speakers.

>

>Steve F.

>

I feel that this is a excellent and informative perspective on this loudspeaker and its place in history. Steve F has described this speaker design in comparison with its peers from over at Acoustic Research, and shown the important critical review specs on this speaker. It is this type of data that is important to all of us in better understanding this design's place in history. Thanks for the excellent review, Steve F!

--Tom Tyson

[soundminded]

"the Classic AR speakers had bass performance that continues to amaze, even today. No “for its time” qualifier needs to be applied to the bass performance—both in terms of accurate frequency response and freedom from distortion—of the original AR speakers."

Recent experience with the monster 15" Empire woofers and the seemingly puny AR2a 10" woofers is just more convincing evidence of the truth in this. The reason for the more linear extended response of the AS woofer occurred to me about fifteen years ago when I realized that all woofer/enclosure combinations could be analyzed using Newton's second law of motion which when applied to forced oscillation gives a well known solution for FR which correlates very well with actual experience. But it was only recently that I considered the reason for its substantially lower harmonic distortion. It occurred to me that the restoring force on the cone in and AS woofer is uniform over its entire surface including the surround to the degree that it is restored by air pressure (there is some mechanical restoring force.) This means that there is no radial or circumferential force gradient to create shear across the cross-sectional thickness of the cone which would tend to break it up into harmonic modes. The paper's lack of physical strength is therefore unimportant. OTOH, for mechanically suspended woofers, this force is virtually inevitable because it is impossible to maintain precisely uniform restoring force along both the inner and outer circumferences and any difference will tend to break the cone up. The solution many driver manufacturers use is to employ stronger cone materials such as plastic, aluminium or even magnesium which are more resistant to shear. But unlike paper, these materials do not damp internal vibrations well and tend to ring at higher frequencies. Look at any FR for a metal cone woofer and you will see an FR peak around 2 khz. They have a natural tendency to vibrate at these frequencies because unlike the paper pulp fibers which internally damp energy quickly, their structure especially in the case of metal cones is very efficient at tranmitting vibrations within itself without much loss. I can't say if this was considered in the original design of AR woofers when most speaker cones were made of paper anyway but we certainly are fortunate that it happened that way.

[Guest gregounours]

Hi everybody,

I just picked up a pair of 33 in incredibly good condition. The only thing missing I believe is the logo on the orgibal grill cloth. The owner must have removed them to keep them more visulaly unoptrusive.

Anyway they came with the original documentation that I can scan and send to however wants it. I havent trried them yet as I want dont want to mess up my existing installation (with sweet sounding 23's).

I removed the grills and has pointed out by other they have this strange glue or epoxy pattern on them. I got my pair from an original owner who has not tampered them so that is the original design. There also seem to be to point of solder on the two cones. Very stange. I can send picture if people are interested.

Greg

[Guest mcwest79]

>Anyway they came with the original documentation that I can

>scan and send to however wants it. - Greg

Hi, I just acquired a set of Model 33's that my dad bought new and quit using relatively recently. I just got them home and plugged them in, and I'd forgotten how great a decent set of speakers really sounds. I might be interested in a scan of your documents - I'll check to see if we still have our originals somewhere.

[JKent]

Greg sent it to me and I scanned it and converted it to a 9.3 meg pdf file. Seems to be too big to upload here but if you want I will try to email it to you

Kent

[JKent]

Greg

I just noticed a pair of KLH logo plates on ebay that look like the right ones for the 33s

Kent

[Andy]

If you're talking about no. 250108876434, those look correct. 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. I'm pretty sure it was 1968 when KLH changed to badges made of sheet aluminum which glued onto the grills. prior to this they were die cast and were the screw on type like AR badges.

PS; ask the seller the size to make sure they are the bigger ones.

Andy

[Andy]

Forgot to mention, KLH did have glue on type prior to 1968...models 8, 11,14, 15,19, but many of the model 11,15,19 did not have badges. The Model 8 badge was unique, not used on any othe speaker.

Andy