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Andy

KLH history update....model six

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Through the years, various forum posts have mentioned the year of the model six's introduction as 1958, 1959 and 1960. I've just found a review of the six in 'Audio Magazine' from May, 1958 and they state the speaker was introduced in March of '58. In the review they go on to say "It is capable of performance which we have come to think of as unbelievable for such a small cabinet", then going on to say that it sounds almost as good as the KLH model one which costs four times as much. Also of interest, the staff went to the KLH factory, saying "We have seen evidents of much experimentation in the "junk box"where several hundred tried-and-discarded cone types have accumulated. Finally noting that as far as they know, KLH and Bozak are the only U.S. manufactures to make their own cones.

Henry Kloss himself stated in 1996 that the model six was his most important product. I myself am lucky to have found a very early pair of model six's with serial numbers in the 00600's making them early (maybe in the first few weeks of production). What I find most amazing about them besides the exellent sound.....is the cabinet construction, 12-ply 3/4" plywood! I can't think of any other loudspeaker from this era that used 12-ply, it really makes for a beautiful cabinet.

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I purchased a pair in the summer of 1965 serial Nos 39709 and 004940 used. They were apparantly very early models having the woofer cast into the baffle board and the grill cloth non removable. They were the first serious loudspeaker I owned. Immediately on delivery, one tweeter didn't work. I called KLH and they sent me a carton I used to ship it back to them in and the total cost was about $5 for shipping one way. They repaired it and shipped it back for free and offered me an apology. Try to get that today from something you bought even new. Unfortunately, mine are not so beautiful. They were apparantly the unfinished utility versions and the previous owner had painted them brown. You can still see the signs of where a tool was inserted to pry the baffleboard loose in this original repair. Both have been back to the factory while it was still in Cambridge mostly for crossover network repairs. At least once, they removed the cone of one of the woofers to work through the basket and then reconed it. This was not one of their better ideas and the design was of course later changed to have a removeable woofer with an integral full basket. One day I will reseal the surrounds but I'm sorry to say it will be at the sacrifice of the grill cloth material. That's life.

I've always loved the sound of these speakers and although they don't test as well as AR3 or AR3a in may important respects, they always sounded more musical to me in their timbral accuracy and clarity of instuments using commercially made recordings. IMO, they are lightyears ahead of AR2a. Interestingly, on another message board, their smaller counterpart KLH 17 seems to have become a sort of cult speaker. Go figure.

Kloss claimed in his advertising that a great deal of thought went into what he called the octave to octave balance of these speakers and if that means what other people call "voicing" it shows. He said in an interview that he would always use equalization in his subsequent designs to contour the frequency response of his drivers and that he had heard a competitor's model (he didn't say which one) which out KLH6ed the KLH6. Times change and progress eclipses prior achievements and frankly, the way my AR9s are configured now, they have the same basic musical balance as KLH6 (accuracy is accuracy no matter how you arrive at it) but beat them by far in every conceivable way. However, even after 40 years, I still enjoy listening to these speakers very much, a sure indication of their inherent attributes and remarkable value. They were far ahead of their time.

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A low-resolution image of an early, epoxied-in KLH-Six woofer:

http://www.classicspeakerpages.net/dc/user_files/391.jpg

Note the Alnico woofer encapsulated in epoxy, with aluminum legs extending to the front baffle, and epoxied into that surface. Note, too, that the front baffle is MDF, not plywood, as the latter is less well suited for this type of installation. There was some hoopla regarding the 15-layer marine plywood used for the early cabinets, but the front baffle had to be MDF, as it is denser, harder and more stable than plywood.

Henry Kloss got a patent for this method of mounting a driver, and the patent involved the method of alignment and installation details. This method of woofer installation insured that the speaker voice coil and suspension were properly aligned, and the production-line QC was apparently improved over the conventional method. Note that the treated linen surround was inverted, which helped protect the surround once the speaker was mounted, and allowed the baffle to be placed on a flat surface for work (before completion) without mashing in the half-roll cloth surround material. There is an oil-filled capacitor in the rear of the image; most early KLHs, as well as ARs, used these war-surplus capacitors well into the early 1960s.

--Tom Tyson

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Wonderful science, awful engineering. Performance especially in light of cost was a dream, but a necessary repair is little short of a nightmare. Only repairable at the factory which is now a continent away and probably isn't even willing to look at one. No user replaceable parts inside. No way to even get inside short of a crowbar or a sawzall. If I never need another serious repair, it may very well be the end. What a shame.

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Guest palomar

Was there any noteable change in the sound of the KLH-6s when they switched to the standard, removable woofer basket?

Gary

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KLH had a reputation for consistancy of the performance of their speakers. The promised specification was that every production unit would be within +/- 1db of the prototype. I assume that they stuck to that. This was a remarkable achievement for a company producing so many units especially in that era.

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>Was there any noteable change in the sound of the KLH-6s when

>they switched to the standard, removable woofer basket?

>

>Gary

I think that the KLH people at the time would say that there was no difference, but I have heard that the original versions were better. For one thing, the epoxied-in woofer insured a perfect acoustic seal, so gaskets were not a concern, and speaker-to-speaker consistency could be assured. But the real issue now is with collectors of these old KLHs: if a woofer, tweeter or crossover is damaged for whatever reason, repair is virtually impossible, and the speaker is literally rendered junk. It is possible, as soundminded suggested, to literally take a Sawzall (Milwaukee trademark) and cut into the back of the cabinet to try to work on the crossover, but if the woofer voice coil is damaged, the cone has to be literally ripped out of the front of the speaker and a new one put in its place.

http://www.classicspeakerpages.net/dc/user_files/393.jpg

KLH Model Six crossover with oil-filled capacitor

http://www.classicspeakerpages.net/dc/user_files/394.jpg

KLH Six Woofer (inverted surround)

For quite some time a fellow in Massachusetts repaired KLHs, and had extra cones and crossover components and so forth with the capability of repairing these components. He was a former plant manager at the old KLH. I had an old number for him, but it no longer is current:

Dominic DeAngelis

Abington, Massachusetts

617-878-4425

Incidentally, the early KLH Model One, Model Two, Model Three, Model Four (the early Model Five was a tweeter-only box), Model Six and Model Seven all had this epoxy construction. By the mid-1960s KLH did away with this method, but only the Model Six survived out of that original group, and the woofer was changed to the conventional mounting. An updated version of the Model Seven was the KLH Model Five-derived Model Twelve.

--Tom Tyson

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Guest palomar

Tom,

You mentioned that you've heard that the early KLH's might have sounded better. I saw a photo of an old KLH 6 with the epoxied woofer, and it showed the tweeter with no protective screen. (The grill must have either been ripped off, or it was a photo from KLH before the grill was glued on.) If available, it is at the following website:

http://fisherdoctor.com/pictures/other/Speakers/KLH6.jpg

I hadn't gotten an answer in another post, but this seemed like a good time to ask again. Could the addition of a protective screen over the tweeter have been a factor in the difference? I know that the screen changes the sound somewhat (I have newer KLH 6's that I removed the screens from - they now sound a bit more open and less conjested), but I didn't know if KLH made changes to the crossover and/or tweeter to at least try to compensate somewhat for the change.

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>Tom,

>

>You mentioned that you've heard that the early KLH's might

>have sounded better. I saw a photo of an old KLH 6 with the

>epoxied woofer, and it showed the tweeter with no protective

>screen. (The grill must have either been ripped off, or it was

>a photo from KLH before the grill was glued on.) If available,

>it is at the following website:

>

>http://fisherdoctor.com/pictures/other/Speakers/KLH6.jpg

>

>I hadn't gotten an answer in another post, but this seemed

>like a good time to ask again. Could the addition of a

>protective screen over the tweeter have been a factor in the

>difference? I know that the screen changes the sound somewhat

>(I have newer KLH 6's that I removed the screens from - they

>now sound a bit more open and less conjested), but I didn't

>know if KLH made changes to the crossover and/or tweeter to at

>least try to compensate somewhat for the change.

The original KLH Model Sixes didn't have a protective screen on the tweeter. That was added after the system was changed to the conventional mounting methods. The Alnico magnets went away, also, such that the newer ones had ceramic magnets.

The protective screen might have slightly affected the sound of the tweeter, but not by much. If you were to do a "double-blindfold" test of speakers with and without the screen, it might be difficult to detect the differences, even though they probably do exist to some slight extent. The screen was very open, so not too much sound is blocked.

The biggest differences seem to be in the change in the magnets on both the tweeter and woofer, and perhaps other changes to the crossover in the later versions. To lower costs, I believe that the crossover was simplified toward the end of production, but I'm not sure of what the changes were. These changes were made long after Henry Kloss sold KLH. Some others may have additional information on the differences in the original Model Six and the later versions.

--Tom Tyson

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Guest rickcee

Hi I've always wondered about this - any info - Klh 6 vs 17 speakers - the tweeters look the same, the woofers somewhat different, 17 boxes smaller.

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As far as I know the tweeters for the model 6 and 17 (mid to late 60s version of the model 6)are the same. The model 6 woofer had a bigger magnet, a longer voice coil winding.....this, along with bigger cabinet volume gave them deeper bass then the model 17, but not by much if you listen to them side by side. The 17 came out in 1965 for $69. each and it was a great buy at that price, especially considering the model 6 cost twice as much at about $135 each.! I think KLH sold 2:1 more units of the 17 then 6 during this time. It must ghave been a bit of a thorn in the side of Kloss' old company Acoustic research since it's price was about the same as the AR-4x, many folks thought the 17 put out nicer sound then the 4x, plus it had a 10" woofer compared to the 4x having a 8" woofer.

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>As far as I know the tweeters for the model 6 and 17 (mid to

>late 60s version of the model 6)are the same. The model 6

>woofer had a bigger magnet, a longer voice coil

>winding.....this, along with bigger cabinet volume gave them

>deeper bass then the model 17, but not by much if you listen

>to them side by side. The 17 came out in 1965 for $69. each

>and it was a great buy at that price, especially considering

>the model 6 cost twice as much at about $135 each.! I think

>KLH sold 2:1 more units of the 17 then 6 during this time. It

>must ghave been a bit of a thorn in the side of Kloss' old

>company Acoustic research since it's price was about the same

>as the AR-4x, many folks thought the 17 put out nicer sound

>then the 4x, plus it had a 10" woofer compared to the 4x

>having a 8" woofer.

I think this is true that the tweeter used in the later KLH-6 and the KLH-17 were the same, but the speakers had different crossovers. The bass response was better in the Model Six, but as you comment, not by much. This points out the exponential differences in product engineering that have to occur when you seek to go just slightly lower in bass: the AR-3a over the AR-2ax is a good example, in that the AR-3a speaker cost twice what the AR-2ax cost, yet had only a one-third-octave lower bass response. The AR-3a had lower distortion and deeper bass output, but it was not readily noticeable on most music. To get this, the woofer had to have a lower-resonance, heavier moving system, more voice-coil overhang and a larger, beefier cabinet. All this costs a lot of money.

I don't recall the KLH-17 ultimately outselling the AR-4x, but I know that it was close. The 17 could go lower in bass than the 4x and was a bit more forward-sounding, but the 4x was smoother and had better off-axis response. I think that *Consumer Reports* and others generally concluded that the AR-4x was at the top level in accuracy for speakers in this price range. Side-by-side comparisons, however, and the KLH-17 generally came off sounding better than the AR-4x, and this certainly hurt AR's sales somewhat.

--Tom Tyson

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Once again this shows the strange dichotomy between the accuracy of AR speakers reproducing recordings made under the most carefully controlled conditions and the seemingly more natural sounding and accurate reproduction of KLH speakers playing recordings made commercially. AR4x was absolutely amazing reproducing that 1905 nickelodeon at the trade show almost keeping up with AR3 at a fraction of AR3s price. But in the showrooms with almost any recordings, the KLHs just sounded more like live music. Personally, I attribute it to the coloration of the recordings of the day. Many studios in the US used Altec A7s which had a rather harsh upper midrange so characteristic of the horn drivers of the day and recordings made in Britain often used a comparable Tannoy. I recall how excited one sales rep from Altec was telling me he had just sold 59 A-7s to Columbia Records and another telling me that Tannoy was modifying their Concentric Monitor to sound slightly brighter to compete head to head with the Altecs. If the recording is equalized to sound flat in the studio in the final mixdown then the more accurate AR speaker will reflect that sounding muted and remote while the more forward KLH speaker will compensate for it. What a strange irony that the more accurate speaker loses out at all to the design which overcomes the consistant limitations of the recording industry. Today many studios use B&W 801s and 802s which have an entirely different tonal balance. Personally, I find the tonal balance of CDs much more consistant than vinyl phonograph records ever were and once a system sound is equalized to sound reasonably well balanced, it seem more satisfactory on a higher percentage of recordings than was the case in the past.

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>Once again this shows the strange dichotomy between the

>accuracy of AR speakers reproducing recordings made under the

>most carefully controlled conditions and the seemingly more

>natural sounding and accurate reproduction of KLH speakers

>playing recordings made commercially.

I don't follow you here: do you mean that you believe that the live-vs.-recorded sessions were recorded under more carefully controlled conditions than commercial recordings? The AR live-vs.-recorded tapes were made with the same Ampex recorders/Neumann/Sony microphones used in most recording studios, and the setup was very similar except for AR's recording in a more anechoic environment to avoid double-reverberation. Why do you feel that the playback reproduction through KLH speakers played with commercial recordings is more natural-sounding and accurate? What can you use for a reference in this type judgement? Without a reference to live music, how can you know it is more accurate or natural-sounding? Do you think it might be due to the KLH's tendancy to be more forward-sounding than the ARs?

>AR4x was absolutely amazing reproducing that 1905 nickelodeon at >the trade show almost keeping up with AR3 at a fraction of AR3s >price. But in the showrooms with almost any recordings, the KLHs >just sounded more like live music.

Again, I don't follow you here. Without an instant reference to a live performance, how can you make this judgement? Could this be personal preference?

--Tom Tyson

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"AR4x was absolutely amazing reproducing that 1905 nickelodeon at >the trade show almost keeping up with AR3 at a fraction of AR3s >price. But in the showrooms with almost any recordings, the KLHs >just sounded more like live music.

Again, I don't follow you here. Without an instant reference to a live performance, how can you make this judgement? Could this be personal preference? "

Ah but there was a reference to a live recording. AR didn't just compare the Nickelodeon to AR3 but to AR4 as well. Both speaker systems one at a time as I recall it at the New York City consumer audio show (it has been 40 years but that's the way I remember it.)

I think in the era of the early to mid 1960s the choice of equalization of commercial recordings during mixdown and/or perhaps the choice of microphones and their placement compensated for the characteristic voicing of the monitor speakers. While speakers like KLH6 and KLH 17 had much smoother response curves than say A7, they were more similar to it than was AR3 or AR4. Therefore when played through KLH6 say, those speakers sounded more accurate than AR3. Just a theory. The creation of a commercial recording is likely much different than a carefully controlled laboratory experiment and demonstration. The decisions of the commercial recording company may take the limitations of the equipment the recording is likely to be played back through into consideration so that it sounds best to the greatest number of people.

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Guest palomar

Tom,

I noticed on your photo showing the front of the woofer cone, and on my photo as well, that the cone appears to have a smooth texture. All of the woofers that have the standard mounting seem to have a rougher texture (see my attachment). I don't know if it is just due to the picture resolution of the older photos, or if the older ones were really smooth.

If they did indeed have a different texture, could that indicate that KLH may have slighty changed the cone formulation and/or the way that they made them?

(The surround is also has a dark rubber sealant on the later ones, although I'm assuming that this is just a different choice of sealer. I don't think this would have any noticeable effect on the sound.)

Thank you.

Gary

post-101238-1115416643.jpg

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>Tom,

>

>I noticed on your photo showing the front of the woofer cone,

>and on my photo as well, that the cone appears to have a

>smooth texture. All of the woofers that have the standard

>mounting seem to have a rougher texture (see my attachment). I

>don't know if it is just due to the picture resolution of the

>older photos, or if the older ones were really smooth.

>

>If they did indeed have a different texture, could that

>indicate that KLH may have slighty changed the cone

>formulation and/or the way that they made them?

>

>(The surround is also has a dark rubber sealant on the later

>ones, although I'm assuming that this is just a different

>choice of sealer. I don't think this would have any noticeable

>effect on the sound.)

>

>Thank you.

>

>Gary

>

Do you think that the dark surround in your image might be a re-foam job or dark butyl-rubber substance put on the surround? I can't tell, but it doesn't appear to be standard, as I think the surround treatment KLH used was a latex substance that dried to a clear texture. But I don't know what KLH actually used on the later surrounds. As far as the cone texture itself, I think that KLH went from a hand-made felting process in the early ones to a production-line process in the latter ones, and this would probably account for differences in cone texture. Sometimes the back of the cone has the rough texture and the front side shows the smooth side of a mold. Both methods are probably viable -- different ways to get the same basic results. Later versions were likely pressed from both sides, with ridges or texture to help the woofer's response both at the low end in long excursions, and at the high end in the prevention of cone "break-up."

You are probably right in your assessment of sound differences in the early vs. late woofers. I am sure that KLH engineers attempted to replicate or even improve performance of the earlier woofer, but at greatly reduced manufacturing costs. The early ones had to be expensive to produce. Whether or not they succeded is something that would have to be measured.

--Tom Tyson

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Guest palomar

Tom,

First, thank you for your answer.

The surrounds on my KLHs were black when I got them(or at least dark -I don't remember for sure), but I did pick them up used. They had lost their seal, so I re-sealed them with a black, latex caulk (watered down) which had a flat-black look. (I should have known that you'd pick that up right away!) I think the original coating may have had a bit of a shine, although I don't remember for sure.

I have also seen a number of pictures on E-Bay, and the later versions do appear to have a dark coating - at least on the ones I've seen.

Gary

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I have just purchased a pair of model 6 from a pawn shop that sound incredible. What can be said about this particular model. Model 6 serial #17060 with the frequency level switch.

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Very early in the run, probably 3 years in. If they sound good, don't worry about getting inside of them, which is a hideous job with the sealed variety that you have. Most likely have oil filled caps, and those are good until they aren't. So..enjoy! Great speakers. I have 2 pairs, all serials below 20K.

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If this would be of interest(?); original untouched KLH Six epoxy woofer with textured cone, serial number 068038

SAM_1332.JPG

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I've seen Sixes in the 70xxx serial range with glued in tweeters, so this example
is a bit confusing. But I'll add it to the list :-)

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