Symptoms For Bad Caps? Causes Of Weak Bass?

[boreas]

I've begun the restoration of the Model Seventeens I picked up recently. So far I've refinished the cabinets, which turned out really well, and redoped the woofer surrounds.

Before I began I listened to them a fair amount to evaluate the sound and concluded that they seemed very, very bright and lacking in bass. I thought maybe they were just relatively bright, compared to the level of the bass, and that redoping the surrounds would bring the speakers more into balance.

That didn't happen. Based on the way the surrounds soaked up the dope, I'm convinced that it was necessary and, with two coats, I think I've done enough but there's little if any change in the sound from the speakers. Now, I've never actually heard Seventeens before so I can't rule out the possibility that it's just the way they sound but I've considerable experience under my belt (like thirty-five years) of listening to Model Thirtys. They have virtually identical drivers and cabinet volume so I'd expect the two models to sound quite similar to one another.

As to recapping, I believe I've read that what you notice after replacing the caps is an improvement in the highs but not the lows. Is that so or might recapping the Seventeens give me some more bottom? If it is so, where else should I look to find the missing bass?

Thanks in advance,

John

PS: I just took the Seventeens down and replaced them with the Twenty-Fours I'm working on (and, judging from the sound, maybe finished) and they sound much better, a lot more bass (from an 8" woofer), much more balanced.

[Guest crusty]

Among some of the speakers I have restored were a pair of KLH Model 24's, similar to your 17's but with an 8 inch woofer. I resealed the surrounds using Aleens Flexible Fabric Glue which I thinned 1 part water to 3 parts glue. I applied one coat then after two hours a second. To test for leaks I laid the speaker on its back, removed the woofer and some of the stuffing and placed a small cone shaped piece of smoldering incense in a cup and place it in the cabinet and reinstalled the woofer. After about 15 minutes or when you think the cabinet has filled with smoke, play some music with a lot of bass content. The pumping action of the woofer against the trapped air in the cabinet will force smoke out through any leaks that remain in the surround or anywhere else thats not sealed.

Caps used on low pass filter sections are usually connected in parallel if they do fail the effect would be subtle and perhaps changing the filters crossover slope from 12db (if so designed) to 6db per octave and not have much of an effect on output level as far as low bass output is concerned. While a 12db filter can be preferred as far as keeping a bass driver within its ideal operating band, some speakers are designed with 6db slopes or even no low pass filter at all. But as a rule of thumb if the loudspeaker is a very good one and the designers designed it with a certain type of slope its best to keep it that way and replacing the ageing caps with new better quality ones will have an improvement on the overall sound quality of the loudspeaker.

On the other hand caps used in high pass filters have a very definite effect on sound quality, output and power handling. Often output ceases all together of the high freq. driver when a cap fails. And much improvement is realized when ageing caps are replaced with better quality ones with values equal to one being replaced in the high pass filter.

[bjornklh]

it could do a lot to the speakers output. these speakers are around 40 years old and the electronic parts in the crossover, which determine the sound going to the seperate drivers, wear out real bad. the post above says everything pretty well. very well actually. my experience is with old caps any thing can happen, i have had sets that work fine, then drop bass, lose treble, get too much treble, one speaker sounds different then the other, and ive had some that run forever with the original parts. the 17 isnt a real bright speaker, so there probably is a problem in there.

the crossover determines basically which frequency's will go to each driver, and when the caps dry out, or leak with age, they drift in value, so higher notes can go to bigger speaker and lower notes can go to tweeter and destroy it, or the speaker can be real unbalenced as far as bass and treble, but as old as they are i think all bets are off on what goes on when these caps go.

amps or radios are even cooler when the caps go, ive only had one do this in years of collecting and using old amps daily, but i had a klh 22 turntable/ amp go on me once and take everything connected with it in a horrid buzzing something or other of sound. you know that "old tube radio" buzz, its not supposed to sound like that, its a cap getting ready to blow things up.

i think im just rambling here, i hope this helps someone, maybe too simple. plus the guy above me explained way better.

long story short if you dont like the sound replace them. they will probably run forever as is, but its an ez fix. and they arent a real bright speaker. put your ear next to the woofer, if it sounds like its trying to make higher pitched noises then it should, the crossover has definately headed south.

replace the parts, it will cost you 10$ish and there is instructions on this site on how to do this pretty exactly, it shouldn't take much more then a half hour or so, you wont regret it.

[bjornklh]

it could do a lot to the speakers output. these speakers are around 40 years old and the electronic parts in the crossover, which determine the sound going to the seperate drivers, wear out real bad. the post above says everything pretty well. very well actually. my experience is with old caps any thing can happen, i have had sets that work fine, then drop bass, lose treble, get too much treble, one speaker sounds different then the other, and ive had some that run forever with the original parts. the 17 isnt a real bright speaker, so there probably is a problem in there.

the crossover determines basically which frequency's will go to each driver, and when the caps dry out, or leak with age, they drift in value, so higher notes can go to bigger speaker and lower notes can go to tweeter and destroy it, or the speaker can be real unbalenced as far as bass and treble, but as old as they are i think all bets are off on what goes on when these caps go.

amps or radios are even cooler when the caps go, ive only had one do this in years of collecting and using old amps daily, but i had a klh 22 turntable/ amp go on me once and take everything connected with it in a horrid buzzing something or other of sound. you know that "old tube radio" buzz, its not supposed to sound like that, its a cap getting ready to blow things up.

i think im just rambling here, i hope this helps someone, maybe too simple. plus the guy above me explained way better.

long story short if you dont like the sound replace them. they will probably run forever as is, but its an ez fix. and they arent a real bright speaker. put your ear next to the woofer, if it sounds like its trying to make higher pitched noises then it should, the crossover has definately headed south.

replace the parts, it will cost you 10$ish and there is instructions on this site on how to do this pretty exactly, it shouldn't take much more then a half hour or so, you wont regret it.

[bjornklh]

and i gotta try that smoke thing. im sure my surrounds are bad, but just sounds cool to watch

[boreas]

Among some of the speakers I have restored were a pair of KLH Model 24's, similar to your 17's but with an 8 inch woofer. I resealed the surrounds using Aleens Flexible Fabric Glue which I thinned 1 part water to 3 parts glue. I applied one coat then after two hours a second. To test for leaks I laid the speaker on its back, removed the woofer and some of the stuffing and placed a small cone shaped piece of smoldering incense in a cup and place it in the cabinet and reinstalled the woofer. After about 15 minutes or when you think the cabinet has filled with smoke, play some music with a lot of bass content. The pumping action of the woofer against the trapped air in the cabinet will force smoke out through any leaks that remain in the surround or anywhere else thats not sealed.

Caps used on low pass filter sections are usually connected in parallel if they do fail the effect would be subtle and perhaps changing the filters crossover slope from 12db (if so designed) to 6db per octave and not have much of an effect on output level as far as low bass output is concerned. While a 12db filter can be preferred as far as keeping a bass driver within its ideal operating band, some speakers are designed with 6db slopes or even no low pass filter at all. But as a rule of thumb if the loudspeaker is a very good one and the designers designed it with a certain type of slope its best to keep it that way and replacing the ageing caps with new better quality ones will have an improvement on the overall sound quality of the loudspeaker.

On the other hand caps used in high pass filters have a very definite effect on sound quality, output and power handling. Often output ceases all together of the high freq. driver when a cap fails. And much improvement is realized when ageing caps are replaced with better quality ones with values equal to one being replaced in the high pass filter.

Thanks for the reply, Crusty. I'm pretty confident that the woofers have been pretty well sealed at this point. I've applied 3 coats using diluted siliconized latex caulk. The first coat disappeared into the cloth completely so they really needed sealing! I've used this on two pair of Model Thirtys and a pair of Model Twenty-Twos (same as the Twenty-Four but not part of a system) and I've been pleased with the results so far.

So, I guess I should be looking at the capacitors for my improvement in sound quality. I'll start that process on Monday. There's a local place where I can probably pick up everything I need.

I hope that does the trick. The refinishing of these speakers really went well. These have particularly nice veneer and I was able to bring them up without using stain to even out the color which is the way I prefer to do it. I had to both replace the grille cloth on these and make new boards and was lucky enough to find some linen that's pretty close to the original.

So, in short, they look really good and I want them to sound that way too.

John

[boreas]

it could do a lot to the speakers output. these speakers are around 40 years old and the electronic parts in the crossover, which determine the sound going to the seperate drivers, wear out real bad. the post above says everything pretty well. very well actually. my experience is with old caps any thing can happen, i have had sets that work fine, then drop bass, lose treble, get too much treble, one speaker sounds different then the other, and ive had some that run forever with the original parts. the 17 isnt a real bright speaker, so there probably is a problem in there.

the crossover determines basically which frequency's will go to each driver, and when the caps dry out, or leak with age, they drift in value, so higher notes can go to bigger speaker and lower notes can go to tweeter and destroy it, or the speaker can be real unbalenced as far as bass and treble, but as old as they are i think all bets are off on what goes on when these caps go.

Thanks, Bjornklh. You've pretty much described what's going on with these speakers. There's too little bass and too much treble. And, no, I wouldn't expect the Seventeen to be very bright since the drivers are basically the same sizes and the cabinets the same volume as the Model Thirty which I know quite well. My Thirties are definitely not what you'd call bright.

Being designed by the same guy at more or less the same time, I'd expect the two models to be very similar. I'm thinking that the Thirty was probably basically a less expensive Seventeen (RCA connection and non-adjustable crossover), designed for use in a modular system. I hooked my Thirties up to the same system as I'd had the Seventeens connected to and did a back-to-back. Quite a difference!

So anyway, recapping seems to be the answer. As you say, they're 40 year old speakers. The woofers are both date stamped "August 25, 1968" so it would be normal to expect the caps to have gone out of spec.

Maybe I'll even drag myself into the 20th century and get a digital camera. I could then take a photo of my handiwork when I've got them sounding as good as they look.

Thanks again,

John

[Guest crusty]

Boreas I hope with that much diluted caulk on the surrounds they didn't stiffen to much, if so that would have quite a negative effect on how well the woofer operates ,ie looseness of the surround allows the cone to travel back and forth in response to the incoming signal and should do so as freely as possible in an acoustic suspension speaker. I remember having listened to a pair of 17's years ago and was pleasantly surprised by the similarity to small advents in sound. A bit bass heavy but had a very nice warmth to the sound.

Should you proceed with cap replacement you might take things a step further and replace all the internal wiring with good quality 16 or 14 ga OFC speaker wire. This would also have a very positive effect on the total output of the speaker, I know many manufacturers back in those early years did not place high importance on the size or type of wire they used. Advent's and KLH's often were wired with just 18 ga or smaller wire, usually just standard hookup wire.

I hope your project goes well.

bjornklh, thanks for the comments but my high tech smoke trick was really a last resort, although jasmine flavored seems to work the best.

[boreas]

Boreas I hope with that much diluted caulk on the surrounds they didn't stiffen to much, if so that would have quite a negative effect on how well the woofer operates ,ie looseness of the surround allows the cone to travel back and forth in response to the incoming signal and should do so as freely as possible in an acoustic suspension speaker. I remember having listened to a pair of 17's years ago and was pleasantly surprised by the similarity to small advents in sound. A bit bass heavy but had a very nice warmth to the sound.

Should you proceed with cap replacement you might take things a step further and replace all the internal wiring with good quality 16 or 14 ga OFC speaker wire. This would also have a very positive effect on the total output of the speaker, I know many manufacturers back in those early years did not place high importance on the size or type of wire they used. Advent's and KLH's often were wired with just 18 ga or smaller wire, usually just standard hookup wire.

I hope your project goes well.

Yes, I hope so too. I've used the same material to seal three sets of speaker surrounds prior to the Seventeens and Twenty-Fours I just did and the results are still good two years down the road so I think they're as stiff as they're likely to get.

I gently worked the woofers in and out to see how flexible they were before I resealed them and again after each coat. I'd be lying if I said there was no change. They are a little stiffer now but really not much.

Since doing those first three sets I've come to learn that using diluted caulk is somewhat controversial but so far I have no complaints. It occurs to me that everyone has their preferred sealant and reasons for their preference but perhaps all of these treatments, properly applied, produce satisfactory results, be it fabric glue, butyl, Permatex, OC Speaker sealant or siliconized latex caulk.

Crusty, I noted in an earlier thread you inquired about the use of latex paint to seal surrounds. Latex paint and latex caulk are fairly similar products and the addition of silicone to the caulk makes it more supple. So, if paint's good caulk might be a bit better.

Also, thanks for the suggestion regarding the wire. I may just do that.

I just took some 19th century photographs of the Seventeens and my Thirties. Apparently, the pictures end up in some sort of reverse image on something called "film" and from there they're transferred to a piece of paper if you can believe it! Well anyway, if this works I'll post some of them here. The Thirties have a D.I.Y. RCA-to-binding post mod I did. Cheap, quick and easy and no need to cut bloody great holes in the backs of the cabinets.

John

[boreas]

Okay, next question. I just pulled the woofers out of the cabinets to get at the crossovers and saw something about the woofers that could explain the missing bass. Both speakers have something resembling the corrosion one sees on, say, a flashlight that's been affected by leaky batteries.

There's a white powdery substance on the baskets that seems to be coming from inside the voice coils. There's also evidence of oxidation/rust wherever the powdery stuff can be seen. One speaker has only a little of this deposit and rust where the magnet meets the basket. The other speaker has more of this stuff at that location plus a trail of it running down the basket. There is no evidence of staining on the diaphragms that might indicate some sort of leakage inside the voice coils.

I pulled the tweeters just now, after beginning this post. One of them has a very small amount of this corrosion around the area where the basket meets the magnet. The other doesn't.

Is this anything to worry about? Might it indicate failing or failed woofers? That would certainly explain the way these speakers sound.

Also, if the woofers and/or tweeters do need to be replaced, are the ones in my Model Thirties suitable replacements? They'd certainly fit and they're 8 ohm speakers but but are the specs on them the same in other important respects?

One set of my Thirties, the ones I've had since new, are looking a little rough. I just figured it out that they've been moved 15 times, the first of which was in the "back seat" of a Porsche from Colorado to Maryland. I've refinished them twice now and I don't think they'll tolerate another stripping and sanding. It may be time to relegate them to the status of organ donor for the other Thirties and maybe the Seventeens.

Thanks again for all your good advice.

John

PS: After pulling the first woofer for some reason I decided to flex the cone in and out. It seemed looser than it had been so I checked the one still in its cabinet. Sure enough, that one was "stiffer". When I had them both out I compared them again and they were the same. So, sealing the surrounds would seem not to have made them stiffer but "sealier". The difference in their springiness in or out of the cabinets tells me that they're less yielding because of the internal pressure in the cabinets. Verrrry interesting.

[Guest crusty]

I've seen this white powdery substance before Boreas. Its an anomaly caused by the cross cultural music thats played through the speakers, ie. early sixies British pop vs 1960's California beach music. Not really. Its as you said, oxidation from the magnet, harmless and normal on old drivers, and easily removed by spraying a little WD-40 on a rag and wiping down the speaker basket and magnet.

You've got me on whether the tweeter is the same on the 30's as it is on the 17's, or any other early KLH's. But I remember reading somewhere that from the Thirties on up in model designation they were the same or at least very similar. But I'm really not sure or this. I will dig out my old McGee Radio catalogs and do some research then write back to you.

I have always tried to solve the mystery of what exactly dig the early speaker builders use the coat their cloth surrounds. I know JBL and Altec use something called Airflex 400 but its a pretty heavy and thick substance. Don't know how it would work on small 8 or 10 inch woofers. I have also read in an old radio book that they used thinned phenolic resin and sometimes corona dope. But then they wouldn't say if it was to seal the surrounds or to dope the cones to add mass and lower the FS of the speaker. Its a mystery.

I'll do some research on KLH tweeters and let you know.

Have a good one..