Capacitors...debunking the shame of vintage crossovers

Posting this thread under High Efficiency... because it concerns choices you might make DiY'ing a killer Passive xover for your horn system using nice, old parts... but this also covers "Restoration" of speaker systems...

While rehoming a pair of Electrovoice Aristocrat speakers – – with the pre-requisite sealed steel can crossovers (namely the X8 and X36.
I received a worried message asking "but what do I do about the old capacitors inside of the crossovers?"

Most of you guys knew that dealers like HiFiTown (aka me) -- really only sell vintage. I mean strictly antique stuff. Sometimes remanufactured items with more than 50% antique components... that too ... soon.

Thank goodness there's a forum like haven – – sage, alert and salty folks have the experience of playing around with actual original components :).

But if one were to say bring home a pair of AR/Advent/Altec/JBL/Klipsch/EV speakers whatever from the dump or CraigsList duJour -- -jump on your favorite Internet group – – proudly exclaim your find – – and after about 30 seconds you'll get bombarded with comments of how you need to get those... "nasty disgusting, horrible leaky, freaky, Time bomb, Time-Smear, quality killing "50 year old" caps out of your Crossover!!!
Right Now .. We're talking 3 Mile Island.... Red Alert!! .. Klaxon Sounds..
You know the drill. You must immediately buy someone's favorite brand of poly propylene capacitors or Teflon specials and stick them in for the immediate 50 to 100% improvement and sound quality... the Best Teflon ones only cost $400 each... do it now!!!

Well guys, I've been telling people for years (and to much extent my father before me) that that's just not always the case.
I would like to soften this rant a little bit, as there are times and reasons that fresh capacitors especially very zippy sounding Poly types – – might help the sound of certain tired speakers or add some tizz to a dull sounding setup-- that's a different thing.. often it's more of an equalization / tweak thing than it is some kind of miracle repair.

The dread and persecution of old capacitors that "might" have gone out of spec -- backed up by claims of iron-clad measurements like ESR.
Yes ESR, IS valid way to test for a failed capacitor -- everyone can afford that meter nowadays. However, you have to take into context what ESR is. Equivalent series resistance, measured at high frequency. And it's typically measured at 100,000 cycles! That's way above human hearing. And ESR does not tell you about caps function as a high-pass filter.... The other use of capacitors – – where that word "leaky" gets thrown around – – is of course in high-voltage applications... that's DC -- not low-voltage AC like audio.

The same people sometimes insert comments like "wow those total fools on eBay" – – they pay 400~800 a pair for a pair of original .. Altec N500, or some sort of collectible Unicorn JBL model – – don't they know what's inside of those things? Of course ... leaky capacitors!

Well there really is a reason that online buyers pay a lot of money for relatively simple, Butterworth crossovers like the Altec N500. They (kind of) sound pretty good (but Diy with old parts is better) for what they do – – and they are easy to hook up. None of these buyers ever actually ask about leaky capacitors or worry about that stuff. They just hook the crossovers up – – they listen to their systems and they're happy! What gives?

Well after years of sitting around griping and changing peoples minds about this stuff – – it was time to apply modern Audio centric testing gear – – I sat down and ran a few experiments to find out. I got very interesting results. Particularly with extremely leaky extremely, super- drifted high ESR capacitors..I had marked "BAD" ..... I picked out my favorite types – – some paper wax some oils – – any (can) go bad or need reforming after sitting on the shelf for many years.
Even if good, most (not all) old capacitors have higher ESR values than the Wizzy tizzy Teflon and poly propylene capacitors... those fancy ones that get kicked around on the Internet as the best..

More heretical Comments coming, you've been warned :
It's likely, that, many, (if not most) old leaky caps are working fine-enough for audio crossovers.

Some cases; cap's actually short out, or fail in other ways that might be bad for delicate tweeters... if that happens, you'll probably notice without the aid of test equipment, most of the time. And, some old caps began life sounding bad, I'm not precluding that, either.

Leaky caps are prone to some drifting. The drifting of course slightly changes the crossover point but only a non-sensible amount... Drifting is typically quite a lot for the capacitors value but not very much in the grand scheme of things. For instance a horribly leaky wax capacitor spec'd at 4UF may drift down to 3.2 up to 4.5 – – yeah that's a little bit of difference but when you look at it on an impedance frequency meter driving a tweeter.... (which I think is a good way to test these things) – – the crossover point appears to be quite relevant, and the slope is normal.... I plan to finish the shoot out with some PolyProp's
I am not looking at ESR, or charging the caps. This is an applied 20-20K sine wave generator, and charting the impedance slope. Normal working caps, of similar value all do the same job. They rise in impedance (resistance at given freq) as they reach their "High-pass" point.
Different values slope different ways, and different capacitor chemistries do have different slope characteristics. This most likely manifests in tone and sound quality quite radically (see, you could hear the difference between that Motor cap and that oozing electrolytic you tried at 4 am!! :) !!

I noticed this many years ago when I restored crossovers – – on a pair of AR3's -- speakers often don't work at all because the potentiometers go completely bad. If you get in there and replace the potentiometer (not an L pad on the AR3) --leave the original (very wooly looking paper wax) you'll notice the speaker sounds really nice.

Vintage bookshelf speakers and other systems and all of the mysterious metal cans furnished by Altec JBL in the lake – – often used the unthinkable...

BIPOLAR ELECTROLYIC CAPS

Oh, man'o'man – – this really offends the speaker-builder gurus. What a horrible type of capacitor to use...
Well actually, some of the most expensive vintage crossovers feature these – including the Altec's I mentioned above.
And impromptu listening over the years has yielded that we also tend to like the sound of the bipolar electrolytic capacitors (cheap brands and Western Electric Long-Life's too) -- some are even killer.
I have friends that say they're killer sounding too :o
I even read on one of the forums once, some, poor, old wise old fellow (not anyone I knew) .. who piped-in to say he preferred them.

Of course it's best to be bipolar, or (sometimes, not always) get some really strange phase-shifty below the High Pass point... One of Walt's old friends reminded me just the other day – – you can hook "polar" ie (caps that have polarity) electrolytic capacitors tail to tail, and make your own bipolar. Very interesting stuff. Something special about certain electrolytic capacitors in audio crossovers.

Others that are good:

Certain Cold War era BathTub Oils (we're actually OEM used by RCA in the LC 1, and they are used them sometimes in the very early 1950s speakers. Altec used (1 single 4uf Aerovox bathtub) in the cute-as-a button Monterey bookshelf speakers – – and Klipsch in his early days used them often.) Most bathtub capacitors paper and oil, and other industrial chemicals --- they usually don't leak DC, but they sometimes need insane amounts of reforming, and they sometimes have higher ESR. Not that this actually matters, but they do have an occasional attenuating effect that can be pleasant in some bright systems and not good in others.

Paper Wax -- guitar guys deserve some credit for keeping the spirit alive for the old paper wax capacitors. Also Western Electric made some absolutely gorgeous soldered steel and extruded aluminum paper wax capacitors – – for all throughout the Bell system in all values perfect for audio. They are quite famously used in Western Electric 757 crossover system – – and other places. One of the famous models is the 437A as it is 4UF and you can stack them together to make nice crossovers. Some leak DC, others don't. I use them here all the time.

Tantalums -- still experimenting with these – – they have a very interesting sound. They will probably last 1000 years. Not bad at all depending on which ones you try. You have to try to get bipolar types – – or you can use the back to back connection method track above. That seemed to work for some very high-quality Western Electric GA types I tried recently.

SoapBox Warning:
Below is the message I penned to said customer on the EV (Metal Can X8 and X36's)
"""
There's a lot of blanket assuming that goes on – – especially on the Internet forums about what you should do “right away” to fix any speaker older than 30 years. Inevitably this includes, ostracizing capacitors deemed automatically bad because they were so old and “must be leaky” in the crossovers of these old speakers.
Electrovoice crossovers they are sealed in a metal can – – there's no way you would ever want to get in there to replace them.
Do you know how many bad (ie “dead”) ones I see – – after handling hundreds of them? Maybe one or two!
How about ones that are malfunctioning so badly that you can actually hear the crossover point is incorrect? Maybe one or two!, Ha ha.

People are simply all wet about their priorities when picking up these old speakers to use. They should listen to them and use them as they are first – – replacing a couple of capacitors in these old crossover is not going to completely make the speaker system sound … probably not even 20% better than it is – – that just doesn't usually happen. Realistically what does happen is when you change these old capacitors – – it brightens the speaker very much – – sometimes it doesn't sound as good as the old capacitor you just replaced…
I know this flies in the face of all the help of you read on the audio forums – – it's just a practical thing — crossover capacitors are very low voltage. Even if they leak or drift a little bit it's not going to be the end of the world.
I know many people here in the USA we disagreed with me on this. To that I say – – why is it that they pay $600 (!) a pair for a set of vintage Altec 500hz crossover's which are also sealed in a metal can and completely non-serviceable using the same "dried out electrolytic’s?” It's because those guys over there already tried making their own crossovers out of modern mylar film capacitors – – and they didn't like the sound.

And, old capacitors are not automatically bad. Sometimes people actually want them back in their componentry. You would be really shocked (pardon the pun).
I make part of my living selling old capacitors ---– you would think how could they be good? I routinely sell 50 to 70 year old capacitors to customers overseas – – wanna know how many complaints I get? None as of late.
Pretty surprising. It does of course depend on the application.

And I am not automatically dismissing the practice of replacing capacitors in speaker crossovers. It's an OK thing to do – – if you already like the speaker and you know you wanna go in that direction.
Even if electrolytic capacitor does go bad. For audio frequency use ...in the loudspeaker, all it does is drift a little bit. This very small amount of drift is unlikely to make much difference at all more than a few DB plus or minus at one frequency or another. Generally the worst case scenario is the crossover point drifts around a little bit maybe only by a few hundred hertz.... Nobody really actually hears that much… I mean, yeah you can hear it… but it’s a tweak best done later … If you want.
So in actuality … you get speedier, brigher tone from the speaker….that is the polypropylene caps’ sound… (likely due to the lower ESR value)…
I've heard a few customers say that they did the job on their old speakers – – i.e. recapping the crossover —some liked it — Best I've heard personally is a marginal difference sometimes – – that's about all.
""
 
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Chops54

Junior Member
Not vintage but my IMF TLS80s must be approaching fifty years old and they’ve been mine for ten years or so. They are still just as IMF made them, totally original. They still sound the same as the pair I first heard over forty years ago. I’m loathe to overhaul the crossovers for fear of changing the character of my beloved IMFs.
 

Salectric

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Early nailed it. Like him, I cringe whenever I read posts talking about replacing crossover caps in vintage speakers with modern film caps. That’s an easy way to ruin the sound of a good vintage speaker.

For a while I did the modern film cap thing in my crossovers—-Mundorf, Solen (Edit: Sonicap Gen 1, not Solen), V-Cap, Duelund CAST, etc.—-but eventually I settled on paper in oil bathtub caps for the woofer and midrange and wax paper caps for the tweeter. All of them are at least 60 years old. I have also tried coils from the same era but so far I still like my modern coils better.

Way back in the 1970s I also liked non-polar electrolytics, at least a particular brand the local speaker supply store stocked. I no longer recall the exact name but it was something like NDE. I later found out Bob Fulton used the same NP caps in his FMI speakers. The NP caps were warmer and richer than Mylar caps and they allowed a more seamless blend between drivers than the film caps.
 
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Thank you Salectric!
Well that was a great response with just the sort of super cool info I was hoping to read...
Even though we've enjoyed old caps over the years reliably – – I sleep a lot better at night reading experiences of others as well as feedback from customers.

I don't want to oversell the possible benefits of using (or keeping) certain antique capacitors – – your experience is reinforcement that it at least sounds different, and not (usually) any worse – and sometimes better(!)
All the results we can hope for by changing components :D– that was the interest I was hoping to propegate....and fortunately, more than ever the old stuff (sleepers) are extremely price competitive with quality new stuff.

Most interesting... on the really nonpolar 'lytic capacitor front. I did not know Fulton did that!
His crossovers were always really custom as I recall.
A few Years ago, I set a relative up with a pair of the FMI 80's ... for the small increase in size they did for him much, much better than his not-shabby previous Rogers LS 3/5A.
Fulton's designs were carefully thought out (esp the twin Peerless tweeters.. even if he tweak things (often per speaker).
The NP caps.. I wonder if that was cap-of-the-day laziness... or I am preferring to think; something he tried, listened and then chose(!)

I want to add test results and notes to my post at some point, I need to do some more bench testing.

Had some advice to ask.... When I line up a bunch of old caps to test (paper oils, electrolytics, and others..) I want to use for control a modern mylar cap .... something that is the go to capacitor for most people who are opting to refit their speakers ...
Didn't wanna get anything too obscure or expensive.
But didn't want to get anything super cheap either.

Of those brands..."' Mundorf, Solen, V-Cap, Duelund CAST, ..." -- which would you pick out for the poster child sound of a modern – – and or mainstay of the budget DIY audiophile?
I was just thinking of something from PartsXpress – – any suggestions?
 

Salectric

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Thank you Salectric!
Well that was a great response with just the sort of super cool info I was hoping to read...
Even though we've enjoyed old caps over the years reliably – – I sleep a lot better at night reading experiences of others as well as feedback from customers.

I don't want to oversell the possible benefits of using (or keeping) certain antique capacitors – – your experience is reinforcement that it at least sounds different, and not (usually) any worse – and sometimes better(!)
All the results we can hope for by changing components :D– that was the interest I was hoping to propegate....and fortunately, more than ever the old stuff (sleepers) are extremely price competitive with quality new stuff.

Most interesting... on the really nonpolar 'lytic capacitor front. I did not know Fulton did that!
His crossovers were always really custom as I recall.
A few Years ago, I set a relative up with a pair of the FMI 80's ... for the small increase in size they did for him much, much better than his not-shabby previous Rogers LS 3/5A.
Fulton's designs were carefully thought out (esp the twin Peerless tweeters.. even if he tweak things (often per speaker).
The NP caps.. I wonder if that was cap-of-the-day laziness... or I am preferring to think; something he tried, listened and then chose(!)

I want to add test results and notes to my post at some point, I need to do some more bench testing.

Had some advice to ask.... When I line up a bunch of old caps to test (paper oils, electrolytics, and others..) I want to use for control a modern mylar cap .... something that is the go to capacitor for most people who are opting to refit their speakers ...
Didn't wanna get anything too obscure or expensive.
But didn't want to get anything super cheap either.

Of those brands..."' Mundorf, Solen, V-Cap, Duelund CAST, ..." -- which would you pick out for the poster child sound of a modern – – and or mainstay of the budget DIY audiophile?
I was just thinking of something from PartsXpress – – any suggestions?
Fulton didn’t use NP caps for any reason but sound quality, of that I am sure. One of his dealers Gene Coggins of Paoli Hifi used to modify FMI-80s by removing the one and only crossover part (a 6uf NP on the Peerless tweeters) and replacing it with a 6uf PIO bathtub cap and a 1.8 ohm series resistor. When I heard the J-Mods in Gene’s basement the 80s had this mod, and the whole system sounded awesome, but then I hadn’t heard the J-Mods without the mod. Sometime later, however, I heard that Fulton was very upset with the mod. He was going around the country fixing customers’ modified 80s by putting the NP cap back in. The NP caps gave Fulton the particular sound he wanted.

Another story I heard about Fulton and crossovers was that he spent a full week selecting crossover resistors for each pair of Premiere speakers, and all of the resistors were 2w Allen Bradley carbon comps. He had to listen to each one to find the best sounding resistors for each speaker.

You ask about modern film caps to use as a benchmark for evaluating other caps. I will suggest two types. For high-pass duty, my favorite was Sonicap Gen 1 which is available in lots of values at reasonable prices. It is sold by Sonicraft. The Gen 1 is clean and detailed with a slightly rising high end. It is also a bit lean in the bass which makes it less than ideal for woofers. For low-pass I like Mundorf Supreme, the regular, inexpensive version, not the Silver, Gold or Oil types. The regular Supreme is warm and very dynamic, with good detail. It isn’t well suited for high-pass because the Supreme is slightly soft and rolled off in the highs, but on woofers it is very musical. The combination of the Sonicap Gen 1 on the horn and Mundorf Supreme on the woofer was overall the best sounding caps for my old Jensen/Altecs (P15LL and 802G in 32B). The caps were a major factor in the speakers’ marvelous coherency.
 
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Fulton didn’t use NP caps for any reason but sound quality, of that I am sure. One of his dealers Gene Coggins of Paoli Hifi used to modify FMI-80s by removing the one and only crossover part (a 6uf NP on the Peerless tweeters) and replacing it with a 6uf PIO bathtub cap and a 1.8 ohm series resistor. When I heard the J-Mods in Gene’s basement the 80s had this mod, and the whole system sounded awesome, but then I hadn’t heard the J-Mods without the mod. Sometime later, however, I heard that Fulton was very upset with the mod. He was going around the country fixing customers’ modified 80s by putting the NP cap back in. The NP caps gave Fulton the particular sound he wanted.

Another story I heard about Fulton and crossovers was that he spent a full week selecting crossover resistors for each pair of Premiere speakers, and all of the resistors were 2w Allen Bradley carbon comps. He had to listen to each one to find the best sounding resistors for each speaker.

You ask about modern film caps to use as a benchmark for evaluating other caps. I will suggest two types. For high-pass duty, my favorite was Solen Gen 1 which is available in lots of values at reasonable prices. It is sold by Sonicraft. The Gen 1 is clean and detailed with a slightly rising high end. It is also a bit lean in the bass which makes it less than ideal for woofers. For low-pass I like Mundorf Supreme, the regular, inexpensive version, not the Silver, Gold or Oil types. The regular Supreme is warm and very dynamic, with good detail. It isn’t well suited for high-pass because the Supreme is slightly soft and rolled off in the highs, but on woofers it is very musical. The combination of the Solen on the horn and Mundorf Supreme on the woofer was overall the best sounding caps for my old Jensen/Altecs (P15LL and 802G in 32B). The caps were a major factor in the speakers’ marvelous coherency.
I think you meant Sonicap not solen.

Im still very happy with mine, and wasn’t planning on touching my crossovers any time soon but now curious about the wax paper you and Early have mentioned…
 

Salectric

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I think you meant Sonicap not solen.

Im still very happy with mine, and wasn’t planning on touching my crossovers any time soon but now curious about the wax paper you and Early have mentioned…
You’re absolutely right! I edited my post to avoid confusion. Thanks for the correction.

I am not sure which types of wax paper caps Early uses. The ones I use are old Aerovox 1uf, 400v red caps. I would tell you the part number but my entire hifi was just put in storage for the next couple months while we are moving house. These particular caps came with my original Deja Vu speakers. The 1uf was in series with 16 ohm tweeters to give a first-order 10K rolloff. At one point, I was experimenting with a different crossover point and I needed a second pair. That led to a couple purchases on EBay which were all Aerovox 1uf with the identical part number as Vu’s caps. The only difference was they were yellow instead of red. Unfortunately the yellow ones just didn’t sound as good so eventually I bought a second pair of red caps from Vu and all was well. Bottom line—even with the same part numbers vintage caps may not sound the same. Vu said the red Aerovox caps were from the 1940s but I don’t know if that’s accurate or not.
 
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FloriduhBoy

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You’re absolutely right! I edited my post to avoid confusion. Thanks for the correction.

I am not sure which types of wax paper caps Early uses. The ones I use are old Aerovox 1uf, 400v red caps. I would tell you the part number but my entire hifi was just put in storage for the next couple months while we are moving house. These particular caps came with my original Deja Vu speakers. The 1uf was in series with 16 ohm tweeters to give a first-order 10K rolloff. At one point, I was experimenting with a different crossover point and I needed a second pair. That led to a couple purchases on EBay which were all Aerovox 1uf with the identical part number as Vu’s caps. The only difference was they were yellow instead of red. Unfortunately the yellow ones just didn’t sound as good so eventually I bought a second pair of red caps from Vu and all was well. Bottom line—even with the same part numbers vintage caps may not sound the same. Vu said the red Aerovox caps were from the 1940s but I don’t know if that’s accurate or not.
The Tube Store has Amp Ohm paper in wax caps. I don't know how they compare to the Aerovox.
 
I purchased an old pair of Mission 765's. I am guilty of changing componets in the crossover and the speakers just sound better. I sent the original crossovers to Solen and had them duplicate the crossover with their components. My question is simple, they replaced some of the original inductors that had wire as thin as a human hair. Also I replaced the internal wire with Solen's silver wire. Changing the original inductors with Solen's perfect lay inductors along with with the silver wiring, is that making the sound improvement?
 

Audionut

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Interesting thread to say the least.
Speaking of old caps, I stumbled across a metal cabinet full of these. Are any worth sampling/keeping? Probably more for guitars I’m guessing. 070D2DCB-B635-4A79-A095-01528717DDF1.jpeg
 
I purchased an old pair of Mission 765's. I am guilty of changing componets in the crossover and the speakers just sound better. I sent the original crossovers to Solen and had them duplicate the crossover with their components. My question is simple, they replaced some of the original inductors that had wire as thin as a human hair. Also I replaced the internal wire with Solen's silver wire. Changing the original inductors with Solen's perfect lay inductors along with with the silver wiring, is that making the sound improvement?
That's a good question -- Of course, I can only guess as to why they sound better. My guess? Having parted out many such systems of the era (early KEF, and B&W, but never Mission) – – the joints soldering, and wire – – just like you mentioned are not always so great after 40 years... the vinyl insulation often oozes chlorinated chemicals and sometimes greens up the red/black OEM copper wire adding capacitance (1980s Monster Wire anybody?). Resistors drift and corrode too. But primarily my best guess is – – that the capacitors were what improved the sound of your speakers. That's because some speakers like them....modern capacitors render things "cleaner", speedier and brighter sounding. I probably didn't give this effect enough fanfare – – but this can be a very good thing especially if your speakers leaned on the mellow or "stuffy" side (a very common trait on 1960s forward ported systems)... In vintage horn systems (Altec, JBL, EV, etc) with tons of highs, midrange this, in essence is a form of "EQ" can be really harsh and fatiguing and not all that realistic.
 
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Interesting thread to say the least.
Speaking of old caps, I stumbled across a metal cabinet full of these. Are any worth sampling/keeping? Probably more for guitars I’m guessing. View attachment 48772
The guitar guys definitely still use some of these. Yes, those are mostly not going to be Xover values... Some may have gone bad if you were using them for coupling capacitors. The oval/wide yellow one is a 1960s mylar and it's surely good. You've got all sorts of interesting ones there – – that you see. The black one with yellow bands is referred to as a bumblebee it's most likely good – – those are treasured in Mac and Marantz (even if they do leak!).
The red one on the far right, – – we used to call those "Fire Chief's or Atomic / RedHot's I think..interesting, materials in those, some are mica coated paper, phenolics and oil hybrid... like the Sprague bumble bee they are incriminated as part of the classic tube amp sound.
The debate on whether or not to change these out rages online far worse than Xover's.
Customers who want these originals to stay , infuriate careful Tech's (who want them removed faster than a Surgeon looking at green-hued gallbladder).
Problem is, these capacitors absolutely have a sound.
And if you have one of the valuable preamps or amps that runs them – – you're probably best off to track down original parts and only replace the ones that are bad.
That is if you are concerned with resale value.
If you want something to turn on without worry for the next 40 years and run 24 seven – – sure replacing capacitors is often a good idea. It's a judgment call for tube voltage. Fortunately for crossovers, it's not nearly as critical.
((offtopic -- Don't get me started on selenium rectifiers. That I think is even more of an argument to keep things as they are. There seems to be rampant worry that these selenium rectifiers are going to blow and smoke power transformers – , but they've been buying selenium original rectifiers since the 1970s or 80s in Japan – – because they sound smoother. Changing them out in favor of Silicon might really be sound altering.)))
 
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You’re absolutely right! I edited my post to avoid confusion. Thanks for the correction.

I am not sure which types of wax paper caps Early uses. The ones I use are old Aerovox 1uf, 400v red caps. I would tell you the part number but my entire hifi was just put in storage for the next couple months while we are moving house. These particular caps came with my original Deja Vu speakers. The 1uf was in series with 16 ohm tweeters to give a first-order 10K rolloff. At one point, I was experimenting with a different crossover point and I needed a second pair. That led to a couple purchases on EBay which were all Aerovox 1uf with the identical part number as Vu’s caps. The only difference was they were yellow instead of red. Unfortunately the yellow ones just didn’t sound as good so eventually I bought a second pair of red caps from Vu and all was well. Bottom line—even with the same part numbers vintage caps may not sound the same. Vu said the red Aerovox caps were from the 1940s but I don’t know if that’s accurate or not.
Gee, Actually it depends – – and really I appreciate the "neutral" sound that many of these selections have.
for upcoming tests... I slightly deviated and ordered just the standard high-grade, Made in France Solen's in a few values (4uf, 8uf and 14uf) -- to keep costs from blowing R&D :) – – and I figured it would still be a fair fight if I compared them to some of these ancient, well-regarded units mentioned below. When I get a chance I'm going to pull a few frequency-impedance / speaker load charts and will try to share them when time allows...

As I often say, using caps to alter or improve a speakers sound, is a little like using EQ... so use caution.
Some caps, just like Vu may have noticed, are crazy-good and if not that, then harmless to your tone... and they are not necessarily expensive, or large.
Historically, if we are talking Western Electric... they used CDE and GE Oil caps in the 753 system, and WECO made paraffin wax 137A and 437A 4uf caps in the WE 757 monitor.
I find the WE wax caps sound very nice, very neutral, good clarity. They usually have normal-ish to high-ish ESR (as judged by modern standards)
In this photo, some of the usual suspects...
Complete xover, made by IPC with a huge (polar?) Alum Electrolytic cap -- people like this simple 2 way rig
Aerovox "Bathtub" 1940's Paper Oil
Western Electric 137A soldered Steel (painted gray in rear) paper wax (predecessor to the bright aluminum 437 laying on side)
Western Electric 437A extruded aluminum paper wax (both the 137 and 437 were used by WE for Xovers)
The heavy looking Western Electric sealed oil, in 4uf rating is the 287A and it has other Navy/Dpec names too... these are very popular with customers in Asia... they go for higher and lower prices... Surely the highest quality and going to be the longest lasting capacitor shown here – – I regularly test units from the late 1930s all the way up to beyond rated 400V and they don't even flinch.
The tropicalized on on far right is a CDE Paper Oil -- these tend to be very good, them and the batch tubs have an even higher ESR)
In a way, the most interesting – – the little black one with the red ends – – branded Temple – – you sometimes find these in various bookshelf speakers made in the 1960s – – some of them were made in the USA others in Mexico – – they sound absolutely great! It's one of our favorites from a shootout years ago... Would probably cost you pennies if you could find a box of NOS units. It is a nonpolar electrolytic...sure enough. Surely used because it was the most inexpensive thing possible. It does not sound as smooth or as neutral as some of the others above.
The two grey cylindrical capacitors -- these are sort-of what Selectric was referring to on the Fulton topic – – improper polar electrolytics (just ginormous ones). In this case these are long life Sprague made for Western Electric, Marantz and other heavy duty aerospace power supplies and 1950s Computer applications where eventual failure was not an option. Amazing most of these are very good when I test/reform them at high voltage even after 50 and 60 years! I've been giving some of these a listen for High Pass – – and they really do sound nice when I have tried them – – some thing they do is interesting.Hard to find correct lower uF values for Xover's though... other 'Lytics seem to perform the same as these... much like the large one on the IPC xover in photo.... The impedance/phase it's a bit choppy in low frequencies -- once they get to application frequency – – they seem to behave quite normally.
The little itty-bitty one, that is slightly goldish and color color is a Western Electric tantalum from 1960s Jet Bomber power supplies – – same story here I'm still experimenting – – but the sound of these seems quite good, but these do seem to do better connected back-to back for Non-Polar performance....Super good quality...
Interestingly enough, I had a crossover discussion last year with one of DejaVu's excellent young protégés.... And their findings are very similar to ours over the years. Vu definitely a careful listener – – and most certainly selected some good units.

Salectric, When you are done moving some lazy day – – track one of those red Aerovox down and I will check to see what I have that is similar or same. That would be interesting.

1940s-70sxovercaps.jpg
 

Salectric

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Gee, Actually it depends – – and really I appreciate the "neutral" sound that many of these selections have.
for upcoming tests... I slightly deviated and ordered just the standard high-grade, Made in France Solen's in a few values (4uf, 8uf and 14uf) -- to keep costs from blowing R&D :) – – and I figured it would still be a fair fight if I compared them to some of these ancient, well-regarded units mentioned below. When I get a chance I'm going to pull a few frequency-impedance / speaker load charts and will try to share them when time allows...

As I often say, using caps to alter or improve a speakers sound, is a little like using EQ... so use caution.
Some caps, just like Vu may have noticed, are crazy-good and if not that, then harmless to your tone... and they are not necessarily expensive, or large.
Historically, if we are talking Western Electric... they used CDE and GE Oil caps in the 753 system, and WECO made paraffin wax 137A and 437A 4uf caps in the WE 757 monitor.
I find the WE wax caps sound very nice, very neutral, good clarity. They usually have normal-ish to high-ish ESR (as judged by modern standards)
In this photo, some of the usual suspects...
Complete xover, made by IPC with a huge (polar?) Alum Electrolytic cap -- people like this simple 2 way rig
Aerovox "Bathtub" 1940's Paper Oil
Western Electric 137A soldered Steel (painted gray in rear) paper wax (predecessor to the bright aluminum 437 laying on side)
Western Electric 437A extruded aluminum paper wax (both the 137 and 437 were used by WE for Xovers)
The heavy looking Western Electric sealed oil, in 4uf rating is the 287A and it has other Navy/Dpec names too... these are very popular with customers in Asia... they go for higher and lower prices... Surely the highest quality and going to be the longest lasting capacitor shown here – – I regularly test units from the late 1930s all the way up to beyond rated 400V and they don't even flinch.
The tropicalized on on far right is a CDE Paper Oil -- these tend to be very good, them and the batch tubs have an even higher ESR)
In a way, the most interesting – – the little black one with the red ends – – branded Temple – – you sometimes find these in various bookshelf speakers made in the 1960s – – some of them were made in the USA others in Mexico – – they sound absolutely great! It's one of our favorites from a shootout years ago... Would probably cost you pennies if you could find a box of NOS units. It is a nonpolar electrolytic...sure enough. Surely used because it was the most inexpensive thing possible. It does not sound as smooth or as neutral as some of the others above.
The two grey cylindrical capacitors -- these are sort-of what Selectric was referring to on the Fulton topic – – improper polar electrolytics (just ginormous ones). In this case these are long life Sprague made for Western Electric, Marantz and other heavy duty aerospace power supplies and 1950s Computer applications where eventual failure was not an option. Amazing most of these are very good when I test/reform them at high voltage even after 50 and 60 years! I've been giving some of these a listen for High Pass – – and they really do sound nice when I have tried them – – some thing they do is interesting.Hard to find correct lower uF values for Xover's though... other 'Lytics seem to perform the same as these... much like the large one on the IPC xover in photo.... The impedance/phase it's a bit choppy in low frequencies -- once they get to application frequency – – they seem to behave quite normally.
The little itty-bitty one, that is slightly goldish and color color is a Western Electric tantalum from 1960s Jet Bomber power supplies – – same story here I'm still experimenting – – but the sound of these seems quite good, but these do seem to do better connected back-to back for Non-Polar performance....Super good quality...
Interestingly enough, I had a crossover discussion last year with one of DejaVu's excellent young protégés.... And their findings are very similar to ours over the years. Vu definitely a careful listener – – and most certainly selected some good units.

Salectric, When you are done moving some lazy day – – track one of those red Aerovox down and I will check to see what I have that is similar or same. That would be interesting.

1940s-70sxovercaps.jpg
Early, I hope you didn’t order those Solen caps based on my post above. As noted by @joe83 my reference to “Solen” was in error; it should have been “Sonicap.” I apologize for the error. I must have had a brain freeze when I was typing.

Solens are also inexpensive and available in lots of values, but sonically they are greatly inferior to Sonicap Gen 1. The Gen 1 caps are good enough to be used in a high quality system; Solens are not.

By the way, I just remembered Greg Roberts of Volti speakers uses Sonicap Gen 1 caps in all of his crossovers including his top model the Vittora (or at least he did a couple years back when he had his crossovers on display at a CAF show).
 
I’ve have positive experience with Sonicap. I only have one use case, but the Sonicap Gen 1 replaced the caps in my GR Research speakers. The previous caps, inductors, and resistors were of a higher quality than those in my Proac Response 1SC speakers. The upgrade, including caps, Erse air core inductors, Mills resistors, wire and shrink tubing was a bit more than $200. The speaker was literally transformed. The speaker remained neutral, but had vastly better transparency and depth. I wouldn’t necessarily call the speaker polite in either form but it can be a tiny bit forgiving on some material while remaining open and airy. The GR Research guys bypass them with Miflex copper foil caps.

A nice thing about Sonicaps is their availability in a few more values than some other caps, as well as being reasonably affordable. They run about the same price as Jantzen Superior Z Caps that are popular right now (CSS, Buchardt(.
 
Early, I hope you didn’t order those Solen caps based on my post above. As noted by @joe83 my reference to “Solen” was in error; it should have been “Sonicap.” I apologize for the error. I must have had a brain freeze when I was typing.

Solens are also inexpensive and available in lots of values, but sonically they are greatly inferior to Sonicap Gen 1. The Gen 1 caps are good enough to be used in a high quality system; Solens are not.

By the way, I just remembered Greg Roberts of Volti speakers uses Sonicap Gen 1 caps in all of his crossovers including his top model the Vittora (or at least he did a couple years back when he had his crossovers on display at a CAF show).
Salectric, no worries on the confusion guys. Sounds to me like the Sonicap's are well regarded. If the budget is not busted, for R&D... I should like to try some of those warmer-modern Poly's also. The seller's webpage certainly had reasonable sounding sales talk and proper representation.

It was really great hearing the Volti's too in my experience... forgot all about them.... And I noticed the crossover back then – – they caught my eye too. Very nicely handmade.
I definitely thought the Volti setup (circa 2017-18?) were one of the better systems at the show with very few others in the realm. To me they were sort of like super Klipsch – – or what you would want Klipsch to sound like under ideal circumstances.

For now, the Solens (hey at least they are French) will easily do for Question/Hypotheses #1 -- are old "failed" or "drifted" caps inferior to modern "0 DC leak" types... I think not.. but have never had a shoot out....
I hope to be able to see this on the impedance / freq chart... we'll see.
 
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Bear in mind that Solens are considered boutique caps for a number of production speakers. A couple of decades ago they were pretty much the upgrade cap for speaker builders.
 
Bear in mind that Solens are considered boutique caps for a number of production speakers. A couple of decades ago they were pretty much the upgrade cap for speaker builders.
Thanks..ok, really good... That will let the R&D dept. sleep better tonite.... That's what I was after. I know they are not something many of us would want to load our speakers up with -- but electro-frequency speaking, they'll be "sans défaut" 😀
 
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Far from someone with definitive conclusions, I will offer up my current (and easily changed) opinions on this subject.

I hate to be the contrarian, but- Not a fan of Sonic Cap anything... They all sound sterile, zippy and white washed to me. Maybe some people like that with the "Altec" designs to dry up the sound a bit.

I'm also not a fan of the high end booster network common with Altecs crossovers. It sounds like to me that it causes phase issues... especially in the mid bass. The simpler the crossover the better the midbass has been my experience.

Different horns benefit from different caps. The 32 just naturally blends so well with direct radiators. This presents a more flexible tweeter cap choice where as a straight horn benefits from some "help" with integration. Straight horns like the big vintage oil caps. I read somewhere on a Western Electric owners thread that the oil cans "slow down" the higher frequencies which helps the coherence with the big and small drivers. Not sure if that is actually true but it describes what I hear.

My current cap of choice for the 32 horn is Mundorf MCap Supreme Aluminum Cap.

Regarding Resisters: I don't like rolling R's due to the rocky burn in period. If anyone likes something better than Mills, I would love to hear about it.







 
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