[Stimpy]

Hello all,

I've just found this Circle, even though I've been an AC member for years.  Very interesting info here too.  So much so, that I just opened an account at SonicCraft.com.

The reason for my interest is speaker restoration.  Specifically, my original Acoustic Research AR90's, bought directly from the AR factory, when I once worked at a Teledyne company.  They're in very good shape.  I've refoamed the woofers and the lower midranges.  But, the cabinets need a bit of a clean-up, and I'd like to recap the crossovers, being that the speakers are around 35 years old.

Now, my questions.  Are certain crossover caps more important in regards to sound than others?  Series caps more important than parallel?  Tweeters, over mids, over woofers?  I want to use decent parts, but I am admittedly on a tight budget.  I want to change what counts, using the best that I can afford, and the rest with 'good enough', if there's little sonic impact?  Lot's of NPE caps in my 90's: 4, 6, 8, 24, 40, 30, 80, & 350uf, so I want to budget my money where it'll make the most difference.  I'll attach the crossover schematic, for illustration.  I've been driving myself crazy over this, and just need some guidance, and a 2nd opinion!

Thanks in advance,

Stimpy





(For reference) 0.75" tweeter, 1.5" dome mid, 8.0" lower mid, & dual 10.0" side-mounted woofers.

[FullRangeMan]

This is a 4 way xover, better dont be on a budget.

[Stimpy]

This is a 4 way xover, better dont be on a budget.

Yea, I know!  Hence my anxiety!       But, a little at a time!   As I can.       I just didn't want to go the standard Solen route, as I've only read OK things about them.  Nothing glowing!  Though I guess anything is better the 35 year old NPE Callins caps.   

[FullRangeMan]

I sure Jeff can help you with the usual ability,
he is very competent with xovers.

[Stimpy]

Thanks, I hope so.  I'd like to hear that I should concentrate my money towards the 4, 6, 24, and 80 caps.  Then a lower level for the 8, 40, & 30, and that the 350 shunt cap was fine with anything?   Please, oh please, oh please...?   

And for what it's worth, I'm looking for anything with good air, clarity, detail and decay, and correct timbre, not necessarily warmth.  Honesty, I suppose.  I'm a bit backwards too, as I listen bottom up.  I listen for bass tautness and quickness, midbass snap, an open mid, and a smooth treble.  Smooth but not rolled off.  But since my high end extension isn't what it used to be, I'm not as picky about treble performance, as bass.  I don't do Boom!   

[FullRangeMan]

Thanks, I hope so.  I'd like to hear to concentrate my money towards the 4, 6, 24, and 80 caps.  Then a lower level for the 8, 40, & 30, and that the 350 shunt cap was fine with anything?   Please, oh please, oh please...?   

And for what it's worth, I'm looking for anything with good air, clarity, detail and decay, and correct timbre, not necessarily warmth.  Honesty, I suppose.  I'm a bit backwards too, as I listen bottom up.  I listen for bass tautness and quickness, midbass snap, an open mid, and a smooth treble.  Smooth but not rolled off.  But since my high end extension isn't what it used to be, I'm not as picky about treble performance, as bass.  I don't do Boom!   

I will refrain to say anything on the caps electric values as I not a tech, Jeff have much knowledge of electronics applied to music what is very useful in your case.

What you are asking for is a list of hi-end sound qualities to be drawn from this vintage speaker.

[Stimpy]

What you are asking for is a list of hi-end sound qualities to be drawn from this vintage speaker.

Thankfully, the AR90 is already a speaker that exhibits many of those "hi-end sound qualities", even though it is definitely a vintage speaker.  But, a very well designed, engineered speaker, regardless of age.  Otherwise, I wouldn't be so addlepated!   

[Stimpy]

Oh yea, another thing that I've been wondering about is cap mixing?  If I'm using a Brand A cap on the tweeter, should I continue with Brand A for the mids and Brand A on the woofers?  Or can you and should you mix-and-match, depending on the specific drivers?  I want consistency of sound across the speaker, and was hoping that using one primary brand would achieve this?  Then, I was wondering about bypass caps, and even cascoded bypass caps?  Should you or shouldn't you?  If using multiple brands, this is where that I thought that they'd come into play?

Again, Thanks.

[Stimpy]

Double Post - Deleted.

[FullRangeMan]

Oh yea, another thing that I've been wondering about is cap mixing?  If I'm using a Brand A cap on the tweeter, should I continue with Brand A for the mids and Brand A on the woofers?  Or can you and should you mix-and-match, depending on the specific drivers?  I want consistency of sound across the speaker, and was hoping that using one primary brand would achieve this?  Then, I was wondering about bypass caps, and even cascoded bypass caps?  Should you or shouldn't you?  If using multiple brands, this is where that I thought that they'd come into play?

Again, Thanks.

Voicing an audio product is a difficult, costly and time consuming task for the factory designers, it demand detailed knowledge of the circuit and in the case of speakers knowledge of acoustics, drivers, music and hypothetical average custumer room oriented, its a Herculean task.

[Stimpy]

Voicing an audio product is a difficult, costly and time consuming task for the factory designers, it demand detailed knowledge of the circuit and in the case of speakers knowledge of acoustics, drivers, music and hypothetical average custumer room oriented, its a Herculean task.

That's pretty much my feeling too.  I don't think that happened at AR?  While I've read that AR did put serious engineering into their products, including diffraction control and room interaction, the resulting crossovers used pretty much the same stocked brands of caps, throughout all of their various models.  So I'll probably look for a single brand of caps, that offers a range of cap values that covers my 4uf to 80uf needs, and use that brand for all the values, except the 350uf.  The 350 will have to be a NPE, which I actually have; an Erse 250 and an Erse 100.  Will they be good enough? 

Next, I think I'll buy samples of several brands of low value caps, both poly and film & foil, to just play with the different bypass caps, and see if I can hit on a voicing that I like?  I've already picked up 20 Russian paper in oil 0.01uf 1000v caps, to start with.  And now that I think about it, I have 8 0.1uf 600v Auricap's floating around here somewhere too.  I can try those also.  I'll even try some cascoded bypass combinations and see how that sounds as well.   

Thanks for lending a shoulder to cry on!   

[Jeff]

Welcome Stimpy!

Let me see if I have this straight.  You want to know if certain cap positions in a XO are inherently more sonically important than others.  Mostly, because you are on a tight budget.  Then, the initial post is followed by more questions up to the point were it sounds like you are interested in playing around with the XO...  More of an educational exercise?  While there is absolutely nothing wrong with this, there will be a conflict.  Education, and cheap do not coexist in audio.  And do not confuse less expensive with "cheap".

Now, to answer a few of your questions (direct or implied):

1) Series caps typically influence the sound with greater magnitude over a larger bandwidth than paralleled caps in a paralleled network.
2) Caps in paralleled RLC networks tend to have the least amount of impact on the network with the exception of parallel cap operating no higher than 300Hz.
3) Optimizing a crossover often calls for different brand and construction caps.
4) While bypassing (XOs) was a very viable thing 15-20 years ago, it is seldom the solution today.  This is due to the quality, and shear number of different flavors, available today.

A few things to note.  That speaker sounded good with "all" electrolytics.  The age of the caps has caused their ESR to rise, so not they sound darker, slower, and have less detail.  Replacing all the electrolytics with new electrolytics would be the best bang for the buck.  If you are trying to stretch your money, trial and error (an education) don't live here.  I have had a couple of poor experiences with erse electrolytics, so I no longer recommend them.

I'd be happy to make an official recommendation, but I need a couple of things first.  Budget?  Top six sonic improvements you are looking for?  If you have less than six, that is OK.

[Stimpy]

Welcome Stimpy!

Let me see if I have this straight.  You want to know if certain cap positions in a XO are inherently more sonically important than others.  Mostly, because you are on a tight budget.  Then, the initial post is followed by more questions up to the point were it sounds like you are interested in playing around with the XO...  More of an educational exercise?  While there is absolutely nothing wrong with this, there will be a conflict.  Education, and cheap do not coexist in audio.  And do not confuse less expensive with "cheap".

Thanks Jeff.  I appreciate your welcome and your responses.    Also, no experimentation or playing with the crossovers is planned.  Just a straight substitution of like-for-like.  And no problems with less expensive.  I like bang for the buck.

Now, to answer a few of your questions (direct or implied):

1) Series caps typically influence the sound with greater magnitude over a larger bandwidth than paralleled caps in a paralleled network.

Great.  That's what I was hoping to hear.

2) Caps in paralleled RLC networks tend to have the least amount of impact on the network with the exception of parallel cap operating no higher than 300Hz.

Again, nice.  Good about the 300Hz cut-off too, as I didn't want to have to use anything exotic for the 350uf cap.

3) Optimizing a crossover often calls for different brand and construction caps.

Good to know.  That allows for some tuning to the strengths of the different drivers.

4) While bypassing (XOs) was a very viable thing 15-20 years ago, it is seldom the solution today.  This is due to the quality, and shear number of different flavors, available today.

I wasn't expecting this.  I had assumed bypass caps were more accepted, and the norm?  Aren't the SoniCap Gen II caps bypass caps?

A few things to note.  That speaker sounded good with "all" electrolytics.  The age of the caps has caused their ESR to rise, so not they sound darker, slower, and have less detail.  Replacing all the electrolytics with new electrolytics would be the best bang for the buck.  If you are trying to stretch your money, trial and error (an education) don't live here.  I have had a couple of poor experiences with erse electrolytics, so I no longer recommend them.

I'm not opposed to using NPE's.  It's just that I've read comments from retired AR engineers, stating they would have used poly caps in their crossovers, if they'd been available then.  In fact, I've recapped speakers, using NPE's, and been happy with the results.  Just looking to 'step-up' to the next level, if the 90's are capable of that?  Which I think they are.

I'd be happy to make an official recommendation, but I need a couple of things first.  Budget?  Top six sonic improvements you are looking for?  If you have less than six, that is OK.

Budget?  Ha!  I sometimes feel as though I work for the U.S. Government, as my funds seem to always get reallocated to another project, without my prior knowledge or approval.  So, I usually buy a little at a time, when the mood arises!  In secret!

Sonic improvements?  The 90's are a really good vintage speaker, but a little more overall detail, especially in the lower mids, would be good.  Plus, a bit more air, and openness in the upper mids, lower treble, would be welcome.

Thanks again.   

[Jeff]

Good about the 300Hz cut-off too, as I didn't want to have to use anything exotic for the 350uf cap.

It should be noted that this cap will effect the dual 10" drivers 50Hz up, and the lower mid from the bottom to around 800Hz.  On a budget, this range is of less concern.  Electrolytics tend to be less offensive in this range.  If these were going to be your pride & joy, and you had the extra coin laying around, a high value (340uF) Mundorf 330uF EVO would do nicely.

http://www.soniccraft.com/product_info.php/mundorf-mcap-evo-330uf-250vdc-p-4156

If your last name was Rockefeller, a stack of Sonicap G1s would be about as good as it gets.

http://www.soniccraft.com/index.php/sonicap-gen-c-301_49_50

I wasn't expecting this.  I had assumed bypass caps were more accepted, and the norm?  Aren't the SoniCap Gen II caps bypass caps?

The key phrase there was, "seldom the solution".  The general public often trails behind with tales of urban legend, rules of thumb, and other such misinformation.  This is amplified when it comes to a pursuit that might best be described as an alchemy.  FYI, the G2 was not built to be a bypass cap.  The motivation behind their creation some 15+ years ago is a long winded bore, but in a nut shell, they were intended to be a budget option for electronics that sounded like the original Auricap.

I'm not opposed to using NPE's.

This would solve any potential budget issues, and satisfy your meager sonic goals below IMO.

It's just that I've read comments from retired AR engineers, stating they would have used poly caps in their crossovers, if they'd been available then.

I know nothing of this, but I can tell you that there were plenty of satisfactory film caps available at that time.  Easily for 10 years prior to the construction of those speakers.  As a matter of fact, there were likely a boat load of surplus caps that would have kicked ass in those speakers.  Those same vintage caps bring stupid money today.

In fact, I've recapped speakers, using NPE's, and been happy with the results.

You might ought to listen to yourself

Just looking to 'step-up' to the next level

Yeah...?  Cheap don't live here

Budget?  Ha!  I sometimes feel as though I work for the U.S. Government, as my funds seem to always get reallocated to another project, without my prior knowledge or approval.  So, I usually buy a little at a time, when the mood arises!  In secret!

 

a little more overall detail, especially in the lower mids, would be good.  Plus, a bit more air, and openness in the upper mids, lower treble

Now all I need is a budget.  There are too many ways to skin this cat.  Not to mention the improvements you would love, but don't know about yet

[Stimpy]

Thanks for the reply.  Now, 2 additional questions, to give me something to think about.   

First, is there a good brand of electrolytic that you'd recommend?   Does one exist, IYHO?  And second, if I use SoniCap G1's for the series caps, are they caps that are equally good on the bass end as well as the treble?  Oh, to cheat a bit, are the GenII's only compatible with Gen I's, or are they an 'acceptable' by-pass cap with other brands?   

[Jeff]

1) I like the Mundorf Ecap, but then I carry them...
2a) They are rather balanced, so yes.
2b) I do not understand the question, but I'll take a poke at it anyway.  The G2 will function parallel to any cap.  With absolutely nothing to go on, I could not tell you if you would find the result pleasing.

[Jeff]

The following is really not what you asked for.  However, it is what I would do if I owned these speakers, and was on a "tight" budget.

High-pass:

Mills MRA-5 resistors: http://www.soniccraft.com/index.php/mills-watt-c-29_53_62

4uF G1/200VDC: http://www.soniccraft.com/product_info.php/gen-sonicap-uf-200vdc-p-429

6uF Dynamicap E/210V: http://www.soniccraft.com/product_info.php/dynamicap-6uf-210vdc-p-155

Upper mid:

Mills MRA-10 resistors: http://www.soniccraft.com/index.php/mills-10-watt-c-29_53_295

22uF Supreme: http://www.soniccraft.com/product_info.php/mundorf-supreme-22uf-600vdc-p-4213  If you are concerned about trimming it up, this would be the most economical match: http://www.soniccraft.com/product_info.php/kimber-kap-22uf-200vdc-p-4650

8uF G1/200VDC: http://www.soniccraft.com/product_info.php/gen-sonicap-uf-200vdc-p-446

6.8uF + 33uF Ecap: http://www.soniccraft.com/product_info.php/mundorf-cap-plain-68uf-70vdc-50vac-p-4076 + http://www.soniccraft.com/product_info.php/mundorf-cap-plain-33uf-70vdc-50vac-p-4078

Mills MRA-5 for the RLC network resistor: http://www.soniccraft.com/product_info.php/60-ohm-mills-mra-p-564

Lower mid:

5 Ohm parallel a pair of these: http://www.soniccraft.com/product_info.php/10-ohm-mills-mra-10-p-3609

3 Ohm parallel a pair of these: http://www.soniccraft.com/product_info.php/ohm-mills-mra-12-p-687

33uF + 47uF EVO Oil: http://www.soniccraft.com/product_info.php/mundorf-mcap-evo-oil-33uf-450vdc-p-4163 + http://www.soniccraft.com/product_info.php/mundorf-mcap-evo-oil-47uf-350vdc-p-4167

Low value 33uF EVO Oil: http://www.soniccraft.com/product_info.php/mundorf-mcap-evo-oil-33uf-450vdc-p-4163

Low-pass:

350uF Ecap: http://www.soniccraft.com/product_info.php/mundorf-cap-plain-82uf-50vdc-35vac-p-4073 + http://www.soniccraft.com/product_info.php/mundorf-cap-raw-270uf-63vdc-23vac-p-4065

1 Ohm resistor: http://www.soniccraft.com/product_info.php/ohm-mills-mra-12-p-696

[Stimpy]

WOW!!!       That's above and beyond.  Much more effort on your part than I expected.  Thanks Jeff!       Let me study up on the suggestions, and crunch some numbers, and see where that leads me.  But this should be fun!   

One other thought, are the Mundorf E-Caps polarized?  It's just the style of their shape that made me think they were?  A cap with that indented shoulder usually signified the positive end of the cap.  So, I just didn't know for sure?

Now, I'll leave you alone, so you can get some real work done.

Much appreciated!   

[undertow]

Stimpy,

My question is how do you plan to execute this? I will warn you now that likely the original board, or boards that are containing your crossovers in that speaker will likely not accommodate the components necessary to even go to the "Next Level" because of space issues. I assume these older AR's don't have bi-wire posts on the back? In any case I would likely suggest you do not experiment to much, because taking these crossovers in, and out to just keep adjusting small portions of the boards at a time and see if you like one cheap cap vs. another will likely wear out woofer screws, and your patience.

My honest opinion in this case you go for all or nothing. In other words pull the crossovers, and if you can salvage some of the better inductors off the boards go for it, but definitely replace all the resistors as stated above with the Mills or something available which will be better than what is in there. Plus starting with fresh resistors all around will be far easier to remount, replace on all other levels, and sound better.

As for the caps I like the suggestions above, but as a warning these caps can be HUGE, they may not even fit anywhere in your speaker if you build the boards bigger. I would seriously consider just taking the originals out, and coming up with a plan to then run "Outboard" crossovers. Basically they are in their own box outside the speaker. This of course presents one other challenge which is to run a 4 way speaker you need to have 4 different binding posts added to the back to individually hook each driver to their corresponding filter outside the box. This also allows easy cap replacement, and access to everything else if you want to change something or fine tune. Because this is a rather complex passive crossover compared to most run of the mill 2 or 3 way speakers in this case.

There is a way to get around this with a single connector however made by Neutrik called a "Speakon" connector which is basically a cannon plug style that will let you run 4 or 8 separate wire connections in each connector. They are relatively cheap as well, and many high end companies use them to connect not just outboard crossovers, or separated cabinets containing different drivers as well back to the cabinet with the crossovers or main amp inputs installed.

Like I said if you do decide to take on this project go all in, because not only will this save you headache, you will get better results, and you will have much more flexibility to do it correctly in the end actually saving you more money. I would not try to piece meal this project as it seems you sorta think would be your method here.

[Stimpy]

Hi Undertow,

The AR90s have a low pass and a high pass crossover board, but unfortunately both use a single input.  Though, I could add bi-amp inputs.  Each board is at least 9.5" x 9.5" square.  So, I have quite a bit of room for the new parts.  Plus, I have a secret, I have a second set of AR90 crossovers.  That will let me rebuild one set, and have a second set for comparison, or for emergencies.  That also lets me have a second set of crossovers, to rebuild, when I have an unlimited cash flow, to build the high-end version!  I'll hate to see Jeff's recommendations for that one, considering the totals so far, on the 'tight' version!     

Thanks!