New capacitors for AR-9

[JeffS]

I've recently acquired a pair of AR-9's. For the first week or so they sounded fine, but after playing a variety of CD's I noticed that some of the bass frequencies are much more potent than others. It dawned on me that the room I have them installed in is essentially a square, 20 feet by 20 feet, and that I'm hearing a standing wave. I borrowed a low frequency swept sine wave CD to hopefully confirm what my ears and a wavelength calculation tells me, and that is that there are two humps in the room curve (~ 28 Hz and 56 Hz).

While listening to (and feeling) the 'Bass Mekanik Sonic Overload' CD, I also noticed that at frequencies below 40 Hz I could hear sound coming from the lower and upper mids on one speaker, and from the lower mid on the other. The sound is best described as the static noise you might hear from turning a dirty pot, or pops on a vinyl record, but they were more evenly spaced in time. Also, the speaker with the noise coming from both mids seems to exhibit "grainy" sounding vocals on some material. I also played this CD on another system I have using a pair of 303's. I did not hear this noise through either the woofer or the mid.

My first question is: does this sound like a symptom of bad capacitors? If so, I would like to replace them with something that will make the speakers sound as close to original as is possible. What would be the most cost effective route?

Thanks,

Jeff S.

[Guest hilltroll67]

Cost-effective? If you can run a soldering iron, the only expense is the caps themselves. Your concern is to duplicate the original capacitance value (microFarads); the voltage rating of the replacements can be higher. Dayton polypropylene caps are reasonably priced and will perform better than the originals. You may need to be a little creative finding room for them.

How are the surrounds?

Bob

[Carlspeak]

>I've recently acquired a pair of AR-9's. For the first week

>or so they sounded fine, but after playing a variety of CD's I

>noticed that some of the bass frequencies are much more potent

>than others. It dawned on me that the room I have them

>installed in is essentially a square, 20 feet by 20 feet, and

>that I'm hearing a standing wave. I borrowed a low frequency

>swept sine wave CD to hopefully confirm what my ears and a

>wavelength calculation tells me, and that is that there are

>two humps in the room curve (~ 28 Hz and 56 Hz).

> While listening to (and feeling) the 'Bass Mekanik Sonic

>Overload' CD, I also noticed that at frequencies below 40 Hz I

>could hear sound coming from the lower and upper mids on one

>speaker, and from the lower mid on the other. The sound is

>best described as the static noise you might hear from turning

>a dirty pot, or pops on a vinyl record, but they were more

>evenly spaced in time. Also, the speaker with the noise coming

>from both mids seems to exhibit "grainy" sounding

>vocals on some material. I also played this CD on another

>system I have using a pair of 303's. I did not hear this noise

>through either the woofer or the mid.

> My first question is: does this sound like a symptom of bad

>capacitors? If so, I would like to replace them with something

>that will make the speakers sound as close to original as is

>possible. What would be the most cost effective route?

>

>Thanks,

>Jeff S.

>

It looks like you encountered a room mode. You should, however, get the same mode with your 303's since it's strictly a function of frequency and room size, not speaker brand. This statement, of course, assumes both speakers brands can function with equal loudness at the same, low frequency.

The link below is to a room mode calculator. Check it out to confirm your findings.

http://www.mcsquared.com/modecalc.htm

The most cost effect way to duplicate the original is with electrolytic caps. They are less expensive and are not the best, but are/were used in many speakers of that era.

It's all about the music

Carl

Carl's Custom Loudspeakers

[JeffS]

>Cost-effective? If you can run a soldering iron, the only

>expense is the caps themselves. Your concern is to duplicate

>the original capacitance value (microFarads); the voltage

>rating of the replacements can be higher. Dayton polypropylene

>caps are reasonably priced and will perform better than the

>originals. You may need to be a little creative finding room

>for them.

>

>How are the surrounds?

>

>Bob

Thanks for the suggestion on the Daytons, I'll look into this further to see what they offer. I'll be doing the soldering myself and I hope that I'll be able to easily remove the old caps from the crossover boards.

My son and I replaced the surrounds on the woofers and low mids when he acquired the speakers a couple of years ago. He's since switched to using smaller speakers (10 Pi's) and had these stored so I offered to "borrow" them for awhile. They sounded great in his setup and I never noticed any problem with the midrange. Either I'm now doing more critical listening or the caps have gone bad in the last year or so. Regardless, I'd like to make them sound as "original" as possible. One other decision I'll have to make is whether or not to replace the 470 and 2500 microfarad caps in the woofer circuit.

[JeffS]

>>I've recently acquired a pair of AR-9's. For the first

>week

>>or so they sounded fine, but after playing a variety of

>CD's I

>>noticed that some of the bass frequencies are much more

>potent

>>than others. It dawned on me that the room I have them

>>installed in is essentially a square, 20 feet by 20 feet,

>and

>>that I'm hearing a standing wave. I borrowed a low

>frequency

>>swept sine wave CD to hopefully confirm what my ears and

>a

>>wavelength calculation tells me, and that is that there

>are

>>two humps in the room curve (~ 28 Hz and 56 Hz).

>> While listening to (and feeling) the 'Bass Mekanik Sonic

>>Overload' CD, I also noticed that at frequencies below 40

>Hz I

>>could hear sound coming from the lower and upper mids on

>one

>>speaker, and from the lower mid on the other. The sound

>is

>>best described as the static noise you might hear from

>turning

>>a dirty pot, or pops on a vinyl record, but they were

>more

>>evenly spaced in time. Also, the speaker with the noise

>coming

>>from both mids seems to exhibit "grainy"

>sounding

>>vocals on some material. I also played this CD on another

>>system I have using a pair of 303's. I did not hear this

>noise

>>through either the woofer or the mid.

>> My first question is: does this sound like a symptom of

>bad

>>capacitors? If so, I would like to replace them with

>something

>>that will make the speakers sound as close to original as

>is

>>possible. What would be the most cost effective route?

>>

>>Thanks,

>>Jeff S.

>>

>

>It looks like you encountered a room mode. You should,

>however, get the same mode with your 303's since it's strictly

>a function of frequency and room size, not speaker brand. This

>statement, of course, assumes both speakers brands can

>function with equal loudness at the same, low frequency.

>The link below is to a room mode calculator. Check it out to

>confirm your findings.

>http://www.mcsquared.com/modecalc.htm

>

>The most cost effect way to duplicate the original is with

>electrolytic caps. They are less expensive and are not the

>best, but are/were used in many speakers of that era.

>

>It's all about the music

>

>Carl

>Carl's Custom Loudspeakers

Carl,

Thanks for the calculator. It goes into even greater detail than the one I found and is in agreement with what I calculated for the axial mode of the room.

You mention electrolytics and I know some folks prefer not to use them. Is there anything wrong, sonically speaking, by replacing electrolytics with electrolytics (I'm assuming that there may be some in this crossover) or do they simply not last as long as other types?

I fully agree that this room should have the same influence on my AR 303's (they have a similar low end extension to the 9's). I thought about bringing them down to the room where I have the 9's installed just to confirm what I've heard but they are being used in a room 2 stories up from this room and they are ~ 55 pounds apiece. It's easier to believe the calculator!

Thanks

[Guest linedrive]

Another consideration could be the level control switches, which might have become noisy over time.

[Carlspeak]

Jeffs.

With regard to your electrolytic question. They are the most cost effect way to replace bad ones or older oil filled or wax paper types. Most electrolytics sell for a $1 or less. They will last a long time. Look for ones with the highest voltage rating you can find.

If you decide to go with metallized PP (i.e. Solens or similar), you'll find the price goes up rather quickly with increasing uF and voltage ratings.

It's all about the music

Carl

Carl's Custom Loudspeakers

[Guest hilltroll67]

>Thanks for the suggestion on the Daytons, I'll look into this

>further to see what they offer. I'll be doing the soldering

>myself and I hope that I'll be able to easily remove the old

>caps from the crossover boards.

>

>My son and I replaced the surrounds on the woofers and low

>mids when he acquired the speakers a couple of years ago. He's

>since switched to using smaller speakers (10 Pi's) and had

>these stored so I offered to "borrow" them for

>awhile. They sounded great in his setup and I never noticed

>any problem with the midrange. Either I'm now doing more

>critical listening or the caps have gone bad in the last year

>or so. Regardless, I'd like to make them sound as

>"original" as possible. One other decision I'll have

>to make is whether or not to replace the 470 and 2500

>microfarad caps in the woofer circuit.

Modern electrolytics are durable, and tend to be much more compact (easier to fit to the pcb). Audiophiles say that they produce a 'grainy' sound compared to polys; I can't hear any difference, but my hearing isn't audiophile-class. Given the same capacitance values, polys will not otherwise change the 'original' sound. Those high capacitance caps in the woofer circuit will damn near have to be electrolytics - the poly version would be huge.

Like the man said, use the highest voltage ratings available - that will fit.

I hope to get to hear some AR9s someday, before my hearing goes too much farther south.

Bob

[JeffS]

>Another consideration could be the level control switches,

>which might have become noisy over time.

>

Your right and I'm sure they could use cleaning. I'll have to figure out how to remove the little cup that the stem comes through so that I can get some contact cleaner inside.

[Guest linedrive]

It'll pop off, if you can work a thin tool under the edge. Be careful, though - the cup is very light aluminum, so it will easily bend or nick. Just place a small bit of Elmer's glue on the inside edge, when you put them back into place.

I've never cleaned the switches in place, but have always unthreaded the nut, and pulled them into the enclosure, still attached to the wiring harness.

[rrcrain]

Electrolytics may be the most cost effective solution, but they also have a shorter expected life.

based on my own experience from recapping a pair of AR90s with poly caps, I have to agree there isn't a discernable difference in sound between caps 6 months to a year after they are installed. Initially and until the poly caps "break in" they are, or can be a bit harsh.

Concerning bass coming from the lower and upper mids, this is indeed due to old caps and is the same issue I had with my 90s. In addition, my tweeters were nearly silent.

[JeffS]

>Electrolytics may be the most cost effective solution, but

>they also have a shorter expected life.

>

>based on my own experience from recapping a pair of AR90s with

>poly caps, I have to agree there isn't a discernable

>difference in sound between caps 6 months to a year after they

>are installed. Initially and until the poly caps "break

>in" they are, or can be a bit harsh.

>

>Concerning bass coming from the lower and upper mids, this is

>indeed due to old caps and is the same issue I had with my

>90s. In addition, my tweeters were nearly silent.

It looks like Parts Express has just about all the caps I'll need in poly versions at reasonable prices. I'm not sure of what tolerances AR chose for the originals, but I see I have a choice of either 5% or 1% for most of them.

Did you replace your woofer caps, and if so, can you suggest a good source for them? The 2500uf caps I'm finding seem to be polarized (max DC voltage ratings). Bob mentioned that modern electrolytics are smaller than older caps. The caps I'm finding (assuming they are suitable) are much smaller physically than the caps currently in the speakers. Is there any reason to replace the woofer caps with something of the same physical size?

Thanks for all the input.

http://www.classicspeakerpages.net/dc/user_files/1899.jpg

1898.txt

[rrcrain]

The 9 uses massize caps in the woofer crossover compared to the 90, and the only realistic option you have is an electrolytic cap. If you want, and I've no idea if it will make a hoot of difference, try bypassing a new electrolytic cap with a small poly cap. Some people claim this does wonders, others say it's hogwash. I suspect it depends on the speaker and the person listening to it.

The electrolytics I took out of my 90 crossover weren't polarized and I can't imagine them being polarized in the 9, nor can I think of a good reason they should be polarized. Depending on cost, you might take a look at some of the new oil filled caps for the woofer section.

Concerning 5% versus 1% caps. Use whichever you feel more comfortable using, some of the original caps were 20%. If there isn't a major cost differential, I'd go fore the 1% personally.

[Guest Bret]

Jeff -

I've done this multiple times to multiple speakers in multiple stages. My opinion has its detractors, but I think you will find that if you will do what I experimentally found was best, then you will be satisfied with the result and save yourself a lot of time and energy, and maybe even money in the long-run.

I would tell you that both the 9, 90s, and 10pi will all benefit from being recapped. The problem you describe is exactly the situation I found with a pair of 90s (the tweeter, upper-midrange, and lower-midrange crossovers are the same in 90s and 9s). I experimented on those 90s and later did an "in stages" re-capping to my 9s, learning something every time I changed something.

Using cheap capacitors for the 4uf, 6uF, 8uF, 24uf, and 40uf is to be avoided. I'm not talking about buying $300 honey-filled, super-duper audiophile, cost-more-than-gold-capacitors, but I am saying, "Don't buy the cheap ones." Fortunately, these smaller values don't break the bank even if you choose "audiophile" brands. I would tell you the best combination I found, but you can't buy those anymore so there is no point in my being that specific. Just get "good" ones.

All the stuff you read about a capacitor-is-a-capacitor-is-a-capacitor is based on something other than capacitors used in a high-current filter circuit.

I would also encourage you to use a "by-pass" capacitor across the 4uF on the tweeter. That's just a .1uF film cap in combination with a 3.8 or 3.9 poly (parallel). Why? Because it sounds good. Why? I dunno. All the engineering stuff I've ever seen says it shouldn't make any difference at all. So why do it? Because it sounds good. Why? I don't know and obviously neither do the engineers who will say that it makes no difference. They are absolutely certain that if you do that it will make no difference at all. Okay, let's say they are 100% right and I'm easily duped. It costs you a few dollars for you to do it, so even if they are right, and I'm wrong, it isn't that big of a deal. If you DON'T do it and find the treble a little "brittle and harsh". . . you get to pull the woofers again and break-out the soldering iron and the glue gun and buy some by-passing capacitors. (My advice? Just spend the few dollars, by-pass those 4uF caps (the 6uF isn't necessary) and be done with it).

I would avoid the Daytons *only* because someone who tried them reported less than acceptable results with them vs another brand, and he ended-up replacing them. Your mileage may vary, but why drive any more miles than you have to just to have a chance to reinvent the wheel?

The 80uF probably does not matter as much, the 30uf might. I ended-up replacing all the electrolytics I used with fairly expensive polys and was not sorry I did.

Having said all that, I have not yet replaced the 470uF and 2500uF caps. The reasons are many and explained thoroughly elsewhere on the forum. I'm "chicken" to change the 2500uF for some properties it has which building a bank of cheap electrolytics would not replicate. Like you, I have been unable to find NPE 2500uF capacitors likely to share some important specifications with the originals. I may change the 470s just for the heck of it. . . or I might not. I suspect that the frequencies in question are a lot harder to hear than the upper-cabinet's capacitors.

Getting capacitors that are within 1% of each other is, for me, worth paying for - if only so I don't have any excuse to imagine something is mismatched. They absoultely should also be within 10% of their labeled rating.

The woofer capacitors have nothing whatsoever to do with the problems you are describing. Cheap-o-rama electrolytics in the upper cabinet will correct the problems you are describing IF the drivers have not been damaged by playing them too loudly with bad capacitors attached. Expensive(relatively)capacitors also clean-up some issues that cheap-o-rama capacitors introduce. You only live once and we're talking about a few pizzas', one good bottle of wine's, or one SUV's gastankfull's difference in price between "cheap-o" and "expens-o."

Good luck and happy listening.

Bret

[mluong303]

Hi JeffS

I would de-solder the wires off the 2500uF caps temporary and take a measurement and see if both are within 5% of rated value. If they are then I would leave them alone.

By the way, I love the picture you posted in the thread. What brand and model of camera did you use to shot this picture? What resolution is it?

Thanks,

Minh Luong

mluong303@aol.com

[tysontom]

>

>By the way, I love the picture you posted in the thread. What

>brand and model of camera did you use to shot this picture?

>What resolution is it?

>

>Thanks,

>Minh Luong

>mluong303@aol.com

Minh, it was a Canon EOS Digital Rebel camera: I use an XTi and I recognized the pixels...what do you think?

--Tom Tyson

[JeffS]

>Hi JeffS

>

>I would de-solder the wires off the 2500uF caps temporary and

>take a measurement and see if both are within 5% of rated

>value. If they are then I would leave them alone.

>

>By the way, I love the picture you posted in the thread. What

>brand and model of camera did you use to shot this picture?

>What resolution is it?

>

>Thanks,

>Minh Luong

>mluong303@aol.com

Minh,

As Tom said, it's a first generation Canon Digital Rebel (6.3 mp). It produces nice creamy and noise free pixels through ISO 400. With the prime lenses I tend to use with it, in this case a Canon EF 28mm f/2.8, I get nicely saturated and relatively distortion free pics. Canon crippled the first generation Rebel by disabling some of the firmware features, but a "Russian firmware hack" became available shortly after the cameras introduction that unlocked some features that were available on Canon's 10D. The newer Rebels, like Tom's XTi, have a significantly higher mp count (10.1 mp, I believe) plus all the features the older model lacked.

[JeffS]

>Jeff -

>

>I've done this multiple times to multiple speakers in multiple

>stages. My opinion has its detractors, but I think you will

>find that if you will do what I experimentally found was best,

>then you will be satisfied with the result and save yourself a

>lot of time and energy, and maybe even money in the long-run.

>

>I would tell you that both the 9, 90s, and 10pi will all

>benefit from being recapped. The problem you describe is

>exactly the situation I found with a pair of 90s (the tweeter,

>upper-midrange, and lower-midrange crossovers are the same in

>90s and 9s). I experimented on those 90s and later did an

>"in stages" re-capping to my 9s, learning something

>every time I changed something.

>

>Using cheap capacitors for the 4uf, 6uF, 8uF, 24uf, and 40uf

>is to be avoided. I'm not talking about buying $300

>honey-filled, super-duper audiophile,

>cost-more-than-gold-capacitors, but I am saying, "Don't

>buy the cheap ones." Fortunately, these smaller values

>don't break the bank even if you choose "audiophile"

>brands. I would tell you the best combination I found, but

>you can't buy those anymore so there is no point in my being

>that specific. Just get "good" ones.

>

>All the stuff you read about a

>capacitor-is-a-capacitor-is-a-capacitor is based on something

>other than capacitors used in a high-current filter circuit.

>

>

>I would also encourage you to use a "by-pass"

>capacitor across the 4uF on the tweeter. That's just a .1uF

>film cap in combination with a 3.8 or 3.9 poly (parallel).

>Why? Because it sounds good. Why? I dunno. All the

>engineering stuff I've ever seen says it shouldn't make any

>difference at all. So why do it? Because it sounds good.

>Why? I don't know and obviously neither do the engineers who

>will say that it makes no difference. They are absolutely

>certain that if you do that it will make no difference at all.

> Okay, let's say they are 100% right and I'm easily duped. It

>costs you a few dollars for you to do it, so even if they are

>right, and I'm wrong, it isn't that big of a deal. If you

>DON'T do it and find the treble a little "brittle and

>harsh". . . you get to pull the woofers again and

>break-out the soldering iron and the glue gun and buy some

>by-passing capacitors. (My advice? Just spend the few dollars,

>by-pass those 4uF caps (the 6uF isn't necessary) and be done

>with it).

>

>I would avoid the Daytons *only* because someone who tried

>them reported less than acceptable results with them vs

>another brand, and he ended-up replacing them. Your mileage

>may vary, but why drive any more miles than you have to just

>to have a chance to reinvent the wheel?

>

>The 80uF probably does not matter as much, the 30uf might. I

>ended-up replacing all the electrolytics I used with fairly

>expensive polys and was not sorry I did.

>

>Having said all that, I have not yet replaced the 470uF and

>2500uF caps. The reasons are many and explained thoroughly

>elsewhere on the forum. I'm "chicken" to change

>the 2500uF for some properties it has which building a bank of

>cheap electrolytics would not replicate. Like you, I have

>been unable to find NPE 2500uF capacitors likely to share some

>important specifications with the originals. I may change

>the 470s just for the heck of it. . . or I might not. I

>suspect that the frequencies in question are a lot harder to

>hear than the upper-cabinet's capacitors.

>

>Getting capacitors that are within 1% of each other is, for

>me, worth paying for - if only so I don't have any excuse to

>imagine something is mismatched. They absoultely should also

>be within 10% of their labeled rating.

>

>The woofer capacitors have nothing whatsoever to do with the

>problems you are describing. Cheap-o-rama electrolytics in

>the upper cabinet will correct the problems you are describing

>IF the drivers have not been damaged by playing them too

>loudly with bad capacitors attached.

>Expensive(relatively)capacitors also clean-up some issues that

>cheap-o-rama capacitors introduce. You only live once and

>we're talking about a few pizzas', one good bottle of wine's,

>or one SUV's gastankfull's difference in price between

>"cheap-o" and "expens-o."

>

>Good luck and happy listening.

>

>Bret

Bret,

Your comment about the Dayton's is interesting. My son recapped his 11's with Dayton polys and to him they sounded harsh afterwards. I couldn't hear a difference that I would attribute to the caps, because when I heard them after the recapping they had been placed in a different location.

On the 9's, listening to a test CD allowed me to hear the lower and upper mid "noise", but when playing music they sound OK, except for some occasional graininess on vocals on the left channel. But, you know, as you mentioned in a previous thread it could be that there is more light on that side of room! It might be worth it to try an "equalization by light" experiment sometime.

But there is really no doubt that the noise I heard, and that rrcrain and yourself did on 90's, let's me know that new caps are needed. And as long as I'm doing the job, I want to use quality parts. The "in stages" idea is good also. If the noise is gone after the recapping, I'll leave the 2500uF and 470uF in place and hope they live a long time!

I'm starting to think that I should have never loaded that test CD into the player. I'm probably going to have to tame the not to frequently heard 30Hz resonance with a 10 band EQ. Also, it showed me that I have some windows that are due for replacement!

Jeff

[mluong303]

Hello Tom and JeffS,

Thank you for the info regarding the Canon Rebel digital camera. I love the picture quality with JeffS 6.3mp. Tom's 10mp XTi must be poping out of the page then... I am looking at the Canon G7 compact and wondering how it will compare to the Rebel XTi?

Minh Luong

[Guest Bret]

>But, you know, as you mentioned in a previous thread it could be that there is more light on that side of room! It might be worth it to try an "equalization by light" experiment sometime.<

Well, Jeff, you know I'm completely mad. For my next trick I'm going to hold a bottle of Pinot Noir under one nostril and a Cabernet Sauvignon under the other and see if the stereo image shifts when I swap bottles.

I can't wait for your reaction once you change the caps.

Bret

[JeffS]

>>But, you know, as you mentioned in a previous thread it

>could be that there is more light on that side of room! It

>might be worth it to try an "equalization by light"

>experiment sometime.<

>

>Well, Jeff, you know I'm completely mad. For my next trick

>I'm going to hold a bottle of Pinot Noir under one nostril and

>a Cabernet Sauvignon under the other and see if the stereo

>image shifts when I swap bottles.

>

>I can't wait for your reaction once you change the caps.

>

>Bret

Mad?, not at all.

Years ago I realized that higher humidity made the sound less desirable. But was it actually the humidity or my perception of its possible effect, or its effect on my mood that altered the sound?

Do light levels have an effect on balance if they aren't evenly distributed throughout a room? No, I don't believe so, but they do influence my perception and if I want a better idea of what I'm hearing then I'll listen in the dark.

I've never gotten into trying esoteric cables, choosing to believe that decently constructed cables of the proper length and gauge will suffice, and allow me to save some money for retirement! And even if someone could demonstrate an improvement with high end cables connected to my modest equipment, I'd still blame it on perception.

Bad caps are bad caps, and I'm looking forward to hearing the 9's with new ones. I'll probably even try the tweeter cap bypass if I can find the values.

And then it's on to the things that resonate in the room, and what I'll use to dampen them. Silicone caulk, 3" coated drywall screws, maybe a smaller amp? (nah).

Jeff

[rrcrain]

I won't assume to know if new caps in the woofer section of the AR9 will make a difference or not, but I can absolutely confirm they improved the bass in my 90s.

If you can find new electrolytics or oil filled caps of the proper value, do consider it.

[Guest Bret]

Just so nobody gets the wrong idea I'll agree with you even though you don't need me to.

The AR-90 benefits greatly from replaced woofer caps. Yes. I don't know about the AR-9. That's an entirely different breed with the crossover serving a unique purpose in addition to a crossover's usual purpose.

As I said, I'm chicken to change it. It's a matter of my being afraid that I may correct one thing while completely screwing-up something else. Since what's in there seems to be working well (smooth transition of bassoon from high to low notes without apparent bloat or dip) I'm leaving it alone.

When I do change them, I will definitely experiment in a non-destructive manner so that I can easily restore the originals if need-be.

Bret