AR15s and Degrading Sound

[Guest vanmeter]

I've posted about this on another forum (AA) a couple of times and want to mention that up front since I've been fishing around for input on this for a while.

Basically, I have a pair of AR15s I bought off ebay a couple years ago and refoamed and fixed the cabinets up on, and they sounded great...until about 9 or 10 months ago. This was about the same time I started using solid core hookup wire for speaker wire, and I can't help wonder if the two are or not related, as I thought for a long time that the gradual deacrease in highs and increase in graininess was oxidation.

I switched to magnet wire with no real changes; with brand new wires, or unhooked, cleaned wires (with Deoxit) they sound fantastic for about a day, and then back to being dull and tizzy sounding. I also just switched back to stranded wire thinking that my wire experimentations might have been causing this, which is essentially what a person at the other form has told me a couple of times now, that the problem is likely using solid wire on the AR terminals, and on my amp's terminals, which are meant for stranded.

But in looking around and reading I keep seeing about ESR, and asked my brother-in-law tonight about it's possible role in what I'm dealing with. He's an electronics person, but not really an audio person, and was admittedly just guessing, but he felt like the electolytics in my crossovers might be way off in ESR and had to build up some resistance before the problems showed, which is why after unhooking the wires and possibly discharging the cap, I have great sound temporarily.

Does this make sense with how these caps work in these circuits, and if so, or even if not, does it sound like I may have ESR issues, or should I be focusing elsewhere? This has been getting steadily worse for close to a year, and I'd love to really know what is causing what I'm hearing. The problem doesn't seem to change when I change amps.

[speaker dave]

But in looking around and reading I keep seeing about ESR, and asked my brother-in-law tonight about it's possible role in what I'm dealing with. He's an electronics person, but not really an audio person, and was admittedly just guessing, but he felt like the electolytics in my crossovers might be way off in ESR and had to build up some resistance before the problems showed, which is why after unhooking the wires and possibly discharging the cap, I have great sound temporarily.

Does this make sense with how these caps work in these circuits, and if so, or even if not, does it sound like I may have ESR issues, or should I be focusing elsewhere? This has been getting steadily worse for close to a year, and I'd love to really know what is causing what I'm hearing. The problem doesn't seem to change when I change amps.

ESR* is not an insignificant parameter but it is hard to say if it is really your problem. There used to be some poor ESR electrolytics on the market before everyone was offering "low ESR" and the difference could be enough to measure and hear. I have built up crossovers with new capacitors of high ESR and seen some treble loss versus another cap.

What we are talking about would be the main series capacitor for the tweeter. I have seen new caps (not older failing capacitors) with several ohms of resistance. The net effect would by 1 or 2 dB of treble loss. This is on the order of the effect of a typical two position treble switch or maybe of some moderate rotation of a treble L-Pad. Capacitors in other locations of the network would have there own effects but probably would not be as noticeable.

In the last decade the trend has been to use only "low ESR" caps and to tend to use film capacitors (inherently very low ESR) for the treble section where values tend to be modest. Certainly in a new product the losses are quite small and no different than any padding resistors that are usually in circuit.

I know that vintage audio people now preach the religion of "change all caps" and that this probably keeps more than a few parts jobbers in business. But I suspect that only 1 in 10 capacitors that gets changed was bad enough to have an audible or measurable effect. (I guess the trick is knowing which 1 in 10!)

Change your caps if it will give you peace of mind. you might also try putting a 1uf film cap around the primary tweeter capacitor while listening to pink noise. 1uf shouldn't change the crossover corner much but if the upper treble jumps up then you can surmise the ESR was significant. If it doesn't increase then you just don't have an ESR problem.

*ESR stands for Effective Series Resistance. It is a property of the construction of the capacitor or the dielectric (electrolyte) that determines the minimum impedance that the capacitor exibits at high frequencies where it really should be a short circuit. An ESR of 1 ohm is the same as having a ideal capacitor with 1 ohm soldered in series. As capacitors age and the electrolyte possibly dries out the ESR may rise. This causes a lot of real headaches in switching power supplies and consternation amongst audiophiles!

David

[Guest vanmeter]

Change your caps if it will give you peace of mind. you might also try putting a 1uf film cap around the primary tweeter capacitor while listening to pink noise. 1uf shouldn't change the crossover corner much but if the upper treble jumps up then you can surmise the ESR was significant. If it doesn't increase then you just don't have an ESR problem.

I'm definitely hearing something going of that's causing the highs to be brittle and harsh, but that is intermittent. I'm not really just wanting to change out the caps for the sake of changing them, if I came across that way, just wondering if aging caps could be what I'm hearing. However, your suggestion sounds like I would know pretty quickly - I may even have a couple around somewhere and it'd be a quick test. Thanks!

I wonder, though, what the AR designers intended with the 15s in terms of ESR. I don't know that I'm comfortable just replacing them if they weren't intended to be low ESR in the first place, and with no schematic or anything I'm not sure if I'd be helping or hurting since I don't really know at this point if that's what is even causing what I'm hearing.

[speaker dave]

I'm definitely hearing something going of that's causing the highs to be brittle and harsh, but that is intermittent. I'm not really just wanting to change out the caps for the sake of changing them, if I came across that way, just wondering if aging caps could be what I'm hearing. However, your suggestion sounds like I would know pretty quickly - I may even have a couple around somewhere and it'd be a quick test. Thanks!

I wonder, though, what the AR designers intended with the 15s in terms of ESR. I don't know that I'm comfortable just replacing them if they weren't intended to be low ESR in the first place, and with no schematic or anything I'm not sure if I'd be helping or hurting since I don't really know at this point if that's what is even causing what I'm hearing.

You had mentioned dull and tizzy, which seem a bit like opposites. Brittle and harsh I would interpret as excessive in the lower treble. I know of no way that high ESR could result in more treble energy. It would create more resistance in what is generally always a series crossover element, hence a treble loss.

I certainly wouldn't worry about replacing components with "lower ESR than originally intended". Nobody designs in high ESR as a parameter of the network. It is more the case that a manufacturer, if they are really cheap, may use high ESR components in positions that don't matter.

Are you sure that you just don't like the sound of this particular speaker? The normal faults of aging don't usually raise treble level (alhough I suppose the woofer could have lower output somehow). I wonder if you have a tweeter rub causing distortion? Some other fault in you electronics?

Anyhow, elevated treble is not an ESR byproduct.

David

[Guest vanmeter]

Are you sure that you just don't like the sound of this particular speaker?

David

I love the sound of them when they're, in my estimation, working correctly. When I say dull and tizzy, I mean rolled off probably above 14k and with a grittiness that makes cymbal crashes sound like can lids. Perhaps tizzy isn't the right word. Not AM radio dull, but dull and strained sounding. And this comes and goes, it's not constant. It could very well be something else, I realize, that's why I was asking if an overabundance of ESR in the original caps could be causing what I'm hearing since I can't really seem to trace it to anything else but the speakers. I realize this is one of those vauge things that's hard to both describe and find, but it's quite real to me here!

[RoyC]

I love the sound of them when they're, in my estimation, working correctly. When I say dull and tizzy, I mean rolled off probably above 14k and with a grittiness that makes cymbal crashes sound like can lids. Perhaps tizzy isn't the right word. Not AM radio dull, but dull and strained sounding. And this comes and goes, it's not constant. It could very well be something else, I realize, that's why I was asking if an overabundance of ESR in the original caps could be causing what I'm hearing since I can't really seem to trace it to anything else but the speakers. I realize this is one of those vauge things that's hard to both describe and find, but it's quite real to me here!

I agree with David...

Things such as ESR and speaker wire would be way down on my list. Speakers are not usually that variable.

I would be looking at other possibilities. Perhaps try a different amp, etc.

Roy

[Guest vanmeter]

I opened up my amp and preamp tonight to look specifically for problems, and have leaky main filter caps on both units, and several other visibly leaking caps on the preamp. This is probably a good place to start...I'm not really hearing any hum but I can't help wonder if the lack of extreme highs and graininess I'm hearing is the failing of the main caps in both pieces.

Meanwhile I don't really have another amp of any quality, so I may ask around and see if any of my audio buddies have something I can borrow for a few days.

[kkantor]

"This was about the same time I started using solid core hookup wire for speaker wire, "

Using solid core hookup wire for speaker wire is not a good idea. My guess is that you might have two different things going on: intermittent problems in your electronics, and a very high resistance between your amp and speakers.

-k