Yes, I have the owner's manual. It has some very basic assembly instructions on how to bolt the upper panel to the woofer box. I also have the interface schematic. But I believe there was a Service Manual that has information on taking apart the upper (ES) portion and servicing it. Do you know where I can find a copy?
Thanks
Acoustat Spectra 3
I have just acquired a set of Acoustat Spectra 3 speakers and have no idea how to use. anything I should check before plugging them in? what are the switches and connection for? Don't know if it matters but I plan to drive them with a Denon PMA-920 amplifier.
thank you
R
I have just acquired a set of Acoustat Spectra 3 speakers and have no idea how to use. anything I should check before plugging them in? what are the switches and connection for? Don't know if it matters but I plan to drive them with a Denon PMA-920 amplifier.
thank you
R
Suspect VR flyback
I've been using Acoustat 1+1 with a Krell FPB 300 amplifier since 2008, and I've posted in this thread before.
In the last few months, my amp has been intermittantly shutting down, and I've been going through a long process of "elimination" to find out what's wrong.
The shutdowns do not necessarily occur at high output levels.
This started when I was trying a tweako DAC (I'm back using a good DAC now) which created an unexpected high power blast that blew the Acoustat fuses (I was using 5A at the time, I've now switched to 3A as recommended by Roy). The shutdowns started later that same day and I started doing (at first not very well planned) elimination tests to determine what was wrong.
I first feared damaging the speakers, perhaps creating a HF transformer short (I cross the Acoustats at 100hz, so there's not much bass). But I still got shutdowns playing only one speaker at a time with the HF transformer disconnected.
Another test showed that I could consistently get either speaker to shut down the right channel of the amplifier, but not the left channel.
So I sent the amplifier back to Krell (who had just done full capacitor service on my unit a few months earlier). They found a fault in the left channel, and repaired it and returned it to me for free because of the earlier service done. They explained that a fault in the left channel could cause shutdown to occur in right channel.
Well, now I can get either channel of the amplifier to shut down, and with either speaker. I think the repair essentially restored the correct operation of the protection system. And correct operation is to shut down instantly when the signature of an electrical short appears. (A 6800 class computer in each channel figures this out looking at voltage, current, offset, and rail voltage regulator margin. It would be interesting to know what makes it decide "short", and even if that is what it is deciding now. On shutdown you can get one or two lights remaining on, and the "1 light" condition includes short, heat, and insufficient AC. I'd like a display panel telling me what the situation is in more detail...some very high priced amplifiers do that now.)
My thinking NOW is that it was actually the speakers all along. Since the problem started after a particular incident, that incident changed something in the speakers. I have already "eliminated" the HF transformer as a potential cause.
That leaves various things, the variable resistor and LF transformer among them. I am now strongly suspecting that the variable resistors in my factory C mod interfaces have a problem.
There had always been considerable green corrosion around (and probably under) the wipers on the resistors. I've been too lazy to clean that off, knowing I'd have to do it completely or not at all. I now have a fresh bottle of deoxit and this is now my plan for this coming weekend.
I'm thinking that if the wiper is sufficiently corroded, there may be intermittent dropouts in connection, or slight rectification even. This could, I think, produce a flyback voltage from the energy stored in the HF transformer when the connection is resumed, and this flyback voltage, though brief, could be what is causing the Krell to believe there is a short. (BTW, my Aragon amplifier has a much simpler protection system, and it just plays along fine, although I like the Krell better. I did see shutdowns with a newly purchased Eagle 2 amplifier, but I figured that was because it simply wasn't up to the task, but perhaps it had the same issue as with the Krell. I know from many years use that the Krell can play these speakers just fine, and you would think so also.)
If mere cleaning doesn't fix the problem, or even if it does, I'm also thinking of replacing the variable resistor with fixed resistors anyway. I intend to measure both of my VR's first however, to make sure I am not changing that. I find the high frequencies to be plenty strong up and measurably flat up to their limit at 19kHz now. I still use supertweeters just so I'm not missing 19-40kHz, in case it makes a difference (in sighted testing, it always seems to, even though I can't hear anything coming out of them, I can measure it). I find the Acoustat 1+1's slightly too strong in the 3-10kHz region (I make an intentional dip there using DSP EQ roughly following recommendations by Linkwitz).
So I'm not interested in boosting the highs by reducing the resistance from input to HF transformer (aka 'air mod' if I understand that correctly). The highs are just fine.
I might be interested in lowering the LF cutoff point in the interface. The region 100Hz to 300Hz has some broad depressions I've never fully worked out.
I don't think it would be a problem to use the entire 16 ohm variable resistor as the load for the capacitor to do that, with no wiper, then add an additional 1-6 ohms to feed the HF transformer as needed to get the best balance in extreme highs. This is sort of like replacing the VR with a slightly bigger VR and moving everything up.
From where I was reading a few years ago, the air mod does that also, by adding 10ohm below the VR. I would be using the entire VR as a fixed resistor, and adding more resistor(s) at the top.
Any fixed resistors should be low inductance, right? Replacing the big VR with a low inductance fixed resistor would be expensive, and would require holes in the box for chassis mounting to dissipate heat. So I'd avoid that, unless additional evidence points to the VR having internal damage.
I've been using Acoustat 1+1 with a Krell FPB 300 amplifier since 2008, and I've posted in this thread before.
In the last few months, my amp has been intermittantly shutting down, and I've been going through a long process of "elimination" to find out what's wrong.
The shutdowns do not necessarily occur at high output levels.
This started when I was trying a tweako DAC (I'm back using a good DAC now) which created an unexpected high power blast that blew the Acoustat fuses (I was using 5A at the time, I've now switched to 3A as recommended by Roy). The shutdowns started later that same day and I started doing (at first not very well planned) elimination tests to determine what was wrong.
I first feared damaging the speakers, perhaps creating a HF transformer short (I cross the Acoustats at 100hz, so there's not much bass). But I still got shutdowns playing only one speaker at a time with the HF transformer disconnected.
Another test showed that I could consistently get either speaker to shut down the right channel of the amplifier, but not the left channel.
So I sent the amplifier back to Krell (who had just done full capacitor service on my unit a few months earlier). They found a fault in the left channel, and repaired it and returned it to me for free because of the earlier service done. They explained that a fault in the left channel could cause shutdown to occur in right channel.
Well, now I can get either channel of the amplifier to shut down, and with either speaker. I think the repair essentially restored the correct operation of the protection system. And correct operation is to shut down instantly when the signature of an electrical short appears. (A 6800 class computer in each channel figures this out looking at voltage, current, offset, and rail voltage regulator margin. It would be interesting to know what makes it decide "short", and even if that is what it is deciding now. On shutdown you can get one or two lights remaining on, and the "1 light" condition includes short, heat, and insufficient AC. I'd like a display panel telling me what the situation is in more detail...some very high priced amplifiers do that now.)
My thinking NOW is that it was actually the speakers all along. Since the problem started after a particular incident, that incident changed something in the speakers. I have already "eliminated" the HF transformer as a potential cause.
That leaves various things, the variable resistor and LF transformer among them. I am now strongly suspecting that the variable resistors in my factory C mod interfaces have a problem.
There had always been considerable green corrosion around (and probably under) the wipers on the resistors. I've been too lazy to clean that off, knowing I'd have to do it completely or not at all. I now have a fresh bottle of deoxit and this is now my plan for this coming weekend.
I'm thinking that if the wiper is sufficiently corroded, there may be intermittent dropouts in connection, or slight rectification even. This could, I think, produce a flyback voltage from the energy stored in the HF transformer when the connection is resumed, and this flyback voltage, though brief, could be what is causing the Krell to believe there is a short. (BTW, my Aragon amplifier has a much simpler protection system, and it just plays along fine, although I like the Krell better. I did see shutdowns with a newly purchased Eagle 2 amplifier, but I figured that was because it simply wasn't up to the task, but perhaps it had the same issue as with the Krell. I know from many years use that the Krell can play these speakers just fine, and you would think so also.)
If mere cleaning doesn't fix the problem, or even if it does, I'm also thinking of replacing the variable resistor with fixed resistors anyway. I intend to measure both of my VR's first however, to make sure I am not changing that. I find the high frequencies to be plenty strong up and measurably flat up to their limit at 19kHz now. I still use supertweeters just so I'm not missing 19-40kHz, in case it makes a difference (in sighted testing, it always seems to, even though I can't hear anything coming out of them, I can measure it). I find the Acoustat 1+1's slightly too strong in the 3-10kHz region (I make an intentional dip there using DSP EQ roughly following recommendations by Linkwitz).
So I'm not interested in boosting the highs by reducing the resistance from input to HF transformer (aka 'air mod' if I understand that correctly). The highs are just fine.
I might be interested in lowering the LF cutoff point in the interface. The region 100Hz to 300Hz has some broad depressions I've never fully worked out.
I don't think it would be a problem to use the entire 16 ohm variable resistor as the load for the capacitor to do that, with no wiper, then add an additional 1-6 ohms to feed the HF transformer as needed to get the best balance in extreme highs. This is sort of like replacing the VR with a slightly bigger VR and moving everything up.
From where I was reading a few years ago, the air mod does that also, by adding 10ohm below the VR. I would be using the entire VR as a fixed resistor, and adding more resistor(s) at the top.
Any fixed resistors should be low inductance, right? Replacing the big VR with a low inductance fixed resistor would be expensive, and would require holes in the box for chassis mounting to dissipate heat. So I'd avoid that, unless additional evidence points to the VR having internal damage.
There is no service document other than the owner's manual. There are no serviceable parts inside the panel structure (other than cleaning perhaps), so unless you want to change the grille sock, there is no reason to disassemble the panel.
Disassembly is difficult, and reassembly is even harder. Begin by removing the wooden trim on the sides of the panel. These are held on with pin nails, and can be pried off. Next remove the metal top plate and the bottom plastic piece. This will reveal the many staples that hold the sock in place, top and bottom.
The difficult part is reattaching the wooden trim strips, because the nail heads are hidden beneath the brass trim, which is held on with adhesive tape. You can remove the brass, but it will almost certainly be damaged in the process. Then the pin nails can be hammered out or ground off. You can reattach the trim with similar nails, and throw away the brass trim. That's what I had to do when I replaced the socks on my Spectras, and I have yet to find a suitable replacement for the brass inlays.
If you do open up the panels, it's a good idea to (gently) blow out both sides of the panel with compressed air, and make sure the felt blocks on the rear of the panel are secure. But unless you are having trouble with the panel, or want to change the grille sock, I would leave it alone.
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It's not impossible that the HF balance resistors are damaged, or that the slider is corroded and making a bad connection, but I seriously doubt the resistors have been damaged or that a corroded slider could cause an amp shutdown.
My first suspicion would be the LF transformer. It is susceptible to high-voltage breakdown. After a damaging incident such as you experienced, the transformer can play fine up to a certain level, and then arc-over and present a short circuit. You can test this theory by temporarily disconnecting the LF transformer tap and see if the problem continues. Of course, you won't get much sound from the speaker under these conditions.
I also do not suspect the HF transformer. They are quite rugged, are not exposed to the same high voltage levels as the LF transformer, and historically have been pretty reliable.
BTW, you can't modify the signal going to the LF transformer. It's driven directly from the amplifier (through a 1-ohm resistor). You can modify the step-up ratio of the LF transformer by trying a different LF transformer tap, which may or may not address your issue with the frequency response.
Remember that the LF and HF transformers overlap considerably in their range of operation. There is no crossover feeding the LF transformer, it just rolls off naturally. The HF transformer does have a crossover, and it gradually rolls in as the LF transformer rolls off.
Sounds like low bias....low bias can kill parts in the mixer an the low fr transfourmer as Andy I never seen.... a dead high fr transfourmer
If you can do the work your self....put new diodes an caps in the 30 years 24/7 on all the time......... old bias....
I buy a lot of used Acoustat...1+1 2+2 ,M3,M4,with MK121interfaces......first thing I do is this $50 in parts for the pr... If you cant do the work get a tec...may be $100ea....thats were I would start.
9 times out of ten....if the trans are not dead....new bias parts get the bias back up to 5k....work like new...
This is the first thing Roy E will do with any interfaces.....even the 500 meg panel feeder res..I have some his work here...but I find the stock 500meg is fine a sound great..
With new bias ...I can run 2+2 M3-M4s with a 60 watt tubs amp...loud...your amp fine.
good luck have fun
OK, thanks
Thanks Andy! That sounds quite reasonable and you are probably correct.
One curious thing, however, is how the shut downs are not correlated at all with the level currently playing. It seems to take 60 minutes at medium level, and then it goes. It's as if something is heating up, and goes through some kind of change at a particular temperature. "heating up" made me think of the power resistor. I had previously thought transformer damage would show up at a particular instantaneous voltage, and as the damage gets worse the failure voltage would get lower, and not be affected so much by heating up beforehand.
However, the LF transformer will heat up also. And since it doesn't have very good HF response, the energy in that range will be converted to heat. (Since my speakers are highpassed at 100 Hz, the big bass voltage swings aren't there.) And there could be a particular temperature where things are stressed to the exact point which realigns the damaged windings so the short can occur again.
The most curious thing of all is how that once it has heated up, it will just play very loud for hours without a problem. Presumably this is because it has passed some critical temperature range.
At least that's the way it has seemed many times so far. Which is another thing, it's hard to make generalizations about intermittent problems.
The LF transformer could have been damaged by DC. My highpass filtering is done in DSP, which the midrange DAC converts to analog for the power amp. Normally there is no signal below 100 Hz going to the speakers. However, if the DAC fails, it may well output enough DC to cause damage--and in fact, that was one problem with the DAC, the servo failed and it started outputting DC.
Thanks Andy! That sounds quite reasonable and you are probably correct.
One curious thing, however, is how the shut downs are not correlated at all with the level currently playing. It seems to take 60 minutes at medium level, and then it goes. It's as if something is heating up, and goes through some kind of change at a particular temperature. "heating up" made me think of the power resistor. I had previously thought transformer damage would show up at a particular instantaneous voltage, and as the damage gets worse the failure voltage would get lower, and not be affected so much by heating up beforehand.
However, the LF transformer will heat up also. And since it doesn't have very good HF response, the energy in that range will be converted to heat. (Since my speakers are highpassed at 100 Hz, the big bass voltage swings aren't there.) And there could be a particular temperature where things are stressed to the exact point which realigns the damaged windings so the short can occur again.
The most curious thing of all is how that once it has heated up, it will just play very loud for hours without a problem. Presumably this is because it has passed some critical temperature range.
At least that's the way it has seemed many times so far. Which is another thing, it's hard to make generalizations about intermittent problems.
The LF transformer could have been damaged by DC. My highpass filtering is done in DSP, which the midrange DAC converts to analog for the power amp. Normally there is no signal below 100 Hz going to the speakers. However, if the DAC fails, it may well output enough DC to cause damage--and in fact, that was one problem with the DAC, the servo failed and it started outputting DC.
One of my interfaces was a NOS unit I bought in 2010, never before used. The other was the original that came with the speakers (which I purchased from previous owner in 2008). Both of these interfaces produce exactly the same speaker output level, and the same level as the damaged one (still working until the short occurs) I put in storage in 2010 (but brought back out recently for re-testing). So I have 3 interfaces with very different usage histories with exactly the same level. That leads me to believe the bias levels are correct.
Rather than go through rebuilding, something that doesn't come easy to me, is there something I can just measure? I do have the 40kV probe for my fluke.
Your experience with 60W tube amp leads me to believe my 120W Eagle 2 should have been OK also. However, with such an old amplifier, never serviced, I don't know whether the amplifier itself has an internal problem, or had its protection triggered by the same speaker fault as the Krell.
Now that I'm almost certain both speakers have a serious issue, it's more likely that the shutdowns in the Eagle 2 were happening because of the speaker issue than an internal one, though it could have both.
Yes open up the box.....then plug in the Ac wire..... ck for 5k at the output end of the 500k bias feeder res.....leave the wires in place
For the last 30 years...I have owned a lot of Acoustats ....an I always come back to the 1+1s.....why...thay give 97-8% of the sound of any of the biger ones ...but...there the hardest to drive full rang...an hardest on the interfaces....but with each added panel you get 3db more output so drive wise...the M3 is the best....
In the end.. any ESL with out the right bias ...thay well be hardest too drive..hardest on the interfaces parts......an sound off....
all just one mans finding.....good luck
For the last 30 years...I have owned a lot of Acoustats ....an I always come back to the 1+1s.....why...thay give 97-8% of the sound of any of the biger ones ...but...there the hardest to drive full rang...an hardest on the interfaces....but with each added panel you get 3db more output so drive wise...the M3 is the best....
In the end.. any ESL with out the right bias ...thay well be hardest too drive..hardest on the interfaces parts......an sound off....
all just one mans finding.....good luck
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OK, thanks, I'll check that after I clean the variable resistors this weekend.
I don't recall ever experiencing amplifier shutdowns before having the 1+1's.
Even when working right, they are difficult, and when things go awry, worse to very worse.
Not all electrostats are like that. I'm told the ESL-63 delay line makes the ESL-63 load essentially resistive, so it's no problem for wimpy amps.
I don't know how it could have been otherwise with 1+1's. You want all that bandwidth, and ruggedness (relatively thick membrane, insulated wires, wide gap) in a one-way system with limited radiating area...then it is going to be a tough load no matter what.
Yes....when I say harder to drive...I have my 121 interfaces open when I work on bias....an I run M3,M4, 1+1 with the same interfaces....
It the two 9" panels...when ran in the M2 setup...side by side or 1+1 the bass trans is set on the red input wire.....even with new bias parts...the 500 res in the mixer get hot if I run a krell or sunfire300 or my QSC 400 watt pro amp....that I use to ck out all ESLs.....why ...QSC has fans...when your stat to drive any ESL used,old... the fan well step up to the high... if there a problem...if all is well ,stay on low fan..saves time...there can be bad trans,wire...,bias,or what ever...
But like I said....98% of the time it the bias...so I do just what Roy E an other do....an say you should even if you get 5k..look these parts are 30-35 year old an on all the time....bias is what makes any ESL work!
Ok now the Quad 57 great speaker....63 not so much...an no quad well play
with half the output of My Acoustat or ML CLSs ...I run my new cls panles with a Acoustat bias....the CLS is only thing better than my Acoustats
Stock CLS....no thanks.....
All just one mans finding
Resistor cleaning didn't stop shutdowns
Sadly but not unexpectedly, my slow and careful cleaning of the 16 ohm resistors in my Acoustats last weekend had no effect on the shutdowns. It seemed to make for better sound though.
Next thing will be disconnecting the LF transformers, almost certain to be the cause of the problem.
However, that will have to wait two weeks because I am attending an audiophile BBQ and attending a symphony on Saturday, and hosting a Sunday party this weekend. I plan to switch to my other amplifier and play at modest levels for the party which I have barely enough time to get ready for.
Sadly but not unexpectedly, my slow and careful cleaning of the 16 ohm resistors in my Acoustats last weekend had no effect on the shutdowns. It seemed to make for better sound though.
Next thing will be disconnecting the LF transformers, almost certain to be the cause of the problem.
However, that will have to wait two weeks because I am attending an audiophile BBQ and attending a symphony on Saturday, and hosting a Sunday party this weekend. I plan to switch to my other amplifier and play at modest levels for the party which I have barely enough time to get ready for.
1+1 resistor set to 14+2 ohms
I measured the resistor in one Acoustat disconnected from the hot side of the transformer. Even so disconnected, I found it necessary before measuring any resistances to short the terminals being compared for a few seconds, to discharge any stored energy. The interface had been powered down and disconnected for days.
From the wiper (seemingly factory set at 0dB) to the transformer I measured 1.85 ohms, and the other side measured 14.2, coming almost exactly to 16.0 ohms total.
When the hot side is connected, the resistance at the top leg appears to go down (because it is shunted by the HF transformer). In that condition, the resistance measured 1.6 ohms. I used that value as a target when re-setting the wipers to 0dB.
I haven't read this entire thread, but I've never seen these values reported here. People often say the values are 10+6, or sometimes 13+3, but I'd never seen anybody say 14+2.
My ultimate plan is to get a 2 ohm non-inductive resistor and use that for the top part, and use the current 16 ohm variable resistor as a fixed resistor for the bottom part. This will only have a small effect on the HP crossover for the LF transformer (16 vs 14 ohms) but in the direction I think is good for me (since I highpass the entire input at 100 Hz).
I measured the resistor in one Acoustat disconnected from the hot side of the transformer. Even so disconnected, I found it necessary before measuring any resistances to short the terminals being compared for a few seconds, to discharge any stored energy. The interface had been powered down and disconnected for days.
From the wiper (seemingly factory set at 0dB) to the transformer I measured 1.85 ohms, and the other side measured 14.2, coming almost exactly to 16.0 ohms total.
When the hot side is connected, the resistance at the top leg appears to go down (because it is shunted by the HF transformer). In that condition, the resistance measured 1.6 ohms. I used that value as a target when re-setting the wipers to 0dB.
I haven't read this entire thread, but I've never seen these values reported here. People often say the values are 10+6, or sometimes 13+3, but I'd never seen anybody say 14+2.
My ultimate plan is to get a 2 ohm non-inductive resistor and use that for the top part, and use the current 16 ohm variable resistor as a fixed resistor for the bottom part. This will only have a small effect on the HP crossover for the LF transformer (16 vs 14 ohms) but in the direction I think is good for me (since I highpass the entire input at 100 Hz).
How can there be a short???
I'll be testing the LF transformers in a couple weeks. Meanwhile, I remember one reason why I didn't think the problem could be in the LF transformers, was simply this:
The LF transformers are connected to the input terminals of the speaker through a 1 ohm resistor. This means that even if the transformer had zero ohms impedance, the speaker load would still be 1 ohm.
NOW, I suppose it could be a little less than one ohm because the HF circuit is in parallel. However, that circuit has two paths: through at least 10 ohms of a 16 ohm resistor (and my measurement showed that part to be 14 ohms), and through the remaining resistance, 2 ohms in my case, in series with the HF transformer. Since we're considering worst cases here, at very high frequencies the capacitors have 0 ohms, so there 10 ohms in parallel with 2 ohms plus the transformer. Only if the HF transformer is shorted could this load be less than 2 ohms.
My amplifier is known to be able to drive 1 ohm loads, though it doesn't have a power rating for it, people have shown that to be true in testing, that it gets close to 1800 watts or something like that into 1 ohm.
But what I hadn't thought of is this: the amplifier may be putting out peak voltages it can sustain into 2 ohms load (at very high frequencies), but if the LF transformer suddenly shorts and brings the impedance suddenly down to 1 ohm, that voltage is no longer sustainable.
I'll be testing the LF transformers in a couple weeks. Meanwhile, I remember one reason why I didn't think the problem could be in the LF transformers, was simply this:
The LF transformers are connected to the input terminals of the speaker through a 1 ohm resistor. This means that even if the transformer had zero ohms impedance, the speaker load would still be 1 ohm.
NOW, I suppose it could be a little less than one ohm because the HF circuit is in parallel. However, that circuit has two paths: through at least 10 ohms of a 16 ohm resistor (and my measurement showed that part to be 14 ohms), and through the remaining resistance, 2 ohms in my case, in series with the HF transformer. Since we're considering worst cases here, at very high frequencies the capacitors have 0 ohms, so there 10 ohms in parallel with 2 ohms plus the transformer. Only if the HF transformer is shorted could this load be less than 2 ohms.
My amplifier is known to be able to drive 1 ohm loads, though it doesn't have a power rating for it, people have shown that to be true in testing, that it gets close to 1800 watts or something like that into 1 ohm.
But what I hadn't thought of is this: the amplifier may be putting out peak voltages it can sustain into 2 ohms load (at very high frequencies), but if the LF transformer suddenly shorts and brings the impedance suddenly down to 1 ohm, that voltage is no longer sustainable.
Direct sunlight is bad for anything, really, unless maybe you're a tree.
That being said, I am not aware of any long term damage caused by sunlight on Acoustat speakers, especially if the grille cloth is intact. You might experience some fading of exterior wood parts (if your model has real wood parts). Many of the models used a plastic laminate for the "wooden" look on the base, and whereas these might fade with extreme exposure, they are much more fade-resistant than real wood surfaces.
But if we're talking about the occasional sun beam sneaking in a window and shining on your speakers, I wouldn't worry about it too much. In 30+ years of answering questions about Acoustats, this is the first time I've encountered this concern. If you have a really large window that shines a lot of sunlight on the speaker, and it really concerns you, you could always consider using some drapery or a sun-blocking screen or film on the glass.
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Thanks!
In Toronto we have had a uncharacteristically prolonged spell of sunny days over the last 3 weeks.
My window face a southern direction and get direct sunlight.
It was never my concern the effects on the sock or wood trim.
I was wondering if the concentrated sunlight would have an effect on the panels as the sun penetrates through them.
The beams of light would be concentrated in just a small area as it moves across.
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If the windows of concern are the hexagonal windows behind the speakers, I wouldn't worry too much. Although the grille cloth does pass light, it will attenuate the intensity by a considerable amount. And since the windows are small, the spot of light projected on the speakers will be small and move quickly. And, due to your northerly latitude, the sun isn't all that intense anyway (as compared to, say, here in Arizona).
Prolonged exposure to direct sunlight is harmful to plastics and adhesives, but due to the low intensity and exposure in your situation, I doubt it will materially affect the lifespan of your speakers. And as I said before, if it would set your mind at ease, you could always cover the windows with draperies or use one of the sun-blocking films made for windows (very popular stuff here in Arizona). And maybe covering those windows might be a good idea anyway, so no one can look in and see all that very cool gear you have.