SDA-1C Right Channel No SDA Effect

PolksTillIDie

I bought a used pair of SDA-1Cs a few months back and have yet to get the SDA effect from the right channel. I had thought it was a room acoustics problem as I have them in a very asymetrical placement. But I used a set of audio test files a few days back. When I ran the file with a out-of-phase signal, the right channel SDA effect burst to life. Even though I've quadruple-checked the polarity of the speakers, I just reversed the polarity of the right speaker and then I had the full two-channel SDA effect ... glorious. Then I realized the regular stereo effect was out of phase. Reversing both speaker's terminals causes a normal stereo effect, but no SDA in either speaker.

My thinking is the left channel SDA driver(s) are defective/reverse-wired/etc.

Am I thinking this through properly? I think I need to have a good idea of the problem going in before I tinker myself or send it for repair. Also, I thought the out-of-phase SDA drivers were the mid-woofers, but the SDA effect I get is in the mid- AND high-range, so could it be a tweeter too?

Thanks.

PolksTillIDie

I just tried the absolute phase test from the manual with the interconnect cable and red (+) wires left in. Dead silence at the normal center balance point, but even with a slight move to right/left I get sound from both speakers, and from the right speaker more than the left.
Any ideas?

F1nut

There is no SDA signal to the tweeters.

You have something wired up incorrectly. Check that the red binding post is on the left for both speakers. If so, the problem is inside. The schematic is posted here, print it out and dive into each cabinet.

SDA wiring as follows:
Black or blue is positive
White or green is negative

PolksTillIDie

Thanks F1. That leads me to another question. I just hours ago installed new tweeters. Problem is, the wiring orientation is ambiguous. The old tweeter had a crosshatch mark kinda like a (+) sign on its back plate and the black/blue wire was attached to that. The replacement tweeters have only one contact colored red and no other markings to designate polarity. These tweeters are the OEM RD0194-1 SL2000, from Polk supposedly (got from www.midwestspeakerrepair.com).

I checked the forum and could not find the final word on which way is correct to wire them: whether the red "dot" marked terminal is pos/neg and the same for the black/blue and white wires. One of those discussions you were on.

So looks like you've decided on the polarity of the wires; any firm conviction on the terminals? Is the red terminal on the tweeter pos or neg?

Thanks for the help.

F1nut

Red dot is positive.

PolksTillIDie

OK, so I guessed right. So now another followup. Do these tweeters need a break-in period? I'm getting a strong harmonic disortion at 1 kHz (and possibly other freqs) that I didn't have before with the old tweeters. I can hear it and see it (on audio freq spectrum).

Thanks again.

Gardenstater

The crossover should not be allowing 1kHz to pass to the tweeters. The free air resonant frequency of the RD0194 is 1189.70 Hz as measured by DarqueKnight. That is where the maximum impedance of 27.85 Ohms occurs (SL 2000 is 1,144.60 Hz and 24.5 Ohms). If you are playing a 1kHz test tone through the entire speaker and hearing distortion then it must be coming from one of the MW drivers, unless your XO is malfunctioning due to bad capacitors or the like.

Gardenstater

It would be typical for harmonic distortion to rapidly rise below 2,500 to 2,800 Hz, depending upon the sPL. Here's an example of the KO10DT Peerless tweeter THD, just to give you an idea:



This is what DarqueKnight got for the RD0194:

Gardenstater

According to your SDA 1C manual, the crossover point for the tweeters is 2 kHz. I believe the lower tweeter gets 2 kHz to 4 kHz and the upper one gets 2 kHz to 20 kHz + .

PolksTillIDie

Here's a 1kHz test tone sampled by microphone just a bit ago from a zero (OK, < 0.001% THD) source (from audiocheck.net). I usually run a pink noise sample for before and after adding something new; just wished I'd done a 1kHz THD test also before the tweeter switch today...

I check these frequently (but never snapshot them) just so I can silently gloat over the M-80's freakishly low THD (<0.007% at 6 ohms). ;-)

As you can see, there are harmonics at 2,3,4,5,6 and probably 8 kHz. I usually get a small spike at 2 kHz only. Sorry for not using the %THD view, then we could see the actual number. But my whole-system %THD is usually around 0.3-0.4% THD (.wav file on blu-ray/cd player/USB key>Yammy receiver>M-80.

But what led me to all this is I could hear it, a buzz when playing a test SACD.

Oh yeah, and I did hear/feel a big "clunk" on the left speaker when I tilted it for the tweeter switch ...

Gardenstater

So.......if you heard a clunk then worst case scenario maybe an inductor got damaged, or maybe some other component(s) of one of the crossover boards in that left speaker. Are you experiencing the same harmonics when you send that 1 kHz test signal to the right speaker only as compared to the left only?

PolksTillIDie

...or maybe a brick the guy before me put in there to prevent them from being so top-heavy.

The test was done on both speakers together, but I listened to both speakers separately and could hear it with both. The clunk felt heavy like something already at the bottom of the enclosure rolling over as I tilted it flat to re-tweeter.
Oh, here's the %THD view with the reading in the upper left hand corner. 14.4% THD.... yeah, just a little more than 0.4%.



But back to an earlier question, is there a break-in period for these tweeters typically?

Gardenstater

There is a large 16mH, 18awg inductor in each of your speakers that is supposed to let all 4 MW's regardless of whether they are dimensional or stereo, play freqs below 150 Hz. That *may* be mounted on the bottom of the speakers. I'm assuming you're joking about the brick lol.

I'm sure there is some minor amount of breakin where the tweeter surround becomes a little more compliant and that may result in a different sound over time. Nothing like what you are experiencing. Why don't you try the test again with 125 Hz and the IC cable disconnected and send the signal only to left, and then only to right. See what you get.

PS: Or first remove the passive radiator from that left speaker and see what the heck is broken loose in there!

PolksTillIDie

OK, stand by....

PolksTillIDie

Oh, I forgot, I can only calibrate for 120 or 130 Hz (presets only) and only have a 125 (and 1kHz) test file. But you can get the idea:

Right-


And left-


IC cable disconnected.

There's a 240 Hz harmonic in both and a missing 3xx (harmonic ?) on the right. Anyway, they're not identical in the 300-400Hz range.

PolksTillIDie

Actually, I think it looks like about 260Hz. I'll redo it later with 100Hz-1kHz isolated to get a closer look. Gotta get some sleep ...

Gardenstater

I tried the 1 kHz sine tone on my Polk 7B's with modded XO's and this is what I get (left channel). Right channel was similar. No harmonics really visible at all:

Gardenstater

4 kHz sine tone. Perhaps someone else with the SDA 1C could try these and report results.

PolksTillIDie

I tried it again after I got back from work just now and the harmonics are fading a bit and are a little inconsistent when sampled 10-15s apart. One gave a 0.8%THD. A guy from Midwest Speaker Repair got back to me (on a Sunday?) and agreed with the idea of a break-in period. He also said to try taking off the front plate with a screwdriver, then putting it back on. And finally I wondered whether Polk had replacement gaskets for their tweeters and he said no. I guess this could be an issue, but I'd expect lower resonances rather than higher (harmonics)

F1nut

Of course, the brand new tweeters need to burn in.

Gardenstater

Mine have been inconsistent as well, and I got some where I could in fact see some harmonics. I am just using an android phone app with it's built in microphone and I believe the harmonic spikes are there, but they are mostly hidden in the noise. How many harmonics do you need to take into consideration in the THD calculation? I noticed that DarqueKnight only did 2nd, 3rd, 4th, and 5th harmonics, although he didn't calculate %. When I summed them (the dB's of the harmonics) I got that you had about 1.4% THD in your first plot, but the app you are using calculated 14%? Hmm.

I believe it's important to use a very thin gasket to couple the tweeter plates to the speaker baffle as best as possible, unless you want to go the decoupling route which is a different approach that can work. I'm sure the billet aluminum plates that xschop is fabbing are a big improvement over the plastic ones that the RDO's come with.

Have you looked into the cabinet yet to find out what is thunking around in there?

Total harmonic distortion calculation
Nonlinear distortions are given as Total Harmonic Distortion (distortion factor k) in percent or as distortion attenuation (ak) in decibel (dB). THD itself is defined as the ratio of the sum of the power of all harmonic components to the power of the fundamental frequency.

The distortion factor is always smaller than 1 or less than 100%; consequently, distortion attenuation has to be a negative dB value.

distortion attenuation: ak = 20 * log (k/100) in dB (input k in percent).

distortion factor THD: k = 10^(ak/20) * 100 in % (input ak in dB with a minus sign).

pitdogg2

Tightening down the plastic bezel too much can also negatively affect sound. Some of us needed to glue small #10 washers under the faceplate screws to make up the difference from the back of the sl2000. If you look you'll see the stand off under the screws is slightly less with the RD-0194/198 than the sl2000/sl3000 tweeters.
The front bezel is also thinner and more flexible than sl2000/3000

You can also cut armacell pipe tape to make a new gasket if you feel yours are not in good shape.

I'd keep old gasket as a back up, unless torn badly I never throw those away.

PolksTillIDie

Well, a lot to answer. Here goes.

Gardenstater, I've been using a freeware application on windows 10 called Visual Analyzer that has a quite nice array of features. I'll have to say that mostly I consider the visual appearance of the freq spectrum to decide how much THD I have. This is mostly because I have no way of calibrating to 1 kHz (or any other freq) right now through my speakers except via the system itself. So, I can't use the system I'm testing to also be my calibration source. I do use an internal source in the software, but it doesn't account for the mic I use to measure. But maybe its close enough.

If I can see spikes of declining amplitude above the fundamental freq in integer multiples of it, then these are the component frequencies of the distortion (so if 1 kHz is the fundamental, the 2,3,4,5, etc, for 2 kHz, then 4,6,8, etc). At least this is the way I understand it. So I never remember seeing those higher spikes before when I first started playing with that 1 kHz .wav file of zero distortion, but could easily visually see them in the spectrum when I played the files with designated distortion.

By the way, as others have said, I can't *hear* the distortion of those files with less than 1%THD. Though the test files I have are in "jumps" in distortion in orders of magnitude like 1, 0.1, 0.01, 0.001% THD. Maybe I could hear something in between 1 and 0.1%...

As for the gaskets, I've contacted a few speaker repair shops and so far they have no answer for me. I seem to recognize the material mine are made of, I just can't remember where I've seen that material before. The present ones, which I left on, were warped each in a similar place and way that makes me think it was from the factory.

I might get brave and take off and back on the tweeter faceplates if the problem doesn't go away on its own.

No, I haven't looked for the source of the "clunk" yet. Mostly because I'll have to take off the passive radiator to get to whatever it is and I don't want to have a gasket problem with those. If anyone has any ideas on that then I'm ready to listen.

Thanks for the %THD calculation. I'll try some new tests in a day or so. Of course, on the 120 Hz measurement, I had no source for 120, just 125 Hz, so I expected that calculation to be off, I was going visually on that one.

pittdogg2, thanks for the tweeter info. I wish I had some recommended torque numbers for the screws on the tweeters. Seems without that, I'm going to be introducing another variable if I follow the "take-off-and-put-back-on" advice I got.

With all that said, I'm listening to them now and they sound great, the missing sda effect of the left speaker notwithstanding. I can't hear any distortion in the music right now. A lot more going on in the high-end 10-20kHz than before. I guess only Polk speakers could have something clunking around inside and still sound so good.

Gardenstater

Thanks for the software. I was going to ask you what you were using and that looks very interesting

As far as tweeter gaskets goes, I believe I would like to try 1/32" Cross Linked Polyethylene Foam but I haven't been able to find a place to purchase yet. I have only two original Peerless gaskets that came with my 7B's and all the tweeters I have been able to purchase as backups were shipped to me by eBay sellers without any gaskets.

This is sort of what I have in mind:

https://www.atlanticgasket.com/materials/spec-sheets/6A-Volara-Crosslinked-Polyethylene.html

Another idea I have that might serve in a pinch is this Eppco Enterprises Drawer Liner. I have 3 rolls of the stuff that I purchased many years ago to put in my roll around tool chest drawers and never got to it lol. The stuff measures 55 mills uncompressed and 20 mills compressed (give or take). Might not be as good as the stuff above but is worth a try:

https://www.amazon.com/EPPCO-Enterprises-1861-Drawer-Liner/dp/B000FG9XJS/ref=sr_1_5?dchild=1&keywords=eppco+premium+drawer+liner&qid=1607539230&sr=8-5

pitdogg2

https://www.armacell.us/products/armaflexinsulationtape/

We've used this on drivers and tweeters. Works great and compresses easily without fear of distorting baskets or tweeter faceplates. Once used it looks just like Polk original gaskets. I've used it on a lot of drivers small to large and it has never stuck to the box so you need to pry the driver back out like some gasket tape from audio suppliers. To make holes for screws I just use an old soldering iron to melt the proper slightly undersized hole.


Gardenstater it's no help to put forth something you cannot find nor used.

This stuff works and many here have used and recommend it.

Gardenstater

All good pitdogg2. Everyone is free to use what they want and I'm glad that has worked well for you. I'm trying to source the same thin stuff that Polk used for the tweeters and I believe it is polyethylene foam. Shouldn't be impossible to find and would come in sheet sizes large enough to cut the tweeter gaskets out without having any seams and it is not adhesive backed, which I prefer for the tweeters.

I understand that that stuff compresses and is soft. I'm looking for thinner stuff to couple to the speaker baffle a bit better. That stuff will get the job done but may not be the absolute best. Just my 1c opinion. No pissing contest

I'm holding the drawer liner stuff in my hand and I really do think it will do a great job actually, for the tweeters.

PS: What works well for the plastic bezel (hollowed out with ribs and bosses) may not be as good for the flat plate aluminum bezel tweeters such as Peerless and SL1000. So what you say may be perfectly fine for the OP with his tweeters if he doesn't mind seams and adhesive backing.

PPS: Next time I swap out a tweeter I will make a gasket out of the drawer liner and will report back on how it works out. So.......if anyone is hyper concerned about taking a chance on it then I suggest they wait for that

pitdogg2

Well one member here has already found and sold 1 piece gaskets cut to size exactly like the polks. Many of us went in on a group buy and hundreds were made. I still have some actually.
The gaskets the group buy had made were about 1/8 thick and mashed down to be just like the polk original.

Other than color they were identical to polks after use.

Gardenstater

Thank you for that. Without having the stuff in hand to test it's compressibility it is pretty hard to prejudge. I was thinking maybe 1/16" might work well but I would've thought 1/8" would be too thick in a closed cell polyethylene but it is worth a try in light of your experience. I have found 1/8" at Graingers for a surprisingly low price.



Graingers does have Buna N/PVC foam sheets in 1/16" which might be worth a try as well:

pitdogg2

Measured best I could. 1/16 is correct. I was guessing at the 1/8.
Either way here they are.


The older peerless/sl1000 gaskets were 1/8" as seen below

PolksTillIDie

Well, thanks guys. You've given me several options for the gaskets. Surely something will work. Any ideas on the passive radiators and my chance to peer in without setting up a no-gaskets-for-the-passive-radiators scenario? I'm getting a little curious myself.

Does anyone have a pic of the inside of a 1C, specifically the crossover and lower?

I did a few %THD measurements just now and something just occurred to me.
Volume might have been different on my previous measurements before the new tweeters. All because of different speaker cables. Here's one just now at -30 dB:



And at -40 dB:


You can see that there's much less THD in the -40 dB graph and that's what I'm probably remembering from before the tweeter switchout. That said, I don't hear the distortion I heard a few days ago when I'd just changed them out, so maybe they are getting better with some break-in.

My previous measurements before these tweeters were always at -30 dB (reported by my Yammy receiver, not measured), but -30 dB on my system isn't what it used to be. Its louder, since switching speaker cables to 10AWG, high-strand count OFC. You might recall my posts asking about best AWG for speaker cables. My ancient Monstercable ones were about 10AWG, but were oxidized-looking and 35 years old. So I switched to 14AWG KableDirekt cables that were brighter, but without change in volume (dB, actual). I finally bought some 10AWG from MidwestSpeakerRepair and the change was big: I had to lunge for the remote and decrease the volume it was so much louder. So that answered my "is bigger AWG better?" question for systems with high-current amps. The whole thing was driven by me thinking my M-80 sounded under-powered. It was, it was the speaker cable.

So, yeah, lemme know about any pics you might have and I'll screwup some courage to break into my 1C's left speaker and see what's going on.

Thanks guys for the help.

Gardenstater

You shouldn't have any trouble removing the passive radiator without damaging the gaskets if you work a sharpened putty knife in shallowly and gradually at opposing places between the passive's mounting flange and the speaker baffle. I like the 5 in 1 painters tools because they are already sharpened blades. The gasket should remain attached to the passive without any hassles. I'd do it with the speaker horizontal but you already know that.

Here's another link for polyethylene foam sheet in 1/16" and 1/8". I think either one may turn out to be ideal for tweeter gaskets. That 1/8" crosslink polyethylene foam I posted above is way too firm so scratch that off the list. Turns out it is about 9x firmer than the 1/8" foam in link below!!

https://www.mcmaster.com/foam-sheets/backing-type~plain/food-industry-super-cushioning-polyethylene-foam-sheets/

Looks like you may be proving that the graph I posted earlier that shows increasing THD from the tweeter at higher volumes is in fact the case. That software produces really nice results. What are you using as a microphone if you didn't already say?