What happened to my Polk SR tweeters?

jay27

I noticed the sound from my Polk SR components was way off. I took a look at them, and this is what I found. I was using the SR crossovers at the time and thought it provided tweeter protection. Any idea what may have happened to them?

MacLeod

The crossovers do provide tweeter protection but its not bullet proof. If you were overpowering your speakers or clipping a smaller amp it is quite possible that youve blown it. That does look like its been forced out which would be from overpowering.

dakatone

I agree. Check your gain settings on the amp (if using one), many times tweeters are killed through high gain settings. Nothing much to be done about that tweeter, I would order a replacement from Polk:

Customer Service / Parts
5601 Metro Dr.
Baltimore, MD. 21215
1-800-377-7655
Fax- 410-764-5470

And tell them you are a forum member you should get a discount. The main work should be on making sure this doesn't happen again. I am not sure about those crossovers but check to see if they have a tweeter booster on board. It might be just too much for the little guy to handle.

Good luck

jay27

That's strange because they were hooked up to a Nakamichi amp rated at 100 watts per channel on the nose. Would the fact that the amp and deck are 8v matter? Gain set too high on the amp (half way)? The highest frequencies turned up too much on the eq? Perhaps they were just defective? Any help is appreciated as I do not want this to happen again.

dakatone

Well the gain can be tricky. It can damage speakers if too high and it may take some time adjusting it to find the right level. But after that it should be a set it and forget it detail. There is a formula to use that results in a voltage rating for the gain but unless you have a way of measuring the voltage output it is pointless:

sqrt(combined RMS * impedance) = gain (v)

I have my Alpine amp powering the components a bit overrated for them (it pushes 100 RMS while the fronts handle 60 RMS) but I have the gain at around 9 o'clock. The gain on the sub amp is around 10-11 o'clock. What I do is just set it lower than expected and run the system and if it suits your needs with no clipping leave it there. Half way (12 o'clock) might be too high of a gain setting depending on the RMS output of amp versus the RMS acceptance of the tweeter. Maybe try it at 10 o'clock and see if that is still suitable for your tastes.

The voltage from your amp and deck should be fine at 8 since the gain adjusts the total output of voltage to the drivers. If you are driving the comps only off a single amp then here is an example of the formula:

sqrt(200*4) = 28.28V

The EQ settings are a different story and I am afraid far out of my league. Perhaps someone will post some great advice on tuning EQ settings. At the least right now I would contact Polk and see what they can a) do about the situation and b) if they have any recommended settings for your specific model (serial number) tweeter and component set.

BTW, just wondering how long you had the set running at the current settings before this happened?

jay27

I actually just put in a new deck about a week prior to this happening and therefore spent a lot of time trying to tune. As I was tuning one day, I noticed the sound went from decent to bad and I couldn't get it back to decent again. That's when I thought something may be wrong with the speaker itself. I guess the weird thing about this is that I've never actually blown any speaker prior to this experience and this so happens to be the most high-end system I've had. It's ironic that I've cranked up some $90 Boston coaxials, among other cheaper speakers without fail, and it's my $900 Polk SR speakers that somehow I have issues with. I seem to be the only one that this happened to however, so that makes this all the more puzzling.

Jstas

8V outputs? That gain should be barely off the 0 level.

As far as the crossovers go, the SR crossovers are quite stout and there is no "boost" on them. They are adjustable for response settings in relation to the woofer but that's it. A "boost" implies that the tweeter is getting more power than the woofer and that's just not true. The only thing the sensitivity settings do is change the impedance of the circuit which presents a different load for the amplifer to drive.

From the SR manual:

TWEETER LEVEL
The jumper levels inside the crossover box
adjusts the level (volume) of the tweeter
relative to the mid/woofer. Start with the
jumper in the “0dB” position and listen.
If you want a “brighter” sound, move to
the left position, “+1dB,” (“+2dB”: SR5250)
and listen again. The “+1 dB” (“+2dB”:
SR5250) setting provides the greatest
amount of tweeter output. -1.5dB and
-3dB reduce output to a greater degree

SR whitepaper: http://www.polkaudio.com/downloads/sr6500.pdf

The SR's are not super sensitive. They aren't slouches at 90 dB either but the RMS rating is at 125 watts. If your Nak amp is rated at 100 watts, is that peak or RMS value? If it is peak, you are probably around 40-60 watts RMS and that's half of what the max RMS value of the speakers are. Consequently, because of the moderate sensitivity rating, you are going to have to push the components of your setup hard to get higher levels of performance out of them.

If you have your 8V outputs plugged in to the Nak amp, even if both are rated at 8V, the gain being halfway up would be clipping the signal. When you clip the signal, you amplify the clipping and that is the quickest way to diaphragm destruction like what you have.

What you need to do to set gains without a meter is to find out what the input gain range for your amplifier is. If it is an 8V maximum then that means that your lowest gain setting is your 8V max. If you have an 8V output on your headunit then you are hitting the max on that gain and the gain should be at or near zero. If you have a 2V output on your headunit then your gain will likely need to be set quite high, around the 3/4ths of full gain mark. I honestly wouldn't push it any father than that because if you have a head unit that has a output voltage lower than 2V, it's probably pushing a pretty crappy signal and honestly, if you put junk in, you get junk out.

If you have 8V outputs on your head unit but 4V inputs on your amplifier, you are going to need to set that gain as low as possible and then make sure that you don't overdrive the speakers.

But without more accurate info on the setup, I can't give better advice.

jay27

Right now, I'm running an Eclipse headunit that's rated at 8v unbalanced. The amp is a Nakamichi pa-2002, which as I understand, is 100 per channel rms and 8v max. I actually have the SR5250 and not the SR6500, which I think are rated at 100 watts instead of 125.

cadenceclipse

dont believe it was asked or mentioned but the real question here may be where your volume is set. what model eclipse?

jay27

If you mean how high I had my volume when the tweeters went out, I can't say exactly. I tend to listen to my music fairly loud, so it may have been in the 50's. It is an Eclipse cd8053.

cadenceclipse

thought so. though i thought u'd say higher volume. i had 8053 last 5 yrs. bad a$$ deck! 50's out of 80 is not very high so my idea ain't helpn. i assume your not biamping neither..i have balanced line driver if your interested. also 2 extra NOB remotes..

jay27

I don't know if I'm keeping this deck for very long, but I'll keep it in mind.