Blowing Tweeters

tinman67gz

I just purchased a Denon reciever 100W per channel. Along with it I bought two Monitor 70 towers. I blew the tweeters in minutes. As I soon found out my Denon can't power these speakers. Crutchfield took them back and refunded my purchase and I bought some Monitor 40s. They were supposed to be a better match for my Denon. They sounded great I love the highs and mids and mid bass. My Denon has a high pass filter which helps. I also have a PSW10 sub to help with lows. The problem is now a month later I blew a tweeter. Can bi-wiring help this or am I just expecting too much from the speakers. I had an old set of Radio Shack speakers for 15 years with no problems. I am just dumfounded at the issues I am having with these Polks. I have four Polk door and 2 Polk subs in my truck and beat the heck out of them daily for three years and no trouble. that's why I got the Polks for my home system. Any help?:(

Jed Leland

Hey Tinman,
Welcome to the Forum, with a little coaching I think we can be of help preventing blown tweeters. It's important to know when you're clipping your receiver. The tweeters are being damaged from high frequency distortion caused by reaching the limits of what the Denon can make. When you're listening to your system at fairly high volumes pay attention to how high frequencies are sounding. When you start hearing any harshness or brittleness this is a clue that the receiver is running out of power. Words that have "S" at the beginning will sound like "TS" or "ZS" instead. A friend of mine calls it "tizziness" for that reason. You want high frequencies to sound smooth and "warm" with no harshness or extra brightness in the sound.
Another thing is to make sure you have the receiver's tone controls set to "flat" or neutral and any "loudness" compensation turned off. Listening for clipping will go along way to keeping your sound system for many years with no trouble.
Jed

nikolas812

Welcome to the Club.

Turn it down!!:p:D

ShinAce

A bigger amp will help to prevent clipping, but the volumes you're listening at might still blow the tweeter.

Best bet is to lower the volume a tad. If you're using any kind of bass boost, disable it. Loudness, don't do it.

Knowing when the sounds starts to get 'harsh' is the best way. As soon as the quality of the sound begins to lose any clarity, you are clipping the amp. Back off the knob at this point.

Really, what Jed said.

tinman67gz

Thanks guys, I pretty much knew the problem may be my listening levels, but sometimes I just can't help it. I guess my best bet is an amp for more power and some bigger speakers. The one thing is I really did not notice distortion this time. With the original speakers I did but it was too late (they were already smokin).

What are your thoughts on the bi-wiring. Might this help some? My wire lengths are not very long 10 to 20 feet and I used monster cable (definitely overkill for this application) but I did single wire.

dpowell

What is the model of Denon receiver you're using? At higher listening levels, your amp may just not be capable of putting out a clean enough signal. I'm not sure that bi-wiring would help. If your source is introducing enough noise at high levels to kill the tweeter, you may have to change the source.

tinman67gz

It's the Denon DRA-697CI. It's supposed to be 100wx2.

rskarvan

Try some Klipsch horn speakers. Your ear-drum will break before you damage those.

Jed Leland

Hey Tinman,
It's doubtful bi-wiring will make a difference. In my opinion bi-wiring gives the listener a slight reduction in inter-modulation distortion. As any moving coil transducer (mid range drivers and woofers) move forward and backward they generate a reverse Voltage in opposition to the incoming audio signal's Voltage. If you are in a mood to see the evidence of this back EMF remove the speaker wires from the back of your speaker and connect an AC Volt meter across the speaker's terminals. Then gently push on the woofers or mid range drivers of your speaker. You should see an AC Voltage being registered on your meter. This is the result of the driver's voice coil being moved in the magnetic field of the permanent magnet. The same thing happens when you play your speakers, there is a Voltage that opposes the signal that is coming from the receiver. That's one reason the full amount of power your receiver makes never gets heard. The receiver is measured with a dummy load resistor which doesn't generate any opposition to the incoming power. Next take a short piece of speaker wire and place it across the positive negative terminals of your speaker and push again. It should seem harder to push, since the short piece of speaker wire is shorting out the voice coil causing an electro-mechanical braking of the moving part of the woofer or driver. In fact, one of our British speaker manufacturers would short out the speaker's terminals, during shipping, to prevent the woofer from moving too freely and damaging the suspension. The owner would remove the wire after it was received.
Back to the point; bi-wiring. In a standard non-bi-wired speaker the internal crossover connection connects the woofer and drivers and their part of the crossover to the tweeters and their section of the crossover. The back EMF can very slightly cause a modulation of the tweeters. As the woofers are moving forward and backward the Voltage pulses they are producing can, slightly, modulate the tweeter. As the tweeter is working to produce sound it is being effected by the modulation caused by the electrical linking of the woofers and drivers.
When you bi-wire your speaker you are separating the connection between the low/middle frequency devices and the upper frequency devices. Then you connect each section to the lowest impedance point in the audio chain, the output devices of the receiver/amplifier. The low impedance of the receiver's output devices acts as a short (remember the piece of speaker wire causing the woofer to be harder to push?) and also acts as a "sponge" for the back EMF. Instead of the tweeter being effected by the back EMF it is now part of the receiver's negative feedback circuit (designers like judicious amounts of negative feedback because it tends to further lower the output impedance).
However, as in all things audio, the effects of what you might hear are going to vary since the receiver's output impedance, feedback network, speaker wire resistance and inductance, the number of drivers and woofers the speaker has, the BM (motor strength) of the drivers and woofers and the listener's acuity all will effect the results.
But, if everything is working correctly, with good program material a careful listener should hear a slightly less veiled mid-range and a bit of a more controlled bass response.
Jed

SuperG

Thanks for clearing things up Jed :D

Jed Leland

Hello,
You're correct, I did ramble on a bit. Sorry for that, probably pretty confusing. Must have been the high-test coffee.
JL

tinman67gz

You may think you were rambling a bit but I know a fair amount of how electricity works but nothing about electronics. Thank you for the info. In any event I did bi-wire the system and I can tell a definite difference in the clarity of the highs. It does sound much better. I'm sure I will still have to turn it down, but I can live with that.

tinman67gz

As for the Klipsh, I have heard that horn speakers sound rather harsh to the ear and the thing I like most about the Polks is the clear crisp highs.

wizzy

Just out of curiosity, do you leave your treble knob on flat, or do you turn it up?

Also having a sub can greatly increase the power going to the tweeters. For example - speakers rated at 200watts are done with the knowledge that most of your power is used to drive the woofers. This 200w speaker may have a tweeter capable of handling as little as 30w RMS.

If you have a sub hooked up and the internal xover set the receiver can dedicate more power to the higher end - so your 100w receiver only amplifying say 120Hz-20k really has more power going to the mid/tweets when cranked up before clipping.

Then if you top that off with cranking up the high end via treble controls ...

But yeah, sounds like clipping or distortion.

Jed Leland

Thank you, Tinman, I sometimes don't know when to shut up. I've been such an "audio-nut" for so long I relish the ability to trade points of view with fellow enthusiasts. You fellows are so generous with your experience it's a real delight being able to have a good "chin wag", as my old grandpa would say.
Jed

mmadden28

Man I hate that; I spend about 10-15 minutes writing a reply, and something causes me to go to another page and when I come back everythign I wrote is gone.. Lets see if I can remember what I wrote (darn it all!)

I have been reading about bi-wiring, here and there, in this, and other forums, but this is the first explanation I've read about why bi-wiring might be feasable. Jed, Thanks for your detailed description of the issue. I have a background in electronics, and so I was probably able to grasp your description easier than most but I still think it was clear enough without going too deep into theory.

Of course everything else I read (and no, I'm sure I didn't read it all-still learning here) all leaned towards bi-wiring to reduce the high audio signals from messing with the lows within the same wire, etc, etc. Then I also read that bi-wiring could reduce the wattage going to each driver, since they would effectively now be a parallel circuit each getting half the total current. I don't know enough about crossovers to understand how they impact the final circuit layout, or if biwiring bypasses any of that ciruitry but it certainly sounds feasible as well. Perhaps that's why some 'hear' a difference? Because they are not over driving the drivers as much?

Anyway, I would like to think that the speaker manufacturers, or should I say designers, would have figured out a way to take care of the back EMF issue in the crossover circuits? After all wouldn't it behoove (is that a real word) them to create a great sounding speaker 'out of the box' rather than rely on the end user to figure it out that bi-wiring is better? Or is that exactly why higher end speakers actually have bi-wiring posts at all? Or is that really only for bi-amping?

-Madden

mmadden28

tinman67gz wrote: »

...I did bi-wire the system and I can tell a definite difference in the clarity of the highs. It does sound much better. I'm sure I will still have to turn it down, but I can live with that.

What did you listen to to hear the difference? At what level?

treitz3

mmadden28 wrote: »

After all wouldn't it behoove them to create a great sounding speaker 'out of the box'

Most manufactures do. To them.

Synergy with that and what you have? Good luck and happy trails in your journey..........

[Deleted User]

Hello,
I remember reading, a few years ago, an article written by Bob Carver explaining why he felt having high available power was important. He described how the back EMF cancelled out a fairly significant amount of the incoming power given by the amplifier. So that a specification of 200 Watts into 8 Ohms was made into a dummy load power resistor. But, when playing moving coil type speakers (voice coils and permanent magnets) a considerable amount of the power was being opposed by the back EMF. So, you are really not giving as much power to your speakers as you think. The amp works to push the cone forward, but the cone is pushing back. Move a coil of wire in a magnet field and you get electricity, this electricity is opposite to the incoming electrical force. You're using electricity to create sound and additional electricity is the bi-product. A microphone works in reverse, the sound wave causes the microphone element to generate a small amount of electricity. The more speakers in a room, each one acting as a huge "microphone" picking up the airborne vibrations of the other speakers means you are generating more and more back EMF caused by sympathetic vibrations between the other speakers.
I don't believe there is a way to eliminate this, it is just another limit to the efficiency of amplifiers and speakers. But it also points out how specifications can describe only a small portion of what is happening.
Have fun, Ken

Jed Leland

Hello,
I'm certainly glad we're having this level of dialogue on this type of subject, most interesting. I've always felt amplifiers should be tested using "real world" loads, things with complex inductive and capacitive elements. What chap would buy a car if the road testing were only done on straightaways? None that I know of.
Has anyone else had a favorable experience with bi-wiring?
Cheers, Jed

nikolas812

Jed Leland wrote: »

Hello,
I'm certainly glad we're having this level of dialogue on this type of subject, most interesting. I've always felt amplifiers should be tested using "real world" loads, things with complex inductive and capacitive elements. What chap would buy a car if the road testing were only done on straightaways? None that I know of.
Has anyone else had a favorable experience with bi-wiring?
Cheers, Jed

No.

I have never found any benefit from bi wiring. Or at least anything that sounded better to the ear.

On a second note. I have only tried bi wiring with AVR"S.

I would like to try bi wiring a speaker with separate amps though. I think if ever there was going to be a favorable difference it would be with separate amplification.

Just my experience and thoughts on the matter.

wizzy

nikolas812 wrote: »

I have never found any benefit from bi wiring. Or at least anything that sounded better to the ear.

Any other part of the body? :)

mmadden28

nikolas812 wrote: »

No.

...

On a second note. I have only tried bi wiring with AVR"S.

I would like to try bi wiring a speaker with separate amps though. I think if ever there was going to be a favorable difference it would be with separate amplification.
....

Do you mean bi-amping with separate amps?

tinman67gz

mmadden28 wrote: »

What did you listen to to hear the difference? At what level?

Thanks to all. I found out I had a defective Denon and sent it back for another.

As for my music preferences I listen to everything from Zeplin to BB King and Collective Soul to Norah Zones.

I have noticed the most difference in piano heavy tunes like Alicia Keys and Norah Jones.

As for listening level, as loud as possible. I do notice the difference in lower listening levels as well though. (sometimes my wife makes me turn it down, she thinks I'll go deaf or something)

tinman67gz

P.S. to mmadden28 your speakers are already a parralel circiut whether by wired or using the factory shorting bars.

mmadden28

I'll have to re-find what I read-I know it was something like that-Some series/parallel change that happens. Of course I don't know what the speaker/xover circuit looks like (yet).

ShinAce

The idea with bi-wiring is that you are properly damping the woofer at the amp so that it doesn't interfere with the tweeter circuit.

This theory only really works modern amps. An old tube amp would not benefit from bi-wiring. At least it shouldn't, in theory.