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I keep blowing out tweeters
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Author:  Falcon10 [ 25 Sep 2019, 21:23 ]
Post subject:  I keep blowing out tweeters

Hi everyone, this is my first post. I've got one of these tweeters https://www.amazon.com/gp/product/B01IC0XR6S wired into the front right speaker outputs on an old amp from Goodwill. The amp works fine when plugged into normal speakers, but when there's only a tweeter wired into the amp's right-speaker output, and I play a 1.5 kHz tone at about half volume, after a bit, the tweeter pops, smokes, and fades out.

The setup is:
* a laptop audio out going to the amp's CD inputs
* the laptop plays a 1.5 kHz sine wave
* amp volume dial is about 1/2. The left/right and forward/rear knobs are on the middle.
* the tweeter is impedance matched with the amp (8 Ohms)
* there's not a crossover in front of the tweeter

In trying to characterize the power that the amp is sending to the tweeter, the results were confusing. With a multimeter (or a scope) on the amp-tweeter leg of the circuit, in series it was seeing milliamps, and in parallel, it was seeing millivolts. Since the tweeter is popping and blowing, and the tweeter has a 300W rating, it would seem that the meter should be picking up way more than milliwatts. (This was with the volume knob on the amp maybe a quarter of the way to max volume).

Any ideas for measurements I can try, or any obvious thing I've missed here in the setup?

Author:  M. Gregg [ 07 Dec 2019, 16:21 ]
Post subject:  Re: I keep blowing out tweeters

Its just an idea,

NB as with all things its just suggestions and at your own risk!
If you are wiring the tweeter direct to the amp output its wrong!
It should be fed via a crossover network never direct to the amp output.
The crossover is selective for frequency and is not just about splitting frequencies between midrange and tweeter.
Reason is that the impedance is probably wrong and or there are overtones and spikes appearing on the amp output.
Things like cross over distortion and harmonics.

NB you should never run an amplifier into an open load, if parasitic oscillation sets in it will fry the tweeter and even the amplifier.
Any frequencies that get through to the tweeter that are outside the range of operation will blow it very quickly.
One other thing is I have never seen a perfect power supply so if its not through a crossover you have hum which is the same as low frequency to the tweeter. Without a load on the amp output to sink any transients you could get all sorts of problems.

Another thought, is the tweeter rated at continuous power or transient power. Its not "normal" to run a tweeter at continuous set frequency.

Regards
M. Gregg

Author:  Joegtech [ 23 Feb 2020, 22:35 ]
Post subject:  Re: I keep blowing out tweeters

The RMS rating for those tweeters is 150W, a better number than the peak watts for what you are doing, no?

Probably more importantly, the frequency range for those tweeters is 2000hz and above. You were sending 1500hz.

My strong opinion is that no one should ever buy a speaker without seeing a frequency response curve for it. The basic numbers a manufacturer provides can be quite deceptive.

Even if you plan to use a 31 band GEQ or parametric EQ with the speakers, it is best to know the frequency response curve.

For example, check out the curves of two tweeters attached below, GT-324 and GT-510.

The mfgr website lists the 510's response as 3k to 20k, the 324's as 2k to 20k. That is fairly similar. The price at parts express is very similar.
https://www.goldwood.com/goldwood-sound ... t-tweeter/
https://www.goldwood.com/goldwood-sound ... d-tweeter/

However when you look at the frequency response curve, sensitivity (SPL) and resonance (Fs) they are quite different!!

The power handling of the two units is similar 50 W for the 510 and 60W for the 324.

However, after fixing the huge bumps in the response of the 324, your SPL will be around 86db. The 510 will be at closer to 93db. Don't you expect the 510 to be louder even though it will handle fewer watts?

Finally it is best to also see a polar frequency response but not all mfgrs provide it. The other attached pic shows the polar response for an old Radio Shack ( Motorola) piezo tweeter. Notice the terrible drop in the highs when you move more than 15 degrees off center!

I successfully used the piezo tweeter in a stage monitor because I could aim it at the seated pianist. The piezo was a good, inexpensive option because it did not require a crossover. It matched quite well with the woofer I selected--a 15" without extended frequency response in the upper mids.

I'm just an experienced hobbyist, not a sound engineer. Others may be able to say more about the specs, for example, the pros and cons of a silk dome vs titanium dome.

So beware of speakers that are sold with minimal specs!

Author:  Falcon10 [ 26 Feb 2020, 15:25 ]
Post subject:  Re: I keep blowing out tweeters

Great points. Thank you!

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