Can a bad crossover blow the tweeter?

[Ron10]

I'm working on repairing my (4) Infinity Reference 1's and (2) Infinity Reference 2's I've owned and enjoyed since 1991. I've been noticing that they are sounding muddy and less bright so I ran some tests and found:

The tweeters are blown on both of the Reference 2's and (3) of the (4) Reference 1's. The speakers could not play a 10khz test MP3 and when the tweeters were resistance tested out of the enclosures they had open impedance.

I swapped the Reference 1 good tweeter with each of the 5 speakers with bad tweeters. The Reference 2 speakers played the good Reference 1 tweeter perfectly, sounding fine and playing 10khz test tone, 100hz and music well. Then I swapped the good tweeter with the (3) Reference 1’s that had blown tweeters until it died on the last speaker. It initially didn’t work in the (3) speakers. Then I fiddled with the cable and then it played fine. Testing the last speaker the good tweeter died.

The weird thing that I observed is all the speakers, both Reference 1’s and 2’s, that have bad tweeters is that they have an impedance at the speaker terminals of 4.0Ω to 4.3Ω. The Reference 1 speaker that had the good tweeter in it has 6.3Ω. All the speakers are rated by Infinity at 6Ω. Putting the then good tweeter on the 4.0Ω to 4.3Ω speakers didn’t change their impedance at the terminals.

I inspected each speaker's crossover. They visibly look perfect, no oozing from capacitors and no smell of burnt components.

Could the crossover kill the tweeters even though it seems to work? The bad tweeters are all original.

Is there an easy way to test the crossover or have I done that by swapping the tweeters and playing the 10khz test tone?

Should I just replace the tweeters and hope for the best?

I had the surrounds replaced on the mid/woofer driver years back and it's holding up fine. Just the problem with the tweeters now.

Thanks!

Ron

 

[TLS Guy]

Several things: -
From what you say, I would definitely recap those crossovers, especially those in the high pass filter.

The DC resistance below spec. indicates over heating of the VCs due to too much power. The insulation burns and the coils start shorting and then you get burn out and open circuit.

Be very careful testing speakers with HF test tones. In music there is little power in the HF band. It is easy with a test tone to put a lot of power to a tweeter, damage it and burn it out. I'm inclined to think that your test procedures are the cause of your trouble, and not the crossover, but I can not be certain. To test caps, you need a capacitance bridge, or a device that contains one. It will be simpler for you, and less expensive, to just recap.

When using high frequency test tones, you need to keep the power very low indeed, or you will buy a lot of tweeters.

 

[Ron10]

Thanks for the reply and advice. You have quite the audio video room put together!

I just watched a good video on replacing capacitors:

Capacitor Replacement Tutorial (YouTube)

I could probably handle that. The video shows leaking and bulging capacitors. The crossover capacitors on all six of the speakers look really clean, no bulging, no leaking. If I were to replace any I would need to figure out which capacitor to replace and the polarity for mounting. The one's on the Infinity crossover don't have the polarity well marked.

I just bought on eBay a pair of tested working tweeters and two additional crossovers for the Reference 2 pair. I see what that parts swap accomplishes first.

If I'm reading your reply correctly, you said be careful testing the speakers in the future with a high frequency test.

Would the volume level at a low to normal listening level, the same as when listening to full spectrum music, playing 10khz tone for even up to two minutes be damaging?

Ron

 

[TLS Guy]

Thanks for the reply and advice. You have quite the audio video room put together!

I just watched a good video on replacing capacitors:

Capacitor Replacement Tutorial (YouTube)

I could probably handle that. The video shows leaking and bulging capacitors. The crossover capacitors on all six of the speakers look really clean, no bulging, no leaking. If I were to replace any I would need to figure out which capacitor to replace and the polarity for mounting. The one's on the Infinity crossover don't have the polarity well marked.

I just bought on eBay a pair of tested working tweeters and two additional crossovers for the Reference 2 pair. I see what that parts swap accomplishes first.

If I'm reading your reply correctly, you said be careful testing the speakers in the future with a high frequency test.

Would the volume level at a low to normal listening level, the same as when listening to full spectrum music, playing 10khz tone for even up to two minutes be damaging?

Ron

If you play a high frequency tone at normal listening levels, you will blow lots of tweeters and fast. When doing what you are doing, it must be way below normal listening levels. Tweeter wire is thin. A sine wave gives the VC no break, and will burn out at half a watt or so if you keep it up. You have to be very, very careful playing high frequency sine waves through speakers. Tweeters are fragile items and are easily blown doing what you are doing.

After what you say, I would be 99% certain you have blown those speakers with your testing procedure.

The rule for high frequency tones and tweeters is KEEP IT LOW and SHORT.