tweeters, crossovers, or other problem?

[dore_m]

I just noticed that my left channel sounds different from my right channel (I have a pair of NHT ST4's).

Specifically, the right side lacks the "sparkle" and sounds a bit more muted than the left. When I say "a bit", there is a noticeable difference, yet the right side doesn't entirely lack high frequencies. I ran a test tone of 5 khz at it, and could hear signal from both speakers.

I've swapped speaker channels (it's the speaker, not the amp or wires)
I've checked the polarity, and it seems ok.

Any suggestions on what the problem might be?

-Dore

 

[Swerd]

My first guess is the tweeter on your right speaker is dead. That's more likely than something wrong in the crossover. Because the crossover from the mid-range to the tweeter is 2.6 kHz (see page 7 of this)
you'll still hear sound from the mid range with a 5 kHz test tone.

Try this test. Play that 5 kHz test tone while gently touching a fingertip to the mid range cone. Don't press your finger in, just let it gently contact the surface. Feel it vibrate. Try the same with surface of the tweeter's dome. Do this with both the left (good) and right (suspect) tweeters until you are sure that one tweeter isn't vibrating or that both do.

If one of your tweeters is dead, contact NHT about finding a replacement.

 

[dore_m]

Just tried your suggestion - thanks. There is a grill around the tweeter so its difficult to touch directly. However I notice this when comparing the two:

Neither mid range drivers feel like they are moving at 5khz. The left tweeter is louder, and if I touch the grill that surrounds the tweeter, I can affect the sound (either by shifting the speaker assembly or by muffling the sound.

The right tweeter, which I think has the problem, is similar, but the sound level is noticeably lower, but still exists. It exists loud enough that when I put my system into 7 channel mode, it wasn't noticeable. It wasn't until I started to do some stereo imaging tests where I realized it.

Is it possible the tweeter is bad, but still working at about 60%?

-Dore

 

[j_garcia]

Sounds like the voice coil on the tweeter is damaged and that would be the normal failure point. Yes it can still partially function like this.

 

[dore_m]

Thanks. I'll see if I can get another tweeter.

 

[dore_m]

Stupid question - anyone know how to remove the tweeter from an NHT ST4 (SB1, SB2, SB3, SC1?) Whats the best way to pop it out?

I thought I could get to it if removed the 6.5" driver first, but it looks like it has to come out with snaps or something.

-Dore

 

[dore_m]

There's a wall between the 6.5 driver and the tweeter....

 

[TLS Guy]

You will have to ask NHT how it comes out.

Can you get to the crossovers?

If the tweeter has failed causing this problem, then the affected tweeter will have a lower DC resistance than the other.

If you disconnect both tweeters from the crossover you can measure the DC resistance of both and compare them.

If they are the same then there is a bad cap in the crossover. I would say this is about equal chances. There is always at least one cap in series with the tweeter and often two and sometimes four. These caps can fail. In fact failed caps in crossover is not rare. In my experience because these caps to the tweeter carry the total current to the tweeter, this is probably the commonest way for crossovers to fail.

If the tweeters have the same DC resistance through the voice coils, then you need to replace the caps in the high pass crossover.

 

[dore_m]

NHT suggested that I open both my speakers and switch the tweeters to confirm that it's the tweeter and not the crossover. The particular guy I talked to didn't know how to take the tweeter out. So first I need to get it out of the case...

If it indeed is the crossover, I'll refer back to your post. Thanks!

-Dore

 

[dore_m]

Someone on another board told me to take off a sticker on the backside of the speaker to expose the screw that holds the tweeter in. Looks like that 's the solution.

 

[Swerd]

Good. Glad you found a way to do that. The suggestion to swap tweeters will determine if its the tweeter or the crossover board.

The next time you call NHT back, if the customer service person doesn't know much, get a bit whiney, and insist he get someone on the phone who does. Short of that, get a phone number or email address of service guy at NHT who is familiar with one of their older models.

Good luck with your repair effort.

 

[TLS Guy]

NHT suggested that I open both my speakers and switch the tweeters to confirm that it's the tweeter and not the crossover. The particular guy I talked to didn't know how to take the tweeter out. So first I need to get it out of the case...

If it indeed is the crossover, I'll refer back to your post. Thanks!

-Dore

If it is the tweeter causing this then i can only be caused by shorted turns in the voice coil from overheating. You can test this with a multimeter without removing the tweeters. Don't remove tweeters unless you have to. My route will be much quicker and better.

 

[dore_m]

Don't I have to disconnect at least one of the tweeter contacts to test with a multimeter? If I have to disconnect the contacts, I may as well swap them (?)

-Dore

 

[TLS Guy]

Don't I have to disconnect at least one of the tweeter contacts to test with a multimeter? If I have to disconnect the contacts, I may as well swap them (?)

-Dore

It should be easy to disconnect at the crossover end.

 

[dore_m]

Tweeters were easy to disconnect after I unscrewed the aluminum rod. My right tweeter needs to be replaced. Wasn't easy to re-assemble, but I got it with some patience.

 

[Dinø]

My NHT SB3 has the same problem, with the same exact tweeter. Did you contact NHT for a new tweeter?