Tweeter noise

[Draekon]

Hi,
I recently built my second pair of speaker cabinets and chose to use some titanium dome tweeters (reasons based on budget constraints and power handling) and at first they seemed to sound decent, but I started noticed an almost metallic sound at certain frequencies, usually just when someone is talking (like in radio commercials). I'm not sure if its hitting a resonance frequency, or why it is doing it. The tweeters I'm using are Audax TM025F7 tweeters.

Is it probably the tweeter design that is causing this sound, or could it be because of the box volume causing a resonance? Is this fixable with the current tweeter, or do I need to find replacements?
Thanks

[planet10]

Originally posted by Draekon
titanium dome tweeters... its hitting a resonance frequency

Ya gotta "love" those metal tweeters... most suffer from a VERY big resonance spike as the cone finally breaks lose. You can try suppressing it with a notch (but that is never totally effective), swap in a tweeter with more benign resonances, or try tweaking the existing tweeter to mechanically damp its resonance (which will have other side-effects)

dave

[Shaun]

What is your crossover frequency and slope?

If it happens when dialogue is played, then it is possibly distortion due to too low crossover frequency for that particular tweeter. You may need to raise the crossover frequency and/or use a steeper roll-off rate. Check Zaph's web site and see whether he has any comments on this tweeter.

[Cal Weldon]

Metal tweeters always seem to sound better when crossed over nice and high. The titanium units I have are XO'd first order at 12K and don't seem to suffer those "metal" problems.

[Draekon]

The current crossover frequency is at 5000hz with a 12db/octave roll-off. The midranges are listed with a frequency response of up to 6kHz, so going with a much higher crossover frequency may cause some issues with that.

[Dr.EM]

Datasheet doesn't show any major anomalies:

http://www.hautparleur.fr/_audax/tm025f7.pdf

Are you certain its not an artifact of the midrange? It is crossed rather high.

The cabinet volume won't affect it (tweeter must be sealed) but the baffle width/shape could. Ensure you have suitable baffle step compensation in the design; some baffles could create peaking but not usually this high up. Check with the edge software:

http://www.tolvan.com/edge/help.htm

Or even better measure if possible

[Lynn Olson]

Quick debugging: disconnect the tweeter and listen to the system without. Still sounding metallic (even occasionally)? You've found the culprit - the midrange.

If the tweeter is disconnected and the speaker NEVER sounds metallic, even at high levels, then attention must be focussed on the (titanium-dome) tweeter. Every diaphragm material sounds different, and this is not always reflected in the measurements.

[mart.s]

Would need to see a diagram of your x-over but try mocking up a notch filter, this should help. personaly I love metal domes.

[Shaun]

Good points about the midrange. Which mid is it you are using?

Most tweeters crossed over at 5kHz will not be driven into distortion with normal use.

Perhaps you should give us a more complete description of your system.

[Dr.EM]

We don't know the size of the mid but at 5khz the CTC spacing should be very small. It might be larger (much larger?) than ideal causing comb filtering effects. That shouldn't sound metallic as far as i'm aware but worth checking.

Kind of hope that isn't anything to do with it as I also plan an around 5khz crossover in a 3 way