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Old 28th November 2004, 07:18 PM   #1
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Default Protecting Tweeter from low frequencies...

I'm going to be doing an active 3-way design here pretty soon with the Seas 27TDFC and I'm curious what steps I need to take (if any) to protect the tweeter from low frequencies. The Fs of this tweeter is 550Hz, so would I need to put a capacitor in series with the tweeter starting a 6dB/oct rolloff at 550Hz? Higher? Is there any way to protect it without introducing any phase-shifting? Thanks..
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Old 28th November 2004, 07:28 PM   #2
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If you do have an aktive design - you use an aktive crossover. So - why would you need added protection when through that xover you only feed it the approbriate frequencies?
Am I missing something?
BTW - from my experience the best way to use aktive x-over iare minimum slope of 24db/octave. For the last four years I run 48 db?octave.
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Old 28th November 2004, 07:37 PM   #3
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I'm going to use a 24dB/oct crossover and it will probably be around the 2500Hz mark. I'm worried about protecting it from any sort of stray DC that may come out of the amplifier, or perhaps a configuration error in the active crossover. Basically I'm looking for a buffer between the tweeter and the rest of the system so I don't have to worry about making a small mistake and blowing my tweeters. Maybe this is unfounded, is it hard to blow tweeters (generally speaking)? Is this a problem I should even be concerning myself with?
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Old 28th November 2004, 07:50 PM   #4
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Hi - no, believe me it is not hard to blow tweeters - but this is more a problem of just wearing out when playing at high levels. I never had a problem other than that (my tweeters usually last about three years), I use Vifa T 27 TDG.

Other than that - I am not that much of a theoretician, but I would not be willing to compromise the clarity of an aktive xover by introducing another passive element.
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Old 28th November 2004, 07:57 PM   #5
boholm is offline boholm  Denmark
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What amp is going to drive it? Ready-made or homebrew?

If the amp sends out low frequency *after* the HP-filter, then that amp or the filter is broken and needs to be fixed.

If you still is that scared you may introduce (or adjust) a servo, that has a cut-off frequence of - say - 1 kHz. Yes, you can put in a capacitor, but you will add a fase-shift that is unnecessary (as well as the capacitor ;-) - oh, and so will the servo.

IMHO

And BTW: Always measure output, before connecting next step !
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Old 28th November 2004, 11:31 PM   #6
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Most likely BrianGT gainclone.
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Old 29th November 2004, 12:07 AM   #7
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My amps dont produce any low frequency noise except for a very low lvl hum from the mains etc.

I am active and use a scanspeak d2905/97 as my tweeter which is a very expensive tweeter to just brake due to some amp failure or some unforseeable problem occuring. The biggest problem is the turn on thump from the amplifier, so for my peace of mind I put a 70uf cap in series with the tweeter. This rolls off about 300hz I think, not enough to impinge in the least on the 3khz xover frequency, but stops my tweeters from frying.

We all no solder joints go wrong every once in a while and fuses blow etc. If a problem were to develop in some equipment, bang dead tweeter, im not going to take that risk.

By the way, I have removed the cap and I cannot hear any difference. Its a high quality wilmslow audio supersound polyprop. Yes they are expensive but nowhere near as expensive as the tweeters.
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Old 29th November 2004, 01:51 AM   #8
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Yes, this was exactly my plan, putting a largish (30uF or so) cap in series with the tweeter, "just in case". Still seems like a reasonably good idea to me, i doubt i could hear the difference with and without.
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Old 29th November 2004, 02:41 AM   #9
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Use a cap that would nominally represent a 1st order crossover at 1/2 the frequency where your active crossover is. Aside from DC issues in case of amp failure it also protects against turn-on transients that can pop a tweeter VC in a heartbeat. In pro-sound where active crossovers are the rule rather than the exception this is usual practice.
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Old 29th November 2004, 03:10 AM   #10
Davey is offline Davey  United States
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I doubt you'll have any problem with normal usage if you don't use a capacitor. These tweeters are more robust than you might think. In any case, the darn thing is only $28.00. Cheap to replace. I'd skip the capacitor if I were you.

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