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RE: Tweeters use a few watts max ...

Posted by andyr (M) on February 15, 2017 at 14:35:55

In Reply to: wattage, more than low impedance.. Tweeters use a few watts max. posted by 3+4=5 on February 15, 2017 at 12:34:49:

True - and up until last weekend, I would've agreed with you.

But I found something out about feeding HFs into a 2 ohms load that has changed my mind.

I run triamped Maggies - so I have an 70w (into 8ohms) ss amp driving my ribbons directly. The amp is stable into 2 ohms - ie. it hasn't blown up! :-)) - and my treble sound is great (or so I've always thought!!).

But I recently did some sweeps using REW and a calibrated mic ... and noticed that the FR graph showed a steep drop-off after 16Khz. (Given the mic is calibrated, the FR should be flat to 20Khz.)

So I did some crude measurements, driving my tweeter amp directly (bypassing the miniDSP XO) with a signal generator and measuring the voltage at the ribbon terminals.

To my surprise, the voltage I read at 16Khz was much lower than the voltage at 6Khz ... and at 30Khz, it was down a lot more! This says to me that my tweeter amp - even though it is "stable" into 2 ohms - cannot perform at HFs into a 2 ohm load! :-(( I have been told by an amp designer (not the designer of my amp!) that this is typical of the 'power envelope' of Mosfet power amps.

So I am going to borrow a transistor-based power amp which is renowned for being able to drive 2ohm loads and see if the REW sweep becomes flat to 20Khz!

So my point is - just because an amp:
* has bags of power for a 2ohm driver
* and is "stable" into this load

... doesn't necessarily mean it will perform well into that 2ohm load.

Andy


Andy

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