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Topping L30 II to drive tweeter in 2 way active setup?

mike7877

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Nothing below isn't relevant (everything below is relevant - there, I'm being positive! lol):

Tweeter: 91.5dB/W
Woofer: 85.0dB/W

Tweeter: 7 ohms
Woofer: 7 ohms

Topping L30 II: extremely low output impedance, capable of 0.5A current per channel (12 ohms 6.3V and 16 ohms 8V evidenced in voltage/impedance chart in L30 II ASR review)

The tweeter's nominal impedance is 8 ohms - I can't remember its lowest impedance, but being conservative and calling it 7 seems wise.

0.5A and 7 ohms is 1.75 watts.
+6.5dB is 4.5x power, so 7.875W if the woofer and tweeter were the same efficiency.

I plan to drive the woofer with my LA90 Discrete, which puts 41 watts into 8 ohms. The woofer is probably 7 ohms as well (they're very polite drivers and the woofer's box is sealed which makes it even more polite...)

Crossover point I'm thinking of is 2kHz or so. The passive 3rd order Butterworth currently in use is 2.1kHz (not relevant but interesting: made with massive low gauge air core inductors and 1% parts).

We have 8W (normalized for dB) and 40W. Almost the 20%/80%!
If the total was supposed to be 50W, we'd have 16%/80%

The tweeter's impedance peak is about 24 ohms, resonance is ~1000Hz, and because the suspension is very stiff, the raised impedance is very, very wide. I don't think it completely bottoms until somewhere between 2.5 and 3.0kHz. I mention this because the crossover point I'm targeting (2kHz) isn't itself 7 ohms, but something around 10-11. Since in music, the lower the frequency, the more energy there is, this makes the 2kHz target not so on the cusp of possible IMO.

Questions:
Is there any reason to believe that the L30 II would not behave as well at 7 ohms as it does at 12?
Are there any other reasons I shouldn't spend $200 to make my currently passive setup an active setup with insanely low distortion?
 
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mike7877

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It's not exactly ideal but should work. Given that you have about 6 dB of sensitivity to spare in the tweeter, you could make the amp's life a bit easier with an extra series resistor (its effect on FR should be easy enough to compensate for with measurements and DSP XO).

Yeah, good idea! The L30 II has the voltage that'd be required to combat the impedance rise. If I remember right, I hink 2kHz is around 11 ohms, and ...quick math estimate in head... if I put 8 ohms in front of the tweeter, I should still be able to get 2-3W from the tweeter.

I could have 2 modes, one with the resistor in (normal listening) and the other out (for louder).

Edit: do you think it'd end up being any easier on the amp this way though? Since half power would be wasted, the current would still be the same for every amplitude - the only difference being at a higher voltage.

Edit2: Aside from stability, from a purely heat generating perspective, does an amp putting 0.5A into 16 ohms run cooler than than 0.5A into 8 ohms? It seems it would get hotter, no?
 
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