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Re: Lower treble emphasis?

Posted by Al Sekela (A) on March 28, 2002 at 08:30:33

In Reply to: Lower treble emphasis? posted by david on March 27, 2002 at 13:22:35:

I have the Magnepan MG-20s. I don't know how Jonathan Valin was driving them, but I use my MA-1s to drive the midrange-tweeter inputs directly, and bypass the Magnapan outboard crossover box. I use small capacitors in series with the MA-1 inputs to achieve the high pass filter.

The Magnepan outboard crossover capacitor is not as good as the tweeter, so perhaps the midrange glare was emphasized by the crossover in Valin's audition.

Keep in mind passive crossover corner frequencies depend on total output circuit impedance, and will be shifted in some cases by the higher Atma-Sphere output impedance.

Also, using a 6SL7 in place of the 6SN7 constant current tube in the MA-1 input stage makes a subtle difference. It seems to increase the solidity of the treble, if that makes any sense as a description. The type of 6SN7 used as the cathode follower driver also affects the sense of solidity, lack of which could be interpreted as glare.

Finally, the higher output impedance of Atma-Sphere amplifiers may affect midrange driver damping. The Tomcik article discusses woofer damping thoroughly, but other drivers in multiway systems also have mechanical resonances. These are supposed to be out of band for all but the woofers, but their damping is important and may depend on amplifier output impedance.

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