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RE: update on the Al Sekela tweak

Posted by Davey on February 1, 2015 at 07:23:11

In Reply to: RE: update on the Al Sekela tweak posted by Roger Gustavsson on February 1, 2015 at 05:05:07:

Al's theory (which I agree with in this aspect) was that it probably wasn't necessary for the bass driver since there is already a substantial low-pass network in operation on that driver. In that case you have one or two large value inductors already in series and possibly a shunting capacitor as well. It makes little sense to add a 10uH inductor in series with a multiple-millihenry inductor. The woofer is effectively disconnected from the power amplifier at high frequencies and the higher frequency driver(s) have the dominant connection.

You are obviously correct about the drivers themselves being (possibly) antennas. HAM radio operators and engineers who specialize in RF issues have a lot of appreciation for these types of situations since they've been dealing with them for years. Audio and RF have many similarities that most don't fully appreciate. Shunting RF with an appropriate filter is a technique that has been used for decades.

That impedance trace is an interesting one and I'd like to know a bit more about how it was generated. However, if realistic, it does show the issue with a speaker/wires picking up transient RFI and presenting it to the amplifier output.

Al's initial premise (a perfectly viable one) was that RFI pickup by the speaker/wires needed to be prevented from making its way back into the power amplifier output. A simple series inductor attacks that issue directly. However, he didn't consider the other direction......where the real low-pass filter formed by the inductor alters operation of the tweeter, relative to what it was. Intuitively, you would think that low-passing the tweeter right above the audio band would also be a beneficial effect. It seems to be a win/win configuration, but think about it a bit further, and think about all the environmental issues and different types of power amps that are employed. In fact, the Gilmore Raptors that Al used are a very interesting case.......as are all switching amplifiers that have high-frequencies present on their outputs. When those high-frequencies are applied to the materials of a Maggie ribbon tweeter, what will happen? Will it be beneficial...subjectively? What will happen to the amplifier operation when you remove the high-frequency load from its output LC filter network? I don't think some of the posters here are appreciating what a potentially complicated interface this really is.

Cheers,

Dave.

Edits: 02/01/15 02/01/15 02/01/15

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