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Crossover transformer question


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Klipsch uses autoformers to lower (or raise, as the patent goes) the output of a driver, or drivers to match the output of the other drivers in a system. The manipulation changes to apparent impedance of the driver affecting the other components in the network.


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Autoformers are used because the output of a horn and driver combo is not necessarily flat across it's operational band. The loading characteristics in many(not all) cases require the use of an autoformer to deliver equal output with respect to frequency within the pass band.

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PWK wrote an article on this.

His gripe was that "pads" made up of resistors, similar to a fixed L-pad, causes anomalies in the frequency response.

The use of resistances results in a condition where the speaker is no longer "seeing" an amplifier with a low output impedance.

I've improvised "real" autotransformers using the voice coil connection side of 70 volt line transformers. I was expecting these to have altered frequency response. This was because I thought they'd exhibit some inductive effect. However, they were remarkably flat. So I assume that because of the good coupling, there is little inductance.

To answer something that Jerohm (Ohm?) was getting at, the actual inductors and capacitors supply frequency tailoring functions, as usual, not the 'former. (The latter is at least from what I can tell. Master Al K. might be able to explain his findings!)

One application is where the midrange of the K-Horn is about 3 dB more sensitive than the bass or tweeter and the 'former knocks it down by 3 dB. The Heresy uses a 'former in a similar way. The bass unit has much less sensitivity and both the midrange and tweeter output is reduced using the 'former.

I don't have a schematic for the non-Heritage units but I assume the same technique is used.

In one patent, PWK used a 'former to increase the output of the tweeter. It seems that there the bass and mid were okay but the tweeter was a few dB down. This is "step up" voltage application.

I won't go into specifics of impedance matching here. But generally, when the 'former is used in a step down mode, the amplifier "sees" a high impedance in that portion of the auto spectrum. PWK and D.B. Keele showed this can result in lower amplifier distortion when the amp is pushed close to its limit. There is an AES Preprint on it.

Of course, pushing an amp to the limit is rare given the efficency of our speakers.



This message has been edited by William F. Gil McDermott on 06-17-2001 at 08:10 PM

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