[PaulHilgeman]

The small black boxes that have been touring the states with the Ronins are what can be called impedance compensation networks.

They are attached in parallel to the speaker and will flatten the impedance curve of the speaker.

Most speakers that have a crossover in the upper midrange will have a large impedance peak, usually peaking to 10-40 ohms.  If this peak is even on both sides, in that it rises up in a similar way to how it goes down on the other side, a simple network can be used to flatten it, with no consequence in the frequency response.  It consists of a resistor, inductor and capacitor connected in series, then the whole bundle is connected in parallel with the speaker. 

It will force your amplifier to push more current through, however, as a benefit, the amp will see a flat impedance curve through the midrange.  This will make the speaker appear more like a resistive load, and not have the large impedance phase shifts associated with a peaky impedance curve.

It is relatively easy to design a filter like this for the midrange, however for the peak that occurs in the bass region, the components would be the size of a small dorm room fridge.  Therefore, there will still be a single peak for a sealed box, or a double peak for a ported box below 100Hz or so, but a relatively resistive load from that point on up.

The whole benefit of doing this is to 'harmonize' performance between amplifiers with different damping factors.  The flatter the impedance curve will be, the less colored the speaker will be by it's own variations in impedance (The frequency response will morph into a look-alike of the impedance curve as damping factor decreases).  If the speaker has a big peak in impedance at 2000Hz, it will sound thin, shouty and overly present with an amplifier with a low damping factor.  However, if an amplifier has a high enough damping factor, as most SS amps do, this network is totally unnecessary, and in general completely inaudible due to the fact that the frequency response will not 'morph' towards the impedance curve.

Hope this helps,
Paul Hilgeman

[Bob Reynolds]

Paul,

Thanks for the post. Interesting information. I've read of impedance compensation in a few speaker reviews. From that I've assumed that some speaker manufacturers go the "extra mile" in their crossover design to present a more resistive load and others make no attempt at all.

You comment that a compensation network for the bass region would require huge components and thus, is not done. Could it be accomplished with an active network?

-- Bob

[PaulHilgeman]

Unfortunately no.  It deals with the direct amplifier - speaker interaction, therefore it needs to be placed in the signal between them.

Yes, it is possible to just include this right in the circuit from the get-go, but I figure why put extra stuff in there to begin with.

It seems as though people around here lean slightly in the tube direction, as the whole audiphile comunity tends to lean in the silicone direction.  Either way, it needs to be an included accessory.

It certainly could be done for the bass reigon................................. ..........

Just ran some simulations.  It would *only* require 3200uF of capacitence.  It *could* be acceptable to use an electrolytic here due to the parallel nature and low frequency.  The inductor would need to be a 9mH, which is pretty big.  It could fit in a womens shoe box sized enclosure or so.

Also due to the LF nature of the network, it might get a little bit warm, but I would have to build it to check that.