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WRONG and WRONG

Posted by Duke (D) on September 30, 2014 at 22:46:01

In Reply to: RE: Series connection of drivers in hi-fi speakers? posted by BigguyinATL on September 30, 2014 at 07:07:56:

"A series connection also doubles the inductance that both speakers see, so - if used for woofers - or better mid-woofer - the low pass filter may be unnecessary."

Wrong, because while the series inductance is doubled, so too is the series resistance, so the drivers' inherent inductive rolloff characteristic is unchanged. The same goes for parallel connection - the frequency response stays the same.

"Also note that placing the woofers in series pretty much distroys the idea of damping for either woofer..."

Wrong, and in fact the effective system damping of the speaker/amp combination increases.

While a woofer's Qes (electrical damping) goes UP (damping is reduced) as series resistance is increased, it also goes DOWN (damping is increased) as the BL (magnetic field strength) is increased. With series connetion Re is doubled, but so is BL, so Qes STAYS THE SAME.

As a thought experiment, think of a single woofer... the first half of the voice coil is in series with the second half. Does the one destroy the damping factor of the other? No, because BOTH halves come with their share of magnetic field strength. This is electrically and magnetically analogous to two identical woofers wired in series.

Now let's bring in a high output impedance (low damping factor) amplifier. Let's say it's a specialty tube amp with no global negative feedback, and its output impedance is 4 ohms. Into an 8 ohm load, that would give the amp an effective damping factor (input impedance divided by output impedance) of 8 ohms/4 ohms = 2. But into a 16 ohm load. the effective damping factor is 16/4 = 4! So by going with series wiring, we have doubled the effective damping factor of the amplifier/speaker combination.

(This doubling of effective system damping factor would hold true regardless of the type of amplifier used or its output impedance, but the impact on the system's frequency response is greatest with high output impedance amplifiers, so that's why I chose such for my example.}

"...and the resonance peak in impedance will be seen by both woofers."

True but irrelevant. Recall our thought experiment where the first half of the woofer's voice coil is in series with the second half. The whole impedance curve is doubled in value, so the doubling of value at system resonance is of no greater or lesser consequence than what's happening at any other part of the impedance curve.

* * * *

I normally wouldn't be so in your face when someone is mistaken, but your profile says you're an acoustic engineer who works for Bruel and Kjaer. Imo your position as an engineer with one of the most respected companies in its field holds you to a higher standard than the average audiophile.

Duke

Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.

Edits: 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14 09/30/14

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