🚀 go-pugleaf

On Wed, 17 May 2000 13:06:11 GMT, DPierce@world.std.com (Richard D
Pierce) wrote:

>In article <3922537c.1132967@news.one.net.au>,
>Johnny <johnny_c@NOSPAM.one.net.au> wrote:
>>On Wed, 10 May 2000 12:30:58 GMT, DPierce@world.std.com (Richard D
>>Pierce) wrote:
>>
>>>The argument is advanced that the series inductors in a
>>>crossover ruin the amplifier's high damping factor. That's wrong
>>>on two fronts:
>>>
>>>1. As has been stated here and elsewhere numerous times,
>>>   "damping factor" is meaningless and misleading single-
>>>   number advertising spec that has no significance in
>>>   loudspeaker performance in all but the most pathological
>>>   of cases. It is the resistance of the voice coil that is
>>>   THE single greatest factor in determining the damping of
>>>   the system, and all other electrical losses fall FAR behind
>>>   that in significance.
>>>
>>>2. The competent engineer will have already compensated for
>>>   these and other losses in the design of the INTEGRATED
>>>   system, and removing these coils can, in fact, undo the
>>>   system tuning that leads to a speakers good performance
>>
>>Are point 1 & 2 not contradictory?  
>
>No, they are not.
>
>>Surely if the total AC impedance
>>of the inductor was not an issue as you claim in point 1 it would not
>>need to be considered as part of the design as you mention in point 2.
>
>It's not the AC impedance of the inductor that's the issue,
>because it is not the inductive part of the impedance that
>provides the damping, rather it is the equivalent series losses.
>
>>My experience with 3-way designs is that a large inductor of (say 6mH
>>and DCR = 0R8) has a very significant effect on the bass tuning.
>>Which agrees with point 2, but not point 1.
>
>Well, let's see. Assume a driver with a DC resistance of 6.5
>ohms, a Qmc of 4.0, a Qec (with zero source resistance) of 0.86
>and a system Qtc of 0.707 (Butterworth, maximally flat
>response). Your claim is that 0.8 ohms series resistance will
>have a "significant effect" on bass tuning.

My whole point here is that the total AC impedance of the inductor has
a significant effect on the frequency response of a ported bass
system.  

The reactive impedance of the inductor does interace with the reactive
impedance of the driver enclosure system.  And will significantly
affect the fequency response in the bass region.

For the 6mH inductor, I am not claiming that the 0.8 resistance is a
big deal, as you have shown it is clearly not.  Although many
commercial design would often use a cheaper component of slightly
higher resistance, I choose this DCR to make my point of the effect of
total AC impedance

A 6mH inductor will have a reactance of 1.88ohms at 50Hz and 3.77ohms
at 100Hz.  However the effect of this is not a reduction in level in
these ranges it will actually increase the level in this rance due to
the interaction with the speaker impedance.

As you will know, if a bass driver has an impedance peak at say, 40Hz,
it will have a significantly negative reactance (like a capacitor) in
the region between 50Hz and 150Hz.  Anyone who knows something about
reactive circuits can see how this will produce a resonance of its
own.  For the uninitiated, the positive reactance of the inductor and
the negative reactance of the driver cancel out so more power is
applied to the bass driver in this range.  In practice you will
typically get a peak of 2-3dB in the 50-150Hz region.  Typically, the
effective bass extension is reduced, because of this increase in
midbass level.  

This effect of passive crossover AC impedance is very easily
demonstrated in speaker simulation packages. I can't believe you did
not address this issue in your discussion of active crossovers.  It is
much more significant than the effect of 0.8 ohms of DCR.

regards,
Johnny.