In article , John
wrote:
On Thu, 08 Oct 2009 16:18:42 +0100, Jim Lesurf wrote:

In article , John
wrote:


Excessive length could mean a long run. I didn't do any long/short
comparison.

Perhas also worth adding that how 'crappy' the amp is may not be the
issue when considering runs so long that the series
resistance+inductance becomes high. What might then matter is the
impedance variations with frequency of the loudspeakers chosen.

It's my understanding - please tell me if I'm wrong - that the cab type
and size can affect the frequency/impedance response too. It's many
years since I built any cabs.

Yes, it can. Part of the impedance properties of the LS unit stem from the
physical movement of the coil in the magnetic field field, altering the
'back EMF'. Changing the cabinet or its contents can alter the amount of
movement caused by a given applied audio signal, and this then changes the
current demanded. So the observed impedance changes.

However in most cases this is only likely to be obvious at low frequencies.
At high frequencies the movement for traditional 'cone and box' speakers
tends to become dominated by the mass of the driver. But it explains why
the impedance of reflex or ported or transmission line designs at LF tend
to differ from infinite baffle types. Typically with a single LF resonance
in impedance being converted into a pair. Bit like over-coupling a pair of
tuned circuits.

Slainte,

Jim

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