Serge Auckland wrote:
"Bob Latham" wrote in message
...
In article ,
Serge Auckland wrote:
"Jim Lesurf" wrote in message
IIUC Some loudspeakers use a large capacitor in series with the LF
unit to alter the low frequency behaviour and interaction with the
cabinet effects. I think KEF did this with various speakers, but I
don't know how widespread the practice may be.

I haven't come across this at all, so I don't think the practice can
have been very widespread. Of course, before split power supplies were
common, solid-state power amps had a large capacitor in series with the
output, but that was for DC blocking reasons. I can't imagine why a
loudspeaker manufacturer would deliberately roll off the extreme LF,
unless it was for power-handling reasons at the time when the main
source was LPs and consequently there could be a lot of subsonic energy
due to warps and the like.
KEF did do this with models 101,103 and 105 and probably others. IIRC they
referred to it as a bass loading technique. Surprisingly, the implication
was that it increased the low frequency extension though I don't
understand the mechanism unless there was some resonance going on somehow.

Cheers,

Bob.

--
Bob Latham
Stourbridge, West Midlands

Thanks for that. I used to have a pair of 105s, and very much liked the
101s (much better than LS3/5A, I thought) and 103s, so KEF must have done
something right. I can't understand either how a series capacitance would
increase LF extension except, as you say, by some sort of resonance, perhaps
with the L equivalent component of the enclosure resonance. These KEF
'speakers were all sealed boxes, so there would be a resonance between the
air volume and cone suspension, and cone mass. Clever though!

A high-Q bass resonance and a series capacitor would give some extra
bass extension but a higher order rolloff, compared to a properly sized,
i.e. larger, box.

--
Eiron.