On Tue, 26 Sep 2006 23:39:40 +0100, "Keith G"
wrote:


"Don Pearce" wrote

Your guess would be as good as mine! :-)


Eyeballing the pic of the Jericho, I reckon that's about seven feet of
line. That would put the tuning point at around 86Hz. You can expect
the output to drop pretty rapidly below that. The Fidelios will be
correspondingly higher.

The sums go like this: speed of sound (345m/sec) divided by the line
length in metres (2) divided by 2 again for half wave, which is what
you need for the back wave to reinforce the front radiation.


OK.



In a traditional transmission line speaker the line is filled with
absorber


Whaaat??

Hexcuse me - I'll have none of that *stuffing* malarky, thank you....!!

The first horns I heard were a pair I borrowed from my mate P the T (he ha
dollied them up) and my mate SN was round. They were queer upward-firing
things with Richard Allen drivers in them and had been loving stuffed with
fibre. They didn't sound particularly good, so we upended them and SN
started ripping the fibre (armfuls of it) out of 'em saying 'they don't need
all this crap' - and booger oi if they didn't sound a lot better without
it!!


which does two things - it tames the resonance peak (which is
probably what sounds like good bass in these) and slows the sound
wave, making the line effectively longer.

Which presumably means the sound goes lower, but why mess with it if they
sound good *with* a resonance peak, or am I missing summat?

Last octave or no, there's certainly no shortage of bass on these speakers -
even as I type!!


What you're hearing isn't the real deal. It is pseudo-bass - just the
harmonics of the true bass which your brain, by a bit of psychological
hocus pocus translates into an impression of actual bass. The big
resonant peak no doubt helps that along a bit. I'm not surprised your
mate's speakers sounded "better" with the stuffing out, although they
were in fact simply boomier. Get some stuffing in there to tame the
honk then add that decent sub and you will find out what bass is
really all about.



There is a really useful paper on transmission lines speakers here
http://www.t-linespeakers.org/projec.../response.html
yours is sufficiently close to a transmission line that this stuff
will apply just fine. The effect of filling on the speed of sound is
the part of main interest.



Scanned it, got a headache, bookmarked it for when I feel a bit more
brave.... :-)


Skip the details for now - just move on down to the relative speed of
sound graphs.

d

--
Pearce Consulting
http://www.pearce.uk.com