i rember the old Ar adds about how low the distortion was in the
AR3s. John Crabbe of Hifi News was impressed by the bass from the AR
LSTs when he compared them with his Mk2 concrete horns many years
ago. I suppose it's swings and roundabouts. The BBC seemed to have
been worried about the effect on the roll surround at the edge of the
speaker cone, rather than the cone itself.
I'm mildy surprised that the air loading of the box is sufficient to
substantially damp resonances within the cone though. Sealed boxes
tend to use heavy speakers as part of the design, in order to keep
the fundamental resonance as low as possible and I imagine air
loading would only have a small effect on the material within the
cone, but maybe I'm wrong. I'd previously assumed that air loading
was only significant in the case of lightweight diaphragms like
electrostatics or in the damping of lightweight cones / diaphragms in
pressurised horns (i.e. throat smaller than cone).
Bass reflexes were also meant to reduce distortion too by reducing
the cone movement, but the way AR used the air in the box as the main
cone suspension is obviously effective as regards distortion. The
more gentle bass roll off in sealed boxes compared with reflexes is
also desirable of course. Noting this fairly common knowledge stuff
is a way of getting round to mention that the Isobarik principle
presumably removes the BBC objection about the effect on the roll
surround, as the air pressure behind the outside cone is much reduced
and at the same time bass extension and power handling are
Isobariks seem to have somewhat gone out of fashion, but M&K used to
make a reasonably priced Iso sub until recently, which I've heard
good reports about and wouldn't mind trying. There is a more
upmarket large UK made Iso sub (name escapes me) too, that's supposed
to be very good. As it happens, at the recent London hifi show
Martin Logan were demonstrating their new CLX electrostatic model,
the bass panels of which, they said used this principle, which sounds
intriguing. They were in a large room and weren't playing loud and
no really bassy music, but they sounded nice there.
--- In email@example.com
, "Tom Mallin" <tmallin@...>
> Yes, the air pressure certainly presses against the cone. That's
part of the idea. It keeps the cone moving linearly with less
breakup. The original AR-1 woofer from the 1950s has distortion
figures in the low bass that are probably lower than most modern
speakers which don't use acoustic suspension. About 6% at 20 Hz with
10 watts of input, and 10% with 20 watts input, as I recall. A 1970
brochure shows a medical school auditorium where four AR speakers are
used to reproduce heart sounds, which have most of their information
below 40 Hz, for the listening students.
> I have restored AR-3as and AR-5s and the bass sounds very good even
today. No, they will not play as loud in the bass as large reflex
designs, but the bass quality is special, very solid, very natural.
The old KLH 5 and especially the 12 (a musician friend had a pair in
college and I heard these a lot for a few years) also have this kind
of bass and the 6 is no slouch either.
> >>> laurie483000@... 10/7/2008 9:33 AM >>>
> I think I mentioned a while ago that I read somewhere that the BBC
> deliberately decided not to go for Acoustic suspension in their
> powered monitors as the air pressures stresses the speaker unit
> surround in a way that affects the sound. They felt that the Bass
> Reflex was a better overall compromise. I wish I could find this
> article which I did read a very long time ago (I'm sure it was by a
> --- In firstname.lastname@example.org, "Robert Greene"
> > .............................
> > 3 GF likes sealed box alignment, and actually so do I,[hey an
> > agreement!] other things being equal. I think it was a bad idea
> > historically to go away from the sealed box a la AR to the all
> > ubiquitous ported box. But not one asked me at the time!
> > And one cannot just willy nilly convert one to the other by port
> > stuffing and expect it always to work. Sometimes it works,
> > sometimes it does not. Experimentation is the rule. It is worth a
> > try but it can affect other things further up to disadvantage.
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