Stromberg-Carlson 145L acoustical labryrinth
TwoMuttHeads
was surprised to see all the cardboard. I checked the patent and it
seems to make sense. I've heard some SC consoles that had only the
backboard and not the cardboard.
Phil Nelson
I have a 440M with the acoustical labyrinth. I could never decide whether
it's a real improvement, or mostly gimmickry. It sounds nice, but so do my
other radios with comparable audio circuits and the same size speaker. If it
was such a hot idea, you would think other manufacturers would try to copy
it somehow . . .
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.htm.
TwoMuttHeads
contact.htm> wrote:
> Do you have the patent number? Patents can be interesting to read.
I looked up both patents and printed out 2,041,777. That's the one
that looks like what I have. I think the other one, 2,031,500 has a
good explanation of the how and why. The designers admit that proper
cabinet design will eliminate most of the "boominess". They also
wanted to retain a slightly smaller speaker (10") to get some treble
and use the cabinet to get lower bass response. I've seen a Truetone
cabinet with a closed back but it wasn't really sealed. Now I'm
wondering how hard it will be to get the speaker out.
Richard Knoppow
"TwoMuttHeads" <menw...@msn.com> wrote in message
news:3f54fa9a-6f35-4490...@p19g2000vbq.googlegroups.com...
The acoustic labrynth is covered in many standard texts
on acoustics. It is essentially the acoustic equivalent of a
1/4 wave matching section in RF. The idea is to provide
loading on the back of the cone at frequencies where direct
air load is low. In effect it is the same as a bass-reflex
but the reflex is a lumped constant rather than a
distributed constant (transmission line) form. Either can be
analysed as a matching filter. When either is correctly
designed and matched to the speaker they can extend flat
bass response without resonances.
Keep in mind that most radios of the period had simple
open back boxes for the speaker, not very good from an
acoustical standpoint but cheap. Stromberg-Carlson
originated the acoustical labrynth and Jensen the bass
reflex although there are Western Electric patents for what
amounts to the bass reflex which predate Jensen. Jensen
owned Bass Reflex as a trade-mark but I am not sure they had
any patents. Sometime around the late 1940's Jensen found
that bass reflex had become so nearly generic for the
enclosure that they simply released the trade-mark.
--
Richard Knoppow
Los Angeles
WB6KBL
dick...@ix.netcom.com