[R-390] R-392 help - Green Speaker-ology

Sat Oct 15 20:42:39 EDT 2005

I have an old Klipschorn I built in 1966- they are VERY efficient- have it
out in the shack- maybe I'll try it with the 390A- right now it's connected
to my McIntosh MC-60 and my Sherwood tuner- possibly could take the IF out
into the MC-60 and then into the Klipsch.

I got the plans from Paul Klipsch back in the early 60's and built a couple
of them while in the AF

They are FANTASTIC.

Sam

v
----- Original Message ----- 
From: "Ian Gallimore" <iangallimore at rogers.com>
To: "Barry Hauser" <barry at hausernet.com>
Cc: "R-390A Group" <r-390 at mailman.qth.net>
Sent: Saturday, October 15, 2005 6:13 PM
Subject: Re: [R-390] R-392 help - Green Speaker-ology

> Hi, Gang,
>
> For what it's worth, I picked up a Hammond 119 DA transformer today, wired
a
> U-77 connector to its 600 ohm primary, and connected a small 8 ohm bass
> reflex speaker I had kicking around. Much better sound from my R-392 than
> from the LS-166. Volume not huge, but quite useable. I think the Collins
> Collectors group was instrumental in getting Hammond to produce this
> transformer. Does anyone have any information on this last comment?
> If someone has a folded horn speaker, like one of the old Klipsch horns,
> which I understand are very efficient, volume might be even better.
>
> 73
>
> Ian Gallimore VA3ODA
>
> ----- Original Message ----- 
> From: "Barry Hauser" <barry at hausernet.com>
> To: "Mark Huss" <mhuss1 at bellatlantic.net>
> Cc: <r-390 at mailman.qth.net>
> Sent: Friday, October 14, 2005 12:56 AM
> Subject: Re: [R-390] R-392 help - Green Speaker-ology
>
>
> > Hi Mark & gang:
> >
> > I coulda' told ya' ... the primary limiting factor with the LS-166 (and
> > LS-454, etc.) is not necessarily the transformer, it's the basic
> > speaker/enclosure design.  They are built to be waterproof and
> > blast/concussion resistant.  The R-392 is waterproof, which was
> > bathtub-verified by one of the list members a few years ago -- and
> > actually floats, though face-down -- which is not particularly
convenient.
> > ;-)
> >
> > The LS-166 and others of the series, can be called Accidental Acoustic
> > Suspension design.  In addition, the cone is made of heavily
> > varnished/sealed cloth and has two form-fitting grilles or baskets front
> > and aft as part of the water-proofing and blast resistance,
respectively.
> > The suspension is very stiff.  Also, the intention is to cover the code
> > and voice frequency ranges, to hopefully improve intelligibility, as
with
> > other "communications" type speakers.  That's on the presumption that
much
> > of the signal content outside the range of, oh, 300-3,000 Hz is likely
to
> > be noise or not needed.
> >
> > I used to home brew speaker systems years ago -- with hightly variable
> > results -- so had studied up on it.  So here's some more background for
> > what it's worth.
> >
> > There are two basic types of speaker enclosure designs -- unsealed and
> > sealed.  For the most part, until the late 50's or so, maybe mid 60's,
the
> > unsealed were the rule.  These ranged from simple open back designs -- 
> > like many popular acccessory speakers for communications gear, to rather
> > elaborate bass-reflex designs.  It all has to do with the back-wave.
When
> > a speaker driver physically oscillates, it produces both.  For HF
> > transducers, it doesn't matter much as high frequency audio is
> > directional.  However, the back wave of a regular or LF/woofer speaker
> > cancels out much of the front wave.  If you run a woofer driver outside
of
> > an enclosure, sometimes you can barely hear it.  If you do the same with
a
> > full-range driver, it will lack bass and you'll mostly be hearing the
> > higher frequencies.
> >
> > So, a primary challenge in speaker design is to deal with the back wave.
> > Simple open back speakers sort of deal with it -- providing side walls
> > which suppress/redirect some of it.  Then there were the bass-reflex
> > designs and variants which generally attempt to make use of the energy
by
> > physically reversing the phase of the back wave and putting it out the
> > front of the enclosure through a tuned port.  Just how well in-phase it
> > becomes as well as a bunch of other parameters would determine resulting
> > frequency response and overall fidelity.  Bass reflex designs usually
> > benefitted from size --  the bigger the better -- but not always -- as
the
> > "monsters" I built proved out.
> >
> > Along came the acoustic suspension design.  The basic idea was to bottle
> > up the back wave -- but as with most things, there's a lot more to it.
> > This design is inherently less efficient, requiring more power, but
> > allowed for a more compact enclosure.  (Remember the wattage wars of the
> > old days? --  Triggered by the introduction of lower efficiency
speakers.)
> > Not only is the back wave not make use of, but sealing the enclosure
puts
> > much more physical resistance on the movement of the cone -- the driver
is
> > basically "trying to" compress and expand a given volume of air.  This
> > begat the need for more compliant suspension parts - -surround and
spider
> > (corrugated disk that supports the voice coil), yet stiffer cone
material.
> > Many drivers are specifically designed for either accoustic suspension
or
> > free-air enclosures.  In fact, some of the more extreme suspension
drivers
> > can self-destruct if operated at high volumes in free air because the
> > thing is supposed to be impeded by the trapped air and there's nothing
to
> > restrict movement.
> >
> > Anyway, you can buy a small metal speaker unit about the size of the
> > LS-166 that is acoustic suspension and will sound pretty good.  That's
> > largely because the driver is high-compliance and acoustically matched
to
> > the enclosure.  They also sell a lot of small bass-reflex speakers of
> > similar size -- they have small ports either front or back.
> >
> > Which reminds me ....   If you take an old National, or similar, open
back
> > communications speaker and place it so the back is about 12 inches from
a
> > wall, it will improve the lower frequency end.  You can experiment with
> > varying the distance -- effectively tuning the phase of the reflection
of
> > the back wave.  Also may benefit from being in a corner - as with many
> > speakers - for that and other reasons.  There are a number of other
> > relevant parameters re speaker systems, such as dealing with peak
> > resonance of the drivers and enclosures, etc.  Fortunately, I don't
> > remember the rest of it all that clearly. ;-)
> >
> > Back to the LS-166.  Here's a simple experiment -- try running it with
the
> > back off, if you haven't already, and vary its position.  There may be
> > some improvement.  However, the tinny sound is also due to its
> > construction --  the stiff, waterproofed cone and suspension materials,
> > etc. which restrict movement.  In addition, the enclosure was not
designed
> > and "tuned" for best fidelity either.
> >
> > The next step would be to replace the driver, however, I'm not sure what
> > would be the best choice.  A unit made for acoustic suspension may
require
> > higher wattage than the R-392 can put out. Probably better to use a
> > universal type and leave the back off.  There would still be the
> > limitation of the transformer, but you could use a Hammond instead.
> >
> > Or, leave the LS-166 for display and use a different speaker, or even
> > amplified computer speakers and bypass the audio stage of the R-392.
(You
> > can remove the 26A7 and reduce heat.)
> >
> > Oddly though, the speaker in the "Angry-5" -- AN/GRR-5  R-174 "gas"
> > receiver -- built into the power supply half, is of similar design -- 
> > waterproof, concussion-resistant -- front and back screens, etc.
However,
> > they sound a good deal better -- actually not all that bad.  I'm sure
part
> > of it is due to the larger enclosure space -- the power supply
section -- 
> > but the driver is somewhat different and, I suppose, other factors are
> > involved.  They were from the same time frame as the LS-166's, though.
> >
> > Probably more than you wanted to know about speakers, eh?
> >
> > Barry
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > Mark wrote:
> >
> >> Change 1;  Just got my hands on an old LS-166/U speaker.  I repeated my
> >> experiment with the low frequency cutoff of the 600 ohm to 8 ohm
> >> transformer.  Either I mis-remembered, or they changed the transformer
> >> design.  It swept 3dB down at 4 Hz to 0dB down from 10 Hz to greater
than
> >> 200kHz!  Noted a few peaks and troughs less then 3 dB from the speaker
> >> load. as I swept it.  I did note that it sounds quite as tinny as I
> >> remembered.  But the speaker itself is entirely different from what I
> >> remembered.  So changing the transformer won't work on the LS-166/U for
> >> bettter lows.  At least not without changing the speaker itself.
Cabinet
> >> size probibily has something to do with it, but the sound does not
change
> >> with the back off.  Can't do an audio sweep because the Sound Level
Meter
> >> brought the farm many moons ago.  Sorry about the bum steer.
> >>
> >> Mark Huss wrote:
> >>
> >>> That was my first thought, too.  That is why I tried Stand-By.  I
think
> >>> Barry is right.  Sounds like an AGC problem. I also own an R-390A from
> >>> 1955, Origional Collins #2792.  And if anybody has a spare PTO they
want
> >>> to part with, I am buying. (the origional one has about a khz of
'slip'
> >>> from wear).
> >>> As for the LS-166.  I actually need the UG-77 connector on it.  As a
> >>> point of note about the tinny sound.  Researched this while stationed
in
> >>> Korea for the RATT Rig operators, who liked to tune in shortwave on
the
> >>> secondary receiver.  They couldn't use stereo speakers because 2nd LT
> >>> 'Crash' Rothman objected to the 'Unauthorized Equipment'.  The little
> >>> 600 to 8 ohm transformer is the main culpret.  Manually swept it using
> >>> an audio oscillator and there is a nice rolloff below 300 hz.  Cured
the
> >>> problem by replacing the transformer with a 70.7 volt one, and
stuffing
> >>> the metal cabinet with fiberglass.  The ops were appreciative.  Said
it
> >>> sounded a lot better.  And 2nd LT 'Crash' Rothman was none the wiser.
> >>> R-392/URR, Stewart-Warner, Sn# 2681R, Order nr. 11653-PH-52.  And from
> >>> the paint on the case, belonged last to the Radio PLT, Co B, 198 Sig.
> >>
> >>
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