[R-390] R-392 help - Green Speaker-ology
Dan Merz
djmerz at 3-cities.com
Sat Oct 15 21:10:43 EDT 2005
Ian, I've seen this transformer advertised by Antique Electronic Supply
with the comment that the Collins Collectors group prompted its production,
so I assume this is accurate. Hammond seems responsive to making items that
fill a need for old radio collectors. I haven't tried one, as I have other
types of transformers around to make the match when I've needed it. It
should be high quality based on its size, rated at 12 watts, and about $18.
Dan.
-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Ian Gallimore
Sent: Saturday, October 15, 2005 5:13 PM
To: Barry Hauser
Cc: R-390A Group
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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