[R-390] R-392 help

[Roy Morgan]

At 09:20 PM 10/13/2005, Mark Huss wrote:
>Change 1;  Just got my hands on an old LS-166/U speaker.

Mark,

When I read your first post about how you helped the "RATT Rig operators, 
who liked to tune in shortwave on the secondary receiver", I imagined the 
19-inch rack mount two-speaker thing.  In one version this is known as the 
LS-206A/U.  The main compartment of this thing is divided into to parts, 
each with a transformer and speaker and each side about 8" high by 9" wide 
by 9" deep.

To refresh my memory, I found a picture of an LS-166/U speaker. It's about 
four inches square by 2-1/2 inches deep and has a big mounting bolt on one 
side face and a switch and cord on another side face.  (I presume the 
switch cuts the transformer in and out.)

>   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.

My guess is that your memory is more consistent than the equipment 
performance compared among the many, many contracts the LS-166 was 
purchased with.  The LS-166 was meant for ruggedness and dependability 
under "field" conditions.

"Holy Precipitation, Sarge, Is it EVER gonna stop raining?  We ain't seen 
the sun since Spring."

>   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.

What is it you were measuring?  The acoustic output?  The input 
impedance?  It seems unlikely that something 4 inches square would produce 
sound across a range extending to 10 Hz.  And I would not expect its input 
impedance to be very constant, either, unless there is lots of loss in the 
system as a whole (which is quite possible).

>...  changing the transformer won't work on the LS-166/U for bettter 
>lows.  At least not without changing the speaker itself.

If the LS-166 produces acoustic power more or less level down to 300 Hz, 
I'd not be too surprised.  Much below that would surprise me a lot.  By 
"changing the speaker" do you mean replacing the whole thing, speaker 
driver, transformer, case and all?  If I had to get more lows out of an 
LS-166, I'd scrap the case and transformer and build a completely new 
enclosure, likely of the bass reflex sort, and it might wind up as big as 
the LS-206.  I would expect to then figure out that the driver is 
completely wrong for the job.

>Cabinet size probibily has something to do with it, but the sound does not 
>change with the back off.

Yes, indeed!  I think the case on those I've seen is not very "sealed" - 
that is closed from air leakage from the action of the driver.  However, 
the water sealing on the thing may actually do a good job of acoustic 
sealing also.  Even if it were well sealed, there is not enough volume of 
air inside the thing to make it work well at lower frequencies.

It is very interesting to put a moderately well sealed back on our 
boatanchor speakers, such as the older Hallicrafters and black Collins 
ones, and then in addition, stuff the now-closable box with absorbing 
material. It's also very interesting to compare normal radio type speakers 
to even modest "hi-fi" type speakers.

Roy


- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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