Re: Best horn driver for 145?

[Brad Baker <bpb@bpbsn.cca.rockwell.com>]

"TP" == Todd A Phipps <b3nut@madison.tdsnet.com> writes:

 TP> Hi - I have a couple 145's and a 21H, and I was wondering what
 TP> the best 16 ohm horn driver was for them.  I play in a rock
 TP> context and would like a nice sing when backing off the volume
 TP> and a good bark when I light the afterburner.. ;-)

There are (at least) three 16-ohm drivers that are used. I believe all
give a brighter sound than than the original Jensen. Two require
1-3/8" adapter plates and one uses the stock mount.

Stock mount - available from fine Leslie parts and service dealers
everywhere - bolts to the original adapter plate with slight
modification. I think this one is what's in the current production 122
cabinet. Is said to be 60W - no one has reported a failure on this
list yet. Cost about $130 to $150.

EV-1829 - This is a 60W driver and is the one referred to in
"Unearthing the Mysteries of the Leslie Cabinet", April 1981,
pp130-143, by Clifford Hendricksen, Recording-Engineer/Producer
magazine. (Everyone should read this article if possible.) It's been
around quite a while, is manufactured by University (EV now). It is
said in that article to sound quite close to stock and is able to
withstand significantly higher power than the stock amplifier
provides. $130 or so - requires adapter plate.

Atlas PD-60 - Also 60W and is used often for this application. How
much brighter than stock is it? How much does it cost? It requires an
adapter plate.

I use the stock bolt-on replacement. It is a bit bright though not
objectionably so, and I am quite happy with it actually. I have not
compared it to a stock driver because, alas, all the ones in my
Leslies were blown when I got them.

 TP> Also, are there any replacement woofers that could give my 145 a
 TP> bit more bottom?

Be careful here. The bottom end of a Leslie is very much dependent
upon the characteristics of that driver. The no-feedback-from-
secondary of the 122 and the series feedback of the 145 amplifier
cause the output impedance of those amplifers to be high at
low-frequencies. The resultant damping factor allows the speaker's
resonant point to provide accentuated bass response. A speaker with a
lower Qts, or a f0 at some other frequency, will change the sound of
the bottom end quite a bit.

The FAQ says JBL models E-140, K-140 have been recommended. The E-140
has a Qts of .17, the K-140's is .21. These are very low and are
typical of loudspeakers whose suspension assemblies are stiff enough
to allow them handle 200W without turning into powder. I'm skeptical
about these drivers working well but - hey, it's just my
opinion. (plus they're 8-ohm anyway).


(and on another, but related, topic...)

The technique of adjusting feedback to adjust the bass response was
used back in the good old days of tube amplifier "hi-fidelity", back
before Thiele and others developed the electrical analog for
loudspeaker analysis and synthesis. Langford-Smith mentions somewhere
in his book (1950s) about too low of an output impedance hurting the
bass response, and he mentions some optimum numbers for damping factor
for flat bass response. Solid-state amps look like voltage sources at
low freqs, very low output Z. That's why when I replaced the Leslie's
tube amplifier with a higher power, but solid-state amplifier, the
bass response wasn't as good. Also, the so-called synthetic bass was
greatly reduced, really hurting the sound of left-hand bass. The
frequency response could be fixed by equalization. I could get all the
bass response I wanted and more. But the solid-state amp was too
linear to effectively create the synthetic bass tones. No amount of EQ
will help in this case. This is really an important characteristic of
the Leslie tube amp and driver combination and shouldn't be
overlooked IMHO.

I really wish we had the Thiele-Small parameters for the stock
woofer. This would be quite useful for comparison purposes. Also, as
long as we're wishing and hoping, a listening test with data comparing
Jensen, Atlas, EV-1829 and the bolt-on stock replacement treble
drivers would be nice. Oh yes, while you're at it, a curve of the
complex output impedance of the 122 Leslie amplifier would be useful
too.

Seriously though, if someone could provide a comparison of the treble
drivers, or perhaps setup a test... (Tony?) 

--
brad baker
bpb@cca.rockwell.com