Re: Best horn driver...

[GOFFProf@aol.com]

Brad wrote in a very good post on speakers, drivers, etc:

>Seriously though, if someone could provide a comparison of the treble
>drivers, or perhaps setup a test... >

A little technical & historical perspective....My own unofficial $1.25 cents
worth.....
For those board members who bitch about 'long technical posts', please don't
go any further. This will be pretty boring stuff and may cause you heartburn.
 

Here goes-- Due to requests from our customers, we have seen and tested
virtually every known type of replacement driver in Leslie's, complete with
tube Leslie amps and others with high-power solid-state amp replacements.
 Other people have done this testing, including the factory. Recently,
(during the mid 1980's) when the Recora Company owned Leslie (just prior to
the HAMMOND Suzuki purchase), I was asked by the then-president od Recora,
Carl Spinoso, to test driver alternatives, as Carl and Warren Brunsting,
Manager of Product Service (now Vice-President and National Service Manager
for HAMMOND Suzuki), were also interested in finding a replacement driver for
new Leslie production. Carl's son John took over Recora after his Dad's very
untimely death, but we never were able to find a driver good enough to
replace the latest Leslie driver specially made by Atlas. Warren and I also
have gone over this topic many times over the last 10 years, and we both
still keep testing as we want to try to find a new Leslie driver. (Recora
makes many products including a neat pressure sensitive mat used in hospital
beds to help keep track of patients, and other products for the manufacturing
industry.)

In my own opinion, the Atlas PD-60, PD-60T, and other very good quality PA
drivers by EV, JBL, Altec, Eminence, etc. simply do not have the correct
power handling and freq. response characteristics to deliver the original
Leslie sound. Some 16 ohm drivers will work (as a PD-60), but due to
excessive high-freq response, differences in efficiency, lack of low end
response, and the screw-on type of mount into the plastic horn, none are
accurate enough to actually be an OEM replacement.  If they did, we would all
use them because as stock PA-type production items, they are less costly than
our custom product.  (Even the Leslie woofer is custom, as the efficiency is
critical and bass response has to be good below 16 hz.  Forget guitar
speakers, and most high power bass speakers.  Absolutely forget the
Radio-Shack 15" woofer!) 

As info, ANY screw-on driver delivers different tonal characteristics than a
bolt-on type driver, even those from the same manufacturer, identical except
for mounting method, when used in conjunction with the original Leslie
plastic horn and spindle / plate assembly.  

I certainly am aware that people use other any kind of driver and woofer as
replacements, and that's great if they like the sound. But due to our
extensive studio, touring and shop testing, all of our touring pro equipment
have the same equipment we sell mail-order, except a few custom Leslie's with
rack mounted 200 watt solid-state MOSFET amps and special crossovers, etc.
 These Leslie's also have retuned cabinets (tuning ports are radically
different) and the cabinet structure itself is beefed up so as to not rattle
apart.  Corners are sealed, added vertical struts are installed, etc.   The
physical resonance points of each cabinet are located, and a speaker
installed with a similar response characteristic.  Then the cabinet can be
"tuned" for maximum bass response.  Bass response is lessoned if the Leslie
cabinet is on wheels or otherwise off the floor.  (try it, you'll see.)

We get many Leslie's in for repair / rebuilding with blown expensive
high-power EV and JBL and Atlas drivers due to an 8 ohm woofer being
installed sometime in the past. This woofer change from 16 to 8 ohm loads the
crossover incorrectly, causing a change in crossover point from 800 hz to
around 400 hz, thus sending far too much bass to the horn.  At 12 dB per
octave attenuation (of a second order Butterworth xover), the bass level at
the original 800 hz crossover point is difficult enough for an upper driver
to handle!  Lowering the crossover point to 400 can be suicide for the upper
drivers, and they also sound different as a great deal of program material is
between 400 and 800 hz. This sound was originally in the woofer, but now is
in the horn. Think about this and how it would change the sound. 
   
Unfortunately, NO 8 ohm upper driver or woofer will suffice as a stock
replacement. When the xover freq changes, the classic HAMMOND / Leslie sound
also changes. The tube amp output transformer / crossover / upper driver and
woofer are all designed for 16 ohm use.  Another problem in high-power 16 ohm
replacement woofers is their inefficiency.  They require far too much power
to sound good, and at relatively low drive levels, say at 1/2 volume from a
Leslie amp, (15 to 20 watts) they simply do not perform at all.  Even at 40
or even 60 watts from a freshly beefed up Leslie tube amp, the high power
woofers will not be driven to their optimum drive levels.  High power
replacements require high power amps. Replacement crossovers for 8 ohm
speakers can be designed for 800 hz, but they rarely deliver the results
intended, as they load the amp incorrectly.  
None of the currently available upper driver replacements have anywhere near
the freq. response of the original Jensen, or the current Leslie replacement
driver.  The original Jensens were originally designed for bolt-on use with
4' horns used in skating rinks. The new replacement driver is a very special
design, custom made.  They are rated at 60 watts, versus the old Jensen
rating of 40 watts, so that's why so few fail in continual use. They are
generally much more efficient, can handle the bass to below 800 hz without
buring out, and have much improved "high end" response, which in our use is
really mid range, due to the highest freq of around 6000 hz.  There is NO
real high end in the classic HAMMOND sound (As Bt1055 and others always
correctly mention). 

There are always many options for speaker replacements, so owners will have
to choose for themselves.  Remember, spending more money is NOT necessarily
better or smart.  Same thing with amplifier changes and rebuilding, tubes,
etc.  This is why I personally suggest that board members always study the
issues (buying an organ, rebuilding, repairing, portablizing, etc.) and ask
questions, then make informed decisions based upon the answers received among
all of the talented owners and techs on the board.   
We may disagree on these issues, but all also have different end-results in
mind. 

(Brad and others interested -- I have plotted the original Jensen and new
Leslie driver freq. curves.  They were measured with a SPL meter and swept
from DC to above 15Khz while the driver had an actual plastic horn attached
to deliver correct loading.  Take the horn away and the test is useless!
  The new Eminence driver (16 ohm) is also plotted, as it was the real
subject of the test.  The others were for reference.   

I'm always looking for new drivers to test, so please let me know if you find
a particularly good one.  A-B tests are the only way to go.  (Mark & Will--
get ready; gas up the truck!)

Al