[HAM] Speakers and frequencies .. what's it all about

[Kon Zissis]

Hi Benjamin.
Thank you for your reply and the crossover calculation link.
Judging by the replies that I have  received about this , It looks like
the best option is to replace the stock 925 amplifiers and power supply
with a new power supply and a new high power stereo amplifier that can
safely be used as a biamped stereo amplifier with an active in line
crossover or  in the bridged configuration .  
 
I understand that the active in-line  crossovers are used in  a biamped
system in order to minimise inter modulation distortion especially in
very high quality  hi fi systems , however in the real world application
of Leslie speakers,  the Leslie 122  , 147 etc  which have passive
crossovers still sound great and my own modified Leslie 122 that I often
use with an external solid state amplifier  still has the stock  Leslie
800 Hz crossover ( but  I have replaced the original old capacitors with
new polypropylene capacitors of the correct stock specs  ) and this
Leslie 122 which has the JBL 2482  treble driver in it ( which is the
same treble driver as that  in  the Leslie 925 ) and my this Leslie 122
sounds better than my friend's stock Leslie 925.    Even though there is
a passive crossover , there is no noticeable problem with inter
modulation distortion. As well as that , I did an experiment to see if
the stock Leslie 122 passive crossover  causes any volume level loss . I
disconnected the speaker wires from the crossover and I then joined the
bass speaker and the treble driver directly together in parallel and I
then fed the direct audio signal from the power amplifier to the
speakers and there was hardly any noticeable difference in the volume
levels of the sound  so therefore it appears that the stock Leslie 122 /
147  crossover is of a decent design that does not produce a noticeable
signal loss. 
 
Because my own Leslie 122 with the JBL 2482 treble driver and the
passive crossover and an external solid state amplifier  sounds better
than my friend's biamped Leslie 925 , I decided  that it would be a good
idea to replace the old and primitive  quality  stock biamped 925
amplifier  with a new high power amplifier  and a passive crossover
similar to how the  stock Leslie crossovers are wired up.  
 
The tech Bruce Wahler of Ashby Solutions told me that he also prefers to
use  mono high power amplifiers with passive crossovers  in his
customized high power Leslies.
 
Because the Leslie  925 has a 4 ohms speaker , I would have to change
the inductor  value in order to take into account the 4 ohms.
 
If my friend  does decide to replace the stock 4 ohms speaker with an 8
ohms speaker , then I could just use the same passive crossover
component values as that of the stock  Leslie 122 crossover ( 5.2 milli
Henry  inductor and 12.5 uf capacitor for the bass speaker and 3.2 milli
henry inductor and 7.8 uf capacitor for the treble  driver  ) because I
used to have  an 8 ohms bass speaker in my modified Leslie 122 with the
solid state amplifier , and the impedance mismatch did  not cause any
frequency response gap or adversely affect the sound quality   in any
other way.  Apparently if an 8 ohms bass speaker is used , then a lower
crossover frequency is sent to the treble driver but this is not a
problem with my Leslie 122 because the JBL 2482 can safely go down to
around 300 Hz at 120 watts RMS .
 
I understand that if you are using the stock Leslie 122 / 147 amplifier
then both the bass speaker and the treble driver need to be 16 ohms in
order to not damage the output transformer.
All the best.
Kon 
 
-----Original Message-----
From: benjamin [mailto:benjaminmassy at hotmail.com] 
Sent: Friday, 28 December 2007 6:47 AM
To: kziss at ozemail.com.au; hammond at zeni.net
Cc: benjaminmassy at hotmail.com
Subject: Speakers and frequencies .. what's it all about
 
Hello Kon , 
 
Very nice  to find somebody who respects good music-reproduction within
our fysical limits of hearing . Me to, I am leaving the scene if it is
to loud and the risk of eardamage is to high . 
 
Now about your your Bi amped 925  project : 
 
First of all the passive 12 db slope is a problem to make with coils and
caps between the amp output and the speakers , why , because the coils
and caps you need are loosing a lot of power since they will have to
pass high currents and these components do have an internal resistor
that you will have to take in account . plus for 12 db slope you need a
lot of coils and caps .... in short : to much for what the results will
be . Also it will put a difficult load on your amps since part of it is
capacitive load and the other part is an inductive load combined with
the speaker impedance , it could give unpredictable results in some
cases..even burning out your amp by oscilation and if it is supersonic
oscilation you will not even notice it unless you have attached an
osciloscope to see what happens; in short  an amp is build for a certain
application and a certain load that is matched to it ; 
 
second point : the gain by doubling the power output is only 3 dB louder
theoretically , practically there will be no noticable gain here if you
take into account the losses you will have by the passive components
between speakers and amp 
 
third point ; do you know why speakersystems are split up in active
systems ?  mainly because of  to avoid DISTORTION  , the distortion that
you get is the mixing product of different frequencies  and is called
intermodulation distortion , I give you an example:  if you have two
frequencies entering an amp  like 100 HZ and 2000 HZ  ; since no     amp
is completely linear in amplification there will be produced mix
frequencies and they will be the 2000 Hz minus 100 Hz  thus 1900 Hz and
also the 2000 Hz plus the 100 Hz thus 2100 Hz  so your amp will produce
at the speaker  not only 100 and 2000 Hz but also 1900Hz and 2100 Hz
plus the harmonics from these frequencies .. if you have only harmonical
distortion  you have not a big problem since the harmonics are sounding
ok  ( every octave is the double from the one that sounds lower so
harmonic distortion is not a bad thing that it will give you an ugly
sound) , but the Intermodulation products  from the intermodulation
distortion    , These are very bad in the ear ! unless you like that
sound , but most people don't like it ; 
so to avoid these bad distortions , music systems are split up in active
frequency splitted amps and speakersystems ... that is the whole secret
.. 
If you are going to distroy this principle you will always have a bad or
worse reproduction then the original and in this case practically no
gain , or marginally in sound production .. 
the distortion  is mostly in the end or power  amplification  , it is
rarely in a preamp since preamps have to deal with low power low voltage
signals , but in the high voltage , high current portion of the final
amps , there is what you get from distortion due to non linear behaviour
of the circuits ; 
 
If your friend wants to make it sound louder then let him buy a second
925  instead of spoiling his system that he owns now . or buy a tuneable
active preamp splitsystem that is used in caraudio and put more powerful
amps in the 925 , but DON'T try to filter after the amp.. this is the
wrong way of doing ; 
 
I give you here some calculations and a bit of insight about
speakerfiltering on this link
http://64.233.183.104/search?q=cache:lx2-F3scZOIJ:www.bcae1.com/passxovr
.htm+passive+crossover+filter+calculation
<http://64.233.183.104/search?q=cache:lx2-F3scZOIJ:www.bcae1.com/passxov
r.htm+passive+crossover+filter+calculation&hl=nl&ct=clnk&cd=1&gl=be>
&hl=nl&ct=clnk&cd=1&gl=be
 
So dear friend Kon , I am sorry for my bad English , but I tried to
explain you and some other non technical people what it all is about . 
Hope it helps you and some other people . 
 
all the best from Belgiums  Benjamin  ( and yes 16 Hz is a revelation to
feel in the belly and to let it blow away your pants )   :-))