Impedance Matching Volume Control

Have a question or want to start a discussion? Post it! No Registration Necessary.  Now with pictures!

Threaded View


Hello!  I have searched the archive but can't find what I am looking for.
Similar question but mine has a little extra that I can't figure out.

I want to distribute the sound to some speakers at various location in the
house and have control of the volume locally.  Using Impedance Matching
Volume Control (IMVC) seems to be the solution.  However, If I want to add
an A/B switch in one location so that I can use the speakers in that
location for the central source or the local source, it changes the
impedance of the central circuits.

I've been told I need to use a speaker selector box (and leave them all ON
if I want) but I am not sure I understand.

Please see my installation here:
http://img518.imageshack.us/img518/4228/imvclc1.jpg

It shows want I want to do.  There are some questions too.  All the help is
welcome.


Thanks


Chris
thespade13YOUneed2removethis@yahoo.ca



Re: Impedance Matching Volume Control


Quoted text here. Click to load it

That is correct.

Quoted text here. Click to load it

Switching one set of speakers out of the central amplifier will not hurt
anything.  It will lower the load on that amp but that is
not a bad thing.  If you're using auto-former (virtually all popular impedance
matching VC's are auto-former)  volume controls,
changing the level or even switching out one room will not affect the volume in
the others.

In short, go ahead.

Quoted text here. Click to load it

That's bullshit.  You don't need a selector box.  Just set the IM circuits on
each VC at least as high as the number of speaker
pairs you're installing (ie, if you have 6 pairs, set the VC's to "8X").

Quoted text here. Click to load it

Nice drawing.  Scratch the selector box.  Switching A/B won't adversely affect
anything.  The only issue I see is you seem to be
planning to install 2 pairs of speakers peakers per volume control./  It would
be far better to install one VC for each pair of
speakers.  With 5 pairs of speakers, set each IM circuit to "8X" and you'll be
fine.

BTW, I used to install these systems for a living.  Now I just sell them online.
 Call if you need more help.

--

Regards,
Robert L Bass

=============================>
Bass Home Electronics
941-866-1100
4883 Fallcrest Circle
Sarasota Florida 34233
http://www.bassburglaralarms.com
=============================>



Re: Impedance Matching Volume Control



Thanks a lot for your reply Robert!

I have modified my drawing.  It can now be seen here:
http://img382.imageshack.us/img382/1479/imvcv2rt3.jpg

I have followed your advice to have one pair of speakers per IMVC.  It also
means that I need 2 A/B Switch (one per IMVC in that room).

Scenario 1: all speakers set to AMP 1 (assume IMVC set at 8X)
AMP 1: 1/64 +1/64+1/64+1/64+1/64 = 5/64 ? 64/5  ? 12.8 Ohm
AMP 2: 0 ????

Sceanrio 2: room 3 on Amp 2, others on AMP 1
AMP 1: 1/64+1/64+1/64= 3/64 ?64/3 ? 21.3 Ohm
AMP 2: 1/64+1/64 = 1/32 ? 32 Ohm

Are my calculations correct?  Aren't 12.8, 21.3 and 32 Ohm too high for the
amp?  What about AMP 2 in scenario 1, doesn't it see a short?)

From your previous replies to other posts, you mentionned that not all the
IMVC needs to be set at the same X level.  In my setup, room 1 and 2 will
likely always be played louder than room 3.  Maybe this changes the X level
I should set them at.


Also, please note that the second set of speakers in room 3 will be
installed at a later date IF 1 pair isn't enough/doesn't sound good enough
in that room.  Does that change anything?


Chris


Quoted text here. Click to load it



Re: Impedance Matching Volume Control


Chris,

Your new drawing is the correct way to do it.  As to figuring the IM settings,
you are correct.  Most speakers are nominal 8 Ohms.
Most amplifiers are very happy feeding an 8-Ohm load.  To keep it simple, I tell
most people to just set the IM circuits to be equal
to or greater than the number of speakers which may be fed from the same amp at
any given time.  In your case that is 5 pairs.
Since the settings are typically in powers of 2 you have correctly selected 8X.

If you have one room for which you would like to provide more power you can
safely set that room at 4X.  The system will be about
10.5 Ohms.  If you set that one room to 2X your system will present an 8-Ohm
load to the amp.  You already know the math so as long
as you don't hit the amp with an inordinately low resistance (high amperage
load) you won't hurt anything.  Beginning with a low
volume level, experiment a bit to see what sounds best.

Don't worry about a higher than spec resistance for Amp 2.  That won't hurt
anything although purists will point out that radically
altered (from design spec) loads color the audio.  If these rooms are not
primary listening rooms (i.e., it's background music) it
won't matter.

BTW, if you need additional parts (speakers, IMVC's or whatever) I sell them
online.

--

Regards,
Robert L Bass

=============================>
Bass Home Electronics
941-866-1100
4883 Fallcrest Circle
Sarasota Florida 34233
http://www.bassburglaralarms.com
=============================>


Quoted text here. Click to load it



Site Timeline