Home Automation - Impedance Matching Volume Control

Author

Impedance Matching Volume Control

2007-01-06, 8:28 pm

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

Robert L Bass

2007-01-06, 8:28 pm

> 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...

That is correct.

> 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.

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.

> 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...

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").

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

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
=============================>

2007-01-06, 8:28 pm

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

"Robert L Bass" <robertbass1@comcast.net> wrote in message
news:AeidnUaMOL5_BgHYnZ2dnUVZ_tyinZ2d@comcast.com...
>
> That is correct.
>
>
> 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.
>
>
> 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").
>
>
> 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
> =============================>
>
>

Robert L Bass

2007-01-06, 8:28 pm

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
=============================>

"C" <thespade13YOUneed2removethis@yahoo.ca> wrote in message news:fjbnh.13945$WB6.37022@wagner.videotron.net...
>
> 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
>
>
> "Robert L Bass" <robertbass1@comcast.net> wrote in message news:AeidnUaMOL5_BgHYnZ2dnUVZ_tyinZ2d@comcast.com...
>
>

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