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Author Topic: Low impedance passive attenuator  (Read 3310 times)

Corey Scogin

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Low impedance passive attenuator
« on: September 16, 2014, 01:27:45 pm »

I'm in the process of adding some under-balcony fills for my church and also speakers in 2 small rooms that flank the under-balcony area.  I'm using all 8-ohm speakers (EV ZX1i's) to keep the amp requirements simple (use amps we have on-hand) and because the amps are physically very close to the speakers.  I will be feeding the room speakers separate from the under-balcony fills so I can control content and volume but it would be nice to have a local attenuator in each room in case one needs to be turned down or off quickly for some reason. 

Is there a readily available product that can handle up to ~200W (to be safe) and attenuate an 8-ohm speaker for my application?  It needs to fit in a 1 or 2-gang electrical box.  A couple of Internet searches didn't yield anything promising.
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Scott Holtzman

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Re: Low impedance passive attenuator
« Reply #1 on: September 16, 2014, 01:49:44 pm »

I'm in the process of adding some under-balcony fills for my church and also speakers in 2 small rooms that flank the under-balcony area.  I'm using all 8-ohm speakers (EV ZX1i's) to keep the amp requirements simple (use amps we have on-hand) and because the amps are physically very close to the speakers.  I will be feeding the room speakers separate from the under-balcony fills so I can control content and volume but it would be nice to have a local attenuator in each room in case one needs to be turned down or off quickly for some reason. 

Is there a readily available product that can handle up to ~200W (to be safe) and attenuate an 8-ohm speaker for my application?  It needs to fit in a 1 or 2-gang electrical box.  A couple of Internet searches didn't yield anything promising.

I would use a multi-zone Lutron or Control 8 compatible amp.  You can put the wallbox with volume and source selection.  If there is video it can take care of that too.



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Lee Douglas

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Re: Low impedance passive attenuator
« Reply #2 on: September 16, 2014, 02:45:08 pm »



Is there a readily available product that can handle up to ~200W (to be safe) and attenuate I'm in the process of adding some under-balcony fills for my church and also speakers in 2 small rooms that flank the under-balcony area.  I'm using all 8-ohm speakers (EV ZX1i's) to keep the amp requirements simple (use amps we have on-hand) and because the amps are physically very close to the speakers.  I will be feeding the room speakers separate from the under-balcony fills so I can control content and volume but it would be nice to have a local attenuator in each room in case one needs to be turned down or off quickly for some reason. an 8-ohm speaker for my application?  It needs to fit in a 1 or 2-gang electrical box.  A couple of Internet searches didn't yield anything promising.

I found a 400 watt transformer based volume control at one point.  It was for a "there's no other way possible" scenario, although further prodding showed that there were in fact several other ways.  The best way ended up being a fairly simple control voltage device that allowed for a remotely placed control, with a small three wire connection, for a device to attenuate before the amp.  I'll try and look for the speaker level solution (and the thread it was in) later.  I'd also suggest that if this were truly for an easily accessed sound cut off type scenario, that a simple appropriately sized and labeled switch to break one of the connections to the speaker might be more easily sourced and installed, and provide less of a variable to become part of a problem later.  It's either on or off. 
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Corey Scogin

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Re: Low impedance passive attenuator
« Reply #3 on: September 16, 2014, 05:46:29 pm »

I would use a multi-zone Lutron or Control 8 compatible amp.  You can put the wallbox with volume and source selection.  If there is video it can take care of that too.

It's good to know that such a system exists but to keep costs low, we're sticking with the amps we have on-hand.

I'd also suggest that if this were truly for an easily accessed sound cut off type scenario, that a simple appropriately sized and labeled switch to break one of the connections to the speaker might be more easily sourced and installed, and provide less of a variable to become part of a problem later.  It's either on or off.

That's my plan.  The volume control isn't absolutely necessary but I wanted to see if there was an easily available product that fit the bill.

Thanks for the answers guys.
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Stephen Swaffer

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Re: Low impedance passive attenuator
« Reply #4 on: September 16, 2014, 11:02:27 pm »

MCM Electronics has several options-I purchased some constant impedance volume controls from them a few years ago. The other way I have done this-actually at my church is to drive a 70 V transformer with the amp, then use a 70 volt attenuator at the speaker (speaker has to have a 70 volt transformer as well).  I think MCM sells a 100 watt transformer that you can drive with an 8 ohm amp output-essentially letting you use any amp to run a 70 v system.

take a look at this:

http://www.mcmelectronics.com/product/50-7845
« Last Edit: September 16, 2014, 11:05:51 pm by Stephen Swaffer »
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Corey Scogin

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Re: Low impedance passive attenuator
« Reply #5 on: September 17, 2014, 12:51:29 am »

MCM Electronics has several options-I purchased some constant impedance volume controls from them a few years ago. The other way I have done this-actually at my church is to drive a 70 V transformer with the amp, then use a 70 volt attenuator at the speaker (speaker has to have a 70 volt transformer as well).  I think MCM sells a 100 watt transformer that you can drive with an 8 ohm amp output-essentially letting you use any amp to run a 70 v system.

take a look at this:
http://www.mcmelectronics.com/product/50-7845

That appears to be what I'm looking for. I guess I never searched for the right thing. "Impedance Matching Volume Control" are the keywords I should have been using.

I know about the option to buy transformers and use 70 volume attenuation controls...heck, there's already a 70V attenuator in one of the rooms from a previous installation.  I just didn't want to buy transformers at both ends when I'm not running very far.
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Lee Douglas

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Re: Low impedance passive attenuator
« Reply #6 on: September 17, 2014, 09:41:54 pm »

MCM Electronics has several options-I purchased some constant impedance volume controls from them a few years ago.
take a look at this:

http://www.mcmelectronics.com/product/50-7845

I tried to leave this alone all day, but just can't bring myself to do it.  This product is designed for residential use, with an RMS rating of 50 watts.  While you personally may never intentionally exceed it's rated use, someone else may well decide to "see what the system can do" and give it a good goose.  The thought of something burning up in the wall to save a couple of bucks just doesn't sit well.

If it's that close, running a remote controlled line level attenuator shouldn't be a big deal. Search through RDL's site for ideas.  Here: http://www.rdlnet.com/product.php?page=683#!prettyPhoto . Hell, even a inwall line level attenuator (http://www.crutchfield.com/S-c2hD2WlINp2/p_190LVW1W/Niles-LVW-1-White.html) would be better than cramming all that potential wattage into tiny transformers.
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Stephen Swaffer

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Re: Low impedance passive attenuator
« Reply #7 on: September 18, 2014, 08:39:33 am »

Unless you have one amp and multiple zones...which is what I understood the plan to be.
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Steve Swaffer

Corey Scogin

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Re: Low impedance passive attenuator
« Reply #8 on: September 18, 2014, 11:30:03 am »

Unless you have one amp and multiple zones...which is what I understood the plan to be.

That is the plan.  At the moment I'm going to do without a switch or attenuator and see how it goes.  If needed I'll install a switch.  If I were to run across a passive attenuator that fits the application better, I'd consider it.  I was just surprised that such a thing existed as I hadn't found any before.  I was most likely ruling out any home audio categories when searching. 

If I weren't trying to save as much money as possible by using on-hand gear, I would probably install QSC K8's in each room and use the built-in volume attenuation control circuit.  Since this particular application is low priority, I don't want to spend much money on it so that I can spend it on more important things later.

Thanks for all of the replies.
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Jason Lavoie

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Re: Low impedance passive attenuator
« Reply #9 on: September 20, 2014, 11:54:34 am »

That is the plan.  At the moment I'm going to do without a switch or attenuator and see how it goes.  If needed I'll install a switch.  If I were to run across a passive attenuator that fits the application better, I'd consider it.  I was just surprised that such a thing existed as I hadn't found any before.  I was most likely ruling out any home audio categories when searching. 

If I weren't trying to save as much money as possible by using on-hand gear, I would probably install QSC K8's in each room and use the built-in volume attenuation control circuit.  Since this particular application is low priority, I don't want to spend much money on it so that I can spend it on more important things later.

Thanks for all of the replies.

Is it literally one amp channel that you have to send to multiple places or do you have at least a couple channels to work with?
if you have separate channels you could use something like http://www.rdlnet.com/product.php?page=523 upstream of the amp and control the volume with a regular potentiometer remotely.

Unless you're talking about a lot of wattage, I think purchasing some new amps for the various zones would be cheaper than proper high wattage low Z volume controls

Jason
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Re: Low impedance passive attenuator
« Reply #9 on: September 20, 2014, 11:54:34 am »


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