What size 70v taps for SC60i, SC6s, and MC60's

JoshCodes

The application is a whole house audio setup featureing a Proficient M4 selecting what audio to feed the 8-channels of a QSC CX 108V. The output of the CX108V runs to different areas of the house. Within each area, there are 70v volume controllers for each room, or each part of the room. The output from these volume controllers then runs to some combination of Polk SC60i, SC6s, and MC60's in the ceilings.

The question at hand is: what sizes of 70v taps should be installed to get the most out of each of these speakers. Polk recommends a 100w amp with these speakers so does that mean they each need a 100w tap (in which case more amps are needed)? It's no problem to turn them down but there is no point in spending the money for 100watt transformers and more amps if the speaker will fail to handle that load anyway.

Also, the system will be used to "rock out" while cooking, getting ready, and etc. and for the occasional house party but does not need to shake the walls or anything.

[Deleted User]

Hello,
Each of those speakers should be able to handle 100 watt of low distortion (always the important consideration) power. However the 70.7 volt volume control will have a certain insertion loss, meaning 1 watt produced at the amplifier will not be 1 watt at the speaker's terminal. Also the volume control will have a limited frequency response as will the matching transformer at the amplifier's end.
If fairly critical listening is a goal get the best transformers you can afford.
Regards, Ken

Dennis Gardner

Each volume knob will have its own transformer built in with 4 different wattage taps up to its max rating. You should plan to use 20 % less wattage on each channel as a rule of thumb to avoid clipping on a 70V system. When clipping occurs on a 70V system, it is very noticeable in the quality of the sound. Basically that would allow for 80 watt taps to be used on each of the 8 channels that your QSC amp has.

One consideration that hasn't been discussed is that if you are using an M4 or M6 controller, you might want to consider wiring Proficient's control pads throughout the house instead of simple volume controls. They allow for total control of sources from each room with remote control ability too.

JoshCodes

Thank you both very much for the help. Sorry if I'm kind of slow in understanding this. Some specifics might help.

Kenneth, it's not overkill to place a 100watt transformer on each speaker listed above and put each transformer on it's own channel?

Maybe my real question is will 200watts (2 SC60i's with 100watt transformers) be too much for a 10'x15' bathroom? It can always be turned down but there's no point installing that much power if it never gets turned up above 1/4 volume.

And, is 100watts from a 70.7 volt transformer w/ commercial amp the same as 100watts from a standard home amp. I know that sounds silly but I keep seeing example 70.7v setups with 5-20 watts transformers. Also, in some types of products commercial numbers are more "real / accurate" than the marketing numbers on consumer products.

Dennis, are you saying that a transformer isn't needed because a volume control like this will output a low impedance / 8-ohm signal?

Right now the M4 is being used to control a "zone / area" (mostly select what is playing, not the volume). The volume controls then determine the local volume of different parts of the zone. For example, there are four zones for which the M4 control pads determine what music is playing: Master Bedroom, Bonus Room, Lower Level (kitchen, office, living, dining, entry, etc), and Outdoors. In the "Master Bedroom Zone" there are three volume controls (shower, bath + closet, bedroom).

[Deleted User]

Hello,
Maybe a little clarification might be helpful. The "100 watt" rating for both the speakers and the transformer are merely capabilities not actual power. Think of a Michelin tire being rated for 120mph, obviously it's the engine and drivetrain that actually propel the car not the tires. They have a capability to go that fast. The same with the speakers and the transformers, they can process that amount of power into sound, but the actual amount of power comes from whatever the amplifier has.
The goal of any sound system should be have enough available power to avoid distortion at peak level demands. There are several variables that effect this, the size of the listening area, the efficiency of the speakers, the type of music and whatever volumes the listener prefers. The bigger the room, the lower the speaker's efficiency, the more demanding the music and the higher the listening volumes the more power has to be generated by the amplifier.
In all likelihood being able to deliver 100 watts per channel to each speaker is a good performance range. But, remember that's going to depend on the amplifier, not the speaker or transformer ratings.
When I used to be involved with designing "whole-house" sound systems I would recommend using a good quality 200 watt per channel power amp (Adcom GFA555 was a favorite) a combination of Adcom speaker selector boxes and Niles stepped volume controls at each location. I'm sure some of those systems are still sounding great, years later. Sometimes the layout of the room would work fine with a pair of speakers. Other times, two or three pairs were needed, Polk, KEF and Boston Acoustics were my choices for speakers.
Regards, Ken

Dennis Gardner

With the Proficient control pads, they control the signal through a network type signal that uses (for better understanding) a "preamp" type of signal to control the functions that include source changing/volume/ muting/ remote control sensor/ etc. This signal is sent back to the M4 so no transformer is needed within the wall installation, but one will still be needed at the speaker to accept the 70V signal. The use of these are by no means required, but they can really add some user friendly functions that make the installation more customized and upscale for sure. Imagine changing the source and volume from your bedside table instead of having to go into the living/media room. Of course a mixture of passive volume controls and Control Pads could be used since they operate with different signals.

I simply wanted to bring them to your attention, since I am familiar with Proficient products and wanted you to consider how they could be used.

proficientaudio.com/products/accessories/m4-a-m6-keypads