Big room, needs how much power?

SteveLeach · 12-23-2003, 04:29 PM

Lets say the room is 22' x 16' x 9', that's about 3200 cubic feet of space to be filled with sound.
So the question is how much power am I looking for in a amp to fill this room with sound?
I'm thinking a 7.1 set up running 150 to 200 watts per.

Thoughts?

John S · 12-23-2003, 04:38 PM

I use a living room, that is about 30'x20'x10' cielings.

I use a Denon 4802, I probably could have just skated by with a Denon 3803 as I have a lot of headroom right now above "reference" type levels.

It is not quite so easy, as manufactures aren't really that truthfull about real world power in their specs.

So use the two examples as a loose guide and nothing more.

You will want a 15" Velodyne Sub sort of minimum for this large of a room though for sure. In others words, a mean arsed sub of some sort.

SteveLeach · 12-23-2003, 05:32 PM

John
If I remember the specs of the Denons correctly, you're filling your 6000 cubic feet of space with about 125W per? I guess that is a little less than I was thinking that I'd need. Your room is about twice as big as mine, so if I went with 100W per then I should be ok.

Thanks John,
Anyone else?

Chip E · 12-23-2003, 05:43 PM

I have a 20' 6" x 15' room with 8' ceilings and run a 7.1 rig..i use a B&K Ref50,Ref200.5,Ref200.2 setup. Plenty of headroom. I use an SVS PB2+ sub. The whole rig rocks my basement

JohnMW · 12-23-2003, 05:46 PM

I have roughly 8000 cu ft of space that my home theater fills with ease (check my sig)

100w per ch with be plenty if you have efficient speakers.

**HTF Ads**

MikeTz · 12-23-2003, 08:23 PM

There are a couple more considerations besides room size. Speaker efficiency, room liveliness (wood floors and windows=lively, carpet, bookshelves, curtains=moderate), and speaker impedance.

An efficient speaker with 89dB SPL/w/m or higher will require less power to reach the same volume as a less efficient speaker. For instance, you will get the same volume from a 100w/ch amplifier driving a speaker with 89dB SPL/w/m as you would with a 200w/ch amp driving a speaker with 86dB SPL/w/m. So speaker efficiency is important.

Room resonances and reflections can also make a difference. The more reflective (lively) a room is, the lower the amplifier power required to achieve an equal volume in a "deader" room.

The speaker impedance also makes a difference when considering amplifier power. Amplifier power can be reduced to a simple formula: Power=Voltage x Current and Voltage=Current x Resistance. So for a constant peak to peak voltage out of your amplifier, a speaker with half the resistance (i.e. 4 ohms vs. 8 ohms) will require twice the current. Assuming your amp can deliver the current, there will be a corresponding doubling of power. There are many amplifier design trade-offs that sometimes prevent an amplifier from doubling in power going from 8 to 4 ohm loads. But let's just say that you should understand how the amplifier being auditioned operates at both 8 and 4 ohms.

I can't recommend an amplifier power because I don't know what speakers you are considering. But if the speakers are efficient, and your room is between lively and dead, then an amplifier that is rated at 100w/ch (and doubles or nearly doubles power into 4 ohms) would be a good choice to audition in your room.

MT

Paul S · 12-23-2003, 08:37 PM

100 watts a channel will be more than sufficient. Remember, even if you double the wattage, you will come nowhere close to doubling the volume. In fact, a 200 watt amp will not go noticibly louder than a 100 watt amp. To double your volume you would have to go 10 times the power level.

As far as a sub goes, a 12 inch sub will be more than you need.

SteveLeach · 12-24-2003, 10:58 AM

Thanks for your thoughts everyone. I'm amazed at the wealth of information that is provided on this forum.

Michael R Price · 12-24-2003, 11:12 AM

Steve,

What you really need is a set of large and hopefully efficient (>90db actual efficiency, not manufacturers specification) speakers. They are the real limiting factor in output. It's mostly pointless using a 200 watt amplifier with speakers that have a single 6.5" woofer, for example. A bigger amp might sound better with small speakers, but that's because it's a better quality amplifier and not just more powerful.

With large, low efficiency tower speakers, peaks of 100 to 500 watts are not out of the question. I would personally look for high efficiency speakers so a huge expensive amp isn't necessary.

John S · 12-24-2003, 11:33 AM

I was a little paranoid about it, that is why I spent the extra bucks on the 4802, lots of headroom above reference levels, means your loud reference levels are still nice and clean.

Power is never a bad thing, and don't regret going for the extra expense of the Denon 4802.