In a 7.1 home theater system,how many watts would I need per channel if each speaker is 8 feet away from me?

Question

I want powerful/satisfying sound, but I don't want to pay for extra volume I'll never use...

Answer 1

Get 7.1 if you want but most DVDs don't utilize it... You said you didn't want to pay extra...

I would get a Pioneer/Onkyo/Denon 5.1 DD/DTS receiver with 100watts per channel, then get a subwoofer (of your choice) with 250watts. You shouldn't have too much trouble finding one of these in the $300 - $400 range. The sub will probably cost you another $200. Consider spending AT LEAST as much on your speakers as you do on your receiver.

You really don't give us a price range so I don't know what "I don't want to pay for extra volume" means. A more powerful system won't necessarily be louder but will be able to recover more quickly from strenuous passages.

Answer 2

Well, it depends. It depends upon how efficient your speaker system is and how reflective your room is (i.e. wood floors or carpeting? bare walls? bare windows? low ceiling?). If you haven't experimented with a power meter to monitor how much power you are using, and/or a SPL meter to measure loudness within your room, you'd be surprised how loud just 1 watt is from 8 feet away with a speaker system of an average sensitivity rating (i.e. 90 dB @ 1w/1m). At 8 feet away, you will probably loose about 3 dB of loudness at 1 meter (approx. 3.3 feet).

90 dB = A crouded room of people talking.
95 dB = Riding in a convertable at 60 mph (with the top down)
100 dB = A typical car horn honking next to you
105 dB = A typical rock concert (average volume -not peaks)
110 dB = A semi or train horn blowing in close proximity
115 dB = A sonic boom from a fighter jet
120 dB = A canon blast from close range

That being said, a good quality receiver with 65 watts per channel RMS or more will be sufficient if your speakers are 90 dB or higher. Also, a good 12" powered subwoofer (10" if you have a small room under 200 square feet) will provide a great deal of dynamics and strength to your home theater system. Bass frequencies do need much more power to match the midrange and high frequencies, so at least 100 watt RMS powered subwoofer is recommended (200 watts RMS or more is prefered).

TO INCREASE 3 DECIBLES OF LOUDNESS IT TAKES 2 TIMES THE WATTS, so the higher the sensitivity rating of the speakers, the much less the watts you will need to reach the desired volume level.

Here are 3 examples...

EXAMPLE 1: A speaker system that is rated at 87 dB @ 1w/1m

At 1 watt driven = 87 dB
At 2 watts driven = 90 dB
At 4 watts driven = 93 dB
At 8 watts driven = 96 dB
At 16 watts driven = 99 dB
At 32 watts driven = 102 dB
At 64 watts driven = 105 dB
At 128 watts driven = 108 dB
At 256 watts driven = 111 dB
At 512 watts driven = 114 dB

EXAMPLE 2: A speaker system that is rated at 92 dB @ 1w/1m

At 1 watt driven = 92 dB
At 2 watts driven = 95 dB
At 4 watts driven = 98 dB
At 8 watts driven = 101 dB
At 16 watts driven = 104 dB
At 32 watts driven = 107 dB
At 64 watts driven = 110 dB
At 128 watts driven = 113 dB
At 256 watts driven = 116 dB
At 512 watts driven = 119 dB

EXAMPLE 1: A speaker system that is rated at 97 dB @ 1w/1m

At 1 watt driven = 97 dB
At 2 watts driven = 100 dB
At 4 watts driven = 103 dB
At 8 watts driven = 106 dB
At 16 watts driven = 109 dB
At 32 watts driven = 112 dB
At 64 watts driven = 115 dB
At 128 watts driven = 118 dB
At 256 watts driven = 121 dB
At 512 watts driven = 124 dB

To get the most efficiency from your system, try to place (or point) the tweeter height of each speaker (especially the front 3 speakers) as near to your ear's listening position as possible.

I hope this is of some help to you. If I can help you further, please e-mail me anytime.

H a p p y
H o m e
T h e a t e r i n g !

Answer 3

There are a lot of variables to consider.

Note that in the following numbers are an approximation to illustrate some of the considerations.

One of the most important variables is the efficiency of the speakers. Most (good) speakers will include a specification something like "90 db @ 1 watt @ 1 meter". This means 90 decibels output (a measure of loudness) measured 1 meter from the front of the speaker for 1 watt RMS power input (i.e. NOT "music" or "dynamic" power). The rating typically varies from a low of about 87 db (efficient) to a high of 95 db (inefficient).

If you keep in mind that decibels are non-linear, and each 3db increase in loudness (barely perceptible to the listner) requires double the input power, and that loud music can be 105-110 db, a speaker with this rating would require in the order of 35 watts to achieve this level -- and that is at 1 meter distance. Since loudness varies by the square of the distance, at 8 ft you would need about 3 times that power. (Note this all ignores the additive effect of multiple speakers and variations at different frequencies).

So ... 90 watts doesn't sound too hard, with so many "100 watts/channel AV receivers on the market, BUT ...

Manufacturers of most lower end equipment typically inflate the ratings of amplifiers. First, they take advantage of the fact music is generally transient (vs sustained) and therefore use "music power" or "dynamic power" rather than RMS power (the right way to rate an amplifier). Where "dynamic power" is essentially the number of watts available for short periods of time and RMS power is the number of watts available over a sustained period of time. There are other tricks used to distort power ratings. For example, since many amplifiers can provide more power into a 4 ohm load than into the most common 8 ohm speaker, manufacturers sometimes inflate power ratings by quoting power into 4 ohms rather than 8. Power ratings also need to take into account distortion levels since distortion rises significantly at high power. Finally, amplifiers can rarely generate rated power when all channels are driven ... in fact most can't even meet their rated power in stereo!

The end result is that a typical 100 watt/channel amplifier rating may only be accurate with only one channel driven, into 4 ohms, with 1% (or more distortion), and when measured as dynamic or music power (vs rms). When more conservatively rated as RMS power with "all channels driven into 8 ohms with 0.01% distortion", the same amplifier may actually be rated as a 10 watts/channel amplifier.

This means that achieving anything like the 90 watts required to generate the volume discribed in the introduction above is not possible with this type of amplifier.

HOWEVER, there are several points to consider that make this not as bad as it might seem. First, you would likely never need to achieve 105-110 db into all channels. And remembering the 3db pwer doubling relationship, and that a 80-90 db average volume is still quite loud, even a 10 watt RMS amplifier is probably adequate. Also remember that low frequencies require the majority of power and they should be handled by the sub-woofer -- i.e. the .1 in 7.1 -- which generally have their own amplifier so do not load the main amplifier.

Bottom line: almost any 7.1 receiver/amplifer will be adequate to generate the volume you require IF:
- the speakers are relatively efficient (ca. 90 db @ 1 watt @ 1Meter);
- you use a powered subwoofer;
- you do not intend to play very loud sustained notes (e.g. organ);
- you are not overly sensitive to distortion; and,
- you don't have a very large room.

That said, weight is a quick indicator of amplifier quality -- everything else being equal ... because heavier amplifiers generally have a better power supply.

Hope this helps

Answer 4

Watts are not directly proportional to volume. Three watts will fill a room with music. With todays solid state amplifiers at high volume, you need many watts so that you do not have to crank the volume wide open. If you do, you'll experience "clipping". That's solid state componentry's answer to "distortion". If you desire stereo, I'd recommend 100 watts perchannel or 100wX2.
It will probably be rated @ 200 watts. Quadraphonic would be 100wX4 or 400 watts total. Make certain your speakers can handle the wattage! Best wishes from an old '50's HIFI nut.

Answer 5

Your bigger issue is the 7.1. Get a 7.1 system, and it will have all the power you need. No one is making weak 7.1 systems. I recommend the Yamaha HTR series. Get one with the YPAO auto calibration system, and it will even attune itself to your room, compensating for each speaker's distance to your noggin.

Then, focus on your speakers. If you buy a choice receiver but use 18 guage wire and crappy speakers, power still won't be your issue. You don't need powerful speakers, just good ones.

Answer 6

40 watt under a 4 ohm load would be sufficient

Answer 7

You will almost certainly buy much more than you ~need~ - I never turn my equipment nearly as loud as it will go.