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# Help calculating the volume of the room to help select the speakers

Hi all,

This is my first time posting in this forum. I am trying to setup my first entertainment system and any advice for a beginner would be appreciated.

I have an “L” shaped vaulted ceiling room. The Home Theater will be located in one corner of the longer leg of this room. While calculating the volume of the room to help select the speakers, should I consider:

a. the volume of the entire “L” shaped room or
b. the volume of the longer leg of the room or
c. just the volume where the Home Theater is located (i.e. volume covering the home theater and the couches)?

Thanks so much for your help!

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Calculating volume really isn't necessary. What you want to do is calculate required SPL based on the distance from the speakers to the listening position. SPL decreases by 6dB for each doubling of distance. For instance, if you want 100dB capability at 4 meters you need speakers comfortable putting out 112dB at one meter. This is worst case, as with room reflections the actual decrease is less than 6dB.

On caution, almost all manufacturers fudge their maximum SPL numbers. Assume that they're overstated by at least 3dB.
The information was very helpful. I will try to read more on the SPL. Is there a recommended dBSPL at the distance where one sit and listen?

The reason I posted my original question was because, I was looking at Hsu website and they have 7 speaker packages deals (Sub+L+R+C). Each of these packages mention the room in cu. ft. it is suitable for. Some up to 2000 cu. ft. Some up to 3000, 4000, 4500, 5000 and 6000 cu.ft. Going over it in deal an hour back, I found it interesting to see that for all these 7 packages, the L+R+C is same and the Sub differs (its power increases as the room's size increases). So is it the power of the Sub and not of the L+R+C that matter when the size of the room changes?
Quote:
Originally Posted by jayshields

I found it interesting to see that for all these 7 packages, the L+R+C is same and the Sub differs (its power increases as the room's size increases). So is it the power of the Sub and not of the L+R+C that matter when the size of the room changes?
That has to do with the ability of the sub to pressurize the room, which is related to room volume. But don't automatically assume that a big room requires a big sub. Another factor is room modes, which affect subwoofer response. Taming room modes is best accomplished with using multiple subs, so you're always better off with two smaller subs than one larger one, and if the room is large enough to require more output than two subs can deliver you'll usually get best results with four smaller subs than two larger. I place a higher priority on how low the subs will go rather than how loud.
Thanks Bill for the information. I will definitely consider how low the sub can go when selecting it.

How about L+R+C? Does the size of the room or the distance determine its wattage requirement?
Hope fully a last question - Is there a recommended dBSPL at the distance where one sit and listen?
Quote:
Originally Posted by jayshields

How about L+R+C? Does the size of the room or the distance determine its wattage requirement?
Hope fully a last question - Is there a recommended dBSPL at the distance where one sit and listen?
Sound levels aren't measured in watts, they're measured in decibels, and there's no direct correlation between the two. As for SPL, if you want full blown rock concert levels you need 110-115dB at the LP. Most users find that 100-105dB at the LP is plenty.
WAF tends to lean towards 80-85dB.
A key factor you need to consider is the sensitivity rating of the speaker. This is a somewhat unreliable number from what I read, but it is as close as you will get to the number you need to turn watts into decibels.

The rating, usually somewhere between 80 and 100, although the range is larger, indicates the decibels you can expect at one meter from the speaker with one watt of power running through it. Each time you multiply the power by ten will add ten decibels, until you reach the maximum SPL of which the speaker is capable. All of these dB numbers will then decrease as your listening position moves farther from the speaker. There are online calculators that try to give you an idea of how loud you can expect your system to play given these factors and others.
Quote:
Originally Posted by Bill Fitzmaurice

Most users find that 100-105dB at the LP is plenty.

Can I please know what LP stands for? A search on it related to sound or speakers does not yield a good result - Thanks.
Listening position is my guess.
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