Axiom Home Page Forums General Discussion Technical Questions Room size

But there's another factor: The level of the input signal and the preamp.

On my Denon, CDs are incredibly loud at -10dB, but my Comcast DVR box tuned to a digital music channel can go "0" or a few dB above that even.

Certainly, in theory you inputs should be at 1v, but the reality is that there are several variables before anything even hits that last stage of amplification.... and the volume knob.

This is why I love when someone posts that "Brand X makes great receivers because they have one and only need to go to -15dB on theirs". Or that a particular speaker should be suficiant for someone's application because they only need to turn up their volume 1/2 way to get sufficiant volume in their room.

It's all relative, and all indications are that it's not standardized.

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Given the exact same system, played at the exact same sound level in a small room, a large room and a concert hall... what is the difference?

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It all comes down to the cubic feet of area to be filled with sound.The larger the area the more it takes to fill the room.

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If I am playing something at a certain sound volume, how does the room size fit into the equation? More specifically, if I am playing my receiver at -10 with my Epic system... in a small room, in a large room, in a concert hall.... what is the difference?

Is there a difference in the work that the reciever goes through by being in a different sized room, cinsidering the exact same system played at the exact same sound level?

Or does everyone just consider the fact that if you are in a smaller room you will just play everything at a reduced level?

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Shag:
A smaller room will, because of more reflections, "fill up" easier than a very large room in comparison. If you played identical systems at a -10 level on your receiver, the sound in the small room will be louder. Of course, the multiple reflections that contribute to that louder sound also muck up your imaging.

In that above situation, a receiver will not work any harder (assuming it's still at -10dB) in a large room; it doesn't know (or care) what the room looks like, only the load that the input signal creates and the load that the speakers present. What will make a difference is that a person listening in that room might prefer turning down the volume knob to -15dB so that smaller room isn't now "too loud". IOW, 85dB is 85dB, whether you're in a closet or amphitheater. It's just that you don't have to ask the amp to give you as much gain in that smaller room to achieve the desired level.

Another factor that comes into play is that it's different at different frequencies. Asking an amp to produce satisfactory bass volume in a large room requires much more power than in a smaller room. The upper ranges are not as power hungry and don't factor in to the same degree. This is why somone with a moderately large room might end up liking M22s just fine is they're mated with a strong sub that can take much of the "hard" bass frequencies off a smaller speakers' shoulders.

Yes shag, forget the numerical setting; whatever it is, the amp output at that setting stays the same regardless of whether it's in a bathroom or Carnegie Hall. What's different of course is the sound level at the listener's position, and that depends mainly on the distance from the speakers and the size of the room. The direct sound from the speakers drops off 6dB(from the standard speaker sensitivity rating taken at a 1 meter distance)with every doubling of the distance to the listener. However, the direct sound is only part of the story and the reflected sound from room surfaces makes the actual level decrease much less than the theoretical 6dB figure if only direct sound was considered. So, although a room doesn't have to be "filled" with sound if the sound is loud enough at the listener's position, in a smaller room the reflections add more than a larger room would.

Now that shag's question has been answered I'm still kinda interested in the receiver dB scale thing.

Like Pmbuko I've got an Onkyo and the factory default scale goes to +10. But it can also be set to show a scale of 0 - 100 dB. I have it that way and a little while back I was recalibrating some M3's and noticed the dB output reading while emitting pink noise from the receiver was coincidentally within 1 dB of the actual SPL reading on my SPL meter (over an SPL range of 60-85 dB). I say coincidentaly cause I'd expect with significantly more or less efficient speakers the two wouldn't have matched so closely.

Probably for the reasons Mark Johnson mentions it doesn't mean all source music will actually be playing at the db scale shown by the receiver, but at least it gives me a decent idea of the volume.

I wonder how/why other receivers choose the relative scale they use.

Paul

My understanding on the H/Ks is that 0 is supposed to correspond to reference level (or 90db or something). Anyway, mine goes to +15, I think, although I've never had it above -10.

And what is that reference level?

We use -12dBFS as "reference" at the arena, for instance (since most of us are ex-CBC) but it could just as easily be -15dBFS or -8dBFS.

Bren R.

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Anyway, mine goes to +15, I think, although I've never had it above -10.

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That sounds about right for mine also, and lke you I've never had mine above -10.

I asked 'Uncle Tom' Cumberland, Axiom engineer, what he thought, and he said that usually most manufactures set +10 dB as the clipping of the system, whether it's a pre-amp processor or a receiver. And then they just default down 10 dB to 0. It's a meaningless thing that is simply a psychological way of telling somebody that when they get to 0 dB, they've gone as far as they should go, and + 10 would make the system clip. Now, when it comes to THX, there is in fact a standard. With a certified THX system, zero dB will reference to a recommended sound pressure level that corresponds to what the movie maker believes to be the right sound pressure level for his motion picture. So it is more meaningful in a THX system, but of course, YMMV and your situation is dictated by personal preferences and babies in the house / neighbours at the door!

>>More specifically, if I am playing my receiver at -10 with my Epic system... in a small room, in a large room, in a concert hall.... what is the difference?

VERY roughly speaking... if you are sitting at the same distance from the speakers in all three rooms you should hear almost exactly the same volume in the mid / high frequency range (where sound is relatively directional) but at lower frequencies I *think* you will have a relatively lower volume in the larger rooms. I imagine the dividing line between "same volume" and "less volume in larger room" would be around the 100-200 Hz range but that's just a guess.

The problem is that we tend to sit further away from the speakers in a larger room. When you sit further away the inverse square law comes into effect so the sound would be quieter when you sit further away.

If you have a big honkin' room but have your HT system and listening position in a small area the power requirements are about the same as for a smaller room *except* for the lowest frequencies.

If you're set up in a small corner of a large room then the "M2s + EP600" system starts to shine