Axiom Home Page Forums General Discussion Technical Questions What is "to fill the room" ?

As one moves further away from a sound source, the SPL decreases. Why?
Molecules lose energy often through heat.

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The actual energy loss through collisions is quite small. The main affect is pure geometrical. The farther away from the source the more surface area the sound has to go through . In open space the area goes like 4*pi*r^2, therefore the inverse square law. Think about the light energy- the closer you get to the Sun, the hotter it gets.

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The actual energy loss through collisions is quite small.

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This is a broad and inaccurate statement. Collisions of air molecules occurs more often with active movement in the medium, but we are not talking about collision of the nuclei directly here, but rather the interaction of their electron clouds, the fabric by which energy is transferred in sound waves.
The main "effect" of sound waves is not straight geometrics. Air molecules in a vacuum may apply to this principle.

The bottom line, volume is related directly to distance.
Speaker driver size is related to the movement of air.
Air movement and hence the sound that reaches our ears relates to each.
Bigger driver, bigger speaker and more power to push it, equals more air moved, more sound in a larger volume.
One can "fill the room" with sound.
The general principle is not complex.

Again, sound absorption is small. There is not much friction, or viscosity in the air. Look at this calculator - http://www.csgnetwork.com/atmossndabsorbcalc.html

The attenuation for f=1kHz is 5 dB per 1 km!!!!. It's much less than the open space 'geometric' 6 db per doubling of distance.

Gena, i don't think we are discussing the same concept, or rather in different terms.

Yes, i can hear a jet plane 10,000 feet in the air from the ground.
Does that sound "fill" the entire air space around you?
No. Sound energy is dispersed in multiple directions and lost over the distance AND volume of the medium in which it is presented.
Volume is missing from this equation as is any in room variables that apply to reverberation per my earlier post.
Quit thinking linear.

Hi all,

Bridgman's, JohnK's and Chesseroo's contributions are all useful but left out of this discussion is the simple fact that "filling the room" is really a euphemism for distortion levels as small drivers (and fewer of them) in smaller speakers have to work harder--much harder--to achieve satisfying SPLs in bigger rooms than do big multi-driver speakers.

As the small driver's excursion increases it becomes non-linear as the voice coil moves out of the magnetic gap, and distortion rises. A small speaker may begin to sound "edgy" or "congested" when it's driven beyond its limits (these are terms we used in double-blind tests of speakers, small and large) and that's what you risk when you put small compact speakers in very large rooms.

This also relates very closely to preferred loudness levels--and that can vary significantly from one person to the next.

What we can't know at Axiom is exactly what volume levels a listener prefers and the degree of absorbency or reflectivity of the listening room. So I believe "filling the room" is a kind of insurance against the potential of a listener trying to force compact speakers to reproduce very high SPLs in a big room. We know the M60 and M80 will do that and that they'll sound clean at very loud levels. Colleagues of mine often listen at levels 10 dB or more louder than I prefer, (and that is the more common scenario) with peak levels well above 100 dB SPL at the listening area.

I don't care whether customers want music "louder than life"--it can be thrilling, I know; I just want the speakers to be able to do it and still sound really clean. Besides, even "louder than life" has very different meanings. If someone frequented discoteques or heavy-metal concerts and got used to 100 dB-plus levels all the time, then that's his reference. It isn't louder than life to him or her.

Regards,

As always, I like Alan's answers...simple, too the point, and easy to understand.

Alan,
Thanks for you answer, but I'm afraid I was not quite clear with my question.

I am not comparing small and large speakers. I'm comparing small and large rooms. For the same speakers (say M60) at the same listening distance and the same power applied to the speaker - what will be the SPL difference for small and large rooms? 1 db? 3db? 5db? That was the question.

If you consider 'thinking linear' is NOT piling all the phenomena on the plate and pouring over a thick souse of vague definitions and misconceptions then, yes, I'm thinking linear.

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...Basic physics....
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If you want to talk physics you have to learn to isolate different affects and consider them in order of their importance and applicability.

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...Molecules lose energy often through heat. They lose energy by colliding with other molecules...
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...Not, the actual energy loss through absorption is small. I gave you the link...


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...Easy home experiment.
Get in the tub...
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Your water tub experiment is not what I was asking. What I was asking, in your 'rubber ducky' terms, is the following. Take your 4L pail lid and go sit in a small pond. Make waves. Notice the wave amplitude at, say 3m. Now do the same in the ocean. Will be the waves much different at 3m? I don't think so.

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...Collisions of air molecules occurs more often with active movement in the medium...
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This is not true. The collision frequency depends on the molecule size and their thermal velocity. The 'active movement' in the medium is usually sub-sonic, that is much slower than the molecules thermal velocity. Therefore, the collusions do not occur more often with 'active movement'.

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...Sound energy is dispersed in multiple directions and lost over the distance AND volume of the medium...
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How is that?

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...Volume is missing from this equation...
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What equation?

It's OK to admit that you don't know something. Just don't give a macho pseudo-science instead of a clear answer.

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It's OK to admit that you don't know something. Just don't give a macho pseudo-science instead of a clear answer.

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Perhaps Gena, you should take your own advice.
Nice jargon filled, non-explanatory sentences though.

It is quite obvious you cannot clearly express this concept of physics any more so than myself without going into a very detailed dissertation but try to keep in mind you are not the only educated person on these forums. Scientists often have differing views on molecular physics and how various models of interactions are more accepted over others and you should know that. Providing a link to one piece of information/model is not a be all end all of how this all works. I was simply stating that the ideas portrayed stayed linear (e.g. non-complex) rather than encompassing all the variables involved and that the link you provided was very generalistic of a linear (e.g. non-complex) model for which things are missing from the equation when relating it to room acoustics and driver sizes.

Fortunately your previous post clarified your initial question which makes most of the info that followed inconsequential, including Alan's succinct post answering what i also thought was what you were asking.

Speakers depend on listening distance first, room size second.

If you are in a big room and a small room, both listening at the same distance, what is going to be different? Well, let's see, first, you are going to hear the sound from the speakers. That volume will remain constant. If there are walls close on the left and right of you, the reflection of that sound will make the sound louder and sound different. Then, the sound reflected from all other angles of the room will eventually reach your ears, adding slightly to the sound level.

So, sitting at the same distance in a big and small room, the small room will sound different, and possibly "fuller" because the reflected sound will be louder, giving a surround type effect. In the bigger room, the speakers might sound more directional and a bit less loud.


So really, if the listening distance is constant, a big room and small room are just going to sound different. Not really a volume difference, but an acoustical and imaging difference. Once you start getting into this category, you are getting more into acoustics, reflections, absorbtions, room characteristics, etc.

Kind of a big bone to swallow, but, it's kind of hard to convey this effect on forums without just dragging speakers into different rooms and trying them yourself.

Those are just my two cents. If I have made a controdicictory mistake creating a black hole sucking all of my points in and collapsing my entire argument, please let me know.

But, I think you are there in terms of understanding.