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

I frequently see an expression "to fill the room". As in "... you can't fill a big room with that speaker...".

I'm trying to understand what it is. To me, the size of the room per se should not matter, shouldn’t it? It's not like a bucket that needs to be filled with water. The room's wall and the reflections, I think, should play a much bigger role. Indeed, if the walls are made of an absolute sound absorber it wouldn't matter whether the room is 100 cubic feet or 10,000 cubic feet. It will be the same as outside in the open space.

When I read speaker specs the difference in the efficiencies in-room and in anechoic camera is only 3 dB. This is peanuts. So the only thing that should matter is the distance from the speaker, not the size of the room. Ok, ok, those measly 3 dB..

Gena, the meaning isn't clear, but it appears to arise out of an overestimation of amplifier power and speaker sound output needed in big rooms. Taken literally, of course there has to be some sound level in all parts of the room, so in that sense it's "filled". But the desired sound level at the listener's position is the relevant consideration and this can be at least roughly calculated. In addition, your own recent tests have put good numbers out and showed that even for your large room the actual power required at your 4 meter listening position was only a bit more than a fourth of what the inverse square law would require if only direct sound was considered.

Ok, that's what I hoped to hear. So the size of the room enters primarily through the distance from the speaker, not as a volume to be filled. In particular, the height of the ceiling should not play that big of a role. Again, within the 3dB of the 'room gain'.

Gena, volume is a factor(for the reverberent field, it makes no difference to the direct sound), but not to the extent that seems to be sometimes imagined(e.g. twice the room volume in no way requires twice the amplifier power or twice the speaker output to get the same level at a listener's position). The Linkwitz and Voelker material on room acoustics that was previously linked includes volume considerations in the analysis. Incidentally, out of curiosity, even before you reported the latest SPL numbers on your room I'd run it through the speech intelligibility calculator at the MCSquared site which has some pretty good calculators I use when I get lazy and don't want to do the math(nearly all the time). I used a 120 degree horizontal dispersion factor for the M60 and came up with about a 9' "critical distance" which I fooled around with to get some theoretical sound numbers which your measured values were in good agreement with.

The way I understand it - say, I'm reading a book using a desk lamp as a light source. Well, I will see the pages almost equally well whether I'm sitting in a small room or in a huge dark castle. The lamp is right here, it does not need to 'fill' the castle.

Again, theoretically the light intensity will be a bit higher in a small room with white ceiling and walls but, by no meas, not even by a factor 2.

regards,
Gena

That's right; in the light example the total light on the book would be just a tiny bit higher in the small white room. In a sound measurement though, the strength of the reverberent sound is equal to the strength of the direct sound at the "critical distance"(the total sound is therefore 3dB higher than either at that point)and at longer distances, as the direct sound continues to fall off at 6dB per doubling of distance while the reverberent sound is essentially constant at home distances, the reverberent sound is the principal sound factor.

I've always felt that "fill the room" was relevant primarily when making a subwoofer decision. Is this accurate?

There are obviously conflicting views on this

My take is that distance matters for the mains and surrounds, while volume matters more for subwoofers. To earlier comments, sure it's only a few dB we are talking about but a few dB can translate into twice the amplifier power or twice the number of drivers in a speaker so it does make a difference...

In my case I was running M2s with a good sub and found them to be a VERY capable music system when I was sitting relatively close (say 6-8 feet) but as I moved further away and had to turn up the volume to keep the same SPL the M2s hit their limits pretty quickly. M60s in the same scenario had no problems playing cleanly at a "loud" SPL for a listener anywhere in the (13 x 23) room.

Thanks John. That is sorta what I figured. Speakers=listening area; subwoofer=room area, including (perhaps) adjoining open spaces(?).

Room volume is not dependant on what again?
Are you mad?

Sound is about the movement of air and the molecules that make up air. Sound is very much a volume related concept just as it is distance. Energy is the key word here.

Reverberation plays a large factor as the energy from those air molecules hits and reflects off of walls. The surface material then comes into play before you can make any calculations about how effective a reverberation effect will be in any given room. The preceding assumption on reverberation effect seems to only account for bare walls. Check that assumption at the door.

As one moves further away from a sound source, the SPL decreases. Why?
Molecules lose energy often through heat. They lose energy by colliding with other molecules and transferring a partial part of that energy in the process, the remaining is lost as heat (sometimes light depending on the molecules colliding). In a larger room, the amount of energy lost (and number of molecules involved) by the time a molecule hits a reflective surface will determine the amount of energy remaining by the time that sound wave hits the ear. Larger room, more volume, greater distance to each surface, more molecules available for pushing (in numbers, not density but numbers relate to a linear distance nonetheless), more resistance to an endpoint (again in a linear concept) as well. A small driver can move x # molecules per sq area, less than a larger driver of same design. Sound is about moving air and i'm sorry, but a larger driver in a larger speaker moves more air. It can "fill" a larger room with sound much easier than a small speaker with small drivers simply because it can move more air molecules. This requires more energy to do.

Easy home experiment.
Get in the tub.
Take a spoon and a lid for a 4L ice cream pail.
Push both through the water and tell me how much water moves (wave size) in your tub and how much resistance energy you require to push each of them. Yet, notice, do waves from both of these actions still make it to the wall of the tub? Of course, but at what size? At what equivalent uses of energy?
Air in rooms is finite (when sealed). There is always resistance.
Basic physics.

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.

__________________
...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...
____________________________
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.

_____________________________
...Collisions of air molecules occurs more often with active movement in the medium...
____________________________
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.

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

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I agree with Sonic.

Is it just me or does Gena come up with some weird sh!t sometimes?

Do folks like you *ever* take a moment to enjoy your systems Gena?

Yeah, I'm not into trying to figure out how everything works, I just wanna relax, watch a movie, listen to some music and not worry what part of the room the electrons are ending up in, as long as they sound good.

God loves diversity.

We've all got our own endearing idiosynchrasies.

The official motto of the American Homebrewers Association is "Relax, Don't Worry, Have a Homebrew".

I'm gravitating to JohnK's sig line more all the time.

BB, i enjoy my system every time i get, but much like those crazed modkit and tweakers have an interest in finding way to make things sound better, some of us have a keen interest in the science behind the system and want to know why it sounds the way it does.
To each his own.

Bob, it's not you

Doesn't it interest you, how things work technicaly? The forum, btw, is called technical questions.

I actually thought it was a good question. I had wondered myself how relative room size is to bookshelves if you're only using a small portion of a large room for music listening.

I think the question should have been emailed to Bose though, we all know they're the experts on speakers that produce 'room-filling sound'.

I actually think it is interesting, up until the point I feel like I've been educated beyond my intelligence But it is great to see so many knowledgeble folks with different interests.

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I think the question should have been emailed to Bose though, we all know they're the experts on speakers that produce 'room-filling sound'.

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While this may have been in jest, Mirage does have an opinion on this.

They base the design of their speakers on the theory that a lot of the sound we hear is reflected sound. This is true in a lot of cases (how often are we in open fields?). That being said, the smaller the room, the greater the reflections. I believe that Decware also bases their room designs paying close attention to primary and secondary reflected waves (anything beoynd that is neglected due to energy losses and time delays). Thus, the perceived sound loudness should be greater in a small room than a larger room at the same output level. How much louder? That would have to be measured and would also be dependent on room finishes.

You guys are right...this *is* the technical forum and I should know better than to type while having a good beer buzz going on. Lord, I apologize (and be with the starving Pygmies down in New Guyana).

Carry on you geeks, strike that ... you technical people you! <----<<<< (look ... a smiley!)

The size of the room does make a difference, no matter how far away you are from the source of “air movement”. Sound does bounce around a bit.

Instead of getting into a technical debate, I’ll use one example that anyone who’s ever served in the military can relate to.

Percussion grenades………

Twelve bad guys in a 100,000 cubic foot gymnasium. One toss into the gym. They all get their ears rang, but they can all still shoot just fine. Don’t go in.

Same twelve bad guys in 767’s first class compartment of abut 2500 cubic foot. One toss into the compartment. They will all be disorientated and unable to react quickly.


Think of the M3’s as one grenade and the M80’s as four. Four well placed grenades in that gymnasium will definitely improve the operation’s odds of success.

Nice analogy.

Mike,

First, please don’t take it as a personal attack; nothing can be farther from the truth.
We are talking about very specific issue and the difference in opinions should be only welcomed.

Since this issue is technical I feel that it MUST be argued on a technical basis. I can’t relate to the military service. While your example looks compelling, I also doubt that many of the forum participants have used or watched, or heard, besides watching war movies real explosion from hand grenades.

So let’s go back to the realm of cold facts. It happened, I did these measurements (sorry, I like to measure) several days ago, but the thread was dieing so I let it go. Now, when we have returned to the subject, I feel it’s necessary to publish the data for nothing, but dispelling certain myths and misconceptions.

So, here is the experiment. It happens that my listening area in the basement is adjusted to the office room. The listening room size is 16’x29’x9’=4,176 cubic feet. Let’s call it Large Room. The office area is 15’x15’x8’=1,800 cubic feet. Let’s call it Small Room. I moved one of my m60 (HEAVY!) back and forth and played the receiver’s calibration pink noise on that channel at the same level. There is a door between the rooms, so they can be isolated and the rooms are “typical” = carpeted floor, drywall walls and ceiling. I measured the SPL using C-scale, slow, at different distances from the speaker and here are the results:


Distance 3' 6' 12'
Small room 80dB 78dB 75dB
Large room 79dB 77dB 75dB

We see there is a very small (if any) difference at 1dB. Even that difference can be attributed to the accuracy of the Radio Shack meter. At my listening distance 12 feet there is no difference.

Here are the facts. And let me reiterate my conclusion. The room size has a very small effect on the sound level at the same listening distance and at the same power output. The major factor is the distance from the speaker. The room size comes as a factor indirectly, simply because the listeners can sit farther away from the speakers.

Now, back to the music.

No Gena, same thing. I said “percussion” grenade. Very big difference with them and a typical explosive devise. Percussion grenades use sound energy to disorientate and immobilize. The key word being energy. They pressurize an area with ‘sound’ energy. The larger the space, the lesser an effect they will have.

Same principle applies with underwater noise. Ever dive? The energy from sound under water can be very uncomfortable.

You are concentrating too hard on SPL. There are other factors here as well. Cup your hand and smack your ear. Hurts like hell doesn’t it? But yet there is no sound. It is this energy that also plays into the perception that a listener will have while listening to sound from two separate speakers (one large, one small).

No one has reported inaccurate information here.
Both views are right but which question is being asked has been obscured. I'll try taking another stab at this at the risk of falling short of a complete (technical) explanation.
1) Does a same size speaker in a small room vs. a larger room have higher or lesser SPL at the same listening distance?
No. Gena measured this and is supported by sound principles (pardon the pun).
2) Does a small vs large speaker have higher or lesser SPL at the same listening distance in a small vs. a larger room?
In a linear distance sitting in front of a speaker, small or large room, Gena is correct. The SPL will still be the same. That is an undebated fact. Mdrew (and earlier myself) has also tried to point out the change that occurs in using a smaller vs. a large speaker in a small vs. a large room is where room volume plays a role.
So, question 3) Will the sound from a small vs. a larger speaker be different in a small vs. a larger room? (the idea of 'filling the room'). This question now depends on more variables which throughout this thread have been presented, but have perhaps gone beyond what Gena was originally investigating.
To me, filling the room with sound does not equate to straight dB but rather, the ability of a speaker to provide good imaging across a larger area (and again, volume since more than one linear direction, such as listening only directly in front of a speaker, is being suggested; up, down left or right).

With a larger room there are greater distances to side walls, ceilings, certainly. Will SPL differ between a small and large speaker at a 9' distance sitting directly in front of the speakers in that room? No, not within the dB range already noted by Gena and JohnK.
However, sit off axis, left, right, up, down from a large speaker driver compared to a small speaker driver, and room volume (again directly related to linear distances) makes a difference, primarily b/c in a small room, one cannot move that far off-axis (or very far period) from a speaker. Some of the largest sound changes occur by shifting even slightly left or right, up or down and with a larger room, more spread in the speaker spacing, the issue of smaller and larger drivers now comes into play. Straight SPL does not say anything about the sound dispersion (e.g. imaging).

If i can go back to my rubber ducky idea of a spoon vs an ice cream pail lid to make waves in water, yes, at 3m the wave amplitude may be the same in a tub or in the sea, but how wide is the spoon produced wave compared to the pail lid produced wave?

Perhaps the specs of off-axis response should be brought into this thread since i believe it is more the topic of discussion when referring to "filling the room with sound", but that is my interpretation of the expression..
I was playing around with off-axis dispersion when i first bought my large Tannoy speakers. I could move something like 2 feet to the left or right of the speaker and receive a pretty equal sound quality. If i move only a foot to the right of my M60, the sound begins to change. Don't quote me on the distances (try it yourself and see), it was awhile back that i played with this, but the conclusion is the same.
Electrostatic speakers are good examples of 'larger' units that provide an amazingly wide dispersion in this regard.
Another fun test i did was to play pink noise and then squat down and slowly stand up in front of a speaker. Listen to the sound change as your ear becomes level with each distinct driver. Find a speaker that reduces the change in noise over a wider distance and you have a 'better' room filling speaker IMO. The only way i know to do that is by using a larger driver.

You are concentrating too hard on SPL
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Mike, that what determines the intensity of sound. I don't know what you mean by 'sound energy'. The full acoustic energy? The energy per unit volume? The flow of energy per unit area? It's very hard to compare apples to apples unless we agree on what we compare and definitions. The SPL is a standard value, it has units, it can be measured and can be compared.

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Cup your hand and smack your ear. Hurts like hell doesn’t it? But yet there is no sound.
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What is it then? By smacking you ear you created a high SPL sound wave. At a high intensity you don' hear it as a 'sound' but rather it feels like pain, since the SPL exceeds the pain threshold. It' the same idea behind "concussion" grenades. By the way, the term 'percussion ' grenade refers to the old type of grenades that explode on impact. They are not used anymore, instead timed fuses are used.

From Wikpedia:
The percussion grenade detonates with impact. Timed fuse grenades are usually preferred because percussion grenades could explode while being carried. Some percussion grenades have a slow fuse as a backup ignitor. Some militaries have also created and used percussion grenade guns in the past.

Good point about the axial dispersion. It's beyond my knowledge and understanding. It's too complicated, I'm used to a more simple models

I also agree on the point that there is no correct or incorrect views here. I consider it as an excellent opportunity to exchange different views and ideas and to learn something.

Regards,
Gena

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The larger the space, the lesser an effect they will have.

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SPL is king. No two ways about it. Regarless of room size. A person closer to any given sound source will hear it louder than a person further away. The only reason concussion grenades are more effective in smaller rooms is that you can only be so far away.

For example, I'm sure you could disorient quite a few people standing close together in an open field if you were to toss on in their midst.

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For example, I'm sure you could disorient quite a few people standing close together in an open field if you were to toss on in their midst.

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Time for a field test. We just need a couple of volunteers. . .

Percussion is slang. The “correct” name is overpressure. It is also referred as concussion as you most clearly pointed out. The slang term was derived from a combination of pressure and concussion. I should have known to be specific with an engineer.

It works off pressure waves created by the explosive charge. The overpressure damages the inner ear causing disorientation, and fatality if that is the desired outcome. They are more effective than stun grenades as stun grenades only effect optical sensory and recovery is commonly within seconds.

So, bad example after all. I tried to use common sense to demonstrate the effects of sound waves. I should have known better. I give up.

You'll know it when you hear and feel it.