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Re: What is "to fill the room" ?
#134405 04/08/06 06:45 PM
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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.


Re: What is "to fill the room" ?
#134406 04/08/06 07:26 PM
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Nice analogy.

Re: What is "to fill the room" ?
#134407 04/09/06 02:38 PM
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Gena Offline OP
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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.


Re: What is "to fill the room" ?
#134408 04/09/06 05:36 PM
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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).


Re: What is "to fill the room" ?
#134409 04/09/06 06:32 PM
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axiomite
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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.




"Those who preach the myths of audio are ignorant of truth."
Re: What is "to fill the room" ?
#134410 04/09/06 06:36 PM
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Gena Offline OP
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You are concentrating too hard on SPL
-------
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.

________________________
Cup your hand and smack your ear. Hurts like hell doesn’t it? But yet there is no sound.
_______________________

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.


Re: What is "to fill the room" ?
#134411 04/09/06 06:45 PM
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Gena Offline OP
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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


Re: What is "to fill the room" ?
#134412 04/10/06 12:37 AM
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In reply to:

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


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.

Re: What is "to fill the room" ?
#134413 04/10/06 01:50 AM
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axiomite
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In reply to:

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.




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


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"Nothin' up my sleeve. . ." --Bullwinkle J. Moose
Re: What is "to fill the room" ?
#134414 04/10/06 01:56 AM
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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.


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