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Best way to maximize sound system setup?
March 10, 2012 3:07 AM   Subscribe

Physics/Sound Engineering/Speaker Setup Question. More = lower volume?

I'm setting up my newest bar. As always with bars, one of the concerns is to minimize the sound from the sound system that leaks out into the neighbourhood, without killing the volume level inside. Here's the question. Imagine Bar A. It has 6 large speakers spread out throughout the bar. They play on volume level 10. Imagine Bar B. It has 20 small speakers spread throughout the bar. They play on volume level 3. Will it sound just as loud inside Bar B as in Bar A?
My logic on this is that in Bar B customers will always be close to a speaker, so there's no sound "wasted" as it travels (relatively) long distances, as in Bar A. That means less leakage out of the bar and less problems with neighbours.
Any sound engineers or physics people out there can help?
Cheers.
posted by conifer to Science & Nature (13 answers total) 1 user marked this as a favorite
 
Yes, mostly. You can prove it by extrapolation: one speaker to fill an entire gymnasium with sound is going to be loud and leak sound all over the place. Compared to giving everyone in the gymnasium headphones.

The only question that remains is, does the 20 speakers setup move you close enough to the headphones side of the curve to make a difference? I would think so, but it might depend on how loud the music is supposed to sound inside the restaurant.
posted by gjc at 4:26 AM on March 10, 2012


I have read that, to be perceived as twice as loud, an audio system needs either 2x the speakers or 4x the power. I'm not totally sure that is true, but it sounds plausible, as this kind of inverse square relationship turns up all over the place in physics.
posted by thelonius at 4:55 AM on March 10, 2012


Bass is going to be your main problem, it travels through floors and walls really easily. Be really careful about where you place your subwoofers... if you don't want bass to travel as far, put them away from walls, for example.

Also, high frequency sounds are absorbed by bodies, so you need more/louder speakers where the bar is going to be busiest. They're also fairly directional, so try and make sure they're pointed inwards, (not towards open windows, etc)

There are going to be people in your city who install sound systems for bars. Ask around at other bars where you like the sound to find out who installed their systems for them. Getting someone who knows what they're doing to put it together for you is really worth the money, especially if you ever plan on having djs/dancing.
posted by empath at 5:07 AM on March 10, 2012


IF your goal is primarily to have background music, lots of little speakers at low volume scattered throughout the bar will make things more pleasant for your patrons. Everybody in the place will be able to hear the music without being near a REALLY LOUD SPEAKER.

It won't necessarily help with sound leaking out and disturbing your neighbors. 120 db is 120 db whether it's from 20 speakers on "3" or 6 speakers on "10." Sound leakage is very often an "architectural" or "environmental" problem rather than a "sound system" problem - how well are your windows, doors & vents sealed ? How close are your neighbors ? Are your busboys opening the back door 10 times an hour to take out the garbage and catch a smoke break ? What kind of neighborhood are you in ? If you're in a younger, hipper area that already has other bars & clubs and is a nightlife destination, your neighbors will probably be more tolerant of volume.

Strongly seconding empath's suggestion that you consult with a professional on this.
posted by soundguy99 at 7:36 AM on March 10, 2012


The stuff is fairly well explained in the JBL Professional Sound System Design Manual - 1999 Edition (Pt.1, Pt.2) [pdf].

The gist of it is that, in a first approximation, sound pressure waves radiating from a loudspeaker follow an inverse square law. For each doubling of distance, you get 1/4 the pressure. Or, in dB (SPL), for each doubling of distance, you lose 6 dB.

To get 1 big speaker to give you, say, 100 dB at the farthest point in the room, 16 m away (24) you'd need a speaker that produced 6 × 4 + 100 = 124 dB at 1 m. If you didn't have walls, at the street, 32 m away, you'd still have 100 - 6 = 94 dB going on.

If you arranged your speakers to that no point in the room is farther than 4 m (22) away from any speaker, ignoring the fact that the sound field would add up, to get 100 dB at any one point, you'd need speakers that did 100 + 2 × 6 = 112 dB. At 32 m, any one of them would only give you 112 - 5 × 6 = 82 dB — but you'd actually get a little more.
posted by Monday, stony Monday at 7:46 AM on March 10, 2012


But indeed soundguy99 is right — it's likely that leakage and soundproofing are going to be your actual concerns, and acoustics isn't something you can learn in an afternoon; you'll need professional help.
posted by Monday, stony Monday at 7:48 AM on March 10, 2012


Another reason to seek pro help is that if you do decide to go the "lots of smaller speakers" route, you can't just grab a bunch of home stereo stuff from the Spanish equivalent of Best Buy and hook it all up. See Speaker Impedance for a hopefully-not-too-technical explanation of why this won't work. Pros will have access to the right gear to do this properly.

Also, cheers to Monday, stony Monday for digging up the reference & demonstrating the math.
posted by soundguy99 at 8:11 AM on March 10, 2012


Thanks for the suggestions. We're in a residential neighbourhood, albeit one with lots of bars. In Barcelona, there are lots of very narrow streets, too narrow for a car, and we're on one of those. We would like to do everything, within reason, to minimize neighbour problems, although many times this is just the luck of the draw. There is almost always one neighbour who will complain no matter what one does. Our bars aren't the kind where you sit and have a quiet cocktail with your significant other, they're the kind where you come in for a good party, loud music and general debauchery. This is our third bar in Barcelona. I know the main problem is going to be leakage. To better state my question:
Will I have to turn the music up as high within the bar for it to sound as loud to a patron within the bar if I have lots of little speakers as opposed to a couple of big ones?
posted by conifer at 8:51 AM on March 10, 2012


I haven't calculated the math, but I think the answer you might be looking for is that with multiple small speakers, each speaker won't have to put out as much sound as a few large speakers would in order to fill the room (reach each patron). However, the volume on the amplifier itself will probably have to be turned up to around the same level in order to power all the speakers anyway (possibly higher due to inefficiencies multiplied over the number of speakers). A side effect of this would be that patrons will be able to sit closer to any given speaker due to its providing less of a share of the volume than a larger speaker handling a greater share of the volume coming from the amplifier.
posted by rhizome at 9:27 AM on March 10, 2012


Im using my wife's account. I am an audio engineer with training in audio production and acoustics from Boston U. More speakers will introduce phase issues which are bad. You can account for these phase issues with strategic delays between speakers but it gets complex. That said, level (loudness) intensity is a factor of proximity to the speakers. An increase of 6dB will be a doubling in level. Your 3 and 10 numbers are arbitrary. The bottom line is you need to have the speakers in close enough proximity to the listeners to equal what more distant speakers would allow for while being careful of the effects of phase. This is all determined by your seating and club size. I recommend you hire an acoustician to look at your room and help you. Every room and system are a whole new animal that require unique planning and consideration. If the combined dB output is equal in both situations hyoid only solution is isolation and not internal acoustic treatment. In other words, do not expect any acoustic absorption or diffusion to lessen bleed of (especially low frequency) sound into surrounding areas. I'll be happy to offer further assistance if you want to contact me at Matt@tweeksound.com.
posted by PrettyKnitty at 9:32 AM on March 10, 2012


Will I have to turn the music up as high within the bar for it to sound as loud to a patron within the bar if I have lots of little speakers as opposed to a couple of big ones?

Well, technically, yes.

The thing I think you're not quite grasping is that in any given audio system, the volume knob is not an absolute - it's completely relative to the power of your amplifier and the efficiency of your speakers.

"How loud is it ?" is (more-or-less) measured in dB-SPL. If you stand in the center of the room, and listen to music, and decide that 100 dB is a good party music level, you can get there with a couple of really efficient speakers and a 10,000 watt amp turned up to "3", you can get there with a couple of inefficient speakers and a 200 watt amp turned up to "11", whichever. (note that I'm totally making those numbers up.) Loud is loud, no matter how you get there.

It's like you're asking, "If I want to drive at 75 miles-per-hour, is it better to do it with a small engine at high RPM or with a big engine at low RPM ?" And the answer is, "It doesn't really matter, you're still going 75 mph and if you do that in a 25-mph-zone you're gonna be in trouble."

Now, how directional the sound is does vary with frequency - lows spread out wider & farther than highs. Low tones are large waves with high energy, and as empath points out, they can travel a long distance and transmit through building structures. So small speakers pointed inwards might help your neighbors across the street not get blasted with shrill high-end every time someone opens the door - they won't prevent the guy two blocks down and one block over from hearing a constant "thumpa-thumpa-thumpa."

Except insofar as small speakers don't do "thumpa-thumpa-thumpa" very well - but if you want a party atmosphere, you're gonna need some speakers that do.

BUT . . . the possible advantage of lots of small speakers isn't so much in the absolute measurement of dB-SPL as it is in the perception of your customers as to "how loud is "good party" loud ?" If they are surrounded by music everywhere they turn, they very well might feel that a volume that measures at, say, 90 dB is great. So you're actually providing a "good party" atmosphere at a lower absolute volume.

I don't feel like I'm explaining this very well - not to be mean, but how you're thinking about this is "almost but not quite" correct and I can't quite sort out how to correct or clarify things for you. Another reason to get a local pro involved - they can give you an actual hands-on demonstration that might clear things up for you.
posted by soundguy99 at 10:56 AM on March 10, 2012


Yeah, in all seriousness, find a bar in town with really good sound and ask them who set it up for them. It'll cost you, but it pays off so much when you have a really well designed sound system. If music as an integral part of your bar, then you should invest a little money to make sure it gets done right.

My suggestion would be lots of well placed speakers on medium volume and just a couple of strategically located sub-woofers, but a good sound guy can tell you which speakers to buy and where to put them -- it might actually save you money later on not having to buy new speakers when your current ones turn out to be a problem, or when you miswire something and blow out an amp.
posted by empath at 7:57 PM on March 10, 2012


Thanks for all the answers. I guess I'll take that as a qualified yes. We're going to give it a go with a bunch of small speakers and a powerful enough amp.
posted by conifer at 1:42 AM on March 12, 2012


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