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Author Topic: Speaker system for Youth building  (Read 29807 times)

g'bye, Dick Rees

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Re: Speaker system for Youth building
« Reply #60 on: April 05, 2012, 02:14:48 pm »

Just so I am sure I am looking at this spl thing right, with a 131db rating at 1 meter and at a distance of 20' away I should be able to have 105db continuous correct? How does that translate into the various weightings? Caveats?

Kent...

You'll be able to get more than 105 at that distance.

Here's a link to an interesting bunch of sound stuff:

http://www.sfu.ca/sonic-studio/handbook/Sound_Propagation.html

From a point source the signal falls off at a rate of 6dB per doubling of distance.  If you're getting 131dB at 1 meter, then at 20 feet (approx 6 meters) you should measure somewhere around 115dB.

1 meter  : 131dB
2 meters : 125dB
4 meters : 119dB
8 meters : 113dB
16 meters : 107dB
32 meters : 101dB

My FOH at outdoor gigs tends to sit right around 75 feet from the speakers.  I'm using 2/side rated @ 128 dB continuous/box, so I figure I gain around 3dB by doubling the cabinets (40 degree horizontal on the horns) and I hit 105dB tops.  This pretty much agrees with the formula>     

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Kent Thompson

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Re: Speaker system for Youth building
« Reply #61 on: April 06, 2012, 11:17:15 am »

Kent...

You'll be able to get more than 105 at that distance.

Here's a link to an interesting bunch of sound stuff:

http://www.sfu.ca/sonic-studio/handbook/Sound_Propagation.html

From a point source the signal falls off at a rate of 6dB per doubling of distance.  If you're getting 131dB at 1 meter, then at 20 feet (approx 6 meters) you should measure somewhere around 115dB.

1 meter  : 131dB
2 meters : 125dB
4 meters : 119dB
8 meters : 113dB
16 meters : 107dB
32 meters : 101dB

My FOH at outdoor gigs tends to sit right around 75 feet from the speakers.  I'm using 2/side rated @ 128 dB continuous/box, so I figure I gain around 3dB by doubling the cabinets (40 degree horizontal on the horns) and I hit 105dB tops.  This pretty much agrees with the formula>     

Is that true even if the 1m rating is peak rather than continuous? I guess I should have stated that in my post...
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Ivan Beaver

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Re: Speaker system for Youth building
« Reply #62 on: April 06, 2012, 11:37:28 am »

Is that true even if the 1m rating is peak rather than continuous? I guess I should have stated that in my post...
The same numbers apply.  If you start with a "peak" rating-then at a distance it will still be a "peak" rating.

Of course what exactly does "peak" mean?  Some random freq that is higher than all the rest?  Or an "average" of the "peak" output?

There are all different kinds of ways of lookng at the numbers-even for the same loudspeaker.

One example I like to use is a particular cabinet-that I will not mention- who claims a "peak" output of 142dB.  And yes the cabinet will produce that-HOWEVER it is right around 1300Hz.  There is a large peak in the response there.  THE REST of the freq band is around 131-132dB max output.

So while the cabinet WILL produce that SPL-nobody wants to listen to a response that has a peak in it (especially at that freq).  So that peak has to be eq'ed down to the rest of the response.

While the manufacturer is not lying-they are not telling you the information in a way that you think it would be useful.  So when you eq that peak down, the maximum you can get out of the cabinet is 10db LESS that you would think,  That would be twice as loud.

To me-THAT is a big deal-not being able to get anywhere near the published spec-but the spec was not wrong-but how people "understand it" would lead to a wrong conclusion.

Sometimes you HAVE to dig a bit deeper.

BTW our undustry is FULL of misleading specs like that.  Not every manufacturere does it-but a lot do.  And some of the guys who say they hate misleading specs-are the worst offenders!!!!!  LIke trying  to "redirect" to say "Look how wrong he is".  While they-themselves are worse.

Kinda like politics-Let's shift the focus to someone else-so maybe they won't notice how bad I am.

But we don't want to get started going down that street.
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Ivan Beaver
Danley Sound Labs

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Kent Thompson

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Re: Speaker system for Youth building
« Reply #63 on: April 06, 2012, 11:52:29 am »

What I was trying to get to was a continuous figure from the peak figure.
Note to self put on glasses before reading spec sheets... The number I was looking for was posted lol.
« Last Edit: April 06, 2012, 12:00:48 pm by Kent Thompson »
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Ivan Beaver

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Re: Speaker system for Youth building
« Reply #64 on: April 06, 2012, 04:32:59 pm »

What I was trying to get to was a continuous figure from the peak figure.
Note to self put on glasses before reading spec sheets... The number I was looking for was posted lol.
As I was trying to say-the "peak" figure can very different things.  sometimes it is 6dB greater than the continuous rating.

Other times (especially when no other figures are given) the "peak" is some freq that is really loud-and may not be representative of what the average user would expect the cabinet to actually produce.

But it can do it (at least for a very brief time period)-so the manufacturer is not lying-just not telling the whole truth-as you would like it.

Products without complete data sheets can very often be suspect and need to be looked at very closely.

Don't just take a single figure and "try" to figure out the rest from that.  You may end up being very wrong-and not in a good way.
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Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

ProSoundWeb Community

Re: Speaker system for Youth building
« Reply #64 on: April 06, 2012, 04:32:59 pm »


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