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Old 17th March 2005, 02:45 AM   #1
DougL is offline DougL  United States
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Default Max SPL theory Question

I am designing a speaker, and have decided that 105 db one meter would be an appropriate target. My thinking was I listen at 2 meters, 92 db absolute max. So at 1 meter with dipole, add 3 db for 95 db plus 10 db headroom. So I started by specifying drivers and amplifiers so any tone would play at least 105 db, both power, thermal and Xmax.

I am bi-amping at about 300 Hz, so for pink noise, I can add 6 db.
Also, for 2 speakers, add another 6 db.
Does that bring the max volume up to 117 db for pink noise at 1 meter, two speakers driven?

This seems a bit excessive to me, but I am looking for other perspectives.

Thanks in advance.

Doug
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Old 17th March 2005, 03:48 AM   #2
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Excessive?

Nothing is truly excessive. You can never have too much.
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Old 17th March 2005, 07:36 AM   #3
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Default Re: Max SPL theory Question

Quote:
Originally posted by DougL
[B]I am designing a speaker, and have decided that 105 db one meter would be an appropriate target. My thinking was I listen at 2 meters, 92 db absolute max. So at 1 meter with dipole, add 3 db for 95 db plus 10 db headroom. So I started by specifying drivers and amplifiers so any tone would play at least 105 db, both power, thermal and Xmax.
If you need to play at 92 dB at 2 m, it will be 98 dB at 1 m (a 6 dB loss for every doubling of distance -- ignoring room load & reflections). ie REALLY loud. 10 dB is not all that much headroom.

Quote:
I am bi-amping at about 300 Hz, so for pink noise, I can add 6 db..
It doesn't add any dB -- just means you require less total power before overload if you are playing a tone below the crossover & one above the crossover.

Quote:
Also, for 2 speakers, add another 6 db.
For 2 speakers add 3 dB

Quote:
Does that bring the max volume up to 117 db for pink noise at 1 meter, two speakers driven?
No. If each speaker is able to play 105 dB without overload at 1 m, 2 speakers will provide 102 dB at 2 m (ignorning the room)

dave.
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Old 17th March 2005, 11:36 AM   #4
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Default Re: Re: Max SPL theory Question

Quote:
Originally posted by planet10


If you need to play at 92 dB at 2 m, it will be 98 dB at 1 m (a 6 dB loss for every doubling of distance -- ignoring room load & reflections).

That is correct.

As a practical matter, though, with all those reflections, I think you will find in an average room that the average SPL is only a few dB less than the 1 meter@1 watt level-wherever you are in the room. I don't think that you are going to walk 12 feet away from the speakers in a room and find that the SPL is 12 dB down from the 1 meter/1 watt measurement.




Quote:
Originally posted by planet10
For 2 speakers add 3 dB
Two speakers hooked up to a single channel will increase 3 dB over one speaker hooked up to a single channel.

I believe that two identical speakers, each powered by a separate amplifier channel playing at 1 watt, will play 6 dB louder than one speaker powered by a single amplifier channel playing at 1 watt.
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Old 17th March 2005, 11:49 AM   #5
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Default Re: Re: Re: Max SPL theory Question

Quote:
Originally posted by kelticwizard
I believe that two identical speakers, each powered by a separate amplifier channel playing at 1 watt, will play 6 dB louder than one speaker powered by a single amplifier channel playing at 1 watt.[/B]
Yes, supposedly, as long as they're also playing identical material -- but they usually do not reproduce identical sounds...
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Old 17th March 2005, 12:03 PM   #6
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Quote:
Originally posted by Gregm
Yes, supposedly, as long as they're also playing identical material -- but they usually do not reproduce identical sounds...
True, but when you are dealing with excursion requirements, we usually concentrate on the loudest sound.

Bass puts a strain on excursion, but that tends to be mixed equally between channels. Lead vocals tend to be the loudest sounds above bass-but most lead vocals are mixed equally between channels.

There is no guarantee that this need be the case, but it is true more often than not. So on the sounds that tax excursion, most of the time, both channels will be contributing equally.
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Old 17th March 2005, 01:10 PM   #7
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Default Re: Re: Re: Re: Re: Max SPL theory Question

Quote:
Originally posted by kelticwizard
[B]
...Bass puts a strain on excursion, but that tends to be mixed equally between channels. Lead vocals tend to be the loudest sounds above bass-but most lead vocals are mixed equally between channels....
Yes, yes, I see what you were getting at. I'm a bit slow at the uptake -- sorry
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Old 17th March 2005, 02:40 PM   #8
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Greg:

No need to apologize. Fact is, when I first read of the dB increase in an article, my first reaction was, "See here, each channel has different material, that's why they call it stereo....."

It took a little while for me to understand why they phrased it like that.
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Old 17th March 2005, 05:04 PM   #9
GM is offline GM  United States
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Greets!

>I am designing a speaker, and have decided that 105 db one meter would be an appropriate target.
====
OK, but depending on what source material you have, this could limit you to as little as 75dB/m average, or ~ how high folks listen to prime time TV at.
====
>I am bi-amping at about 300 Hz, so for pink noise, I can add 6 db.
====
?? What's pink noise got to do with it?
====
>Also, for 2 speakers, add another 6 db.
====
Uh-uh. We're summing SPLs in this case, which is different from adding a second driver/doubling power to a speaker, so:

10*log10(10^(SPL1/10)+10^(SPL2/10), + etc.) = 3.01dB for two identical SPLs.

Of course for stereo this will be frequency dependent due to all the source/room phase issues, but is close enough for calcing power requirements in the BW above where the room gain curve kicks in.
====
>Does that bring the max volume up to 117 db for pink noise at 1 meter, two speakers driven?
====
So far, with 105 dB/m we're at 108.01 dB/m with two speakers. In free space SPL falls at the square of distance so a 'worst case' at 2m:

108.01 - (20*log10(1/2)) = 101.99 dB/2m

Due to room issues, the average drop in the typical HI-FI/HT room is 3-4 dB, but if using the free space calc then you never have to worry about clipping the speaker and/or amp if you start with a realistic peak SPL requirement.

For most folks the DD/DTS HT reference of 105 dB peaks/channel/listening position is plenty loud so this seems a reasonable goal for most music. For symphonys and/or organ music, then up to 112 dB/channel/listening position; and if ~live levels are desired for these, up to 127 dB/channel/listening position in the 250-500 Hz BW is required if you want to experience ~ a 'front row center' seating position.

For 'headbangers', I was at one outdoor 'rockabilly' concert back in the mid '70s where I measured >130 dB peaks (kept pegging the meter)/~100yds from the stage, so factoring in all the compression they use(d) to increase average SPL and low loss over distance in the humid night air, I figure it was at least 115 dB/m average! For sure it was loud enough that my eardrums compressed and I wound up wearing plugs to keep the upper mids from painfully 'drilling' me.

GM
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Old 17th March 2005, 11:32 PM   #10
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Doug,

What are you really asking? What volume do you require? You seem to say 105 dB target for headroom then 92 dB max listening volume. Not sure what you are looking for. What is the system for?

80 dB = nice volume
90 = having to talk louder to hear each other
100 = yelling to be heard
110 = ears starting to buzz
120 = girls leave the party
130 = increased chance of nose bleed
140 = knocking the feathers off a chicken
150 = deboning the same chicken

My outdoor system with multiple drivers and amps has a theoretical top end of 130dB. Absolutely insane volume.

My indoor gear rarely exceeds 100 dB and that's only when someone puts on the Jimmy Buffett and passes me a margarita.

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