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Old 25th July 2002, 09:45 PM   #1
cm961 is offline cm961  Canada
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Question Speaker Efficiency

Hi guys!

Given the efficiency of the speaker, (1W 1meter), and the max R.M.S power, is it possible to calculate the max SPL at 100W 1 meter?

Pete
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Old 25th July 2002, 09:52 PM   #2
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Pete,

10 times the power gets you 10 more decibels, so since 100 watts is 10 x 10 x 1 watt, you should be +20 decibels.

This assumes perfect linearity, which you will not achieve, so your real world result will be less than this due to compression and losses. I don't know how much you could expect to lose, it would vary with the driver.

Cheers, Dan
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Old 25th July 2002, 10:20 PM   #3
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If you want to know the max spl in a room with reflective walls the result will be quite different from the ideal case of infinite baffel in an anechoic space.

It will depend on the room dimensions, frequency, etc.

There is no easy way to arrive at a specific answer. I think there are some software simulation packages that can give you an answer to this sort of problem, assuming the room is simple enough.

MR
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Old 2nd August 2002, 01:46 PM   #4
cm961 is offline cm961  Canada
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Thanks for the info guys!

Pete
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Old 2nd August 2002, 03:16 PM   #5
Eric is offline Eric  United States
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Default SPLs of room interaction

Theoretically (which NEVER happens), each "close proximity" room boundary such as walls and floors will add 3dB to the sound level. This is why corner loading your subwoofer can add up to 9dB to response in the 20-40Hz region. However, reflections from walls and other objects will cause the sound wave to interact. The results of the interactions will nodes and antinodes, some will increase your SPL while others will decrease your SPls.

Have a look at the Room Mode Calculator and plug in your room dimensions. The basic idea is that you don't want the room modes (given in Hz) to be too close to one another. You want to seem them fairly evenly spread out rather than be "clumped" together.

To more directly answer your question, each time you double your speaker input power, you add 3dB to the SPL:

If 1 watt at 1 meter = 90 dB, then
2 watts at 1 meter = 93 dB, and
4 watts at 1 meter = 96 dB... just keep adding 3 dB. The final results are, of course, subject to the limitations indicated above.

Hope this helps! Eric
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Old 5th August 2002, 01:49 PM   #6
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Yet again the myth of room boundaries adding 3dB appears!!
Every boundary actually increases low frequency sound pressure level by 6dB, easily verified by measurement and theory. Just look up in Acoustical Engineering by Olsen, amongst other classic textbooks.

Andrew
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Old 5th August 2002, 03:21 PM   #7
Eric is offline Eric  United States
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My mistake, I stand corrected.
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Old 5th August 2002, 03:33 PM   #8
AGGEMAM is offline AGGEMAM  Denmark
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Quote:
Originally posted by Eric
My mistake, I stand corrected.
Not entirely, while it is correct that in theory, each boundaery add 6 db, that only works if the point of origin of the sound is an infininetely small point placed directly in/on those boundaeries.

The effect in RL measurements varies depending on frequency between a 0 db and 6 db increase.
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Old 5th August 2002, 06:20 PM   #9
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Eric, sorry to correct you so publicly. Re reading my post, I hope I didn't come over as rude, it was not my intention.
Aggemam, I did carefully qualify my statement by saying low frequencies, and boundary reinforcement is by definition reinforcement by a boundary, not a "near" boundary!
One has to be very careful on a forum such as this to make clear the conditions that apply to statements being made. They are open to misinterpretation due to either being inconcise when making statements, or being misinterpreted when read. At least it can lead to lively discussion!
Regards

Andrew
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Old 5th August 2002, 06:34 PM   #10
Eric is offline Eric  United States
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Andrew: not a problem, thanks for your message! Indeed, sometimes more can be learned through disagreement, especially on the part of the lurkers
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