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Speaker efficiency vs. power requirements

Recently someone gave me the "math" behind speaker efficiency ratings and power requirements. Although I am not sure if the information below is 100% accurate, it is what I have been told. Can we lay this on the table for discussion and try to resolve this confusing issue once and for all?

0 db is a power ratio of 1. Records and tape have dynamic ranges of 30-40db. To achieve a 30db dynamic range requires a power ratio of 1,000:1 and 40 db requires 10,000:1. So if you assign 1 watt of power to a speaker yielding 90db SPL, you need 1000 watts to deliver a true 30db dynamic range. With digital material we find dynamic ranges of 60-70db requiring power ratios of 1,000,000:1 & 10,000,000:1 respectively. Power amps of 1-10 million watts are not feasible today but the point is, more power offers more dynamic realism. Forget power vs. loudness because that really is not a factor in the overall scheme.
bwhite
ezmeralda11
303 posts
 
I may have screwed up in my previous post. But I don't want to think about it anymore. Try this.

Based on a 90db efficient speaker.

Desired SPL Needed Power
90db 1 watt
100db 10watt
110db 100watt
120db 1,000watt
130db 10,000watt
140db 100,000watt
150db 1,000,000watt
160db 10,000,000watt
killerpiglet
373 posts
 
And that would give you a dynamic range of 160db, and it'll probably kill you along the way!
bwhite OP
807 posts
 
Hello great information and thanks for the input - just to clarify - the information I posted at the top is NOT my conclusion. This is however what *I* was told by someone who claims to know this stuff. As I pondered the statement, I grew unsatisfied with the logic and chose to post for discussion.

To clear some things up for some of you:
The mention of 90db is in regard to the speaker efficiency. I believe this number was selected since it was the rating of my speakers.

Another couple questions to further enhance this discussion:

1) Given the rated efficiency of a speaker - how does the Ohms rating effect power requirements? For example, a 90db speaker at 6Ohms.

2) Depending on which speaker, isn't it true that different frequency requirements may have more or less efficiency at varying ohms? What does this do to the overall power requirements?

And to top it off, what about impedance?
fatparrot
1,314 posts
 
Just to further complicate the issue... a 3 db increase doubles the power (wattage). To double VOLTAGE, it takes a 6 db increase.
sean
6,229 posts
 
Drjjpdc: Your comment "Therefore a 200 watt amp has twice the wattage of a 100 watt amp and is only 3 db louder, which is about the limits that you can detect by ear." is WAY off base. I use a dB meter on a daily basis at work and differences of less than 1 dB are easily discernable on my less than "hi resolution" test bench using a 4" communications grade speaker and test tones. Some people have demonstrated hearing differences down into the millibel range under test conditions.

Herman: 100 dB's is too quiet. I would say that a system should be able to do at least 110 dB's at the seated listening position. This is not too hard to accomplish so long as you have enough amplifier for the size room that you are in and relatively efficient speakers that don't go into massive compression when fed some juice. Obviously, using more efficient speakers in a smaller room would put most people WAY ahead of the game. Sean
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