What's your understanding of efficiency ratings?

[Fricasseekid]

I was discussing efficiency with someone the other day and they pointed out that a rating taken at 1w/1m is useless for comparing subs that will be given 100s or 1000s of watts. He made a few good points but the one that stuck with me the most is how different motor material's characteristics will change as they are run at hotter and hotter temperatures. Increased pressure takes it's tole too.

Basically there are many more variables that come into play as you increase power and SPL that a 1w/1m rating does not account for.

Not to mention the discrepancies on how a 1w/1m rating is come to from company to company.

Do you think efficiency is a useful spec?
How much emphasis should we put on sens. ratings?
What other variables do you think come into play effecting sens. at higher wattage?


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[Hi-FiDelity]

you are correct that there are far more variables involved in the SPL a speaker reaches at a given power than most people think. Though with that said if you are comparing two subs; One that has a sensitivity of 77dB @ 1watt and one that has a sensitivity of 90dB at 1watt. I think you can extrapolate that the later of the two it more likely to have a higher SPL than the other at a given power. While this may be 100% true there isn't much in car audio that is, most of the specs we see are there to give us a rough approximation of what a product can do. For example your amp may be rated at 100x4 at 4 ohms at 12 volts with a THD of .02% but in reality it will do 144x4 at 4 ohms at 14 volts with a THD of .006%. The problem I have with sensitivity/efficiency ratings is that a lot of people use them to judge the SQ of a given speaker/sub when in reality the sensitivity has a very small effect on how good a driver will sound. I've heard plenty of what would be considered inefficient speakers (both home and mobile) that sound wonderful when given a decent amount of power and I've heard efficient speakers that sound like ass when you given them more than 15 watts.

[Fricasseekid]

So, would agree that when comparing two speakers with a 4db difference in sens. that its not worth splitting hairs over and you probably can't get a good idea of output based on that difference?


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[Hi-FiDelity]

Yes, I would agree with that. I would also say that you would be hard pressed to notice that 4dB difference with out measuring equipment and that if that difference is even that much at the output you measure. The sensitivity could change drastically if you go from 1 watt to 10, it could go from 4dB to 2dB or even .2DB.

The only time I can see picking between two subs based solely on sensitivity is when you are using the power output of your amp to decide. if you only have 250watts to play with than you may want a more efficient woofer though if you have 600watts to play with than you should look more at power handling.

[Fricasseekid]

So what specs would be more useful in determining which sub would play louder in a particular install?


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[Fricasseekid]

I'm surprised more people didn't chime in here. I guess it's just not worth discussing and I'm a cotton headed ninny muggins!


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[tantric sounds]

there is no short or simple answer to this question...it is relevant if you understand the complex nature of a speakers operation and have a full set of parameters for that driver. by itself the measurement is worthless..SPLo is a calculated parameter and is only a mathematical representation of an average SPL from 100hz to 1000hz. seeing that we are using the drivers for frequencies below 100hz and with a long voice coil that has a high inductance which rolls off with higher frequencies it would automatically lower the sensitivities in the 100hz to 1000hz range. lots of small things to keep in mind while reading parameters and what they are used for. smith & Larson laboratories are working on new software to measure subwoofers all the way up to full linear xmax so that we can get a better understanding of the woofer is really doing and what true parameters are below 100hz. a good test you can do is measure the woofer in several applications. first in standard placement...then in a sealed box on the floor, then in the car. take all the information and come to your conclusion from that

[chad]

Power compression. Good motor designers do everything thy can to fight it.. JBL is a big player in that game.

[Fricasseekid]

So what's the trade off with inductance. Why is making low inductance motors not the simple fix?


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[chad]

I like low inductance motors but generally speaking, the lower the inductance, the less copper in the gap. Gets pricier in terms of better gap geometry and flux. Can't be as sloppy.