are 3db important?

what is the point where yours ears pop?, ive heard of it, and my car seems to come close but i was just wondering. is there one?

Huh?

Thanks for reposting those bits of info, stevedart.

gbear14275 if you hit 134.4 with 450 watts, that simply means your subwofer system coupled with the cabin gain in your car is about 107.4 db/watt-meter efficient.  Nothing magical or non-conforming about that.  It's pretty high, though.

t-roy, if you are talking about "popping your ears" due to sound pressure levels, that is a myth.  However, if you are talking about hearing damage, OSHA has set the following limits as the point where irreversable hearing loss occurs.  Note that it is a volume level in dbA (which is simply a method of measuring decibels) and the time you must be exposed to that level before you begin losing your hearing.  Also note that it has nothing to do with the frequency of the sound, it is just gross SPL measurements.  Many doctors think the limits are too high and the times too long:

Any exposure to levels higher than that will cause hearing loss, and exposure to sharp momentary impacts less than 1/10 of one second of 140 db or greater will permanently damage your hearing.

The answer?  Turn it down or wear hearing protection.

I'm not so sure I understand this after all.  I would have guessed 119 db just with the doubling of cone area alone...which means the same 400 watts is being shared with both subs.  Doubling the power, too, should give us an additional +3db, making it 122 db.  Otherwise, why do we make a point of the doubling of cone area if we're achieving the only gain by doubling power?

Typo?  Or do I not get it?

No, it's not a typo.  Adding two EQUAL sources together (assuming no cancellation or other ineractive effects, and assuming the measurement is taken from the same distance) results in approximately a +3db SPL increase.

If you simply increase the cone area and keep the gross power the same, you realize no net increase.  For example, take a single sub with 400 watts going to it and let's say it produces 100 db SPL.  Add a second sub (doubling the surface area) but keep the same 400 watts, and now the power for each sub is reduced to 200 watts.  The first sub's output will be dropped by -3db (power cut in half) to 97 db SPL, and the second sub at 200 watts will add +3db due to doubling the surface area, resulting in a net 100 db SPL.  Exactly where you started.  Now if the power to both subs is maintained at 400 watts, the 100 db SPL output from the first remains, and the second sub adds +3db for a net 103 db SPL.  Adding two equal sources is the same as doubling the power to one source.

Make sense?

Yeah, thanks for clearing that up for me.  I think that for about 2 years I've been figuring this "cone area" increase wrong and posting wrong numbers on this forum.  It must be something I read one time and it just became embedded in my mind.

Then the only reason for adding sub cone area is to handle the extra power that you're applying to increase the db level.  So  "double the cone area for +3 db", if it's said at all and is not just a figment of my imagination, is a myth.  Without the power being doubled, regardless of number of subs, the +3 db doesn't happen.

Anybody who has gotten through this thread this far should know that my lengthy response on the first page was only partly correct.

I responded, "Not everytime you add a sub...it's everytime you double the number of subs increases 3 db's."  That is wrong, because neither is true.

And I said, "Look at the case above where we increased the number of subs from 1 to 8 to achieve a 9 db gain....we just about doubled the loudness."  That is wrong, because of the same reasons.  I wasn't considering a change in power, only an increase in number of subs.

This is a question where we first have to find out some pertinent details before we can respond. 

• Are you keeping the same size sub or are you switching to a larger or smaller size?
• Will you switch the subwoofers to a different coil configuration so that the impedance load on the amp remains the same as it was when you were using one sub?
• If you're adding a sub identical to the one you already have, what will the amplifier output at this different impedance load?  How does it compare to the output into the single sub?

This can only be a "theory" response unless we know these details.  It becomes a complicated calculation and can be different with each situation.  And we still have that shadowy gray area to consider:  the increase in cabin gain that happens when you increase the decibels.

Like I hear the pros say it, "Build it and read it with a meter."