adding one more sub, noticeable difference?

You da man haemphyst.

Heres a suggestion but it does go against my ethics..however I might be willing to let it slide for the good of science and this discussion.

Go to one of the "big" stores...purchase a double sub divided enclosure..2 identical subs..and 2 identical amps..DVC subs and 1ohm stable amps would probably be the best for this experiment due to versatility..however anything should work and give a conclusive result.

When you are done with the test pack everything back up in the original boxes like new and return it..the old "I bought it as a gift but the person doesn't want it..or they went to jail...got in a accident etc"...

I can't believe I suggested this...I really need a new SPL meter...anyone in the NY metro area have a working professional SPL meter? I will supply the lab and all other equipment and materials..

I can't believe you suggested that either.  ;)

We still need the physics, regardless of shade tree testing (and I will secretly suspect the possibility of biased results if certain characters who will remain nameless are doing the testing).  I'm looking for the math, but I'm no injunear.  There must be a calculation relative to Sd and efficiency factor.  Sedate's summary is logical but doesn't sell me.  But what sells me is the fact that the modeling programs calculate the db increase.  We should be able to locate this math formula.

Jus' jabbin' at ya, haemph.  :)

If I play around with the parameters of my "unknown15sub" that is up in my Unibox program, I find that it is actually not Sd that causes the 3db increase, but the doubling of Vas.  If I double the Sd, no change is made to SPL.  But if I change the Vas to double the number, an increase of 3 db is calculated.  So when adding more woofers, Vas is increased for each one and when it doubles the previous amount we get the +3 db.  When I (earlier) added only one more woofer to the pair I had modeled, the db increase was about half of 3 db.  Right now, Vas looks like the ticket.

Why the need to complimicate things??

I never heard of a speaker with a way to change it's vas parameter (well at least not on purpose or with any predictibility so where is this going?

But anyhoo..still enjoying this. I will state again if anyone in my area has an SPL meter I will have a non-biased witness present, notary and 3 forms of ID and fingerprints.

Kidding aside..I really don't think anyone (well at least not on this thread) would sku results. But I am still having difficulty as to where and when the 3db rule changed? The math is sooooooooooooo basic..double the speakers..gain 3db...double the power..gain 3db.."in theory".

Has this been disproved yet or do I also need to break out the books?  lol

You guys are ok.

Ok I hit the books. Here is some notes I found from back in school.

decibels are logarithmic.....10logX/Y  

a 2-fold power increase yields a 3db gain ...4 fold=6db....16 fold= 12db...a 100 fold increase yields a 20db gain..therefore a speaker rated @ 1watt/1meter has 20db added to calculate it's power @ 100w.

Drivers connected in parallel increase efficiency but not power handling..the reverse is true in series. 2 drivers in parallel increase efficiency by 3db. A pair of identical drivers connected in parallel "act" as a single driver would but provide a 3db gain with an impedance drop of 1/2. On a side note drivers can be attenuated 6db by connecting a resistor in series the;the value equal to the drivers impedance......

here is some more stuff I found but i can paste the following...

"For example, a speaker like Axiom's M80ti has a measured sensitivity in an anechoic chamber of 91 dB SPL at 1 watt at 1 meter. But putting the M80ti in a room raises its sensitivity rating to 95 dB SPL at 1 watt, 1 meter. A 95-dB sound level happens to be "very loud," as most of us would subjectively describe it. And it is--from 3 feet (1 meter) in front of the speaker. But let's move our listening seat back twice as far, to 6 feet. Guess what happens? We instinctively know that sound gets weaker as the distance from the source is increased, but by how much? A formula called the "inverse square law" tells us that when the distance from the source is doubled, the sound pressure weakens by 6 dB. Among sound engineers, there's a common saying: "6 dB per distance double." So at a 6-ft. distance, the M80ti is now producing 89 dB. Now let's double that distance again to 12 feet, a fairly common listening distance. The speaker now produces 83 dB, which isn't all that loud at all. And if you sat 24 feet away, a not uncommon distance in big rooms, the speaker would produce 77 dB SPL.

But what about stereo, I hear you shout. Here's another oddity of loudness and the decibel. When one speaker is producing a level of 90 dB, adding a second speaker playing at the same level only increases the overall loudness by 3 dB! (The loudness does not double!). So the two speakers in stereo produce a loudness level of 93 dB.

So adding a second M80ti will raise the loudness at 12 feet from 83 dB to 86 dB. And don't forget we're still using 1 watt of amplifier power output into Axiom's most sensitive speaker. But how loud are real-life instruments, orchestras and rock bands? Now, while 86 dB SPL is "fairly loud," it's not nearly as loud as what you might hear from a good seat at an actual rock concert or from an orchestra or pianist in a concert hall. A solo grand piano can reach peak levels of 109 dB SPL, a full orchestra and chorus in a concert hall will measure 106 dB, and a rock group, 120 dB SPL. Now let's try and get our peak speaker sound levels to 96 dB, "twice as loud" as our 86-dB listening level. That isn't that difficult because right now we're only using 1 watt per channel to drive the M80ti's to 86 dB. So we'll need ten times as much power, or 10 watts, to reach 96 dB. Big deal."

I don't know if this will or will not add some clarity to the topic but at least others have tested this and done the physics (well long, long before most of us were born). It seems simple to me but still open for debate.

Oh wait..there is some confusion.

In the above example it states a 3db gain by adding another speaker to make it stereo.but it still doesn't explain if EACH speaker is recieving 1watt...or 1/2 watt. In other words if adding the 2nd speaker should give a 3db gain...what about the other watt..which effectivly has doubled the total SYSTEM power..where did those 3db go???  Or does it not exist>  Is this a 6db gain or a 3db gain?

either the author fouled up..or this is totally back to square one..darn it.

Ok again..lol  nevermind brain fart.

This actually goes back to the original post..remember where he wanted to know if there would be a noticable increase in bass if he added another identical sub and ran it off an identical amp...well in finally came to me..no math or charts or parmeters needed..it just clicked.

after re-reading the paragraph about the stereo I noticed it states "adding a second speaker playing at the same level only increases the overall loudness by 3 dB! "

That statement says it all..makes sense so I believe it to be true. If a 2nd sub is added..with an identical amount of power.. it will provide a second speaker playing at the same level...and hence will only yield a 3db increase...an increase nonetheless..but not 6db or 9db...ain't gonna happen in this world as we know it.

It is not a matter of "total" system power in this case but simply about doubling the cone area with EQUAL power as the original.....a 3db gain. To yield a 6db gain would require a doubling of power to BOTH speakers..or using 4 speakers with the same power on each. Well I know I get it now.

No more rambling from me tonight but curious of others opinion..is this a "eureka" moment for me or am I on crack?

Thanks all  : /

custom audio ny:  the text example you produced is worded too ambiguously to reach a conclusion on this subject.  The context of his writing indicates that he was using a very simplified approach to explaining about a +3 db increase due to doubling of power alone.  His use of "stereo" speakers rather than the "single" speaker was meant only to form a visual for his analogy, and clearly didn't delve into the result of doubling cone area.  The gist of all he said (in that) was, in fact, nothing more than teaching about the relationship of power to decibels.  This text quote has caused you to turn aboutface.

haemphyst:  look at some of the reasons builders use line arrays.  The biggest subject in regards to using these is on the lines of increased efficiency and SPL per watt.  Here's a chart someone made that shows SPL gain over a single driver by using arrays of several drivers: