adding one more sub, noticeable difference?

haemphyst, I don't believe you looked at the graphs closely enough.  The center box shows max SPL and total system wattage.  The circled box on the left is the power given to a single driver.

I didn't say that the OP was doubling power to each sub, but doubling system power.  The graphs demonstrate what I said.  Leave them up on your screen and look through them again.  It is, of course, true that if I halved the power to the single driver the SPL would decrease by 3 db.  Your logic with that argument DOES NOT account for the added cone area gain.  You are doing nothing but adding and subtracting power with that reasoning.

So, I've shown that Unibox calculates +3 db gain SOLELY by doubling cone area.  In addition to what I've already shown, I've also looked at it using one driver compared with three instead of two, and the results stand as previously calculated.  System power remains the same whether it is one sub or three, but SPL is calculated as +3 db due to doubling of number of drivers alone.

three_drivers_total_system_150w_50w_each.jpg

Add that picture to the ones I linked before.  It shows that with three drivers, each with 50 watts for a total system power of 150 watts...115.7 db.  Compare this to the graph that shows two drivers with 75 watts each (114 db)...still 150 watts total system power.  A net increase of 1.7 watts (roughly half of 3 db) due to the calculation for the additional single driver but no added power.

Now, why do WinISD and Unibox calculate additional SPL for merely adding cone area when system power remains the same?  Because, I think, it must be true.

Edit:  sedate, we are just arguing the same point with two different proofs.  But I understand your demonstration as well as the one I put forth.  (BTW, you are a silver member;  you can upload a file of up to 500 Kb.  I normally take a snapshot of the program using Simply Capture which saves a 2+ Mb file of that size in .bmp format.  Then I pull it up in MS Picture It and save it as a .jpg file.  That drops the file size down to 200-some Kb.)  Ha ha, yeah, like I'm telling you how to use modern technology :)

You have twice the cone area/excursion and twice the power = twice the output. That's how I see it, anyways.

I hope this helps (confuse you all some more,).

You have twice the cone area/excursion and twice the power = twice the output. That's how I see it, anyways.

I hope this helps (confuse you all some more,).\

"Theoretically" it takes a 10dB gain to be twice as loud so I am not so sure that statement is correct....however doubling the # of speakers AND doubling the power to EACH speaker should yield a 9dB gain..which is close..but still there seems to be debate.

As for everyone else I can only hope there is something to be learned here as alot of discussion is going on about this...but since I was a wee lad...it was common knowledge in THIS industry (and I imagine physics as well) that doubling the # of speakers = 3dB gain...doubling of power = 3dB gain. Not to beat a dead horse (well one I thought was dead for the last 10-15 years) I have never heard any debate about this from anyone...ever....anywhere. 

But somehow this topic has become interesting, I must admit you all make great ponits and get us thinking, can't ask for much more then that.

Well.  SPL is a function of air moved right?

Okay well, 1 watt might make a speaker move 1mm right?  But 2w is not necessarily going to move it 2mm right?  Maybe the 2 watts only moves the speaker 1.5mm.  So the air moved would be equivalent to 1.5mm x Sd right?

But if we have a pair of drivers and put 2w to them, or 1w/1 driver, then each driver moves 1mm...  so the total air moved would be 2mm x Sd right? 

This is why I understand multiples of drivers to be louder than multiples of power. 

One of many reasons I consistantly use the term "theorectically" when dealing with this topic.

But you don't really need charts and graphs and a physics degree to realize more speakers and more power will produce more SPL.

I am still waiting for someone to perform a lab experiment. I would do it but my SPL meter is broken and I don't wish to replace it until busy season..if that ever comes in car audio again.

To do this test simply hook an amp to a test bench with a sub..take a reading @ a given wattage and mic distance..add another sub/amp and take the next reading.

Repeat the experiment at different wattage levels and various mic placment and record the readings.

I would be willing to bet overall on average the readings would indicate the results expected...3db increase per doubling of speakers...3db per doubling of power..or close enough to it to be conclusive.

I second that notion.

There is no way I could afford equipment that would take adaquate measurements.

Any takers?