adding one more sub, noticeable difference?

In "theory" doubling the power or # of speakers will give a 3db increase. So, yes..you will definatly notice a difference. But this assumes the same power is going to the speakers (which you state you are adding an amp for it..which is good) and that everything is installed/wired properly.

Now if you had 8- 12'' subs I would say adding one more would not be noticable by ear. As far as doubling power to gain 3db you would have to make sure the components could handle it.

custom audio ny wrote:

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In "theory" doubling the power or # of speakers will give a 3db increase.

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sedate, whats up?  Ok not looking for an argument but who told you simply doubling the number of speakers yields a 6db increase? It would defy all the physics and audio theory I have come to understand.

Not to say I can't be wrong about this..just would like a little backup to substantiate that claim.

Peace.

Also I think we should discuss the terminology as well. "Doubling cone area". Does this mean adding another sub of the same size/model or increasing the physical size of one woofer to twice the area of the original? Now in either case it would still be unpredictable exactly how much gain would be realized but wouldn't a much larger speaker need a much larger motor to move that much more mass? So with the same power how could one predict the gain increase (although as far as I know it would not exceed 3db at most..simply due to physics)

There are many factors to take into consideration. In actuality the physics involved with gain predictions should be discussing the adding of one sound to another sound of the same amplitude (volume) and, adding one sound to another sound of the same amplitude and correlation.

In other words if you had a speaker playing at a certain dB and then had someone in the car yelling at the same level you would have a gain in overall dB but... where is the "cone area" in that case?

Well anyhow I didn't really want this to turn into a physics lecture but don't mind sharing tidbids I pick up. If anyone feels I am giving the wrong info I am more then open to debate.

Oh..to the point...lol

Doubling the power = 3db gain "in theory"

Doubling the # of speakers = 3db gain. "in theory"

So if you add another sub......PLUS another amp of = power..you MAY net up to a 6db gain..which is nice..remember a gain of 10db = twice as loud (hope no ones getting confused..lol)  But a 6db gain will be quite noticable by ear as well.

The reason I say "in theory" as discussed earlier there are other factors..well many factors that effect output such as car environment, accuracies of ratings, performance of products and a host of others. But this is not to say you will never gain 6db in doing this..it is possible.

Another thing..but this is important. It is not really an accurate "rule of thumb" to state that doubling of power will yield a 3db gain...why?? you might ask.

Well that would be like stating "if I dump 10 times as much fuel and air into my car engine..the HP will double"..well it might..for a second..then blow up.

Physical limitations apply. So for example if we have a sub that can handle 600w..but we were only running 300w to it...upping to a 600w amp should (or "may") give us a 3db gain. Now if we take the same 600w amp and add another sub to it..the db level would also depend on impedance. (what is the amp stable too??, what is it's output at different loads??)

If it was wired in a configuration that cut the power in half..we would (in theory) lose 3db..but..we added another speaker so in theory we would gain 3db (basically right back where we started).

But if we wired it to "double the power" but the amp was not stable (example running a 2ohm stable 600w amp to 1 ohm in an attempt to extract 1200w out of it) something would surely give in a short time as the amp can not handle the lower impedance. This factor takes into account human error, poor judgment, ignorance, whatever you want to call it.

Basically be realistic in what you expect from your equipment as well as the physics involved and you shouldn't be dissapointed.

Now either some of you are really confused...or..get the idea.

Huh.  I coulda sworn the rule of thumb was +6db for the doubling of cone area.. but maybe that rule assumed the same amount of power to each speaker.  Anywho, I just modeled it in WinISD and I was.. I was...

I was *gasp* wrong.  Adding a second woofer and running the *same* amount of power to the subwoofer system would only yield 3db.  However, running the same amount of power to the second speaker that was being run to the first would then yield the +6db.  And doubling it in the end, I think, would *then* give us +9db.

I dunno I'm sure if I wrong someone will jump on me here soon.

Nah..I think ya got it now.

In a nutshell......if he adds the other sub AND an identical amp to that sub..he gains "in theory"(sorry have to say that evey time..lol) 6dB...(3dB from doubling the speakers, 3db from doubling the power).

NOW..if he doubled the amount of power to EACH sub..he would have a 9dB gain "in theory"(3dB from doubling the # of speakers.....3dB EACH increase from doubling the power of EACH sub .....3dB + 6dB = 9dB.

Hope that helped..I know this topic can get confusing.

sedate wrote:

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And doubling it in the end, I think, would *then* give us +9db.

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custom audio ny wrote:

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The reason I say "in theory" as discussed earlier there are other factors..well many factors that effect output such as car environment, accuracies of ratings, performance of products and a host of others.

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This is truly just a theory question, so answers are rightly subjective.

The added part about "doubling the power AGAIN" confuses the issue and shouldn't be included in discussion.  We should presume a maximumly powered subwoofer to begin with, as the question posed is about how to get more SPL.

So yes, doubling of cone area (when you are starting with one woofer you need only add one identical woofer) nets +3 db due to increase in sensitivity.  Given another identical amp, the power to the sub system is doubled so the sub's output is 3 db higher than it was before.  Net gain of +6 db.  Then there is added cabin gain...  The overall output could actually well exceed +6 db gain as long as  ALL NECESSARY IMPROVEMENTS AND ADDITIONS to the car (that are necessarily required by the upgrade in equipment) are added.  This may mean that alternator, battery and system wiring needs to be upgraded, for example.  And that the sheet metal damping is multiplied in critical areas.  As long as you don't begin to experience a higher loss ratio because of excessive sheet metal vibration, or that the amplifiers are now starving because of the power-hungry addition, you can look at achieving a very noticeable SPL improvement by doubling your subwoofer system.

heamphyst wrote:

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Am I right?

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Strangely enough, no, you do not appear to be.

As I believe I correctly stated in my second post here, if he adds one more 12 and another amplifier of equivalent output, he will net +6db.

Yellow = 1x12" @ 1w/1m

Red = 2x12" @ 1w/1m

Blue = 2x12" @ 2w/1m <-- +6db Gain

Green = 2x12" @ 4w/1m

sedate wrote:

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Blue = 2x12" @ 2w/1m <-- +6db Gain

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haemphyst, Unibox confirms what sedate is demonstrating.  The nominal power as shown in Unibox is power to an individual driver.  The circled area on the right of the screen shows number of drivers.  SPL is shown circled in the center.

A single sub with 150 watts, yielding 111 db:

single_sub_150w_total.jpg

Now, two subs but each only have 75 watts for a total of 150 watts, yielding an increase of 3 db:

double_sub_150w_total_75w_each.jpg

This is the single sub with double the power, yielding a 3 db increase:

single_sub_300w_total.jpg

Unibox demonstrates that either doubling cone area or doubling power yields +3db.  This last pic shows both, for an increase of +6 db, which is what the OP said he wants to do by doubling cone area and doubling total power:

double_sub_300w_total_150w_each.jpg

And so I shall stand as well (although I must admit, tenuously, as DYohn also has told me what you have stated ;)

(Expand the images and flip back and forth through them.  It looks like a decisive conclusion to me.)

So....aside from the predictibility of an anechoic chamber and the unpredictibility of a mobile environment lets look back at the original posted question and possible scenerios.

The author is basically asking if he will gain an improvement in bass output if he adds an identical sub/amp to the existing. Well with twice the cone area and twice the "total" power alone of course there will be a noticible gain assuming all is installed/wired properly (we can't really predict how body panel flex and resonance will effect anything until it is operating, then fixing that if it is causing a negative result is another issue).

Now as far as any other way to approach this we would need to know the voice coil impedance..if the subs are DVC or SCV(to determine final ohms load) ,max power handling and what ohm load the amplifiers are stable down to as well as thier max power output. Since I personally am not familiar with the specific equipment, if the specs are posted we can possibly suggest alternate ways to increase output without damaging any equipment.

If in the case as haemphyst stated the amp he already has can handle the additional sub wired in parallel, and the amp is capable of putting out twice the power if wired that way...he then will have twice the cone area and twice the power as well..surly a more economical way to go. If (and this is all conjecture for now) he gets the other amp and the woofers are DVC there may be a way to achieve 4 times the power.............."in theory"  lol 

BTW, I must say I am very impressed with some of the infomative people on this site. You guys really know your stuff..good going and thanks for sharing. I will be contributing as much as I can when I have the time and hope to learn plenty as well. Also a donation from us will be coming soon. Thanks

Okay first of all, can we do something about this 30k image limit?

Anywho, uhh...  well heamph I still believe I'm correcct.

The blue line does not represent 4 watts, it represents 2.  

It says so right in the little box I used to make WinISD make the graph.  Each of these lines represents a 12w6 with 1 cft of air space assigned to it, with the wattage I listed.  I believe this is for the input power for the box, not the individual drivers.

https://linearteam.proboards12.com/index.cgi?board=winisd&action=display&thread=1154421440

Here is the graph before I cropped it for upload earlier. 

stevdart wrote:

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haemphyst, Unibox confirms what sedate is demonstrating.

A single sub with 150 watts, yielding 111 db:

single_sub_150w_total.jpg

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stevdart wrote:

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Now, two subs but each only have 75 watts for a total of 150 watts, yielding an increase of 3 db:

double_sub_150w_total_75w_each.jpg

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stevdart wrote:

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This is the single sub with double the power, yielding a 3 db increase:

single_sub_300w_total.jpg

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stevdart wrote:

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Unibox demonstrates that either doubling cone area or doubling power yields +3db. This last pic shows both, for an increase of +6 db, which is what the OP said he wants to do by doubling cone area and doubling total power:

double_sub_300w_total_150w_each.jpg

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stevdart wrote:

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And so I shall stand as well (although I must admit, tenuously, as DYohn also has told me what you have stated ;)

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Hmm.  It seems as though Grand Moff heamphysts' verbal tap dancing isn't doing the force justice.  Darth Yohn will not save you.

Doubling the SYSTEM increases the output by 6db, not 3db.  All this individual woofer talk is running us in circles. 

Again, our yellow line is 1x12 @ 1w/1m and our red line is 2x12 @ 2w/1m... or a mirrored system.  A 6db increase.

100db+100db = 106db.

Ok, so in effect what is being stated is that you would need to double the power to EACH sub as well to net the overall theoretical 6db gain?

Hmm..does make sense when you look at it that way. The same holds true in reverse I suppose....if you added the 2nd sub..but cut the power of each in half....nothing gained...so it makes sense that doubling the power to each would net the 3db gain.

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.

heamphyst wrote:

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"voltage gain vs. efficiency" or some BS like that...

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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?

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:
https://ratch-h.com/arrayimpedance-revised.html
There are others who have written spreadsheets and programs that are specifically designed to calculate the increase in efficiency and SPL by using multiple drivers.

stevdart wrote:

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the text example you produced is worded too ambiguously to reach a conclusion on this subject

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Wow stevdart.  Way to be diplomatic. 

custom audio ny wrote:

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is this a "eureka" moment for me or am I on crack?

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Oh boy.

LOL....well I understand what everyone is saying. 

Ambiguous or not it still makes complete sense to me in every way shape or form, common knowledge or physics that for another speaker to produce any output at all it must have power going into it... cone surface area alone does not produce any SPL.

However, in this example if we are starting with a given single speaker with wattage going to it...and add another identical speaker with the indentical amout of power....regardless of it being from a seperate amp or the other channel of a stereo amp, we will yield the mystical and oh so illusive 3db gain.

Is there still a problem or is this correct and everyone is simply looking to hard to find problems with this?

Thanks again for the fun all.

custom_audio_ny wrote:

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common knowledge or physics that for another speaker to produce any output at all it must have power going into it... cone surface area alone does not produce any SPL.

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Now you're starting to worry me.  How did you take it, from anywhere in this thread, that there was no power applied to the second woofer??

]if we wrote:

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are starting with a given single speaker with wattage going to it...and add another identical speaker with the indentical amout of power....we will yield...3db gain.

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+6 db.  You said so yourself a few times in this thread, examples as follows:

]it wa wrote:

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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.

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]I wou wrote:

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d 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.

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You now don't believe such common knowledge?  Are you still having your Eureka! moment?  I mean, gee, it's fine to change your mind about it but....  Look at your textbook quotes again, only this time look at this part:  "...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..."   How would your epiphany have panned out if you had settled on this quote instead?

Everyone must be careful of using...and let me say this again...ambiguous terms.  Like, what does "identical power" mean?  That the second sub is fed the same amount of power that the original sub has?  Or does "identical power" mean that the power to the sub system is still identical to what it was before the second sub was added?  If you meant that he is clearly doubling the number of drivers AND the total power to his subwoofer system (not to each sub!), the answer is +6db.  See your quotes above.

One of the biggest problems this topic is subjected to is imprecise terminology.  Lack of defined numbers.  For example, like haemphyst's apparent inference that "doubling cone area" automatically assumes a doubling of power to the subwoofer system;  that the second sub automatically comes with the same power as the first sub.  If there is no defined addition to system power level, multiplying drivers cannot assume a power increase. It has to assume a sharing of the power level previously defined, and in a more perfect world, spelled out in specifics.   What you can assume, for sure, is that any driver included in discussion will have power applied.  We're not throwing an old speaker into the back seat and proclaiming more SPL! 

Eureka!!!  I can now explain the confusion about my confusion..if that makes any sense. It's not so much that I changed my mind per say..it is about the way I was looking at the actual physics.

First off..I will admit to using sarcasm in my statement "common knowledge or physics that for another speaker to produce any output at all it must have power going into it... cone surface area alone does not produce any SPL" .... but I will get to where I was coming from with that statement soon.

OK..now the next issue with the amount of dB gain. This is where I stand ..and did before as well..but was confusing some explainations.

Yes..I still stick to the fact that doubling the number of speakers will yield 3db (I won't even use the term "theoretically" anymore..I accept this as a fact)  I also stick to the fact that doubling power yields a 3db gain...but you need both. In other words you can't have gain by adding a speaker with no power to it..and you can't add power by using an amp with no speaker on it.

I am not meaning to imply that anyone else has implied that..but looking at it that way helped me to understand what is going on. Now..there is a difference between adding another speaker by connecting it in parallel to the same amp or adding another speaker driven off an amp of equal power (either a seperate amp or the other channel of a stereo amp. What paralleling will do is double the power to EACH speaker (of course assuming the amp is stable..blah blah blah..for the sake of this discussion all is assumed to be compatable) as well as double the number of speakers...wallah..or should I say "eureka!"  theres the 6dB gain.

Now...assume you either add another identical speaker powered by an identical amp playing at the same level....or..in the case of my previous example...added another speaker to the other channel of a stereo since the example was only using one channel to take the initial measurments. This is where you only gain 3db. I understand that total system power has doubled.....but this is simply the addition of one more speaker playing at the same power level...hence only a 3dB gain.

Did this sound sensible or is there still something I am missing?..or does anyone have trouble understanding my explaination?

Peace

One additional note....where some other confusion may be arrising is the difference between the way different amps react to bridging.Some amps will double power...some amps won't.  Some increase power by a percentage..but not nessecarily double.

For the sake of the discussion..I am assuming double the power output when bridged..which is the way most car stereo amps are designed..but certainly not all.

If this information is not specified stated in the test results, it is undoubtedly inconclusive.

Oh ..I want to cuss but won't. But I fouled up again. Why oh why is something so simple confusing like this?

Technically...there should be no differnce in gain from adding an identical speaker/amp setup or adding another speaker in parallel to a single amp that doubles power when bridged.

If we use an amp rated @ 100w@ 4ohms...200w @ 2ohms for the sake of this discussion...either setup leaves us with 2 speakers..each powered by 100w.

So...either setup according to what I believe, will yield a 3db gain in comparison to the single speaker setup.

Now lets look at the scenerio of 2 speakers..each with 100w powering it.

To gain an addition 3db, we would need to either double the amout of drivers to 4 (each with 100w to them as well) or double the power to EACH driver..for a total system power of 400w. Either setup will yield a 6db gain from original..any dispute there?

On the other hand,if we added the 2 addition drivers in series, this would cut the power in half..so a loss of 3db. The  drivers being doubled would add 3db..so in that case doubling the cone area did squat..well at least "in theory" ... lol

This sound more like it?

You know...what I liked about this particular thread was that the OP wants to add a second identical sub system.  There is no "But, if's" involved regarding differences in impedance loads on the amp, bridging, or any other miscellaneous items to muddy the issue.  Why bring them up here?  I'd like to use this thread to clear it up...for myself, if that's the case.  Leave out the extraneous nonsense that has no bearing on this particular case.  The question still remains if doubling the subwoofer system will result in a noticeable difference.  I need to know why this is a divided issue.  At least we've narrowed it down to either 3 db or 6 db.  That's wonderful.

Has any reader of this thread done this before, doubled up his sub system like this?  Did you notice a difference?  Big?  Little?  Too loud now?  Stil not loud enough?

Unibox or WinISD can't add two separate systems together.  One has to add the drivers and manipulate the power to each driver so that the total power remains constant to see results of the doubled cone area on a level playing field.  Unibox calculates the db increase whether the drivers are connected series or parallel, by the way.  It sees another driver is added.  Vas is doubled.  Sd is doubled.  As I noted earlier, Unibox seems to look at the Vas as the key in its +3 db SPL increase calculation.  And, again, without the addition of power but of equally shared original power.  And, as sedate and I both showed using the programs, when the second sub is given the original amount of power that the first sub has, the increase is +6 db.  There's a reason for it.

It seems very odd to me that someone would use the term "doubling cone area" when what they really meant was doubling total power.

So the program assumes the amplifier divides the power when additional speakers are added? In other words it assumes addition speakers are added in series every time?

Sounds self defeating to me...but I am unfamiliar with those programs, call me old school.

Anyhow..to the real world (no insult intended whatsoever..but we need this as well) I used to compete in SPL as well as judge iasca and usac sanctioned events. And this is why I probably can not deal eith this topic without discussing amplifier capabilities and series/ parallel wiring etc..I do not read SPL in a chamber..but I  have in vehicles.

To gain a 3db increase you need to double the amount of speakers. However...there is no way to do this off a single amp without deciding to series or parallel..and DVC speakers and amplifier capabilities have alot to do with that decision.

This is why I have not tested this scenerio in the past. But I have had customers come in complaining of not enough output due to poor product purchase. Example..bridging an 8ohm sub to a 2ohm stable amp. In that case the sub is only realizing 1/4 of the amps power.

A computer program can not fix that problem. You either have to a) switch the sub to a 4ohm sub...or b) purchase another  8ohm sub/enclosure and parallel it @4ohm to the amp.

But the issue at hand in this discussion I think is we can't decide if adding an addtional and equal sub/amp setup will yield 3db or 6db gain?  I fully understand why the program can't deal with that.

I will eventually get ahold of a working SPL meter and do the measurments...but I hypothesis this...

Adding an additional speaker with the SAME power as the original will yield a 3db gain...you would need to add an additonal speaker AND double the power to both to gain 6db. It just makes sense to me however I have not performed any actual tests to verify this so we will have to wait until myself..or someone else does..the programs can't seem to deal with it.

There is a way the programs deal with it.  You input amount of power to the driver that you are working with.  When you multiply the number of drivers the program gives them each the power that you inputted.  It seems to answer the question quite clearly to me, but what I said is that I'm telling the program that this is one amplified enclosure...not the two separate amplified enclosures that this topic is concerned with.  But it should all be same if total power is kept in mind.

You tell the program how the drivers are connected.  There are changes made due to the different ways you connect the drivers, but I see the same +3 db calculation due to number of drivers alone.  It's not defeating at all, but a tool to build great speaker enclosures.

Here's three more pics of the program's calculation for max SPL.  First is one driver with 1 watt.  Second is one driver with only half of a watt.  Notice the -3 db decrease.  Third pic is two drivers connected in series, each driver with only half a watt for a total power of 1 watt.  haemphyst and you are saying that since it is still only 1 watt, and you can see that both drivers are given half a watt, it should be the same as the original 1 sub-1 watt SPL.  You see here that Unibox adds +3 db for the additional driver.  And when you look back at the single driver with half a watt, you see that now there is a +6 db increase due to doubling of power and doubling of drivers.  Also notice the change in calculated efficiency when the second driver is added.

single_driver_1w.jpg

single_driver_0.5w.jpg

double_drivers_1wtotal.jpg

Anybody who models driver enclosures are going to get this type of projected SPL response based on number of drivers and total system power.

I understand that programs can be an excellent tool for system design/enclosures e tc but i  was under the impression by what you stated that is was hav ing problems predicting the gain in this particular instance.I look at it simply. 

If  for example we have a single sub/amp setup that measures.. 100db at 50w. another identical setup would also measure 100db.I guess if anyone agrees with me that these 2 setups combined would be 100db+ 100db...which  should = 103db  can solve some of this dilema.

Now to gain another 3db we can double the power...right? In the above example we have 2 equal setups with 50w on each...a total of 100w. if we replace the 50w amps with 100w amps we should have 2 enclosures which measure 103db each. Combine those and you have 103db+103db...which = 106db....a grand total yield of 6db over the original single setup with one 50w amp.

Is there really a simpler explaination then tha?..I am sure a few here can find a more confusing one however....

Sorry if the typing is a mess..i am on a friends laptop and it is major FUBAR'ed.

Ok back on my PC now..what a difference. Anyhow no more rambling..at least until I am coaxed into replying..but the link below is to a simple db calculator in case anyone is having issue with the math in my last post..although I would hope at the very least anyone involved with this thread already agrees that doubling the output yields a 3db gain.

https://www.jglacoustics.com/acoustics-dc_1.html

Oh yeah, I am back., it's me....again..Mr. foot-in-mouth....lol..but only to correct myself..or you can look at it as an additional note.

As I mentioned in one of my earlier posts..but somehow forgot until I actually read the note that is along side the db calculator......duh...correlation....in the case with subwoofers operating in mono..pretty much correlated..... so....

in THAT case....you add an additional 3db..so I regress...revert..again..but I am not 100% wrong or making blind u-turns....seems both can be correct...it comes down to 2 simple words.

                                        "IT DEPENDS"

I am ashamed being a car audio guy not remembering this impotant tidbit.

So final answer to the original post....as I said way earlier...lol....  you "may" gain 6 db by adding an identical sub and amp.

Now thats all, for now.

Here is a really in-depth book I found.  https://www.pispeakers.com/ssdm_99.pdf  (JBL  Professional Sound System Design Reference Manual)  This manual was referred to as a point of reference in this post on theDIYSubwoofers discussion forum.  Some more threads and individual posts are listed below, and demonstrate a consensus over the past several years that doubling cone area when both woofers are playing the same sound is adding +3 db just as much as doubling power to a woofer adds +3 db.  They are not one and the same and never have been.

Some say +5 db, some say +6 db.  Ultimately, with sound there will be variances.  The point of my post here, though, is to try to settle into a frame of reference on db increase with a scenario like this thread has opened up.  It has bothered me for a couple of years that sometimes I would hear that it is doubling of power only that gives the +3 db, and other times that doubling cone area gives an additional +3 db itself.  Now I am satisfied with the +6 db answer re: this thread.  Since the second sub will have the same signal input as the first we will hear the sound louder with two subs over one sub.  The db increase is proven with math and will result in about +3 db.  And since the second sub will have an equal amount of power as the original sub had all along, there is a +3 db increase there also for doubling of power, which is also proven with math.  That, combined, is +6 db.

Read through the threads/posts below to understand why the effect on hearing is multiplied only if the woofers are both playing sounds that are very much similar.

The JBL manual is way over my head, at least at first sight.  But I'm happy to have found it and will sneak some time to read it as I can and try to learn from it.  Regarding this issue, though, I went to Chapter Two as mentioned in the post.  On pages 2-2 and 2-3 is a reference to sound pressure and how it is calculated. 

"Sound pressure is analogous to voltage, and levels are given by the equation:  db level = 20 log { P1 / P0 }"

If you follow this text, you will see that there is a db increase using sound pressure as much as there is one for voltage and current.

Here is a short list of forum threads on the subject going back to 2001, in the DIYSubwoofer forum:

https://www.diysubwoofers.org/talkshop/messages/24905.htm

https://www.diysubwoofers.org/talkshop/messages/40131.htm

https://www.diysubwoofers.org/talkshop/messages/40141.htm

https://www.diysubwoofers.org/cgi-bin/talkrec.cgi?submit=List+Thread&baseurl=https://www.diysubwoofers.org/talkshop&msg_num=10861

https://www.diysubwoofers.org/cgi-bin/talkrec.cgi?submit=lt&baseurl=https://www.diysubwoofers.org/talkshop&msg_num=35194

https://www.diysubwoofers.org/talkshop/messages/35195.htm

I have one sub in a small sealed box with less than 200 watts, running at 2 ohms.  It is a little too loud, and I'm thinking about switching back to the 4 ohm sub I have as a spare.  I seriously can't imagine that I wouldn't "notice" a difference if I had TWO subs and 400 watts going to the sub bass region.  Yes, I say, unequivocally and without believing that I need to conduct a test, that you will notice a difference.  My bet:  a BIG difference.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

stevdart, I appreciate you taking the time to contribute to this discussion. It is clearly apparent this topic has been difficult with getting some of us to reach an agreement  and any kind of conclusive result. I have been going in circles myself and I hope it has not annoyed anyone. Although I don't feel I need to defend my opinions, in my own defense I don't have the luxury of deleting my posts..if I did I would have been able to cut down on my posts quite a bit.

I have reviewed the links you left..as well as doing my own research and going over old notes I took when I was studying electrical engineering in college.

Before I go any further, I would like to say that I find this forum mentally stimulating. I have never meant to insult anyone and I sincerely hope no one has taken anything I have said personally. In the same token, if anyone has issue with me contributing my opinions and experience....no one is forcing you to read it. I am new here but do have enough experience to be of service..I also fully except that I can make mistakes...or have a change of heart. This at times is due to the information that others have left..and I can't see that being a bad thing. It's called debate.

Alrighty...that's out of the way. Back to the task at hand.

In my last post I stated my view..which came down to "it depends". Allow me to explain why.

The OP simply asked if he would realize a noticable increase in bass if he added an indentical sub/amp setup to his existing. To be realistic..with all of this theory and physics and parameters and computer programs and analogies..what does it all mean when we no nothing about the equipment he has?..it's ratings..how it's wired..and an endless host of variables..apparently we all got way off course.

But since this discussion came to this point..we might as well play it out..once again, if anyone doesn't like it..move on, I am happy here and feel comfortable and within my element.

Unless I have missed something..which is quite possible, there are a few things being overlooked..but for now I will only discuss two....phasing and correlation; but along with this comes other interesting and perhaps debatable issues, such as physical distance from source to listener (or mic) and the effect the environment may have on adding or subtracting SPL.

First off for the sake of this thread only...I am going to look at an amp/sub/enclosure unit as a single unit. So...one sub with an amp is one unit...two subs with an amp is also ONE unit. This may help to simplify what I post...in addition we assume all db "additions" to be equal. The math involved to calulate the addition of output with uneven numbers is well beyond the scope of this thread, although it could apply.

In the next example,,what is the total db if we add a steady bass note of a sub measuring 100db on its own with a mic placed on the center of a dashboard..and someone in the vehicle blowing a whistle which also measures 100db own its own? I can say with confidence that you would measure 103db. This is a simplified example of uncorrelated. Now with most music..in stereo, there is a different situation. At times, if we were viewing the sine wave on a scope, we would see overlaps, sometimes the 2 channels would be in phase..other times out of phase..by random and varying degrees. In that case all you can do..at least on paper, is realize an average.

This has nothing to do per say with cone area..the whistle is not a transducer..we are simply looking at sound level..that we can all agree upon, I would hope.

With a correlated system..and I need to use the term "system" since one speaker on its own is not correlating to anything, it is putting out a measurable amout of spl, plain and simple. Without going batty..I will use an example of what the OP should accomplish if he adds the additional and equal amp/sub/enclosure unit. The identical setup (in a perfect world) should measure the same output. That will yield a 3db gain when combined. But IF..and this should be asumed since these are subwoofers and the information is identical as well as 2 speakers in phase...you gain an additional 3db. On a scope the 2 signals would be in phase..so overlapping all the time. So there is no need to avaerage...at all times the speakers are working together.

Where there may be some argument..is if the power is divided..in others words one amp/sub/enclosure "unit" has 50w to it. We then compare TWO amp/sub/enclosure units with 25w to each. I would hypothesize that the original unit has had its power cut in half..hence a 3db loss. But you add another indentical unit and get a 3db gain...back where you started. But..if these to "units" are correlated..you gain an addition 3db. Can you see where I am going with this?

I also have to add..not only does "it depends" deal with the electrical and physical...it also seems to have some weight with whom is lecturing on the subject. For example....one of my professors was a genius when it came to home systems..but with car audio he was a lost soul. Then there are the "engineers" who were basically musicians that had some talent..but lots of drive and intelligence. They are a bitter group, generally..but...they really sacraficed alot to learn everything they could about music and performance.

They as well....look at an amp/speaker/enclosure as a unit. As well they should..many guitar amps are what's known as a "combo" unit..amp speaker and enclosure all in one. Now they will swear up and down on a stack of bibles (I know this first hand..I am a musician as a hobby) that if they want to be heard twice as loud..they need to increase output by 10db (I also hope we all agree on that). So they may look at it this way. They have a 100w amp/speaker combo. To increase the output by 3db..they need another indentical setup. To gain another 3db..4 combos...another 3db.....8 combo,s  we are at 9db..so roughly... to double thier loudness they would need to use 10 identical amp/speaker combos to achieve this. But.... all the combo units are playing the same thing..what about correlation? Is it different in a live performance where everyone is in random listening positions..and room sizes vary..dynamics..acoustics..anyone think these metrics come into play?

And as we observe..this is just scratching the surface.

In closing.....do I feel I need computor programs or an engineering degree or expensive measuring equipment to predict if adding another amp/sub/enclosure unit playing a correlated signal at equal power will net a certain db gain in a typical automotive environment?

Perhaps that is the question..but I still say 6db can be expected or, at the very least....the OP can be assured of a substantial "noticable" increase in bass, to put it bluntly.

Ok I am done...thanks to anyone who will listen to me...and thanks for your patience and tolerance, as far as I see it there are plenty of destructive ways to spend some free time so it is nice sharing knowlege and opinions of an industry (or hobby) I enjoy with others.

Your input is very much appreciated Jeff...well at least speaking for myself. And the SPL levels you are achieving are impressive to say the least. (like sticking your head into a jet engine type levels..lol)

Not so much that this is "so important" to me...or anyone else i would assume, but more about a conclusive result..well maybe a little ego..but no harm in that.

With that said....and being in agreement with you...your results are inconclusive because of the reasons you stated. Also you did not measure your wattage so how can we be sure the power actually doubled? There has to be some major curent draw invovled with those setups..and I really don't think if the OP was in the 150db+ zone..or anywhere near it..he would have posted that question.

With the OP we were dealing with a much simplier scenereo..although I stated and AGREE, that we did not know anything about his equipment, installation, wiring etc... and we got way off course in the discussion.

So "it depends" still seems to be the case.

Thanks for your input.

Jeff, glad you gave input.  I'd be willing to bet a that there could be a truer and more realizeable db increase at the lowest level...1 sub to two with double power...than it could be when you are up into the comp extremes.  At your high comp levels, the difference is more measureable than it is "noticeable", and probably less of an increase, wouldn't you say?  My thinking here is that at the lowest level like this thread deals with, there would be less environmental limitations to the SPL increase that would come into play.  Windshields pulsing and those kinds of things.

And, again, while this thread has grown to unreadable proportions and the OP has long ago left the building, I just wanted to clarify in my own mind what the physics were behind "doubling of cone area" and its effect on SPL.  When I can make some tiny progress in beginning to understand the enormously complex relationship of forces that combine to make sound, I know I've learned something.  Logarithmic math hurts my head!

custom_audio_ny wrote:

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apparently we all got way off course.

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That's okay.  Some of us like a good argument from time to time.

Yes stevdart, a good argument is refreshing..as well as a debate where the participants really know thier stuff. It seems there is an endless amount of material to learn on this subject..as well as the field in gerneral.

As far as what you wrote in your last post "I just wanted to clarify in my own mind what the physics were behind "doubling of cone area" and its effect on SPL" do you feel we have found a conclusive answer?...or will only a percise lab experiment satisfy the topic?

As for myself, I feel satisfied in a general sense. I know there are endless variables that can effect "measured" output but the theoretical answer seems correct.

With all else being equal in a perfect environment..this is what I conclude......

Doubling the number of speakers (I am more comfortable with that terminology over "cone area"..just me) using a correlated "sound" and the identical power to each speaker should a theoretical 6dB increase....uncorrelated yields a 3dB increase.

If the power is halved and an addtional speaker is added....this should yield a theoretical 3dB if correlated...no increase if uncorrelated.

For now I would appreciate some opinions for the above situations without getting Einstein on us. If adding 2 or more dB's of different value I would need a program..I also get brain melt when dealing with logarithems on paper..I am done with school..lol. But since we are only dealing with 2 equal numbers..we only need to agree on how they add correlated and uncorrelated and put the physics aside.

Thanks again everyone for contributing and impressing me.

Didn't you already link to a caculator that adds uncorrelated values?

custom audio wrote:

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do you feel we have found a conclusive answer?

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I thought that I had clearly stated in a previous post that I was satisfied with the information I found.

Yes I did stevdart..but it is not really needed when adding 2 equal outputs together..all you need to do (at least according to what I have been taught) is add 3db. And that is all the calculator does as well if the numbers are equal..its would come in handy for lets say..an  OSHA inspection. If you measured for example a drill press...an air tool and a racing engine individually..they would have different values..the calulator would certainly come in handy to determine the combined SPL, unless you enjoy tons of mind boggling mathematics and have plenty of free time (not to mention the great chance of error).

But there still seemed to be disagreement..well, I was emailed something to the effect "where did you get that goofy calculator?":..lol. well I guess we all learn things differently..hence the debate.

BTW I wanted thank jeff for taking the time to do these tests. Keep posting results..maybe they will prove these theroies conclusivly. I would stick to much lower power levels however, for the sake of this discussion. This will help with any inaccuracies due to body flex, current draw and a host of other issues. The amount of things you need to deal with to bring 157+db to 160+db is much more then required to prove this theory.