adding one more sub, noticeable difference?

Wow stevdart.  Way to be diplomatic. 

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.

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??

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

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.