adding one more sub, noticeable difference?

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.

http://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.  http://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:

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

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

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

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

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

http://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.

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.