dep, out of curiosity.... what's your source on this? i wouldn't mind having some proof in either direction for +3 dB = double cone area or +3 dB = triple cone area. your comments ring a bell, but i'm not confident in the recollection...

 

sharpen your pencils and start your calculators ladies...

we've got a doosey

 

yup, i think definitely worthy of the FAQ assuming we can verify the info...

 

LOL this thread went off on a tangent, my bad. A new thread containing this info would be helpful. The original poster's probably like wtf I feel like an old fogey forgetting a lot of these things, it's good to get a refresher. I graduated with CS with a minor in math - you can tell my memory's shot.

 

[QUOTE=PJK3,Jul 6 2005, 11:01 AM] double power = 3 dB.

 

Here we go

When one adds a subs say from 1 to 2 subs (in a planer array) each with the same power being feed to each sub and assuming each sub performs exactly (cone excursion) as the original; one would only gain +1.5 dB due to the destructive interference that happens between the effective radiating piston areas.
Another way (more technical) is to say that there would be the phase angle difference between the two subs and the listener, which prevents the pressure waves from adding completely to each other preventing the ideal +3dB rise form becoming reality.

I use this phase angle as well as the theory of half-space radiating sound pressure waves in the design of a sub woofer enclosure. This is why power wedges and compression chambers are know to produce substantial increases in db output over standard planer arrays.

There is another way to get +3dB gain from just adding another sub but it requires a substantial amount of digital signal processing to cause a time delay in the second sub to cause the pressure waves to add coherently. This delay would be change very rapidly due to each frequency has a different period. This type of processing power is not feasible in a car audio environment due to other factors such as road noise and panel vibration that takes place in a car.

Another thing to look at is the back EMF (electro motive force) that is generated by adding an other sub. This back EMF causes more of the electrical energy to be converted to heat instead of the magnetic field causing the speaker to have mechanical movement.

I am a mechanical engineer so I will leave the electrical side of things to the EE

 

The poor guy just wanted to know whether to replace his speakers and look what happens.

One thing deppenma's post tells me is that:

In a box with more than one sub, the relative locations of the cones to each other will partly determine how loud the box can get.

If this is a fair summary, here is a related question:

What about port locations in vented boxes? Will they also make the box louder or not depending on where they are in relation to the cone(s)? As you travel the various forums, you see all kinds of configurations but it's hard to know what works best for ultimate loudness and sound quality.

I have a ported multi-sub box design in mind but have no way of predicting how it will perform. I can briefly describe it here or start a new thread. Either way, I would greatly appreciate any constructive comments.

Thanks.

 

dierk, start a new thread with diagrams and measurements. i'm sure you will get some feedback.

 

this, i can easily agree with....

this, i have to raise some questionable flags on... i'm sure you've heard of a double slit interference pattern?
if you have 2 point sources providing the same wavelength output (ie the slits), depending upon the frequency, source separation, and ambient surroundings -- you will have both interference AND reinforcement patterns.
so, your argument doesn't completely hold up because you are using an approximation of the +3 dB enforcement and 0 dB cancellation and averaged them together for a 1.5 dB output.... kinda fuzzy, but.... heh. *shrugs*
not to mention -- any time correction efforts are still not going to be successful in eliminating this entirely regardless of processing power -- that's simply due to the fact that if you delay one to reinforce the other in 1 direction, the other directions will (more or less) shift in or out of phase based upon the orientation of the speakers to each other.
(ie, if you put the subs in a line facing 0* and phase them to syncronize for 0*, then at 90*, 180*, and 270*, you'll be potentially out of phase (or at least for sure not IN phase) depending upon the output frequency (wavelength) and point source location spacing.



and regarding back EMF -- i think that will really only be an issue if the speakers are wired in series or are in close proximity. if they are in parallel, back EMF should be a non issue with enough speaker to speaker spacing since magnetic field strength falls off as an exponential.
if they are in series, then you have some losses because the movement of each voice coil w/in a magnetic field induces a small current that will affect the other voice coils as they move... and vice versa.



am i making sense?


regarding ports dierk -- heh, that's a whole other ballpark. i'm not the strongest for knowing all my port info either...
i'll have to do some reading and look for your other post....

 

I was trying to simplify the example by using only +1.5db reference I was wondering is some one would pick up on that.

Very interesting link

Again I did not want to make the example to hard to understand.
Yes in this particular example there is both constructive and destructive patterns. The only values that I posted were approximations of the net effect of the constructive and destructive patterns.

On the Electronic DSP issue again I was trying to keep it simple.
PJK3 It would appear that either you have some experience in either acoustics or wave theory.

Ported/vented enclosures is another issue entirely.
In most cases as a good rule of thumb a port (cylindrical/round) can be places anywhere in the enclosure as long as the port openings are no closer than 1.5times the diameter to a wall or object. With a slot port again no closer then 1.5times the dimension that is perpendicular to the nearest wall or object. But most design us an exterior wall of the enclosure to make the design more simplistic.

Note that a well designed ported box will have +3db over a sealed enclosure over a wide frequency range but will have a