Frank Mowry

two sub effects on SPL?

I'm looking at making my first sonosub and had a question regarding the effects of second sub (exactly the same) added to the mix. Is there a formula that computes the added SPL achieved while adding another identical sub? I played around with WinISD and notice if a select 1 vs 2 drivers in a vented box tuned to 25 Hz it appears that I get about a 3 dB increase vs the single across the board.

My dilemma is wanting to use "what I have sitting in the parts bin". I've got the tools, connectors, MDF, etc. Just need to pick up a plate amp and the sonotube.

I've currently got 2 Phoenix Gold XMAX 10s. I know using a car sub won't provide the best performance but despite them being pretty nice subs for small car encosures it doesn't seem that anybody even considers tens for their cars anymore. I can't even sell both for the price of a Shiva. Haven't put them up on ebay yet but similar sales seem to indicate they go for 50-60 bucks a piece. That's why I figure I'll at least start the project to see how it works. These subs are in the WinISD database. I'm getting the standard PE 250w amp to drive on.

In WinISD I played with these numbers which seem doable:
Number of drivers : 1
Box type : Vented
Box size : 85.9 l
Tuning frequency : 25.00 Hz
Vent : 1 vent(s)
14.74 in length for each
4.02 in round

Tube would be only about 23 inches tall at 18 inch diameter. Call it Stubby. SPL would be a rather anemic 88 db max at 30 hz dropping to 86 across the board. Is this a total waste of time? Adding the second driver with the same parameters yields the 3 dB increase across the board. It also yields the cost of another amp which could be put towards a better driver. The second driver in the same tube isn't practical for me from a design standpoint but replicating the first sub would be. Does 2 drivers in 1 enclosure yield the same increase as 2 drivers in separate enclosures (given the same total volume)?

Feel free to tell me if this is a waste of time (aside from gaining experience).

Thanks,
Frank

Travis Cain

I'm no expert, but since none of the experts have chimed in...

From my understanding, it works like this:

Say for instance you have 1 driver with x number of watts in a 50L box and it gives you a max of 100db.

Now, if you build another identical box seperate and do NOT increase the power applied, you won't gain a single db. If you double the power applied since your power handling doubles due to having 2 motors, you gain 3db.

But, if you were to take 2 of those drivers and put them together in a 100L box and still do not increase the power, you will gain 3db from acoustic coupling. But once again, if you double the wattage you gain another 3db for a total of 6db.

So, it is by far the most economical to put them both in the same box to get the free 3db from acoustic coupling.

Something else to consider is when you have 2 seperate subs in the same room, you have to deal with them cancelling each other out at some freq's in different parts of the room. Since I have never used 2 subs in the same room before, I know very little about it. I'm sure there are lots of folks here that can fill you in on that aspect, should you decide on seperate boxes..

Frank Mowry

Thanks for the info. I'd still like to hear others chime in for my curiousity, but it is probably a moot point as it looks like I've got a deal to trade for an Adire Shiva.

Frank

Joel X

This doesn't quite feel right.

MichaelAngelo

Acoustic coupling occurs outside the box. Two boxes can be placed together to achieve the same effect as having the drivers in the same box. The back sides of the drivers don't contribute to coupling. It's the face of the drivers being in close proximity to each other that produces the coupling effect. Theres a formula, I couldn't find it, that determines the coupling of 2 drivers, based on distance apart. But whether they're in the same box, or separate boxes, doesn't matter, as long as the cones are as close as poss.

Kicker states that's one "benefit" of their square drivers- better acoustic coupling, because they can be placed close together with a minimum of wasted space.

Ryan Schnacke

Once I've got my 2 sonosubs level-matched and in phase I get +6dB by running both subs rather than just one even though they're 12 feet apart. Yeah, 12 feet! At the time I was running 80Hz tones to get everything (both subs plus mains) in phase at the crossover point.

I've also tried level matching a sub with the main speakers at the crossover point. I get the same +6dB gain by running speakers + sub vs just the sub or just the speakers. This worked at 2 friend's houses where, in both cases, the sub was across the room from the mains. But you've got to have the phase adjusted correctly to get this. In fact, this is a great indicator of whether you're sub is phase matched with your mains.

Frank Mowry

Well now that my trade fell through it looks like I'll go ahead with the original project and start with a single sonotube for the 10 inch Phoenix Gold Xmax.

Thanks for the info guys.

BTW, if anyone wants to trade me a decent Home sub for my two car Xmaxes, drop me an email or PM. Lemme know what you have. Pics available on request. Phoenix Gold recommends a .3-.6 ft^3 box. I had mine in a ~.35. Pretty nice bass for limited space. I'm in Baltimore, MD.

Frank

Travis Cain

Sorry for the misinformation. I recall reading a similar thread before, and I apparently misunderstood it regarding acoustic coupling.

David Lorenzo

You got almost everything right Travis. Just the fact that acoustic coupling occurs outside of the enclosure was throwing you off a little.

Considering how big the wave lengths are of sub woofer frequencies, it makes sense that coupling would occur even if the subs were located across the room from each other.

Bill Fagal

Let Ryan's experience be your guide--two equivalent subs driven by two equivalent amps (wired identically) will give you 6dB more than a single at a given amp gain.

Some rules of thumb:

A) Two drivers will yield 3dB more than one. Four drivers will yield 3dB more than two. (Assumes a single amplifier, equal total impedences, and equal power levels.) This is a result of the doubling of the cone radiating area which yields a better acoustic impedence match (i.e. moves air more efficiently.)

B) If you cut load (speaker) impedence in half, an amplifier will pass double the current at a given voltage setting (which equals a 3dB gain, all else being equal). Double the impedence, and the inverse is true.

Therefore:

2 drivers wired in series to a single amp will yield a gain of 0dB over a single driver (+3dB for doubling cone area, -3dB for doubling impedence).

2 drivers wired in parallel to a single amp will yield a gain of 6dB over a single driver (+3dB for doubling cone area, +3dB for halving impedence).

2 drivers wired to two amplifiers will yield a gain of 6dB over a single driver & amp (+3dB for doubling area, +3dB for doubling amp power).