dual subwoofer box wiring

[skeletonT]

hi, this is actually for my car so i hope nobody minds me posting here... 

 

i am building a little box with two 8" subwoofers. they are dual 2 ohm voice coil design, with a power handling of 100-350 watts rms.

 

heres how i plan to wire them...

 

 

so my ideal amp would be stable at 2 ohms and put out between 200-700 watts RMS?

 

thanks! -nic

[BATMAQN]

Why don't you try the car audio forums they would be all over this sort of set up and they can suggest parts you'll need.

[L J T]

hi, this is actually for my car so i hope nobody minds me posting here...

i am building a little box with two 8" subwoofers. they are dual 2 ohm voice coil design, with a power handling of 100-350 watts rms.

heres how i plan to wire them...

so my ideal amp would be stable at 2 ohms and put out between 200-700 watts RMS?

thanks! -nic

Most decent monoblock amplifiers are stable into two ohms. Is the enclosure sealed or vented?

Are you using software to model the enclosure?

[henry218]

watts related to how loud you want to play the sub.

as long as the amp can handle 2ohm, (some even 1ohm) i dont see any problem with it.

[Grumpy]

So! do the drivers have 2 sets of connection posts each?

[shaky]

Dual voice coil subs have a set of connections for each VC Grumpy. Just a design to help with flexibility in setting sub loading for amp. Quite common in car audio subs and has been around for many years now.

[henry218]

its common for subwoofers, whether its for car audio or home, this is useful for multiple subwoofers wiring. 

 

for the servo controlled sub, similar to DVC but one set goes to the output and one set goes to the servo coil sensing controller.

[Paul Spencer]

Car audio is not really my area, however, I believe 2 ohm loads are common and often preferred in car audio. Regarding how much power you need, that will depend on the design of your box, and your particular driver. With the information provided there's no way we can answer on how much power. Your design may be thermally limited, excursion limited, or both. We simply can't say. What you will need to do is model your design and find out. If you are using EQ, that's also a factor.

[bjc]

Buy an amp with as much power at 2ohm as you can afford in your budget Nic.

We call it 'Headroom' in car audio!

 

Sign up to the MEA Forums if you haven't already- http://www.caraudio.com.au/forums/

[skeletonT]

heh car audio forums seem to be rife with bad attitude and pissing contests so i have avoided them for the most part. i kind of like the vibe here to be honest, so i thought i would push my luck and just post here! i will try that forum you mentioned though and see how it goes for those interested i am just going to put a couple of 8" subs on the rear shelf of my car. they will be in small sealed enclosures. totally *not* for annoying everyone within a kilometre radius with douchebag amounts of bass... i really love to have very loud and present mid bass?i guess you would call it? or low mids? high bass? not sure on the lingo heh, but i remember buying my first 12" subwoofer and thinking "damn that was not the frequency i was hoping to boost". 

 

im just a bit confused with the wattage thing, i have heard its bad to under power speaker, and then its bad to over power them. then people say its only bad to overpower speakers if you dont adjust the gain properly, then other people say something about thermal handling or such, and that underpowering speakers only is bad if the amps clipping... seems to be one of 'those topics' where you just end up with people screaming at each other and you walk away more confused than before. i guess this topic is not specific to car systems in particular, so i was hoping to get a calm and rational response out of you guys

 

i figure its a safe bet to just get the highest RMS the speakers are rated for - 700W. but theres not exactly a dearth of 700W amps out there, so i wonder if 500 would be sufficient. but then i suppose if it would depend on exactly which amp and speaker you are pairing together, then i might have to put on my flame proof suit and wade into car audio forums land !!

 

just in case anyones interested the exact speaker is an alpine SWR-823D. the box will be small, sealed around 0.39 cu ft. so two of these each in their own little box. just read my post again, and this was not at all clear originally that they would be housed separately. the boxes would be cylinder or a long hex type of shape, like a tube basically...

[SBL]

Just some sims on 2 of the alpine 8's. Don't expect these to be 100% accurate as Alpine hasn't published some important numbers. But it should be pretty close.

 

Based on this your ideal sealed box with a qtc of 0.707 would be 1cubic foot for both of them. So 0.5 cubic foot a piece.

 

500w will put the drivers on their linear excursion limits. So all you need is a 500w 2ohm stable amp.

 

F3 around 50hz, will be much lower in a car.

Max SPL of around 112, again will be more in a car.

 

[skeletonT]

wow, cant thank you enough for doing that for me! a 500W amp is ideal and can make the boxes slightly bigger too. really awesome stuff

[L J T]

Remeber to include the effects of cabin gain when modelling for a vehicle also. Lower frequencies can be boosted by as much as 20db in a car.

[SBL]

Remeber to include the effects of cabin gain when modelling for a vehicle also. Lower frequencies can be boosted by as much as 20db in a car.

 

Are there any rough guidelines to what sort of boost cabin gain would get you with a typical car setup? I know the F3 will be significantly lower, but didn't include the effects of cabin gain in the models. Im not really a car audio person.

 

I would have thought every car would be quite different, making it difficult to model without measurements.

Edited August 11, 2013 by SlowBarless

[davewantsmoore]

difficult to model without measurements.

 

Correct.    However, If you make sure you have EQ/DSP available.....  then it won't matter   (well, at least the worst case will be you didn't need such a big subwoofer, due to underestimating the gain).

 

 

Install  >  measure  >  filter/EQ  >  BBQ!

[L J T]

Remeber to include the effects of cabin gain when modelling for a vehicle also. Lower frequencies can be boosted by as much as 20db in a car.

Are there any rough guidelines to what sort of boost cabin gain would get you with a typical car setup? I know the F3 will be significantly lower, but didn't include the effects of cabin gain in the models. Im not really a car audio person.

I would have thought every car would be quite different, making it difficult to model without measurements.

I will post a graph when I am home later to give you an idea of cabin gain.

[L J T]

Here is a graph showing the natural gain of a sealed subwoofer when placed in the car environment.

This is just a representation of the effect.

 

cabin gain.bmp

 

Green line is the predicted response.

Orange line is predicted response in the vehicle.

 

Different cars have different respones. 

 

 

[SBL]

Here is a graph showing the natural gain of a sealed subwoofer when placed in the car environment.

This is just a representation of the effect.

 

cabin gain.bmp

 

Green line is the predicted response.

Orange line is predicted response in the vehicle.

 

Different cars have different respones. 

 

So an F3 of 31.86 in car, 52hz out. Fairly substantial difference. 

 

I don't get why the graph shows flat to 5hz though

[L J T]

Yes not entirely accurate, but shows how different the frequency response is in car can be.

5hz will cook almost any voice coil

[skeletonT]

i see my faith in this forum was well placed. (but i did check out that car audio one and it was not so bad )

[bjc]

Yes, there is plenty of helpful and knowledgeable people there also. It's a matter of patience if no one has responded quickly. There are tonnes of tutorials etc there to learn also as with any good forum...