First enclosure construction

[Matthew Bibby]

Hello, I am completely new to the world of speaker construction etc.. and so require some help.

My first project will be a sub woofer box for the boot of my car, after that I will add to it, but for the moment I will just be making the sub. I wish to use 2 x Skytronic 902.222 12" 300W drivers as I am on a limited budget and have found these at a reasonable price.

The specs of this driver are as follows:
Power max:300W
Power rms:150W
Voice Coil:6.25 cm (2.5")
Diameter:30cm (12.0")
Frequency response:20Hz - 6kHz
Magnet weight:1.4kg (50oz)
SPL @ 1W/1m:91dB
Re:7.1 Ohms
Fs:29 Hz
Qms:1.62
Qes:0.71
Qts:0.53
Sd:346 Cm2
Vas:49 litres
Cms:288
Mms:59g

I assume that when putting 2 drivers in one enclosure you add the relavant specs of the two drivers together, in this case the same drivers, when entering them into enclosure calculators etc?

Finally, could someone recommend the best enclosure size calculator to use as some I have seen are quite confusing.

I was told that this would be the section of the forum where I would find the best advice. I will also be looking for some advice concerning wiring at some point.

 

[jinjuku]

I would start with what the manufacturer is spec'ing out for enclosure volumes. Then simply double it up.

As example the Infinity Reference 1260w has a recommended 1.2 cubic foot enclosure. So two would be 2.4 cubic feet.

 

[mattsk8]

For sure what jinjuku said, just double it up for 2 subs. Also, for wood I'd definitely use 3/4" MDF.

As far as calculating the enclosure size, it's LxWxH/1728 on the inside of the box. Remember, you're using 3/4" mdf so you'll basically subtract 1 1/2" from the outside box's dims.

For instance, if I had made a subwoofer box that was 14"deep x 12"tall x 13"wide (inside the box), it would be 1.26 cubic feet- that would be for one sub. If I were running 2 subs, I'd just make the box 26" wide w/ the same height and depth and it would then be a 2.52 cubic foot box; good for 2 subs that required 1.26 cubic feet each.

You also have to subtract a teeny bit of airspace for what the sub uses up in the box; your subwoofer manual should state that info.

The info I just gave you is fairly generic, but a good rule of thumb. Sealed boxes are the easiest to build FYI, but ported sub boxes generally give you a little more boom. I was always particular to the sealed boxes myself for subs in a car for 2 reasons, easier to build and they take up waaay less space. A ported box requires a lot more air space, so its a lot bigger box.

 

[GranteedEV]

As far as I can tell, especially for a car, this driver will work best in a sealed enclosure of about 50L

So two drivers will want about 100L - about 3.5 to 4 cu ft

I couldn't simulate the inductance hump with the Le paramter, otherwise it's possible the driver could sound good in as little as 30L/driver. IMO the larger box would be worthwhile.

Either way though, I would recommend being able to tone down the ~40-60hz range where you may have some peaking in the car environment.

 

[annunaki]

In all honesty without an Xmax number those specs are somewhat worthless. If you can provide them a better simulation can be run to get an optimal enclosure design.