Car subs for home theatre

[Vivek]

Hi all,
I have a couple of Infinity Reference 1230W 12 inch car subs which I plan to use for home theatre. I was thinking of using both of them in a sealed box (placed magnet to magnet). My friend suggests there might be lumpiness in the bass since these are car drivers. He thinks an aperiodic box may be the solution.

Could anyone help me out here?

Thanks,

Vivek

[navin]

You should post the T/S specs as well. incl stuff like B/L, Mms, etc..

[Vivek]

Here are the TS parameters:

voice coil dc resistance: 3.40 ohm
voice coil inductance @ 1 khz: levc (mh) . . . . . . . 2.54
driver radiating area: sd (in2) . . . . . . . . 82.48
motor force factor: bl (tm) . . . . . . . . 14.63
compliance volume: vas (liters) . . . . . 78.50
suspension compliance: cms (µm/n) . . . . 195.40
moving mass, air load: mms (grams). . . . 174.21
moving mass, diaphragm: mmd (grams) . . . 167.15
free-air resonance: fs (hz) . . . . . . . . 27.27
mechanical q: qms . . . . . . . . . . . 6.14
electrical q: qes . . . . . . . . . . . . 0.47
total q: qts . . . . . . . . . . . . 0.44
magnetic-gap height: hag (mm) . . . . . . . . 8.00
voice-coil height: hvc (mm) . . . . . . . 32.50
maximum excursion: xmax (mm) . . . . . . 12.25

[GM]

Greets!

Well, there will be a mid-bass rise due to the high Le if you don't parallel them, but for a critically damped alignment (Qtc = 0.5) there shouldn't be any 'lumpiness' in its response other than what the room does to it:

Vb = ~12.89 ft^3 (365 L), F3 = ~51 Hz, Fb = 33 Hz.

Not exactly HT LFE performance and while raising Qtc will reduce Vb, it will raise Fb, so you may want to re-think your choices unless your room is small and constructed well enough to get some additional acoustic gain BW down low.

For instance, a Fp = Fs end loaded Alpha TL will have a similar Qt and much better damped to below 10 Hz in a smaller, though still large cab:

L = ~122"
CSA = ~104.1"^2

If it must be any smaller, then your friend is correct that it will require a ~aperiodic alignment, which means a high F3, Fb.

GM

[Vivek]

Do you mean to say that I need to try a ported or some other type of box?

The room is not very big and there are a couple of corners which seem to provide some gain with the Vifa MTM speakers I am using now.

The portion below I just did not understand. sorry.

For instance, a Fp = Fs end loaded Alpha TL will have a similar Qt and much better damped to below 10 Hz in a smaller, though still large cab:

Vivek

[GM]

Greets!

Some movies have content to near Dc and significant output to ~10 Hz, so you want the sub's and room's combined response to be ~flat to as low a frequency as the available budget and space for the sub allows and I seriously doubt your room has enough gain for a ~33 Hz or higher Fb.

I don't recommend a vented alignment since the vent would be so large, long, but this means that a reverse tapered TL (TQWT) will work well and would be ~the same size as the Alpha TL, but with more gain down to ~15 Hz. Transient response would be slightly worse, but still far better than vented and why they are popular.

I'm referring to a simple straight pipe TL (which of course can be folded) tuned to at least Fs made popular by Rick Schultz (AKA 'Exolinear'), which will be smaller (~7.35 ft^3/208 L) with better overall performance than the sealed sub.

GM

[Vivek]

A TL is an interesting idea. I wouldn't mind trying it but I am not very experienced at woodworking.

How about an isobaric sub?

[richie00boy]

Forget big boxes and poor response, build a small sealed box and use a Linkwitz Transform. It will take more power, but the end result I'm sure you will be more happy with.

[Vivek]

I don't know what to do now.

[richie00boy]

Well you can rule out aperiodic as Qts is not all that high.

So it comes down to if you have enough power to do an LT, or if you can live with a box the size of a cupboard that requires some woodworking skills.