Question: Can I use a 12" Infinity mobile sub in a DIY home sub?

[Rob_63]

I was rooting through the attic yesterday and found an Infinity Reference 1242W sub in a box (new). It was for a project a summer or two ago that I never got around to. I would leave a link to specs but evidently I don't have enough of a post count yet to do that?

Anyway it has 2 X 4ohm voice coils and is rated 60 -300 watts rms, 1200 peak and a freq. range of 23 to 400 hz.

Is this possible? If so then it would save me a few beans on a driver.

thanks!

 

[TLS Guy]

I was rooting through the attic yesterday and found an Infinity Reference 1242W sub in a box (new). It was for a project a summer or two ago that I never got around to. I would leave a link to specs but evidently I don't have enough of a post count yet to do that?

Anyway it has 2 X 4ohm voice coils and is rated 60 -300 watts rms, 1200 peak and a freq. range of 23 to 400 hz.

Is this possible? If so then it would save me a few beans on a driver.

thanks!

I need the Thiel/Small parameters before giving you an answer. They are not in my data base.

 

[Rob_63]

I need the Thiel/Small parameters before giving you an answer. They are not in my data base.

The PDF with the specs I downloaded does not mention T/F parameters, and I am unfamiliar with this term, does it go by any other name?

Thanks!

 

[TLS Guy]

The PDF with the specs I downloaded does not mention T/F parameters, and I am unfamiliar with this term, does it go by any other name?

Thanks!

No they do not. If you can't find the T/S parameters you can't design a box. If you can't get them you will have to have them measured or get the equipment to measure them.

Look at this pdf.

The T/S parameters are under mechanical/electrical/mechanical electrical parameters. These are the numbers we need to answer your question and design a box.

 

[no. 5]

...and I am unfamiliar with this term, does it go by any other name?

Thiele/Small parameters perhaps?

 

[Rob_63]

OK, I had my head up my arse, here is what you were asking for,

 

[Rob_63]

Here is another that may be of importance.

Could you recommend a thread / article that would explain what it all means?

Thanks!

Rob

 

[TLS Guy]

I have taken a good look at this driver. It is really suited to car use and not home audio.

It is designed for a sealed box around 1.5 cu.ft, including displaced driver volume, amp and bracing.

The bad news is that the F3, the point at which the driver is 3 db reduced in volume and rolls of 12 db per octave is 43 Hz. At 20 Hz it is 15db down.

Now the driver has no excursion to spare, as it is at the limit of driver linear excursion. It could only be equalized if you played it very softly. Here is the sealed alignment.

So this really will not work for the LFE channel of home theater.

Name: 1242W
Type: Standard one-way driver
Company: Infinity Systems Inc.
No. of Drivers = 1
Fs = 24.23 Hz
Qms = 6.63
Vas = 98.64 liters
Cms = 0.244 mm/N
Mms = 175.8 g
Rms = 4.037 kg/s
Xmax = 12.5 mm
Xmech = 18.75 mm
P-Dia = 260.3 mm
Sd = 532 sq.cm
P-Vd = 0.665 liters
Qes = 0.52
Re = 1.85 ohms
Le = 1.12 mH
Z = 2 ohms
BL = 9.76 Tm
Pe = 300 watts
Qts = 0.48
no = 0.26 %
1-W SPL = 86.3 dB
2.83-V SPL = 93 dB
-----------------------------------------
Box Properties
Name:
Type: Closed Box
Shape: Prism, square
Vb = 1.312 cu.ft
Qtc = 0.707
QL = 19.19
F3 = 43.39 Hz
Fill = heavy

Now this driver can be put in a vented enclosure, but the T/S parameters are such that the box has to be very large. It is over 5 cu.ft. and when you add driver volume, bracing and amp, it will be about 5.5 cu. ft. You would have to build a slot vent around the inside of the enclosure, of 2" X 10" X 26". to tune the box to 19 Hz. The vent air velocity would be 18 m/sec.

Here is your vented alignment.

Name: 1242W
Type: Standard one-way driver
Company: Infinity Systems Inc.
No. of Drivers = 1
Fs = 24.23 Hz
Qms = 6.63
Vas = 98.64 liters
Cms = 0.244 mm/N
Mms = 175.8 g
Rms = 4.037 kg/s
Xmax = 12.5 mm
Xmech = 18.75 mm
P-Dia = 260.3 mm
Sd = 532 sq.cm
P-Vd = 0.665 liters
Qes = 0.52
Re = 1.85 ohms
Le = 1.12 mH
Z = 2 ohms
BL = 9.76 Tm
Pe = 300 watts
Qts = 0.48
no = 0.26 %
1-W SPL = 86.3 dB
2.83-V SPL = 93 dB
-----------------------------------------
Box Properties
Name:
Type: Vented Box
Shape: Prism, square (optimum)
Vb = 5.109 cu.ft
Fb = 19.29 Hz
QL = 6.108
F3 = 20.3 Hz
Fill = minimal
No. of Vents = 1
Vent shape = rectangle
Vent ends = one flush
Hv = 2 in
Wv = 10 in
Lv = 26.12 in

So that would work, if you are prepared to build and brace a large box.

If you are interested in still using this driver, I can load all the details and graphs to my web site. The files are too large to attach here.

If you did build it, then F3 is at 20 Hz and it will play 10 db louder than the sealed sub, which is a lot.

One other issue, is that, that driver has two four ohm voice coils. So if you wire them in parallel (preferred) you will have an impedance of 2 Ohm. It will take a much more costly amp to drive a 2 ohm load.

If you wire the coils in series then the impedance will be 8 ohm. However most plate amps do not put out much power into 8 ohms, normally half their rated four ohm power.

 

[Rob_63]

Thanks for all of your effort! I guess it would probably be more beneficial in the long run to just purchase an appropriate driver. It wouldn't make sense to spend more money on an amp just to save a few beans by using that sub. I really doubt my wife would want a box that big in the living room anyway, heck I wouldn't want one that big either.

I built a box for my daughters boyfriend last year using two of those speakers, one box with two compartments using MDF, with 1.5 cubic ft. both cabinets. They seemed very deep in his car, but like a typical younger generation music listener the bass was very overdriven making it impossible for me to enjoy listening to it.

TLS Guy could you recomend a site/thread that would explain how to understand/use those specs for beginner like myself?

Thanks again for your help!

Rob

 

[TLS Guy]

Thanks for all of your effort! I guess it would probably be more beneficial in the long run to just purchase an appropriate driver. It wouldn't make sense to spend more money on an amp just to save a few beans by using that sub. I really doubt my wife would want a box that big in the living room anyway, heck I wouldn't want one that big either.

I built a box for my daughters boyfriend last year using two of those speakers, one box with two compartments using MDF, with 1.5 cubic ft. both cabinets. They seemed very deep in his car, but like a typical younger generation music listener the bass was very overdriven making it impossible for me to enjoy listening to it.

TLS Guy could you recomend a site/thread that would explain how to understand/use those specs for beginner like myself?

Thanks again for your help!

Rob

I would start here, and also get this one.

 

[highfigh]

Seeing that The Loudspeaker Design Cookbook is version 7 makes me feel old. My copy is version 2, IIRC.