Sub box specs for SR124 SVC

2.5gl

History:
I have had two major car audio systems in the past, both were made of components that I found here and there for cheap, at the right time, or were given to me from others moving on... It was a miss match of good, bad, and some junk... Now, two houses, two children, two jobs, and 11 years later, I have more money and time to put towards this the right way and look forward to the kids helping with some of it. Minor remnants of previous systems remain spread across two cars, simply to hear the radio on my commute. This time, I would like to make a calculated attempt at installing a more proper audio system in my car. As I write this, I am realizing I have more questions beyond the box specs. I'll save those for future posts when I need them answered. I am new here, and new to car audio again after 10+ years, I'm sure much has changed since I last attempted anything new.

Car:
98 Subaru 2.5RS

Speaker:
Polk SR 124 SVC

I have come to understand that a sealed box provides for more accurate bass, not necessarily volume. That is why I am going this direction...

Polk states a sealed box with external dimensions of 16x18x11.5. Totaling 1.20 Cubic feet.
Using 1/2" MDF yields an internal dimension of 15 x 17 x 10.5 which equals 1.549 cubic feet.
Using 3/4" MDF yields an internal dimension of 14.5 x 16.5 x 10 which equals 1.384 cubic feet.
Using 1" MDF yields an internal dimension of 14 x 16 x 9.5 which equals 1.231 cubic feet.

I guess that 3/4" MDF is used, as that is what I hear about the most. This, I figure, accounts for the volume the speaker takes up inside the box? (0.18 cu. ft +/-)

Do I really need to be this accurate?

Am I over analyzing this?

Should this be as square of a box or rectangle as it can be, or can I angle one edge to fit against the back of the rear seat?

In either box design, should the sub face forward, to the seat, or rearward, to the trunk lid? (previous experience says rear, but that was a 2 12" bandpass)

Finally: How much amp should I be looking for to run this sub? (brand, model, etc...)


Many thanks for your input!
Lewis

2.5gl

Funny, When I bought it, it was boxed and sold as a SVC unit. Just unboxed it to check, It is a DVC unit! Going to check the math on this and see if Polk recommends a different enclosure size...

Nope, still the same...

2.5gl

Still digging and finding more contradictory information...

Polk's user manual for this speaker states .88 cu. ft. + .14 for driver volume = 1.02 cu. ft.

#1 post was referenced from Polk's site on sub enclosures.

Any clues which direction to take this?

pentoncm

Yes, I can answer your question.

Use a box in the range of 1.2 -1.5 cu.ft. Flatter response, more low end extension at 1.5, more of a bump in 50-80Hz region with 1.2.

The size in the manual was a mistake, I mean look at the size of the SR124. No way that is going in a .88 box.

2.5gl

Got it, I'll run with that.

Any choices on the best amp to use for this sub?

pentoncm

If you don't mind slightly underpowering, you can go with the Alpine MRX50 which is typically underrated by 10-20%. So it would be producing 550 to 600W RMS. I ordered this one for my MM1240 sub, it costs $187 from cartoys.com. Its an authorized retailer and the amp normally comes $300.

Not many amps out there that I know of power 700W, there are tons that are 5-600 or 1000W. You could spend a little more and check out the new Polk D1000 amp which outputs 800W RMS at 2ohm. It goes for $322 at onlinecarstereo.com

Just so you know how amplification works, the difference between 600W and 700W is minimal. For every 3db increase in loudness, you have to double amplifier power. So just to get a 3db bump compared to the 600W amp you would need a 1200W amp. Going to 700W/800W you are looking at a very small difference in output.

2.5gl

Thanks, I'll check those out.

On the sub... Does shape of a sealed box matter? Cube, rectangle, trapezoid(ish)?

pentoncm

I have heard from multiple places that hatchback works out really good as opposed to cube/rectangle. Something like this with an angled back. http://www.crutchfield.com/p_777BB1212S/Sound-Ordnance-Bass-Bunker.html?tp=554&nvpair=FFSpeaker_Size%7c12%22

The angled back is supposed to prevent the backwave from interfering with the woofer cone.

Vital

Polk made a mistake when they first came out with info on enclosure size and even thou they changed it online old .88 stayed on most paperwork which abviously leads to a bunch of confusion.

From what i know eclosure is supposed to be 1.20 and then .14 for sub placement which means 1.34 cu ft TOTAL.