n0catchyname

I'm in the beginning stages of working on a box design for my '77 Celica liftback. I have lots of time before the car will be actually ready for the build and final dimensions can be figured, but I'm running some numbers and calculations so that I can get this as close as I can to how I want it and have a rough idea of what I want to do (when I get the chance to do it), without having to build it 6 times. I'm running into some design issues that could gain me volume, but unsure if they would be effective.

The car will be used as a summer driver, designed for how I like my bass. I'll be running a Orion HCCA 15.2 firing upward.
Starting internal box dimensions of 22'W x 16"H x 25"D = 4.8 cu.ft. gross

First off, to get the space, I'm having the spare tire wheel well removed and a metal box built down between the frame rails, I'm figuring on ~9" height gain (but could be anywhere 8-10" so I used 9"). So my starting internal box dimensions will be roughly 22'W x 16"H x 25"D = 4.8 cu.ft. gross. My thoughts were, if I deaden the hell out of it, would I be able to use it as a lower portion of the box, without using wood? Effectively I could gain ~1" height and 2" width, effectively bringing my volume up to ~5.5cu.ft. Of course, the top of the half box would have to be sealed to all hell to make sure that there were no air leaks at the seam, but I'm not worried about that. I'm just wondering how using completely dead steel would compare to 1"MDF. Also how the deadening might affect how the sub reacts compared to the mdf.

My 2nd question is, when making those calculations, I calculated that the sub would be on top of doubled 1" baffle board. If I sunk the sub down one layer, I could effectively gain another 1" height (by being able to build the box 1" taller), bringing gross internal up to ~5.9, which after sub and port displacement is ~5.1 cu.ft. But would I need extra bracing to support the sub, or would the 2nd layer of MDF have a similar effect either way?

Lastly, if all this is possible without any foreseen issues, I was planning on using dual 3" x 7.5" x 14.75" slot ports (port frequency = 26hz) firing upwards, but unsure if that'd be enough port area. My only other option to create more port area would be front firing ports. But I'd prefer to stick with upwards if those port sizes would work well.

Any input would be greatly appreciated. Thanks

Dukk

As much as you deaden the metal, it will flex, and that is bad. Line the metal with fibreglass, 8-10 layers or 3/8-1/2" and you'll be set.

n0catchyname

Awesome, thanks for the info.

MTA

iTrader: (1)

that was my suggestion, good call.

but does he really need 5cu ft?
and whenever you do box calculations use internal dimensions not external or your results will be very inaccurate

n0catchyname

Yes, I know to use internal dimensions. As for do I need a net of 5 cu.ft....no, technically I don't need 5 cu.ft., but I would definitely like to have it if I can get it.

n0catchyname

To furthur my explaination



The image above is a comparison between net volumes of 4.0 (red) vs. 5.0 (green) with a port frequency of 26hz with a flat car response. I'm still working on what frequency I want to tune to due to in car response, which I won't really know until I get something set up and can actually test. As you can see there isn't much of a difference. Having used a 15" HCCA in the past - given it was about 8 years ago and 1/2 the physical size - I know, back then, they loved bigger boxes with lots of port area (hence the question on port area). I can't imagine that's changed, given what I've researched of others using them.

Like I said before, these dimensions aren't exact or definite. Long story short, if I can't get 5cu.ft. net (~5.8 gross), I'm not overly concerned, but I want to take full advantage of the little amount of space I will have and make the box as big as I can. So if I can gain 1" W x 1/2" H x possibly 1" D (which I didn't even calculate in earlier) by using 1/2" of fiberglass instead of 1"MDF, without any adverse effects, every little bit helps.

MTA

iTrader: (1)

now the question is... with such a big bump at low frequency, do you want to have excessive lows? or more balanced sound? with using such a big box and tuning low it will very efficient at low frequency and the room gain of your car will give you around 6-18dB gain at most frequencies below 60Hz causing that low frequency peak to totally throw off any tonal balance. but if that is what you're after then all the power to you.

n0catchyname

Yea, I'm a bit of an extremist when it comes to my lows and highs (excessive lows + screaming highs = very happy me). But thank you for bringing up that point, duely noted. I just looked up the manual to check Orion's recommended box designs and they say a 3.05net cu.ft. box with a port frequency of 38hz (represented by the yellow line) for 2000+W input or 4.5cu.ft. @ 38hz (hard-to-see blue line) for 1500-2000W input.



Either way, I thought that peaking @ 38hz how the graph shows would be much worse than the peak tuned at 26hz. Am I wrong? I'm still learning how these curves can be interpreted.

Dukk

Depends if you want 5+ db under 30hz where there's not a lot of content but its reeaally low or 3db at 50hz where it will bump more

n0catchyname

Ah, alright, I think I understand a little better. My tuned frequency is where I will notice the biggest gain in car, so tuning at 26hz will give me huge gain @ very low frequencies, but will drop off a lot before reaching most musical tones. Where as tuning at 38hz will peak higher but will give me a more musically tuned box. And the where it peaks on the graph with a flat response is roughly the frequency it will be in-car @ 3dB.

So if I tuned 32 Hz in a 5cu.ft. box (red line), compared to the recommended 38hz in a 4.5 cu.ft. box (green line), it would be more musical than tuning at 26Hz, and provide more powerful lows than tuning at 38Hz, basically a compromise between the two? Or am I not getting this at all? I thought I had a rough idea of what I was doing, but now I'm unsure.