Box design questions

[Jkm3141]

Hello,

I posted my first dual 15 setup about two months ago and was told by several people that the box design was holding me back. I recently took a vacation to west virginia with some fellow audio friends and built another box while down there, to my friends specifications, and am seriously unhappy with the way it sounds. I was wondering what approach I should take when building a new box, something I would like to do this weekend sometime.

My first box/setup is shown here,

It hit very hard and hit a LOT of very low notes by comparision to other systems I have heard. The only issues I had with that box is the size of it (7 cubes) and that I had no good place to mount the amp (Amp blew up recently, I assume due to being mounted to the box). The port on that box was 2 inches wide, and about 8 inches back.

My friend who helped with the design of the second box said there was no reason to have the box that big and also said the port completly wrong on the first box (not big enough, not far enough back). He went ahead and designed a box which had the subs and port facing up, with a 4 inch port in the middle. The port goes down to 4 inches from the bottom and splits towards each side of the box ending about 4 inches from the sides. The new box is 5 cubic ft and fits much better in my trunk, and from what I was told it is tuned to 34hz.

Also, I did not replace the blown Power Acoustik A3000DB amp with the same model, as I am sick of Power Acoustik issues (my friends have had terrible luck), so I picked up a Hifonics Brutus BXI2010D amp and planned on wiring it at 1Ohm instead of 4Ohm like the A3000DB. This should be netting me a max of 2000W instead of 1200W.

My impressions of the new box are that it punches beats much nicer, making rock sound loads better. but it just cannot hit constant notes with any kind of force. It does alright on higher frequencies but not low frequencies. I cannot seem to understand why it cant hit the lower notes better if its getting at least 500W more power and is truely tuned to 34Hz. My only guess is the smaller volume of the box is really holding it back. Audiopipe specs the TXX-BC15 speakers I have to between 3-3.5 cubic feet per speaker.

Would a drastically under volumed box cause these problems?

What type of design should I use when I create the new box. I really am up in arms about speaker enclosures now as the box that seems wrong for all reasons sounded much better with less power than the box that appears to be meeting all specifications except volume.

I appreciate any help, I know you guys will be able to hook me up with a good design. I can build nearly anything once I get a good design thought up.

- John

[AI James]

try subs up port back in the car or subs and port up. and try 3 cubes each with 90sq in of port. mount the amp on the back of the seat

[1992Chevy K1500]

If your subs neen 3 cubic feet of airspace per sub, then you need at least a 6 cube box. The 5 cube box will hold them back. The recommended port area is 12-16 square inches of port per cubic foot of airspace.

[Jkm3141]

Thanks for those rules of thumb, I am trying to learn box theory and it is quite hard to get good information on. Any specific design on the port, or just one rectangular port going back. Like I assume things sound totally different with a 2 inch wide port going far back versus a 4 inch port going half as far? The port on that 5 cube box is rather intricate, as it is not just a single rectangular port going back which is why I ask.

After posting earlier, I went and messed around on my setup a bit, and after facing the box down where the port and subs are facing back, it sounds a lot more like my old box, but still doesn't hit the low's as well. I just assume its starved for air? I am also confused as to why the whole system isn't a bit louder, since 1ohm on that Hifonics amp should be pushing at least 500W more than the old Power Acoustik was at 4ohm. I might not be pushing the amp far enough to have noticeable volume differences, but I want to get the box situated first.

Anyone know any good reference sites on port theory?

I'll let you guys know how it works out, I plan on buying wood tomorrow after reading some more.

- John

[1992Chevy K1500]

http://www.the12volt.com/caraudio/boxcalcs.asp#top

I use this calculator, but some people have different preferences.

And I can't take credit for those rules of thumb. I learned them here from other members. Thanks to those members for being helpful!

You can make just about any port design you want, just as long as it has the needed area.

Edited August 15, 2009 by 1992Chevy

[Jkm3141]

http://www.the12volt.com/caraudio/boxcalcs.asp#top

I use this calculator, but some people have different preferences.

And I can't take credit for those rules of thumb. I learned them here from other members. Thanks to those members for being helpful!

You can make just about any port design you want, just as long as it has the needed area.

I've been using that for a while. Great site. However the 12-16 square inches number is a useful thing to know.

[Torres]

also what you want to keep in mind is, the more port area you have, the longer the port will need to be to get the same desired tuning of the smaller port. and in doing this, can take up lots of box volume. could be good, could be bad.

[Jkm3141]

also what you want to keep in mind is, the more port area you have, the longer the port will need to be to get the same desired tuning of the smaller port. and in doing this, can take up lots of box volume. could be good, could be bad.

I kinda think thats whats hurting me now. A Lot of the box area of my current box is port. However the 5 cube number I am coming up with is the entire box, not minus the port.

- John

[Boon]

Subs back port back works MUCH better in those cars. Tried flipping the box? It's probably also a bit small to really murder the lows.

[Jkm3141]

Well I built a 6.4 cubic ft box yesterday and threw my speakers into it today, and I gotta say that it sounds loads better. I went with a center port again, however 3 inches wide and it sounds good.

Also, I have another question of a different sort. I have been looking into a single Fi BTL 18" for a while as an upgrade. I would build the box between 6-7 cubic feet as that is the most I can comfortably fit in my trunk. As for the box design, I am wondering what I need to do to support that kind of speaker. Most people I see use at least 1.5" MDF for the speaker surface, and some kind of internal bracing. How much strengthening is nessessary to support 3-4kw of power from a BTL?

Thanks for all your guy's help.

- John