Advice on building some SPL sub boxes

[acarmody]

dont port it

Ports sound better in the car but unported kills it outside

????? I don't understand what you are trying to say. These are definitely going in my car. And sealed boxes aren't going to do to well in SPL comps.

 

[holdenboy]

When i get time tonight i'll run those measurements through the BassBox Pro calculator and give you some advice.

 

[acarmody]

Thanks Holdenboy. I'm entering the 'Street B' category, thats 3x10" or 2x12" or 1x15" with 750-1500WRMS, I have 1400wrms. I'm really going to go see the Rep and Pro cars but a trophy would sure make the day awesome :yeah:.

I'm going to see if I can somehow shoehorn some 3cu.ft + port boxes in the boot, by my preliminary numbers say no. My ol' man can't start work on the boxes until next weekend anyway so I got time.

Also would 45hz be better for burping tones? And would flaring a slot port help any? http://www.subwoofer-builder.com/flares-rectangular.htm

 

[holdenboy]

Smaller boxes are generally louder than larger ones. This is for a number of reasons, but the main ones are:

* Smaller hatches have a high peak frequency (54+hz) and this suits the smaller boxes which are easy to make peak in the mid 50hz region.
* Specs / Evidence suggests smaller boxes are "peakier", which means they've got a larger peak in frequency response when compared to larger boxes.
* Smaller boxes are easier to position in small hatches, especially using large external ports etc.

Anyway, none of that really applies to you as your using a large sedan (will peak 45-50hz). So instead of going with a 2.8-3.0 cube box for both (the norm in hatches with 3+kw), 4-5 cubes after displacement is better for a lower peak.

A smaller box peaks 7-10db higher than what its tuned at, larger boxes tend to peak closer to the tuning frequency (probably 2-4db). So if you were to tune the box/s to 40hz it would peak around 42-44hz mark in car. This is about right for some Commodore sedans, but by tuning there you can just cut down the port length a few cm at a time to try and raise the tuning freq. Thats just for your SPL port, i'd suggest adding a sheet of 16-18mm MDF to the port wall to reduce the port area, should lower the tuning nicely to suit music.


Im rambling, so i'll stop it there and make up a few box designs

 

[holdenboy]

Alrighty, heres one design for you......

350mm (H) x 950mm (W) x 450mm (D)

Equals 5.28 cu.ft. before sub and port displacement. The triangle braces arent required. So take the sub and port disp. out the equation and you'll still be over 5 cubes (so 2.5 each).

Port would be around 14.5-15" high, and 3" wide. Depth for 40hz tuning is approx. 8", but i'd probably start with a longer port, 10-12".

Subs / port go on the same side.

i know its a single box but it wont be overly heavy, you can split them into two, just make them 450mm wide, add on the 2 x 25mm sides and you get 500mm, which side by side will just fit into your boot

If you wanna split the boxes then make the ports 15" x 2", 14" deep to get 40hz tuning.

 

[acarmody]

OK so those are inside dimensions. If I divide the Width by two wouldn't I get 475mm? Add the 50mm of wall and they will be too big for the boot.

EDIT:: I just thought well if I swap the width dimension with the depth dimension its exactly the same box and it fits fine. Let me get my Paint skill ready.

 

[acarmody]

Ah screw it I'll go with the single box, can't be any heavier than the kegs I sometime have to lift into the dumb waiter.

I was just in my boot with the measuring tape, if I remove the plastic resting cover on the boot (the one that has the hook in the middle that the latch catches) I can just jimmy it in.

 

[acarmody]

Only problem I can see is that I can't go below 33hz for the port for everyday use.

 

[acarmody]

Do you maybe think I should use a round port? I know Bunning sell some friggin big and hard stuff, I could try and flare it at home?

 

[holdenboy]

No those dimensions were outside

Yeah youre better off with a single box, means less work for you dad

Your better off going with the port on one of the sides, its easier to make and wont make a big difference to SPL. Also you wont need as much port depth as the side of the box is one wall of the port if you get what i mean.

So yeah, that box is 5.28 cu.ft. before sub / port displacement (wood thickness already taken out to get that 5.28). Take out probably no more than 0.1cu.ft and thats what your left with. Using a slot port to get 33hz tuning (with that port width) you'll need a port depth of 36.5cm, take into account the baffle thickness and you get a port wall of 34cm. Now, your box is 450mm deep (internally), which means you can go to a maximum depth of 40-42cm max. 42cm only leaves a 5.5cm gap between the rear wall and the port end, but as its only for daily use it wont be noticeable (probably 0.3-0.4db difference).

If your dad cant round over the mouth of the port and the end of the port wall really well (like in that link from subwoofer builder), then i'd go with 6" PVC pipe. Just flare the ends like this.

If you do go with a round port, my suggestion would be go 2 x 6" ports, one above the other in the centre of the box. It will give you more port area than the 3" x 15" slot, which is good for SPL purposes. To lower the frequency for music just plug one of the ports with a towel etc. That'll lower the tune to 28hz, haha.....thats a nice low tune anyway, but you can shorten the depth and up the tune if you want.