What box for my subs


mr man

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Jan 11, 2021
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I have 4 Gas alpha 15D2 with a 2000 watt rms amp. What box should i put them in? I am looking to play pretty loud and decently low (decent down to 28hz). When i look in winisd the range of the subs look absolutely shit, in a 400L 36hz tuned box the spl is like 55 hertz and it doesnt even play good down to 36 hz. Please help me!
 

hispls

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Are you certain you even have 14 cubic feet net airspace after the displacement of wood/bracing/box? What sort of vehicle do you have? I hope you know what you are getting into as far as what a proper box for so much cone area will require.
 
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Buck

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mr man

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Jan 11, 2021
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Are you certain you even have 14 cubic feet net airspace after the displacement of wood/bracing/box? What sort of vehicle do you have? I hope you know what you are getting into as far as what a proper box for so much cone area will require.
I am very sure i have more than enough space i have the whole space from the front seats to the trunk in my volvo 945. Theres no backseats or anything..
 
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Buck

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I am very sure i have more than enough space i have the whole space from the front seats to the trunk in my volvo 945. Theres no backseats or anything..
I'll design you something nasty for those if you let me. Are you in europe or something?
 

hispls

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volvo 945
Nice. Those are really easy to get loud and will want to peak around 42-43hz. A friend of mine was doing some great numbers out of one of those Volvo wagons in amateur class in our regional competition circuit several years ago.

Just making sure you know what you're getting into. A very common newb mistake is underestimating how much air space you need to make subwoofers function properly. The other thing I will mention is to be certain you make the box airtight at the seems and very rigid. Use multiple layers of wood if you can and/or use plenty of bracing to keep the box's sides from flexing. Also be sure you have a plan to secure it in place in the vehicle. Not only will that gain some output but it will prevent the box from moving and crushing you if you ever get in an accident.

Please post a build log thread here when you get going and report back your results.
 

mr man

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Jan 11, 2021
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i
Nice. Those are really easy to get loud and will want to peak around 42-43hz. A friend of mine was doing some great numbers out of one of those Volvo wagons in amateur class in our regional competition circuit several years ago.

Just making sure you know what you're getting into. A very common newb mistake is underestimating how much air space you need to make subwoofers function properly. The other thing I will mention is to be certain you make the box airtight at the seems and very rigid. Use multiple layers of wood if you can and/or use plenty of bracing to keep the box's sides from flexing. Also be sure you have a plan to secure it in place in the vehicle. Not only will that gain some output but it will prevent the box from moving and crushing you if you ever get in an accident.

Please post a build log thread here when you get going and report back your results.
I have decided im going to make my own designed box that will be 800 Liters and tuned to 36 Hz but the port needs to be so huge how do i fix this?
 

mr man

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i

I have decided im going to make my own designed box that will be 800 - 1000 Liters and tuned to 36 Hz but the port needs to be so huge how do i fix this? And is this a good idea for a box or will it be too big? And i dont want to tune below the free air frequency because everyone says bad things will happen.
 

hispls

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i

I have decided im going to make my own designed box that will be 800 Liters and tuned to 36 Hz but the port needs to be so huge how do i fix this?
800L (28 cubic feet) net is probably too large for those subs. Very few 15's will do well in greater than 5 cubic feet per sub and your frequency response may get peaky as you increase volume too much. "Space makes bass" is very true and larger box almost always = louder and more efficient but you will hit a point of diminishing returns where adding more space gives you less and less return in output gains.

Download WInISD (it is free) and you can plug in your subs TS parameters and play around with modeling size/tuning and see predicted performance.

As you have discovered, big box and low tuning will both require a very large port. You will probably have to sacrifice something either tune a little higher or go with less port area. A safe rule of thumb commonly used is to allow 15 square inches of port area per cubic foot of net box volume. You will need to convert this to liters and cm. 15" per cube has been very reliable in my experience, going up to or even over 20" per cube may be acceptable in SPL/burp only box, and you probably won't get into too much trouble until you get below 10" per cube if you have to shrink your port a little bit to fit it all in the box.
 

mr man

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Jan 11, 2021
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1
sweden
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  • #14
800L (28 cubic feet) net is probably too large for those subs. Very few 15's will do well in greater than 5 cubic feet per sub and your frequency response may get peaky as you increase volume too much. "Space makes bass" is very true and larger box almost always = louder and more efficient but you will hit a point of diminishing returns where adding more space gives you less and less return in output gains.

Download WInISD (it is free) and you can plug in your subs TS parameters and play around with modeling size/tuning and see predicted performance.

As you have discovered, big box and low tuning will both require a very large port. You will probably have to sacrifice something either tune a little higher or go with less port area. A safe rule of thumb commonly used is to allow 15 square inches of port area per cubic foot of net box volume. You will need to convert this to liters and cm. 15" per cube has been very reliable in my experience, going up to or even over 20" per cube may be acceptable in SPL/burp only box, and you probably won't get into too much trouble until you get below 10" per cube if you have to shrink your port a little bit to fit it all in the box.
I have checked a little bit in winisd and i think 700 liters looks good and plays decently low with a 36hz tuning.. But with the ports i think i will do 3 smaller ports in the front and use bracing to make it steady. And i think the subs does better in a big box because of the low ebp value.
 

hispls

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I have checked a little bit in winisd and i think 700 liters looks good and plays decently low with a 36hz tuning.. But with the ports i think i will do 3 smaller ports in the front and use bracing to make it steady. And i think the subs does better in a big box because of the low ebp value.
I have never had good luck with using multiple smaller ports but I have seen others have good success. Hopefully it will work for you.

The good news is that it is much easier to make box volume smaller than it is to make it larger after it is finished and you begin testing. If you decide it is too big later it will be very easy to test by just adding wood or bricks to see how less volume changes output/response/tuning. On the same thought you may also consider a method to easily change port length(s) after you have it installed. I have had fine results with "sono tube" for large diameter round ports, I'm sure there is a similar product used for concrete pillars in Europe.
 

Buck

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I have checked a little bit in winisd and i think 700 liters looks good and plays decently low with a 36hz tuning.. But with the ports i think i will do 3 smaller ports in the front and use bracing to make it steady. And i think the subs does better in a big box because of the low ebp value.
Don't base your box size off what winisd tells you.
 

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