Custom box advice

Apr 25, 2018
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0
1
Oregon
#1
I'm new to this forum so I'm actually not even sure I chose the correct room for this question, lol, but I'll give it a shot.
I'm wanting to build a custom box for my subwoofers and I'm a little confused about some things. First thing is: why does vented SQ call for more volume than vented SPL? I thought SPL called for more volume than SQ, but this is what the manufacturer recommendations say.
I'm also having a little trouble coming up with the design. I went on to re box calculator and played with some numbers. I got to the correct volume, port width, height, and length, yet at the end, the tuning was a little off. I'm not sure how this is, given the correct dimensions. I'm open to any helpful input, and I can also post the equipment I'm working with if needed. Thanks!
 
Aug 21, 2012
108
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18
Aberdeen, Scotland
#3
I'm new to this forum so I'm actually not even sure I chose the correct room for this question, lol, but I'll give it a shot.
I'm wanting to build a custom box for my subwoofers and I'm a little confused about some things. First thing is: why does vented SQ call for more volume than vented SPL? I thought SPL called for more volume than SQ, but this is what the manufacturer recommendations say.
I'm also having a little trouble coming up with the design. I went on to re box calculator and played with some numbers. I got to the correct volume, port width, height, and length, yet at the end, the tuning was a little off. I'm not sure how this is, given the correct dimensions. I'm open to any helpful input, and I can also post the equipment I'm working with if needed. Thanks!

I'm not sure what you mean by "vented SQ" vs "vented SPL"?
They're fairly general terms when designing a box rather than specific "alignments", are they from a particular piece of software or textbook perhaps?
The best thing is to model your proposed project in something like WinISD and work from there.
If you're sure you have the right volume and tuning, then converting that into a practical box can still take some work.
For example, remember that the box volume from any modelling program etc will be the net space after accounting for the space taken up by the driver, port(s), bracing, handles etc, not the gross internal volume.

HTH,
David.
 
#4
I got to the correct volume, port width, height, and length, yet at the end, the tuning was a little off. I'm not sure how this is, given the correct dimensions.
It sure would be great if things were that easy, but the real world often differs from the calculated model - often times for the reasons David mentioned.

It may be helpful to watch this - measuring impedance is a way to determine your tuning and you can then experiment with port adjustments.
 
Jan 3, 2016
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#5
hey

yeah as said, the two common issues is that firstly the volume you get from the software is the net volume of actual air that needs to be in the cab. The volume of air inside the ports isn't counted in this, so the cab has to be larger by this amount to make it work, and everything else inside the cabinet that takes up space also needs to be acconted for (braces, handles, and if you really want to be accurate even small things like pole mounts etc). Depending on what sim software you're using, it may already account for he volume taken up by the driver itself, and if you enter the port dimensions you plan to use (for calculating air velocity in the ports) it may also take these into account. But you need to check what the software says and make sure everything is accounted for to give you your final gross volume for the cab.

Secondly the positioning of the ports can be important. if you use shelf or corner ports that use the sidewalls of the cab as one wall of the port then the fact that the sidewall continues on past the end of the port adds a little bit of virtual extension onto the length of the port, it'll tune slightly differently than the length on it's own may suggest. Similarly if the end of the port is close to a boundary or brace (for example if you use big, long ports that almost reach to the back of the cab) that can also affect the air travelling in and out of the entrance to the port and change things slightly.