Some questions on port sizing

[wrxified]

Bear with me. Very new to this and working through some ideas in my head as I work on my 1st DIY set. I have a couple quick questions related to port sizing.

1. Are most of the manufacturers port recommendations fairly accurate as it realtes to their box size recommendations? For example, a Hi-Vi L64R driver recommends a .50 cubic ft enclosure, with a 1.5" x 4.25" port. So if I build that size box would I be fairly safe to assume that it is what it is and not deviate from the port recommendations.

2. If I go with a an MTM and put 2 drivers of the example above in a 1.0 cubic ft enclosure would I use 2 ports or could I use the calculation where the port length remains the same and I multiply the width by 1.41. Ending up with an estimated 2.82" x 4.25" port. Don't remember where I saw that calculation. Somewhere on the forums someone gave a calculation for how you would double the volume of a port. They mentioned keeping the length the same and multiplying the width by 1.41. Would it be better to use two ports or increase the single port?

[Chris Roemer]

Re: Some questions on port sizing

(Never heard of a HiVi L64R before?) If you use a PAIR of drivers in a cab that's double the size (as in your example), then yes, you can also use a pair of the recommended ports to achieve the same tuning. If you use a pair of ports that have the same cross-sectional area as a single port (and keep the length the same), then the tuning will also be the same (so all your statements are true). The thing about a single port is that it will end up with less perimeter than a pair of smaller ones, which should cut down on chuffing. It would end up with only 0.707 times as much.

BUT, 1.5"d x 1.41 is NOT 2.82, it's more like 2.1"d, right?

The best thing to do is to model it yourself using something like WinISD ( www.linearteam.org ) which is FREE (and a heck of a lot of fun).

[wrxified]

Re: Some questions on port sizing

Thanks. This is the Hi-Vi L64R driver I referenced.

http://meniscusaudio.com/hivi-l64r-p-1294.html

Appreciate your response. Thanks for the correction on the calc. I accidentally multiplied 2 x 1.41 when I was looking at some specs. So based on your response, I would be better served to look at utilizing one port vs. two.

[Chris Roemer]

Re: Some questions on port sizing

That's an interesting looking driver (at ms). For a pair in 1cf, I'd use a 2-1/2"d x 5-1/2" long port to tune it to 42Hz (5" would be fine, also).

[wrxified]

Re: Some questions on port sizing

That's an interesting looking driver (at ms). For a pair in 1cf, I'd use a 2-1/2"d x 5-1/2" long port to tune it to 42Hz (5" would be fine, also).

Would you follow their recommendation on the single driver in a TM configuration?

[Chris Roemer]

Re: Some questions on port sizing

Sure.