port size/length for a 3-way tower? (2 Viewers)

[RaphaelZ]

I'm building a large 4way tower simmilar to the NHT VT series. It will have 2 sepearate chambers with a side firing (closed)10" woofer on the bottom, and a 3way, vented chamber on the top (8", 6.5",1"). The mid will have its own enclosure in the upper chamber. The dimensions of the upper chamber are 22H x 9.5W x 25D, all in 3/4 MDF. My question is regarding the port. WinISD gives me options for various port diameters. Is it generally better to go with wider and shorter, or narrower and longer port, whats the difference? Space is not an issue beacause the cabinet is very deep. I'm planning to put the vent on the back, directly opposite to the 8" woofer. Also, the 6.5" (radioshack 40-1011) mid woofer will be my midrange driver (800hz-5000hz). WinISD recomeds a ported enclosure but I'm not worried about its base capabilities so I'm putting it in a small 3.3l closed chamber. Is this okay? Sorry for the long post.

Raphael

 

[Patrick Sun]

You shouldn't put the port directly behind the woofer, rather, locate it behind the tweeter/midrange.

Midranges don't need to be ported if you have woofers.

Wide ports tend to be longer than narrow ports for the same tuning frequency for the enclosure, but narrow ports increase the possibility of port noise from port turbulence (so it's a trade-off between wide/long ports with lower port noise vs. narrow/short ports with higher port noise).

The main reason to port an enclosure is to extend the low end bass response. So my inclination would be to port the 10" woofer enclosure, and seal up the rest of the enclosure for the tweeter/midrange/8" woofer.

 

[Chris Carswell]

I'm with Pat. Seal that top part up and open up the bottom. It works for NHT so why not you What are your other drivers/tweeters you will be using? More Radio Shack stuff or ???? What about x overs ??? Have you checked out PE, Apex, or Madisound for parts?

 

[RaphaelZ]

Thanks for the replies. I think I'll take the advice and seal the upper enclosure. It gives me a flatter curve. If I port it I could tune the top part 10db lower, but I guess the bottom will take care of the low end base anyways. The NHT towers dont port the bottom, its listed as acoustic suspension (VT 2.9). My radio shack driver (10"), does better closed also. Yes, all the other drivers and x/overs are also radio shack. Thjey recently had a huge clearance on all of their speaker stuff in Canada, 50% off or better. I could'nt help my self. It'll do for my first project. The boxes are plenty big, so I can always upgrade to better drivers later and add the ports then. My midrange will be on top, with the tweeter and then the 8" below so that the tweeter will be at ear level. Should the tweeter be closer to the mid or to the 8" woofer? Also, if the two chambers are in one big cabinet divided by a 1.5" MDF wall at the bottom of the upper chamber, will I get base interference from the lower sub enclosure? I'd rather not have to make two seperate cabinets. Let me know what you guys think
Raphael.

 

[Patrick Sun]

The tweeter should be closer to the midrange, and the center-to-center distance should be within one wavelength of the crossover frequency (13560/frequency in terms of inches).

I prefer the tweeters to be slightly above ear level to get the speakers more "air" to their sound, so I like the midpoint between the tweeter and midrange to be at ear level.