port shape? suggestions?

[mondogenerator]

hi!

im begun embarking on my 3rd loudspeaker project, using visaton al130 woofer and gc20 tweeter. using winISD as a tool to try various tinkerings with Vb and ive ended up using Weems' book and come to a conclusion about box size. The only trouble is that to obtain a port with sufficient area to keep vent mach reasonable(ie 7-9%) the port is too long for the box , or at least it voilates the 3" from rear wall rule. considering using a slotted port so i can have a longer port of larger area...anyone have any input on this idea? Is it worth it ? currently the circular port required is 1.5" diameter which i consider too small for a 5.5" woofer. thanks for any advice

Greg

[Ron E]

Flare the ends and it will be fine at 1.5"

[richie00boy]

If you want to use a bigger diameter port you can put a bend in it.

[tinitus]

Its a 5"
Maybe it works better in closed

Fore what its worth, with a 2" port I get a 200mm length
Which I would also consider a bit long fore a 5" woofer

[Borat]

long ports are not the best idea for full range speakers ( as opposed to subwoofers ) because of the standing waves in the ports.

for non subwoofers i would avoid ports altogether but if ports must be used i would not use long ones.

at least if the port is very short / small you can use damping material to reduce the energy available inside the speaker to excite its modes because the modes will be higher up where acoustical foam is effective.

also the bigger the port the more it begins to look like a tube. a very small port looks more like a hole. a hole is less likely to sound like a tube than a tube

[mondogenerator]

cool thanks all.

I was thinking that 1.5" pipe would be ok and maybe only a problem at ear bleedingly loud levels. Either way i agree, i think its better than a 3" pipe at some 12" long with a bend along its length to fit it in the box.

oh and the EBP comes to about 95 so...NO i think its more suited to a vented design of some kind, although i have modelled a sealed design and response wouldnt be terrible...F3 at about 85Hz Qb of .7 in a 5 litre box...not bad but certainly not no LS3/5A....

[J.R.Freeman]

Originally Posted by Borat

also the bigger the port the more it begins to look like a tube. a very small port looks more like a hole. a hole is less likely to sound like a tube than a tube

Hehe, I enjoyed that explanation