Multiple ports to reduce excursion?

[Nappylady]

Modeling a driver in a ported box in WinISD shows me that, at the port tuning frequency, the excursion of the driver is very low. Unfortunately, it ramps up quite fast below the tuning frequency! I got thinking, though, what if you put two ports in the box, tuned to different frequencies, in order to control excursion below the main tuning frequency?

I figure there has to be some reason no one is doing this... but maybe there's some way to get the depth of a ported enclosure without the bottoming out below the tuning frequency.

I looked at aperiodic vents, since the main concern here is SPL and box size, but I don't know how to model sealed boxes with aperiodic vents in them. (Can this be done in WinISD? If so, how?)

Thanks.

[Circlotron]

At the lower frequency instead of the longer port working as you would hope, the shorter port just makes the box think it has a huge leak, just the same as it does when the longer port is not there.

[xplod1236]

How do you figure out the excursion of the driver in winisd?

[sreten]

You need to use WinISD Pro (Alpha) freeware sreten.

[Stephen D]

For dual port tuning you need dual chambers & people are doing it & have been for some time (myself included). It's a way to extend the bandwidth for which the ports limit cone excursion. There have been threads on this here in the past which should come up in a search. The only program I know of that does any
modeling of "Dual Chamber Reflex" is lspCAD which isn't freeware.
There is more than one type of "dual chamber reflex" design. lspCAD models all but the "Augsperger" style that is described by David B Weems in his books & which I have had experience building.

[Svante]

Putting two ports in the same box still only gives you one resonance frequency.

[kelticwizard]

Originally posted by Stephen D

There is more than one type of "dual chamber reflex" design. lspCAD models all but the "Augsperger" style that is described by David B Weems in his books & which I have had experience building.

Here is a thread on that very topic, with an important excerpt from Weems.
article about double chamber speaker enclosure

It does not, however, cut down on excursion below the lower tuning frequency. If you have a 10 inch in a 2 cu ft box tuned to 30 Hz in a normal reflex, it will act the same in a double chamber reflex tuned to 30 Hz. It is the cone excursion above the box tuning frequency that is lessened. Below the 30 Hz box tuning frequency, the two are identical.

[Nappylady]

Okay... so, since the distance between the two tuning freqs is an octave, what if I tune it to 15 hz instead of 30? My thinking (probably wrong) is that this would control excursion at 15hz and 30hz... and that's really the range I'm worried about.

[claudio]

Sure you can do it, if that is the type of reflex response you want.
However Weems suggested to tune his DCR at a frequency equal to the driver Fs. And also remember that if you tune the DCR at 15 Hz, you will have a dip at 30 Hz too: I think the 2 frequencies are too close to each other not to interfere.

Regards
Claudio

[Nappylady]

How about 20hz and 40hz? (Since those would be the operative frequencies for the drivers I'm looking at.) The distance is still one octave no matter where I start, so I don't see how the interferences would be any worse.

Next question: If I model a 2cuft box in WinISD tuned to 40hz, it's quite nice-looking, flat and ready for a little room gain. If I drop the tuning frequency to 20hz, it suddenly looks, um, not yummy anymore. Is this what the response will be like if I tune everything 20/40? Or will it magically look (and sound) like the first graph?