lots of very small ports

[daverave]

Hi there,

I was playing with winISD tryin to figure what ports to use, then came across the fact that you could have say 15, 4mm diameter 18mm long ports, which would produce a green vent mach (not sure what this means, but i assume you want it green)

This would allow for the ports to simply be holes straight through 18mm mdf, on one panel.

I'm sure there are reasons not to do this, i have a feeling it might be to do with port noise. But would it work? and would if any port noise be noticeable?

cheers. dave.

[owen]

It would be an aperiodic box...

And there is nothing wrong with those either

Infact they tend to be better damped at 'port' resonance than a normal BR.

I say build it, and give it a listen, the worst you'd have to do is fill the holes, and drill a true port.

To that end, try to use a standard dowel size


Owen

[richie00boy]

No I don't think it would be an aperiodic box. However it would seem that the tuning frequency is pretty high and a low displacement volume driver is used. Perhaps once you get above a certain number of ports maybe the software screws up?

[daverave]

based on Seas H1124 (real specs from zaphs measurements)

volume = 11.7l
Tune = 48hz

[daverave]

This is more an experiment, using this driver in a small enclosure, form over function is the name of the game here.

I kind of need a satisfactory result (project deadline is soon) first time.

My plan is:

5 liter box, tuned to 50hz using 101, 1mm diameter 18mm holes.

As as far as I can tell using this driver in this size cab, would otherwise need ports far to long to easily integrate(I have a fair bit of electronics to cram in, active and wireless...)

Or should i just use a sealed enclosure, and forfeit the little extra low end extension?

cheers.

[richie00boy]

I think WinISD must be breaking above a certain number of ports, or you're doing something wrong. To tune a 5 litre box to 50 Hz with only 18mm port length would be a 12mm diameter single round vent. This is way too small diameter for any usable drive unit.

[Geoff H]

Hi daverave.

If you want to try aperiodic try tuning the box to about 100 - 200 hz (where the Z curve starts to rise) using 10-15 holes about 3/8 - 5/8" then stuff the holes with tontine etc and some extra damping in the box.

Manipulating the damping can flatten out the z curve, improving phase response and good bass response from an undersized cab, at the expense of a bit of efficiency.

It does take some time, and many sweeps to get it right. Don't aim for too flat a z curve, it kills the dynamics.

Geoff

[Tenson]

Originally posted by daverave
Hi there,

I was playing with winISD tryin to figure what ports to use, then came across the fact that you could have say 15, 4mm diameter 18mm long ports, which would produce a green vent mach (not sure what this means, but i assume you want it green)

This would allow for the ports to simply be holes straight through 18mm mdf, on one panel.

I'm sure there are reasons not to do this, i have a feeling it might be to do with port noise. But would it work? and would if any port noise be noticeable?

cheers. dave.

I like this idea, but I think the software will not be accurate. You will have to try it and see. Then try another and see.. and maybe another and another until it works well!

[Ron E]

This is a bug within WinISD in the calculation of port mach. ARe you using "WinISD beta" or "WinISD "Pro" alpha"? Most software doesn't tell you what's inside, and testing these fringe conditions on complicated systems, using simple models, won't get you anywhere.

Simple port equations assume that mass dominates. Anytime you get really small in diameter you will have a mixed mass-resistance element. It no longer acts as a port and starts to act mainly as a leak. You won't gain any extension this way - in fact you may lose some. The resistance in the mass-resistance element will be nonlinear and in order to do a nonlinear sim of a speaker you would need a lot more than Fs, Qts, Vas, etc....

[daverave]

Hi Geoff, think I will give that a go cheers.

I guess the best way forward will be to make the side panel removable, and then I can swap and change panels with different numbers of holes etc, to try and find an optimum sound.

How would this type of design affect the crossover? are then any particular types of network suited to this? again I have little experience in this area, and simply looking to build something which I like the sound of.

I was originally going to use Zaphs complete design, but the specification of this project needed something different, and now find myself rather lost without a proven design to follow and set of seas drivers! if all fails, after the project is finished I can re-use the drivers.