Ported Enclosure using Surplus Vifa Drivers

[wrenchone]

I recently encountered what appeared to be some extremely nice Vifa 8" drivers at BG Micro, and bought 4 of them for use in a ported enclosure. The parameters are: 77 liters Vas, Qts 0.27, Qes, 0.31, ~17.3cm active diameter, 80W rating.
I did some tinkering around with a spreadsheet and came up with a 90 liter enclosure using 2 speakers. The port is tuned to 42 Hz. I used a 12dB high pass at 38 Hz to limit low frequency cone excursion, and a 300Hz 12dB low pass to match the low frequency enclosure with the midrange drivers. These will be 8 pieces of a 4.5" surplus Vifa driver in a closed box. The low frequency response is 6dB down at 40 hz. This all looks very nice in principle, but the required port diameter and length are 20cm and 45cm, respectively. This is pretty much insane for a single port, but I was thinking of using an Onken style cabinet with slots of the same effective area as the single port. Am I crazy, or would an approach like this actually work? What sort of correction factors would I need to use with an Onken enclosure? A link was posted to an Onken spreadsheet in earlier threads, but that link is dead, dead, dead.....

[kelticwizard]

I don't see how you need a 20 cm, (8 inch), diameter port for two Vifa 8 inch drivers. Two 8 inchers together add up to the air moving capability of a single 12 inch, more or less.

How many 12 inchers do you see around using an 8 inch diameter port?

A single four inch diameter port should be adequate. For a safety factor, make it flared on both ends. I would think that is all that you would need.

But if you have your heart set on Onkens for the sake of building Onkens, by all means, go for it.

[kelticwizard]

Hmm, a box that big only requires a 4 inch vent to be 3 inches long. You might have some trouble with flare length there-I am not sure.

You can always just add a second 4 inch vent, and make them both 9 inches long. That will tune a 90 liter box to 42 Hz. They can be flared or unflared-the vents are enormous for the amount of air you will be moving.

[sreten]

I'm lost.

Using a 90L cabinet for 2 8" units and then
filtering them below 40Hz ? whats the point ?

sreten.

[kelticwizard]

Sreten:

Well, he says he is crossing over at 300 Hz to a unit with eight Vifa 4.5" drivers. I don't know if he plans to use these in a vertical line or in an array of some sort.

Just by the looks of things, I think he wants a home version of a high power, high efficiency rock PA system, put together with decent quality units bought on sale.

[wrenchone]

Here is a screen shot of the spreadsheet showing what I'm trying to do. I reduced the cabinet size to 60 liters, and added 2 ports instead of one. Thanks - that makes things a lot more reasonable. The 60 liter cabinet is still large enough so that I have room to place ports and speakers. I was angling for a flat passband for the bass unit, with a reasonably extended low end. The midrange drivers will probably be placed in a line array - why not? It looks like the cabinet for the midranges could be smaller, but I don't want to go too gung-ho that way, as I still need a box big enough for the drivers, and 40 liters is a surprisingly small cross section. I haven't quite settled on a tweeter yet, but there are some Peerless units available from Parts Express that are reasonably priced and have a pretty low resonant frequency, giving me some reasonable choices as to where I can place the crossover.

[kelticwizard]

Where did you get that spreadsheet? Is that the Onken box calculator spreadsheet? If not, I can give you directions to the Onken spreadsheet.

[wrenchone]

I got the spreadsheet from a colleague at work. He got it through Spice Island. It's not the Onken calculator, but it seems to give satisfactory results woth two reasonably sized ports. It also has a couple of other sheets that show things like maximum excursion. I've looked at all the posted URLs for the Onken calculator, and they are all dead. If you have a live link, I'd like to see it.

[kelticwizard]

Well, I don't have a live link, but I have a map. Just like looking for buried treasure.

If you want the route to the Onken enclosure calculaton program, you go:

http://melhuish.org/
Single Driver Website
Other Stuff
Software Tools For Speaker And Audio
Onken Box Calculator (Cyr-Marc Debien)

You might have to look around each individual page, but the links I wrote will be there. For some reason, when you get there and try to give the URL to someone else, it comes out as a dead link. But the spreadsheet is there.

[kelticwizard]

As for your idea of eight 4.5" drivers in a vertical array, I would say such a thing is beyond my buidling experience. However, there are several people here who have buildt several and one, Jim Griffin, who has written a "white paper" on the subject.

Here are some interesting threads, and some nifty pictures, on this issue:

physics of line arrays

Line Arrays. Are they superior to point source??

line source speaker

Also, if I might add a suggestion, have you considered a bipole? That is where you have mirror images of a speaker facing front and back. With two Vifa 8 inchers and 8 Vifa 4.5 inchers, you could have one woofer, four midranges & tweeter facing front and one woofer,four midranges & tweeter facing back.

Many people like bipoles because they give a nice ambient sound. But it is up to you-just something to think about.