3-Way Cabinet Question

[69stingray]

If I build a small 3-way speaker, do I need to seperate the woofer from the midrange and the tweeter or can they use the same volume? How does that effect the volume calculations for the cabinet? I am thinking about a 8" woofer, 5" mid and a 1" tweeter. I would like the 8" F3 to be under 40 Hz.

Thanks.

[pinkmouse]

Hi Zach

Yes, in general, each driver needs to have it's own volume. However, 99% of tweeters, and some mids, have a sealed back design.

What drivers are you thinking of using, and how big can the box be?

[69stingray]

Thank you for the quick reply.

The goal of this project is to build a pair of 3-way that are a similar size of some really old, really poor quality speakers my father-in-law currently has.

They measure 13" wide x 11.25" deep x 21.25" tall, which, when using 3/4" MDF, results in approx. an internal volume of 1.44 ft3 or 40 L

I started looking at the Dayton 8" Woofer (Vas = 2.04 ft3, Fs: 29 Hz, 88 SPL, 29-3,000 Hz, Xmax= 4.5 mm, Qts: 0.38, Qms=3.23 & Qes: 0.44

The Dayton 8" looks interesting because they are inexpensive, have a low freq. range and are inexpensive.

Playing with WinISD, a volume of 30L gets a F3 of 33 Hz

Keeping the same width and depth, after the 30L, I have only have about 7 inches of height to use for midrange and tweeter, assuming that I made two different volumes inside the cabinet.

What inexperience options to I have for sealed 5" midranges? I do not have my catalog around, but they usually describe the speaker as sealed? I plan on buying a 3-way cross-over with 375 & 3,000 cut-offs.

What happens if a 8" and a 5" midrange share the same volume?

[AndrewT]

Hi,
an unsealed mid range will face the pressure from the bass pushing or pulling the mid cone away from central position.
Mid range cones usually have a small Xmax and so distortion will be very noticeable in the mid when bass is working, particularly at low frequency.
Are sealed mids common?

[pinkmouse]

Originally posted by AndrewT
Are sealed mids common?

Morel do a reasonable dome mid that's sealed, and I think Vifa do one as well. Of course there is the ATC, but just one would cost more than the entire rest of the system!

The box size for the mid can be quite small for your planned crossover point, just model a few drivers and box sizes to give a smooth roll of at about 300Hz. It might well be as small as 1/2 a litre or so.

[planet10]

Originally posted by AndrewT
Are sealed mids common?

Certainly they were very common... i have a ton of them lying around here. I'm not a big fan of them, but they are very common in older 3-ways (and Tom Danley had closed backs built for his unity horn.

dave

[69stingray]

Thanks for the replies everyone. I will look at the sealed midranges, I will also model some box sizes. This is my first non-subwoofer project so I don't want to spend to much on speakers--just in case the reasults are up to par!

[jamesj]

Why not just build a separate chamber within the box for the midrange unit? The box you are planning to build will realise 40L and you need only 30L, so there's plenty of scope. A vertical partition between a shelf-brace and the top of the cabinet will work just fine. The extra volume behind the mid will provide more space for fill than any enclosed mid driver could muster for effective absorption of the back wave.

James

[planet10]

Originally posted by jamesj
40L and you need only 30L

Or use the 10L to build a little folded aperiodic TL.

dave

[RJ]

There is a project out there already that''l fit your design goals and pocket book.
http://www.partsexpress.com/projects...ilee/index.htm

Although the Jubillees are in a 40 litre box it'll work just as well in a 35 litre box. The port might have to be re-worked on in WinIsd.