Mounting Multiple Woofers

[mikje]

I'm thinking of putting a few drivers together but I'm not sure of how. I've collected a few 10 inch (MCM 55-1610) and a few 4 inch woofers (Radio Shack 40-1022B) over time. Just for the fun of it, I'd like to mount them in a box or boxes. Is it best to make an enclosure for each driver, or is there a good way to put more than one woofer in the same box? I have 2 tens and 4 fours. Also, if the SPL is different, how would one go about bringing it close to the same level? The fours are 84 dB and the tens are 90 dB. If I run the fours in parallel they should be about 87 dB if I understand the SPL correctly. They're 8 ohm speakers, so that should be safe. The tens are 4 ohm. So, how do I then combine the fours and tens to have a safe impedence level? I plan to run a Radio Shack mid/tweeter (40-1289A) with them too. I've thought about OB, but not sure where to start with baffle size. At least with boxes I can use WinISD.
I also have 4 tens that are from a pair of "dynaco OPTIONS A50" speakers (not THE dynaco speakers, some knock off 3 ways. no specs on them.)
Thanks for any help or suggestions.
Mike

[PeteMcK]

http://www.fortunecity.com/rivendell...d/dddllqd.html

[badman]

The mids in parallel will give you 90dB sensitivity, and a 4 ohm load to match the woofers. Mount a single woofer at floor height to take advantage of the boundary loading, use about a 14" baffle, and cross over at 350-400Hz.

this should do a decent job of sensitivity matching. But without a lot more info, you're going to be (nearly) shooting in the dark.

[mikje]

I think I might shift directions. I'm trying to get the box size for these speakers, but WinISD asks for a couple of parameters I don't have. How do I get the effective diameter and the Qtc? I have an MCM 55-1240 and an MCM 55-1870 I'd like to use, but the box sizes I get from WinISD seem very large(i.e. 7.5 cubic feet for the 55-1240). Any pointers or suggestions?
Thanks.
Mike

[sreten]

Hi,

Your 8" 55-1240 woofers have a Qts of 0.74 which essentially rules
out all the classical box alignments sealed or vented. Sealed is doable
with a highish Q, vented boxes are a no-no. A TL may be possible.
Box volume per driver is going be big as driver Vas is ~ 2cuft.
for a compact sealed box, ~ 1cuft Q = 1.3 you get a bass peak.
Doubling to 2cuft stuffed will get the Q down to ~ 1.

The 5" 55-1870 does have good parameters for compact boxes.

The 10" 55-1610 woofers have a Qts of 0.6 which is still awkward
and ~ 3cuft Vas, box sizes and Q are similar to the 8" allthough
by going up to ~ 3cuft sealed you get down to Q=0.85.
A TL will be possible but it will not be small.

Basically winISD gives silly box sizes for higher Qts drivers.
Once a box becomes larger than driver Vas making it bigger
has less and less effect so you end up with silly sizes.

If you have a few of the 8"ers I'd say go open baffle.

/sreten.

[mikje]

sreten,
Thanks for the input. Is there a good "rule of thumb" to use for OB? Or maybe just get some large sheets of stiff cardboard and experiment? I like the idea of playing with OBs, but haven't quite gotten my pea-brain around the concept of it. Thanks again for the post!
Mike

[sreten]

Hi,

Open baffles are not straightforward, and to a degree there is
not a concencus opinion of the best way to do it, and there are
lots of ways of doing it, with EQ (active or line level passive),
with series resistors, with amplifiers with output resistance
or choosing suitable drivers.

http://www.linkwitzlab.com/
http://www.geocities.com/kreskovs/John1.html
http://quarter-wave.com/

I'd read MJK's articles on open baffles on the last link first.
After that its gets fairly hairy on both of the other sites.

/sreten.