[mike j]

I've got a couple speaker building questions I hope I can get some help with. How do I figure 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), so I'm checking with other speaker building calculators http://www.diyaudioandvideo.com/Calculator/Box/. I'm planning on crossing them at 2K and I have some piezo tweeters I'll use. Not a scientific project as much as "I have these lying around, so I think I'll try to use them" type of project.

I also have some MCM 10" woofers (55-1610) and some RS 40-1289A mid/tweeters, RS 40-1022B 4" woofers, some RS 401349 10" subs, along with a handful of assorted other tweeters and piezos, and four 10" woofers from some knock-off dynacos. I like to think outside the box and would like to make some thing different/experimental. Any ideas or suggestions?

Thanks.
Mike

[richidoo]

Effective diameter is from the center of the driver to the middle of the surround (x2.)  The surround is the flexible strip of rubber on the outside edge of the cone. The middle of that raised rubber bump is the radius you want to use. D = 2R.

Qtc is the total Q of the entire system including the box when all finished. You pick a Qtc to suit your taste in sound quality, .7 is common. To design the box to have a Qtc of .7 you need to know Qts of the driver, then design the box accordingly. .7 is common for bass drivers I don't know about midrange drivers. Really depends on what slope of crossover you want to use, etc.

The driver's Qms (mechanical Q) and Qes (Electrical Q) together make up Qts and can be gotten from manufacturer, or if not available, it can be measured using a WT3, $99 from Parts Express. MTM website lists the specs as:
http://www.mcmelectronics.com/product/55-1870
http://www.mcmelectronics.com/product/55-1240

More:  http://www.bcae1.com/spboxad2.htm
http://www.mh-audio.nl/CalculateEnclosures.asp

There are lots of speaker design software programs available, some even for free. They can get you in the right ballpark. A multiway speaker will need separate compartments for each driver.

The Loudspeaker Cookbook by Vance Dickason is the best place to start if you like to learn and want to do a halfway decent job. Another is Introduction to Loudspeaker design by John Murphy. There is so much to learn but it's fun!
Rich

[mike j]

Rich,
Thanks so much for your post. It will help me tremendously. I was confused about Qtc since it is asked for in order to BUILD an enclosure; but you clarified that for me. If I like sharp but not boomy bass (a la JBL L-40), should I try to keep the Qtc as close to 7 as possible?
I have a copy of The Loudspeaker Cookbook, but I misplaced it. I also have WinISD for my software. I put a WT3 on my Christmas wish list, so if Santa doesn't bring me one next week, I'll be ordering one. I like the idea of putting together different speaker configurations, and sometimes a little help is needed. Thanks again for your post. It's a BIG help!
Mike