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Old 20th February 2002, 09:56 PM   #1
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Post One woofer or two?

I have a basic design question I'd like some input on. I'm designing a two-way speaker and I'm at a fork in the road. Do I go dual 6.5" bass/mids or a single 8" or 10" woofer? What are the pros and cons of each approach? The tweeter I'm using will 'theoretically' blend well with either approach so I'm puzzled why some designers go one way and some the other.

Dan
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Old 20th February 2002, 10:17 PM   #2
subwo1 is offline subwo1  United States
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One thing I have found out concerns polypropylene cones. It has been suggested not to go over 8" for this cone type. But I have found that 6.5" is the largest out of the ones I had which did not distort a lot when placed in an enclosure.
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Old 20th February 2002, 10:57 PM   #3
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Using dual drivers can increase the overall sensitivity of the speakers, thereby making them easier to drive. Also, distortion is kept minimal, since each driver only has to do half the work to achieve the same output levels.

It should be noted that a number of 8 and 10 inch drivers won't blend properly with most tweeters. Although their specs may extend high enough, the distortion is very high, and they tend to generally have poor midrange sound characteristics. The general exceptions to this would be the use of PA drivers.
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Old 20th February 2002, 11:11 PM   #4
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Default Woofer

There are more ways than one to skin a cat but most "woofers" larger than 61/2" are not going to mix well with a tweeter and leave you short in the important 600-6000hz frequencies. Take a look at northcreek, madisound and some places like that and look at their design tendencies with 2 way or 21/2 way mtm designs. If you are just starting out (which it sounds like) don't try to design something new. Buy Vance Dickason's Book, The Loudspeaker Design Cookbook. Best $40 you can spend on speakers. Available at www.audioxpress.com. Consider a kit or backdesign/clone a proven winner. All sorts of sites on cloning good designs. Try www.klone-audio.com for one.

Every path in this hobby is a compromise.

Lots a Luck!!!
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Old 20th February 2002, 11:20 PM   #5
ucla88 is offline ucla88  Tahiti
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in general, using an 8" driver allows a lower fs. but, as super noted, using two drivers gives greater efficiency, and maybe higher spl, but this depends on the xmax of the drivers. also, the vertical polar response will be different.

the trick is that 8" drivers have a horizontal dispersion pattern quite a bit more narrow than 6.5 and smaller midbass units. this, plus their lower top end means that you really have to try to cross an 8 over between 1-2k. that's a tall order for most tweeters, though it can be done.

there's a view out there that only 5-6" or so drivers can adequately to justice to the midrange, but that's a subjective call. there are good and bad examples of both. i would say it's tougher to design a good 8" 2-way, though.

a 10" 2 way is definitely an advanced project.


if you want a good idea of the difficulty in designing a high quality 8" 2 way, check out Joh Marsh's project in the diy section of HTguide. it's the basis for an upcoming audioxpress article.
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Old 20th February 2002, 11:41 PM   #6
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Perhaps I should add some more details here to clarify things. The 'tweeter' I'm using is very similar the Bohlender & Graebeners Planar magnetic RD50 which has a manufacturer stated range of 150Hz-18.5KHz. This makes it the exception to most rules because of it's extremely wide bandwith. This makes crossing over at 1500Hz 'easy' on the ribbon and 'easy' on the 8" woofer I'm thinking of. Hence, this woofer is not being asked to go into the 3-4k range of most two-ways.

Does this new information peak anyone's interest?

Dan :-)
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Old 21st February 2002, 12:07 AM   #7
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Default you have a plan

Before I fold my hand I will ask if you have heard it at the specific frequencies w/ the woofer/enclosure you want to use. I have had some unfortunate experiences relying on manuf. specs. It's a lot more work/tweaking to get a decent speaker from scratch by specs and cad, but maybe that's the fun, eh? Sounds like you have a plan.


Good luck
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Old 21st February 2002, 12:15 AM   #8
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Although it's a first-time project I do have a specific plan. I readily accept the risks and hopefully the rewards of being a DIY'er. I'm reading books, websites, and asking questions of anyone that'll answer. I expect a few bumps in the road but that's all part of the fun!

Dan :-)
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Old 21st February 2002, 12:17 AM   #9
ucla88 is offline ucla88  Tahiti
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how long is the ribbon- and is it a BG or?
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Old 21st February 2002, 12:27 AM   #10
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It's Newform Research's 45" monopole.

www.newformresearch.com

Dan :-)
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