# need some help with baffle layout



## jeremy7 (Feb 7, 2008)

hey guys
heres the deal. Its been a while since ive read the loudspeaker design cookbook, and I cant remember all the suggestions for speaker placement.
This is my first attempt at a 2.5 way. Im using them as left right fronts for a 5.1(movies) and 2.1 (stereo) set up. Without putting much thought into this I started laying out the baffle the way I thought was most logical.
My first Thought was to place the first woofer (the one that plays both bass and midbass) a distance that corresponds to the frequencies wavelength at the crossover point. simple enough.
So I guess my question is with the second woofer (the one only playing bass). I first thought that Id use the frequency that the second woofer is crossed at to find a distance from woofer one. Then I thought. Is that technically a crossover?
So now I'm questioning my entire train of thought. Do I use the frequency that the second woofer is at the same volume as woofer 1, or maybe the high frequency F3 of woofer 2, or something different maybe?
Maybe I'm on the wrong track all together. Oh well, Any help would be greatly appreciated... thanks


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## dyohn (Apr 17, 2008)

As long as your center to center mid-woofer to tweeter spacing is appropriate for the mid to HF crossover (within one wavelength of the Xover knee frequency) then the spacing between the woofers is really not all that important as it is unlikely to exceed 1 wl unless the LP for the lower woofer is quite high.


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## jeremy7 (Feb 7, 2008)

David
Thank you, That is exactly what I needed. The LP for the lower woofer will not be high at all, so the spacing will be well within 1 WL.

thanks again 
jeremy


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## JCD (Apr 20, 2006)

My memory on this one is a little fuzzy too.

Unless one were designing a proper D'Appolitto MTM, I was thinking that I'd always put the drivers as close to together because (and this is SO not backed up by anything I can reference right now) because they'd couple better. I know there is a maximum distance for proper coupling of the drivers, but I was thinking closer would be generally be better.

As for the 2.5 design, I thought the real trick was to make sure that the width of the baffle was the right amount.


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## dyohn (Apr 17, 2008)

Actually the real trick IMO with a 2.5 system is to design the LP filter for the second woofer above the baffle step frequency as one way to avoid using a BSC filter. Keeping the woofers as close together as possible is usually a good idea, but not necessary, and indeed if you read Roy Allison's papers he'd suggest placing the lower woofer as close to the floor as possible - or at the very top of the cabinet.


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## JCD (Apr 20, 2006)

dyohn said:


> Actually *the real trick IMO with a 2.5 system is to design the LP filter for the second woofer above the baffle step frequency as one way to avoid using a BSC filter*. Keeping the woofers as close together as possible is usually a good idea, but not necessary, and indeed if you read Roy Allison's papers he'd suggest placing the lower woofer as close to the floor as possible - or at the very top of the cabinet.


That was what I was thinking the main reason for the 2.5 configuration. Seems like you'd go for a MTM otherwise.

And good to know on the woofer placement.


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## dyohn (Apr 17, 2008)

JCD said:


> That was what I was thinking the main reason for the 2.5 configuration. Seems like you'd go for a MTM otherwise.
> 
> And good to know on the woofer placement.


Yep, although there are advantages to MMT over MTM when it comes to dispersion and lobing. MMT in either a standard 2-way or a 2.5-way is in general easier to get "right" than an MTM.

Reading Allison's papers is highly recommended for any designer, by the way.


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