Need help to solve potential imaging problem!

Hey...I'm working on my full range BR project, and might have run into some trouble...

[IMGDEAD]http://img142.echo.cx/img142/4197/p10100511dx.jpg[/IMGDEAD]

That's a picture of my bookshelf cabinets under construction. The drivers are going to be Fostex FE127E's (4.5"). Will I run into any major imaging problems by having the drivers seperated by that distance (about 16-17") and if so, can the problems be minimized without having to tear the baffle out and rebuilding it?

Need help soon...thanks in advance!
 

x. onasis

Member
2003-01-03 2:48 am
NYS
The neat thing about full rangers is the imaging you get with just a single driver, so I would guess so, but you'll know when you fire them up. Keep the wires easily changeable so you can listen to just one driver and/or both in series and parallel.

If you want to change it, move the lower driver up close to the other or if they're not really for a bookshelf, facing backwards (Bipole) and use the lower hole for the port. Bipole not only acoustically compensates for baffle step, but in some rooms makes the soundstage wider.
 
Unless you are going to run it as a 1 1/2 way getting the drivers as close as possible is good idea -- or put the 2nd driver on the back in a push-push bipole.

Instead of ripping the baffle out you could just ream out the existing baffle and add a subbaffle... this is where a solid wood can be used to turn an error into additional visual appeal.

Here u=is one of Scott's recoveries from a baffle error -- IMHO the prettiest speaker i've seen out of him.

dave
 

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or put the 2nd driver on the back in a push-push bipole.

Forgive me, I'm a n00b :smash:

What is involved in mounting the driver in bipole configuration? Do I just cut a hole matching the front driver on the back, and wire the back driver in opposite polarity as the front one? Does there need to be a mechanical connection between them at all, or do I just reverse the lead polarity...

Does it matter that I have the port going out the back, too? I've heard that dipole drivers have better midrange dispersion characteristics, so I'd be curious about this.
 
jim_vt said:


Forgive me, I'm a n00b :smash:

What is involved in mounting the driver in bipole configuration? Do I just cut a hole matching the front driver on the back, and wire the back driver in opposite polarity as the front one? Does there need to be a mechanical connection between them at all, or do I just reverse the lead polarity...

Does it matter that I have the port going out the back, too? I've heard that dipole drivers have better midrange dispersion characteristics, so I'd be curious about this.

For bipole operation you want both drivers wired with the same polarity, so they are both pushing *outward* from the box at the same time. I gather a mechanical connection between the drivers can be useful to cancel vibrations that would otherwise be transmitted to the cabinet, but I think that's more of an optional benefit of having drivers mounted back-to-back in that way, it's not really critical to proper bipole operation or anything.
 
Hi Jim,
I tried the same thing with two fullrange drivers.
You can see the result here:
http://www.diyaudio.com/forums/showthread.php?threadid=33101&perpage=10&highlight=&pagenumber=3
(post30)
See also the comments in the following posts.
I thought the sound is somewhat magic but only in certain places.;)
High frequency lobing is not a good thing really...

Solution as mentioned is to mount them as near as possible or bipole.
http://www.omegaloudspeakers.com/ts33.htm
http://www.omegaloudspeakers.com/super%203%20bpc.htm

greets
 
Originally posted by HeatMiser
but I think that's more of an optional benefit of having drivers mounted back-to-back in that way, it's not really critical to proper bipole operation or anything.


Mechanically coupling the drivers is an opportunity to increase downward dynamic range, and to reduce vibrations from the speakers passing to the box, but not necessary for bipole operation.

dave
 
Thanks for all the help so far! I think I've decided on going with a bipole setup - build a new baffle for the front, and cut out a hole in the back.

Can I leave the port where it is (rear-firing), or do I need a port going out the front, too? The only reason I ask is because Omega Speaker's Super 3 BPC has both front and rear ports, so I was a little unsure if I needed two ports when I've got one big enough for both.

Sorry for the newbie questions ;)
 

ScottG

Member
2003-02-04 12:23 am
US
jim_vt said:
Thanks for all the help so far! I think I've decided on going with a bipole setup - build a new baffle for the front, and cut out a hole in the back.

Can I leave the port where it is (rear-firing), or do I need a port going out the front, too? The only reason I ask is because Omega Speaker's Super 3 BPC has both front and rear ports, so I was a little unsure if I needed two ports when I've got one big enough for both.

Sorry for the newbie questions ;)

You know you don't have to do it this way - you could always use a large air-core inductor on one of the drivers (i.e. a "1.5" way speaker).

You'll have baffle step to compensate for:
http://www.t-linespeakers.org/tech/bafflestep/

So this gives you an estimate (200-250Hz) of where you want to place the 1st order crossover (i.e. the inductor) for its -3db point.

Values given here:
http://www.colomar.com/Shavano/crossover6db.html

Winding tech. here:
http://www.colomar.com/Shavano/inductor_info.html

or purchasing an appropriate value from Madisound here:
http://www.madisound.com/cgi-bin/index.cgi?keywords=goertz
matching value here:
http://www.madisound.com/cgi-bin/index.cgi?cart_id=7792656.5944&pid=47