MLTL Bipole experience

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Philfr

Member
2012-12-16 1:20 pm
Hi all,
It's just to share experience with MLTL Bipole..
For me, this design means drivers wiring in phase and parallel. In my design the rear driver worked until around 150/250 hz.
I have not read much articles about that, except the nice Microtowers of Planet10, but I know nothing about xover.
Thank's in advance for comments.
Phil.
 
My first bipolar MLTL experiences are documented at:

http://www.diyaudio.com/forums/full-range/61753-bipolar-mltl-speaker-fr125s-wr125s.html

I did have a small on axis bipolar dip (3-4 dB) in the 400-500 Hz range because of wrap around interference between the two drivers. In-room performance was excellent and the speaker was well received (and cloned) by other builders.

I later added a rear firing planar super tweeter which was intended to lift the treble response.
 
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Philfr

Member
2012-12-16 1:20 pm
Hi Jim,
Nice speakers !
I don't read all your thread, but ( if I am right ) you don't use any filters.
I try this way (with two 5" fullrange driver), it was good for classic or acoustic music.
What kind of music did you listen ?
One big problem in my case was the placement of the speakers in the room, like OB in fact..
Phil.
 
Phil,

My bipolar pair were full range speakers with no crossover. Later I added a pair of rear facing planar super tweeters with a simple first order crossover to the tweeter. Most of my music is acoustic with a little classical for variety.

Room placement is critical as too close to the wall behind the speakers will create too much reflected sound which will excessively widen the soundstage. I find that 1 meter is the minimal spacing but 2 meters sounds better to me. These distances are akin to the spacing needed for dipolar (open baffle) speakers. The key is to have enough propagation time so that a reflected signal will be lower in amplitude versus the direct signal. The brain does the signal processing to reject a late arriving reflected signal.

Jim
 

Philfr

Member
2012-12-16 1:20 pm
Hi Jim,
I agree that you said about placement and room. This kind of speakers need a big room and some acoustic treatment like absorber pannels..
Finally I left this way of bipole without filter. The reason is that I listen to Jazz music (fusion, electro, jazz-rock..) or amplified music like rock, drum and bass..
So I need some deep and "loud" bass. For example, on "We want Miles" I feel like the massive bass of Markus Miller.
After, playing with MJ King sheets, I discover the MLTL Bipole. After dozens of trials, I found a good design. My first project, response curve with effect of walls, rear side and floor :

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Mesurement at 1 meter :

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Other design with differents drivers in same conditions :
Three Bipole
Phil.
 
Quite, although not exactly news there. Bipoles, by their nature, need a reasonable amount of space to work, although if the rear unit is suitably low-passed you can get away with slightly greater proximity to the front wall. The question of course then becomes what the prime motive for using the configuration is -whether to help compensate for step-loss if necessary, or to increase the ratio of reflected to direct sound at the listening position.
 

Philfr

Member
2012-12-16 1:20 pm
Thank's for comments..
Exactly as you say, the biggest challenge is to find the right location according speakers, room and xover. In my case, distance between rear side and rear wall are about 60 cm, side wall is about same. Cause cutoff is 250 hz.
I spent several days (and nights) to found a best compromise. I also made several comparisons with monopole.
Abakak can make a prediction with walls effects, like in MJ King sheets ?
About sounding ?
I can not say much more, cause today I build only one for mesurement :mad:
But in mono it looks promising.
Just one thing, for far listening, I think add a tweeter, cause high frequencies level much lower (about 3 db below 3/4000 hz). Always compromise !
Phil.
 
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