MLTL Bipole experience

[Philfr]

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.

 

[Jim Griffin]

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.

 

[Philfr]

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.

 

[Jim Griffin]

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]

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 :

An externally hosted image should be here but it was not working when we last tested it.

Mesurement at 1 meter :

An externally hosted image should be here but it was not working when we last tested it.

Other design with differents drivers in same conditions :
Three Bipole
Phil.

 

[Philfr]

Hi,
I come back with new MLTL Bipole project..
The predict :
MLTL Bipole W5 1611 and Hivi M5N, MLTL Bipole vs Monopole
Mesurements :
MLTL Bipole W5 1611 and Hivi M5N, Mesurements
Phil.

 

[Scottmoose]

Good job.

 

[xrk971]

Nice work and great to see that it is consistent with the bipole sims I have run in AkAbak that show a minimum back wall distance of 60 inches or 1.5 m for a bipole MLTL to work well.

 

[Scottmoose]

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]

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
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.

 

[xrk971]

Yes, AkAbak can include effect of walls floors ceilings but not both ceiling and floor. It can do corners with two walls and either ceiling or floor.

 

[Philfr]

Thank's Xrk..
Maybe it was interresting to compare Akabak and MJ King sheets..
Do you know other software for a predict with walls ?
Why try to make a straight line (or almost) if the listening room otherwise and "destroy" your work
Phil.