Advice please: Truncated Line Array or Bessel Array for rear speakers?

[ppataki]

Dear ASR Members,
I will be soon finishing my new Murphy's Corner Line Array system that will replace my current front speakers.
If this project succeeds I will potentially replace my current rear speakers (12" Audio Nirvana Classic) with either a truncated line array solution using 6 or 8 speakers or a Bessel array solution using 5 or 6 speakers - Dayton ND91-8 in all cases
The rear speakers are pointing towards my ear, totally on-axis (so they are in line with my ears) and the speaker-ear distance is approx. 160-170cm

I have simulated all the options with BassBox Pro and all of them seem to be just fine for me but what I would like to ask advice about is to understand which solution will give the best results in terms of 'merging' of the drivers' sound given the relatively short distance between my ears and the speakers.
Can this be simulated in any fashion maybe?
ps. I am/will be using Dirac Live 3 multichannel mode to optimize my system (super happy with it!)

Thank you very much

 

[Ericglo]

I would have to look it up, but IIRC Don Keele modeled this when doing his CBT research.

 

[Ericglo]

Don wrote a paper thirty years ago. I thought he compared the Bessel with other arrays in his paper ten years ago. You can look at them.

AES Papers -- Official website of D.B.Keele

I tried attaching his comparison paper, but I guess it is to big. It is the last paper on the link above dated 2010

 

[ppataki]

Thank you @Ericglo, I just checked the comparison paper - it is really informative indeed
Unfortunately it does not mention truncated arrays or Bessel arrays

 

[somebodyelse]

The "Effective Perfomance of Bessel Arays" one includes a 5 source line array and 5, 7 and 9 source Bessel arrays.
https://www.xlrtechs.com/dbkeele.com/PDF/Keele (1989-10 AES Preprint) - Bessel Arrays.pdf

 

[ppataki]

Thank you @somebodyelse, really great material!
The only concern I have is that Keele presumes a working distance of 20 times the length of the array which equals to approx. 7 meters in my case whereas my listening distance will be about 1.6-1.7 meters....so not sure what consequences that would have

The regular truncated line array at least has a nearfield behavior within the critical listening distance....maybe that would be better in my case

 

[Wesayso]

A short array will not behave like your current corner arrays. You may be able to get away with it, as usually they don't play much over 3 KHz. But it isn't an ideal solution for surrounds. Making it act like a CBT might be a better solution.
A very quick simulation of a 5 driver array (easiest to simulate quickly ) shows what I mean:

A short array will act like a needle point in the vertical directivity. If you would make it CBT it would have a wider beam vertically.

Making a quick 6 driver Bessel looks like this:

I simulated both at 1.5 meter distance. The Bessel has a wider beam vertically but is a bit uneven due to the short distance.
(see the white vertical stripe of higher output and the null between 5-6 KHz)
See updated next post

So if you do use a short array for surround, make sure you're in the beam vertically.

 

[ppataki]

Thank you very much @Wesayso I really appreciate it
So to translate this to practice: I shall keep them at ear height and not raise them high above ear level, is that the correct conclusion?

 

[Wesayso]

Yes, if you'd use a short array, that would be the best option.

Personally, I'd use a more diffuse source for surround. That way you can use it to augment Stereo as well.
I have single driver surrounds, as you don't need nearly as much SPL, I let them diffract/reflect off of nearby
objects etc. and use them for ambience in Stereo as well as surround in HT.
No direct path from speaker to listening area.

 

[voodooless]

Making a quick 6 driver Bessel looks like this:

That doesn’t look like a Bessel array at all.. it should have about the same directivity as one driver. Also note that 1.5m might not be enough to yield decent merging of all units. I would not recommend using them so close.

 

[Wesayso]

You're right, I made a mistake here,let's see a better one (5 drivers!):

At a large enough distance it does work. It might even function as a surround at medium distance if not much above 3 KHz is used.
These can be placed high and still have enough spread with a little aiming. (still at 1.5 meter distance above)
Outside drivers at half power, one of the 'in-between' drivers next to the center inverted.

He still isn't going to use a surround at a large enough distance to make it a Bessel i.m.h.o.

The same schematic as above at 5m distance:

 

[ppataki]

Yes, I agree Bessel is not an option for me at a listening distance of 1.6m....
I will go for the truncated line array using six drivers each
I need a bit more power for the rears as well since I often listen to quadraphonic recordings and those have a lot of energy there too
+ I need to take into account WAF....the rear smaller array will look nice with the front big ones in the corner

 

[LTig]

There's no day where I don't learn something new at ASR, and just as often I' m impressed by the knowledge members have and give freely when asked for.

 

[Newman]

Personally, I'd use a more diffuse source for surround. That way you can use it to augment Stereo as well.
I have single driver surrounds, as you don't need nearly as much SPL, I let them diffract/reflect off of nearby
objects etc. and use them for ambience in Stereo as well as surround in HT.
No direct path from speaker to listening area.

Hi there, have you described this more fully somewhere, anywhere? Link? I’m quite curious about the detail.

cheers

 

[Wesayso]

From the first post of my enormous thread on DIYaudio.com:

Adding Ambience!
Taking control over the room

With installing a virtual Haas Kicker I'm trying to restore some of the energy I "robbed" from the room with my damping panels. I had some clues it might be interesting from my Car Audio days and always wanted to try a proper version in my home. By far one of the most fun tests I have done!
It starts somewhere here... with a later revisit of the theme here! The second part is concentrating on adding reverb to the ambient channels. I can highly recommend playing with this Haas Kicker idea, be it virtual or trough diffusive panels.

The links should be working again as I had to fix them after the DIYaudio forums were moved to a new server.

 

[Newman]

Thanks, I'm still none the wiser as to what are these single driver surrounds, where are they positioned in your room, and which way are they pointing?

 

[fluid]

Some of the links in wesayso's thread are broken now but these should give you a better idea

https://www.diyaudio.com/community/...ver-full-range-line-array.242171/post-4498030

https://yabb.jriver.com/interact/in...HPSESSID=cb2achm5kknn9gki4qlsnppqc6#msg737178

 

[Newman]

Great, thanks guys!

 

[Wesayso]

Driver used: Scan Speak 10F 8424G00. They are band-passed (and delayed) between about 150-3.5 KHz, for surround duty it could be more fun if there was potential to go lower. For stereo augmentation going lower would potentially mess with bass output...

A schematic (always up for review in experiments):

The top 2 are the mains, the bottom two are ambience channels.
There is mid/side EQ to battle cross talk in the main channels (which is more obvious the less 'very' early reflections you have).
Ambience channels are not meant to be heard (as in surround) separately but are used to create a more solid stage presence.
You should hear the difference if they are turned off, but they should not attract attention to themselves.
Using absorption to lower first reflections robs a lot of energy from the room. If I had a bigger room I'd use reflection and diffraction to move that energy around in the room itself (like it's done in some in studio's). Basically it is trickery to create the feeling of being in a larger (hopefully more pleasing ) environment.

Some may say it isn't HiFi, I'll bow down and accept that view and just call what I have MyFi. As it's done to please my listening enjoyment.
Basically it's an artificially created substitute for a Haas kicker in a (too) small (a) room. It's always better to be in a pleasant acoustic environment. Lot's of inspiration was drawn from reading the works of David Griesinger. If you scroll past his most recent experiments there really is a tonne of information on perception of rooms/environments etc. Most of what we hear in our home is dominated by the room, so we better make it a good one! .