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Old 11th February 2013, 08:38 AM   #1
4real is offline 4real  Netherlands
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Default Sandwich B&G Neo3 PDR

I'm curently in the initial stages of making a WMTM dipole using Peerless SLS400, 2xPeerless HDS Excl. 6.5", and B&G Neo3 PDR. I'm not gooing to say more about the design, because that would spoil the fun

Anyway, I happen to have four Neo3 units, and so I thought that I might Sandwich two Neo3's by just putting one right in front of the other, and connecting them in parallel, in phase as a dipole. I hope for the following:

- reduced THD
- more efficiency
- a thicker package would benefit my design

But I'm not sure my reasoning is sound. An isobaric monipole only gives you the volume advantage, and has a closed space between thee woofers. That is not the case here.

Another Idea would be to give each Neo3 a separate chamber, but that would impair the low end extension (the dipole version wil go much lower).

So, what do you guys think?
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Old 11th February 2013, 10:08 AM   #2
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Simply putting 2 open Neo3s onto each other as a sandwich will get you neither lower THD nor higher efficiency. It will only give you a thicker package.

If you want higher efficiency in the bottom end as a dipole, either use them as WMTTM or use 1 per side in a symmetric waveguide to boost the lower end.

The monopole (closed back) version of Neo 3 has less bottom end, but is significantly more efficient above 3kHz or so IIRC. So, it also depends on your design: you might want to use 2 closed back Neos "back to back" (you can still use waveguides !) if that is more advantageous

I am using a single Neo3 as a dipole in a symmetric shallow waveguide crossed at about 3.5 kHz with a LR2-ish acoustic slope.

HTH.
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Old 11th February 2013, 10:46 AM   #3
4real is offline 4real  Netherlands
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I had the feeling that would be the case

The datasheet of the Neo3 mentions a tuned rear chamber as also having the low end extension (and the lower efficiency). I could make two of those chambers back to back. But it is not specified how that rear chamber should look like? I imagine it would not need to be very big with a bit of stuffing. The question is how big?
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Old 11th February 2013, 05:34 PM   #4
4real is offline 4real  Netherlands
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About the tuned chamber: I found this picture:

http://gr-research.com/images/cup.jpg
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Old 11th February 2013, 06:46 PM   #5
Rudolf is offline Rudolf  Germany
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Quote:
Originally Posted by 4real View Post
I could make two of those chambers back to back.
It is an absolutely wrong move to increase the distance between the front firing diaphragm and the back firing one. You will have noticed the dip in the "naked" Neo3's frequency response at 7-8 kHz. By increasing the distance you will move that dip to lower frequencies and make it much deeper.

I don't know how your German language skills are, but you might probably try to read this: www.dipolplus.de/Dipol_Schallwand.pdf
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Old 11th February 2013, 07:45 PM   #6
4real is offline 4real  Netherlands
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Hi Rodolf. Thanks for the link. My German is excellent, so no problem there. The math is more of a chellenge

I think there is a simple solution to your problem however: My system is active, and I have a spare channel on my amp and DSP. I can delay the front Neo (and the rest of the woofer accordingly) so it will line up with the rear Neo. I guess that would work?
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Old 11th February 2013, 09:58 PM   #7
Rudolf is offline Rudolf  Germany
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Quote:
Originally Posted by 4real View Post
Hi Rodolf. Thanks for the link ... The math is more of a chellenge
Math? ...Were is the math? It's all sexy pictures.
Quote:
I think there is a simple solution to your problem however ... I can delay the front Neo (and the rest of the woofer accordingly) so it will line up with the rear Neo. I guess that would work?
I'm afraid, no. There is no "simple solution". When you put some distance between both Neos, you "delay" them only along the 0 axis. Electronic delay works along every conceivable axis in space. You will loose the dipole character immediately.
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Old 12th February 2013, 07:57 PM   #8
4real is offline 4real  Netherlands
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Well, it was fun while it lasted I'll just use the second pair for another project.

Your paper is very interesting however. Did you do simulations/measurements with baffleless units, but mounted in an shallow cilinder (10 to 15 cm for a 15 to 18 cm woofer). It's like a U dipole, but with round frontend. I'd like to know the effect of that. Not for the Neo, only for bass and mid section woofers.

Edge can't simulate this type of dipole I think. Boxsim can do it for rectangular U frames, but not for round ones.

And I'd like to add another touch, maybe cut out a semicircle of the rear of the tube, hoping to spread even the response a bit more. It would look something like this:
Attached Images
File Type: png dipole_U_wave.png (246.1 KB, 242 views)
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Old 13th February 2013, 09:55 PM   #9
Rudolf is offline Rudolf  Germany
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Quote:
Originally Posted by 4real View Post
Did you do simulations/measurements with baffleless units, but mounted in an shallow cilinder (10 to 15 cm for a 15 to 18 cm woofer). It's like a U dipole, but with round frontend. I'd like to know the effect of that. Not for the Neo, only for bass and mid section woofers.
I didn't simulate/measure U frames. For a deeper understanding look at DIY-dipole-1
U frames change their radiation pattern rapidly from dipole to monopole behaviour. Damped U frames have a cardioid pattern.
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Old 14th February 2013, 09:20 AM   #10
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4real,

my understanding is that the shallow stock chamber is pretty small, restricting low end extension but improving sensitivity further up mainly through reflection from the back of the chamber. Any large and anechoic chamber should give you the improved low end extension.

As for using two Neos to exhance maximum LF SPL, why don't you stack them vertically and taper one off through a low pass at about 4 kHz?

PS: where did you get the SLS400? I saw the announcements be Peerless but never found a dealer who'd cary anything beyond the SLS12.

Last edited by capslock; 14th February 2013 at 09:36 AM. Reason: PS
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