Sandwich B&G Neo3 PDR

4real

Member
2004-05-27 8:51 pm
Steyl
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?
 
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.
 

4real

Member
2004-05-27 8:51 pm
Steyl
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?
 
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. :eek:

I don't know how your German language skills are, but you might probably try to read this: www.dipolplus.de/Dipol_Schallwand.pdf
 

4real

Member
2004-05-27 8:51 pm
Steyl
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?
 
Hi Rodolf. Thanks for the link ... The math is more of a chellenge ;)
Math? ...Were is the math? It's all sexy pictures. :D
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. :(
 

4real

Member
2004-05-27 8:51 pm
Steyl
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:
 

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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.
 
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.
 
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4real

Member
2004-05-27 8:51 pm
Steyl
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.

I've seen that link.

People (And you too, according to your PDF) use H and U frames for bass, for obvious reasons, also without the cardioid pattern, mostly undamped. I though that using a shallow U frame would would give me best of both worlds, and making it rounded on the back, helping me smoothing response.
 
People (And you too, according to your PDF) use H and U frames for bass ...
Where do I give the impression that I use U frames? I haven't built one in the last 50 years. :)
I though that using a shallow U frame would would give me best of both worlds, and making it rounded on the back, helping me smoothing response.
A real U frame will typically change from dipole to almost monopole within two octaves. If the side wall depth is less than a quarter of the frame diameter, I would not call it a U frame. To me it would be just an OB with the backside reinforced. ;)

Rudolf
 

4real

Member
2004-05-27 8:51 pm
Steyl
Hi Rudolf,

You are right, I was having some kind of a nervous breakdown and my toughts got mangled... obviously, H frames do not suffer from the same quirks as U frames. My bad :usd:

I'm sober now ;) and will never ask about U frames and dipoles again :D

I have gotten some interesting new design idea's now, and will go and work them out. It will involve not having any (real) baffle while getting a stiff mounting construct, and also a very nice and original design (at least from my point of view). And it won't feature a sandwiched Neo ;) . I won't say more right now though..