BG neo8s DIY PDR'ed and used as tweeter

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I am using neo3 pdr open backed on my speakers. However, I would like to cross them lower. So I am thinking of trying neo8s. The only problem with neo8s as tweeter is the vertical dispersion. So I am thinking of giving them a PDR treatment on the vertical axis. If you look at the picture, neo8s is pretty much like three neo3s stacked on each other. My plan is to cover upper and lower 1/3 of the driver with felt (just like neo3 PDR does horizontally. This will hopefully increase vertical dispersion with the only negative of some reduced efficiency. And then I will try to cross at around 800-1000 to a 8" cone midrange.
Has anyone tried this or something similar?
Can it work?
Is 800-1000 crossover point achievable?
And how much equalization am I going to need on the lower end of neo8s (baffleless)?
 

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Well, there is no question; neo8s would play down to 800 naked.
My question is whether it would play down to 800 after 2/3 of its front and back surface is covered with 1-2mm thick wool felt. This is definitely going to reduce the overall efficiency and will probably damp down the rising response.
 
My gut feeling is that it'll cause more problems than it solves, but clearly the only sensible way to proceed is to prototype it and measure. I'm just getting to this stage with the Neo 8/ RAAL 70-10D combo I'm building for a friend. When time allows I'm going to skill up on REW some more and use my new USB mic. to measure it all. There is the possibility that the Neo 8 might sound better for you without the foam, even if the vertical off-axis response is scary. On axis at least! Try it out, that's the best thing. Have a go with different thicknesses and profiles of foam too. Although not as simple as just using the '8 all the way up, it has to be worth trying it out crossed over to the '3, maybe somewhere in the 3-4K range? Less isn't always more!
 
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Yes, it is the same idea RAAL uses in its taller tweeters.
I am a bit sceptical about the wedge shape though.
It pretends to mimic a waveguide.
But the more important effect probably comes from covering of the radiating surface making the driver physically shorter.
So, I think a layer of pure wool felt might be a better solution.
And yes, one can try different thickness and different angles.
If placed at an angle away from centre, it would look like a waveguide anyway.
Thanks to miniDSP, I blew one of my neo3s.
But if all does not go well, I can buy a new neo3 and cross them around 3k.
 
My neo8s arrived in the weekend.
Initial experiment with compressed wool felt is promising.
I covered upper and lower 1/3 with a thin sheet of compressed wool felt.
Same on both front and back surface.
Think of an MTM: upper and lower sections of the driver are low-pass filtered physically (rather than an electrical crossover).
This theoretically will have two beneficial effects:
1. filter some of the HF output thus reduce the peak around 12kHz
2. HF comes from a 2/3 reduced radiating surface thus an increased vertical dispersion
The felt I am using is very dense. Next, I will experiment with different profiles of open cell foam to tweak the filter effect.
A small 90 degree waveguide is also in the making.
In terms of music reproduction I am not missing anything at the higher end: cymbals sound like cymbals. Perhaps there is some loss of "airiness". Once the 3 way speaker is optimized, I may add a supertweeter to see if there is any major benefit with doing so.
 
experiences with the neo8-s

@zmyrna:

I am planning also with the BG neo8-s in a dipole project. How would you comment the audio experiences with the neo8-s?

The neo8 needs an equalization at 10kHz. How do you manage this?

At which xo frequence(s) do you separate the neo8-s?

Ruediger
 
Ruediger,
I tested Neo8S briefly without baffle.
It does not sound more peaky than Neo3.
And with the felt tweak it did not sound peaky at all.
I am now building a design similar to Martin Logan Mosaic (pic).
Neo8S will be dipole and horizontally placed covering 800 to 3000-4000Hz.
HF will be taken care of by Fountek CD3.5H (this design dictates a horn tweeter).
And I will definitely try the foam wedges on Neo8S to match dispersion at higher crossover point.
 

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I have to translate your English into German and sometimes I check LEO what´s the meaning of a special word. English - German Dictionary - leo.org: Start page

Is peaky equivalent to sickish or weak? This would be a bad result for the neo8.

How do you equalize the frequency response of neo8?

Do you make frequency measurements in 0 and 30 angle degree? Horizontal and vertical? Do you know these measurements? Please scroll down to the link wth the pdf document. http://www.audax-speaker.de/index.p...articles][data][shop_articles_id]=105&lang=en

What is the distance of neo8 backward to the wall? One meter is good, 1.5 meters are better.

Please consider: Neo8 as a magnetostat beams its sound vertical stronger than horizontal. User tomahack has built a line array with a very good sound result. http://www.diyaudio.com/forums/multi-way/6228-bohlender-graebener-neo-8-magnetostat-2.html#post67829
http://www.diyaudio.com/forums/mult...graebener-neo-8-magnetostat-4.html#post131084


Ruediger
 
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Neo8 does indeed have good HF extension.
But the problem with using it as a tweeter is its vertical dispersion.
Mind you, it is not much taller than the tall ribbon tweeters from Raal or Aurum Cantus.
I am pretty sure Neo8 would perform reasonably good as a tweeter if tweaked with the foam wedge method and crossed no lower than 1500 (ideally a driver should not cover more than 3 octaves - multi driver linearrays are different story).

By peaky, I mean the rising HF response and the peak at 12k Hz.
Someone has shown that the rising response of B&G planar drivers is partly because of the perforated front and back plates: every hole synergize with the one next to its neighbor. In theory, foam wedge method should also help reduce the rising response.
And my experiments with felt sheets tell me it is indeed the case; I have no measurements to prove it though.
 
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