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capslock 22nd September 2002 01:37 PM

Bohlender&Graebener Neo 8 Magnetostat
Sometimes a good new driver will appear when I had never heard of the maker before.

In the 6/02 issue of HobbyHifi, the Neo3 PDR and the Neo 8 were tested. The Neo 3 has good frequency response and good disto.

The Neo 8 has increadibly low disto, second harmonic well below 0.3% for most frequencies above 1 kHz at 90 dB, third at or below 0.03%, fifth below detection (0.01%). Between 500 Hz and 1 k, second is between 0.3 and 1.2%, third still benign.

Resonance frequency is 200 Hz, step response looks excellent (perfectly aperiodic except for traces of the 200 Hz resonance). Waterfall just perfect.
Frequency response rises very linearly between 400 Hz and 10 k by 10 dB, but there is a 6 dB peak around 12.5 kHz. I am not sure how much of this is due to the infinite baffle with unknown rear damping and the microhorn they routed into the 19 mm MDF.

Except for the semi-nasty frequency response, the Neo 8 seams to beat AMTs like the ESS AMT-1 or the Eton ER4 because it goes lower, has lower disto and a better step and waterfall behavior. Only the Manger might be a little bit better in the very low frequency range, i.e. below 500 Hz.

- has anybody used this driver?
- what would be the easiest way to correct the very linear rise out to 10 k?


- ha

Variac 22nd September 2002 09:36 PM

I think Grey Rollins has used one of the bigger ones. Alas, he seems to have abandoned us, and I can hardly blame him. One obnoxious person poisons about 200 sincere people. Maybe you can write him.

capslock 23rd September 2002 07:25 PM

2 Attachment(s)
Response plots from HH 6/02

capslock 23rd September 2002 07:31 PM

2 Attachment(s)
part 2 disto

capslock 23rd September 2002 07:34 PM

2 Attachment(s)
response pt 2

capslock 23rd September 2002 07:36 PM

disto, 2 nd attempt (the downloadable picture above probably has the graphs invisible)

The measurements below were taken at 90 dB average SPL according to the magazine

capslock 23rd September 2002 07:40 PM

2 Attachment(s)
another attempt

JoeBob 26th September 2002 08:18 PM

I've have a pair lying around (I didn't want to try a line array like everyone says, without first hearing how they sound) and I just ordered the woofers I'll match them with (stryke 7" glass-fibre cones, forget the exact part number, will put them in a sealed enclosure). So hopefully soon I'll have something to report back.

capslock 26th September 2002 08:28 PM

Yeah, I have been wondering too how many would be needed to make a good line source. After all, a 20 cm source will begin to loose its line source qualites after 12 cm at 1 kHz and 1.2 m at 10 kHz. Enough to get rid of baffle edge reflections but not for room reflections.


GRollins 2nd October 2002 01:11 AM

The thing about constructing a line source out of smaller units (e.g. the older Infinity models using EMIMs and EMITs) is that you've got to watch out for frequency-related comb filtering/lobes. If you run them at low enough frequencies you're okay, but if you start getting up too high you get alternating constructive/destructive interference between the drivers. Spacing them as close as you can will help a lot.
I've got the RD-75s and love them. They're crossed over to ribbon tweeters at 5kHz, and to woofer panels at (I think) 250Hz.
At least as far as the RD-75s go, I wouldn't attempt to use them over about 5-8k. The Neo drivers, I have not heard. The rising response is easily enough tamed--just start playing with a 6dB/oct lowpass filter. A simple series capacitor will do the trick. Set the 3dB point for where the driver gets 3dB over whatever you consider your target 'flat' response to be.
Keep an eye on the Scratch & Dent page. I believe they have a BG driver on there even as we speak. If you're patient, it's a great way to pick up drivers cheaply.


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