Bohlender&Graebener Neo 8 Magnetostat

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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
Response plots from HH 6/02


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    neo 8 response.gif
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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.
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.

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.

6dB/oct lowpass filter

Grey are you refering to a rising high frenquency response on the RD75 drivers or the Neo drivers? Isn't a capacitor in series with a driver a high pass filter. Wouldn't an inductor in series be a low pass filter. Sorry for the confusion but I am sort of new to speaker design.


The RD-75s are quite flat from ca. 150Hz to about 12kHz or so (I'm quoting from memory). The high end rolls off of its own accord; the low end is excursion limited. If you're willing to listen at low volumes, you can run the RD series drivers somewhat lower. Note that Genesis used the RD-75 in the 1.1 down to (I think) 70Hz, and that in a speaker that played at thunderous volumes. I don't push mine that hard. My comments about fequency tailoring were directed towards calming the rising response on the Neo.
You're quite right about the lowpass filter. I should have said either series inductor or parallel cap.
Silly me.

Just got a couple monday. Will be actively crossing them at ~4-600hz to 10" peerless CSX on a dipole main panel that will be crossed at~ 80-150hz to a pair of W baffle dipole subs I have built-
Last night I simply taped them slightly off center in 2 circular peices of cardboard left from the last 12" drivers I mounted in a test baffle. I didn't futz with the 10" csx(yet), but crossed them at 200 hz directly to the dipole subs, hung them from the ceiling and just did some listening. The only equalization I did was to pop them up 3db at 150hz. My first impression was not great, but as I listened and things warmed up, I realized that these were the most solidly centered, cohesive vocals I have ever heard. I could hear the slightest breath that Cheryl Crow took, and did not miss a tweeter at all (I love live recordings, which don't contain much info over the reach of the neo8's high end).
After throwing on some live George thoroughgood, I was shocked to find the image firmly BEHIND the speakers, with great depth. I could hear someone whistling to the left of me in the audience with a palpable sense of air, and for the first time ever I was able to discern a stadium reflection when George ended a line with a "s". There appears to be some cross talk cancellation going on with these little dipole panels, because I am hearing things BEYOND the the physical width of the speakers. I am very happy for the price, even though I understand they make them in the Phillipines for a few bucks each.
Also, it was a very strange experience to stand at the side of the setup and look at panels with drivers no deeper than the cardboard throwing such a huge sound stage. I could not detect highs "sitting" on the speakers, which was one of my concerns. This was a nearfeild test. I beleive I will by two more, and stack two per side to give higher power handling, and increase soundstage height. My brother plays drums, and this 2 way dipole setup gave the most realistic kick drum(which IS a dipole) I have ever heard also, even though I'm sure there must have been a hole in the mid-bass.
I built a line array using 8x Neo8 per side à la Alpha LS. I hi-passed them at 1500Hz using a Marchand active crossover. They are driven by two Halo SPM25 monoblock tube amps. For the midbass, the Peerless 6.5 HDS midbass (10 per side) is bandpassed between 50Hz and 1500Hz. Two Marchand MB201 amps drive them. The Neo8 are very transparent. They don't have any signature of there own. They just let the music flow. Very natural and only limited by the electronics. The soundstage is so wide, sometime I feel like I got rear speakers playing! I truely recommend these drivers.

Setup: Source: Arcam 9Se Bentaudio TX102 passive preamp
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