Let's forget for a minute that the Neo 8 is nla, and let's also forget that I burned one of my (two) Neos doing some baseline testing in an open back box. Caught some feedback or something in my mic pre and smelled that magic smoke 
There have been a few threads about horns for the Neo 8 over the years but nothing meaningful. I've had these laying around for a few years and I've been thinking they might do well in a large horn. My goal here is to build a test horn and see what it can do. Ideally I'd like to run it from 300 or 400hz all the way up. I have my doubts about it's ability to play that low at high enough spl, even with horn loading, but I don't know until I try. This test horn is just a simple radius......about 35" in the horizontal plane. I'm not looking for constant directivity, but I am looking for a narrow pattern over most of its' bandwidth. Nothing beamy like a le'Cleach horn though. The mouth on the test mule is 35" h&v with a depth of about 15", and the back chamber is 5w x 8h x 7d (stuffed with Bonded Logic). The horn simmed well enough in AxiDriver to give it a shot. Of course AD can't accurately sim a driver like this but it gives me an idea. Enclosed is a contour plot generated by AxiDriver normalized to 0°.
Yes, its really fugly. IF it works out (big if!) I have plans for a much nicer version in fiberglass.
The glue is drying right now so hopefully the weather cooperates tomorrow and I can get some data......
There have been a few threads about horns for the Neo 8 over the years but nothing meaningful. I've had these laying around for a few years and I've been thinking they might do well in a large horn. My goal here is to build a test horn and see what it can do. Ideally I'd like to run it from 300 or 400hz all the way up. I have my doubts about it's ability to play that low at high enough spl, even with horn loading, but I don't know until I try. This test horn is just a simple radius......about 35" in the horizontal plane. I'm not looking for constant directivity, but I am looking for a narrow pattern over most of its' bandwidth. Nothing beamy like a le'Cleach horn though. The mouth on the test mule is 35" h&v with a depth of about 15", and the back chamber is 5w x 8h x 7d (stuffed with Bonded Logic). The horn simmed well enough in AxiDriver to give it a shot. Of course AD can't accurately sim a driver like this but it gives me an idea. Enclosed is a contour plot generated by AxiDriver normalized to 0°.
Yes, its really fugly. IF it works out (big if!) I have plans for a much nicer version in fiberglass.
The glue is drying right now so hopefully the weather cooperates tomorrow and I can get some data......
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This thread is pointless without data
I got the horn fully assembled and setup in my basement for some initial measurements. The pc I used is iffy and my basement is not a good space for loudspeaker measurements but I wanted to get an idea of what's going on. Spl is not calibrated and there was a 200hz 2nd order hp in place. Measurements were taken about a meter from the horn mouth with the Neo's location relative to the mic the same for the comparison. One meter is much too close for a horn of this size but it's raining out this morning. Hopefully this afternoon it clears up. 3ms gate. Also, the horn/driver interface needs a bit of adjustment.
The first plot is a comparison of the Neo on an 11x15 baffle with the open back chamber as described in the op. Red is the Neo no horn and blue is with the horn. Not bad! It looks so far like it's doing exactly what I'd hoped: horn gain over most of the band and enough boost on the low end to equalized the response fairly well. The second set is the horn directivity out to 40° in 10° steps.
I got the horn fully assembled and setup in my basement for some initial measurements. The pc I used is iffy and my basement is not a good space for loudspeaker measurements but I wanted to get an idea of what's going on. Spl is not calibrated and there was a 200hz 2nd order hp in place. Measurements were taken about a meter from the horn mouth with the Neo's location relative to the mic the same for the comparison. One meter is much too close for a horn of this size but it's raining out this morning. Hopefully this afternoon it clears up. 3ms gate. Also, the horn/driver interface needs a bit of adjustment.
The first plot is a comparison of the Neo on an 11x15 baffle with the open back chamber as described in the op. Red is the Neo no horn and blue is with the horn. Not bad! It looks so far like it's doing exactly what I'd hoped: horn gain over most of the band and enough boost on the low end to equalized the response fairly well. The second set is the horn directivity out to 40° in 10° steps.
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I got some polar measurements outside yesterday. It started to sprinkle, and in my haste to get everything out of the rain I didn't get the data saved properly so I only have 0-30° to show right now
There's more testing I want to do and I need to do some work to the throat before I do that but I wanted show what I've got. First is my real data and second is the AxiDriver sim. Looks like AD did a really good job of showing the basic trend in the FR. Never mind the hf slope on the sim, that's due to the driver parameters I used. I think that dip from 7-9khz may be due to the throat mismatch..........the side walls bow in a bit and obscure the outside slots on the Neo just a little. As I recall the directivity was around 100° at 400hz and AD shows this as well. FR is not calibrated here but it's pretty close to the level I was measuring at. 300hz 4th order hp with a mic distance of about 10' and a 7ms gate. I plan on doing some testing at higher levels and with different hp filters, and I want to measure the Neo on a baffle to get a baseline again.
I found some T/S for these over on diyMobile Audio and they say Fs is around 350 hz. I've included a distortion plot from the outdoor data and in the rough testing I've done in my basement the distortion around fs drops dramatically with a steep xo at 400hz though that data is questionable in that environment.
There's more testing I want to do and I need to do some work to the throat before I do that but I wanted show what I've got. First is my real data and second is the AxiDriver sim. Looks like AD did a really good job of showing the basic trend in the FR. Never mind the hf slope on the sim, that's due to the driver parameters I used. I think that dip from 7-9khz may be due to the throat mismatch..........the side walls bow in a bit and obscure the outside slots on the Neo just a little. As I recall the directivity was around 100° at 400hz and AD shows this as well. FR is not calibrated here but it's pretty close to the level I was measuring at. 300hz 4th order hp with a mic distance of about 10' and a 7ms gate. I plan on doing some testing at higher levels and with different hp filters, and I want to measure the Neo on a baffle to get a baseline again.
I found some T/S for these over on diyMobile Audio and they say Fs is around 350 hz. I've included a distortion plot from the outdoor data and in the rough testing I've done in my basement the distortion around fs drops dramatically with a steep xo at 400hz though that data is questionable in that environment.
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I wish I had something more formal to say than, "this project is ridiculous and therefore awesome."
But that's what I've got. Don't know what to make of the 8k resonance, other than it seems a little accentuated in the horn? You're definitely getting good loading, although it's probably a *wee* bit oversized if you're planning on an xover around 400. I guess it does help with loading through the xover region.
But that's what I've got.
Don't know what to make of the 8k resonance, other than it seems a little accentuated in the horn? You're definitely getting good loading, although it's probably a *wee* bit oversized if you're planning on an xover around 400. I guess it does help with loading through the xover region.Your making some sawdust man! Awesome!
Isn't the neo8 more or less controlled in the vertical dimension? I did some measurements some time ago and there was significant drop off once you moved off axis in the vertical dimension. You might try measuring the things without a horn. Might make the job of designing the horn a little easier... or maybe not
Isn't the neo8 more or less controlled in the vertical dimension? I did some measurements some time ago and there was significant drop off once you moved off axis in the vertical dimension. You might try measuring the things without a horn. Might make the job of designing the horn a little easier... or maybe not
Yeah, I measured it without a horn.......that's what makes me think these things are just screaming for a good one! I have some data from a while back of the Neo as a dipole vertically. I'll get to measuring the vertical of the Neo without the horn but I'd think it would be fairly wide in the midrange due to its' short length. Do you still have your data?
I don't, I just measured and dispensed with the data. I have about 3 of these per side, so if you stack them vertically, it should give reasonable control down to maybe 500 Hz. My big idea was to put them in a corner and flank them with woofers near the top and bottom. Never got to it though.
Polar data for a dipole Neo8 about it's long axis can be found here:
http://www.diyaudio.com/forums/plan...ispersion-planars-how-much-2.html#post2271679
http://www.diyaudio.com/forums/plan...ispersion-planars-how-much-2.html#post2271679
The resonance around 6-8khz is shown on the B&G factory plots, my own without the horn and others I've seen. I've attached the factory plot. Like you say the horn seems to be making it worse. I'm in the process of refining the throat......the side walls kind of bowed in and weren't sitting flush with the driver creating a sort of diffraction slot. I knew this would cause issues! Hopefully I can get a nice day this weekend and get all the testing done that I would like.
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The pinching together of the curves in the B&G factory plots is related to the baffle width(~3.5”) of the “naked” Neo8 driver.
A dip on axis transitioning to a peak off-axis is normal diffraction effect for dipole radiators with baffles not much larger than the diaphragm.
The dip seen in your measurements stays a dip as you move off axis, and is a little higher in frequency.
I think you are right that it is likely coming from the throat-to-diaphragm area transition.
Any luck smoothing it out?
Also, I kept meaning to ask, does AxiDriver provide you with a plot of throat impedance?
That would be interesting to see, as it would allow you to get a feel for how much of the SPL increase is coming from power gain and how much from directivity gain.
bolserst - I did the throat mod but honestly don't remember how much impact it had on the fr. The sound was strained and fatiguing before and after, and it was pointed out to me that there was probably too much loading for that diaphragm. It wasn't meant for a horn of course. I went ahead and slapped together a 60deg conical with the secondary flare of the same mouth size as my radial horn. Subjectively this was MUCH better with good gain down to 300hz. The horn certainly needs work but I'm not going to pursue that at this time. The idea of building a nice waveguide of this size is daunting.....to end up with a driver/horn combo that's "only" about 94dB sensitive. I will be using it with a couple of 15s below as a basement gym speaker. Once I get that setup again I'll retake the data and post it up.
I don't remember but I'm pretty sure AD can plot impedance as well. Good call...I'll have to check that out at some point.
Bill - as a bit of a spelling Nazi myself I'm not sure how I missed that.
It was fun to build, and I think I learn more from my failures than I do things that actually work!
I don't remember but I'm pretty sure AD can plot impedance as well. Good call...I'll have to check that out at some point.
Bill - as a bit of a spelling Nazi myself I'm not sure how I missed that
.It was fun to build, and I think I learn more from my failures than I do things that actually work!
No, and you wouldn't want to build the radial horn anyways.....the loading is too much for the diaphragm. I could get dimensions on the conical and in time some measurements of that.Do you have some plans or dimension for this? Looks very interesting!
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