[stereogeek]

My next project will be a pair of Alpha 15's and a pair of Neo 8's that I have laying around.This project may be a few months away as I am currently building some baffles for a pair of Silver Iris' I have.I thought I would throw out the idea anyway and start getting some input.

I had envisioned this project a while ago,but with Martin's latest paper,I have renewed interest in the project.

I have always loved the openness and sound of the Neo 8 drivers.The Alpha 15's are a great value and have what I believe to be "workable" T/S parameters for OB(as reinforced by Martin's paper).

Driver information can be found here-

http://www.partsexpress.com/pdf/264-712s.pdf

http://www.partsexpress.com/pdf/290-407s.pdf

I'm looking for ideas,thoughts and comments.Crossover considerations are my main concern.

Thanks,Steve

[scorpion]

It will be interesting to follow this project. I suppose we are talking, like MJK, about a passive OB design.

I see four main issues: Efficiency element matching, crossover frequency, Alpha 2 kHz hump and Neo8 12 kHz hump.
It might be helpful to give a reference to the Neo8 description paper: http://www.gr-research.com/pdf/NEO8.pdf .

You will of course make some prototype baffles. I think you will need 18"/45 cm width for the Neos to produce 90 dB at 500 Hz 1 watt which will match the Alpha 15"s quite well at that frequency. I suppose that you would like to cross over to the Neo8 at this frequency, 2nd order Linkwitz/Riley or perhaps better
3rd order network.

Let's start with this !

/Erling

[stereogeek]

Yes,this is going to be a passive design.I also thought that the crossover should be in the 500 to 700 range.I may have to use a notch on the Alpha 15's peak at 2k and also B&G's recommended notch at 12k for the Neo 8.The rolled off highs of the Neo 8 aren't a concern(at 52 the old ears aren't what they used to be!).

One thing that interested me in MJK's paper was the fact that he lowpassed the Alpha 15 at 200Hz to smooth out a midrange peak and then highpassed the wideband driver at 500Hz.This may be something to look at in my design also,as it would keep the 2k peak above the crossover range and eliminate an unneeded notch filter.

The initial baffle for testing will be 18" X 36".The Alpha 15 will be centered and 2" up from the bottom for floor reinforcement.I have not decided if the Neo 8 should be centered or off center to help with diffraction issues.My final baffle will probably incorporate a magnet mount for the Alpha 15's.


Steve

[markC]

I admire your determination, Steve.
I believe that you have a lot of work ahead of you to get these two drivers to marry. Judging only by the FR charts, they don't even like each other
If your going to cross over as low as 500 hz, your xover better be real good, 'cause as you know that's a critical area and if it isn't damned near perfect, you'll hear it. Personally, I'd try a little higher, say 800-1k and keep the notch and experiment with adding a zobel as well.
Whatever order x-over you plan on, remember at 500 hz, that nasty peak of the 15 is only 2 octaves away!
With a 2nd order, I can almost gaurantee that it will interfere.
If you have spice software it will help alot.

[wikin]

If I remember correctly the neo8 in open baffle might be a concern if placed too cosely to the alphas due to modulation of the woofer to the thin membrane of the neo8. Just becareful.

will

[zobsky]

I admire your determination, Steve.
I believe that you have a lot of work ahead of you to get these two drivers to marry. Judging only by the FR charts, they don't even like each other
If your going to cross over as low as 500 hz, your xover better be real good, 'cause as you know that's a critical area and if it isn't damned near perfect, you'll hear it. Personally, I'd try a little higher, say 800-1k and keep the notch and experiment with adding a zobel as well.
Whatever order x-over you plan on, remember at 500 hz, that nasty peak of the 15 is only 2 octaves away!
With a 2nd order, I can almost gaurantee that it will interfere.
If you have spice software it will help alot.

Or try a crossover simulator program like this http://www.geocities.com/f4ier/xoversimStart.htm if you're going passive . For starters, you could set up your PC sound card as an active crossover  to see how you the various crossover points / slopes sound http://sourceforge.net/forum/forum.php?forum_id=514601

[stereogeek]

To let you guys know where the Neo 8's came from,they are left over from a car stereo competition car that I did several years ago(ok,back off you purists!).The Neo 8's were mated with some 8" drivers that were mounted in the front doors and the Neo 8's were mounted by the windshield.They were crossed at 700Hz with a series crossover and the Neo 8's never sounded stressed even at high levels.As an assessment to our success,the car did very well at competition.

I think I can solve the problem with the Alpha's modulating the Neo's by using a magnet mount on the Alpha's and mounting the Neo's to the baffle.

The reference I made to MJK's paper and his 200/500 Hz crossover was to point out that underlaping the crossovers was a good way to handle the baffle rise of the Alpha 15's and that this could be done with a passive crossover.It was not to be meant that I was stuck on a 500Hz crossover.Maybe I should have been more clear!

My main interest in this design,is the fact that this will be a pure dipole combination.Many of the OB designs these days are only dipole for part of the spectrum,including my own Silver Iris'.Even Linkwitz has determined that there is a benefit from a dipole design in the upper octaves.

This is a very LOW budget project with whatever I have laying around.I may determine in the long run that this is not a feasible project.As I stated in my original post,that this project may be several months away.I just wanted to throw out some feelers and see what everyone else thought of the idea.

Thanks again for any ideas and/or comments.

Steve

[scorpion]

The quality of a 500 Hz crossover will of course also depend on the Alpha 15 but Martin Logan uses Neo 8 (and Neo3) in the Mosaic and Fresco speakers.
Crossovers are 450 resp 500 Hz for the Neo 8 in their design. If you go steeper than 12 dB/octave then I think you could cross even lower than 500 hz.
Keep us posted ! 

/Erling

[Daygloworange]

Martin Logan uses Neo 8 (and Neo3) in the Mosaic and Fresco speakers.
Crossovers are 450 resp 500 Hz for the Neo 8 in their design.

Are they using the Neo's with the back cups off?

Cheers

[scorpion]

The Mosaic which I once saw and heard at a HiFi-show was a dipole. But the Fresco evidently is a box speaker. Neo3 is used in dipole style in the Montage.

/Erling

[stereogeek]

After modeling the Neo 8 in Edge last night,I have renewed hope for this project.I modeled the
Neo 8 on a 18" x 36" baffle,approximately 3" below the top edge of the baffle and offset to the side approximately the width of the driver.The baffle helped the sagging response of the Neo below 1 kHz And had an almost flat response down to 300 Hz.Of course,I would not go that low because of the excursion limits of the driver.

Just in case any body is wondering,I settled on that baffle size because of space limitations in my living room.This is the size I used for my Silver Iris' and it seems to fit my space well.As with my SI's,I will have to tip them back about 10 degrees to help the soundstage height.I would also imagine that this will help to smooth the response ripples caused by floor bounce.

Steve

[JANDG]

Looks intresting...I am watching close. Are yu going to run to Neo 8's perside, w/ 1 - 15" Alpha perside,..?

[Angaria]

There was a thread on diyaudio about improving the freq response of the neo8 with a waveguide.  You might consider scrounging it up.

[stereogeek]

You guys may have to hold on a while.I stated before that this is a future project that I wanted some feedback on.I am presently working on my final baffles for my Silver Iris' and this project is probably a couple more months away.

This is an "el-cheapo" (I've heard that term before! lol)project using some drivers that I have laying around.I only have one set of the Neo's.I realize that I may have to pad down the Alpha's a little.Measurements after I build test baffles will determine how much.

Steve