DIY: Dipole 8" array with Neo 130cm Ribbon

[Bent]

Bill; I was wondering if you were frequenting the forums and what your latest project was....

2m long ribbons.....where did you manage to find those (or did you build them) Are there photos or are they a bit hush hush at the moment.

Very nice choice of 12"! and 1.5db is an excellent result....

I was planning around 400 Hz for crossover point on the ribbons. Initially at 1st order and then 4th/6th or 8th order at 280Hz.

I wish you hadnt told me about the 2m ribbons, they are exactly what I couldnt find!! :-( Anyway, there is never an end to excellence is there?

[cowanaudio]

G'day again

Don't stress about not knowing about the planars I'm using. They are a one off experimental design by David Graebener, who now is with Wisdom Audio. http://cowanaudio.com/images/planar.jpg They are not available commercially. Sensitivity is one or two dB higher than the ribbons you have. Power handling is much higher too. They are a push pull planar using neo magnets. Running monopole because of the problems integrating dipoles with monopole bass.

At 400Hz your ribbons will exibit point source behaviour at distances greater than about one meter. That is the reason you need a higher X/O. As you move further back you will have a dip in your response above your ribbon X/O. I had this problem with my 1.2M ribbons. Didn't realise what the problem was at the time. Look up the paper by Jim Griffin for more info on true line sources. My system will exibit true line source behaviour throughout it's bandwidth.

Cheers

William Cowan

[Bent]

Hi Bill; OK, so all will be Monopole. I thought Dipole when you mentioned them. The drivers you have shown are very sharp looking.

I will have to check the paper you referred to to see optimum XO point. I am guessing from what you are saying that 650Hz will be about right for mine....

What does the horizontal dispersion vs frequency look like on the BG Driver?

I really liked my old RD75, so I can only imagine what yours would be like.

I just noticed your challenge - yes I will have it done by then. I will be very dissapointed if it is not complete in 3 months. It is VERY close to assembly and painting! 4 solid days of routing and biscuit joining, 4 days of gluing and sanding, 4 days of painting. Hmmm, maybe longer than 3 months...... BUT, will have it finished before you get here.

[cowanaudio]

I'd aim for 1KHz or there abouts.

My drivers are not BG, or anything to do with them.

Cheers

William Cowan

[Bent]

Not BG, OK. They look like an entirely different application of the technology as well.

I edited my last post too

[Bent]

For the length of the ribbon I have, I am then extra glad I went with the drivers I have, they are excellent to 1.2khz, in fact where they compete best with the Excel drivers and the like is from 150Hz and up.

I was thinking that I should have gone with the SLS 12", but it wouldnt have worked with the shorter ribbon, crossing so high on a 12" wouldnt be such a good idea I would have thought

Are you going Soffit mount again?

[Bent]

Bill: after re-reading your post, I realise that you have set up a temporary solution to listen to the DG Planars. I will be very interested to see your final design.

Re: Dipole Bass/Monopole Bass.

I will have this problem (integration). I plan to equalise each section "flat in room at listening position, removing all nodes" independently before crossing over, hopefully that will do it.....

[Few]

Bent:
If you're going to place your speakers on a floor that is quite reflective at mid and high frequencies, the reflection from the floor has the effect of doubling the effective ribbon length--or at least an approximation to that. You might find that in practice you can get away with a lower crossover than is predicted while ignoring the floor bounce. Just a thought.
Few

[cowanaudio]

G'day Few

His ribbons are too short for that. He'd be above the ribbon if he stood up.

Cheers

William Cowan

[Few]

His ribbons are too short for that. He'd be above the ribbon if he stood up

I'm not sure I follow your point. Based on the photo in his first post his ears are going to above the ribbon when he stands up no matter what, so serious listening will be done while seated. And there's always going to be some reflection from the floor--a lot of specular reflection if its smooth and hard and an attenuated reflection if it's carpeted--but a reflection in any case. I'm just suggesting that in "real world" applications (meaning a typical living space) the problems introduced by departures from ideality are sometimes less troubling than a simple theoretical treatment would suggest. The ever present floor reflection might be helpful in Bent's case.

Also, it may be true that restricting the listening position can be considered a compromise, but changing the crossover frequency from 300-400 Hz to 1 KHz is a compromise as well. The spatial separation of the drivers (woofer to woofer, and woofer array to ribbon) will cause more polar response problems than would using the higher cutoff point, and woofer response anomalies are more likely to intrude. Even if the woofers look great to 1.2 KHz, a 1 KHz crossover point isn't going to provide much attenuation just above that point unless the slopes are very steep.

Few