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-   -   phase issues with mounting 2 ribbon drivers next to each other? (http://www.diyaudio.com/forums/planars-exotics/83741-phase-issues-mounting-2-ribbon-drivers-next-each-other.html)

thadman 25th July 2006 09:19 PM

phase issues with mounting 2 ribbon drivers next to each other?
 
Im working on a DIY ribbon project and would like to be able to reach 80hz (with at least a 48dB, if i got a PC xover than 96dB+) with an 84" x 2" midbass/midrange ribbon crossed over at 3500hz to a 84" x 1/2" ribbon.

I will have 2 rails of magnets per driver, so 4 7 foot rails of Neodymium N50+ per tower.

1st rail: S-N
2nd rail: N-S
3rd rail: S-N
4th rail: N-S

there will be a void between both lines where both South poles will be focused within a gap

could I place another 2" ribbon within this gap? would I get cancellation? If I reversed the phase, could I get around this?

how much excursion can I expect from a ribbon? Is there any place I can purchase aluminum embedded on mylar?

thadman 25th July 2006 09:23 PM

I dont have the necessary funds to purchase enough drivers for a midbass/bass array, so I have decided on purchasing 4 of those Acoustic Elegance IB 15s for $400 and mount them dipole (2 per tower) on an H-Frame and cross them over at 80-100hz to minimize the issue of them integrating with the line array

LineSource 26th July 2006 09:47 PM

thadman,

You'll probably want to download a free copy of FEMM 4.01 and simulate your ideas before you build.

I think you will find that any non-symmetric sharing of magnetic fields creates a modestly non-symmetric field in gap and hence modestly non-symmetric forces on the ribbon(s). You'll have to decide between cost savings/SPL and a perfectionist target.

I favor a MT with the T on the inside soundstage over a MTM or MMT ribbon linesource topology. Correctly sizing and constructing one good M seems to work best.

The motor design and suspension will determine the max excusion on a midrange ribbon. A good M design can achieve +/- 0.1"

For diffraction control, the front bezel shape and possible use of wool felt are good areas to experiment with.

thadman 27th July 2006 05:14 AM

how much displacement would I need with a dipole setup at 80hz?

I read in a previous thread that it requires 375cm^3 of displacement for 80hz @ 110dB for monopole speaker, is that peak to peak or just xmax?

LineSource 27th July 2006 10:39 PM

[QUOTE]Originally posted by thadman
[B]how much displacement would I need with a dipole setup at 80hz?


84" x 2" ribbon on an 18" wide x 84" long dipole baffle could reach 107db SPL @1m with +/- 0.1" excursion, a total of 266 cm^3 of volume displacement. You will need to get clever with your motor design and ribbon construction to reach this goal.

thadman 28th July 2006 05:26 AM

how much would I gain by making the baffle 24"?

the motor design on a ribbon is pretty straightforward from what ive read (J.V. Verhagens book + threads over here), other than using super powerful magnets (neodymium n50-n55) and lightweight diaphragms what can I do?

what did you do for your bass ribbons? You mentioned you were able to achieve 80-3000hz with a 48dB XOVER.

would a mylar ribbon with aluminum embedded be considerably better capable for maximum excursion?

How high could I go with the 15s (-6dB) and not get integration problems with the ribbon (linesource -3dB)?

LineSource 31st July 2006 12:39 AM

Quote:

Originally posted by thadman
how much would I gain by making the baffle 24"?

would a mylar ribbon with aluminum embedded be considerably better capable for maximum excursion?

How high could I go with the 15s (-6dB) and not get integration problems with the ribbon (linesource -3dB)?


thadman,

Putting the midrange ribbon linesource in the center of a 24" baffle increases the SPL by about 1.2db over an 18" baffle.


My ears favor the tweeter ribbon linesource right on the inside baffle edge, and the midrange ribbon linesource next to the tweeter, separated with a 0.25" woof felt . A line array of standard woofers next to the ribbons tilted slightly outward provide the bass with the same wave launch as the linesources. In this configuration, widening the baffle from 18" to 24" would increase SPL about 0.6db.

I've never gotten good integration even at 80Hz with a couple woofers on the floor. My ears like a woofer line array next to the ribbon linesources. If you family can live with a 84" x 24" wide baffle, you may want to consider just mounting 2-4 of your 15s IB woofers on this baffle to create a bass line array.

thadman 31st July 2006 12:53 AM

my plan was to mount the AE IB 15s on the baffle, 2 per baffle.

Could I mount them each at the bottom on top of each other? or would I need 1 at the very top?

LineSource 31st July 2006 02:42 AM

Quote:

Originally posted by thadman
my plan was to mount the AE IB 15s on the baffle, 2 per baffle.

Could I mount them each at the bottom on top of each other? or would I need 1 at the very top?


thadman, there are free programs on the web like edge and baffle diffraction simulator you can use to model your ideas. I was surprised by the large smoothing effects a 4"-5" radius on the baffle sides made in the simulations.

Even at 80Hz I would try to mount the 2 woofers 1/3 *84 from top/bottom to optimize the line array effects and minimize floor bounce effects. 80 Hz wavelength ~ 170 inches, quater wavelength ~ 42". For dipoles I favor using woofers with Qts between 0.57 and 0.71 plus electronic equalization. My ears think the high Qts woofers have poor mechanical control of transients.

thadman 31st July 2006 06:46 AM

can you recreate the line array effect with DRC?


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