OB help needed

[ondesx]

Hi Guys,

I plan to build an OB in dipole mode (i. e. a couple of mids and subs, but the tweeters, one looking to front the other to rear, out of phase from each other). I already have the ribbons tweeters and the woofers for the subs (Dayton 12" RSS315-OH 4). I miss the mids drivers for now... I'll use an active xover and obviously separated amps.

I would appreciate any help for the design of a "single" panel with the mids and the lows. If this is not advised, since the major drawback of this design remains the wave cancellation, I probably would try the "Linkwitz H or W" dipole for subs. The question is : "how do you derive the best size for the OB panel if there are on it:
- only the mids,
- both mids and lows.

TIA for any feedback,

[jerome69]

Hi,

A new post might be better.

Originally Posted by ondesx

... I already have the ribbons tweeters
....
I'll use an active xover and obviously separated amps.
....

Forget active crossover with ribbons. Ribbons work with passive crossovers.

Originally Posted by ondesx

I would appreciate any help for the design of a "single" panel with the mids and the lows. If this is not advised, since the major drawback of this design remains the wave cancellation, I probably would try the "Linkwitz H or W" dipole for subs. The question is : "how do you derive the best size for the OB panel if there are on it:
- only the mids,
- both mids and lows.

Take a look, search on the web site. You have a lot of design of OBs and you could have some ideas. The response is not simple and short. OB is hard to do it right.

[Drew Eckhardt]

Originally Posted by ondesx

Hi Guys,

I plan to build an OB in dipole mode (i. e. a couple of mids and subs, but the tweeters, one looking to front the other to rear, out of phase from each other). I already have the ribbons tweeters and the woofers for the subs (Dayton 12" RSS315-OH 4). I miss the mids drivers for now... I'll use an active xover and obviously separated amps.

I would appreciate any help for the design of a "single" panel with the mids and the lows.

You don't want to do that. Wide baffles which give you enough bass don't sound natural in the midrange, presumably because of what's going on with polar response.

An open baffle speaker only approximates a cosine alpha polar response up to an octave below the first dipole peak. It broadens and then collapses into multiple lobes an octave past the dipole peak.

John Krevosky (equalized for flat on-axis response)

Dipoles and Open Baffles

and Siegfried Linkwitz (unequalized)

Constant directivity loudspeaker designs

have illustrations on open baffle polar response.

To provide good polar response at higher frequencies the baffle must be narrow.

But to keep displacement requirements reasonable it must be wide.

The common flat or shallow midrange baffle plus a similar width H, U, or W frame addresses that while keeping the entire thing in a visually attractive package.

If this is not advised, since the major drawback of this design remains the wave cancellation, I probably would try the "Linkwitz H or W" dipole for subs. The question is : "how do you derive the best size for the OB panel if there are on it:
- only the mids,
- both mids and lows.

Don Maurer iterated over about 30 test baffles and picked the ones with the most uniform polar response

Prototype Test Results

[gainphile]

Originally Posted by ondesx

The question is : "how do you derive the best size for the OB panel if there are on it:
- only the mids,
- both mids and lows.

Width of the baffle should be less than 2*midrange diameter. This generally means narrow baffle.

So it's not ideal to have 5" mid with 10" woofers. But 8" and 10" woofers is great (hence Orion).

If your mid is small see my avatar pic ...

[ondesx]

Originally Posted by jerome69

Hi,


Forget active crossover with ribbons. Ribbons work with passive crossovers.

Bonjour Jerome,

I'm not sure to understand why active xovers aren't usable with ribbons... My active xover is presently followed by the dedicated amp for each ribbon, and it work pretty good indeed. Passive or active limitation of the frequency range wouldn't affect the behavior of the following driver IMHO. But perhaps do you have some precision on this particular point.

[ondesx]

Thanks to Drew and gainphile for the inputs and the links...

It seems clear that mids and lows must be separated in two different size and form panels. The mids will be reproduced by 8" drivers.

I contacted John and he kindly answered my first questions about DP/OB design.

I now have to define if I go for only a driver in the middle of a rectangular panel or 2 in an opposite arrangement (i. e. one looking to front the other to rear out-of-phase from each other). And in this case, the final size and position of the drivers in the panel for the best result...

[jerome69]

Originally Posted by ondesx

Bonjour Jerome,

I'm not sure to understand why active xovers aren't usable with ribbons... My active xover is presently followed by the dedicated amp for each ribbon, and it work pretty good indeed. Passive or active limitation of the frequency range wouldn't affect the behavior of the following driver IMHO. But perhaps do you have some precision on this particular point.

Salut

Are you sure you have real ribbon tweeter ? Perhaps you put a 10uF capacitor on them ?

I already used Fountek JP3 with active crossover, a nightmare !

1. You cannot connect directly the ribbon, DC resistance = 0, short circuit for the amp.

2. Switch off the amp, plof ! I had two ribbons to repair.

3. The sonic advantage of ribbon in active crossover disappears. A dome does as well.

[jerome69]

Originally Posted by ondesx

It seems clear that mids and lows must be separated in two different size and form panels. The mids will be reproduced by 8" drivers.

It is not a general rule. The size of the panel affects polar response and also bass extension. The best compromise must be found.

Originally Posted by ondesx

I contacted John and he kindly answered my first questions about DP/OB design.

I now have to define if I go for only a driver in the middle of a rectangular panel or 2 in an opposite arrangement (i. e. one looking to front the other to rear out-of-phase from each other). And in this case, the final size and position of the drivers in the panel for the best result...

Why not a MTM arrangement with 2 drivers ?

[ondesx]

Re Jerôme,

Of course, my ribbons are 4 ohms minimum impedance, than they could be directly connected to the amps as explained in my previous post. Otherwise, I agree with you that, depending of the amps, this is not advised... They are the "only true" AMT ribbon from Dr Oskar Heil. With 24 dB slope they can be used from 700 Hz to more than 23 kHz for very high power inputs !... This is an important point for me : the power handling. Most ribbons only accept 30 to 60 W as continuous power input. I plan to use 2 to 300 W for mine (presently driven by 150 W amps).

I will go for separated panels for mids and lows, since the development appears to be largely simplified.

What is "an MTM" arrangement ? Do you mean either for the mids or the subs, or even both ?

[jerome69]

MTM for the mid
Dipole Main Panel