Adire DDR dipole with open-backed Neo3

[capslock]

The DDR (dipole done right) consists of a flat baffle with two Extremis drivers and a Neo3-PDR in between and with its rear cup removed.

It also uses passive dipole EQ, hence the midwoofers, which are used up to 1.8 kHz, have two huge steel laminate inductors in series.


I realize the dipole will not build up any significant pressure, but I am still afraid the midwoofers will make the Neo 3 membrane flip around.

Comments?

[Doug Lockwood]

I am currently running a NEO3 with the back cup removed in an open baffle.
I haven't detected any issues, and the highs sound effortless.
My goal is to run distortion measurements on the drivers and do a proper XO in Soundeasy.

Doug

[JonMarsh]

The DDR (dipole done right) consists of a flat baffle with two Extremis drivers and a Neo3-PDR in between and with its rear cup removed.

It also uses passive dipole EQ, hence the midwoofers, which are used up to 1.8 kHz, have two huge steel laminate inductors in series.


I realize the dipole will not build up any significant pressure, but I am still afraid the midwoofers will make the Neo 3 membrane flip around.

Comments?

Hello Eric,

You've hit on something which I have been investigating for a while- the combination of dipole woofers and midrange or tweeter drivers on the same baffle. Near field investigations will show some substantial SPL from the woofers at locations like a planar mid/tweeter when on a common baffle. I think there is some potential for IM distortion affects across the crossover boundary, if this type of baffle design is used.

There are a few possible solutions- one, don't run sensitive HF drivers in dipole mode- then they won't be subject to front and rear differential pressure. They'll still be subject to the front, though, with the resistance of diaphram compliance and rear chamber compliance. Does this make a difference still?

There are other baffle approaches which may remedy this, but is the cure worse than the original problem? I'm still investigating. However, this work will have a clear influence on the Saint-Saens design, and may cause a revisit to the Arvo also. Depends on how nitpicky I want to be, I guess.

As an experiment, run some tone sweeps through the midwoofers, and look at the output of the tweeter terminated into an 8 ohm load. (i.e., like a microphone.) The voltages will be small, but then 1/100 is only -40dB.

~Jon

[capslock]

One of my stalled designs (Phoenix like, with 2x CSC217 and 1x Neo3) adressed this. It used 45° side wings, and below and above the tweeter, I had a 6 cm deep separating wall, and also a recess that would have allowed me to but a rear wall on the tweeter chamber. However, I was worried that this 1/2 litre chamber would still be too compliant.

Seeing the DDR design made me wonder some more. Maybe Danny's cupped Neo / GR130 open baffle design is a more sound approach.

I still have those baffles (waiting to be repainted after moving), so I can do the test you propose.


Other solutions to the problem would be:

2. leaving large holes in the baffle near the tweeter

3. mounting the tweeter on the mid/woofer cone


Somehow, neither seems too attractive

[Davey]

My curiosity was peaked looking at the low-pass network of the DDR so I simulated in LspCAD:

http://home.comcast.net/~dreite/Temp/DDR.jpg

It's easy to see why the system sensitivity becomes so low when you create dipole correction with a passive speaker-level filter. Also of note is the 1600Hz peak in the electrical response.
I think I would have designed the speaker-level filter sans dipole EQ and then added this either passively or actively at line-level.

Cheers,

Davey.

[mikec]

I think I would have designed the speaker-level filter sans dipole EQ and then added this either passively or actively at line-level

They sure did accept some interesting compromises in their design.