My go at cheaper Orions "Econions"

[spot]

Hi,

Like many others I'm looking at building something along the line of the Orions but greatly reduced in cost. I had thought of the Plutos but the wife didn't like the look .

Anyway what I'm thinking of doing is-

1. Removing the 4x woofers and using the sub to go up to the 120hz crossover (this saves a lot of cabinet making as well as $)
2. Maybe making a second (mono) sub later.
3. Keeping the seas midranges - after all they are great
4. Replacing the 4x$250 tweeters with perhaps 4x $60 B&G Neo3-PDR(with their back on) or 4x $29 vifa D26NC55
5. Using some digital eq for all crossovers and eq (undecided which one)

Please give any comments/criticisms/suggestions etc.
I'm mostly concerned about tweeter choice.

Thanks

[Octavia]

why not just take the back off the B&G and use it dipole?

[spot]

Originally Posted by Octavia

why not just take the back off the B&G and use it dipole?

I was considering it until i read
Comparison Bohlender & Graebener Neo3W and Neo3PDR in dipole mode
and
Zaph|Audio
At $55 each having 4x is OK though.

[a_tewinkel]

Originally Posted by spot

I was considering it until i read
Comparison Bohlender & Graebener Neo3W and Neo3PDR in dipole mode
and
Zaph|Audio
At $55 each having 4x is OK though.

I don't see how this information would make you use two closed-back Neo3's. It's only going to make things more expensive and complex. There are no drawbacks to using only one without the back cup. I've used both versions myself in a dipole, by the way.

[a_tewinkel]

In fact, if you would apply the same acoustic target curve (say, an acoustic LR4 high pass at 1,5 kHz), the version with two closed back tweeters would have higher distortion due to the non-linear compliance behind the diaphragms.

If the same, Orion-like wide baffle would be applied, the polar patterns of the two configs would be virtually identical. The polar pattern with a wide baffle would also be quite different from Keyser's data.

[sreten]

Hi,

For the tweeters I see no reason to use the same model front and back, possibly go
for a cheaper higher value model for the rear, as its relatively attenuated to the front.

rgds, sreten.

(AFAIUI the neo 3 without the back cup has an overdamped response
not suitable for a passive two-way normal x/o point. Might work very
well in an open baffle with some active EQ. I understand you can also
build some form of mini waveguide for it in the baffle, to boost low end.)

[a_tewinkel]

Originally Posted by sreten

(AFAIUI the neo 3 without the back cup has an overdamped response
not suitable for a passive two-way normal x/o point. Might work very
well in an open baffle with some active EQ. I understand you can also
build some form of mini waveguide for it in the baffle, to boost low end.)

A passive XO for an open backed Neo3 might be a little hard indeed. Its response falls off slowly with a peak at the resonance frequency, about 700-800 Hz. With an active XO there is no issue of course.

[bzfcocon]

Originally Posted by a_tewinkel

A passive XO for an open backed Neo3 might be a little hard indeed. Its response falls off slowly with a peak at the resonance frequency, about 700-800 Hz. With an active XO there is no issue of course.

As said, a shallow waveguide will be very helpful in shaping the response, except for the peak at 700 Hz - that can be tamed with a notch. Here's how it looks with a 10uF series cap in my case (it's the Neo3 PDR, sorry about the measurement atrifacts). I chose not to do anything about the 700Hz peak as, to my understanding, this is not actually a resonant peak, given that no air is trapped in any cavity.

[a_tewinkel]

Originally Posted by bzfcocon

I chose not to do anything about the 700Hz peak as, to my understanding, this is not actually a resonant peak, given that no air is trapped in any cavity.

Thanks for sharing the measurement. The peak at 700 Hz is the driver's free air resonance frequency if I'm not mistaken (no cavities involved indeed).

[bzfcocon]

One challenge you will face with the Neo3 in dipole mode will be the assymetry in front/back radiation from the mid-woofers. As you only have one crossover which you will optimize for the front radiation and the midwoofers back radiation starts to differ significantly from the front radiation from a certain frequency (typically in the crossover area 2-3 kHz), you'll typically end up with a hole in the frequency response towards the back.

Some options you have for mitigating the issue:
1. low crossover frequency - I have seen this being used in the Adire MTM design, but requires a steep filter for Neo (they used 6th order @1.8kHz). Also, the original Orions use a very low crossover point (1400 Hz IIRC)
2. a true dipole midrange like the Neo10
3. a helper driver(tweeter) on the back
4. using back-to-back drivers - with this, you have the freedom to shape the rear tweeter response to match the rear response of the midwoofers


Only 1 and 2 will give you a "true" dipole in the strict sense, however I am not really sure if that audibly matters higher than 2 kHz or so, given you get a good power response. I opted for 3.



Liviu