Lower crossover limit for Neo3 PDR dipole

[arc2v]

I've been searching for this and found very little information.

I found a document from 2001 on the GR-research site about the Neo3 PDR tweeter. In it, it says the frequency range of the Neo3 is 1200 to 26000 Hz with the back plate removed, which is how I want to run them.

Every design I have ever seen runs the Neo3 PDR only down to 1800 and most recommend 2000 or 2500 Hz as a minimum. I've noticed that many of these are using the Neo3 with the back cup still on.

So my question to all you gurus out there: why can't I run the Neo3 lower than 1800 in the OB configuration?

It doesn't appear to be a distortion issue, and the FR doesn't get wacky until below 1000 Hz.

I'm interested because it can remove the Mid from my 3 way design if I can run this low enough. And that simplicity is very intriguing to me.

Thanks in advance,
A

link to the gr-research document (which appears to be from BG):
http://www.gr-research.com/pdf/NEO3pdr.pdf

 

[ScottG]

I think the recommended crossover values are with the enclosure only - and then only because of the driver's lower freq. response with that enclosure.

The drivers actual fs appears to be around 850 Hz.

Of course anytime you lower the crossover point on any tweeter you'll run into greater excursion levels and as a result higher distortion levels.. BUT the Neo 3 PDF's distortion levels are really very low (at least with the rear enclosure) and are likely to be decent even without it. So (beyond higher spl's) the real constraint remains the freq. response you have vs. the crossover and accompanying mid/bass driver you are going to use (i.e. trying to achieve a flat summed response).

 

[Curmudgeon]

The recommended range does not include crossover information. Is that 1200 Hz with a first order filter? (Unlikely, rhetorical query only.) Fourth order? Then of course the application, content, level, and room size have a bearing on the issue.

Someone like Chris Mercurio who has first hand experience could give a definitive answer. My own preference would be to stay with a three-way. It may seem more complex, but it makes a lot of issues a lot easier, since you can use a specialized mid up to 3 kHz or so, with much less tweeter strain.

 

[lne937s]

I am not an expert on BG, but I would look at number 4 on the fourth page as a reason not to take the crossover too low.

While the drivers might be able to play that low at 1 Watt, I would expect that they would have more difficulty at higher volumes. The added excursion of the lower frequencies might also cause some problems. Also, the more energy you send through the driver, the more difficulty it will have keeping up with the rest of the speaker. However, you would probably be OK if you kept the volume down... Or set up an array to distribute the load over more drivers.

I would also use a higher order crossover the lower you go.

 

[arc2v]

Thanks for the quick replies.

I wasn't planning on going down to 1200 Hz, only 1500 to 1800 Hz or so. Then I get into the woofer breakup mode issue, but I'm going to try and tame that with a notch filter.

I will probably end up with a 3 way design again, but I really want to test the two way design first to see if I need it.

Thanks again,
AC

 

[sreten]

..In it, it says the frequency range of the Neo3 is 1200 to 26000 Hz
with the back plate removed, which is how I want to run them........



link to the gr-research document (which appears to be from BG):
http://www.gr-research.com/pdf/NEO3pdr.pdf

Bohlender Graebener Neo3 PDR ($55 w/flange) - This B&G tweeter
outperformed everything here, in most cases by a large margin.
Response curve is ok, but nonlinear distortion is excellent. This is a
very clean and natural sounding tweeter. Note: these were tested
with the rear chamber in place. Later, with a different pair,
I also tested with the chamber removed. The tweeter was far
too overdamped in that case, and I recommend leaving the rear
chamber installed.

Above is from Zaph, i.e. response is not flat used open back so
a low c/o point would need lots of EQ, reducing sensitivity a lot.

/sreten.

 

[arc2v]

Well in the spirit of "shoot first and ask questions later" I just built the darned thing at 1500Hz, 4th order L-R and gave it a listen.

The tweeter is fine (only tested moderate levels). The woofer still introduces some its breakup distortion, so that's probably out until I find a good midrange solution or a much better woofer (which will probably be more expensive). If only the Extremis was still available!!!

The tweeter is remarkably flat in the 2k through 7k region and then needs a wide notch filter to tame the rising response. Speaker Workshop optimized a great notch filter that got an almost textbook response).

Below 2k things get a little wacky, but not too bad. The severe rolloff isn't until below 1200 and there's a dip and peak going down from 1800 to 1500.

So this is a pretty robust driver, but I won't be leaving it at this point. I may revisit crossing it at 2k and going back to the B3Ns for midrange. I have another thread discussing that though (It's a baffle problem, not a driver problem).

Thanks again for the advice guys.

AC