Tweeter Designs - Page 7

Yeah it was poorly worded. When you're off-axis (out of the tip of the listening triangle relative to a pair of speakers) do you lose image?

If so, do you think this is related to the change in level - with speakers with poor power responses presumably suffering more - or to timing, because the distance to each speaker isn't the same?

I'd say it's both, because balance controls only do so much.

Anyway Pen, I think Jon's point is that when you move out of the sweetspot, even though you have constant directivity, and the speakers tonal balance doesn't shift, you have other issues. IE The left and right sounds arriving at different times and also the shift in balance since you're now closer to one speaker than the other.

The problem or observation if you will is much less significant if you use a center channel with a steered center feed.

Experiments over many years have concluded that timing is critical in the range from 800hz to 1600hz. Above 1600hz, the ear/brain combination localizes sound based upon pressure level - not phase or time based differences.

So effectively both aspects matter but at different frequencies.

I think our applications are a little different, my POV is more of a HT thing and like Chu posted there is a Center Channel involved that helps with the imaging issue if we are far off axis.

But even in 2 channel, Waveguides offer a much wider sweet spot so moving isnt as lmited but yes If I move outside of even their range the imaging is off, it depends on the content and the wavelenghts involved. It would be interesting to see the different "Listening Triangles" created by different designs.

Thanks, that's interesting to know.

It sure is. A lot of designers (myself included) build crossovers and select drivers based upon this information.

I would enjoy reading more about your approaches and what some of the goals you hope to achieve are. Perhaps some measurements along with explanations?

Well hopefully villastrangiato can add more to this, but just thinking about it logically it means that any crossover in the 800-1600hz range needs to be time aligned and ideally the end result should minimize any phase shifts in this region (maybe that's going to far?). Obviously at the crossover point the drivers must also be in perfect phase.

Or the other approach is to just not have any crossovers in that critical region. My mid horn cross at 400hz and 7.2Khz. Which may be one of the reasons it sounds good .

There is something really special about horns that go low! I think the performance without issue in the 500Hz to 3KHz range is the key to speaker success.

Interesting. Do you have any internet resource or published scientific paper that shows this study you're citing? I would be very interested in this information. Psychoacoustic studies like this could be useful in crossover design.

There are a wealth of resources available to study human localization of sound both online and in published works. Googling "sound localization" will return a sizable chunk of useful information such as can be found here:

http://en.wikipedia.org/wiki/Sound_localization

To me, the subject is fascinating and it's very easy to get lost delving into papers and research studies for days on end. Enjoy the journey!

I have posted hundreds of measured plots of CD waveguides (and systems incorporating them) extending to 20 kHz and beyond over years of EconoWave development. Of late (this year, particularly), I am also providing polar directivity maps, including some of conventional cone and and dome tweeters.

Compression driver exit and waveguide throat size limits dispersion in the last octave; wide dispersion doesn't happen up there with anything larger than 1". If you want it at 30 - 50 kHz, the throat must be smaller than this, even. It's why Geddes doesn't use anything larger than 1".

Further, depending upon compression driver construction and diaphragm material, there are limits to how high frequency response (on-axis included) can be successfully achieved with HF comp; boost some of them beyond pistonic into breakup mode, and they get nasty real quickly.

JBL 2435HPL with beryllium diaphragm is allegedly pistonic up to 18 kHz. Above there, consensus is that it is best (sonically) just allowed to roll off naturally. Look to JBL's TOTL 3-way consumer offerings using compression drivers for guidance as to the appropriate limitations with this technology. Greg Timbers knows what he's doing with them.

As to Revel's use of domes, see the horizontal directivity waterfall measured by John Atkinson where it's clear that Salon2's exemplary wide controlled dispersion collapses in the VHF:

http://www.stereophile.com/floorloud...el/index5.html