gedlee said:
-6 dB defines the beamwidth. The Geddes waveguides appear to be somewhat narrower than 90°, despite the published specs, more like 70° - 75° from the measurements.
In theory, it'd be good if the directivity collapsed outside the specified limits, but in practice, big headphones are not the answer.... 😉
gedlee said:
Yeah, I was thinking the same thing.
According to measurements of the XT1086, it's response is down about a half decibel at 45 degrees in the horizontal plane.
In the vertical plane, it's down 4db at 45 degrees. So it's a LOT closer to constant-directivity in the vertical plane than in the horizontal.
The Summa is down 4-5db at 45 degrees. What's interesting about the Summa is that it's response between 45 and 90 degrees off axis is more consistent than it's response from zero to 45 degrees. I'd never noticed that until today.
Here's the link to the XT1086 measurements:
http://www.htguide.com/forum/showpost.php4?p=316047&postcount=23
ZilchLab said:
Well that reveals some VERY odd behavior with the ring radiator on a waveguide then.
The compression driver on an OS waveguide with a coverage angle of 90 degrees has a beamwidth of 70-75 degrees.
But the ring radiator on a waveguide with a coverage angle of approximately 135 degrees has a beamwidth of 70-75 degrees.
If I'm reading the measurements correctly, that means we can use a VERY shallow waveguide with ring radiators, and still get directivity control.
Attached is a pic of the waveguide in question, it looks to be about 135 degrees to me.
Attachments
Patrick Bateman said:
On Saurav's curves, it looks more like 5 dB although, as he said, he was just eyeballing angles. Whatever the exact angle, it's clearly showing signs of constant directivity.
catapult said:
If the curves go out to sixty degrees, and each curve is equidistant, then the fourth cuve is 48 degrees. And at that point it's about 3 decibels down.
That's the problem in the horizontal axis of this waveguide; all the curves are nearly identical to the on-axis response.
Admittedly, I'm splitting hairs here, but the vertical curves are noticeably better than the horizontal. (assuming we want the response to fall off-axis.)
Patrick Bateman said:
What "ring radiator" is this? The combination is clearly NOT CD in the highest octave, rather, more on par with early AR dome tweeters from 40 years ago.
Patrick Bateman said:
Ugh I am so embarassed - I just realized I made a dumb mistake. I was looking at the sixty degree off-axis curves of the Behringer waveguide, noted that the response was down about 5db, then declared that it had a beamwidth of "70-75" degrees.
But that's completely wrong; you have to double it.
So the beamwidth is about 140-150 degrees, which is consistent with the dimensions of the waveguide.
Sorry!
Patrick Bateman said:
Uhmm, no, we don't want that. It's far better CD in the horizontal; your thesis is wrong again, alas.
Six for six, by my count.
There's nothing wrong with liking Summas; you're just not real good at making a credible case that everything else sucks, is all.
[Not gonna hold it against you, tho, as Earl's having some difficulty with that himself.... 😉 ]
catapult said:
Hi,
The XT1086 is an commercial offer from a major company in Europe. It isn't expected to fall behind it's published qualification to much. The horn has gained good acceptance from all day professionals.
HD1050 with the XT1086:
http://www.eighteensound.com/index.aspx?mainMenu=view_product&pid=192
I found no issues with it that were at odds with the general picture of a very well designed top notch device. An other vendor in Germany is LIMMER. The older EV HP940 for instance is a bit tricky to get right. It is interesting due to the feature in its throat. EV patented two fins to prevent from irregular dips related to the throat diameter. It works. Does that gernerate or hinder HOM? If it sounds good may I dare to trust my ears?
by
ZilchLab said:
In this application, the "holy grail" is to have response that gently falls as you go off axis.
We *don't* want response to be equivalent in level at zero and 45 degrees.
By that standard, the XT1086 is superior vertically than horizontally.
Keep in mind, we're discussing home speakers that are cross-fired with waveguides. When cross-fired, as you move away from the sweet spot the image is stable. This only works if the response decays as you move off-axis.
In a commercial venue, you would prefer the horizontal coverage of the XT1086 because it provides even coverage across a venue. It would also make it easier to array.
ZilchLab said:
Don't be a d1ck - this isn't AudioKarma and I'm not one of your sycophants.
ZilchLab said:
A compression driver with a 3" diaphragm is struggling to reach 15khz. That's why a TAD 2001 uses a beryllium diaphragm, and costs a thousand dollars.
Here we have a fourty dollar tweeter on a twelve dollar waveguide with response that rivals a TAD.
If there's anything else out there at this price point with comparable performance, I don't know what it is.
Admittedly, the TAD will play a lot louder. But does anyone really need 138db in their living rooms? The waveguide will improve the ring radiators power handling by reducing excursion at the low end, and that should be good for 120db with a pair. (They're very sensitive already, due to the small diaphragm.)
An externally hosted image should be here but it was not working when we last tested it.
Here's a graph of the exact same waveguide with a dome, and you can see the ring radiator stomps all over it:
An externally hosted image should be here but it was not working when we last tested it.
The easiest way to improve the response would be to use a smaller diaphragm. Yesterday I ordered a pair of Vifa XT19s to find out if that's true. Should have them on Wednesday.
ZilchLab said:
Maybe I misunderstood your point, is the headphone comment saying that the narrower directivity of the Geddes waveguide is more like a headphone?
If so, my question would be- wouldn't the spaciousness be accomplished by the extreme toe-in with reflection off of the opposite wall though?
This thread has been very informative for the layman like myself. Thanks to all of the contributors for all of the good input.
-Tony
Patrick Bateman said:
Help me, now, Earl EQ's flat at 22.5°, the listening axis. What are the off-axis angles generating the enhanced image rendition at each end of the couch?
It's an artifact that works with any CD speaker system pair, but once you install a center channel, it's totally moot. There are many designs which take on this challenge directly.
ZilchLab said:
I know that quite well, but that doesn't answer why you want to have your small room add reflections just to have a bigger ASW that a) is not on the recording and b) degrades localisation? And what about surround sound?
Best, Markus
TRADERXFAN said:
Others have certainly said so, but that's also routinely accomplished by damping the sidewalls at the locus of the first lateral reflection.
TRADERXFAN said:
I believe so, yes, but I'm having a difficult time convincing others of the "max dispersion" school. It has all of the requisite attributes, low IACC, particularly, for generating enhanced ASW, just as Earl suggests....
markus76 said:
The first part's easy: because we like it. Given the facility to adjust it, listeners will boost it far in excess of reality, even, spectral quality and localization be damned. That's what omni and Bose 901 are about. They also mess with the rest rather well, however.
I agree that early ipsilateral (near wall) reflections degrade not only localization, but also, spectral balance, and there is good reason to minimize them. However it's possible to isolate the ASW cues and enhance it without the deleterious consequences of conventional approaches. With this understanding, imaging and soundfield don't have to be mutually exclusive.
Multi-channel moots all of it, of course, and adds envelopment (LEV) for even more enhanced realism, a level which is not achievable with only two sources.
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