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Old 31st October 2010, 11:44 AM   #4901
doug20 is offline doug20  United States
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Quote:
Originally Posted by Robh3606 View Post
Look at the directivity above 5K on the large screen array systems.




Good luck finding a decent horn/waveguide in a reasonable size that will get you there.

Rob
The Raptor did it down to 700Hz.

When Geddes posted response above 8KHz, I should be assuming polar response and not just the response?

I can not find the polar response on those larger screen arrays, it would be interesting to look at them.
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Old 31st October 2010, 02:49 PM   #4902
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Quote:
The Raptor did it down to 700Hz.
OK but what's happening up top?? Here is the DI curve for the JBL Screen Arrays you mentioned. In a perfect world the directivity would be a straight line. You can see that the bass starts at a very low number and then the DI increases as you change over to the waveguide in the mids and top end. Take a close look above 2K or so. The number is getting higher and above 10K it starts an abrupt change, you can see the hook at the end.

A CD waveguide would have a straight curve like the older 2360 Bi radial horns

http://www.jblpro.com/pages/pub/components/23606566.pdf

That horn family are 2" throats and you can see above 10K they simple loose control.

The on axis response is another matter entirely and can be flat either by the increasing DI from the horn, Electrical compensation or a combination of both.

Rob
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Old 31st October 2010, 03:19 PM   #4903
doug20 is offline doug20  United States
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The Raptor link is in this thread earlier. The measurements look pretty good on and off axis. Yes, there is a drop in off axis above 10KHz but the important question is does that really matter on the audiable side. All reviews of that design say it does not matter and its an awesome sounding speaker (Those reviews are as good as any Geddes speaker reviews too).

I agree 100% on the technical stuff and if having 100% directivity matters more to someone then how it sounds that is their choice. There is always compromises in audio, nothing is perfect, I would rather have low XOs and a drop off up high then higher XOs and Directivity to 20KHz.

Thanks for the JBL DI. I know those screen arrays are widly successful having heard them, I can safely conclude that there isnt anything ultra important about great DI in the upper frequency range. I also know some individuals with HT rooms that have never had a better HT setup then the JBLs.

I was trying to find out the real meaning of "response" POV from Geddes. I know understand that point to be really about the polars in the higher frequencies.

Last edited by doug20; 31st October 2010 at 03:23 PM.
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Old 31st October 2010, 03:46 PM   #4904
gedlee is offline gedlee  United States
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"Response", to me, is polar response. Axial response is simply a "glimpse" at the "real" response, and one that is not really all that meaningful.
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Old 31st October 2010, 06:30 PM   #4905
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The XT1464 in Raptor is a narrow dispersion (60 x 40) 1.4" throat horn that's only spec'd to 12.5 kHz. Check the polars and you'll see it collapses to 30 x 30 in the top octave, and might as well be tractrix or exponential in this respect:

http://www.eighteensound.com/renderPdf.aspx?pid=177

It's about power response in the end, and maintaining room-independence requires constant directivity through the top octave and EQing (rolling off) the VHF for the desired in-room response. The optimum curve shape is indeterminate, and likely varies with listening preferences, but it's more predictably controlled using EQ as in Geddes designs than via a directivity and room treatment crap-shoot.

For multi-channel HT with a center channel, it's all but moot; look at the off-axis angles involved. I provided an analysis of ScreenArray in another forum. It's a defined directivity waveguide intended for a specific application:

From the Screen Array patent:

Quote:
Fig. 13 shows the horizontal beamwidth to be narrowed to about 70 at 10 kHz and to about 63 at 16 kHz, relative to 90 at 1.25 kHz, to compensate for a corresponding amount of anticipated screen spreading, so that when the loudspeaker unit is deployed behind a perforated screen, the spreading effect will increase and converge these values, bringing them up to approximately the target value of 100 degrees....
A particular type of perforated screen is required, not typically used in HT, thankfully, as it reflects back into the waveguide. Bottom line: better than XT1464, but still not all that well suited to 2-channel except, perhaps with a particular deployment.

[Kinda huge, tho, if that's the thing.... ]

Last edited by ZilchLab; 31st October 2010 at 06:48 PM.
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Old 31st October 2010, 10:07 PM   #4906
doug20 is offline doug20  United States
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Originally Posted by ZilchLab View Post
Bottom line: better than XT1464, but still not all that well suited to 2-channel except, perhaps with a particular deployment.

[Kinda huge, tho, if that's the thing.... ]
Well, its a good thing Im as about as far away from 2 channel as you can get.

Everything I do is all about the HT design. Even my music is all digital and uses surround.

As for the Raptor, in the end we can agree that tech specs only go so far and its what listeners like. The Raptor has proven itself in listening tests against other designs so lets agree that a > 1" CD speaker can be a GREAT sounding speaker that lacks the full controlled directivity crowd sign of approval. It still has better directivity then dome design.

I think the advantages of a larger CD/horn overcome the issues of directivity that high up in the frequency. Again, speaker design is about choosing your compromises.

Last edited by doug20; 31st October 2010 at 10:12 PM.
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Old 31st October 2010, 10:34 PM   #4907
ScottG is offline ScottG  United States
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Originally Posted by doug20 View Post
..It still has better directivity then dome design.

I think the advantages of a larger CD/horn overcome the issues of directivity that high up in the frequency. Again, speaker design is about choosing your compromises.
Yes, it's very much about choosing your compromise..

But what is "better" directivity?

Many designs with "domes" are often very uniform in their polar response. The exceptions are classic "two-ways" with a larger diameter midbass coupled to a 1" or smaller dome tweeter, and even then the usual loss in pressure off-axis between 1 kHz and the typical 2-3 kHz range can often achieve an increased sense of depth that often is more natural sounding (..and is found in better implementations that are essentially "flat" horizontally in the same freq. region).

Is *increased* directivity an advantage, and if so why?

Can you achieve that same advantage through other means?

Might there be *disadvantages* to a design that has an increase in directivity?


And particularly:

In the Raptor - isn't there the possibility that what people liked about had little if anything to do with it's polar response? In fact, perhaps people liked the design *despite* it's polar response.
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Old 1st November 2010, 09:51 AM   #4908
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Consensus appears to be that we do not know what comprises the optimum power response. Toole teaches that it is smooth and uniform, tracking the axial response. I'm suggesting that "ideal" may well be variable power response with controlled directivity. See Tannoy et al.

Another observation I consider highly relevant -- we go to DIY and other demo fests and compare various designs in medium to large listening spaces bearing little in common with our own smaller "venues" where the impacts of directivity and power response are far more significant. In many cases, other than the floor (or stage) boundary, it's virtually a freespace condition with long delays and typically uncontrolled reflectivity. Yes, after some time, we adapt and "hear through" the room, but advantage still goes to those designs better suited to the listening conditions characteristic of these larger spaces, and listener preferences must be considered in context of the auditioning environment....

Last edited by ZilchLab; 1st November 2010 at 09:56 AM.
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Old 1st November 2010, 12:11 PM   #4909
gedlee is offline gedlee  United States
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Originally Posted by ZilchLab View Post
Consensus appears to be that we do not know what comprises the optimum power response.
Seems to me that the opposite is really the case as all of the "experts" seem to be in complete consensus. There isn't a "consensus" on evolution either, but that doesn't make it any less a fact. Science is not a democracy.
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Old 1st November 2010, 12:26 PM   #4910
doug20 is offline doug20  United States
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Seems to me that the opposite is really the case as all of the "experts" seem to be in complete consensus. There isn't a "consensus" on evolution either, but that doesn't make it any less a fact. Science is not a democracy.
Listening to any speaker is pretty far removed from evolution or even science.

Again, its fine to like accurate measurements (I do) but lets not think that the only good speaker is an accurate design based on ONE philosophy. There are many different designs for different applications, there isnt one design that is superior to all others since there is not a design that fits all the variables people could want.

Remember speakers are no more then furniture to most people there is no need for superior design. Just a design that fits the specific needs of that individual.

Last edited by doug20; 1st November 2010 at 12:42 PM.
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