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In the Forum: Audio For Dummies ™
In the Thread: It is possible to eliminate some forms of gross side band distortions
Post Subject: Re: OK, how far are you from Boston?Posted by Bud on: 7/11/2005
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It is interesting that you say that the problem is well known. I discovered this application in 1972, while trying to come to a solution for the sonic insults being supplied by a pair of Ohm F speakers. I eventually got them to act somewhat as Walsh envisioned, but they became point source radiators rather than cylindrical. The patent was granted in 1994 and has had 204 official requests for transfer of the document. No one has ever contacted me due to those document releases.
I have no problem with the white paper being posted for others to read and comment on. I would advise caution in experimenting, only because the white paper does not address many practical issues that would have to be divulged in some sort of teaching process. This is not a difficult thing to do but will be tedious. Just as tedious as actually performing the activities required to apply the pattern you are now aware of is.
I would not reccomend applying the full pattern to a Tractix style horn. A benefit would be found in applying a ring of pattern at the middle of the final flare, the portion of the outer bell closest to you when you are in front of the horn, just to quench the Raleigh waves that circulate there. Applying the pattern to both the compression driver surface and phase plate would be beneficial. The caveat here is the level of dynamic intensity that becomes available from treated horns. Most music will end up playing somewhere in your body, in addition to assaulting your ears with pretty unbelievable transient attack and decay. Much as it happens in rows one and two in the symphony hall.
For the EV tweeters a line of pattern across the short dimension at the ends of the long horn flare would be all I would reccomend. I might experiment with the dome compression driver if I had spares.The drawback here is that, just as with the cheap paper cone tweeter in the white paper, the efficiency jumps rather alarmingly when you treat dome tweeters. I assume the EV compression dome is metal so the effect would be moderated. That increase in efficiency does translate directly into dynamic headroom, without noticable distortion, so it is easy to damage your drivers and ears because it sounds so good when you turn the volume up that you do it again and again.
The real result of treating drivers in this fashion is how "polite" they become. Heavy traffic never seems to cause road rage here. Another interesting side effect is that because the drivers do not emit transient standing waves many of the standing wave nodes in your room will not be activated. You will actually have deep bass in the middle of the room, instead of just along the walls. Another thing to consider is the location the speakers are in. No longer will you have muffled bass in an adjacent room. The entire house will become the front chamber of the speakers. The energy is now being emitted in a phase and time coherent manner and so will penetrate most walls, other than cinderblock or concrete, very effectivly. Also upper range frequencies will now travel down hallways and into other rooms intact and intelligable. These characteristics have plagued my wife for the last 30 years.... generaly to my detriment.
I really would reccomend that I treat a less expensive and easier to replace driver set first, just so you have some time to reflect on the results. Hence my suggestion about the table radio. I just need to be able to access the front of the drivers in what I assume to be a boom box style package. Treating both faces, front and back, is not worth the effort when you cannot control what is in the area behind the driver.
Bud Rerurn to Romy the Cat's Site