| First speakers - a little ambitious - curved array [message #60536] |
Thu, 06 August 2009 21:04  |
Villain3g
Messages: 22
Registered: August 2009
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Chancellor |
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When I finally decided to build a pair of speakers, I knew that I wanted to do something different. I also wanted it to be relatively "simple". The first thought was a single full range driver in a transmission line but they look like conventional floorstanding speakers. My second thought would be a line array but they require a mixer to combat the combing effect. This is apparently due to each driver from center being a little further from the listener's ear. So I figured, why not have every driver equidistant from your ear. This would create a pretty nice listening experience for focal point.
Keeping cost and final impedance as factors, I went with 16 peerless 2" full range drivers per channel. I arranged them in a curved line array with a radius of 12 ft. I used 3/4" mdf for the sides and internal bracing. Again for cost, I used hardboard for the curved front and back. I wired it up in a configuration to end up with 4ohms. Attached are some pictures.
Originally I was listening to them in a larger room. About 25' wide by 14' deep. In that room they were placed wider apart and I was sitting at the designed height. At first they sounded messy but as I listened longer the speakers started to fill the range. After they had broken in, I was surprised at how deep they were going. I'm not up with all speaker terminology but their presence seemed broad and quite realistic. I tested the speakers with a variety of music. They excelled with acoustic guitar, vocal, and smooth jazz. Where they seemed to fall off is with electric guitar as in heavy metal. The distortion in the guitar is muddled. Maybe I need an equalizer for the different types of music.
Unfortunately I have to move them to my bedroom. They don't have the same presence but its still ok. While in my room played some test tracks through them. I was surprised to hear sound all the way down to 30hz. Now I don't have any instrumentation to measure the drop-off, but I'd say it was usable down to 40hz.
My next step is to stiffen the enclosure. Any advise from the seasoned veterans would be much appreciated. I plan on doubling the wall thickness to two layers of 3/4" mdf. For the curved baffles I want to use two layers of 1/2" mdf. I think it will bend enough. Flush mounting the drivers and back chamfering the baffle is on the list as well. I'll also round over the edges of the cabinet.
If all goes well with that, I want to incorporate a diy powered sub somewhere in the equation. Either one under a center channel or one under each the left and right speakers.
Quite the lengthy first post. Mostly filled with noobish comments but hopefully you enjoyed it and have some input on the topic. If anything they look sexy...
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| Re: First speakers - a little ambitious - curved array [message #60653 is a reply to message #60650] |
Sat, 22 August 2009 00:57  |
darkmoebius2
Messages: 37
Registered: August 2009
Location: Los Angeles, CA
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Baron |
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| Villain3g wrote on Fri, 21 August 2009 13:58 | I'll whip up some strait enclosures to compare.
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Just follow Dr Griffin's white paper and they'll turn out great. Since you are using fullrange drivers which will be covering HF's all the way up, too, the driver flanges should probably be as close to touching each other as possible| Quote: | Near field. Urban, et al [1] derives a more restrictive criterion of no more than a half wavelength separation between drivers at their highest operating frequency...Wavelength is equal to the velocity of sound (344 m/s or 1130 feet/s) divided by the frequency.
For the tweeter line very close center-to-center spacing is difficult to attain as very small circular drivers would be necessitated for either the one wavelength or especially the half wavelength criteria. Consider operation to 20 kHz where one wavelength is 17.2 mm (0.68") and a half wavelength is only 8.6 mm (0.34"). Without regard to their surrounding flanges, dome tweeters are available in 25 mm (1"), 19 mm (0.75") and 13 mm (0.5") diameters. Hence, with any mounting flange allowance at all, the one or half wavelength c-t-c criteria are very difficult--if not impossible--to satisfy at 20 kHz. But, if we relax the c-t-c criterion, more secondary lobes would appear in the 10 to 20 kHz frequency range. Fortunately, in this octave the ear is less sensitive (per Fletcher-Munson curves) so any secondary lobes likely would be less audible to the listener. Thus, if one wavelength spacing at 10 kHz is adopted as a compromise, then tweeter spacing would need to be 34.4 mm (1.35") c-t-c apart. While more off axis secondary lobes would be generated in the far field, small flange tweeters are available to meet this dimension. The tradeoff is possible sound degradation from comb lines near 20 kHz.
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Experts out there, do I have that right?
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| Re: First speakers - a little ambitious - curved array [message #60654 is a reply to message #60653] |
Sat, 22 August 2009 10:32 |
Eric J
Messages: 71
Registered: May 2009
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Viscount |
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In my opinion, you are pretty much limited to 3/4 inch dome tweeters by the combination of frequency range covered and the need to avoid comb filter distortion.
There is only one dome tweeter on the market that actually allows cutting the flanges to make the distortion occur below between 15K-16Khz, and that is the Dayton Neo 20A. I did that with mine and got the C-to-c distance at just slightly over the actual with of the speaker itself, or .80 inches. If you use a 1/2 have inch dome, you can't go low enough in the crossover to be usable. if you use above a .75 dome, you will have comb distortion kicking in at actually hearable levels. Most people's perception of sounds drops substantially above 14000hz, so for most people the comb filter distortion is un-hearable IF YOU HAVE LIMITED IT TO BE ABOVE 15KHZ.
You are also required to use midranges no bigger than about 4 inches to be assured of not getting nasty CFD in the midrange.
If you want to avoid any possibility of hearing it, AND reduce your massive work of cutting the flanges on the neo's you must use ribbon or planar speakers. However, these speakers are far from flat in their frequency responses unless you are willing to buy those that exceed $75 each. For me this raised the price to unacceptable levels. I was building the best I could for under $1500---complete including electronic crossover, 3 amps and a preamplifier for a full tri-amped system.
So.... you either use Dayton Neo 3/4 inch domes and cut each flange and then put them together tightly, or you use a ribbon. Considering the effort I had to go into to cut each flange, I cannot imagine any manufacturer doing that.
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