| second array already in the works [message #60711] |
Sun, 30 August 2009 23:45  |
Villain3g
Messages: 22
Registered: August 2009
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Chancellor |
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After checking out the recommended reading... I've decided to make my next line array a 2 way setup, crossed around 3k. For the woofers I'd like to use 8 Vifa BC14WG79-08's. They should go low enough to meet up with my subs. My question lies with the tweeters. My plan is to modify the flanges on the Tang Band 13-1264SA it looks like the inner structure is 30mm. If I remove the entire flange, will this get the c-to-c close enough?
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| Re: second array already in the works [message #60712 is a reply to message #60711] |
Mon, 31 August 2009 01:03  |
darkmoebius2
Messages: 37
Registered: August 2009
Location: Los Angeles, CA
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Baron |
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| Villain3g wrote on Sun, 30 August 2009 23:45 | If I remove the entire flange, will this get the c-to-c close enough
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Dr. Griffin answers your question in the 2nd paragraph of pg 13 in his line array white paper| Quote: | 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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| Re: second array already in the works [message #60720 is a reply to message #60716] |
Mon, 31 August 2009 12:57 |
darkmoebius2
Messages: 37
Registered: August 2009
Location: Los Angeles, CA
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Baron |
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| Villain3g wrote on Mon, 31 August 2009 11:27 | I saw that in there, but thought it was a little unclear. Because I know 10k is audible.
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Without going to vertical ribbons, it is going to be nearly impossible to do better than that. Eric J/Marlboro was able to shave enough flange off Dayton ND20FA-6 3/4" Dome Tweeters to get comb filtering out to 15k. But, if I remember correctly, he mentioned that he wouldn't go through all that hassle again if he had the chance. You might want to try the rear-mount version, Dayton ND20FB-4, of his tweeter which has no flange. Could save you a hell of a lot of time, frustration, and get nearly the same, or better, results than the Tang Band.
| Quote: | Next question relates to pairing the drivers. The tweeters are 92db. The woofers are at 88db...I am afraid that they will be too loud compared to the woofers.
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Funny hat should ask that exact question this morning! I was up all night trying to crash-course myself on driver matching and crossover/filter design.
Elliott Sound Products has excellent tutorials on all aspects of DIY Audio. I suggest you read all of these primers related to speaker/crossover design. I did last night and my understanding(while still beginner) is lightyears ahead of what it was before. These are all short (1-4 pages) but pack a lot of information, yet are still easy for the beginner to understand. He also provides free complete designs for working passive and active crossovers, notch filters, etc - all you will need.
Design of Passive Crossovers
Benefits of Bi-Amping (Not Quite Magic, But Close) - Part 1
Benefits of Bi-Amping (Not Quite Magic, But Close) - Part 2
Active Filters
Effects Of Source Impedance on Loudspeakers
Phase, Time and Distortion in Loudspeakers
Baffle Step Compensation
Doppler distortion in loudspeakers - Real or Imaginary?
| Quote: | It looks like 12 woofers power tapered in 2,4,6 orientation is most appealing, resulting in 8.7 ohms. Would that give me an efficiency of around 98db?...If I had 32 tweeters, is there in optimal arrangement that would result in an appropriate efficiency?
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I leave those questions to those with more experience and knowledge than me.
| Quote: | Can I have different impedances for the tweeters and woofers? Does that impact the design of the crossovers?
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Absolutely to both questions. | Quote: | I was hoping the use parts express's 2way 3k 8ohm crossover.
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Don't. Read the links I provided above and you'll see why that would completely undermine all the planning and design you put into your arrays. Build your own, active if possible.
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| Re: second array already in the works [message #60723 is a reply to message #60722] |
Mon, 31 August 2009 15:10 |
darkmoebius2
Messages: 37
Registered: August 2009
Location: Los Angeles, CA
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| Villain3g wrote on Mon, 31 August 2009 14:55 | Wow! Thanks for the reading material. My first array was more of a science experiment. These second ones will take some more planning. And $$$... We'll see how I digest the info. Thanks again.
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No problem, I am just at the beginning of the learning curve, too.
I almost jumped right in, but then came to the mindset that it's best to back off any initial plans, digest all the information on speaker/array design, then pick parts to maximize performance within personal limitations(financial, building skill, time, etc.)
As Eric J has said, and Rod Elliott stresses on the ESP website, it is probably more effective, cheaper or equal in cost, and just plain better to go with active crossover and two or 3-way amping. That will help negate many of power loss/impedance/efficiency/non-linearity/etc. problems in passive crossovers.
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| Re: second array already in the works [message #60724 is a reply to message #60712] |
Mon, 31 August 2009 16:32 |
Eric J
Messages: 71
Registered: May 2009
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Viscount |
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I'd be concerned about comb filter distortion with a crossover of 3000 for those Vifa's. It would seem that 3000 is a bit high for them. I have a Vifa BC14SG49-08 sitting right her in front of me, and unless you cut THEIR flanges(4.75 cut), they are 5.75 inches center to center. The ones they are selling have a truncated edge coming to 5.12, but that means that comb filter distortion starts at 2660. Going to 3000 is too high.
I have an excell database with every c-to-c from .6 inches to 113 feet listed for the start of comb filter distortion, in fractions of an inch. I email it to you if you want it.
Going down to 3000 is too low for the TB's. They drop like a rock after 3000. Below 3000 they are going to screech. You don't say how many you are going to use. To have any hope of using them you would have to be using a 48 db per octave crossover. Look at it this way. The crossover doesn't simply cut the tweeter off at 3000. You need to be able to deal with one octave below where the cutoff is. If you drop 12 db, you pretty much can't hear it. Every 3 db down cuts the sound volume in 1/2.
So if you put in thirty tweeters like I did, then the volume at full power is already cut to 1/30 of the sound that one would have to put out. A simple 6 db octave crossover will cut below the cut off so that each one puts out 120th of the amount of the original sound. But while the recommended range for the Neo 20FA's is 3500, their FS is 2000. The TB's have a lower range of 3000, but their FS is also 3000.
It could work but you better be using a lot of them. The problem is that you really don't want to be crossing them below their FS or you're going to get screeching from them at theat frequency no matter how many you use. And it still doesn't help you with the problem with the mid ranges and their comb distortion.
So this combination gives you a double whammy. The frequency range between 2500 and 3000 is going to have your tweeters screeching like chalk on a board, and the woofers are going to give you dropped frequencies between 2500 and 3000. If you want to use the Vifa's you'll have to use planars or ribbons unless you are willing to use a 3/4 inch dome that can go that low. If you want to use the 1/2 inch domes, then youa re going to have to use a fullrange that will go as high as say 3300 but at the same time can be close enough together to not produce comb filter distortion.
I've said before that the only usable dome tweeter on the market is the 3/4 Dayton Neo 20A. And then you have to use the TB 3 inchers.
What you are setting yourself up for in the speaker category is not going to give you something that you like, I suspect. You'll be complaining about the lower harmonics.
Eric/Marlboro
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