[bdp24]

Spoke with Bruce at Eminent Technologies, unfortunately they won't sell their panels separately for DIY use.

Of course not, but the LFT-8b has separate connections for the planar panel and the cone box woofer. An LFT owner is free to not use the woofer, substituting the OB/Dipole Sub, or any other bass reproducer he/she chooses. The LFT-8b retails for $2499, the MG 1.7i for $2100. They are both fine loudspeakers, direct competition for each other. Both benefit from aftermarket stands, the LFT-8 by Sound Anchor at around $300, the MG 1.7i by Mye at around twice that. With those stands, the LFT-8b and the MG 1.7i are about the same price, and both benefit from a sub, particularly the OB/Dipole, for obvious reasons.

[aceinc]

I am thinking that for fun I am going to use a flock of divers that I have laying about in an open baffle arrangement. I have a bunch of 5", 3" and 5/8" drivers. I will stuff them into a baffle, since the tweeters are silk dome, I will probably put some facing the front and some facing the rear. Wire them all up so their resistance (since I can't easily measure impedance) are similar and hook them to a premade crossover that I have and see how bad it sounds.

I am using REW so I can see visually how bad it sounds as well.

I previously used these drivers for a center channel build that I am still using and it sounds good. See the picture below.

[Danny Richie]

Do yourself a favor and just use one forward facing tweeter. Using multiples like that will just cause comb filtering and some pretty significant peaks and dips.

[aceinc]

In the center channel, it hasn't been a problem, that I can hear, or that anyone has complained about. I have not tried to measure comb filtering, so it may be there but unnoticed.

While I can't do fancy testing I can do a freq plot using REW of just that speaker from the listening position. This has a simple cap only crossover and a couple of L-Pads. So it should look pretty funky.

I believe I have sixteen of each driver, so I was thinking about going crazy with eight of each driver in each speaker.

[Danny Richie]

In the center channel, it hasn't been a problem, that I can hear, or that anyone has complained about. I have not tried to measure comb filtering, so it may be there but unnoticed.

While I can't do fancy testing I can do a freq plot using REW of just that speaker from the listening position. This has a simple cap only crossover and a couple of L-Pads. So it should look pretty funky.

I believe I have sixteen of each driver, so I was thinking about going crazy with eight of each driver in each speaker.

It is a lot worse than you think. Check out this thread and then scroll to the bottom of the first page where I show the measured effects.

http://www.audiocircle.com/index.php?topic=124751.0

[aceinc]

Danny, I read what you referenced. In your test, the tweeters were 6.5" (center to center?) apart. Have you done further testing where the centers were closer together?

My understanding (flawed as it may be) is that there is a correlation between the frequencies generated and the distance between the center of the drivers. The higher the frequency, the closer they needed to be together. When proper distance was maintained, combing was avoided, and multiple drivers would create a single wave front.

<speaking out my nose>
If the obliqueness of the angle were problematic because of time delay, why doesn't a large radiator like a Neo 8 or some of the larger 15 & 30 inch ribbon tweeters, sound bad off angle? Wouldn't the sound from one end of the driver reach the ear at a different time than the other end of the driver?
</speaking out my nose>

Again if I were closer I would run the center channel over for your free check up, and you could test it with your equipment. I am a rather empirical kind of guy, and I think you may be as well.

[Danny Richie]

Danny, I read what you referenced. In your test, the tweeters were 6.5" (center to center?) apart. Have you done further testing where the centers were closer together?

Yes. the effect is less dramatic when the acoustic centers are closer.

My understanding (flawed as it may be) is that there is a correlation between the frequencies generated and the distance between the center of the drivers.

That is correct.

The higher the frequency, the closer they needed to be together. When proper distance was maintained, combing was avoided, and multiple drivers would create a single wave front.

Yes, for two drivers.

But when you have a line of four of them then you also have cancellation between driver 1 and 3, 2 and 4, and 1 and 4.

<speaking out my nose>
If the obliqueness of the angle were problematic because of time delay, why doesn't a large radiator like a Neo 8 or some of the larger 15 & 30 inch ribbon tweeters, sound bad off angle?

Vertically, yes. Anytime you have a line of drivers, or one long driver, you have limited upper frequency range limits above and below the line.

Wouldn't the sound from one end of the driver reach the ear at a different time than the other end of the driver?
</speaking out my nose>

Yes.

But with a continues line of planar drivers (close together), or a single long line, when some drivers are creating comb filtering that drops out the response. Other drivers that you are still on axis with fills in the holes. So what you get is a frequency response up top that is +/-2db or so. And changing heights a little changes the placement of the +/-2db peaks and dips.

Again if I were closer I would run the center channel over for your free check up, and you could test it with your equipment. I am a rather empirical kind of guy, and I think you may be as well.

That would be good.

And running a short line is the same as a tweeter of the same height. So with four tweeters stacked you have a narrow range about the height of the tweeter middle tweeters when you have a reasonable response. Above or below that the upper ranges will really drop off. This creates an uneven room response and takes away imaging and spacial ques that are found in those top octaves.

Generally go with a single point source tweeter for more even coverage, or create a line long enough that keeps you in the near field. 

[aceinc]

I found this;

http://www.audioroundtable.com/misc/nflawp.pdf

I am trying to wrap my brain around all of it, specifically, the near field to far field frequency to line height portion to listening distance, but the center to center distance of my tweeters should keep lobing above 10 khz.

[Danny Richie]

I found this;

http://www.audioroundtable.com/misc/nflawp.pdf

I am trying to wrap my brain around all of it, specifically, the near field to far field frequency to line height portion to listening distance, but the center to center distance of my tweeters should keep lobing above 10 khz.

Careful, some of that data is not correct. What you see on page 15 doesn't really work that way.

[aceinc]

Danny, is there somewhere I can go to find better data about line arrays?

[Danny Richie]

Danny, is there somewhere I can go to find better data about line arrays?

Maybe one day I'll write a book.

I might even release more line array kits one of these days.

I just need more time in the day.

Honestly though, I don't know of any good place to send you.

But if you have a desire to build a custom line source of some kind then I'll be glad to help you with it. Finding the right divers is not easy though. I really couldn't find any suitable and had to resort to designing some for that application. So it really starts with driver design.

[aceinc]

Danny, I was thinking of using some 8" AMT mid/tweeters for an array. Based on James Griffin's paper, If I crossed it over at 2khz, I would need a 4' tweeter array. The maximum woofer size should be 4" with a 2Khz crossover as well. I am thinking 72"-80" woofer array.

This would lead to 6-AMTs and 18-20 woofers.

[Danny Richie]

Danny, I was thinking of using some 8" AMT mid/tweeters for an array. Based on James Griffin's paper, If I crossed it over at 2khz, I would need a 4' tweeter array. The maximum woofer size should be 4" with a 2Khz crossover as well. I am thinking 72"-80" woofer array.

This would lead to 6-AMTs and 18-20 woofers.

The length of the array needs to be taller than 4' to be effective.

The woofer size is not relevant.

And the crossover point is never predetermined. It will have to be based on the acoustic output of the drivers.

Here is the real key. You need to match your impedance's and sensitivity of the drivers.

You won't really gain SPL levels with series/parallel groups of tweeters, but you will with the woofers. So you need high sensitivity tweeters and very low sensitivity woofers.

To match a line of Neo 8 tweeters I had to design a 6.5" woofer with 83 to 84db sensitivity.

[Danny Richie]

I do know of a guy that is about to down size and very reluctantly is going to have to let go of a pair of LS-6's.

[aceinc]

Danny, while that sounds tempting, as do the OB7s for sale in Providence, I am really interested in building something myself.

[Danny Richie]

Danny, while that sounds tempting, as do the OB7s for sale in Providence, I am really interested in building something myself.

DIY line source done right is not easy. I couldn't do it without the tools that I have for measuring, and testing. Textbook crossover or slopes do not apply to line sources. Filters have to correct for coupling that takes place within the pass band of each group of drivers.

Post your ideas though, or driver considerations and I'll try to help you with them if you really want to give it a shot.

[aceinc]

Danny, I'm in it for the fun. I might be getting some of the drivers from dodgy sources (quality wise) and if I send you a couple of samples, could/would you test them for me?

For a 4" low cost driver I was looking at this;

https://www.madisoundspeakerstore.com/approx-4-woofers/hi-vi-m4n-4-wide-range-woofer-copper-color-cone/

The freq/spl graph on Madisound is much nicer than the one on Parts Express, however.

http://b2b.parts-express.com/pedocs/more-info/297-434-hi-vi-m4n--40709.pdf

The tweeters I am looking at say their frequency response is 200-20,000 hz. I think that unlikely so I felt a 2Khz would be a safe xover. Also I remember somewhere that having a single driver covering 100-1,800hz is a good practice. If I do cross at 2khz, what do you recommend is the largest woofer size I use?

Did I mention I was going to try to go OB on this as well?

[aceinc]

Danny, Is this your friend?

http://www.ebay.com/itm/AV123-LS-6-SPEAKERS-/322208442758

He is in Miami, which is very close to where I am.

[Danny Richie]

Danny, I'm in it for the fun. I might be getting some of the drivers from dodgy sources (quality wise) and if I send you a couple of samples, could/would you test them for me?

For a 4" low cost driver I was looking at this;

https://www.madisoundspeakerstore.com/approx-4-woofers/hi-vi-m4n-4-wide-range-woofer-copper-color-cone/

The freq/spl graph on Madisound is much nicer than the one on Parts Express, however.

http://b2b.parts-express.com/pedocs/more-info/297-434-hi-vi-m4n--40709.pdf

The quality level is not great. However, that driver has a good low sensitivity and a really high Qts. So you could use them in an open baffle. But a boxed design would cause the box volume to get huge.

And you can only use them up to about 1kHz. After that the response gets rough and there will be some ringing.

The tweeters I am looking at say their frequency response is 200-20,000 hz. I think that unlikely so I felt a 2Khz would be a safe xover.

You never know until you look at the frequency response. It is often best to work with the natural roll off of the drivers.

Also I remember somewhere that having a single driver covering 100-1,800hz is a good practice. If I do cross at 2khz, what do you recommend is the largest woofer size I use?

Actually 300Hz to 500Hz is the heart of the mid-range that you want to avoid. So one octave above that is fine.

Did I mention I was going to try to go OB on this as well?

Then consider the Neo 8's for tweeters. I also have a modification for them that really helps. They can cross down to 850Hz to 1000Hz depending on how many you use. They are the same front to back (so open baffle is good). They handle a lot of power and they sound great.

[Danny Richie]

Danny, Is this your friend?

http://www.ebay.com/itm/AV123-LS-6-SPEAKERS-/322208442758

He is in Miami, which is very close to where I am.

No, but that is a great price. I used to sell just the parts as a kit for that speaker for $1,995. And those are great sounding speakers. For anyone watching, that is a great deal.