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Old 28th October 2006, 12:07 PM   #1
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Default New Line Array Project - Jim Griffin others?

Just ordered 32 of these Foster 00463 midbass drivers as well as 32 of these DAYTON ND20FA neo dome tweets to build some open back lines. On the surface the response graphs look quite respectable seeing these will be under $300.00 in material costs. Should be high sensitivity and pretty low distortion/linear.

I'm hoping the line will get down below 100 cycles and plan on crossing them at 2500-3000 cycles. I will bi-amp these.

What do you guys think?

Any problems with series induction interaction (rolloff) from partial series wiring of the line array Fosters?

Neo tweeter response

Foster response 00463 - lower of the two

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Old 28th October 2006, 10:00 PM   #2
ScottG is offline ScottG  United States
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Notice the loss in spl here in this array (and this is with 2 inch drivers):

http://www.partsexpress.com/projects...ze3201noeq.jpg

Now some of that sp-loss won't be as exagerated because you aren't using as many drivers as that design had. However, because of the larger diameter of the drivers for yours vs. the 2 inch drivers in this design - sp-loss will likely begin a bit low in freq.

Effectivly what this means is that you'll need to either shelve the midband or add some upper freq. gain to the woofers for a fairly flat response at crossover.

As for the tweeters.. Zaph has them tested and recommends about 3.5 kHz for the crossover point. However you'll be using far more of them, AND you'll likely be using a steeper filter - so 2.5 kHz *may* be OK.

http://www.zaphaudio.com/tweetermishmash/

The tweeter line length at 2.5 kHz for aprox. 24 inches will net you a maximum of 2 meters listening distance to maintain linesource character. If you crossover at 3.5 kHz then add a meter to that figure (..but you'll also have to add even more gain to the woofer's top-end). (..the woofer line should be long enough to net an "infinite" line length.)

I think the thing that will be critical to good sound (not suggested above), will be making sure that there is very little airflow resistance behind the midbass drives.
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Old 28th October 2006, 11:06 PM   #3
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Great info ScottG - Thanks

What I'm thinking - ( I won't have the drivers mounted till next week) - is starting with a narrow baffle say 7-8" wide and it may do some of the shelving on it's own and then adjust the response with with various size slanted wings to try and achieve a wide range linear response.

I have lots of extra wood here to expiriment with.

I'll post more on the woofer/mid line after I get some hands on with these things. I've never built a long line like this before - The hole saw will really be getting a work out next week.

After the Foster line is figured out I'll add the upper treble and try 16 of the domes a side. Another meter of them a side will surely add some cost - maybe it will be worth it..
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Old 29th October 2006, 12:33 AM   #4
ScottG is offline ScottG  United States
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Quote:
Originally posted by Magnetar
Great info ScottG - Thanks

What I'm thinking - ( I won't have the drivers mounted till next week) - is starting with a narrow baffle say 7-8" wide and it may do some of the shelving on it's own and then adjust the response with with various size slanted wings to try and achieve a wide range linear response.

I have lots of extra wood here to expiriment with.

I'll post more on the woofer/mid line after I get some hands on with these things. I've never built a long line like this before - The hole saw will really be getting a work out next week.

After the Foster line is figured out I'll add the upper treble and try 16 of the domes a side. Another meter of them a side will surely add some cost - maybe it will be worth it..

Interesting.. I did some modeling of the baffle and discovered some stuff I *should* have known.. but didn't.

I went through the Edge - which only allowed me to place 7 midbass 5.25 inch drivers on the panel (..but did allow me to make, but not see all of it, a panel that was 85 inches high - strange). Anyway - just bear this in mind (..and note that the exageration in sp loss at higher freq.s are likely greater than my 7 driver version).

The modled baffle was 85 inches tall and 8 inches wide. NOT calculated as an open baffle. The drivers were all set to the outer edge of one side of the baffle.

.. the sp loss IS significant at 1 meter distance for the midbass line. Its only down 1 db at 1 kHz. At 1.5 khz its down 3 db. At 2 khz its down about 5.5 db. And at 3 kHz its down about 6 db. From there its is NOT pretty (..and is pretty much unusable).

Now here is the interesting thing..

At 2 meters + it isn't so bad up to 2 kHz. Pretty much flat to 1.3 kHz. Down 3 db at 2 kHz and down 6 db at 3 kHz.

At 3 meters sp is actually UP about .5 db at 1.3 kHz. Down 1.5 db at 2 kHz and down 3 db at 3 kHz.

So this tells me that unless line array is specifically engineered for set listening distance, that tonal balances will occur with alternate listening distances. (..of course room reflections and total power response will also play a part. Note that at 10 + meters its pretty much the "farfield" and the thing is pretty flat overall - even at much higher freq.s)

As for the low-end - the 8 inch baffle and the midbasses you have selected will be more than sufficient for baffle-loss compensation. Even at 10 meters at 100 Hz the the line is only down about 4.5 db. At 1 meter the line down only 3 db at 100 Hz. So with these drivers you have the "thumbs-up" for the "lower"-end response.

For an Open baffle configuration..

You are 6 db down at 150 Hz for an 8 inch baffle with spl's starting to roll-off at around 500 Hz. This means you'll be -2 db with these midbass drivers at 150 Hz (..assuming the driver curves are an accurate representation). At 100 Hz figure about -6 to -7 db down for these midbass drivers. So for open baffle and a lower freq. response - these drivers just don't "cut it" without some eq.

HOWEVER - with such a high qts they effectivly have "eq", so they might make it open baffle 8 inches.

(note that considering the high qts of the midbass drivers - IF you go with an enclosed backing to them, (i.e. non-open baffle), then seriously consider an aperiodic enclosure.)
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Old 29th October 2006, 01:14 AM   #5
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Well let me build some baffles and see what really happens before you make me change my mind!

What inspired me to do this line array thing was hearing a 96 driver line using 30 cent one by three inch TV speakers at fellows house a couple of weeks ago.

The tiny drivers were in 3' wide sealed baffles with no tweeters and some little 6.5" isobaric bass drivers built into sub enclosures(biamped) in the back of the baffles for below 120 cycles. Other than the size (bigger then my horn systems at over 8 feet tall and 3 feet wide and aaround a fooot and a half deep!) and lack of high frequency extension I was pretty impressed with the sound. Mostly In the way the lines drove the room and the huge sweet spot. The upper bass and mids were very coherent and his line arrays projected a nice meaty, 3D image that was quite enveloping and full size. They also would play at serious levels with little strain like a good horn.

He used no eq at with this and up to 6k or so, I feel this 96 driver system is superior to my Acoustat Spectra 3 electrostats. His line was also easier to drive, no beaming, and walked all over the Acoustats in dynamics and pure FUN - The Acoustat is a pretty good sounding panel speaker with it's segmented panels.

So what I'm hoping to do is get these $ 3.00 drivers to sound as good as his 30 cent drivers with some response above 10K and a smaller footprint.

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Old 29th October 2006, 01:52 AM   #6
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Here is an interesting design by Roger Russel - He uses EQ IDS-25

These go against Jim Griffin's physics on lobing!

I did a search and have found these were very well liked at the Rocky Mountain Audiofest - maybe the best speaker display there.

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Old 29th October 2006, 01:22 AM   #7
ScottG is offline ScottG  United States
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Naw.. those still comb.

- these are the drivers.. notice that they have the right rising response to compensate for the loss of sp at higher freq.s. (..at least in the near field.)

http://www.tymphany.com/datasheet/printview.php?id=116

Notice the combing here (but it has been eq'ed) for the tall 2 inch driver array. Subjectivly from about 3.5 kHz to 12 kHz it will have the subjective effect of a bit of white-noise overlayed on the soundstage and the imaging slightly more diffuse.

http://www.partsexpress.com/projects...eqnosmooth.jpg

The vifa drivers will exhibit this even more and it can't be eq.ed away. It however doesn't really become objectionable until 12 kHz - and even then its pretty benign. The best that eq. can do in this circumstance is to smooth out some of the dips and peaks where its the worst (rather like "averaging").

parts value-wise.. lets see 50 drivers with a manufacturer price less than 30 US each and a little eq., that with all the normal associated business costs and no dealer to deal with *some how* manages to warrent a price tag of 19K US and is most certainly NOT a fullrange design. Sometimes I just want to beat the living cr@p out of "high-end" manufacturers.
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Old 29th October 2006, 01:55 AM   #8
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Originally posted by ScottG
Naw.. those still comb.

- these are the drivers.. notice that they have the right rising response to compensate for the loss of sp at higher freq.s. (..at least in the near field.)

http://www.tymphany.com/datasheet/printview.php?id=116

Notice the combing here (but it has been eq'ed) for the tall 2 inch driver array. Subjectivly from about 3.5 kHz to 12 kHz it will have the subjective effect of a bit of white-noise overlayed on the soundstage and the imaging slightly more diffuse.


based on that I need to see if Madisound shipped the drivers I ordered yesterday and try and switch them to the 'full range' version with the rising response - !

Top response is 'Full Range' - same price
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Old 29th October 2006, 02:08 AM   #9
ScottG is offline ScottG  United States
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Originally posted by Magnetar



based on that I need to see if Madisound shipped the drivers I ordered yesterday and try and switch them to the 'full range' version with the rising response - !

Top response is 'Full Range' - same price
I actually started off writing just that (in my first post). Then I read it a little closer and had seen that you already had made the purchase - so I figured "eh, work with what you've got".

Note that JA (stereophile) measures at 1.25 meters and this seems to correlate well with an in-room response at an average listening distance of 3-4 meters. (..he also averages over a horizontal "window" at the listening position for the higher freq. response.)
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Old 29th October 2006, 04:21 AM   #10
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Magnetar,

A big driver high dynamics guy impressed by a bunch of 1"x3" TV speakers says alot. I wanted to try the ovals, but never found one that sounded good individually.

I don't envy all those holes. That's the only thing I really hate about building arrays. I'm sure you have a high-eff compression tweet around. You may want to try one in place of the center mid at first. It'll need an Lpad to adjust the level to match the array for listening distance, but it solves a number of other issues, not to mention less holes and wires.

Hint- Solder the wires to drivers before installation or you're looking at a back breaking nightmare. Also, the undiscussed secret to good vs great OB's is addressing edge diffraction, not baffle step but actual diffraction at the edges. It's far more important with OB's than boxes due to much greater velocity at the sides (think in terms of rushing to fill the rear wave rarefaction and vice versa). This is even more important with narrow fronts, since you're talking about higher frequencies bending around the baffle. I believe wings increase the effect because the travel distance is even greater (more velocity).

Unless your buddy got some magical 1x3's, yours should be even better. Have fun and keep us posted.
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