Ideas for DIY Line Array With Active Crossover!

megasat16

Well, after about 2 years in waiting and pondering over the affordable and suitable drivers, I am taking a small towards the mids and the lows with 16 of these.

https://www.madisound.com/store/product_info.php?products_id=8863

Heard it has a hump around 10K for Full Range uses but I am crossing them with the tweeters array at 3K-3.5K, so I am all good. These has 9mm Xmax too and OB tested by other DIYers.

Mike, Thanks for confirmation about these drivers!

Qts is higher than I would like for OB woofer but I am using 2 columns of 4 sealed subs arrays so I don't think I need to worry about bass...

20hz

megasat16 wrote: »

Well, after about 2 years in waiting and pondering over the affordable and suitable drivers, I am taking a small towards the mids and the lows with 16 of these.

.." rel="nofollow">https://www.madisound.com/store/product_info.php?products_id=8863[/
Mike, Thanks for confirmation about these drivers! ..

I heard good things on the audiance A3 driver , audiance has a website (lots of info) .

megasat16

megasat16 wrote: »

Qts is higher than I would like for OB woofer but I am using 2 columns of 4 sealed subs arrays so I don't think I need to worry about bass...

Damn...I need to prove read after what I wrote. :redface:

What I meant Qts is actually lower than I would like for an OB woofer.

20hz wrote: »

I heard good things on the audiance A3 driver , audiance has a website (lots of info) .

Thanks! I also heard a lot of nice things about Audiance A3 but these little drivers are quite expensive. I found them on clearance once on E-speaers.com but even then, these are quite expensive for a line array with 16 on each side. A3 is 3" and 82dB sensitivity so needs a lot of them.

So, it's decided on the Alpair 12 with 6.5" driver and 89dB sensitivity.

20hz

megasat16 wrote: »

Thanks! I also heard a lot of nice things about Audiance A3 but these little drivers are quite expensive. I found them on clearance once on E-speaers.com but even then, these are quite expensive for a line array with 16 on each side. A3 is 3" and 82dB sensitivity so needs a lot of them.

So, it's decided on the Alpair 12 with 6.5" driver and 89dB sensitivity.

True I could never buy a A3 ( Price and a 3" ) what surprised me was A3 xmax its almost 1/2" .
Thay alpair looks pricey how much are they ?

geoff727

Megasat16,

I have watched this thread since it's inception, and am really looking forward to what you develop as I have a similar project in the works.

A couple of questions. About the Alpair driver, that is quite a substantial mounting flange on that driver. And, multiple drivers will be combined into your line array. Assuming a center-to-center driver spacing of about 6 inches if the mounting flanges are tucked up against one another, this will result in comb lines forming above about 2200Hz, and the first cancellation occuring above 4400Hz. I was curious if you were planning any mitigation techniques for the comb filtering, and, given the cancellation frequency, what frequency you were planning to bring the tweeters in at.

Also, can you describe your bass tower design (monopole, dipole, or bipole; type, frequency, and slope of crossover, etc.)? Did you finally opt for the Rythmik gear (that's what I'm planning on using)?

Very anxious to see your results.

G~

geoff727

Just read up in the posts and saw the tweeter xover freq.

G~

megasat16

20hz wrote: »

True I could never buy a A3 ( Price and a 3" ) what surprised me was A3 xmax its almost 1/2" .
Thay alpair looks pricey how much are they ?

Yeah. A3 seems well made driver. I think the long throw design with very high Xmax for this little beast is all thanks to the XBL motor.

The other thing I think it's a bit confusing is about how the drivers companies quote the Xmax. The Xmas is usually peak (or one way) measurement but some do quotes Xmax(p-p). And for some reasons, the companies who market these drivers just use the Xmax word without the word (p-p) as they should. It's very frustrating so I usually check with the manufacturing or the store to confirm what it really means.

I found the Alpair 12 on specials at madisound. It's been going on for a while for sure and the ones with Gold cones are sold out. The single driver setup may looks neat with gold cone but for 8 of the gold cones mounted on each channel, I think it may looks a bit too much.

https://www.madisound.com/store/product_info.php?products_id=8864

geoff727 wrote: »

Megasat16,

I have watched this thread since it's inception, and am really looking forward to what you develop as I have a similar project in the works.

A couple of questions. About the Alpair driver, that is quite a substantial mounting flange on that driver. And, multiple drivers will be combined into your line array. Assuming a center-to-center driver spacing of about 6 inches if the mounting flanges are tucked up against one another, this will result in comb lines forming above about 2200Hz, and the first cancellation occuring above 4400Hz. I was curious if you were planning any mitigation techniques for the comb filtering, and, given the cancellation frequency, what frequency you were planning to bring the tweeters in at.

Also, can you describe your bass tower design (monopole, dipole, or bipole; type, frequency, and slope of crossover, etc.)? Did you finally opt for the Rythmik gear (that's what I'm planning on using)?

Very anxious to see your results.

G~

Geoff,

Thanks for the interest! The summary below is my general design intent with regards to the Alpair 12 but it's nothing solid till proven.

The Alpair 12 has 8" frame with 6.5" cone so I am mounting the mid arrays on 3 stacks of 3/4" thick and 16" wide baffle. The vertical driver spacing (center to center) will be between 10" to 11" depending on how the driver performs. I will test a couple of Alpair 12 mounted in a test OB before the final cut and assembly. The 4" baffle on each sides of the Alpair 12 will have enough front to rear wave separation and enough lows to use with woofers array above 100Hz.

Every alternate drivers may be mounted from front to back (i.e. the front of the driver facing backwards) and wired out of phase so the acoustic power will be evenly distributed on the front and the back sides.

I am still debating much on the woofer choice but I've decided it will be a sealed array on each channel. I like to use Rythmik 15" drivers but it's undecided at this time.

I think I'll get the builds for the mids and tweeters arrays completed in a couple of months but the bass arrays will take some time. I'll post some pictures as things going forward.

geoff727 wrote: »

Just read up in the posts and saw the tweeter xover freq.

G~

Yeah, tweeter xover is between 3KHz-3.5KHz.

20hz

whats always thrown me was XMAX & XMECH (what exactlly is the differance ?
That peak to peak is missleading but the effeciancy thing is very important , what is it 3db=twice the needed power ??
I heard the 4 ohm spl rating is actually differant than the 8 ohm rating wheras 83 db @4 ohms compares closely to 86 DB at 8 ohms , now I dont know the exact #'s like many folks on this site but that is just something I heard ..

geoff727

20hz wrote: »

whats always thrown me was XMAX & XMECH (what exactlly is the differance ?

Usually, there are limits of excursion relating to linearity of output, and there are limits of excursion relating to the sheer physical structure of the thing. Xmax is voice coil length minus air gap height, then divide that by two. That's your typical linearity Xmax. As far as the physical structure, moving backwards it will at some point strike the coil former against the back plate. Moving forward, there's also just so far it can go. But, these are outside the limits of output linearity.

20hz wrote: »

That peak to peak is missleading but the effeciancy thing is very important , what is it 3db=twice the needed power ??

Correct, a 3dB difference in sensitivity erquires twice (or half) the amplifier output for the same SPL.

G~

geoff727

Mega...,

I hope it's okay if I do some thinking here, about your intriguing project!

megasat16 wrote: »

The Alpair 12 has 8" frame with 6.5" cone so I am mounting the mid arrays on 3 stacks of 3/4" thick and 16" wide baffle.

With the 3 stacks of drivers, are you going with a 9-driver array then? I thought I read a while back that you were going with 8. Actually, 9 is a good figure to use. With 3 paralleled groups of 3 drivers wired in series, there's an impedance load presented to the amplifier that's the same as the amplifier would see if it were driving one single driver. This is assuming equal drive along the array- no power tapering.

megasat16 wrote: »

The vertical driver spacing (center to center) will be between 10" to 11" depending on how the driver performs. I will test a couple of Alpair 12 mounted in a test OB before the final cut and assembly. The 4" baffle on each sides of the Alpair 12 will have enough front to rear wave separation and enough lows to use with woofers array above 100Hz.

11" corresponds to a wavelength 1232Hz. With a center-to-center (ctc) driver spacing of 11", comb lines will begin forming along the array at this frequency. At twice this frequency, 2464Hz, cancellation will occur, yielding a lobing response when measured up and down the array. This is still well below the proposed mid-tweet xover frequency; in this region, significant comb lines will be present.

This suggests to me that, if that driver spacing is to be used, the maximum mid-tweet xover frequency used should be no higher than 1200 Hz (this is obviously fairly low and would require some robustness in the tweeters). Still, this does not take into account the system power response, but it is something to think about if a constant wavefront is to be presented from the speaker (the goal of a line array).

I was a bit concerned about the driver spacing and baffle width, so I ran a simulation in a simple baffle simulator software that does not take into account the response of the drivers themselves, only the projected response of the (flat) baffle coupled with the locations and shape of the drivers. I used the following parameters: Baffle width of .4 m (about 16 in), baffle height of 2.1 m, drivers spaced evenly along the array with a ctc distance of .25 m (9.8 in, which is a bit under what you listed above, but was easy to graph). With these dimensions, there is an >8dB dipole peak at 500 Hz, followed by a rapidly downward-sloping response to the first significant notch (-6dB) at 1800 Hz. The rest of the response shows deep notch combing above this frequency, extending outside of the -7dB lower limit of the graph.

What the actual musical consequences of this baffle response will be in a real-life line array is beyond my level of current knowledge. I think if it were me, I would still consider four things:

1. Reducing the ctc spacing as much as possible to reduce the comb line formation and adjusting the mid-tweet crossover frequency as necessary. And/Or,

2. Experimenting with off-center mounting of the Alpair midranges on the baffle, running some simulations, and measuring. And/Or,

3. Consider power-tapering the outer drivers in the array so they recieve slightly less signal. Or,

4. Consider going with a lom-m-t-m-lom configuration (lom = lower output, power-tapered midrange). So, you'd end up with a speaker kind of like the Audio Artistry Beethoven Grand, one of Linkwitz's designs.

megasat16 wrote: »

Every alternate drivers may be mounted from front to back (i.e. the front of the driver facing backwards) and wired out of phase so the acoustic power will be evenly distributed on the front and the back sides.

If i'm understanding correctly, then I have a couple of initial thoughts.

1. The response for the rear-facing drivers will be different than for the front-facing ones, due to the sound being emanated by an inverted cone, and working it's way around the magnet structure. This could alter response in odd ways. Measurement is in order.

2. I think I understand your thought about even acoustic power radiation (like an omnidirectional speaker [mbl's]) to preserve the same spectral signature of sounds that are re-radiated from room reflections, thus reducing coloration of the system. I have a couple thoughts here. First, driver directivity in the upper frequency registers will naturally reduce this, as will dipole behavior in the lower registers. Also, it may be worth considering if even power response is an acheivable or desirable goal here, given that the front and rear sides of the dipole are radiating into different acoustic spaces (like one being 4' away fom a wall, the other side into a great big 19'-long room, for example.). I need to keep reading up on this.

megasat16 wrote: »

I am still debating much on the woofer choice but I've decided it will be a sealed array on each channel. I like to use Rythmik 15" drivers but it's undecided at this time.

Going back to the response of the Alpair driver itself, as you noted, it has a Qts of .327. Perhaps we could consider an "ideal" open-baffle Qts as .7 or so. With a Qts of .327, the natural roll-off of the driver will begin at, perhaps, a frequency of Fs x 3. This is reflected in the roughly 12 dB/octave rolloff curve posted on madisound for the driver.

I use a pair of Rythmik 12" drivers on my system right now, the aluminum-coned ones. They recommend not to cross them any higher than about 80 Hz. Going higher, they recommend using the GR Research paper-coned drivers (yes, with those unfortunate foam surrounds!). I imagine this recommendation probably holds true for the 15" drivers as well. I have not actually listened to the 12" drivers at anything above about 50 Hz, so I don't know how musical they are above that 80 Hz recommendation.

So, I will assume for the moment a mid-woof crossover of 100Hz (with whatever woofer). Looking back at the simulated predicted baffle response, the 500 Hz dipole peak slopes down to a 0dB-line crossing point at about 75 Hz. At 100 Hz, there is still a 2dB rise. Looking at the frequency response graph at madisound, the response of the Alpair driver at 100Hz is down about 6dB from the published 89dB sensitivity.

Have you considered building some test baffles out of cardboard of different sizes and geometries, and testing each one for the best response (both on and off axis)?

megasat16 wrote: »

I think I'll get the builds for the mids and tweeters arrays completed in a couple of months but the bass arrays will take some time. I'll post some pictures as things going forward.

I can't wait to see it!

Thanks for letting me expound a bit (and please excuse me for being long-winded!). What you come up with is going to be a learning experience for me as well, and I hope we can have some good forum conversations on your design. It has certainly got me thinking, and very interested. I'm staying tuned....

Geoff

geoff727

geoff727 wrote: »

I think if it were me, I would still consider four things:

One more just came to mind:

Build the array with a concave front baffle, so that each driver is equidistant from the listening position (similar to the Gryphon Poseidon loudspeaker).

G~

megasat16

Hello Geoff,

I've been a bit busy lately so I couldn't post in length yet. However, I've read your thoughts and I appreciate and welcome your inputs.

I'll reply to your posts over the weekend. Please feel free to post any other thoughts and ideas meanwhile.

Thanks,
James

megasat16

Oh..I forgot to say I may have to go with different drivers than Alpair 12. Madisound don't have enough of Alpair 12 I ordered. So, Alpair 10 V2 seems a possible substitute and I can use 12 on each column.

http://www.markaudio.com/pdf/d5.pdf

megasat16

geoff727 wrote: »

Mega...,

I hope it's okay if I do some thinking here, about your intriguing project!

The ideas are always welcome and appreciated, Geoff! Good ideas are worth a fortune.

With the 3 stacks of drivers, are you going with a 9-driver array then? I thought I read a while back that you were going with 8. Actually, 9 is a good figure to use. With 3 paralleled groups of 3 drivers wired in series, there's an impedance load presented to the amplifier that's the same as the amplifier would see if it were driving one single driver. This is assuming equal drive along the array- no power tapering.

I think I said something confusing about 3 stacks of .75" Birch Ply. I meant triple stacks of cut and routed MDF glued together for the baffle thickness to dampen the vibrations.

But since you mentioned 9 drivers, it's true that it represents an 8 ohms impedance for wiring a group of 3 drivers in series and then all 3 groups in parallel. I don't know how it would meaure up for efficiency of the entire 9 drivers.

I don't know how it'll compare efficiency for wiring four groups of (2 speakers in series) which will give me an impedance a bit lower than 4 ohms.

It's up for testing and measuring after I've figured out the optimal driver spacing.

11" corresponds to a wavelength 1232Hz. With a center-to-center (ctc) driver spacing of 11", comb lines will begin forming along the array at this frequency. At twice this frequency, 2464Hz, cancellation will occur, yielding a lobing response when measured up and down the array. This is still well below the proposed mid-tweet xover frequency; in this region, significant comb lines will be present.

This suggests to me that, if that driver spacing is to be used, the maximum mid-tweet xover frequency used should be no higher than 1200 Hz (this is obviously fairly low and would require some robustness in the tweeters). Still, this does not take into account the system power response, but it is something to think about if a constant wavefront is to be presented from the speaker (the goal of a line array).

I wonder where I can get the formula to calculate the comb line. It would be great if I can use that formula to do some calculations when I am doing the testing.

This is a different formula I found a while back.

http://www.mh-audio.nl/calcmaxfreq.asp

I am going to cut a lot of plywoods and test mount the drivers and do both extensive listening test as well as the measurements.

I think the problem with line arrays and lobing is that you'll need to listen from a distance. The closer you sit to the speakers, the more the lobing is apparent even for using the small size drivers and mount them very closely together. But I hope the OB with diffused acoustical patterns will reduce the lobing somewhat than the regular boxed speakers.

I was a bit concerned about the driver spacing and baffle width, so I ran a simulation in a simple baffle simulator software that does not take into account the response of the drivers themselves, only the projected response of the (flat) baffle coupled with the locations and shape of the drivers. I used the following parameters: Baffle width of .4 m (about 16 in), baffle height of 2.1m, drivers spaced evenly along the array with a ctc distance of .25 m (9.8 in, which is a bit under what you listed above, but was easy to graph). With these dimensions, there is an >8dB dipole peak at 500 Hz, followed by a rapidly downward-sloping response to the first significant notch (-6dB) at 1800Hz. The rest of the response shows deep notch combing above this frequency, extending outside of the -7dB lower limit of the graph.

One other thing I wonder is what software lets you to simulate the FR of the Line Array?

I got some Alp 12 drivers landed yesterday. I need to wait a certain time to get the rest of the drivers in but I have 8 now to try out. But looking at the drivers, the frame around the cone is quite large (about 1.5") so mounting them closely (8.25" ctc) would be a good start for a trial cut and mount. I think given the driver size of approximately 8", I am sure there will be a certain peaks and dibs in FR if comb filters are not applied. I was thinking to use DEQX for the speaker control and measurements but looks like I need to wait a while to get one. That's why a lot of people using the smaller drivers in a line array but I opt out for the lower efficiency and awful looks. I think even using smaller drivers, lobing is very apparent when you sit close to the speakers.

What the actual musical consequences of this baffle response will be in a real-life line array is beyond my level of current knowledge. I think if it were me, I would still consider four things:

1. Reducing the ctc spacing as much as possible to reduce the comb line formation and adjusting the mid-tweet crossover frequency as necessary. And/Or,

2. Experimenting with off-center mounting of the Alpair midranges on the baffle, running some simulations, and measuring. And/Or,

3. Consider power-tapering the outer drivers in the array so they recieve slightly less signal. Or,

4. Consider going with a lom-m-t-m-lom configuration (lom = lower output, power-tapered midrange). So, you'd end up with a speaker kind of like the Audio Artistry Beethoven Grand, one of Linkwitz's designs.

Thanks Geoff! I am well considering your advise. Everything including baffle types is also up for the experimentation since I wanted to get it right.

If i'm understanding correctly, then I have a couple of initial thoughts.

1. The response for the rear-facing drivers will be different than for the front-facing ones, due to the sound being emanated by an inverted cone, and working it's way around the magnet structure. This could alter response in odd ways. Measurement is in order.

2. I think I understand your thought about even acoustic power radiation (like an omnidirectional speaker [mbl's]) to preserve the same spectral signature of sounds that are re-radiated from room reflections, thus reducing coloration of the system. I have a couple thoughts here. First, driver directivity in the upper frequency registers will naturally reduce this, as will dipole behavior in the lower registers. Also, it may be worth considering if even power response is an acheivable or desirable goal here, given that the front and rear sides of the dipole are radiating into different acoustic spaces (like one being 4' away from a wall, the other side into a great big 19'-long room, for example.). I need to keep reading up on this.

You read my thoughts exactly on this.

I don't know how it'll work out but there are people who has done this with OB speakers but not with the Line Arrays. I think the SPL is uneven for a cone type driver since the rear chamber has mostly everything that disturbs the sound wave to travel freely to the rear side. But having said that, I think the MA driver has quite open frame type in the rear and plenty of room for the rear waves radiation. I agree measurement and experimentation is in order.

One most important thing above all is to achieve less lobing, less cancellation and better FR graph while maintaining the added efficiency. May be it's everything I wanted but not sure can be obtainable. :biggrin:

Going back to the response of the Alpair driver itself, as you noted, it has a Qts of .327. Perhaps we could consider an "ideal" open-baffle Qts as .7 or so. With a Qts of .327, the natural roll-off of the driver will begin at, perhaps, a frequency of Fs x 3. This is reflected in the roughly 12 dB/octave
rolloff curve posted on madisound for the driver.

I use a pair of Rythmik 12" drivers on my system right now, the aluminum-coned ones. They recommend not to cross them any higher than about 80 Hz. Going higher, they recommend using the GR Research paper-coned drivers (yes, with those unfortunate foam surrounds!). I imagine this recommendation probably holds true for the 15" drivers as well. I have not actually listened to the 12" drivers at anything above about 50 Hz, so I don't know how musical they are above that 80 Hz recommendation.

So, I will assume for the moment a mid-woof crossover of 100Hz (with whatever woofer). Looking back at the simulated predicted baffle response, the 500 Hz dipole peak slopes down to a 0dB-line crossing point at about 75 Hz. At 100 Hz, there is still a 2dB rise. Looking at the frequency response graph at madisound, the response of the Alpair driver at 100Hz is down about 6dB from the published 89dB sensitivity.

Yes, an ideal and critically damped OB woofer should have Qts closer to 0.7. With the Alpair 12, I think the woofer XO would be above 100Hz for the same reason you mentioned. That's why I am not sure of using subwoofers. Subwoofers generally will go lower for deeper bass but can't usually go high on the XO point.

It's one of many things I am not sure how to solve yet. I am looking at a lot of OB woofers and most people use very efficient Pro Audio woofers with their OB setup. But there is options such as lambda series woofers from AESpeakers.

Have you considered building some test baffles out of cardboard of different sizes and geometries, and testing each one for the best response (both on and off axis)?

I got many sheets of plywoods waiting to be cut for the test baffles. I am going to start cutting since I got my router setup again for the circle cutting yesterday. Everything is in order and I am about to get one step closer.

I can't wait to see it!

Thanks Geoff! It's going to take some time to get the speakers build right but when I am done, you are more than welcome to see it and hear it in person.

megasat16

Thanks for letting me expound a bit (and please excuse me for being long-winded!). What you come up with is going to be a learning experience for me as well, and I hope we can have some good forum conversations on your design. It has certainly got me thinking, and very interested. I'm staying tuned....

Geoff

Yes, I enjoy the discussion too. Please feel free to think some more and chime in. And stayed tuned as I post some results of the initial tests.

A few things I wanted to point out.

1. I need to wait for 8 more Alp 12 to arrive (in fact, it'll be on special order since Madisound doesn't has enough for me).

2. I may just as well go with smaller Alp 10 Gen 2 (alp10.2) series since Madisound got enough of them in stock. All depends on how I like the Alp12 in the initial test. But from the data, I think Alp10.2 seems a better choice for the OB line array.

3. If I go with the Alp10.2, I would have to return them to Madisound or just sell it on the DIY forum. I may also make a couple of MTM with Alpair 12 or a single point source OB.

4. Alpair Drivers takes quite a consideration to break in and Mark Audio has very specific info for breakin of their drivers. So, it'll take a couple of weeks for drivers breakin before I can take any kind of measurements.

geoff727 wrote: »

One more just came to mind:

Build the array with a concave front baffle, so that each driver is equidistant from the listening position (similar to the Gryphon Poseidon loudspeaker).

G~

Nice speakers they are. Yeah, I could possibly try that too. Thanks for the suggestion.

James

geoff727

megasat16 wrote: »

One other thing I wonder is what software lets you to simulate the FR of the Line Array?

James,
I'm going to write quite a bit more, as I have time (maybe a little bit each day). As each subject comes up, I'm trying to keep digging into the papers about theory and design (both line array and open baffle, for which the two concepts have to be combined), to attempt to keep everything i say as accurate as possible. As you know, these things are way too expensive to goof up. This is actually really good for me, in light of my upcoming design.

This is the baffle simulator i used, it's called "The Edge".

http://www.tolvan.com/

It simulates the response of the baffle ONLY, so the infinite baffle response of the drivers have to be mentally superimposed onto the baffle response to come up with the system response. The good thing about it is, it allows for multiple drivers on one baffle (i.e., a line array). It can be a diffraction simulator for closed-box speakers (very helpful with baffle step considerations), or can simulate responses of a rectangular open baffle. It?s free, so if you end up downloading it, I can send you the file that I generated (I saved it), and you can tweak it from there, if you want.

Here are a couple others I have used briefly, but only very briefly as they cannot simulate an array. However, they DO take driver parameters into account:

http://www.t-linespeakers.org/downloads.html (This one is called ?xlbaffle?)

http://www.musicanddesign.com/A_B_C_Dipole.html

Martin J. King also has his mathcad worksheets for $25. I THINK they will do pretty much everything that The Edge and xlbaffle will combined, but i'm not sure since I haven't used them (yet). http://www.quarter-wave.com/

The musicanddesign website also has a great open-baffle theory section. I have not used any of the 'payware' software that can model open baffles. I put the freeware version of LEAP V Enclosure Shop on the computer, but I haven't explored any of it yet. I know, though, that it will do some open baffle modeling. Whether it will do it in a line array, I don't know.

For my system, I have the configuration pretty well nailed down. And, I just have to prepare to build a whole bunch of test baffles and measure, measure, measure, and keep experimenting until I have the width, shape, backward curve, etc., all correct (maybe in 3 more years!). I have not as yet found any papers documenting theory of construction of open baffle line arrays. Everything is either open baffle OR line array. So, that means the experimentation time will be a little longer. But, that's okay. Not like anybody hasn't done it before!!

megasat16 wrote: »

But since you mentioned 9 drivers, it's true that it represents an 8 ohms impedance for wiring a group of 3 drivers in series and then all 3 groups in parallel. I don't know how it would meaure up for efficiency of the entire 9 drivers.

I?m assuming a nominal 8-ohm impedance for the Alpair 10.2 here. For 8 drivers (4 paralleled sets of two wired in series, yielding an impedance of 4 ohms), I get a sensitivity of 99dB SPL. For 3 paralleled sets of 3 in series (9 drivers), yielding 8 ohms impedance, it comes up as 96.5 dB SPL. Pretty close, and pretty good.

Here?s a simple online calculator: http://members.optusnet.com.au/~gradds55/arraycalc.xls
It will probably work for your array (circular drivers), but not as well for mine (discrete planar elements), because the dispersion pattern of those drivers is different.

megasat16 wrote: »

It's going to take some time to get the speakers build right but when I am done, you are more than welcome to see it and hear it in person.

I would LOVE to! I actually do make it a point to go see/hear other peoples' systems that are of high quality.

I am envious about those Aurum Cantus tweeters. I've heard them in the big Evolution Acoustics speakers (and probably others without noticing it), and they were great!

Geoff

CoolJazz

First the greatest info on a line array...Dr. Jim Griffin's paper. Here...

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

Second...I wonder just how much to be concerned about comb filtering? For those not sure what it is, you can hear this effect on many TV newscast's when they have multiple mics open and the natural sounding voice goes to a slightly tin can effect. Listen as they go over to a single mic and the hollow effect goes away to a naturally mic'ed voice. What I'm wondering is how much does it come into play and does the number of drivers tend to increase this effect?

I've been playing with OB efforts for a couple of years. The lack of box coloration and the sound stage filling the whole end of the room is wonderful! My "issue" is to try and get the gain, the dynamics more like a horn. This has lead me to multiple drivers. So I've (being cheap) picked up some economical full range drivers from Parts Express. Using 3, 8" full range drivers, mounted on a 20" wide flat board, spaced a little too far apart. This done to allow later reuse of the lumber and to increase the comb filter effect to allow easier investigation. Well...to music you just can't seem to hear it!! In theory, I'd think the duo-cone construction would have the hf coming from at least 4" apart (??) and with about 2 inches between drivers on this, more than that! So where is it? Would it be greater if this was a full line?

Woofer duty is similar and works well. I have on a seperate column, 4 10" drivers, currently crossing at 180hz (as that's a xover handy). This cross puts only a single hq cap in the high pass and is active for the lp. The bass has all you could want and measured to roll off at around 30hz but keep in mind that's only a 6db roll there so energy will be going lower. Pretty cool seeing a total of 14 drivers looking at you and knowing it's still only around $300 looking at you!

But the sound quality has really floored some of my friends which are pretty picky! The 8" full rangers I tried dropping from 3 each side, to two and then to a single. Interestingly enough, a single sounds like a cheap driver but each one you add sounds better and better. Going to try, before moving on, to redo these closer together and add a fourth and see if it gives yet another step up in dynamics and quality.

BTW...the 8's have a qts of about 1, so did try them with no woofer support..hmmm...pretty interestingly good in bass. Need to try to add a little control to keep it from being to flabby, the First Watt F1 being a current source needs something added to control that low end just a little.

Guess I wanted to share the fun a little and encourage the effort and suggest that you can learn a bit without using too expensive of drivers to start out with! I'll be following along too!!

CJ

megasat16

geoff727 wrote: »

James,
I'm going to write quite a bit more, as I have time (maybe a little bit each day).
Geoff

Thanks Geoff! Sounds good and appreciate for the links. I am busy cutting today. I'll post more reply later.

CoolJazz wrote: »

First the greatest info on a line array...Dr. Jim Griffin's paper. Here...

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


Guess I wanted to share the fun a little and encourage the effort and suggest that you can learn a bit without using too expensive of drivers to start out with! I'll be following along too!!

CJ

Thanks Mark! It's nice to see you posting in this thread. I'll post more reply after taking time to read your link. Meanwhile, if you find more info, please keep posting.

James

geoff727

CoolJazz wrote: »

First the greatest info on a line array...Dr. Jim Griffin's paper. Here...

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

Second...I wonder just how much to be concerned about comb filtering?

You know, this is interesting. Here is a picture of a speaker (the Reference 5 LS, I think, from Anthony Gallo), that on the surface, would seem to go against the ctc spacing guidelines set forth in Griffin's paper. Admittedly, I know next-to-nothing on the design of Gallo speakers. Do any of you guys have any insights on this one?

Griffin's paper is geared (and titled) towards near-field arrays. So there has to be some point (going into the far field) where the coalescence of the sound renders the comb line formation much less important or audible.

I do remember reading in different places that some people thought that the audibility of comb filtering was inconsequential. I wonder if they're listening from far enough away so that the sound is coalescing into a more coherent whole. It's an interesting point, seeing that comb filtering happens on a lot of the regular speakers we listen to every day also.

Any thoughts?

About far field listening.....one of the complaints that I've heard people make about line arrays is that they seem to make instruments/voices/images seem much larger than life, like a 10-foot-tall violin. Of the arrays I've listened to, this has never been so. In fact, one array I listened to a couple years ago (the Scaena 3.2's) had an extremely lifelike rendering of image size and depth, in the setup that I heard them in. I wonder if the unnatural image growth that some have complained about is a result of listening from too far away. Remembering back, almost all of the listening I've been able to do of line arrays has been in the near field.

What do you guys think?

For my current system, I listen with a ratio of 77% distance between the speakers as distance to the listening seat, and it's about 9 feet to the listening chair. Now these are line sources, not arrays, but I have never experienced from these speakers any unnatural growth in image size.

G~

geoff727

megasat16 wrote: »

I think the problem with line arrays and lobing is that you'll need to listen from a distance. The closer you sit to the speakers, the more the lobing is apparent even for using the small size drivers and mount them very closely together. But I hope the OB with diffused acoustical patterns will reduce the lobing somewhat than the regular boxed speakers.

Now see, this is what happens when I just think and type as I go without remembering what I just read! I say what's already been said. :rolleyes:

Face

Another take on line arrays: http://www.audiocircle.com/index.php?topic=92134.60

CoolJazz

A couple of quick thoughts...

Thanks for throwing that forum discussion in Face! I'd happened to have just sat and read the Keele paper a few days ago and discussed some of it with some of the guys. To put the link over here...

http://www.xlrtechs.com/dbkeele.com/CBT.php

I would reinforce that what I was commenting on that I'm currently playing with is OB, a short line and full range drivers. My listening position is by measurement 11 ft from ear to full range driver center. I can raise up and down and not notice a change in response really at the listening position. Up real close the drivers finally seperate but I'd never listen real, real close anyway. Any multi-driver seperates up close too or course.

I'm sure the comb effect there and to really find it, I've been meaning to bring up white noise on a between stations postion on a FM rcvr or better yet use a test disc. But the point is, and question too I guess, how much of problem is it?

BTW...one of the 3 most commented on systems from Altanta Axpona was a line array. I believe it was the Scaena name you mentioned Geoff. Big line in a really, really big ballroom sized setup. Very impressive. I'd say a bit big of an image but not huge. But it's hard to just in that big of a room! Probably 30-40 ft behind them and we had to be seated 20ft from them. Very impressive for sure, just unrealistic for mere mortals pricing wise... Speaking of crazy price...the biggest image I ever remember hearing was the larger MBL's. Very open sounding...just couldn't get over the face singing to you sounding like it was Golly Green Giant sized!

Many years ago, I heard the Gallo in the single ball stage and then later a taller 3 way I think with the side firing woofer? Don't know a thing about a line though.

I did hear a build of Dr. Griffin's once about 7-8 years ago. Did set the gears to grinding...just took a few years I guess.

CJ

CoolJazz

Oh...and have you guys seen this one??

http://trueaudio.com/array/index.htm

geoff727

In post #80, I conjectured:

geoff727 wrote: »

I wonder if the unnatural image growth that some have complained about is a result of listening from too far away.

In Griffin, page 20, paragraph 2, talking about the resons for power tapering, he says, "If listeners move away from the array, the image seems to bloom and grow in height."

CoolJazz wrote: »

BTW...one of the 3 most commented on systems from Altanta Axpona was a line array. I believe it was the Scaena name you mentioned Geoff. Big line in a really, really big ballroom sized setup. Very impressive. I'd say a bit big of an image but not huge. But it's hard to just in that big of a room! Probably 30-40 ft behind them and we had to be seated 20ft from them. Very impressive for sure, just unrealistic for mere mortals pricing wise...

I wonder when Scaena is going to come back to RMAF. That's the only show I've been making, and they haven't been for a couple years. You are right about the price. The array with 12 midranges is something like $45,000. The 18-driver array is twice that. I guess that's why guys like us have learn to build our own!:biggrin:

Do any of you guys go to RMAF? It would be fun to meet up for a beer.

Here's some pics of the Scaena's, designed by the same guys who did the Nearfield Acoustics Pipedreams.

G~

geoff727

It looks like those Don Keele CBT speakers are available at P.E. in kit form, here:
http://www.parts-express.com/cbt36/

I think this is the driver they use. Sure is getting lots of very positive feedback from people.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=290-212

Those speakers are just really interesting. Guess I better start reading up.

Here is another interesting system. This one was at RMAF a couple years ago. I think one of the people at Balanced Power Technology custom built it. Open baffle with an RD75 for the treble, and open baffle woofer line. Crossover, OB equalization, and notch filter for the RD75's cavity resonance was all handled by a DEQX.

megasat16

I finished cutting a plywood for 4 drivers test baffle (2 on each side). I am liking FRD (full range driver) coz it works without any bloody XO.

megasat16

geoff727 wrote: »

Now see, this is what happens when I just think and type as I go without remembering what I just read! I say what's already been said. :rolleyes:

The more I read, the better it is. I always think reading or learning something repeatedly as making the ideas or topics sink into you. No harm in anyway.

Face wrote: »

Another take on line arrays: http://www.audiocircle.com/index.php?topic=92134.60

Thanks Mike! It's a curved array. Its sure helps for the lobing but I imagine the soundstage could be a bit stretched?

Scaena

Hello Guys, Pardon the late response, just happened to stumble upon this while looking for something else. I am Scaena. Thank you for your wonderful comments and accurate observation, some of you really have great ears. Its regrettable that our speakers cost what they do, believe it or not even at those prices, they are for a large part subsidized. Yes it cost a fortune to make a good line array and solve all the problems that come along with an array. Did you know Mathew Polk initially made Line Source speakers, I owned a pair. They stopped making them due to the reasons I describe. Essentially unless you are going to put all the drivers in one box, which we resolutely dont do, you are basically making 12 times the product. Every single cost we have is multiplied by 12. By that measure we are actually selling for less than average mini-monitors.

Some of you have rightly commented that we have uniquely solved the problem of creating a false image size. Thats the key and quite difficult to do. Please stop by one of our shows and I will personally give you a demo of accurate the image size can be with a line array if done right. BTW you can never do it with a single big box speaker. The spry members here will know exactly why. Again thank you for having good ears and allowing us to indulge you.

Appreciatively Scaena.

ken brydson

Say whaaaat?

lightman1

Deep left field......