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Build a Mini Line Array

Along with all my other interests in life, audio and speaker building is near the top. The first set of speakers I ever built had drivers that came from Radio Shack in 1978. The tweeters had a 10uF capacitor on the + lead and at the time, I thought that was all you needed for a crossover... Over the next 30 years I learned a quite a bit more. I was also very interested in line arrays as the concept always seemed like a good idea. A line array is a group of audio drivers (speakers) mounted in a row. It does a couple things for you. First, it allows each individual driver to use less power thus, in theory minimizing distortion as the driver does not have to work as hard. Second, all the acoustic energy couples together to provide a sound field that does not drop off at the same rate as single driver, which acts as a point source. For more information see this  and this.  This project started out like a lot of mine. Parts Express had a sale on 3inch audio drivers and I said “I always wanted to build a line array, let me order 16 of them!” three years later I actually got around to building them. I am actually glad I waited because there was more information I needed to learn before I built them.

There is a lot of debate around how good they are and what there issues are. On the down side, multiple drivers can cause interference and acoustic artifacts. Interestingly, the same argument is the same for why an orchestra sounds so good live. Next time you go to a concert look at the PA speakers... They are most likely set up as a line array. If you really want to hear how they sound lets build one!
 
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turbiny2 months ago

i`m new to low/high pass filter or crossovers dont know wich is what, but i was thinking would it be better to design different low pass filter for each driver so every speaker plays at different frequency?
would the sound be clearer or it doesnt matter

i wanna design speakers for home tv/music use front main big speakers 2 smaller for the back and a woffer.
thnx

DJJules (author)  turbiny2 months ago
For a line array, you want each speaker to be the same and to have them add to the combines output.

Jules

Thanks very much for this. Really helpful.

I'm looking to make an extremely compact highly portable PA system for voice and acoustic guitar. Low power - I'm getting acceptable results from a little 40W combo amp at present, and I mean portable on a bicycle. I'm thinking much smaller than a Bose L1 and no sub box

Do you think this would scale down? Maybe a single array of 4 slightly smaller drivers plus tweeters? And to save weight I might make the case by sandwiching foam between two layers of plastic for a stiff light construction. Any comments would be really helpful.

I have built a few of these for the reason you suggest. I would consider building an extremely compact array using 6.5inch coaxial speaker drivers (like you find in cars). You could build 2 lightweight, stackable cabs. The high frequencies would not exhibit the beaming described in the above article but the important mids would throw nicely even with a low power source. Use a driver with a good, clean, flat response down to about 80hz (just lower than the love E on the guitar).
DJJules (author)  michaelduffey0014 months ago
Thanks, I have a box of 4" drivers and some 1" tweeters that were made for car use. I need to finish my CNC router and go for round two on a line array. you are 100% correct on the beaming part.

Jules

Like Chris above, my concept was to build a portable "line" array for PA use for my acoustic band. In the first picture, you can see that I used 5.5 inch coaxial drivers in 2 cabinets of 4 drivers each. The cabinets are purposely narrow to allow for an unencumbered horizontal wide dispersion of sound. In addition, the cabinets had a pole stand mounted on both the top and bottom so that the cabinets can be safely stacked (cannot be knocked over when attached to each other with a short 1.75 inch diameter pole) and can be turned on their horizontal axis for an even wider horizontal dispersion.

The downside of these small drivers is that they did not handle the acoustic bass frequencies very well (would break up) and I added the 15inch sub to handle the lowest frequencies. Fortunately, the Carvin head that I used allows fine control of frequency material and also has 3 x 300 watt internal amps. So the sub ran with one of those amps and rolled off frequencies above 150hz off while the array had it's own amp and carried mostly frequencies above 150hz. This resulted in an amazing sound with astounding throw in the low-mids to high frequencies.

However, I still wanted to have more of a line array system, not half array and half point source, so I decided to build another set of cabinets using full range 8" speakers that could handle the low frequencies and put out nice sounding highs. The drivers I wanted (8" coaxials) were not available for 3 years, so I finally relented and used my second choice which were 8" full range with a "whizzer" cone. I built 2 x 4 driver cabinets. You can one of them in the second picture with one of my original cabinets stacked on top.

By themselves, the larger arrays sound pretty nice, much like how a nice set of large home speakers might sound ( very smooth and full) but with an extremely long distance throw. However, using them in conjunction with the smaller cabinets, music seems more live. The large 8 inch drivers start to roll of at 14,000hz (it didn't seem that I would need that last half octave or so), but I was wrong. The addition of the smaller cabinets fills out the harmonic content and gives a richness to the sound. When I played Tower of Power or Orchestra music, the 8s by themselves sounded smooth and round. With the small array added, they sounded like they were playing right in front of me. I may still change out the 8 inch drivers with the ones that I originally wanted (8"coaxial drivers).

At this point, I bi-amp these cabinets with one amp running the large cabinets and one amp (high pass at 150hz) running the small cabinets. These cabinets can be heard, dead clean, at a distance of over 1/4 mile distance (even through a small forest) running at no more than about 60-110 watts rms.

I have since purchased a set of short PA stands from Yorkville to accommodate these speakers as they stand over 8 feet tall on a regular PA stand at the lowest setting.

Finally, as to the beaming effect of arrays at high frequencies. As we all know, high frequency energy tends to fire in a straight line while low frequency energy tends to fill the space around itself. Knowing this, it seems that not being too concerned with controlling dispersion in high frequencies (by stacking tweeters in a line array also) might be the answer. Unless you are going to stack 60 or so tweeters so that you get an even coverage from near floor to near ceiling, you are definitely going to find serious dropouts when off vertical axis from the tweeter. This is why I was not so concerned with using coaxial drivers. With the low-mid driver of the coaxial properly closely stacked, those frequencies would be controlled in the vertical axis (less reflections on floors and ceilings) while the high frequency drivers in the coaxial would act more like a group of point source drivers with a wider spread in all directions (the nature of these drivers is to be relatively narrow anyway). What I found in using coaxial drivers is that the high frequencies do not beam as harshly and have a smoother roll-off as you move off axis vertically and horzontally (like you might expect from a nice wide dispersion dome tweeter). I believe you could control the coaxial tweeters even more if you used some sort of acoustic lens in front of each tweeter to force those frequencies to a more narrow vertical axis and a wider horizontal axis. However, I have not found there to be any real downside to the design I used and the smoothness of these cabinets is quite astounding, especially when you consider that their total cost was under $300 the two 8" cabinets.

The one thing I would change would be to build four 2 x 8" driver cabinets rather than the two 4 x 8" driver cabinets so that these cabinets would be smaller, lighter and even more portable.

Rebuilt line array.jpgNew build with old build.jpg

Thanks Michael, It's clear that everything is bigger in the USA (our house would probably fit inside your RV :o), so I'm still thinking "tiny" and "could I transport it on a bicycle", We are often playing very small cafe gigs where you just need a little reinforcement, but this is all extremely good food for thought. Best wishes from Sheffield, England, Chris

Hi Chris,

The difficulty is that extremely small drivers "tend" to have practically zero low frequency energy output. You can find some specialty mini woofers, however, they tend to be expensive. In addition, the concept of a line array is that it needs to be a lengthy cabinet for it to produce audio that is restricted in the vertical axis and have a good throw (reach a good distance without having to be turned up loud). I think if you were to find the right coaxial 6.5 inch drivers, you could build two drivers in a cabinet (cabinet would be about 13.5" tall) and two of these stacked at the gig would give you a decent throw and wide horizontal coverage. As long as you are just playing acoustic guitar (or any midrangy acoustic instrument) and voice into these, they should sound pretty good. You could even mount your mixer/amp inside on of the cabinets fro extra space savings! Properly designed, you could throw these two cabinets into your bicycle back baskets and show up to the gig ready to play with your guitar in a gig bag strapped to your back.

That's helpful Michael. I think I have to separate in my mind the wish to have some fun with interesting loudspeakers from the problem of having a PA. If I need something more powerful I'll buy the Maui 11 system, meanwhile I'll carry on using my extremely tiny Behringer 205D monitor as a very small complete PA, and keep working on how to build the most compact practical line array to see if it's better than either of those. The Maui system and others like it achieve amazing results with a tiny column but they all need a bass box, so I'll think hard about 6.5" drivers as you suggest.

Thanks for that Jules, I'll look forward to seeing how you get on, especially as you have 4" rather than 6.5" drivers. I guess that moves the beaming range a little up the scale in a good way?
How many drivers are thinking of? I wondered if 4 was enough?
I used one of those LD systems Maui 12 PA systems recently and it was quite wonderful for me as a performer, for a much better price than a Bose kit, so I'm comparing the compactness, price and effort (and fun) of a custom array system with that well-tuned proprietary set up.

Chris

zephyr681 year ago
Great instructable! One question. You mention that you would arch the tweeter array next time. Would the 3" drivers remain flat? Does it even matter since they don't beam like the tweeters do?
yepvegas2 years ago
Wow that was a quick reply I have read that some will filter one of the Tang Bangs speakers turning it essentially into a tweeter. do you have any thoughts or opinions on this or should I just stick with the plan and use a tweeter in the array.
DJJules (author)  yepvegas2 years ago
That would work but... I would either leave them as a full range (simplest) or use a crossover to the tweeters. Once the wavelength of the sound produced approaches the size of the driver all sorts of things happen. smaller drivers produce higher frequencies with less artifacts of directional lobes and other fun stuff. I have read that at most one driver shoudl only cover about 3 octaves of sound.

Jules
yepvegas2 years ago
Great looking build and thank you for the information. I purchased the same 3 inch speakers for my car. This is the first diy project I have seen using the same driver I have. My plan is to use them full range 6 per side a one tweeter per side in a horizontal line array spanning the entire dash of my car. I will be using an 31 band EQ to tame the smooth out the rough edges on the array. From there my idea is to use a cap to protect the tweeter and run the array on one channel of my amp. What are your impressions of the speaker now that you have had some time to play with them? Thank you in advance for your time.
DJJules (author)  yepvegas2 years ago
Thank you, it is very clean and low distortion. If you use a capacitor on the tweeters that limits them to6K and above it should really complement the 3" driver and sound great.

Jules
Bjorgulf2 years ago
Interesting project :D
I've picked up bulding speakers as a hobby only 2 months ago. Maybe for my next project I'll make an instructable too. Unfortunately I didn't document the building of my current system.
But I have a question for you:Why don't you use fullrange speakers instead of the two different ones? As a reference look at this project I found online at the shop I bought parts of my materials from. It''s german, but the technical stuff should be good to understand. 25 fullrange speakers for each array. packs of 5 parrallel and 5 of those packs in line.
Someone else even developed a line-array-sub to match them :D
speakers: http://www.lautsprechershop.de/index_hifi_de.htm?http://www.lautsprechershop.de/hifi/twentyfive.htm
sub: http://www.lautsprechershop.de/index_hifi_de.htm?http://www.lautsprechershop.de/hifi/twentyfive_s12.htm
DJJules (author)  Bjorgulf2 years ago
You really get a better sound field by crossing over speakers to cover different frequency ranges. You get lower distortion too. It has a lot to with the diameter of the driver and stiffness of the cone. There is a lot of info out there. There are some good full range drivers out there too but a 4" or 3" driver simply cant go cleanly above 7-10Khz without issues. they used to use Whizzer cones in the 70's but there are issues with those too.

Thanks for reading!

Jules
You have a point here. I used 4" fullrange speakers with whizzer cones for my sub-sat-system and the frequency response looks a little "funky" above 6 or 7 kHz. I have yet to buy a good microphone and take measurements. I only used data I got from the manufacturer so far. But, since my room is only 165 square feet, I don't have to turn up the volume much, and I think the sound is pretty good that way. Better than anything I ever bought. They sound shitty when I do though. high frequencies and distortion go crazy :D
Maybe I should double the number of drivers to get a liitle more volume. The speakers-boxes are twice the size they should be due to a calculation error anyway :)
bishopdante2 years ago
With PA line arrays, the tweeters usually have a waveguide, and are spaced out in a similar fashion to the fullrange speakers, although that's usually done for the reason of building separate boxes so that the array can be articulated and assembled in manageable pieces.

In the case of a home system, I'd use a few 1" compression drivers bolted into a waveguide, probably cast out of plaster or concrete using a CNC'd styrofoam former.
Why not build a full length line array? Your "what I'd do next time" picture is similar to what Don Keele has done with his curved line array, but he himself has said that it is a fix for those who don't want a full floor to ceiling line array. His design is an attempt to minimize some of the inherent problems of creating a truncated line array. Also why lump all the tweeters closer together? I understand that you want the drivers to be as close together as possible to extend the upper frequency response of the system but at the same time when you don't extend the radiating area all the way down the cabinet the line array effect is destroyed. Was this a budgetary constraint or a deliberate design choice? If it were for impedance matching reasons, why not go for a lower overall impedance? lots of speakers try and reduce the impedance of their speakers to gain efficiency (Apogee, Genesis etc.), and also I have heard that it deadens the resonance peak of the driver but I am having trouble wrapping my head around how that would work.

Cheers
Having a truncated tweeter array will not "destroy" the line effect. It will diminish it, but to what degree of audibilty is arguable (I and many others say "not much"). I did an array that had one tweeter. It was not as good overall as an array of 27 or whatever, but the speakers as a whole were superior to standard multiways.
DJJules (author)  jordon.gerber3 years ago
I bought 32 4 1/2" drivers on close out and plan on building another one of these. One of the goals of this was a "mini" line array and it works very well. I put the tweeters close together to prevent (or minimize) diffraction effects. they end up with a narrower than I would like beam pattern vertically but they still sound very nice. I should get around to the next array some time this spring. GOt a coupel other projects to knock out first...

Jules
Also, have you ever played around with this driver?

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-113

I am in the process of making my own 90" line array and am thinking about this driver as a mid/bass because of the price, aesthetics, quality, etc.
smirnoff044 years ago
I'm not an audiophile so the technical stuff is lost on me, but I really appreciate the fine craftsmanship on display here. A great looking set of speakers to be sure. I've seen a lot of peoples' diy speakers and while I'm sure they sound as great as they say, 9 time out of 10 they just don't look good. That may not matter to purists but to me a speaker should look as good as it sounds.

Keep up the good work!
DJJules (author)  smirnoff044 years ago
Thank you! I can't tell you how many speakers I have heard that sounded great but were literally unfinished MDF...

Jules
heiney DJJules3 years ago
MDF is the go to wood for building speakers & then veneered. I don't know one manufacturer that uses plywood. MDF is more dense, stable, great to cut & you don't have to worry about any voids which plaque plywood to no end & MDF is just easier to work with. And your choices of veneer is endless.

Older speakers the manufactures use to use particle board (also better then plywood) & then veneered the particle board.

It doesn't make a difference if the factory speakers are $100 or $10,000 there still veneered.
Pretty much like your birch plywood is just with a better substrate & well you can veneer a better surface for staining.
Birch just doesn't take stain well you should have used a pre-stain conditioner 1st.

Besides that I think the speakers look good.

Also on 2-way designs wire the tweeters out of phase with the low frequency drivers,
on 3-way designs wire the midrange out of phase with the tweeter & woofer.
This will eliminate any frequency cancellation at the crossover points.

Thats the reason why on some subwoofers you might see a 0/180 degs phase switch, its there just to make sure there is no cancellation of any frequencies at the crossover point between speakers, You probably will never hear the difference between one way or the other, but thought I would just put it out there as it is an easy thing to do.

Also there are online crossover calculators that you can use to design a crossover.
fwater heiney3 years ago
MDF is denser than plywood. It is not more stable (twice the hydroscopy). It is also not stronger. It is way cheaper than quality plywood, and THAT'S why it's used in commercially-produced speakers, and for ease of machining. MDF also stores energy to be released after it is excited, causing re-radiation of sound. It's inferior in every way to standard plywood except convenience. That being said, I use it almost all the time when I build speakers, exactly because of it's cost and ease of use.

Please don't ever use online calculators for crossover design. There's dozens of factors that make them mostly ineffective. It's like using a wristwatch to design a car engine.
Tachyon heiney3 years ago
You're right on all counts. AFAIR
DJJules (author)  heiney3 years ago
The crossover wiring you mention (in phase--out of phase) all depends on the crossover design. I assure you this one is wired correctly. I had help on the crossover and we measured the drivers impedance and frequency response and put all of that data into a pretty amazing spreadsheet. I need to find time to do an instructable on crossover design. I have a much larger line array in the works for a PA, will try and go into more detail on that one. Ahhh too many projects, too little time...

Jules
I agree they should look as good as they sound
Tachyon3 years ago
This design has me excited about using it as a basis for a project of my own. I can see modifying it slightly to make a clone of the polk SDA's, which I've always wanted to do.

Nicely done, thanks.
DJJules (author)  Tachyon3 years ago
You are welcome!

Jules
heiney3 years ago
To eliminate the "beaming" add an L-pad to the tweeter section in the crossover, just make sure the L-pad has the same impedance as the tweeter array, I'm guessing that would be 4ohms.
DJJules, this instructable could not have arrived at a more perfect time! i am one of those 'hold-outs' who is still watching his old 27" CRT Television. Not because I don't want to embrace the new Flat Panels, rather because the old CRT never stopped performing admirably. UNTIL JUST YESTERDAY, when all of a sudden the color has gone 'STUPID!' NOW it is time to replace it, with a flat panel screen and everyone says they have terrible sound! I have been looking for the answer to the question, "How do I get the 'Best Sound Possible' for the Buck?" And YOU, my friend, just answered that question. BEAUTIFUL pair of speakers, GREAT job, WONDERFUL! BUT!?! You raise several questions as well and I hope I don't make a nuisance of myself, But that is how you learn and speakers have always given me trouble! How do you 'Ohm Match' the Speakers to the amplifier? Doesn't pairing and quadrupling the speaker change the Oms? Four groups in parallel/series, doesn't that change the Ohms to 4 Ohm? Won't that over-heat a standard 8 ohm amplifier? Does that crossover have a terminal to which to connect the Sub Woofer? Can I, or should I, run DUAL sub woofers for extra presence and separation? (I do own dual Subs now!) I REALLY want to make this array a reality for my, fast approaching, New Home Theater System. I will GREATLY appreciate all the information you can provide. I am not afraid to jump all over this project and will rely on all the help you can provide. I already ordered the tweeters, cash was a little low this month. Next Month I have extra cash for the rest of the speakers and I already do cabinetry for people with BIG money! Let's ROCK this new speaker system!!
DJJules (author)  pddonovan20113 years ago
Thanks for your comments, the use of multiple drivers does require matching impedance's. IN a nut shell, if you wire two 8 ohm speakers in series, the become 16 ohm then you wire that with two other drives in series and you are back to 8. My final impedance is 4 ohms which is taken into account in the the crossover design. To your second question, you can use two subwoofers but really do not need them as bass tends to be non directional and does not need two for stereo separation. (Most low frequency sounds like bass and kick drums are panned center anyway)

Good luck and enjoy!

Jules
sysadmn DJJules3 years ago
Your explanation is a little unclear. I think you mean:

if you wire two 8 ohm speakers in series, they become 16 ohm then you wire that in parallel with two other speakers in series and you are back to 8.

In response to the original question, resistors in series add up, identical resistors in parallel are half the original resistance.
DJJules (author)  sysadmn3 years ago
Yea, I flubbed that one. In series they add in parallel it is 1/(1/Resistor1 +1/resistor2) or as you mention, on half the resistance if they are identical in parallel.

Thanks,

Jules
Excellent, really cool stuff! I was not thinking about left and right subs. I was thinking about front and rear subs. But first I am going to buiild my own arrays and then try them and see if the subs are even needed! I was also thinking about three additional Arrays 4 X 4 on the tweets and 3" speaks for the use of front and left/right back spekers!
weeniewawa3 years ago
square drive screws are way safer to use on something like this. actually always better to use. I used to do a lot of woodworking and just bought them online. http://www.mcfeelys.com/ has absolutely the best screws you can find, will not strip or break. It is also nice to be able to find Finish Birch locally. it gets expensive to ship.
Square drive screws are called Robertson screws and come in 4 sizes that are color coded to the screwdrivers: from smallest to largest: yellow, green, red, black. The most common size is red for pretty much everything and green for small work. Once in a blue moon, you'll use a "yellow handle Robertson" for something really tiny like a 4/40 screw. And once every couple of years, you'll use a black handle Robertson for something large. They are absolutely great screws but don't look as pretty as the Philips head screws.
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