Build the Mini Line Array

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Introduction: Build the Mini Line Array

About: I started taking things apart when I was 6 started putting them back together at 8 and they actually worked again when I was 10 or 11...

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!

Step 1: The Design

The Design:

I found a speaker building buddy who happened to live in my neighborhood. The first time I went to his house he had a line array using 9 three inch drivers per side and 9 small tweeters. This reminded me about the 16 I had in my garage. After listening to his I knew I needed to put my drivers to good use. Dave suggested I pair them up with a different tweeter than he used. He used a ¾ inch dome tweeter and recommended the same driver that had a 5/8 inch dome. He had used this tweeter in a couple other projects and really liked them.

I had 16 of these

and ordered 16 of these for use as my tweeter

Dave had substantial experience with speaker design, after measuring my little woofers designed a great crossover. With 8 drivers I chose to wire them 4 in Parallel and then the two sets of paralleled drivers in series giving me roughly a 4 ohm load. This was taken into account for the crossover design. See the theoretical frequency response graph.

Parts List:

Crossover parts (for two speakers:)

(2) 2.4 Ohm Resistor

(2) 3.3 uF Capacitor

(2) 7.5 uF Capacitor

(2) 10 uF Capacitor

(2) .70 mH Inductor

(2).15 mH Inductor

(2) Speaker terminals



Cabinet/Enclosure Parts  (for two speakers:)

½ ” Birch plywood

(2) Front Panel 7” X 34”
(2) Rear Panel 7” X 34”

¾ ” Birch Plywood

(4) Top and Bottom 3” X 5.5”
(4) Side panels 3” X 34”



Miscellaneous

20 feet of Black 18 gauge wire
20 feet of Red 18 gauge wire
Semi Gloss Polyurethane
Wood Stain
Sandpaper
Mounting Screws for the 3” drivers 
One bag of Poly Stuffing to act as acoustic insulation in the cabinet 
Mounting screws for the rear panel.
Electrical Tape or Heat Shrink Tubing


Tools

Drill Press
Soldering Iron
Solder
Orbital Sander
Hot Glue Gun (with a bunch of glue sticks!)
Wood Clamps
Wood Glue
Screw Driver


For the cabinet I chose 13 ply birch plywood. In the Dallas area you can get it here. I wanted the line array to be small and compact. And, easy to build with the tools I have. I drew the front panel in inkscape  (Great Open Source drawing program!) Because the tweeters were so small I decided to just drill the right size hole and then glue the driver in flush to the front panel. I experimented with a 1 ¼” hole and a 1 3/8” hole and ended ordering a 1 5/16” forstner bit from here  that was just right. 

Step 2: The Enclosure

Build the Enclosure:

The most difficult part was drilling the holes for the front panel. This is where a CNC router would really come in handy! I had the small tweeter holes covered with my forsnter bit but I needed to figure out the best way to cut 3” holes in the wood. I had tried hole saws before and they really dont work well for multiple cuts in plywood. Then I found this type of tool: it allows you to adjust it and it makes very nice circular cutouts with a drill press.

After cutting all the pieces out with a table saw I set up my drill press to allow me to move the front panel around while maintaining the correct distance from the side of the front panel. Couple of clamps and some scrap wood are all you need. This way if I was off a little bit the drivers would all line up and it would look good. Then I measured off all the centers of the holes and proceeded to drill away. After finishing the holes I rounded over the front panel with a router and then sanded all the parts. Before you put the drill press away, you need to cutout a hole hole in the back panel for the speaker jack. The one I used conveniently needs a 3” hole cutout. Also, drill pilot holes in the rear panel for the mounting screws you will use to mount it to the enclosure before sanding, staining and varnishing.

I used wood glue and clamps to assemble the enclosures. I cut a couple small braces that you can see in the pictures. I left the back off on purpose as this is where the crossover goes.

Before mounting the drivers and building the crossover I sanded the enclosure then stained it with a dark stain and put on several coats of polyurethane varnish.  

Step 3: The Crossover

The Crossover:

My buddy Dave Thomas was very helpful and he designed the crossover. I am trying to talk him into writing an Instructable on Crossover Design. Stay tuned!

You may have noticed that the design calls out for a 2.5 Ohm resistor and the actual in use resistor is 2.4 Ohms. There will be very little difference. It is important to avoid wire wound resistors as they will have some inductance associated with them that is not taken into account in the design or measured. 

One of things I learned about speaker building is to always print out a copy of the crossover schematic and tape it to the inside of the speaker. This way if you ever have to work on it later, you have the schematic! It also helps with the wiring.

Wiring the crossover is pure point to point. I hot glued all the components to the back panel and then connected them per the schematic. Set the rear panel aside and let's mount the drivers. 

Step 4: Mounting the Drivers

Mounting the Drivers:

Lets start with the tweeters. Cut 16 six inch red wires and 16 six inch black wires. Strip ¼ ” on on end and about ¾ of an inch on the other end and. For each tweeter, solder a red wire to the “+” terminal of the tweeter and a black wire to the “-” lead. (See the Picture) After prepping the tweeters, I placed the enclosure on a smooth flat surface and lowered the tweeters in from the back of the enclosure to sit flush with the front panel. Now comes the fun part, using the hot glue gun, glue in eight tweeters per cabinet. Let them cool before moving anything. Now for the woofers...

In a similar fashion to the tweeters, cut wires for the each woofer and prep and solder them to each woofer. Mount them using four screws for each one. Be careful here, one slip of the screw driver can ruin a driver. I had this happen to me and had to order another one! After all the drivers are mounted, lets wire them up.

Step 5: Wiring It All Together

Wiring it all together and final assembly:

Look at the wiring diagram. We are wiring four drivers in parallel then wire the two sets of drivers in series. Then using more 18 gauge wire, connect the tweeters to the correct crossover section. Repeat this for the woofers. Double check all the connections. Before placing the rear panel on we want to put in as much fill of the poly fill as possible. The goal here is to prevent resonance and internal reflections inside the enclosure. Some of the more astute of you may have wondered about the volume of the box and how that affects the frequency response. I use these speakers as right and left of my home theater setup and I have a sub-woofer. In a bit of heresy, I did not deign around box volume and am not trying for deep bass response. The crossover theoretical response is very good above 200hz or so and listening tests will tell how it all came out. OK, stuff the box with fiber fill and then place the rear panel on the enclosure, making sure that no wires stick out or are pinched in the edge.

Step 6: Listening and Use

Listening and use:

I hooked these up to my receiver and fired them up. They sound great, crisp and extremely clean. I have them setup so that the tweeter array is at head height while you are seated in my media room. The one issue with them is that the tweeter array really beams. If you are in line with it there is no issue and the stereo field is awesome. If you stand up above the tweeter array you can actually hear it drop off a little. This got me to thinking about what I would do if built another one. I would curve the tweeter array slightly. See the picture of what I would change. Dave came over and listened to them and really liked them too. His with the 3/4” tweeter exhibit the same issue with being above the tweeter array. In the mean time, these things are very low distortion and sound awesome. In the stereo field, it is almost like you have headphones on. My wife loves them. Movies usually have back ground effects, music and foley in the stereo field and these speakers put you right in the middle. One of the other things a line array should do is handle a lot of power while maintaining low distortion. We had an event at work and I took these in with a sub-woofer and the rocked the house. I used an active EQ, crossed them over at 150Hz and ran them with a 225W per channel amp. They projected very well and cleanly filled the room with both people presenting and our after party. I used the same setup at a neighborhood block party and once again, they rocked the hood. They only have eight drivers per side and are only 34” tall. One could present an argument that they are not full line arrays. In my opinion, they certainly sound much larger than they are. I also brought them to a couple local DIY audio events and they were well received.

The price of the drivers I am using went up significantly since I bought them. I am keeping my eyes out for close out sales and want to build an even larger line array. Happy Building!

Jules

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    66 Comments

    Interesting project. Did you consider using small coax drivers? I like the arch shape of the Epique (Dayton) 24 array. I'm thinking of building something like that with with 10 - 4" coax per speaker.

    1 reply

    That would be a great project. I used what I had when I built mine. I have some other 3" drivers that I bought I bought bulk that have been waiting to go into a line array... I need to finish that one!

    Please build your design and share.

    Jules

    I love this design. That being said I need more than you outline offers. Is there a way to build in a sequence of speakers to handle down to 30Hz, and, is it possible to build in a capability to handle way High power (power peaks to 1500 watts) and what do you think using Purple Heart (wood) do if anything to the sound quality. Harley480@gmail.com

    1 reply

    To get to 30hz you would need to use larger drivers that I used here. A friend of mine built a great line array using 8 inch drivers for the main array and one inch silk dome tweeters. And... he used Purple Heart for the cabinet. I don't have his design but the concept it the same as what I am doing.

    Jules

    Just sharing the one I built.

    Mine has a bit of a different purpose, a mono system mainly designed to produce clear and well projected highs (150 hz and up) for a performance system, allowing a separate floor speaker to handle the lower register. I learned a great deal from your article as well as many others on line, so I'm sharing mine wherever i can. I am very happy with the way mine turned out, and it has been a major improvement to my sound as a solo performer.

    http://elfintechnologies.com/LineArray.html

    1 reply

    Excellent! Thank you for sharing this.

    Jules

    What are your thoughts on (1) angling the speakers in the horizontal plane, to offer more coverage side to side, and also (2) scaling different combinations of serial/parallel connections, so that the center and upper speakers get more of the available power?

    1 reply

    Those are great ideas and I think comercial line arrays vary the power to each zone. I am planning on building a bigger set of these and redoing the tweeter array. commercial ones are set up as an backwards "J" with the bottom curve facing down. Just am crunched for spare time these days!

    Jules

    linearray.jpg

    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

    1 reply

    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.

    7 replies

    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).

    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

    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?

    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.