Build the Mini Line Array

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. 

Comments

[Tachyon]

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]

You are welcome!

Jules

[heiney]

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.

[smirnoff04]

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!

[heiney]

I agree they should look as good as they sound

[DJJules]

Thank you! I can't tell you how many speakers I have heard that sounded great but were literally unfinished MDF...

Jules

[heiney]

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.

[Tachyon]

You're right on all counts. AFAIR

[DJJules]

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

[jordon.gerber]

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

[DJJules]

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

[jordon.gerber]

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.

[pddonovan2011]

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]

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]

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]

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

[pddonovan2011]

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!

[weeniewawa]

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.

[blanchae]

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.

[mpep]

Thanks for that. Never knew the name of the square drive screws.

[ellisgl]

Suggestion for your next build. Put the wire through the hole of the terminal, wrap it around the the terminal and then solder it.

[jimvandamme]

Why didn't you use the cheaper Tang Band speakers...W3-1053SC? They're only ten bucks vs. 32 for the neodymium.

[DJJules]

I already had these...

[jhulan_111810]

hi mr.dj jules i wanna ask something about the speaker you made...what amplifier did you use and how much watts?tnkz

[DJJules]

I run them on a Sony surround reciever that is 60watts a channel and set to "small" for the front speakers with a subwoofer. I have used these as a PA with a Carvin 225W per channel amp and an EQ to cut everything below 150hz and a Subwoofer.

Jules

[jando915]

have you ever thought about making and selling these to ppl not everyone can can make something like this you can really make some good money doing it

[ninjawasaki]

Nice work! I was thinking about building a line area out of those dayton sound exciters I saw mentioned on another project here. If you are into line arrays and learning about them, read up on the Martin array that we use. Technical sheets can be found here...it's wild how they work and the results are amazing.

http://www.martin-audio.com/softtech/technical.asp

[txsmoke]

The vertical dispersion issue you note is one of the primary by-products of a line array- minimal vertical dispersion and wide horizontal dispersion. This dispersion pattern minimizes floor and ceiling reflections, contributing to the solid imaging you are experiencing.

This is also why they work so well projecting music and speech at presentations and concerts (and block parties :-).

[borus12]

Yes DJ the centre driver at ear level than the distances from each of the other drivers to the ear is the same.

[snolou]

You can do a slight modification to simulate curved mounting of your drivers by using the fresnel lense aproach, that is by progressively angling the drivers from the inner to the outer by either recessing the mount on the box or adding an angled mounting ring under the speakers. You can do this with the midranges and the tweeters. I did this with some arrays I built in the eighties using 4" Dynaudio drivers and tweeters to good affect. The good thing is If you use angled mounting rings under each driver you can undo it if you don't like the results. Great project I am very envious you were able to achieve this. Maybe I'll be inspired to do it again.

[DJJules]

I like the concave idea! Also just tilting them sounds good too. I will take that into account with the next one.

Jules

[snolou]

Oh one PS I would prefer a concave to the desighn.

[blanchae]

For better bass response, put the speakers in the corners of the room. This will cause the walls and ceiling to act as a folded horn and project the bass better. Nice design, I've always wanted to build multiple "small speaker" box ever since I saw the Popular Electronics Sweet Sixteen project in the 60s. I've placed fiberglass insulation quite successfully for inside the box - completely filled. The insulation makes the box appear acoustically bigger than it is, resulting in better bass response.

In one design, I've used prime numbers for the boxes dimensions in order to stop harmonics from occuring - never really could test it if it actually did anything but it does make a good conversation...

[bknight2]

I think what you were looking for is divine ratios. haha!

[DJJules]

Nice! I will check these out and will get my hands on some. Thanks for this tip!

Jules

[Ansis]

Hi!
It looks good!
I think- I know how it sounds- I can "Imagen" , because I am in "sound" from 9 years- now I am 44. My way is 4 speakers in the big desk. All 4 is wide- range and paper with 92 dB/m. I have 2 SE drivers 6P14-EV- Russian military in pentode connection- all power is stabilized.
P.S. If You have interest- I can make some photos and send to You. I have Skype: ansis99 and e- mail: [e-mail]
Good Luck!

[lesizz]

Really cool project. And I agree with '04 that they look really look nice.
How did you get the response chart? You must have some fancy equipment. Do you have a room that you've made aneochic?
Maybe you already know this, but the reason speakers are less distoted when driven at low levels is that the cones essentially have a spring-return. The pressure exerted by the spring is not constant, but increases with the amount of cone distention. Non-linearity is the enemy of fidelity. We get harmonic distortion from non-linearity, not to mention other evils. So, anyway, the less the less the cone is driven, and the less the cone is distended, the less the distortion.
How do these speakers sound?
For speaker-listening I like to use some full-orchestra stuff, but very simple music can be very telling. Something like Abby Dewald of the Ditty Bops singing "It's a Shame", accompanied only by her guitar. Does her voice sound real? That's a severe test of a speaker system.
Now all you need are some good tube electronics, a turntable and a collection of some good vinyl to take full advantage of the speak's.