R-Carpenter
Project Category:
Tower Speakers
Project Level:
Advanced
Project Time:
20+ Hours
Project Cost:
$500 – $1,000
Project Description:
Mid sized line array with improved realism vertical image, low distortions and high power handling.
Bass response projected to 80hz.
Relatively small budget for line array, using low distortion buyout Fountek drivers within desirable passband.
Design Goals:
Affordable Line Array sound in a small package.
Driver Selection:
Tweeter
Enclosure Design:
Sealed enclosure for both midrange and woofer sections. Multiple bracing is highly recommended.
Drawings are for 3/4” thick material.
Crossover Design:
Crossover design is fairly straightforward. Tweeter array is represented by a single T1 driver as well as midrange array is represented by M1 driver and woofers, by W1. This is done so the crossover CAD screen is not cluttered with 16 drivers.
Wiring the array.
Tweeters.
Tweeters are numbered from the top to the bottom. Top tweeter is #1 and lower tweeter subsequently numbered #5. Tweeters #1,#2, #4 and #5 are wired in series to each other. This quartet is wired parallel to the center tweeter #3.
Midrange drivers.
There’s total of 9 drivers. They are wired in 3/series parallel so the final impedance is equal to a single driver. Easiest way to connect the drivers correctly is to lay out 3 groups of 3 drivers. Solder series connections in each group of 3 and then connect 3 groups, parallel.
Woofers.
Woofers are wired parallel to each other.
Tips & Tricks:
The heart of the system is Fountek’s FE87 2-1/2″ full range driver. By itself it has a fairly low sensitivity, limited x-max and limited low end response. The midrange, lower treble are however very extended and the driver even deeps in to upper bass. This extremely wide pass-band lands it perfectly for a line array where it will used in multiples and low sensitivity will not be an issue any longer. Wide response also allows it to be used with low crossed woofers on the bottom and small tweeter to extend the response cleanly all the way to 20khz and makes the crossover network easier to design.
7” Dayton Aluminum woofers were chosen to reinforce bottom end. Positioning them close to the floor will somewhat negate the need for baffle step compensation and using a pair will increase sensitivity and decrease distortions. This will also allow for the form factor of a speaker to remain a slim tower. Sealed alignment, in my opinion is preferred from the various points of view. For starters, it is the volume and appearance of the box. Secondly, ported design for this woofers will entertain the situation where the drivers will quickly overextend below port tuning frequency and may introduce distortions. Sealed response in to 80 hz on the integration hand, makes the use of the dedicated low crossed powered subwoofer easy.
Finally to the tweeters.
It’s a small dome with the neo motor. Using 5 tweeters in the array configuration may invite itself for shading the tweeters and altering vertical image of the speaker.
Box assembly.
Section, housing midrange drivers and the tweeters can be assembled separate. This is really up to the builder. One requirement to both, lower and upper compartment is extensive bracing. Because the upper section is fairly tall, it will produce standing wave. To negate the effect, it is recommended to use 5” or so of Rock-wool or Owen’s corning on the top and bottom of the midrange cabinet. The rest of the chamber can be filled with either Acustastuff (sold by Parts Express) or fiberglass if you don’t mind handling it. Woofer chamber also needs to be stuffed with Acustastuff or fiberglass.
Experiment with the R10 to your own preferences. I ended up using 10Ohm value in a fairly reverberant space. This lowered output of the midrange array by about 3.5 db.
Conclusion:
The system is up for a reviews by enthusiasts and will be shown on the upcoming NY/NJ DIY speaker fest.
About the Designer:
Roman Erlikh is a professional furniture maker and a speaker builder.
Roman also hosts NY/NJ DIY Speaker fest in Brooklyn Navy Yard.
Project Parts List