HT Line Array and T-Line Build

[tHEbLENNY]

This is my first speaker build...Well, not exactly. I have built a hand full of sub enclosures as experiments but didn't seek many references when designing. I have been reading a ton of these threads as well as MJK, and others. Thank you all so much for access to your projects and experiments, and insight.

The room is about 25' x 40' x 11' tall. It is the living room of a loft in an old textile factory.

My Transmission Line uses 2-8" Dayton DCS205-4.
I decided to use a tapered line to help clean up upper harmonics. It is a 10:1 taper; as suggested on "Pearls from MJK". I also slid the drivers 1/3 down the length of the line which is ~68". The drivers are facing opposite directions, pushpush, and are coupled together at 4 of the 8 mounting screws by 4 dowels that span the inside width of the enclosure. I used 3" long deck screws with 3/4" shoulder (3/4" MDF) to really squeeze them tight to each other in hopes they would cancel out each others vibration and keep it from transferring to the box itself. I lined the box with carpet underlayment (I've heard its not the best but my office just got new carpets and I was too excited to listen to look for another option!).


The Line arrays use 8-3" Peerless India W3-LK76-PBK and 1-1" Pyramid TW18BK per channel - MMMMTMMMM. I just multiplied the individual drivers' enclosure volume to dictate the chambers for each pair of four drivers. The tweeter is completely cut off from the 8 mid range above and below it to get precise with volume and add rigidity to the enclosure. The tweeters are also on a separate channel from the mid range at the receiver.


I had the T-line finished for a few weeks before I finished the arrays and I hooked it up with my regular, bought speakers and was very very please with it! I'm not an expert nor do I have the sound equipment to measure it but It sounded great to me. Such a great addition to the atmosphere of the music. The response is fantastic with kick drums and bass guitar, and really encompassing with electronic bass. I tried stuffing the line up to the drivers starting at the closed end. It REALLY muffled output without any noticeable gain in quality so I took it out.

The arrays sound very nice too. Music and movies have a really full presence. Coupled with the sub they really shine. The system seems to sound a whole lot better at high volume. The mid range seem to not show up so well when turned down low. I think my amp has something to do with it. Also I have not crossed any of the speakers yet. I want to do that soon, but haven't looked much into it. I mounted the arrays on a series of door hinges so they can articulate out and face any direction side to side less than 180 degrees. I wanted to be able to "sweet spot" them as well as projecting out into the room at different directions. As most array set ups I have read about the sweet spot is very sweet, but general walking about listening is not so great. At least the swivel effect is good for conversations at a party! The sub is mounted low on the wall. The rear wall of the enclosure is about 4 inches off the brick wall so the rear sub can breath. I originally planned to mount it horozontal, but this filled the room much better for some reason.
In the future maybe I'll build taller arrays. I really like the full stage sound and could use even more. I designed the whole setup in sketchup for an easier and more accurate build.

Here are some pics -

[wintermute]

Hi and welcome to diyAudio A most impressive first project I must say

Tony.

[NewWorldAudio]

Very nice setup.

[tHEbLENNY]

I'm testing out stuffing in the arrays, but not noticing a big change. Guess I'll try different densities and see what comes of it.

[fhperez]

Very Nice Build...

[mdocod]

You have a mid-bass line, and a high frequency point/multi-point source. It's a "partial" line array. It's only a functioning line below those frequencies that the drivers can couple into a line source. In many cases, the benefits of the enormous dynamic capabilities of the semi-line, combined with the "presence" factor, often overshadow all of very significant flaws in your type of application. Such arrangements are common in lower budget sound reinforcement, where sheer volume and spacial averaging will overcome the flaws to the point that the listener is none the wiser. The fact that you have noticed that the system only really sounds "good" when used at higher listening levels is supporting evidence for what I have described above.

The major factors working against your system are as follows:

1. Likely the mid-bass drivers are carrying frequencies above the point that they will blend into a line source. The result "combing" (or lobing, take your pick, google it).
2. A line source has a different "gain" effect than a point source. As the volume is turned up, the line source couples more intensely with limited vertical dispersion. In your case, there is a listening level where the "mid-bass-line" finds a reasonable match to the "high-frequency-point-source" and everything sounds pretty good. Above and below that point, the highs are either exaggerated or nullified.

The project is very neat, and I appreciate anyone who is willing to start cutting the boards and building something. Thank you for sharing it with us! With some guidance, you may be able to improve on the design.

Eric

[planet10]

Nice project. I have some of those tweeters. You might want to pull thenm apart and see if the plastic horn moulding needs some clean up -- mine did. The decorative ring on the front comes off and there are screws underneath.

dave

[chrisb]

It's great to see a flat screen not mounted as ridiculously high on the wall as "interior designers" seem wont to do. Maybe they get a kickback from physio / chiropractic practitioners for adjusting those stiff neck / shoulders

tidy work