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perceval 22nd February 2014 06:49 AM

Short Line Array (line source) build
 
Hi there!

I was on HTShack, and I was told I might get better feedback around here... so hello there!

I have always been interested in Line Arrays... I personally think they look cool, but I have zero experience with them. Never built one, never heard one! So, what better project than starting something completely new to me!

I only have one room available as we share our house between our living quarters and working areas. This room is quite large, it is an open design, has a living room and dining room together, opens to the staircase going up, and... it's all cement! (Cement houses are the norm here (Taiwan) as we get lots of earthquakes and some typhoons (hurricanes for people in the US, cyclones down under).

Also.... it has to be spouse friendly! I know a few here will relate.

The room. It is 10m x 5m, and has a 3m high ceiling. (33' x 16', 10' ceiling). It is roughly a rectangle with some expanding here and there.

The audio shelf (which I have to keep because I need extended storage space.. a rare commodity in shared spaces) is 3.6m long and 50cm high (12' long and 19" high). So no space for tower speakers.

Here's the room as it is now:

https://www.hometheatershack.com/for...livingroom.jpg

I've been researching for full range drivers, and I found this 4", made locally, and available at the reasonable price of $18 a unit. This way, I wouldn't have to design a crossover, which would be another thing to learn! Unless I need to add some tweeters to the mix. ( I have been reading on crossovers lately and it may not be as daunting as I initially thought to get the basics... I'm sure years of experience do help though).

I'm trying to come up with some designs, but I need to understand how line arrays work. I downloaded Jim Griffin's white paper on LA, but I need time to understand the concepts...

Still don't know if I should go with an open baffle (easy construction), or closed back (more work!). Leaning towards open, I can always close later.

This is the driver I found. Anyone could provide some feedback regarding this unit? I'm thinking of using 6 of them per tower. I also found Beston, makers of ribbon tweeters, right here in my backyard. I could always add a few ribbon tweeters later if needed to overcome the combing effect.

https://www.hometheatershack.com/for...600x0400-m.jpg

https://www.hometheatershack.com/for...456x0600-m.jpg

Scottmoose 22nd February 2014 09:35 AM

6 drivers do not a line array make. Not a great one anyway. Think 8-9 drivers minimum before you're getting anything particularly worthwhile, at least in array terms.

Wideband drivers can be made to work in an array, but you will need Eq for the top end (not too much of a problem) if you don't want to run tweeters. If you're running them open baffle, you'll also need dedicated woofers (not subs) since there's very little chance a couple of subs will get high enough to match them -not with decent quality anyway. As far as the drivers go, from the spec. published they should do a decent enough job if used well.

Colin 22nd February 2014 10:12 AM

If space is limited, a closed box may be a better bet. If you built in the right angle for the baffle, they cabinets could wall-mount either side of the projector screen.

A slightly odd layout but here is a system with 8x drivers per side which is designed as part of the room. (Jordan drivers in this case but the same principle applies.)

JdM12 audio project

btw, I'm not sure why that design uses two arrays of 4 per side, possibly an after-thought or because mounting plates are available for 4 units. I'd have built as one long array.

xrk971 22nd February 2014 10:45 AM

Welcome to diyAudio! You will get a lot more air time for your questions here vs HTshack.

+1 on you will need more units to be a line array - preferably floor to ceiling tall for best performance. There is a lot behind this and reading some of the many threads on line arrays will get you started with all the issues and tips on which way to go. Check out the "Cloning the IDS-25" thread, "Stupid cheap line array" thread, and "The Two Towers - a 25 driver line array..." Thread.

A few initial obvious tips:

- use high Qts drivers as they work well in sealed or OB cabinets. The current best value for great sound and most popular for line arrays seems to be the Vifa TC9FD. You will probably not find a more cost effective driver for line arrays or as an OB driver that is capable of the SQ and performance. $12 each is good because you will need a lot of drivers.

- sealed will give you better control of excursion and makes a more ridgid box and lets you get deeper bass than OB. Qnty 25 of the Vifa's with EQ gets down to 30 Hz with a sealed design.

- you will need significant EQ'ing to make it work. There are analog op amp based designs or you can go with DSP which makes it really easy to tweak on the fly.

Good luck!

Overkill Audio 22nd February 2014 11:04 AM

On wall Line Array
 
3 Attachment(s)
Hi Perceval,

I agree with Scottmoose, six of these drivers drivers will not make a good array.
Using conventional drivers you need to have a LA that is at least 50% of your ceiling height, ideally 75%, to avoid various sonic issues.

So I guess around 16 drivers per side is a good start, 24 drivers would be ideal.
Your room is great! Perfect for on wall mounting where you can take advantage of boundary reinforcement to best advantage and keep a high WAF!
Some Eq ( from any good AV receiver or in the fantastic JRiver media centre) around 150Hz to 300Hz to lower this band and a wee bass boost around 40Hz will be great.

I'd suggest a sealed box of around 3 to 4 litres per driver using 12mm thick bamboo plywood and good internal cabinet wall dampening and approx. 0.5 litre volume ( when lightly " fluffed up") of Twaron or similar internal dampening per driver.
Avoid stranded cable and solder joints as this has a big effect when using 40 or 50 drivers per pair of speakers, use 0.5mm silver plated solid core copper and crimp the joints, no solder!
Your suggested driver looks good value at $18...Buy 50 or 100 ( centre channel and rear speakers too?) and you will get a good discount, say $12 each...That would be a deal!
Adding in a line array of tweeters will be expensive, add complexity, introduce crossover phase errors ( unless done with a sophisticated DSP / software like Accurate) and take a lot of test and measurement equipment / experience to get right.
Stick with these drivers for your first build and if you get hooked you will be able to sell them for a profit ( they will sound great!) and then move on to a more ambitious mark two version.
I have attached a few pics of some of my Line Arrays using the fantastic ( but more expensive) 4.5 inch Neo motor BMR driver.

All the best and hope some of this helps.
Cheers
Derek.

perceval 22nd February 2014 12:11 PM

Woah! That's action! Thanks for the feedback!

A couple of things to follow through.

I tried a couple of places to get drivers or kits sent to me... they pretty much turned me down. Seems that shipping to Taiwan from the US or other places is kinda prohibitive (had expected that!) even though the import fees are not overwhelming. So, most places I talked to wouldn't ship to me.

So, I am locked into what is available around here. I've found Beston, which seems to have a good rep for their ribbon tweeters. Usher is also a company that enjoys an equally good rep (I drooled over their CP-777, I think they are gorgeous).

Then I found the company which has the 4" unit I showed above. They also have a 3" unit that is a little cheaper. It doesn't go as low, but has a better response at higher frequencies.

I knew I was not even close to the 70% needed to be a line array, but I was hoping I could get away with only 6 drivers per tower. I could bump this to 8, 9 ... or 10? and power taper this thing as 3-2-2-3? I need to check resistance... This is all new to me, and there's so much to ingest... still... loving it!

I wish I could mount the arrays to the wall, but there's a window on the right side... don't think that would work.

Thanks for the feedback! I think I'm going to love it here! :)

Scottmoose 22nd February 2014 02:47 PM

If 9 or 10 is your limit, use that. That way you'll be closer to useful array behaviour. Some power-shading is likely to be useful as it's still relatively short.

perceval 23rd February 2014 11:54 AM

1 Attachment(s)
Cool.

Now, I can get the 4" with the specs I've showed before, but they also have a 3" full range as well.

The 3" doesn't go as low as the 4", but they keep their strength over 17,000 ... where the 4" falls after 17,000.

Wondering which is better... lower end or higher end in the array. I do have 2 subs in the room.

xrk971 23rd February 2014 12:13 PM

If your sub is capable of crossing over at 200 Hz, go with 3 inch as you keep center to center spacing smaller for reduced comb filtering effects, better HF, etc. This is a good way to do it as you will be running a FAST line array.

perceval 23rd February 2014 12:29 PM

Hmm.. my sub goes as high as 140Hz at the moment.

Ok, I gotta ask... I see that FAST in a lot of posts, but since I am new around here, I have no idea what that means...


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