Cheap, Dirty, and Ugly linear array for all concrete room - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 6 Old 05-23-2020, 11:52 AM - Thread Starter
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Cheap, Dirty, and Ugly linear array for all concrete room

We have a presentation area that is in a concrete bunker at a local church. The acoustics are awful, and the small system we have (aka garage sale special) just doesn't cut it.

Were I to do a simple linear array, perhaps with these (given the cost: https://www.parts-express.com/peerle...8-ohm--299-032 ), would it be theoretically be any better than the single point source we're using now?

Our audience for larger events is fairly large but (as you can imagine) money is tight, and this will be out of my own pocket. We can't meet or do any activities until Quarantine is lifted, and even then we've got to be careful as several adults are immuno compromised.

I'll try modeling or designing something if it's of value.

Thanks kindly-

Jason
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post #2 of 6 Old 05-23-2020, 03:00 PM
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From experience at the ice skating rinks.
I would go with many smaller speakers throughout the room.


See these two old RaneNotes:
https://www.ranecommercial.com/legacy/note136.html
https://www.ranecommercial.com/legacy/note163.html


and these Jim Brown papers:
http://www.audiosystemsgroup.com/3Times.pdf
http://www.audiosystemsgroup.com/ContempAcoustics.pdf
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post #3 of 6 Old 05-23-2020, 04:05 PM - Thread Starter
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Originally Posted by Speedskater View Post
From experience at the ice skating rinks.
I would go with many smaller speakers throughout the room.


See these two old RaneNotes:
https://www.ranecommercial.com/legacy/note136.html
https://www.ranecommercial.com/legacy/note163.html


and these Jim Brown papers:
http://www.audiosystemsgroup.com/3Times.pdf
http://www.audiosystemsgroup.com/ContempAcoustics.pdf
I should have said portable. I'm sorry.

We can't leave anything in the room afterwards- so I was trying to figure out how to pick something up and slum it over to the areas that need it.

I have kicked around the idea of just running multiple speakers (with some cheap speak-on cables) but finding decent cord has been expensive. I'm floored that wire is that expensive.
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post #4 of 6 Old 05-23-2020, 08:43 PM
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Do you have pictures of, or can you make a quick sketch of a floorplan of the presentation area?
Is the system for hearing a speaker present, or possibly for music also? If for speaking presentations mainly, does a portable PA systems not work?

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Originally Posted by purduephotog View Post
We have a presentation area that is in a concrete bunker at a local church. The acoustics are awful, and the small system we have (aka garage sale special) just doesn't cut it.
Our audience for larger events is fairly large but (as you can imagine) money is tight, and this will be out of my own pocket. We can't meet or do any activities until Quarantine is lifted, and even then we've got to be careful as several adults are immuno compromised.
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Originally Posted by purduephotog View Post
I should have said portable. I'm sorry.
We can't leave anything in the room afterwards- so I was trying to figure out how to pick something up and slum it over to the areas that need it.
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post #5 of 6 Old Yesterday, 09:15 AM
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Quote:
Originally Posted by purduephotog View Post
We have a presentation area that is in a concrete bunker at a local church. The acoustics are awful, and the small system we have (aka garage sale special) just doesn't cut it.

Were I to do a simple linear array, perhaps with these (given the cost: https://www.parts-express.com/peerle...8-ohm--299-032 ), would it be theoretically be any better than the single point source we're using now?

Our audience for larger events is fairly large but (as you can imagine) money is tight, and this will be out of my own pocket. We can't meet or do any activities until Quarantine is lifted, and even then we've got to be careful as several adults are immuno compromised.

I'll try modeling or designing something if it's of value.
I built a 3-way line array around 7 years ago for my garage--complete with cement floors and terrible acoustics. Started off simply enough, it didn't work so I went from 2 way to 3 way, added plenty of EQ and a pair of subwoofers--viola! Works well in my garage but a few thoughts and things I learned.

Looking at those drivers, fair enough as 2.5 inch full ranges can be roped into the range of 175 Hz to 12 KHz without too much EQ.
Be aware, the longer (taller) the array the better because--line array. Very generally speaking, you should use the line height at a minimum of 70 percent of the floor/ceiling distance because line array. Say you have a 10 foot ceiling, go for at least a 7 foot tall array, 8 foot ceiling would be around 6 feet and a 12 footer would be around 8.5 feet etc. I went for a 6 footer to get it done with 8 foot ceilings but if you held a gun to my head to force me to do it again--I'd go for a 7.5 foot tall array to simplify my life.

OK, that being said--be aware that line arrays--very specifically the ones using small full ranges require EQ--it is not optional. Also, since you won't get any real response below 175 Hz running sealed (much easier to build) or, if you run enough drivers and EQ ported you can get 100 Hz but not high SPL...either way you slice it, you need subwoofers--not an option. Subs + amps + EQ (parametric prefferred) gets expensive and adds a layer of complexity. No big deal IF everyone that ever uses the system fully understands how the system is designed, what the settings are and why...and does it right every time!

Realistically, it is a church and I have helped build a PA or two for that use. Uuuhhhh...you can say the users mean well but... a lot of people think it is just like their 2 channel stereo and home, plug in a microphone, feedback happens and kiss something goodbye! Throw in that if a teenager can get to it, just by the natural fact that they know everyting they WILL mess with it, blow it up then claim it was not good enough/strong enough or designed well in the first place. Just throwing that one out there...

Basically, are you SURE this is what you want? If so, a few things to know. I would build them as two segments, basically they would be two boxes tall. I would wire the drivers for 16 ohms or high impedance in case they only use one segment and not two. This prevents putting too much power into one segment. I'd wire 18 of those 2.5 inch drivers 6 series and 3 parallel for a 16 ohm load. They are 2.71 inches across so built at 2.9 inches center-to-center, each box would be less that 4.5 feet tall. This would be a little under 9 feet tall for two of them.

Now if those segements are too tall for you, assuming you might be using them in rooms with 8 foot ceilings--need to change the configuration again. You could wire them in 12 driver segments, or 4 series/3 parallel for roughly 12 ohms. Two of those would be roughly a 6 ohm load which would be fine with traditional PA amps rated at 500 watts per channel into 4 ohms. The 12 driver boxes would be about 3 feet tall each and 12 ohms. Two of them would create a 6 foot tall stack at 6 ohms and three of them would be around 9 feet tall at 4 ohms. Be aware that 12 drivers can only handle (real world) maybe 150 watts or so but the high impedance will knock down the power output from the amplifier. This should help because many uses dictate that the operators will think one pair is "good enough" and, because it works that way--the less drivers = less efficiency/output and they will turn it up louder.

Just for fun on paper, say you go with 12 drivers per box and use two boxes for a six foot stack. Twenty-four drivers at 6 ohms would be a good match for around 300 watts max if the sub is setup properly. Would it be loud enough? All depends on what you use them for in reality.

I built my arrays using 12 five inch woofers, 20 three inch midranges and 48 tweeters per fox. Cross them over at 80Hz to a pair of subwoofers and go. They work well in my garage, they can really punch out the volume and should work well for crowds up to 200 people or so. I've never used them for PA purposes, more like BBQs and house parties but when used with the subwoofers, amplifiers and manditory EQ--they work well.

Just be aware they are not inexpensive, they are not easy to build and they require EQ to work properly. Line arrays follow "infinite line theory" and most speakers are "point source"--they are not the same thing and they work differently. This leads to a lot of confusion and utter BS in how they work. Good ol' marketing states they loose only 3dB per doubling of distance VS a point source at 6dB per doubling of distance--very true but only if it is an "infinite line". Whoops! BIG difference there and your line source will turn into a point source at longer distances. How it operates also depends on the frequency, at some points the bass is a point source and the high frequencies are infinite line sources so that can make a serious mess of your frequency response depending on the distance from the speaker. For this reason, if you ever go to a stadium and see vertical line arrays--notice that the farther they "throw", the taller they become because that is how the game is played. There is a minimum height line arrays must be at a specific distance from them if you wish to maintain maximum fidelity, as the distance increases you must increase the height of the array and for stadiums they can be 3 to 6 meters (10 to 20 feet) tall.

Initially, the line array would seem fairly inexpensive, very easy to move around and it covers all bases for all rooms. Technically, it could as long as you adjust the height of the array to match the room, you have proper EQ, subwoofer support and the people that use them fully understand how to set them up. Since many people will be messing around with the thing, there are ways you can idiot proof it. This is what I would do.

First thing is I would use different connections with the arrays and subs to make it impossible to wire them backwards. Don't want to wire the sub bass into the arrays--for obvious reasons. I'd use amplifiers that have the DSP or processing built in to properly set the output limiters (limit power) to "match" the power you wish to use. Then use the parametric EQ in the amp to smooth out response, you'll notice you'll need to gradually boost high frequencies--don't be alarmed, just the nature of the beast. Don't attempt to keep boosting the EQ until you get to 20 KHz--it won't happen so once you get to around 12 to 15KHz with those full ranges, call it good. I use 48 small dome tweeters and by themselves they are flat past 20 KHz. Stack them 6 feet tall and they start rolling off at around 10KHz because--center-to-center distance causes them to decouple from each other and high frequencies roll off. You'd think 48 dome tweeters would not need EQ...well, they do so I bump them up +6dB at 16 KHz. Once I fully understood line array theory and issues, it then makes sense and you play their game.

After having line arrays in my garage for 7 years, I get many questions about them as they tend to stick out. They do very cool things, at distances up to 10 feet they vary only slightly in volume, they have a lower volume drop as you back away from them (out to around 25 feet) and they revert to point source drop after that--well, most frequencies do. The dispersion of them is less than 10 degrees vertical so they don't have any floor or ceiling reflections at the 12 foot distance I generally sit and have a listen. The most common question I answer if I was to build them again...

IF I was to build line arrays again, I would not make them 3-way! I'd use 3" full ranges next time and since you NEED various EQ anyway, might as well use the 3 inch full ranges to simplify things. My favorite to use, oddly enough are designed to be used in line arrays is the Faital Pro 3FE22 (I think) I'd build the arrays in 3 segments with 9 drivers in each segment. Basically, I'd wire the 16 ohm versions 3 series/3 parallel for 16 ohm segments and each box would be around 30 inches or 90 CM tall. Two of them would be 5 feet at 8 ohms and three boxes at 7.5 feet at 6 ohms. The Faital Pros are nice because they are designed to be used in arrays so have a rising response to lessen the amount of EQ required, neodymium magnets to cut weight to half a pound each, waterproof cones because rain/liquids happen and they are very efficient at 90dB or so each and handle real world 20 watts RMS above 160Hz. One segment at 16 ohms handles 180 watts which is not much but it is 16 ohms so the amp power gets cut in half. One segment would be good for small groups, two segments at 5 feet tall for medium groups with the impedance dropping to 8 ohms but the power handling doubling to 360 watts. For larger rooms/outside use I'd use 3 segments at 7.5 feet tall and power handling over 500 watts into the 6 ohm load (above 160 Hz) If you just had to have MORE output, build a forth segment to make it 10 feet tall, a 4 ohm load with power handling over 700 watts for outside use. A completely scalable system!

Cost? Well, the proper Faital Pro neodymium drivers run around $34 each so about $300 per segment. Since I'd always run at least 2 segments for any real PA work, that is $1,200 for four segments and $1,800 for six segments etc. Those segments must be placed on top of the subwoofers because they must be crossed over at 160Hz. If your subs are 30 inches tall or shorter, two segments will fit on the subs in normal 8 foot ceilings and three segments in rooms of 10 feet. Each segment would weigh less than 25 pounds, be around 6 or 7 inches wide and 30 inches tall--nice to carry around, fits in any car and won't hurt your back. If I had to do portable PA again, I'd build eight segments with the Faital Pro neo drivers, use a QSC full DSP four channel amp with adjustable limiters and EQ programs (EQ changes as you add more segments) and build 15" subwoofers with Neodymium drivers so I can run 2 to 4 subwoofers depending on how many segments and if they were to be used outside. Won't be cheap but it would sound good, be very flexible for different sized rooms, simple transport/setup, very durable and all in the 8 segments would run around $2,700 built with 1/2" baltic birch, coatings and metal grills, another $2,500 for four high output 15" subs and $1,800 for the four channel QSC DSP amp (625 watts X 4 channels) Basically, it would run $7,000 for the setup done right.

Now that you know--are you SURE this is what you want? For cost reasons, line arrays can be more expensive because you require EQ and subwoofers--this costs money. They also demand everyone that touches the system knows how to set it up properly and will do it right every time. They do work very well to limit floor/ceiling reflections (why I built mine) and can be scaled up or down by adding/removing segments so a good solution for church use in varying areas and requirements. Just be aware that when done properly, they are not inexpensive, they need EQ/subwoofers and there are acoustic rules that apply to line sources.

To learn more about line arrays, head over to DIY Audio as quite a few people have built them. Line arrays are not common on AVS but the DIY Audio people build all sorts of speaker designs because they can. Other things to read are generaly from professional sound companies like L'Acoustics, JBL, Meyer Sound and other professional venders. If you want to know what a bunch of full ranges made into arrays sound like, JBL has some using multiple 2" full ranges--you might be able to rent them from a pro sound rental place. I'd rent a few of them for a weekend, have your church folks get used to what they entail then make a decision. Be aware that since you opened your pie hole about building line arrays "to save money" , any cost overruns, any lack of anything will be blamed on YOU! When people don't fully understand the system, they tend to kill the messenger which is common when dealing with humans.

In summation, I'd really learn about line arrays completely, what they can do, what they can't do and go find a pair/rent a pair of those JBLs so the entire church learns by doing. If they want to go for it, at least they have a realistic concept of the project. If you desire them because they are low cost--they are not the low cost option. Here is an interesting build that worked very well...eventually! Enjoy the read, has plenty of links and chaos to gain understanding of line arrays issues/solutions when making line arrays with 25 full range drivers. Then you can know before staring at a crate of drivers and pondering what you just did. Enjoy!

https://www.diyaudio.com/forums/full...ine-array.html
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post #6 of 6 Old Yesterday, 02:16 PM - Thread Starter
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Quote:
Originally Posted by philpoe View Post
Do you have pictures of, or can you make a quick sketch of a floorplan of the presentation area?
Is the system for hearing a speaker present, or possibly for music also? If for speaking presentations mainly, does a portable PA systems not work?
I haven't been able to get in since the shutdown. From memory though it's about 90' long and 40' wide. Give or take, I used google maps and estimated where the entrance/exits were. It's a Cafeteria during the day with literally concrete everything. There's not a single sound absorbing panel anywhere on the walls- I don't know how anyone there does it.

It's mostly for speaking- Scout presentations, events, DJ'ing the kids as they get awards and running things.

We don't do music- much- the kids ... you don't want to hear them sing. Really


I just want to try and get the sound to the back without blowing out the people in the front, and making it as easy as possible for whomever comes after me is key. They do have a really nice 933mhz mic that is balanced out.
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