I want to build a line array...

[Znyper]

Hi guys,

I need some input on this PA (!) system...

The specs:
* The people I will play for will all be dancing, which means they will all stand up.
* The room is ~12 m (l) x 9 m (w) x 6 m (h) (approx 36' x 27' x 18')
* If the people in the back get a little worse sound, I can live with it, but the first 8 m should be really good.
* Stereo imaging is not an issue. At all.
* Good room-filling sound is important
* Getting the same sound pressure level at all points in the room is desirable.
* Playing loud is good, but not ear-bleedingly loud. It's not a rock concert...

My thoughts;
To build a line array at least 2-2,5 meters (approx 6'-7,5') tall. I am thinking of building the array using HiVi B3S's. I have already tested a Bose L1 system (which is also a line array) in this room with good reults. I do think the comb filtering on that system is a bit too much, since the room is >10 meters long. And the Bose is waaay to expensive for my taste...

So: My questions:
* This system will be playing mp3's, which are a bit of "frequency degraded" on the top end by nature. You think I will need tweeters on this system?
* Anyone already tried this with these drivers? Results?
* Does anyone have calculations ready for box size and so on?
* Since I want as wide horizontal dispersion pattern, I should make the front baffle as narrow as possible, right? Does it matter?

Many questions, but I hope anyone can please get me some more input on any of them?

Super thanks in advance,
Marcus Lindfors, Sweden

Link to the Bose system

[Znyper]

One day and 55 views later...

Anyone...? Please?

[Cal Weldon]

Hi Marcus,

It may be that others are interested in the project but not able to help.

Is there a specific reason you wish to have a line array? Is it a space issue?

The HiVi is anything but a PA driver. You will need a bunch of them just to get the power handling and sensitivity. You will also need a rather healthy amplifier. I certainly would not recommend them unless there is a reason.

What do you have in mind for the bass?

Is there a reason you can't use a tried and true 15" 2 way?

[Piek]

Hi,

how about this one: twentyfive

regards, Micha

[Znyper]

Thanks for getting back to me!

Originally posted by Cal Weldon
Is there a specific reason you wish to have a line array? Is it a space issue?

Nope. Not at all. I just like the way line arrays seem distribute the sound across the room. We use a pair of 12" + horns today, but the sound is very directed, which means the dancers in the front complain about "too loud" and the ones in the middle says "too soft", while the ones in the back, _near the corners_ agrees with "too loud" beacuse they are right where these speakers a pointing... Also, the speakers need replacing anyhow.

The HiVi is anything but a PA driver. You will need a bunch of them just to get the power handling and sensitivity. You will also need a rather healthy amplifier. I certainly would not recommend them unless there is a reason.

Reason as above.. And since the Bose systems does it with ~3-3,5" drivers, (plus sub of course) why shouldn't I try myself? And even if i fill this box with B3S's (24-30 pcs) and feed it with a monster amp, it's still a lot cheaper than the Bose system. Since stereo imaging isn't an issue, I could do with just one (mono) array. And the Bose is just one array also...

What do you have in mind for the bass?

Haven't got around to this yet. I have a few ideas, but IMHO building bass boxes isn't quite as sophisticated... =)

I was thinking of XO'ing the arrays hard @ about 250-300hz roughly (or wherever it sounds right), but the lower bass sound isn't as hard to distribute as the mids & highs.

If anyone has another idea on how to distribute the sound (without adding echoes using a lot of point sources), I promise you I am all ears !

[MaVo]

perhaps the following forums are more specific for your problem...

http://www.prosoundweb.com/forums/
http://www.speakerplans.com/forum/

i have no clue about pro audio, but i would assume that even 30 b3s wont get you in the spl levels that are necessary. because of the necessary distance they wont give you a +3db for every doubling of driver count. instead of this, you get cancellations, thus the line array effect.

line arrays are for situations where there is a long distance in front of the speakers. here their -3db for distance doubling instead of -6db is good. in your room i doubt a line array is a proper solution.

to get sound equally to all people, i would put the boxes as high as i can, so that sound comes from above and no poeple get in the way and absorb the direct radiation. then i would use horns, since they are fun. at least such a setup was in nearly every disco i was in so far. well, they all sounded bad too.

you could put one mono stack in the middle of the room, above the peoples heads, that radiates omnidirectional, here you have the smalles distance between source and listener. or you put 4 boxes in the rooms corners. directing them into the middle.

(edit for evil words)

[Brett]

I'd just build a high quality 3 way PA box. A pair of them with 500W/ch will easily fill this space.

[el`Ol]

With a 4m high midbass array everyone is in the far field (-6dB at double distance) for the highest frequency and everyone is in the near field (-3dB at double distance) for the lowest frequency. And if you want to have everyone in the far field (assumed nobody is closer than 2m) the array is just 80cm long. The tweeter array would be 25cm long, which is nonsense because of too low vertical dispersion.
You can either use curved arrays (with a lot of math) or use two coaxials as ceiling speakers. This works well because the room is very high compared to the length.

[idaho]

Do some reading around here and or ask your questions here.

http://audioroundtable.com/ArraySpeakers/

[Znyper]

Wow! That's a lot of info... =)

So I'll just try to reply to everyone's input on this matter!

MaVo:
1. I will check those sites out as soon as I can.
2. The active surface radiating sound with the 30 pcs array is ~360 sq.cm. One pair of 15" is ~120 sq.cm. I haven't done any calculations on power req and sensitivity, but I don't really see why it can't be done? And the array will be backed up in the low end with subs. It will not be playing lower than approx. 250 Hz (or wherever the finished speaker sounds right). This will create a "virtual height" of approx. 4,6 meters tall. (2,3 m plus floor reflections)
3. The distance between the array and the people in he front can easibly be made at least 2 meters if far field is desirable. Which I guess it's not, though.
4. The speaker setups you proposed is IMHO not very desirable.
a) Using speakers in the ceiling could work, but will sound a bit funny when (for example) I speak into the system and the sound comes from above. I will consider it, though!
b) The "4 in the corners" approach is simply not usable, since the beat they're dancing to will be echoed & sent from mutliple locatons, confusing them when the actual beat is.
5. I will look into a horn design as you recommend it, but as you wrote:

at least such a setup was in nearly every disco i was in so far. well, they all sounded bad too.

I couldn't agree more... And also; I don't need to play that loud. The sound should be clear and distinct, monster low-end bass is actually a bad thing in this case as it sometimes blurs out the actual beat.

Brett:
Yes, I know. But there is still that directivity issue. It would be a lot easier if I was planning a rock concert where the most eager fans are in the front and not very concerned about hearing loss if you know what I mean?

el`Ol:

With a 4m high midbass array everyone is in the far field (-6dB at double distance) for the highest frequency and everyone is in the near field (-3dB at double distance) for the lowest frequency.

Which suggests I should use tweeters, then? To keep everyone in the near field as far up in freq as possible.

Btw: The last octave (10 KHz-20 KHz) is not really an issue either, since I use mp3's. I don't think there will be much info left "up there"

I am also thinking of the Bose system... Please look at the link provided in my first post. It actually does work in this room. I have tried it out and I think it distributed the sound really really good, except for what I believe is comb filtering after ~7-8 m and back. That is the only reason I got interested in this design at all.

And again: Thank you sooo much for helping me out!! I really appreciate it!