Building a cheap line array system

[chee]

I'd like to build a cheap(inexpensive) line array system. Can anyone talk about what my options might be? Cheap means no more than $1500 total for speakers, cabinet, crossover, and any other electronics I should do it with.

Chee

[Todd G.]

I'd like to build a cheap(inexpensive) line array system. Can anyone talk about what my options might be? Cheap means no more than $1500 total for speakers, cabinet, crossover, and any other electronics I should do it with.

Chee

If cheap is all that matters, you can do better than my suggestion, but here goes.......

Unless you have measuring equipment, getting the LA to sound it's best may be difficult, so the best answer may be to look up a pair of Jim Griffin's Linus arrays. Creative Sound may still offer a kit, as may Selah Audio. http://www.creativesound.ca/index.html

If you could stretch your budget to $2000, the Alpha LS kit from CSS is very nice, and is complete except for the wood.

If you must roll your own, look at the Dayton 5.25" Al driver (#295-330), or the NHT 5.25" buyouts found here http://home.comcast.net/~jhidley/. The NPT-11-081-1 would work well, and for $10 it's a good buy.

Match either to a line of Dayton Pt2c's (#275-085) or possibly Dayton ND20FB's (#275-035) and you should be covered on the driver side of things. You don't need a full line of tweeters, but I would go at least 4' in length and center it on your listening ear level.

For a crossover, either ask for a lot of help designing a passive, or go with a Behringer CX2310 and a good parametric EQ unit, or just go with a Behringer DCX2496 and kill two birds with one stone.

The cabinets shouldn't cost more than $100 in materials depending on finish, so you're likely to be somewhere between $1100 and $1300 for the finished project depending on your driver selection.

[mikec]

How about something like the KUZE3201 with the Tang Band 2"x3" driver for a little better bottom end?http://www.partsexpress.com/pe/showd...number=264-830

At under $25 each 32 of them would leave room in the budget for the Behringer DCX2496, some MDF and some seed money for a woofer.
________
Web shows

[Angaria]

second the dcx2496 suggestion - won't be that much more than a passive crossover and you can reuse it later. Plus bi-amping gives you another degree of control over the final sound.

[Pete Schumacher ®]

I'd like to build a cheap(inexpensive) line array system. Can anyone talk about what my options might be? Cheap means no more than $1500 total for speakers, cabinet, crossover, and any other electronics I should do it with.

Chee

Cheap? If you use a large line of Hi Vi B3N 3" woofers, you'll have the range from 100Hz to 3KHz covered nicely with very tight integration of all the mids. I second the notion of going with a line of ND20, either front or rear mount options, maybe even the ND16. Depending on your listening distance, you may not need more than 20 total. The closer you sit, the fewer you need. If you maintain a long line of domes, the closer you sit, the more the high end will droop in response due to combing issues. Of course, a little EQ in either a passive or active XO will take care of that issue. Fill in the bottom with a nice sub driver, driven actively.

If you don't want to use a sub, then you'll need larger midwoofs, but you'll have to cross lower, and then you may have an issue using dome tweets that small, having to resort to more expensive line source drivers, like ribbons, or the BG Neo8's.

Here's an example of how it may look, minus the line of tweeters.

[Andy_G]

Why not try 8 of these a side wired in 2 lots of 4 (or use 12 in 3 lots of 4, they are cheap enough)

http://www.madisound.com/catalog/pro...oducts_id=1757

use a single tweeter such as the Vifa Dx25
very simple for the cross over between mids and tweet.

then add some active bass using plate amps.

[marlboro]

60 Dayton ND20A's can be had in this bulk for about $3.50 each: $210(or about the same for Planar Pt2b's in the same length)

SAmmi's can still be found on the internet for about $6 each: $204 for 32( i saw a place tonight selling them and they had 90.)

A couple of good 12 inch woofers can be found for about $240 on PE or Madison or ebay

A Rane AC23A stereo electronic analog crossover cost $115 on the internet right now.

a preamp can be found for about $80.

a 60 watt/ch amp for the tweeters will run about $70

a 180 watt/ch power amp for the mid ranges can be found for about $150

a 300 watt/ch power amp can be found for up to $200.

You just have to research and wait for the right electronics to come along, and it will!

Now you have: the whole kit and caboodle speakers and electronics for about $1320 including shipping.

You can put together the cabinet in various ways for under $200 easy, I did.
(one very cheap way is to use PVC tubes and sonotubes with real wood facings for all the speakers)

Now you made your cost numbers. Email me if you have any questions.

Marlboro

[Todd G.]

You might try this guy on eBay too. He has Sammi drivers for $2.49, and a bunch of other 2-3" drivers in case lots that are inexpensive.

http://cgi.ebay.com/3-1-4-SAMMI-WOOF...742.m153.l1262

Also lots of tweeters like the Technics emit tweeter @ $249 per 100.

[marlboro]

If you use the ND20's, use the ones with flanges. You can cut these so that the c-to-c is just slightly above the 3/4 of the dome itself, so that comb filter distortion doesn't start until an almost inaudible 15Khz or so. if you don't move you won't hear it at all. You could probably make a 4-way, and cross again at 13khz, to a very high spl super tweeter and eliminate ALL comb filter distortion at all. I've thought of doing it. I have an additional 24 db/octave electronic crossover I could use to split the tweeter range:


Selenium ST350 Super Tweeter
Part Number 264-362
Price: $39.38 EA (1-3)

Very efficient super tweeter designed to be used in high-frequency sound reinforcement. Recommended for large rooms, clubs, auditorium, theaters, and any other environment requiring smooth, well-controlled high frequency response.

Specifications: *Power handling: 75 watts RMS/150 watts program (above 5,000 Hz) *Dispersion: 50° H x 50° V *VCdia: 1.6" *Impedance: 8 ohms *Frequency response: 2,500-20,000 Hz *SPL: 111 dB 1W/1m *Magnet weight: 16.5 oz. *Dimensions: 5.12" H x 4.76" W x 3.86" D. *Weight: 3.13 lbs.

[chee]

Thanks to everyone for all the answers to my question.

Now I have a little one for Marlboro. I noticed that you put all you midranges in separate enclosures, and they were tubes. Do you have any special reasons for doing that besides the obvious lightness?

Chee

[rickcraig]

Great woofers for a budget array. You could use a single line of the HiVi's (B3S) and a line of Dayton PT2C's. Another option is the RS150 which I've used with the PT2C and had good results.

[marlboro]

Chee,

As you might have guessed, I had more than the incredible lightness of speaker being as a reason for using individual tubes. So here are my reasons which I collected in the design process of the speaker.

This is an unusual design.

1. Unlike a box, as the pressure inside a cylinder increases, the walls of the tube become more rigid not less. As the pressure increases, the amount of flex of the tube itself actually get less. Its pure physics. So you can use thin wall PVC pipes, whose integrity actually gets stronger. With a tube such as PVC, there is no flexing and no having holes opening up in the sides of the enclosure. This also means the tubes don't tend to vibrate like a flat wall does.

2. Standing waves are a huge problem with the muddying of sound from box speakers. Standing waves require parallel flat surfaces. In a cylinder, there aren't any except for the end cap. BUT THE END CAP IS OFTEN many inches away from the speaker through an awful lot of fiberglass. Additionally sound in tubes doesn’t bounce back and forth against the walls, it travels down the tube. The physics of sounds in tubes is unusual. There is also a 3db loss per distance just like a near field.

3. The resonance of air column of a closed cylinder is measurable, but generally its four times the length of the column. So the frequency of the resonance of the tube is usually related to the length of the column. Mine are 23.5 inches long. This comes out to a resonance of about 144.25 hz.(http://hyperphysics.phy-astr.gsu.edu...clocol.html#c2, a formula online for determining the resonance of the air column in a closed tube. A recent doctoral dissertation showed that the speed through fibrous material is about the same as air.) My midranges cross generally at 165, so basic resonance is below the level of anything that the speaker puts out. But the tubes actually don't vibrate due to the rigidity of #1. And if they did, they would actually reinforce the low notes. And the vibration is minimal since each tube only carries 6.25% of the total mid range sound of the channel.

Another way you can do it is to arrange for the resonance to take place at about the lowest level that the speaker will be putting out: near the crossover. This will reinforce the bass. I have found this to be true and it does reinforce the bass at those frequencies. If I had made the tube length about 30 inches instead of 23, I could have obtained reinforcing resonance at about 122.

If the tubes were 56 inches long I would get a resonance at about 65 hz. However, the mid range speakers do need to go low enough without distortion to benefit from this. Mine don’t go that low.

4. Fiberglass is the best sound absorber; Vance Dickenson had research to prove it . Sound doesn't really get absorbed, it gets converted to heat. Fiberglass is better at absorbing heat than the other kinds of insulation. Additionally, the degree to which the sound is absorbed by fiberglass is measured by the inches of insulation that the sound waves have to go through to reach the "end of the enclosure" before starting back. The attenuation is on the order of .90 per four inches(using 4 lb. per cu ft density.) Since my tubes are 23 inches to the back, not your normal 4-5 inches of a standard square or rectangular box enclosure, the attenuation of the absorption is better than 98%---a lot better. My tubes are 289 cu inches. There are 1728 cu inches in a cubic foot. This is 0.16 of a cu ft, or of 4 lb. So the amount of fiberglass that needs to be in each of my tubes is about 8 oz. I wrapped the fiberglass in polyfil batting to protect the speakers from stray strands of fiberglas, and due to the shape of the cylinder pushed the insulation in very tightly.

After much reading, I came to the conclusion that the biggest issue with midrange speakers is coloration of the sound caused by sound returning back through the speaker cone milli-seconds later than the directed output. The combination of high density fiberglass(but still allowing sound to travel through it, length of travel, etc, reduced the return sound coloration to less than 2% rather than the much higher number in non-long-tube enclosures.

And….. the coloration that does come through is only of the odd ordered harmonic variety(increasing clarity), and only comes from the speaker that emanated it in the first place, not 15 other speakers of varying speaker coloration in a giant gloppo of indifferentiated sound wash.

5. Tubes have the unusual characteristic of eliminating the even order harmonic energy because of the physics of sound in a closed cylinder. This means that half of the additional harmonic energy beyond the fundamental tones created by the speaker into the cabinet never appears at all. What is left is odd ordered harmonics, which at high distortion levels are not pleasant(but array speakers never get to distortion levels when the speakers are only carrying something like 6.25% of the total midrange sound). Additionally there is some suggestion that odd ordered harmonic energy is more heat producing than even ordered harmonics. But the small amount of harmonics that do get back out the speaker in the front, if any, will actually increase the clarity of the speakers. I've noticed that too. My mid ranges actually seem to have greater clarity as they are pushed up in sound volume.

6. Using individual tubes for each of the midranges adds lots of complexity to the project, but the isolation of each speaker does wonders for the total clarity of the system.

7. Because it is a closed tube, you can actually calculate the exact resonance of the tube and also its harmonics(which of course are only the F3, f5, f7, etc. which is 50 – 60 db down from the fundamental.) A 23 inch tube has a fundamental of 145hz and F3 of 435,, and a F5 of 740. The fundamental will actually reinforce the upper bass of the small speaker, and actually allow a lower crossover to about 144 or so.

8. The whole speaker is much lighter. When you are talking about moving around a speaker that is 7 feet high by 8 inches wide by 23 inches deep, all that MDF might weigh 400 lbs. That’s an awful lot of weight to be carrying around or pushing around for a man of my advanced age!

Marlboro

[chee]

Marlboro,

That seems like an enormous amount of work, all those tubes, all those amplification stuff. I like the smaller lighter footprint of the picture that Pete Schumacher posted. Can I get pretty much the same quality as yours without using the tubes? My sig other doesn't like the tube motif.

Chee

[marlboro]

Chee,

I'd really like to say that you can make any modifications that you want and everything will be the same.

Unfortunately, line arrays are not terribly forgiving. You have to read Jim Griffin's white paper, and then you need to follow it to the letter if you want to make any mods. There is some guy out in California who used domes but didn't modify the flanges and complains that the system has a severe lack of "air".

My own system was heavily designed prior to any building. I see it as an integrated whole which if parts are not used then I have no idea how the end result will sound. It was designed to be inexpensive in materials as I've described above, but the building was complicated and time consuming and ultimately expensive.

Good luck though. You may find your own formula that works just as well for you. There is more than one way to skin a cat.

Marlboro

[Soupy]

Hi Marlboro -

I've looked at your system at other forums a few times and personally like it but my Wife also doesn't like the look. This is the 1st time I've seen you explain the 'whys' and I'm impressed. I played with something similiar a little over a year ago prior to seeing yours simply because I was messing with PVC as an inexpensive building material and experimenting with NSB's. I just glued 9 tubes together, 6" long each. Sounded pretty decent with some cheap tweets.

I've done just some quick reading on info you provided and not sure I'm totally understanding concept regards heat.

For WAF I'm wondering if using the tubes as you did but encasing such in box would enhance or defeat the purpose? I'm seeing positives regards bi-polar effects but negatives regards EQ? Am I expressing my concerns properly?

Soupy

[marlboro]

Soupy,

Not sure I understand your whole question.

In regards to using fiberglass over holofill because its better at absorbing heat, its probably a hair splitter, but is at least one reason why Vance Dickenson found it to be better pound per pound. As to heat build up, a) the mids don't put out enough sound to be converted that can't be dissipated in the PVC and then the outside air(since PVC is only 1/8 inch thick), b) lack of dissipation only raises the resonance of air column which for my crossover might help though its not by much(not more than one hz at the outside), and c) when the speakers only put out 0.0625 of the total sound, its only a fine tune.

I'm not sure what you are talking about with EQ. Could you be more specific?

Marlboro

[marlboro]

Soupy,

You could cover the tubes with Fabric or some interesting 1/4 inch fine wood ply.

Marlboro

[marlboro]

Vibration and RESONANCE in cabinets

I've been exploring the concepts of vibration and resonance in speaker cabinets for more than two years. Its not a well defined subject in the research. Most people figure that you just build a box, stuff it with fiberglass and let it go. Or don't.

It seems to me that there are four kinds of subjects to talk about: Vibration, Resonance, sound energy storage, and the movement of sound waves within the cabinet itself.

Vibration doesn't really matter as its nonspecific. There will be vibration. We damp it by filling the cabinet with insulation, with damping materials on the sides, with thick materials. But the sound has to go somewhere. It doesn't evaporate; the second law of thermodynamics must be maintained. Some of it can be converted to heat energy in the stuffing, and fiberglass does a better job of this than other stuffing materials. If the material of the cabinet is thick enough it will get absorbed into the material, but this also presents its own problem which is energy storage. The capacitive storage of MDF is not all that great, so storage with release back into the inside of the cabinet can be an issue.

The two more important are resonance and sound wave movement. Resonance is when the cabinet vibrates in oscillation to a certain frequency. Sound movement is whether the sound waves just immediate bounce in all directions inside the cabinet or whether they move in a wave to the back of the cabinet. Resonance has two components, the basic resonance of the air column in the box which can be measured mathematically, and the basic resonance of the material itself which can be measured with a device that is also used for tuning strings on a harp. Additionally resonance has the fundamental tone, and the harmonics which also need to be addressed. You can damp these, but it helps to have the frequency range of the speaker be outside the fundamental. Sound movement is whether the sound moves in a direction toward the back of the cabinet or just immediately bounces in all directions.

In my opinion, these subjects are most impactive with the midrange speakers.

ALL OF THIS AFFECT THE CONE OF THE SPEAKER. SOUND FROM INSIDE THE BOX HAS TWO IMPACTS ON THE SOUND OUTSIDE THE BOX:

1. Interior sound is 180 out of phase with what is going out and if it then comes back out of the box through the cone it will cancel those frequencies that it is out of phase with. This can cause serious muddying of the sound quality.

2. The harmonics of the sounds cause vibrations in the cabinet itself which can serve to add cancellations

3. The harmonics themselves have different impacts on the sound as it goes through the front of the speaker irregardless of their cancellation effects, and these can be addressed.


Second comment:

So what are the issues:

A. The over-riding issue is to limit the amount of sound that returns through the speaker from the back.
B. The second issue is to use the sound that does return through the speaker, if any, in a re-inforcing way.

Let’s start with “A”, how can this be done.

There are a number of issues that have to be considered: Vibration, resonance, sound wave propagation, sound storage, and sound volume. All of these need to be addressed if success is to be reached. Of course eliminating the box altogether is an option and opening the speakers into an open huge quiet anechoic chamber might be an option. Teleported sound?

Vibration: There WILL BE vibrations at all frequencies that are specified by the crossover.
1. Limiting the frequencies by crossover could help.
2. Stuffing the box intensely with fiberglas might also help(if it’s a closed box design).
3. Making the speaker play quieter, by using multiple speakers in separate enclosures will also reduce the vibration by lowering the total volume of sound produced.

4. You can use a cabinet material that is sufficiently thick and sufficiently dense(but not too dense), that it absorbs the vibrations.

5. You can use a cabinet material that is sufficiently thin that it radiates the vibrations into another cavity that is either not directly connected to the room that the speaker is in or that is delayed sufficiently so that the human brain doesn’t hear it, and in such a way that they are not beamed, but are radiated in all directions.

I suggest that four out of five of these are used with every speaker.

Resonance: THERE WILL BE RESONANCE. So it needs to be measured and addressed. Resonance is an oscillating vibration that increases in amplitude, and is affected at certain frequencies. At high levels it causes feedback and could even shake the cabinet seams apart. There are two kinds.

One is the basic resonance of the cabinet itself after whatever stuffing and/or vibration absorbing materials have been put in or on. This can be measured by tapping the cabinet with a mallet and measuring the tone produced. The second is the resonance frequency of the column of air inside the cabinet itself. This can be measured by mathematical formula. A sub area of this the harmonic subtones of the fundamental and their characteristics on the music. These may also need to be addressed or mitigated in some way.

For example, you determine the two kinds of resonance for your midrange speaker. For example, the cabinet resonance is tested empirically and found to be at 79hz. The harmonics of this will be 2nd: 158, 3rd: 237, 4th: 316, 5th: 395. After 395hz, they are likely to be so far down that only sensitive instruments will pick them up.

You also calculate the air column to oscillate at 144hz. The 2nd of this is: 288, the 3rd is 532, the third is 676, the 4th is 820, and the 5th is 964.

Resonance can also be affected by standing wave patterns which are augmented by parallel sides where the sound is not impeded from bouncing back and forth. Visual feedback of this would be parallel mirrors producing multiple reflections until you can’t see any reality at all.

So what can you do? You want to limit resonance in your speaker cabinet as much as possible.

1. Increasing the damping materials will lower the resonance of the cabinet materials itself. Putting some kind of absorbent rubber like coating on the inside and increasing the density of the fiberglass or pillowfill will deepen the cabinet resonance to a level where the size of the frequency is too big to fit inside the cabinet even in quarter wave. In the case above, the 79hz frequency fundamental is 171 inches long---too big to fit inside the speaker cabinet, and the _ wave is only 42 inches, still too big. So this is not an issue. The harmonics are likely to be so low in sound that they wouldn’t play an issue.

The 144hz air column resonance is something else. A 144hz frequency is actually 94 inches long, but the _ wave is 23 which still impacts if the cabinet is 23 inches long. Air column is less affected by the stuffing, but increased stuffing will decrease the volume of air moving in the column and thus reduce this kind of resonance.

2. Limiting the frequencies by crossover could help.
Simply make sure that the crossover is higher than the fundamental of the resonance.

3. Making the speaker play quieter, by using multiple speakers in separate enclosures will also reduce the resonance by lowering the total volume of sound produced.





Part 3:
SOUND ENERGY PRESSURE AND STORAGE

This might be getting into the splitting of hairs category. But it depends on the volume level, and anything which decreases the sound that is inside the cabinet going back out again is important in my book.

I believe that you have two ways of addressing this. Either make the cabinetry so heavy duty that there is lots of extra storage density and that its slow leak outside into either the woofer cavity or into the air cavity is miniscule, or light enough so that there is no storage. The second part of that is dealing with sound energy pressure so that the seams of the box don’t come apart.

SOUND WAVE MOVEMENT

The last is how the sound waves move in the cabinet. If the cabinet is shallow, then the sound will move away in all directions, and the insulation that you use to deal with vibration and resonance will be less effective. If the cabinet is a long and deep rectangle, the sound will tend to move through the insulation, attenuating the sound.

[Soupy]

Marlboro -

Wow!!! Hadn't had time to collect my thoughts to respond and you have all this!

Thanks - this will make it easier for me to re-pen my concerns.

Give me a day, I'm behind at work as usual.

Soupy

[Soupy]

Todd G -

I guess 101 World is no longer a secret.

He has some excellent deals and I've bought a whole bunch of stuff from him but you need to be careful - a few are losers. I would not recommend the Sammi 4.5" cast mid range, better drivers than that right here for same money despite nice basket.

Soupy