My head hurts - please help me out on this unusual project

I have an unusual project that I need some advice on.

My requirements in order of importance:

1. Cheap. Under $40 per cabinet not including building materials (wood, paint, glue etc). I may be able to stretch this if the bang-for-buck ratio is high. As I will be paying for this out of my own pocket, the cheaper, the better.
2. Size. Not too large. Around 2 ft3 or less Smaller is better.
3. Impedance. Cabinet impedance needs to be around 2ohm at the speaker terminals. I will be connecting 2 cabinets in series to each channel of the amp for a 4ohm load at the amp.
4. Low end range. I'd like these to play as low as possible given the above requirements. There will not be any kind of sub to round out the bottom end unless it can be incorporated into the cabinet itself.
5. SPL. Background noise is rather noisy so these need to play relatively loud. I have about 150watts (4ohm) per channel (x5) to be shared by the 2 cabinets on each channel.

In a nutshell:

I work in an automobile assembly plant (the Nissan plant in Smyrna, TN). Nissan has installed a "stereo system" on the assembly line to provide us with music during our shifts. this system consists of an AV receiver and 10 "speakers". The speakers are low end, factory 6x9 (2ohm) full range in a tiny box hanging from the rafters above the line and spaced about 20 ft apart. All of this is wired up with hundreds of feet of 16ga speaker wire. This setup just won't cut it.

I am in the process of trying to figure out what the best option is for replacing the speakers. I had originally planned on just grabbing 5 pair of JBL GTO938s (2ohm 6x9 3-ways) and putting them in some prebuilt 6x9 boxes. The thing is, most 6x9s do not like to be put in a box. They are designed to use an automobile trunk as a box, not some .75 ft3 sealed job. This was going to be about $90 per pair for the speakers and boxes. Total cost: $540

I started thinking that I bet I could build something cheaper that sounded better so I started digging. I've spent every spare moment trying to find a proven design that I could follow but I have come up short. Most of the designs are too expensive or use NLA drivers. I came across the Cabrini and the Stentorian and that got me thinking that if I could somehow merge the two designs, I might really have something. Then I saw that PE has a buyout 6.5" for $4! WOW! How about a couple of those and a piezo horn? I might have something...

I'm in the process of trying to model something along those lines but I wanted to get some input from the community before I head in that direction.

Can anyone think of a proven design that would meet or come close to meeting my criteria? If not, Does anyone have any ideas of which direction I should head? I've looked into 2-ways, 3-ways, MTMs, full range (single speakers and line arrays), horns, TLs, and too many other designs to remember.

My head is spinning and I need one of you guys to make it stop and focus...

This is what I have bought so far for hands on testing:

Woofers:

1 x http://www.parts-express.com/pe/showdetl.cfm?partnumber=295-025
This is my top of the budget woofer. I got this to see what investing in a more expensive driver would get me. 1 per box. 1.1ft³, vented, 48hz f3.

4 x http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-609
I'm heavily leaning toward these just because they are so cheap. 2 per box & I'm still under $10! 2ft³, sealed, 52hz f3.

2x http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-004
I got these to mess around with when I thought I needed to stay above a 6ohm load on each amp channel. That changed. 2 per box, 2ft³, vented, 52hz f3 +/-.

I'm also considering these:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=290-272
These are cheap and look to play pretty low. 2 per box, 1.5ft³, vented, 45hz f3.

http://www.apexjr.com/speakerstuff.html
The 8" NHT woofers at the top of the page. Specs look good but I'd only be able to use 1 per box to get my 4ohm load at the amp. I like that these will work in a smaller box. 1 per box, 0.5-1ft³, vented, around 50hz f3

Tweeters:

I'm looking at using piezo horns. Mostly because of the efficiency and lack of crossover needed. Plus they enable me to only have to worry about the impedance of the woofers when trying to get to my needed 2ohm per cabinet.

2 x http://www.parts-express.com/pe/showdetl.cfm?Partnumber=280-062
I chose these because of the frequency range (down to 1800hz). 1 per box.

Does anyone have any ideas on other designs or drivers that I should be looking at? This does not have to be audiophile quality. It's relatively loud in there and everyone is required to wear earplugs (but no one pushes them all the way in). I'm mostly looking for a fuller, wider range with decent low end extension than what those 6x9s are providing. I'm also TRYING to get by without a crossover. Or, at least a very simple one. I know I'll probably have to put an Lpad on the tweets to attenuate them but if I can get by running the woofers without a XO that would be ideal as far as $$$ goes.

Lastly, these cabinets will be strapped to overhead steel beams above the assembly line pointing down. They'll be about 8 to 10 ft over everyone's head and off axis response needs to be pretty good.

Thanks for getting through this long post and I'm looking forward to your advice.


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Thanks for mentioning the Econowaves. I hadn't seen them before and that has given me some ideas. I like the use of the horn/waveguide. That would give me the sound I need from multiple angles. Goldwood makes a version of the tweeter I had chosen with threads to screw into the back of a horn. I'm thinking the Selenium 60x40 might work.

http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=264-308&scqty=1
http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=270-069&scqty=1

Or maybe
http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=292-450&scqty=1


I did run across that page on piezo crossovers early on and had planned on trying out some of his suggestions.

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Some clarification.

This is a totally open space. The floor is about 15 feet down from where the speakers will be. The ceiling is another 30 ft up from the speaker location. There is one wall about 250 - 300 ft away. The speakers will be pointing directly down with no obstructions until the floor (except for the cars going down the line). They'll be spaced about 20 - 30 ft apart. 10 speakers strung out in a straight line with about 250 ft between the end speakers.

I understand what you're getting at regarding the line array but with the ambient noise level (70-80db), I really don't think reflections & timing issues will be too much of a problem. As it is now, wherever you are in the zone, you can only really hear the output of one speaker. There are actually small dead zones in between that I hope to eliminate by going from our current 8 speakers to 10 and spacing them more evenly.

I didn't set this up. If I had I would have definitely gone with a 70v system. They installed all of this while the plant was shut down and I came back to this setup. Actually whomever wired it all up wired every 2ohm speaker in parallel to 2 channels. We had 4 on each channel in our zone but in other areas they had 6 or even 8 speakers on each channel. As soon as I saw this I told them it wouldn't work and that the amps would fry (home theater receivers rated for 8ohm loads). I went around with a dmm and the amps were seeing loads down to 1.5ohms DC resistance even with the large series resistance from the hundreds of feet of 16ga wire factored in. Needless to say, the receivers didn't last long. The first one blew in 30min and there were a couple still going after a couple of days when they finally took my advice and turned them all off. There were a couple that even started smoking!

That's when they came back to me and asked me to fix it. I spent 3 weekends rewiring everything in series and separating them to multiple channels. Now I'm itching to get to the next step and make some sawdust...!

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Inductor said:

Selenium HM17-25 1" Bi-Radial
This horn (nice looking horn, I have one) might give you problems when making the box/enclosure for sealing the box. It doesn't have the outer contour tight enough, not having a flat surface. I would second try and test this one as second choice... having in account the price.
PRV Audio WG 60-25 90x50 ABS
Other links:
Zilch's AK Design Collaborative - Econowave Speaker - AudioKarma.org Home Audio Stereo Discussion Forums
Harper
Red Spade Audio: B&C 8PS21 pro high sensitivity 8" midwoofer
Red Spade Audio: 8" waveguide surrounds

Click to expand...

Thanks. I'll throw one in my cart to play with and compare. I have a few different styles coming to test out including a couple of the jbl ones from the Econowave design. I really can't afford the $50 compression drivers though. I'll have to get by with the piezo drivers or maybe try a cheap Pyle compression driver. I'm learning more and more every day and I'm confident I can make this work. It's just a matter of where I want to make my compromises to stay within budget...

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