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Multi-Way Conventional loudspeakers with crossovers

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Old 4th June 2012, 11:40 PM   #1
kctess5 is offline kctess5  United States
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Default Senior Project Build Thread

Next semester I will be building my school a pretty large sound system for our football field and I thought I might as well document it here. I have another thread about this here but that was more for design

Although I will not actually start building until summer is over I've already planned the whole thing and started the ball rolling. I've got a little time so I might as well give a bit of background.

My school tends to go through sound systems, we have destroyed two since I was a freshman, I attribute this to not spending enough for adequate hardware and then putting high schoolers in charge of it who want to play it louder than it was built for.

I have been given a $5500 budget to build a system, and by my initial estimates I will be able to build a system to rival much more expensive systems, in the range of $15000.

The plan is this:
4 Bill Fitz DR250
4 C/E/X PA Flat to 30 (FT30) PA TH Awesomeness Bass horns
A bunch of Crown XLS 1000 DriveCore Series Power Amplifier Flexible for Any Pro Audio Amplification Need 245-500
One of dbx DriveRack PA+ Complete Loudspeaker Management System 246-171 to work everything
A few power conditioners, maybe a limiter, some other small stuff...
Some sort of control board, haven't decided which one yet

I am going with the BFM tops mainly because I am unfamiliar with that sort of design where directionality is a concern etc. I ordered and received the plans today, so I will go through all of that and see whats crackin. I am planning on not building the crossover as that will add unneeded cost when I am already buying the driverack, also it's simpler.

The subs I am more familiar with so I'm okay with doing some more improvising, designing, and using a relatively untested design (I think 2 or so have been made).

I need to go through and see where I can save a bit of money because my original budget came out to almost exactly $5000, and that didn't include the wires or the control board. I think I can handle that though because I got an excellent quote on baltic birch ($67/ 4x8 sheet) which is less than I budgeted, and also I am using the $300 18TBX100, which I might be able to replace with a slightly cheaper model. Also I am hoping to work with parts express to get reduced pricing for the large order considering its for a school, but thats not a guarantee.

I calculate that going pretty much full tilt the system should be able to average between 135 and 140 dB at 1 meter all the way down to 35 or so Hz. That's plenty powerful for my school, and the design is such that half the system will be able to be easily used for smaller venues, such as gym dances. One of my main concerns will be just making sure that the ASB is able to set it up and use the system correctly without wrecking anything.

I will have two periods free (either 4 hours every other day or 2 hours a day) to work on this system, for a semester. Sadly it will not be ready for the end of our football season, which is its primary intended purpose. It's main debut will be at my graduation, which is somewhat poetic This is going to a pretty awesome thing for me to put on my resume, also it will be helpful for future sales, having such a large system under my belt. People are often skeptical of buying speakers from me because I am 17 but they generally change their minds when they hear the things I've made, so it will be great marketing to the DJ crowd I know.

Over the summer I will be putting the finishing touches on my design and then I will start posting build pictures basically as soon as school starts again.

Questions, comments, concerns welcome
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Old 5th June 2012, 12:32 AM   #2
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you need limiters hidden somewhere in the amp rack so that users can't fiddle with them
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 5th June 2012, 01:02 AM   #3
kctess5 is offline kctess5  United States
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The driverack has a built in compressor/limiter that I can use to limit signal level, that won't prevent people from turning up the amps but they would have to individually turn every one up and then retune the system to match levels. I'm not giving them the ability to turn at least the subs all the way up, the amps will only give them around 300 watts each with a rated RMS of 1000w. That should at least protect the drivers, not so much peoples hearing though as that will still give over 135dB... At least if people hot swap plugs or accidentally turn it on with the volume all the way up the speakers won't go.
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Old 5th June 2012, 02:01 AM   #4
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put the amps in a rack with a locking door. Also what is the purpose of the power conditioners? is mains power that poor in the US?
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Old 5th June 2012, 03:21 AM   #5
kctess5 is offline kctess5  United States
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Originally Posted by kipman725 View Post
put the amps in a rack with a locking door. Also what is the purpose of the power conditioners? is mains power that poor in the US?
I just thought it would be handy to have power distribution consolidated so I don't have power wires everywhere, and it would provide one more line of defense agains surges. Our power mains are generally pretty good though.

I suppose I could use just fused power strips instead, what do you think?
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Old 5th June 2012, 04:25 AM   #6
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Originally Posted by kipman725 View Post
put the amps in a rack with a locking door. Also what is the purpose of the power conditioners? is mains power that poor in the US?
Have you not heard about some of our failed execution attempts?

Not good...
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Old 5th June 2012, 04:56 AM   #7
qusp is offline qusp  Australia
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^^ I tried so hard not to laugh, but.....

OP: Crown? really?
also getting rid of the crossover is all well and good, but if something goes pearshaped the drivers will see the full brunt of any DC error. love the idea of the bass horns though

Last edited by qusp; 5th June 2012 at 05:00 AM.
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Old 5th June 2012, 06:18 AM   #8
kctess5 is offline kctess5  United States
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^^ I tried so hard not to laugh, but.....

OP: Crown? really?
also getting rid of the crossover is all well and good, but if something goes pearshaped the drivers will see the full brunt of any DC error. love the idea of the bass horns though
Whats wrong with the crowns? I'm under the impression that those are excellent amplifiers.

In regards to the drivers getting fried by something wrong with the amps I am setting the system up to minimize this. The main thing I could see happening would be the Crown amp for the 10" midranges being plugged into the compression horns and killing them. I am designing the wiring scheme such that that would be basically impossible without going and getting several adapters first.

Another thing that could happen I guess would be the XO point on the drive rack being set way too low, but I can just not do that, and once I'm done setting up that part of the system its going to be locked up pretty tight

Also even if the crowns were for whatever reason to fail fully on the subs at least could handle it
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Old 5th September 2012, 05:11 PM   #9
kctess5 is offline kctess5  United States
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Alright ladies and gentlemen, it's almost that time.

School is back in session, and my purchase orders finally went through. I am expecting 400lbs of gear from Parts Express friday, and about that much lumber from the local hardwood store in about an hour.

I will post pictures of the supplies as they arrive, but for now, a few of my toys.

The table saw I get to use is a StopSaw, so there's little worry about getting killed or anything. One of my favorite things about it is that it has measurements in mm and in for the gate, which will be awesome for my metric cut sheets. It's going to be a dream to use, except that my engineering teacher insists that she be there whenever I am using it. Considering that I have been using a saw since middle school, and its the safest saw in the world, that's pretty annoying.

The other toys I should be able to use on my own. We have a couple of scroll saws, some sanders, drill press, chop saw, and a bunch of handheld tools. There is also a CNC but it's out of commission I will also be bringing in my own pneumatic brad nailer to hold everything together until the glue dries.

I should start making saw dust very soon, hopefully this week. I have my work cut out for me
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Old 5th September 2012, 09:04 PM   #10
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Originally Posted by kipman725 View Post
Also what is the purpose of the power conditioners? is mains power that poor in the US?
I have a friend who has a friend...

But seriously, this guy has been hired to do sound for some really big name acts, and he attributes much of his commercial success to his use of power conditioners. Yes, the US grid is less than wonderful. But more importantly, enforcement of noise suppression on equipment is extremely lax. In a football stadium, I can see all sorts of things being plugged in that would create noise, from popcorn machines and drink coolers to computers and radio/video transmitters.
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