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Old 19th September 2006, 08:30 PM   #1
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Question Basic PA speaker rules

Hello,

this is my first post in these forums. Im a hifi nerd that always belived building my own speakers was the way to go, I built a few but never really understood what I was doing. Somehow they turned out alright anyway but that was mostly luck I guess.

For my next project I need to get it done the right way, and for that I need some input. I know how to build & calculate a box, how to put together a crossover and make it all work, but Im lacking some practical basic knowledge.

The Project is this:
A pair of fullrange speakers mostly intended for outdoor use, playing disco style music. Power rating of atleast 800 w rms, capable of 125-130 dB max sound level. What Im looking at is either a dual 15" + a 2" horn, or single 18" + 2" horn, or single 18" + 10" + 1".

Some say that drivers of certain sizes either have or lack the right "punch". In dance music you have the drumbeat at one frequency rance and the bass at another. What Im hearing is that a 15" driver might be right for the drumbeat and bad at the bass, while its the opposite for an 18" driver. Is this true? If I look at frequenzy sheets for different 15" and 18" drivers you could acheive similar results, paper-wise.
Or is this this due to the Qts? At loudspeakerplus there is a table on wich Qts values are good for wich applications.

If anyone have any answers, or can tell me where to go look for information, please let me know.

regards
Daniel
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Old 19th September 2006, 08:41 PM   #2
Variac is offline Variac  United States
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You're in luck I think. Another thread just started that is about this topic:

WINISD beta

I t would be best if you posted there with the above info, and maybe we could delete this thread
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Old 19th September 2006, 09:21 PM   #3
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You won't get that sort of dB level outside with that little power. Close up maybe.

Punch has more to do with good box design than speaker size. I don't use anything larger than a 15" driver (boxes get too big for my liking) and you can get nice low bass with punch that will kick your head in given enough power and a small enough room.

1x15" 1x10" 1x1" per side should do you quite well. Don't get hung up on inches But you WILL need to go active for the bass.

18+2 or 15+2 will sound pretty dire off axis or far away.
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Old 19th September 2006, 10:16 PM   #4
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Default Re: Basic PA speaker rules

Quote:
Originally posted by SPL King
Some say that drivers of certain sizes either have or lack the right "punch". In dance music you have the drumbeat at one frequency rance and the bass at another. What Im hearing is that a 15" driver might be right for the drumbeat and bad at the bass, while its the opposite for an 18" driver. Is this true? If I look at frequenzy sheets for different 15" and 18" drivers you could acheive similar results, paper-wise.
Or is this this due to the Qts? At loudspeakerplus there is a table on wich Qts values are good for wich applications.

If anyone have any answers, or can tell me where to go look for information, please let me know.
No offense Daniel, but you're asking what I consider to be basic newbie questions and trying to scratch design and build what will need to be a high performance system to meet your specs. Either buy stuff secondhand or build known designs. Otherwise you'll end up with a poorly performing system that cost you a lot in terms of money, time and sweat.

By all means learn, design and enjoy, but start a bit more reasonably and there is plenty of experience and advice here for that.
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Old 20th September 2006, 12:03 AM   #5
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Quote:
By all means learn, design and enjoy, but start a bit more reasonably and there is plenty of experience and advice here for that.
I gotta disagree, while several others share your idea of start simple I think if one is prepared to learn, nothing is lost by buying good components. If they dont turn out great you can tweak the crossover, if that doesnt help then you replace the driver that is causing the imbalance. And you get to keep that driver for a future project.
It is your money, so the less you know at the time of purchase the higher the odds that you will have to purchase additional equipment to correct the mistake.
Then again I enjoy taking the time to learn how and why everything works, its almost an obsession.
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Old 20th September 2006, 12:25 AM   #6
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Quote:
Originally posted by nunayafb
It is your money, so the less you know at the time of purchase the higher the odds that you will have to purchase additional equipment to correct the mistake.
You're reiterating my point. There is a massive learning curve to designing good PA gear from the basis of inexperience.
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Old 20th September 2006, 02:57 AM   #7
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Default Agreed with Brett

I built 10 prototype boxes - have a shelf full of drivers left over and zipped up multi-yards of MDF - before I settled on an established design (which I modified later to my GREAT delight).

People who design loudspeakers for a living know what they are doing. Luck is a tiny part of the equation.

You have nothing to lose by starting at a known point - in fact - you'll be knocked sideways by what you'll learn.

The trick is to find an established DIY design that gets close to what you want. Spend less cash, get really spectacular results...

Then... once you get the drift of it - buy the equipment and go wild and start building what you want

Regards,
Tom
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Old 20th September 2006, 04:16 AM   #8
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Hi Daniel,

If you are looking for that kind of SPL and haven't done a lot of this, you can often find manufacturers that have done the work for you.

You should consider going active XO as you want a steep slope to your drivers for protection.

The question then becomes how much do you want to spend? Even a modest two piece modular will cost upwards of a few grand USD. This would be a 2 X 18 in a folded horn and a 2 X 10" or 2 x 12" plus a 2" horn

Or you can start small and go for a 2 X 15" and a 1" horn in a 2.5 way. Maybe throw in a midbass for good measure but you are talikng some serious dB, not sure the smaller unit would do that.
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Old 20th September 2006, 07:13 AM   #9
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Quote:
You're reiterating my point. There is a massive learning curve to designing good PA gear from the basis of inexperience.
Yes Im reiterating part of your point, excuse me if I wasnt clear. Im not saying you save money by jumping in wallet first. The learning curve applies to any speaker regardless of application, design is design and building is building.
One of his plans is a loud 2-way, Im sorry guys but what are you telling him to build... a "simple" and not so loud 2-way! The difference between loud and not is efficiency and power handling, so purchasing big pro audio components will achieve this goal. He still has to design the system the same way, xover and enclosure, etc.
You learn from doing, if you can afford to buy parts for experimentation then go for it they wont be wasted, my other point.
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Old 20th September 2006, 07:33 AM   #10
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Hello,

thanx for intresting answers! Ill definatley check out that other thread.

Maybe the SPL I stated is too much outdoors - I dont need to reach a certain number - but I know these speakers would be enough for a small party for say 50-100 people.

Buying a pair of finished speakers is out of the question, Im not looking for a perfect result but rather a fun project during the winter. I already built a 3-way speaker with drivers that I choosed myself and a bunch of resistors, so I know I can get right given enough time. But ofcourse, building a ready-made kit would make things easier.

Is going with active XO really neceseary? Would I loose alot if I didnt? I would ofcourse do that, and buy a dbx drive rack pa for XO, but I dont have that kind of money to play with. Also I have a limited amout of power at my hands - the generator delivers 2500 watts and I need some left for lighting.
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