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Thread: New to DIY, building 12" PA cab

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    New to DIY, building 12" PA cab

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    So I've always wanted to get into DIY audio stuff, and I figured a speaker cab would be a basic enough device for me to start with (my dad can help me with building the wood cabinet so I'm already a leg up on things).

    I have a poweramp that's 800w total between two speakers. Basically I already have a cheap 400w speaker that I use for vocals and stuff, and I figured another 400w speaker would be cool to have.

    Anyway I've already done net research on cab design and such. Mostly on guitar cabs, since that's what I was originally planning on doing but figured it wouldn't be as useful for me because even though I want to eventually get a nice recording amp for my studio, I actually don't play guitar so its a lesser priority for me. Anyway, my confusion comes from 2-way speakers. From my understanding, speakers usually have a woofer and a horn, or a woofer and a tweeter. I'm pretty sure having the horn or tweeter is necessary for reproducing high frequencies. Anyway, would I need to divide up the total wattage between the two? Like have a 250w woofer and a 150w tweeter? I was looking at musicianfriends for standard speakers and there aren't many 12" speakers that are 400 watts (for the record, my current speaker is a 12") so I was curious if this was because the wattage is divided between the two devices.

    How much harder is it to make a two way cab? I figured the crossover circuitry would make things complicated, but could I get away with just having a woofer, or would I lose out on too many high frequencies?

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    The idea is that the main driver ('woofer') and horn cover the full frequency range, the woofer taking care of the low notes and the horn taking care of the highs. The crossover sends the appropriate frequencies to each, according to the designated cross-over point.

    Here's the thing: high frequencies require less energy to distribute than lower frequencies, which demand high power to move the mass of air in front of the woofer, so you need high power woofers and lowered-powered horns. For example, an old set of Yamaha bins that I destroyed held 120 watt drivers and 20 watt horns.

    You don't need 400 watt drivers for your speakers, and you can safely make do with anything under that. For example, I've been driving a set of homemade foldback wedges loaded with 50 watt drivers and cheap piezo horns with 300 watts for years. There is a greater danger, in fact, in getting higher rated speakers than your amp because it then becomes easy to overload the amp, a much more costly thing to replace than a blown speaker.

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    Hmmm okay I've been doing hours of research and things are making more sense now. I did read that having a higher power amp into lower wattage speaker is a good thing, but the reverse is a bad thing, so thank you for repeating that.

    So basically, what I'm looking at is a fairly basic design: 1/4" input on rear that is wired into a cross-over unit, which then is wired into both a horn and a woofer. Is that all there is? That and building the cabinet.

    I'm building this on the cheap with inexpensive components, so would these do good?

    Woofer: http://www.madisound.com/catalog/pro...oducts_id=8555
    (there's also this http://www.madisound.com/catalog/pro...oducts_id=8565 which has a higher frequency response but lower wattage)
    Horn: http://www.madisound.com/catalog/pro...oducts_id=1358
    Crossover: Now there's two cross-overs I'm looking at, one is a two way and another is a high pass. I'm not understanding the difference. If the high pass knocks out all the low frequencies, then its not actually a splitter, is it? I'm rather confused, I'll link to both of them:
    http://www.parts-express.com/pe/show...number=290-636
    http://www.parts-express.com/pe/show...number=290-602
    Also, depending on which woofer I end up using, would it be more beneficial to get the 3.5k or the 5k?
    Input: http://www.parts-express.com/pe/show...number=092-044

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    Any of those speakers should work fine. The lower wattage woofer with the twin cone might give you a bit more midrange than the other, but I wouldn't sweat on it either way. I'd probably settle for the higher power one.

    The purpose of a cross-over is to increase speaker effectiveness. For example, it's a waste of energy sending low frequencies to a horn which can't reproduce them, and indeed, their presence can mess around with the higher frequencies. It's not so critical going the other way (i.e. high frequencies to a woofer), which is why there are just high pass cross-overs. However, I would go for the full cross-over, rather than just the high pass. Go for the 3.5k cross over, because that seems to be the best for that combination of horn and driver.

    Yoou might like to think again about speaker connections. Even though 400 watts a side is fairly moderate these days, that's still a lot of power going through the wire, and standard jack connectors are not the best for dealing with this power. They can short out against the socket easily, and a broken solder joint in the socket itself can wreak havoc.

    Current practice is to use Speakon connectors. They are designed specifically for (and only for) speaker use. They can deal with large wattages, are non-shorting, and lock into place nicely (i.e. no accidentally pulled out socket which falls hehind the speaker into someone's glass of beer).

    See:
    http://www.parts-express.com/pe/show...number=092-053

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    Hmmm, okay I'll try the speakons then. Thanks for bringing those to my attention.

    So with the speak-on attachment, my setup would otherwise be fine?

    As far as cables go, I'm wanting to start making my own cables due to the fact they're so freaking expensive in store. For example, if I was to make a cable to go from my power amp (which uses banana plugs) to the speaker (which has speakon) these would be what I would need? Cut the cable to the length and put the ends on.

    http://www.parts-express.com/pe/show...number=100-246
    http://www.parts-express.com/pe/show...number=092-190
    http://www.parts-express.com/pe/show...umber=091-1165

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    You're on the right track with connections.

    For cable, though, you need to get stuff intended to carry large wattages, like, for exampel:

    http://www.parts-express.com/pe/show...number=100-482

    Don't use the shielded mike/line cable which is only intended for low level signals.

    If you want to economise, just go down to your local hardware store and get some cheap two-core mains power cable.

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    Hmmm, don't mean to be an idiot, but it seems like 2 core mains seems like a Commonwealth term, as all the websites that I pull up are either UK or Australia (judging from your location, it makes sense). I've been trying to figure out what the American equivalent is called, but I can't seem to find the term. I don't want to walk into a hardware shop and ask the minimum wage clerk if they carry 2 core mains and have them stare at me like "...wut?"

    Thought it might have been bi-wire but that's something completely different.

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    Let me jump in here.

    1. The cost savings suggestion is a good one- I have it on no less an authority Roger Russell, of McIntosh Labratories, Inc. that 10-gauge low-voltage (10 i think, working from memory here) is fine as speaker cable:

    https://homerecording.com/bbs/showth...ht=low+voltage

    I made up a pair of 2-connector speaker cables with the stuff. Only drawback is it is a bit stiffer than round speaker cable and thus does not lay as flat. Eventually it will assume a "twisted" shape, which effectively shortens it a bit, and looks funny. Most hardware stores will have it in stock, by the foot- about fifty cents a foot.

    This article, by Mr. Russell, may be helpful to you:
    http://www.roger-russell.com/wire/wire.htm

    Neutrix's webpage on these connectors (good source):
    http://www.neutrik.com/us/en/audio/2...oductlist.aspx

    I currently have 1/4" connectors on these cables, but will be converting them, or building new ones, with Neutrix connectors: I have aquired another speaker cab pair that are JBL Professionals, and have Neutrix Speakon jacks, and are bi-amplifiable (nore on this later.)

    In case you don't already know, simply put, crossovers send low frequencies to the woofers, high's to the tweeters.

    A simple capacator (I don't recall the value) wired in series with the positive lead going to the tweeter gives you a little bit of crossover, but mostly protects the tweeter from having to deal with low frequencies and thus reduces the likely the power sent to it will blow it out. Do this at the very least.

    As for your question: "would I need to divide up the total wattage between the two? Like have a 250w woofer and a 150w tweeter?" it sounds like you are thinking about BI-AMPLIFICATION. Here's a primer:

    You signal path would look something like this:

    Source(mixing board) >Active Crossover >"Big" amp >2 wire cable >woofer cabs
    >"small" amp > 2-wire cable > horn cabs

    The active crossover allows you to decide what frequencies you send to what speakers. This allows you to use the power amps more efficiently- you are not sending high power (in my case, 1500 watts) to tweeters tha can not handle that kind of power, and don't need it, anyway- a 150-watt power amp is fine. Sound quality is inproved, also.

    If you go bi-amped, and use low-voltage wire for your cable, you can go smaller wire (larger numbers for gauge) for the tweeters- "piz" or "lamp" cord will be less money, a bit more flexible. About 14-gauge should do.

    Neutrix Speakon connectors are available in 2- or 4- or even 8-connectors- use 2-conns for conventional amplification, 4-conns for bi-amped. Be careful about wiring, do some research as to what the industry convention is, so that if you buy commercially made cables you don't end up sending big wattage to your horns and thus blow them out.

    I would not build a PA cab with only a woofer in it. Piezo tweeters are cheap, and your cabs will sound much better with them than without (Piezos are not the smoothest sounding tweeters, but they are cheap- try them first.) You cal get adequate ones from home-audio speakers you can pick up cheap from a second-hand store- they may not last, but they will get you started. This will also be a source for a crossover or capacitor, too.

    There is much more to this subject, but I hope I have helped.

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    Though the question posed by Seafroggys might lead us to assume that bi-amping is being considered, I don't think that is the case. Bi-amping is introducing a level of complexity that is not really called for with this project. And probably nor is an active cross-over. In any case, the power source is a single 400 + 400 amp.

    At the moment Seafroggys has (nearly) all the ingredients for a reasonably powered, simple and low cost two-way speaker system.

    The one part missing is the speaker cable. The simplest (and also pretty effective) option is to get some ordinary mains power cable . . . the stuff used to make extension cords and so on.

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    Okay, I'll concede the bi-amp thing. But I stand by (if it is even a point of contention) the low-voltage cable being preferable to extension-cord stock.

    But to be consistant with the moderate-cost thing, Speakon's are probably NOT the way to go. 400 watts will not overload traditional 1/4" connectors, and chances are the OP has at least one cable with 1/4" TS connectors on at least one end- so it will save him a bit of money if he keeps that cable AND jack, and goes with !/4" TS on the other cable.

    And finally, further in the interest of modest cost, IMHO a simple capacitor between the jack and the tweeter will probably give him sound quality that is "good enough."

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