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Hey guys - I want to start by saying thanks for this forum. I'm quite new to sound reinforcement, but it fascinates me and I love to read what you guys with more experience have to say. I've avoided a lot of purchasing fubar's over the last couple of months based on your recommendations/advice.

 

I have a couple ("a couple" = three) of questions that I haven't been able to find answers for on this forum (or anywhere else (but that sort of goes without saying, doesn't it? :D)). If there is a thread that addresses these feel free to just send me to it.

 

1. What power balance should you have between mains and subs? I know final adjustment is a matter of listening, but is there a guideline? If you're running 1,000w into the mains should there be 2,000w for subs? 500w? 17,000w?

 

2. Is there a sound difference in running speakers parallel? Does an 8 ohm load respond differently than a 4 ohm? I'm still a little confused by impedence...

 

3. And again with impedence, if you have an amp that can run at 500w at 4 ohms and you run two 8 ohm speakers in parallel are the speakers each getting 500w or something less than that? If they're both getting half that wattage (as I think I understand from other posts) what's the advantage of running at 4 ohms?

 

Thanks again, guys! I look forward to continuing to sponge off your wisdom and experience!

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1. What power balance should you have between mains and subs? I know final adjustment is a matter of listening, but is there a guideline? If you're running 1,000w into the mains should there be 2,000w for subs? 500w? 17,000w?

 

Subs should be about 2x the power of the mains, so you first guess of 1000/2000 is right on.

 

2. Is there a sound difference in running speakers parallel? Does an 8 ohm load respond differently than a 4 ohm? I'm still a little confused by impedence...

 

There is a difference in the power output of the amp. The lower the number of ohms, the more power is drawn. Thats why amp specs give several different ratings.

 

3. And again with impedence, if you have an amp that can run at 500w at 4 ohms and you run two 8 ohm speakers in parallel are the speakers each getting 500w or something less than that? If they're both getting half that wattage (as I think I understand from other posts) what's the advantage of running at 4 ohms?

 

Each speaker is getting half of that 500w. (250) There really isn't a big advantage or disadvantage at running 4 ohms vs. 8, it just depends on how your amps and speakers are best matched.

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Wow, thanks for the quick reply. So basically an amp that can run at 4 ohms or 2 ohms is one with the kick to push out that extra current so more speakers can be hooked up to it, not a way to increase the load to each speaker. Which, come to think of it, jives nicely with what I learned about electricity back in high school physics - it would still be the same voltage load across each individual speaker, blah blah. So simple... must... find... more... complicated... answer...

 

Another question, while I'm on a roll. I notice that Carvin and Behringer (I know, I know, bear with me) both sell subs that have built-in crossovers so you can run a speaker cable into the subwoofer from an amp and into a main from the subwoofer and (so they claim) everything will run jes' dandy. Seems to me like they're trying to sell the idea to newbies (like me, although I think I'm on to 'em) who want to avoid buying a crossover to save money/complexity. Is there any merit to the system? Do any higher-end companies make similar systems?

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Mark's comment about sum/mid-high ratio is right on...

 

We also used about a 1:1 ratio, but that will depend on the efficiency of the speakers, style of music, and the bandwidth each box covers.

 

For example with a JBL Vertec system, the top boxes are quite efficient even doen to 60Hz, so crossing subs at 80Hz requires less power to achieve the same power-bandwidth.

 

With heavier type music, that depends on heavy low end (to cover something up???) that ratio will change. That's why a cookie-cutter approach won't work.

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Originally posted by cstime

. . . they're trying to sell the idea to newbies (like me, although I think I'm on to 'em) who want to avoid buying a crossover to save money/complexity.

 

 

For the "extra" price that Carvin/Behringer/etc. will charge for installing those passive crossovers (i.e., the price for a speaker cab compared to the same speaker cab with a built-in crossover), you could purchase an electronic crossover.

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Originally posted by cstime

Crazy how almost nothing that seems too good to be true is actually true, isn't it?


Thanks, guys!

The coils that are needed to block the highs out on crossover frequencies that are in the 100hz range have to be very heavy. Heavy gauge copper and lots of windings. It sucks quite a bit of power,plus those coils get pretty expensive if they don't skimp on quality. Also,going passive on the sub end means that your only way of balancing the system is with the Eq.

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