Need Sound Advice - really!

[charlie]

Ok...all you PA tech gurus....here's the deal. I got a Behringer EP2500 power amp rated at 450 watts (RMS) per side at 8 ohms. My Peavey SP-118 subs are rated at 600 watts (RMS) at 8 ohms. Let's say the dance floor is packed on a Saturday night and I want to pump out some more bass onto the floor. Since the EP2500 is loaded down to 8 ohms per side at 450 watts and my 18" sub speaker can handle 600 watts, if I drive the EP2500 harder to produce more volume...will it clip out and damage the 18" sub speaker. I was told that the "rule of thumb" was to have twice the amp output (RMS) than the speaker rating to give the amp headroom so that it would not clip. Now, if I run the EP2500 in mono-bridged mode at 4ohms...that's 2400 watts. That's 4 times the 18" sub speaker rating...Dont really know which way to go. In mono-bridged mode the EP2500 would seem to have more that adequate power to meet the "rule of thumb"but also could possibly blow the speaker because of distortion while in mono-bridge mode. However, if I leave the EP2500 running in stereo at 8 ohms and I push it to get more volume and the amp clips out...which is worse?

[gibbo]

Hi Charlie,
"Rules of thumb" are a bit like most general advice, you need to take 'em with a grain of salt.
Here's my advice; Don't run your subs in Bridge mode; it can produce HUGE speaker excursions and will probably cook the voice coils. I have a friend who makes a fantastic living out of re-coning speakers and he tells me that this is one of the most common causes of large speaker failure.
It's true that amp clipping can be death to speakers too but I think the EP2500 has an anti-clip limiter built-in (most modern amps do) and you'll hear/see the clipping. All you'll hear from a Bridge-mode overload is a deafening silence as your speakers quit the gig.
Now, to solve your problem... if you want more apparent volume at a really rowdy gig you need to reduce the amount of very low frequencies; ie; pull out everything below say 45Hz and push up the volume. If you need more volume cut off at 50Hz etc. Most punters won't miss anything below 50Hz. I run a 3 way system with the subs handling 40-150Hz.
Again it's another "rule of thumb" from years of experience but it's worked for me; the higher the volume the less extreme lows. It's the extreme lows that produce the biggest speaker excursions (and most heat in voice-coils). I've heard kick drums that almost have the speaker hitting the speaker-grill.
There are a lot of great PA forums around, FOH Online (Front Of House) is one I recommend. Some of the best sound-techs in the world contribute to the forum and give advice.
Good luck, mate.
Cheers, Dave.

[charlie]

Thank you for replying...was starting to worry that noone wanted to touch this thread with a ten foot pole. I realize it was more of a technical PA question, and the FOH Online website may be where I should have posted, but I wanted to try my thread out here so that I might get some common sense practical answers instead of a bunch of PA mumbo jumbo that I wouldn't understand anyway. That's what I really wanted to get back...some input from gigging musicians who have the same needs as I. So, thank you for reinforcing what I thought to be the case. Drop out the excursion frequencies and turn it up. Like you said, most punters won't miss anything below 50hz. By the way, due to the cabinet design of the Peavey SP-118...there is more apparent low end as compared to what I was using, and therefore I can run my EP2500 at 8 ohms per side and it's more than enough low end. For outdoor stuff, I may need to add (2) more SP-118 which would bring the EP2500 down to 4 ohms per side and pump out 750 watts per side. It is true that a lot of people get fooled with the bridged output power claims of an amp. What the amp manufacturers don't want you to know...is that it will sound like rubbish and eat your speakers in the process. Thanks Dave for making sense of the bridged mono vs. stereo scenario.

Charlie

[gibbo]

No worries, mate.
Just as an added note re: outdoor gigs... some of the best advice I ever got about running a PA outdoors is this; for outside gigs always cut-off the lows below 65Hz.
It saves a lot of problems and, outdoors, nobody really hears the frequencies below 65Hz anyway so it cleans up the whole sound projection and prevents amp and speaker overload. As long as you're not doing a Rave/Techno event (and I know you're not!) this seems to work beautifully.
There's a great easy-to-read manual about live sound techniques available for free download from the Yorkville Sound website.
Cheers, Dave.
PS: I noted your comment about wondering when someone would answer the question. I actually replied the same day you posted it so you might need to clear your browser cache or refresh the page more often if you didn't see the answer straight away.

[JazzCat]

Gibbo siad:
There's a great easy-to-read manual about live sound techniques available for free download from the Yorkville Sound website.

There are a lot of great PA forums around, FOH Online (Front Of House) is one I recommend.

---
Would you be able to provide direct links for us? Would be easier than having to search. I come up frustrated so often when not finding what was referred to.
Thanks!

[gibbo]

I could, I suppose, but it's just how I prefer to operate; I advise self-help.
I'm of the opinion that if you do everything for the kids then they never bother to learn how to do things for themselves. I mean to say; How hard could it be?
Oh... OK, but just this once;
FOH online forum = www.fohonline.com (then follow the links to the Wild and Woolly forum under FOH Community) or if you prefer, that'd be: www.fohonline.com/forum/
Yorkville = www.yorkville.com (click on Resources) or go directly there using this link www.yorkville.com/default.asp?p1=6&p2=0&p_id=17
I'm just kidding now
Cheers, Dave.

[JazzCat]

Thanks for the links Dave. I do appreciate it. See, in the past when people have mentioned neat articles I have wasted hours searching feudally for them. I simply don't have the time to do that to come up empty handed and still wind up back where I started, in asking you to post them.

I'm very glad you are kidding. I've already been publicly embarrassed and had my feathers ruffled once today on the forum. Don't think I could have taken a second dose of it. LOL

[gibbo]

You're very welcome, Cat.
I'd hate to think I'd ruffled your feathers in any way... I'd never do intentionally that. I've had the same frustration with tracking articles down on the net.
And, for what it's worth, I don't think Gerry/Tubbs really meant to embarrass you either, we all think you're pretty neat. I understand that the Mods can get a little steamed-up at times, Gawd knows I've caused a few unintentional fracas in my time on various forums.
All that being said, keep smiling through it all and keep on posting, I enjoy your stuff.
Cheers, Dave.