powering pa subwoofers

I picked up a pair of 18" subs a few weeks ago to give my system some more low end but am running into a bit of a dilemma powering them. They are 8 ohm's, so if they are ran in stereo out of the power amp which is rated at 4 ohms then they would only be getting half power and need almost double the power to get the wattage to them that way. With the amp bridged i would need a total 8 ohm load to get the full power from the amplifier. There again is the issue, the speakers chained together are either gonna be a 4 or 16 ohm load. So basically still the same scenario only able to draw around half power. My other option is 2 smaller amps bridged, one for each sub which would end up at 8 ohms bridged and allow each sub to get full power without having to run a big double the power amp just to get these things sufficiently powered. Now my question is, are there any power amps out there that aren't really high end that run at 8 ohms in stereo, and 16 bridged, or that will run 4 ohms bridged. I have been looking and haven't really found much in that department. Any positive input is appreciated.

[The Dude]

You didn't specify the most important specs. What is the power rating on the subs? What are power ratings on the amp? Or, maybe at least provide model numbers for the gear. Without knowing what we're dealing with, I'll make a generic statement. It isn't about power. It's about SPL. It's fairly likely that the difference between running them bridged (if you could) vs. running them stereo wouldn't be noticeable. Don't sweat power ratings. The important question is, can you get enough sound out of the subs without clipping anything?

[nevetslab]

Also, what's the application? Is this for Sound Reinforcement, like a working band's PA system, where the venue constantly changes, or is this for your home system, where the room size is constant, and you can optimize speaker placement to reinforce LF rather than have the room modes cancelling LF? Assuming your wife/girl friend are agreeable with such things. Spkr sensitivity / efficiency likewise comes into play. As The Dude says....it's all about SPL level and NOT so much about amp power.

[The Dude]

To elaborate: Double the power does not equate to double the perceived volume. You'd need 10X the power for that. Doubling the power is something like only a 3dB change. Hardly worth worrying about in most cases.

[bwheat]

To elaborate: Double the power does not equate to double the perceived volume. You'd need 10X the power for that. Doubling the power is something like only a 3dB change. Hardly worth worrying about in most cases.

I wasn't necessarily asking about volume, i was just trying to get at least rms, preferably program power to them which is 750 watts, or 500 rms. They are 1000 watts peak per sub. I was mainly worried about having enough wattage to them to keep up with the loudspeakers which are running at 500 watts a piece and rather loud.

[bwheat]

You didn't specify the most important specs. What is the power rating on the subs? What are power ratings on the amp? Or, maybe at least provide model numbers for the gear. Without knowing what we're dealing with, I'll make a generic statement. It isn't about power. It's about SPL. It's fairly likely that the difference between running them bridged (if you could) vs. running them stereo wouldn't be noticeable. Don't sweat power ratings. The important question is, can you get enough sound out of the subs without clipping anything?

That was my concern is getting enough power to them that they keep up with the loudspeakers which are rather loud for what they are. Also i do not have an amp for the subs yet, i am in the process of looking, but want to get something that will keep up so that is why i asked.

[bwheat]

Also, what's the application? Is this for Sound Reinforcement, like a working band's PA system, where the venue constantly changes, or is this for your home system, where the room size is constant, and you can optimize speaker placement to reinforce LF rather than have the room modes cancelling LF? Assuming your wife/girl friend are agreeable with such things. Spkr sensitivity / efficiency likewise comes into play. As The Dude says....it's all about SPL level and NOT so much about amp power.

As for now it is just a setup in my music room, but will be more used for small outdoor gig's in the future. Kind of got out of it for a while and in the process of assembling a band, but Most of anything that we will play will be outdoor party type stuff. Most all of the clubs around here have a house system, so it probably would never be in to many other places inside.

[bwheat]

My loud speakers have a spl of 96 db, and are 560 watts program and i have 500 going to each. The subs are also rated at 96 db for the spl . So knowing that am i right to assume that i will need close to program power to get a similar volume out of them?

[The Dude]

It'd be better to have the cabinet and amp models. Is that a max SPL spec, sensitivity spec, something else? Sans that, use your ears. Do they keep up at the volume level you'll be running at? There are lots of variables- crossover point, cabinet design (front load/horn load), manufacturer, etc. I'd trust my ears over any specs, which can be grossly inflated by some companies.

[bwheat]

that is not the max spl, that is the sensitivity spec 1 watt at 1 meter. I do not have an amp for the subs yet or a crossover so i have to way of doing the ear test, that is why i started the thread in the first place was to get an idea if there were any amps that would provide max power at 16 ohms bridged vs 8, and to kind of get an idea maybe of the minimum wattage i could get away with at a 8 ohm load on an amp that is rated at 4.

[bwheat]

I think that's a pretty fair assumption. I'd use whatever amp you have on hand, forget about bridge mode, paralleling, series wiring the speakers, no fancy stuff. Run 'em straight up & see if you have adequate thump for your needs. AND you would be better off having more speakers than doubling up on power or trying any fancy modes. What? more subs? Hmm.... if that's what you need. Better to share power over a number of speakers, than stressing the speakers with excess power which, as you know, leads inevitably to silence. Right in the middle of the gig, ugh. We can do without that, right? Plus, more cones moving = more volume overall. Speakers have "power compression" which is just as it sounds: when you whack em with lots of watts, they do not respond in a linear way as you approach their claimed power limit.

I have one power amp, and that is powering the mains, the whole reason for my post is that i was looking for an amp that provides max power at 8 ohms vs 4, so i am in the market to buy one to power them with, and deciding what i need. I am only trying to get the type of power to them that they claim to require not just blindly throwing power at them expecting them to do something. I would never just keep pumping in more power to try and make the speaker louder and go over the maximum rated handling of the speaker. I don't just have an extra amp to hook up to them to see how they sound with that said amp. I want to buy the right one the first time that is the right wattage. I think there is some misunderstanding here where some people think i already have an amp going to them and they aren't loud enough so i am just trying to pump them full of power. That is not the case whatsoever. Any the thought of buying more speakers before i have even hooked these up and know how they perform is kind of silly, there is plenty enough speaker there for my setup, just literally looking for an amp that has a max power rating at 8 ohms instead of 4 so i don't have to buy an amp with double the power to get sound i need out of these because say a 1500 watt amp, which is rated at 4 ohms which would be right at the program rating for these speakers would only produce 750 watts at 8 ohms. Nothing was ever said about just doubling power to the speakers, it is all about having double the power available, because you are only pulling half that at 8 ohms.

[The Dude]

Most amps have an 8 ohm/per channel power rating spec. Since your subs are 8 ohm and you have the specs for them, just look at the 8 ohm amp spec and get an appropriately sized amp. I'm not sure why you're concerned with the 4 ohm spec as it relates to this application?

[bwheat]

Most amps have an 8 ohm/per channel power rating spec. Since your subs are 8 ohm and you have the specs for them, just look at the 8 ohm amp spec and get an appropriately sized amp. I'm not sure why you're concerned with the 4 ohm spec as it relates to this application?

I am aware of that, that is the whole reason that this thread exists. The rating at 8 ohms is usually half the rating at 4 ohms, so if i buy an amp that produces max power at 4 ohms, and it is only producing half it's rated power at 8 ohms than i would need to get an amp that is rated for 2 times the wattage. The reason that 4 ohms means EVERYTHING is that they are all that i have found except for a few higher end ones rated for max power at 4 ohms, and if i buy one that is rated for x amount of power at 4 ohms, i will have half the rated power at 8 ohms so this requires purchasing twice the amp that you would actually need for this application. All i really want to know is if there happens to be something out there that they don't make any more that someone knows about that produces peak power at 8 ohms, i'd sure like to know, because you know buying a 3000 watt amp when you need a 1500 is spending extra money that you don't have to. One would be much better off money wise buying a couple smaller amps bridging them and running each sub of a seperate amp than buying one that makes 3000 rms, just to get that 1500 watts out of. Those aren't exactly cheap. I don't exactly see how that isn't clear here.

[The Dude]

Any amp is more power at 4 ohms than it is at 8. It's ohms law.

[bwheat]

Any amp is more power at 4 ohms than it is at 8. It's ohms law.

Yes, i am aware of that, but some are designed to produce peak power at a certain impedance and not intended to go lower than that. I have a little practice amp that is 15 watts and has a 8 ohm speaker, do you think it would be safe to throw a 4 ohm speaker in there and expect it to put out almost double the wattage, and not overheat? It is all about how it is built that determines that. I don't think you are physically able to answer my actual question and not just tell me a bunch of stuff i don't already know. So i don't know how to not be rude about it. But i guess if you aren't aware of an amp that is 4 ohm stable bridged, or was designed to produce it's rated wattage at 8 ohms which is what i am looking for than i don't need any other input whatsoever. I get that you think you are telling me a bunch of stuff i don't know because i am some new guy with a low post count, but pretty much everything anyone has said has in no way answered my question and only told me things i knew 25 yrs ago.