bridging amplifiers for dual 18 passive subs

[Nathan Ridge]

Hi All,

Like to start by saying im pretty newbie when it comes to sound, I work in IT I just always get dragged into looking at sound issues at a nightclub I use to DJ at, if anyone could help me with this issue would be greatly appreciated.

The club keeps blowing sub drivers, we have had BOSe look at the DSP box and they say its correctly tuned and set and from what limited knowledge I have and help of some local guys at the hire shop we have concluded the amps are crap, they are heating up and clipping under load, they are a chinese clone and I think the quality is not there.

The sub bins we are running are all dual 18" passive with Celestion 1000w drivers, few P-Audio recones and a couple B52 bins also. We have been hiring some EV P3000 amps which aren't blowing subs anymore but also they seem noticeably quiter than other amps, the other amps didn't have a input gain sensitivity control as the P3000 dont also.

Now I have been told by the sound hire guys i should not run the p3000 amps in bridge mode, bridge mode is 2400w @ 8ohms and the sub bins are running two 8ohm drivers would then be 4ohm. Now this is where im confused. They are saying that the P3000 should not be running in bridge mode which i intended to do to give heaps of headroom and leave it in stereo which does 1200w per channel at 4ohm which should match the sub bins.

When i look at the B52 site though ( two of the 4 sub bins at b52 ), it also has 2 x 1000w 8ohm drivers in it yet it states its nominal impendence is actually 8ohms :

http://www.b-52pro.com/products/PA1818S.html

Which then to me suggests that running the p3000 in bridge mode would suit.

So my question is how are some subs 8ohm nominal and some 4ohm nominal when they both have two 8ohm 1000w drivers ? and secondly the sub bins that are rated at 4ohm nominal will it indeed hurt them running a single p3000 amp in bridge mode on them? My plan was to run one p3000 amp on each sub bin in bridge mode, heaps of headroom.

Any help appreciated.

Regards

Nathan

 

[Ivan Beaver]

Re: bridging amplifiers for dual 18 passive subs

Hi All,

Like to start by saying im pretty newbie when it comes to sound, I work in IT I just always get dragged into looking at sound issues at a nightclub I use to DJ at, if anyone could help me with this issue would be greatly appreciated.

The club keeps blowing sub drivers, we have had BOSe look at the DSP box and they say its correctly tuned and set and from what limited knowledge I have and help of some local guys at the hire shop we have concluded the amps are crap, they are heating up and clipping under load, they are a chinese clone and I think the quality is not there.

The sub bins we are running are all dual 18" passive with Celestion 1000w drivers, few P-Audio recones and a couple B52 bins also. We have been hiring some EV P3000 amps which aren't blowing subs anymore but also they seem noticeably quiter than other amps, the other amps didn't have a input gain sensitivity control as the P3000 dont also.

Now I have been told by the sound hire guys i should not run the p3000 amps in bridge mode, bridge mode is 2400w @ 8ohms and the sub bins are running two 8ohm drivers would then be 4ohm. Now this is where im confused. They are saying that the P3000 should not be running in bridge mode which i intended to do to give heaps of headroom and leave it in stereo which does 1200w per channel at 4ohm which should match the sub bins.

When i look at the B52 site though ( two of the 4 sub bins at b52 ), it also has 2 x 1000w 8ohm drivers in it yet it states its nominal impendence is actually 8ohms :

http://www.b-52pro.com/products/PA1818S.html

Which then to me suggests that running the p3000 in bridge mode would suit.

So my question is how are some subs 8ohm nominal and some 4ohm nominal when they both have two 8ohm 1000w drivers ? and secondly the sub bins that are rated at 4ohm nominal will it indeed hurt them running a single p3000 amp in bridge mode on them? My plan was to run one p3000 amp on each sub bin in bridge mode, heaps of headroom.

Any help appreciated.

Regards

Nathan

Let's look at this.

When you run the amps the way you want to you blow drivers. But when you have less power-you don't blow drivers.

Seems pretty simple to me------------------------------

Yes most of the time when you parallel 2 8 ohm drivers you get a 4 ohm load. Typos happen in spec sheets.

The P3000 is 3600 watts into a 4 ohm load bridged.

In most "normal" cases with a pair of 1000 watt 8 ohm drivers that should be fine.

What exactly does the "1000 watts" mean? Is it continuous (or RMS as some incorrectly state), program or peak? That can make a HUGE difference in what the "real" wattage is.

HOWEVER it HIGHLY depends on how hard it is being pushed-what the program material is, how far into limiting you are and so forth.

With some music styles it is advisable to run the speakers at HALF (or less) of the continuous rating, due to the high heating and low dynamic range of the music.

 

[Bennett Prescott]

Re: bridging amplifiers for dual 18 passive subs

Nathan,

Forget amp power. It doesn't matter to this situation. You (or someone) is driving the subs too hard. Either get more / better subs or live with the "quieter" setting that doesn't cause problems. If you have two kinds of subs with three kinds of woofers and a Bose controller (which is fine, but what does it know about B52 subwoofers?) this installation sounds like a nightmare.

 

[Brian jojade]

Re: bridging amplifiers for dual 18 passive subs

The link to the B52 in question states that it's 2 single 18" drivers, each with their own separate connection. If you parallel the connections, it's going to be a 4 ohm load.

The P3000 run in dual channel mode would deliver about 850 watts per speaker. That's a very safe amount of power, and would be difficult to blow speakers unless you rode into hard clipping. Note, I said difficult, not impossible. If driven into hard clipping, the signal from the amp could square off, resulting in a higher average power than the rated output. You also run the risk of mechanical damage to the sub. This can potentially happen at lower power than the rated power of the driver.

If you bridge the amp and parallel the 2 channels, the amp can deliver 3600 Watts, or roughly 1800 watts per speaker. This would net you about a 3db increase in output. However, if you drive the speakers for a significant amount of time at that levee, your average power could easily exceed the 1000 watts that they are rated for, and burn up the speaker. This will happen with bass heavy music, especially that with sustained LF notes. With a lot of current 'DJ' music, I recommend matching RMS of the amp with the speaker, as the dynamic range of the bass is typically fairly small, leaving not much room for error with an oversized amp.

Having heaps of headroom should mean that all pieces of gear in your chain have room to spare. Heaps of headroom on an amp without a speaker that is ready for that power is a recipe for disaster. When you are dealing with unknown operators, match RMS of the amp with the speaker, and you'll be reconing far less often. If you need more output, get more cabinets, or adjust placement of what you've got. Sometimes a reposition of the sub can give you just as much as doubling the power delivered to them.