Power amp RMS vs. Speaker RMS for subs

[RoadRanger]

Everybody knows that square waves open up a direct portal to Hell and the flames blasting though the portal are what burns out your drivers .

[mshifflett]

For that matter I've never understood how you'd do crossover with the subs on a (post fader ?)aux or sub. I see folks post about it once in while but haven't seen a detailed description of how it's "done". I normally run subs off the mono sub output of my Behringer xover but running them stereo with the pan pots centered is the same thing, no?

 

 

You just need another channel of crossover. You would send you normal mid/high signal to one crossover or one channel (depending on your setup) and then send the aux output to the other crossover or channel.

[tlbonehead]

For that matter I've never understood how you'd do crossover with the subs on a (post fader ?)aux or sub. I see folks post about it once in while but haven't seen a detailed description of how it's "done". I normally run subs off the mono sub output of my Behringer xover but running them stereo with the pan pots centered is the same thing, no?

If you run them off of an aux out you control what and how much low end come through on each individual channel by adjusting the corresponding aux knob on each channel.

[mshifflett]

Well one main benefit is the additional power. Under powering speakers can cause more damage than overpowering. And coupling subs is an added benefit. Like I said, it's personal opinion, but in this particular setup, I would recommend it so that he is not under powering the subs. There are pros and cons to both. I've tried both setups and have been much more satisfied with bridged mono subs. Also, running them on a aux is great for bands so that you can selectively send signal from specific tracks to the subs (ex. kick, floor tom, bass, a little keyboards) which cuts out on woofy sound from vocals and guitars hitting the top of your subs crossover point

 

 

+1 on the aux fed subs. As far as bridging the amps, the OP just needs to make sure he will have adequate AC power available as the amp will draw more current when bridged, especially is he is hitting it pretty hard.

[tlbonehead]

+1 on the aux fed subs. As far as bridging the amps, the OP just needs to make sure he will have adequate AC power available as the amp will draw more current when bridged, especially is he is hitting it pretty hard.

Very true. But if the VC s on the woofers are already bumping against their limits, I'm pretty sure more power is only a solution to getting new subs cuz the current ones will be dead.

[mshifflett]

Very true. But if the VC s on the woofers are already bumping against their limits, I'm pretty sure more power is only a solution to getting new subs cuz the current ones will be dead.

 

 

Oh you got that right. The last thing he needs is more power. I was just warning against the added power draw.

[RoadRanger]

Also, running them on a aux is great for bands so that you can selectively send signal from specific tracks to the subs (ex. kick, floor tom, bass, a little keyboards) which cuts out on woofy sound from vocals and guitars hitting the top of your subs crossover point

I'd think that proper eq and matching the level of the sub and tops would take care of all that? I suppose if you run the subs "hot" like many DJs this would be a good idea but I like to start out with a reasonably flat system and eq the channels "to taste" .

 

I've thought it might be interesting to try a different crossover freq for different channels - vocals and most other stuff going to the tops only crossed at 75hz (or just depending on the 75hz HPFs in the channel strips?) and kick, bass, keys, and CD player going to a sub bus that feeds a 125 hz crossover, highs mixed back in to main (to tops) and the lows to the subs. This would keep the vocals completely in the tops for clarity and fullness. Both guitars and male vocals bottom out at 80 hz anyways.

[agedhorse]

I disagree. Many engineers and I agree that under powering speakers may cause more damage. But I don't wish to argue the point.

 

 

Bullsh*t. Period.

 

As a REAL engineer, and one who designs both amplifier AND speaker products for a living, I can say with complete confidense that underpowering a sub will not cause damage compared with overpowering the same speaker. Overpowering subwoofer drivers is by far and away the number one cause of driver damage.

 

You have taken a partially valid point for a FULL RANGE signal into a multiway cabinet, and if the signal is clipped (by the power amp) due to it being too small for the job, the harmonics generated may damage the HF driver because the power sent to the HF driver contains a lot of added harmonics which increases the thermal energy of the resulting signal.

 

For the OP. the amp he is using into 8 ohms per channel is a plenty good match for thoese LF drivers, and bridging would result it WAY too much power if he were to drive the system hard. The popping sound he is hearing isn't likely to be clipping of the amp, nor is it VI limiting due to the 8 ohm load, so it's most likely the bobbin hitting the back plate pummeling itself to an early death due to too much power for the driver/cabinet combination.

 

IF his drivers were (really) rated for higher power (real watts not marketing watts) and the additional power used for headroom, not to push additional snot out ofthe speakers, then bridged mono may be a viable option.

[agedhorse]

I've thought it might be interesting to try a different crossover freq for different channels - vocals and most other stuff going to the tops only crossed at 75hz (or just depending on the 75hz HPFs in the channel strips?) and kick, bass, keys, and CD player going to a sub bus that feeds a 125 hz crossover, highs mixed back in to main (to tops) and the lows to the subs. This would keep the vocals completely in the tops for clarity and fullness. Both guitars and male vocals bottom out at 80 hz anyways.

 

 

In general, not a good idea because you would have different filter phase responses and the tops, and there would be a pretty large bump in the acoustic response where the filters overlap.

[rufert]

I'm a firm believer in running subs on an aux. As you guys have pointed out many of the benefits. I run an L-Acoustic VDOSC setup with Lab Groupen amps with an M7CL for FOH and we have switched from stereo subs to subs on a aux for different shows and the difference is audibly noticeable. Same as for out drum monitor setup, drum sub on a separate aux so we can send only kick, floor tom, bass to the sub and the drummer doesn't get any weird vibrations from stray low end.

[RoadRanger]

In general, not a good idea because you would have different filter phase responses and the tops, and there would be a pretty large bump in the acoustic response where the filters overlap.

I think you misread what I proposed. Those channels that had their HPFs engaged would only go to the tops via the main bus. The other (bass,kick,keys) channels would NOT be assigned to main but would go though a sub bus to a 125hz crossover that would have its HPF returned to main via an aux return and its LPF as the only input to the sub amp. No "overlap" involved .

[RoadRanger]

... drum monitor setup, drum sub on a separate aux so we can send only kick, floor tom, bass to the sub and the drummer doesn't get any weird vibrations from stray low end.

[/rant on]Is this the present fad to always have kick in the monitors, even in the drummer's? Seems to me the more kick you have in the drummer's monitor the softer the lazy SOB kicks it - kinda defeating the purpose. And if it is for tone maybe somebody ought to teach the SOB how to tune drums? As for the drummer hearing the bass why not put the bass cab next to the drummer like a real R&R band?[/rant off]

[RoadRanger]

Iwe can send only kick, floor tom, bass to the sub and the drummer doesn't get any weird vibrations from stray low end.

Where would any "stray low end" come from if not from kick, FT, bass and maybe keys? Any reason not to use your channel strips's HPFs on everything else?

[rufert]

I've had some odd setups where we can't rolloff the low end because we need it in the downstage wedges but the drummer just wants high end to cut through. Typically you could eq the wedge but I find it a lot easier just to have them separate. Saves time when you have 5 bands playing and someone with a leslie or acoustic that wants some extra low end. Give the drummer a cleaner more consistent signal in the drum sub without sacrificing the eq for everyone else's wedges. Hope that makes since, ha typed it kinda fast.

[rufert]

I def agree, haha. I'm a drummer, and typically a little bass and guitar is all I need. I've actually found that they start kickin it harder with it in the monitors though, usually have to end up compressing and pulling back the signal. I agree with moving the bass cab, but typically we try and keep a low stage volume and with the drums on a riser towards the back of the stage, the bassist wants his rig up closer to show off his stack or whatever

[Coaster]

I've had some odd setups where we can't rolloff the low end because we need it in the downstage wedges but the drummer just wants high end to cut through. Typically you could eq the wedge but I find it a lot easier just to have them separate. Saves time when you have 5 bands playing and someone with a leslie or acoustic that wants some extra low end. Give the drummer a cleaner more consistent signal in the drum sub without sacrificing the eq for everyone else's wedges. Hope that makes since, ha typed it kinda fast.

 

 

monitor board. problem solved.

[rufert]

monitor board. problem solved.

 

 

This is on a separate M7 for monitors ha. It seems that a lot of you guys disagree with what I am saying. I understand everyone has different opinions on setups, but I've never received this many complaints on stage, most engineers like the setup quite well. O well

[RoadRanger]

the bassist wants his rig up closer to show off his stack or whatever

As a former bassist I can't imagine not having a strong drummer/bassist thing going. I used to run a 4 ohm 4/10 cab on my side of the drummer and a 15/1 8 ohm cab on the other side. In fact, I suggested it to the band I'm working with now and they love it !

[tlbonehead]

As a former bassist I can't imagine not having a strong drummer/bassist thing going. I used to run a 4 ohm 4/10 cab on my side of the drummer and a 15/1 8 ohm cab on the other side. In fact, I suggested it to the band I'm working with now and they love it !

I wouldn't want a bass cab on my side of the stage as a guitarist. That would mean having to play louder than I want to.

[dboomer]

For that matter I've never understood how you'd do crossover with the subs on a (post fader ?)aux or sub. I see folks post about it once in while but haven't seen a detailed description of how it's "done". I normally run subs off the mono sub output of my Behringer xover but running them stereo with the pan pots centered is the same thing, no?

 

 

Nope ...

 

http://www.peavey.com/support/technotes/concepts/AUX_SUBs.pdf

[RoadRanger]

Nope ... http://www.peavey.com/support/technotes/concepts/AUX_SUBs.pdf

 

Thanks for the link, I'll definitely save this document and study it. It does specifically mention subs run "hot" as I mentioned above. I suspect you can do the same thing via a good eq inserted on a sub channel mix of those same bass sources?

[agedhorse]

I think you misread what I proposed. Those channels that had their HPFs engaged would only go to the tops via the main bus. The other (bass,kick,keys) channels would NOT be assigned to main but would go though a sub bus to a 125hz crossover that would have its HPF returned to main via an aux return and its LPF as the only input to the sub amp. No "overlap" involved .

Definately misunderstood. It will work, may be more trouble than it's worth though.

[charlie13]

Wow....I think the amp RMS wattge vs. speaker RMS wattage question got lost somewhere in the thread, but bascically I see two opposing views. One says a lower powered amp can do damage to a speaker. The other says says a higher powered amp can damage a speaker. Both views I think have merit, but due to my limited knowledge in electrical enginnering, I can only make this simple analysis. It seems to me if an amp is under powered to meet the full output of the speaker, distortion occurs, heat builds up, and the VC is fried. Conversely, if an amp over powers a speaker and causes excursion (we're still talking subwoofers here) then the cone pulls away from the magnet and the leads to the VC are either stretched or torn, the speaker fails. Like I said, with my limited knowledge about the inner workings of a speaker, I can only make these assumptions. It's been very interesting to hear opposing views on this topic. I have always wondered about how to size an amp for subwoofers. Maybe someone could shine a light on that topic.

Thanks guys,


Charlie

[RoadRanger]

[dboomer]

It does specifically mention subs run "hot" as I mentioned above. I suspect you can do the same thing via a good eq inserted on a sub channel mix of those same bass sources?

 

 

Run "hot" or not ... any way you want. Think of it as a super-bass control. It is not the same as inserting an EQ because only sources sent to the aux sub are affected. If you used an EQ it would most likely leak into open mics and cause a bunch of gak. YMMV