new power amp

[gluten]

Hello,

Thanks for the help . Well I went with the qsc rms 1450. using it tonight first time. I am planning on going in stereo mode to 4 - 15" mains about 550 watts at 4 ohms. Sound about right? Having used only powered mixers i am asking lots of stupid ??'s I also have some small spot monitors not sure of ohms or wattage but i would like to run them from a mono 250 four ohm amp? Also is there a proper order to firing this all up? Mixer first , Amps last ? Also will be adding 2 subs about @ 500 each 8 ohms . in the furture, what amp will fill the bill when i add the subs? Could i get another 1450 and run the subs ?

 

 

Thanks

Mike

[Craig Vecchione]

You could run a second 1450 bridged in to 4-ohms for the subs. The 1,400w should be about right for two 500w drivers.

 

The rule of thumb is to provide 1.5 times the rated RMS or continuous power rating of the speakers, so a 550w 4-ohm speaker should get about 800w of amp. Always always remember that this power can and will damage speakers...you can't crank such a system to maximum power....the extra power is only there to keep the sound clean on short spikes. And never allow the amps to clip. If you see the clip light, lower the input until it goes off and stays off. And if your band performs at sane volume levels and/or does relatively mellow music, you can get away with less power. The main thing is....keep it clean. Pushing a system beyond its limits is usually dangerous and always sounds like {censored}.

[flanc]

You say your new subs are 500watts ea. Is that program wattage? If so, either an RMX2450 or RMX1850 would work for you...I'd go with the 2450. The RMX1450 will be too small for you in Stereo mode and too much in bridged mono mode (1400watts). The RMX850 would work if you want to risk bridging an amp into a 4 ohm load (not to mention subs!). If you have the bucks, get the RMX2450 and you'll be fine.

[RickJ]

It would help if you listed model numbers of the gear. But generally for MI-series gear, you're in the right ballpark. (How many spot mons? Two 8-ohm spots in parallel is about all you can run off that 4 ohm amp.)

 

Turn-on order is extremely important.

1. Any stage amps and instruments that are connected to the mixer via DIs

2. FOH and monitor processing gear

3. FOH mixer (and monitor mixer, if you have one)

4. Monitor amps

5. Subs amps

6. Lows amps

7. Mids amps

8. Highs amps

 

Turn-off order should be the reverse.

 

Also, instruct your bandmates to leave the stage gear alone after each set until you've muted all of the channels. A healthy transient pop from the bass player's phantom-powered DI can blow every speaker in your system.

[gluten]

Thanks for rhe replies

 

The subs are 300 watts RMS , All the speakers are PRO a US manufacter mid range cabinet. Quite funny actually i caught a lot of flack on using these... (cheap probably made in korea etc, but the sound is ok ) I had to laugh when i finally shelled out the$$$ for the QSC the first thing I saw when I opened the box was MADE IN CHINA!! made me chuckle.

[flanc]

Then an RMX2450 should be perfect at 500watt/channel.

[tlbonehead]

Originally posted by gluten Thanks for rhe replies The subs are 300 watts RMS , All the speakers are PRO a US manufacter mid range cabinet. Quite funny actually i caught a lot of flack on using these... (cheap probably made in korea etc, but the sound is ok ) I had to laugh when i finally shelled out the$$$ for the QSC the first thing I saw when I opened the box was MADE IN CHINA!! made me chuckle.

I think most Hot Spots are 16 ohms.

[Craig Vecchione]

 

Originally posted by gluten Thanks for rhe replies The subs are 300 watts RMS , All the speakers are PRO a US manufacter mid range cabinet. Quite funny actually i caught a lot of flack on using these... (cheap probably made in korea etc, but the sound is ok ) I had to laugh when i finally shelled out the$$$ for the QSC the first thing I saw when I opened the box was MADE IN CHINA!! made me chuckle.

 

 

I thought you said "will be adding 2 subs about @ 500 each 8 ohms".

 

If they're 300w subs, go with 450w per channel.

 

I don't see any problem with bridging the RMX into 4-ohms, especially for a conservatively powered system.....you won't be pushing that amp at all to power two small subs. But with the lower spec you're giving now, you can easily run the 1450 in stereo and give them exactly what they need.

[flanc]

 

I don't see any problem with bridging the RMX into 4-ohms, especially for a conservatively powered system.....you won't be pushing that amp at all to power two small subs. But with the lower spec you're giving now, you can easily run the 1450 in stereo and give them exactly what they need.

 

 

The RMX1450 will do 280watts/channel in stereo and seems a bit underpowered to me given a 300watt rms speaker. In bridge mono mode the amp will deliver 1400watts into 4ohms (pair of 8 ohm speakers). That's 700watts ea and too much power for the speakers mentioned.

 

I also agree that the RMX's will work when bridged into 4ohms as long as they are not driven hard (with the exception of the 1850hd...it's designed to handle 2ohm loads). I've seen 2450's and 1450's thermal when bridged into subs and ran hard.

 

Just one man's opinion........

[Craig Vecchione]

 

Originally posted by flanc The RMX1450 will do 280watts/channel in stereo and seems a bit underpowered to me given a 300watt rms speaker. In bridge mono mode the amp will deliver 1400watts into 4ohms (pair of 8 ohm speakers). That's 700watts ea and too much power for the speakers mentioned. I also agree that the RMX's will work when bridged into 4ohms as long as they are not driven hard (with the exception of the 1850hd...it's designed to handle 2ohm loads). I've seen 2450's and 1450's thermal when bridged into subs and ran hard. Just one man's opinion........

 

 

The fact that they'll be cruising if bridged into two 500w subs (based on the original info) is why I suggested it would be fine to use. Little chance of going thermal there. 300w subs are really light and definitely no problem for this amp other than being stupid and blowing things up. I wouldn't go smaller than this simply because, what the hell, it's only $400 amp, and eventually they may get more or bigger subs and be able to use the power.

[agedhorse]

 

Originally posted by Craigv The fact that they'll be cruising if bridged into two 500w subs (based on the original info) is why I suggested it would be fine to use. Little chance of going thermal there. 300w subs are really light and definitely no problem for this amp other than being stupid and blowing things up. I wouldn't go smaller than this simply because, what the hell, it's only $400 amp, and eventually they may get more or bigger subs and be able to use the power.

 

Yeah but if those are 300 watt (RMS) subs, I would look at around 400 watts amp power (being a bit conservative) and the 1450 would be a little bit light (by about 1dB) so by putting this into perspective, there's more production variability between sub drivers coming off the production line so why worry about 1dB of underpowering.

 

Since the QSC has a limiter, let the amp hit the limiter 1dB harder and you are back to where you would have been with the "correct power" anyway.

 

That last couple dB is what causes all the driver damage.

[Kennykeys]

 

Originally posted by agedhorse Since the QSC has a limiter, let the amp hit the limiter 1dB harder and you are back to where you would have been with the "correct power" anyway. That last couple dB is what causes all the driver damage.

 

 

Yes, I get the fact that 280 watts to that driver is going to produce almost the same final volume as, say, 350 or 400 watts, just without any headroom, correct?

 

So, are you saying that, generally, when an amp clips enough to toast a driver, it has to clip pretty hard? So what is the ratio between the amp's clip indicator red light and it's limiter?

Without looking it up (no time), I'm guessing that the clip light starts flashing when the peaks are 3dB down from, what, full out hard clipping?. And when does the limiter start kicking in? At the same time? Is it possible to "overdrive" the limiter so that the amp is still clipping square waves?

 

And I'll never promise not to ask you again.

[agedhorse]

 

Originally posted by Kennykeys Yes, I get the fact that 280 watts to that driver is going to produce almost the same final volume as, say, 350 or 400 watts, just without any headroom, correct? So, are you saying that, generally, when an amp clips enough to toast a driver, it has to clip pretty hard? So what is the ratio between the amp's clip indicator red light and it's limiter? Without looking it up (no time), I'm guessing that the clip light starts flashing when the peaks are 3dB down from, what, full out hard clipping?. And when does the limiter start kicking in? At the same time? Is it possible to "overdrive" the limiter so that the amp is still clipping square waves? And I'll never promise not to ask you again.

 

 

As soon as you engage the limiter, headroom becomes a non-issue. The ratio is approximately 1000:1 and the clip light indicates true clipping point (limiter threshold exceeded if limiter is engaged) by comparing the input waveform to the output waveform and looking at the error difference. At very high frequencies, depending on detector design, it is common for the LED to indicate a bit premature but that is not of much consequence since clipping point is not an issue (generally) above 10kHz.

 

Yes, you can overdrive the limiter but you are looking at probably more than +20dBu which is also about the max output of most consoles.

 

The advantage of limiting the subs this way is the "multi-band limiting effect" which can thicken up the bottom a bit while preserving clarity throughout the remaining bandwidth.

[Kennykeys]

OK. with the RMX, the first flash of the clip light indicates the onset of clipping (according to the waveform), correct? I know this may seem obvious, but I've seen some designs where the indicator is adjusted to flash BEFORE clippling.

So exactly when is the limiter threshold crossed?.....does it kick in BEFORE you reach the first flash of the LED or does the limiter start to compress at the same time that the amp starts to clip?

[agedhorse]

 

Originally posted by Kennykeys OK. with the RMX, the first flash of the clip light indicates the onset of clipping (according to the waveform), correct? I know this may seem obvious, but I've seen some designs where the indicator is adjusted to flash BEFORE clippling. So exactly when is the limiter threshold crossed?.....does it kick in BEFORE you reach the first flash of the LED or does the limiter start to compress at the same time that the amp starts to clip?

 

Yes, some designs do indicate clipping before actual clipping occurs. Those are level based, where the QSC is input/output difference based.

 

The limiter starts to compress/limit at the moment the LED turns on.

[kevinnemrava]

 

Originally posted by RickJ It would help if you listed model numbers of the gear. But generally for MI-series gear, you're in the right ballpark. (How many spot mons? Two 8-ohm spots in parallel is about all you can run off that 4 ohm amp.) Turn-on order is extremely important. 1. Any stage amps and instruments that are connected to the mixer via DIs 2. FOH and monitor processing gear 3. FOH mixer (and monitor mixer, if you have one) 4. Monitor amps 5. Subs amps 6. Lows amps 7. Mids amps 8. Highs amps Turn-off order should be the reverse. Also, instruct your bandmates to leave the stage gear alone after each set until you've muted all of the channels. A healthy transient pop from the bass player's phantom-powered DI can blow every speaker in your system.

 

 

I must respectfully disagree, .. As far as I know , the firs thing on should be the mixer.. as it is the hub you want to turn it on first, so that any other problems can use the grounding path through the mixer, and thus preventive any other problems.

 

what are others thoughts on this?