Configuring Live Audio System

[Gamingphreek]

Hey Guys,

I really could use some help in configuring this system that I manage. The more I researched the components, the more I don't understand how the system is running at all right now.

All components are running at 8 ohms impedance.

We have 2 amps right now:
Mackie FR Series 800M rated at 175 + 175 Stereo
QSC Series ONE 1700 rated at 325 + 325 Stereo

The load on the Mackie is as follows:
2x Bose 802 MKII Loudspeakers in parallel (240W - 480W each)
2x Yamaha BR12M Stage Monitors in parallel (300W - 600W each)

The load on the QSC is as follows:
1x Bose 802 Series Acoustimass Subwoofer (480W - 1200W (RMS))
2x System 2000 Stage Monitors in parallel (unknown power draw, but can't be more than 150W each)

Can someone explain to me how in the WORLD this system has not tripped the overcurrent protection or blown something yet?

Thanks,
-Kevin

 

[coaster831]

I don't see too much wrong with it. Some of the speakers may be a little underpowered, but there's nothing wrong with that (unless they are severely underpowered, which these are not). Are the power ratings you're stating for the amp at 4 or 8 ohms? Most of the loads these amps are seeing are at 4 ohms per channel, so it would be useful to list the 4 ohm spec.

Maybe the issue is that you're misunderstanding what the power ratings of the speakers mean? The power ratings aren't what the speakers actually draw, it's the power they are capable of receiving from the amp. Typically, as long as the amp is feeding less than the speaker can handle, you're fine.

 

[LikeLinus]

The speakers aren't actually "drawing" 240-480watts each. That is their max load handling. The amp is only putting out 175 watts to whatever is hooked up to the amp. Of course that changes depending on if the speakers are run in bridge or parallel, but the amp is still only going to output power.

So you're not overloading anything unless you are running the speakers at 2 ohm bridge and the amp can only handle a 4 ohm input. Otherwise, you're just using the avail power the amp produces.

 

[KLin]

Originally posted by: coaster831
I don't see too much wrong with it. Some of the speakers may be a little underpowered, but there's nothing wrong with that (unless they are severely underpowered, which these are not). Are the power ratings you're stating for the amp at 4 or 8 ohms? Most of the loads these amps are seeing are at 4 ohms per channel, so it would be useful to list the 4 ohm spec.

Maybe the issue is that you're misunderstanding what the power ratings of the speakers mean? The power ratings aren't what the speakers actually draw, it's the power they are capable of receiving from the amp. Typically, as long as the amp is feeding less than the speaker can handle, you're fine.

Good explanation. :thumbsup:

 

[Ns1]

The only problem I see with it is that it lacks testicles.

NEED MOAR POWER!

 

[Gamingphreek]

Originally posted by: Ns1
The only problem I see with it is that it lacks testicles.

NEED MOAR POWER!

Haha - how about "Need moar MONEY"

I don't see too much wrong with it. Some of the speakers may be a little underpowered, but there's nothing wrong with that (unless they are severely underpowered, which these are not). Are the power ratings you're stating for the amp at 4 or 8 ohms? Most of the loads these amps are seeing are at 4 ohms per channel, so it would be useful to list the 4 ohm spec.

Maybe the issue is that you're misunderstanding what the power ratings of the speakers mean? The power ratings aren't what the speakers actually draw, it's the power they are capable of receiving from the amp. Typically, as long as the amp is feeding less than the speaker can handle, you're fine.

The wattages listed are all for 8ohms. The speakers minimum draw is the recommended minimum listed on the specifications page, the speakers maximum is the peak power (I assume RMS not continuous) that was on the specifications page.

I don't understand how these aren't severely underpowered. For instance, if the 2x Bose speakers draw 240min each, since they are running in parallel, that would be 480W minimum to drive both of those speakers on one channel. The one channel that they are running off of is rated at 175W max.

-Kevin

 

[coaster831]

Originally posted by: Gamingphreek

Originally posted by: Ns1
The only problem I see with it is that it lacks testicles.

NEED MOAR POWER!

Haha - how about "Need moar MONEY"

I don't see too much wrong with it. Some of the speakers may be a little underpowered, but there's nothing wrong with that (unless they are severely underpowered, which these are not). Are the power ratings you're stating for the amp at 4 or 8 ohms? Most of the loads these amps are seeing are at 4 ohms per channel, so it would be useful to list the 4 ohm spec.

Maybe the issue is that you're misunderstanding what the power ratings of the speakers mean? The power ratings aren't what the speakers actually draw, it's the power they are capable of receiving from the amp. Typically, as long as the amp is feeding less than the speaker can handle, you're fine.

The wattages listed are all for 8ohms. The speakers minimum draw is the recommended minimum listed on the specifications page, the speakers maximum is the peak power (I assume RMS not continuous) that was on the specifications page.

I don't understand how these aren't severely underpowered. For instance, if the 2x Bose speakers draw 240min each, since they are running in parallel, that would be 480W minimum to drive both of those speakers on one channel. The one channel that they are running off of is rated at 175W max.

-Kevin

There is no "minimum" you need to drive speakers (there is a discussion about severe underpowering, but it doesn't apply here). Speakers take whatever power they receive from an amp and convert it into a pressure wave at the driver. If the amp sends power greater than the speaker's peak power rating for a short time, the speaker will probably blow. If the amp sends power greater than the speaker's program rating for an extended amount of time, the speaker could blow. If the amp sends less, it doesn't hurt the speakers at all- it just means you could be getting a little more out of your speakers if you get a bigger amp.

For example, the yamahas are rated at 300W program/600W peak. You would want to match these to an amp that puts out roughly 300W @ 8 ohms. When you add another speaker in parallel, you now have 600W of program handling in the speakers- but since you're now at a 4 ohm load, your amplifier is putting out more power- nice how that works out, eh?

 

[Gamingphreek]

Oh - so because the speakers are in parallel, the ohms resistance is over the number of objects in parallel?

So, for instance, since I have 2 speakers that run at 8ohms each, when in parallel, that is effectively 8/2 or 4ohms? If I were to throw 4 up there, then I would be at 2ohms?

Edit: I am getting a new amp for the system to replace the 22 year old QSC amp. I planned on switching the Bose 802 series, and the Bose sub all to one amp.

Since the sub would still have 8ohms resistance and the speakers would be 4ohms since there are 2 in parallel is that possible?

Would the power delivered to each channel just be different? Is that allowed?

-Kevin

 

[coaster831]

Yes, adding resistance in parallel causes the overall load the amp sees to go down. If you put all 4 monitors on one channel of an amp, that channel will see a resistance of 2 ohms- however, (AND THIS IS VERY IMPORTANT), some amps aren't rated to drive a 2 ohm stereo load- you could blow the amp. You need to read the manual and see what the amp is rated to do. Do you have a link to the full spec sheet for the QSC or Mackie?

I would hold off on replacing the QSC for now until you get a better idea of what you really want. Also, QSC makes some pretty good amps, so as long as it's still works, it's probably pretty good. After you get a feel for your system's shortcomings, you can make a better decision. If nothing else, you could keep the QSC, and bridge it to give that sub some extra power. Then use the Mackie to drive the monitors, and your new amp to drive the mains.

 

[Gamingphreek]

Originally posted by: coaster831
Yes, adding resistance in parallel causes the overall load the amp sees to go down. If you put all 4 monitors on one channel of an amp, that channel will see a resistance of 2 ohms- however, (AND THIS IS VERY IMPORTANT), some amps aren't rated to drive a 2 ohm stereo load- you could blow the amp. You need to read the manual and see what the amp is rated to do. Do you have a link to the full spec sheet for the QSC or Mackie?

I would hold off on replacing the QSC for now until you get a better idea of what you really want. Also, QSC makes some pretty good amps, so as long as it's still works, it's probably pretty good. After you get a feel for your system's shortcomings, you can make a better decision. If nothing else, you could keep the QSC, and bridge it to give that sub some extra power. Then use the Mackie to drive the monitors, and your new amp to drive the mains.

Oh I know exactly what I want - I just got turned around. When I took charge of this system I was told it was in bridged mono - well I just now had the time to look and figure out that wouldn't work and wouldn't make any sense what so ever.

The other thing is, we need to sell the QSC amp for the money. I'm audio coordinator for InterVarsity Christian Fellowship here at Virginia Tech and money isn't exactly something that we have a lot of

How bad would it be if Channel 1 has 4 ohms resistance, and Channel 2 has 8ohms resistance? Is it possible?

-Kevin