# Power Amp & Speaker Q's

Discussion in 'Amps and Cabs [BG]' started by xb100, Aug 3, 2005.

1. ### xb100

Mar 24, 2004
NH, In
Hey guys I was looking at some of qsc power amps. And the 1850HD caught my eye, esspecially after I found out how much it is. Anyways, it says in the manual that it puts out 600 watts @ 4ohms per channel, so if I put 2 and 2 together that would mean if I had 2 4ohm cabs, and hooked each one to a channel (cab A>>>channel 1 and cabB>>>>channel 2) I would have 1200 watts of power right there correct?

I've read the ohms FAQ thread and all the stuff about watts and ect. But I remember hearing that if I have an amp thats say for instance like the qsc that puts out 600 watts @ 4 ohms, for me to be louder I would have to have 3x that to gain like 1db or something?

I could use some help on that topic as well.

Another question I have is about speaker effiency, I'm a little cloudy on this subject as well. My question is, say I have a cab that is rated at 98db and power it with 300 watts. Would it be louder if I had a cab that was rated at 104 db and power it with the same 300 watts? And if it were to be louder how much louder would it be?

-Rob

2. ### xb100

Mar 24, 2004
NH, In
bump anybody??

3. ### Eric Moesle

Sep 21, 2001
Columbus OH
Not really 1200 watts of SOUND POWER, just in mathematic power (not that there are such things definitionally, just to help you get the point).

You will have 600 watts going to each cab, essentially the same volume you'd have with just ONE cab running at 600 watts, but you will appear about 3db louder because of the addition of the second cab. It will be noticeable to you (it was to me when I added a second 410 to my rig). More noticeable in COVERAGE where you stand, you'll have to drive both cabs less hard to achieve the same "oomph" as with one cab.

Or, you could be like a car stereo manufacturer and proclaim addition to eveybody that you are pushing 1200 watts . . .

4. ### Mcrelly

Jun 16, 2003
Minnesota, USA
the way I would read that is...if you could put 2 8ohm cabs on each channel, thus having a load of 4ohms on each side. or you can buy a 4 ohm cabs for each site like you say, but if the amps minimum load is 4ohms per side and you want to hook up more cabs for more volume, you can't.

5. ### xb100

Mar 24, 2004
NH, In

The 1850 goes down to 2 ohms per channel so IF I did go with 2 4ohm cabs I could still daisy chain the other cabs to achieve the amps power @ 2 ohms.

6. ### xb100

Mar 24, 2004
NH, In

Thanks alot, after reading over specs and what not I think I'm going to get the 2 cabs both 8ohms. That way I'll have PLENTY of headroom if I need it.

7. ### Eric Moesle

Sep 21, 2001
Columbus OH
My recommendation:

Get two 8 ohm cabs, run them together for 4 ohms. Set your power amp for BRIDGED mode, use a cable with the proper bridged mode connections, and listen to the thunderous voice of God (or the voice of Darwin) coming through your rig in bass form!

8. ### Richard Lindsey

Mar 25, 2000
SF Bay Area
If you're running one cab on each side of the amp, that wouldn't give you more headroom, it would give you *less*--because the amp would have less power available into 8 ohm/side loads than into 4 ohm/side loads. Headroom is about having more power available than you need to do what you're trying to do.

If you get two 8 ohm cabs, Eric's suggestion sounds like the one to follow--daisy-chain them, bridge the amp, and run both speakers off the bridged mono output. That should give you a ton of power.

9. ### xb100

Mar 24, 2004
NH, In

Ok, so say I do get 2 8ohm cabs and plug em into my amp and set it to bridged mode, which I think is 1800 watts @ 4 ohms for the power amp I wanna get (qsc rmx 1850) Would I take a speakon cable and plug that from my amp into one of the cabs, then take either another speakon or 1/4 to 1/4 speaker cable and hook both the cabs up correct?

10. ### Richard Lindsey

Mar 25, 2000
SF Bay Area
Yes. Just make sure you take the first cable from the correct output on the amp, i.e., the specified bridged output.

11. ### xb100

Mar 24, 2004
NH, In
Another question, avatar cabs only have one speakon input on the back panel, and I will be useing it to connect to the power amp, to daisy chain the 2 cabs I would have to use a 1/4 to 1/4 and I have read that they are un safe when used with high powered heads and watts.

Would a 1/4 to speakon to safer?

Thanks alot

-Rob

12. ### steveksux

Mar 23, 2005
Detroit area, Troy, MI
Correct.

Double the power = 3dB louder. To SOUND twice a loud, the rule of thumb is you need 10x the power, all else being equal. Life ain't fair.

Assuming the ratings are not bogus, some liberties are taken, not a solid standard like RMS power of amps. 98dB cab is 6dB less efficient than 104dB cab, so it would take 1200W (3dB=2x power, 6db=4x power) to be as loud as the cab rated at 104dB.

I agree with the previous posters, 2 8 ohm cabs give you a 4 ohm load. If the amp goes down to 2 ohms per channel, it will drive a 4 ohm load bridged. That lets you extract max# of watts from the amp. Amp rated 600W@4 ohms is probably around 900W @ 2 ohms give or take, x2 channels in bridged mode=1800W available in round numbers. Get a couple of 8 ohm cabs capable of handling at least around 450=500W each and you've got a lotsa headroom and plenty of bass.

Randy

13. ### xb100

Mar 24, 2004
NH, In

^^^^ Thanks alot man, that helped out alot and loads of usefull info provided.

Thanks,

-Rob