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Question about SWR sound and power

#23
You are saying that a 4 ohm configuration will make the amp run hotter and components will fail sooner.

But correct me if I'm wrong:

Suppose that you need 300 watt power for a gig; with the 4 ohm cab you don't have to push the master volume so high as you did with the 8 ohm cab.
So I'm assuming that (with an 8 ohm), to get the same volume that you would get with the 4 ohm, you will have to push the amp harder (and hotter)

Is this thought right?

Another one: Do you know why some swr amp's have a power amp clip led and other's don't?
How do you know if a amp is clipping (without the clipping led)?

Thanks again for your answers.

Pedro Ferreira
 
#24
Originally posted by pedroferreira

Suppose that you need 300 watt power for a gig; with the 4 ohm cab you don't have to push the master volume so high as you did with the 8 ohm cab.
So I'm assuming that (with an 8 ohm), to get the same volume that you would get with the 4 ohm, you will have to push the amp harder (and hotter)
Click to expand...


The problem with this idea is this: As you drop the impedence that the amp is driving, the amp becomes less efficient i.e. it's output doesn't increase proportionally to the drop in ohms (with the SM400, going to 4 ohms bridged only yeilds 100 extra watts which won't really seem much louder for the same speaker configuration). The loss in power output is made up in the form of heat.

Some amps are designed to run more efficiently at 4 ohms than others. If the specs show only a slight increase in rated power at 4 ohms vs 8 ohms as with the SM400 bridged, you'll see a big drop in efficiency (little power increase, more heat). Better IMO to have more speakers at 8 ohms than 100 extra watts at a lower impedence with less speakers if more volume is the goal. A pair of 4 ohm 4x10s in stereo would be better than a single 4 ohm 4x10 bridged in this case. Better still to have more power availble. Headroom is oh so important for bass players especially if you play 5 string.


Another one: Do you know why some swr amp's have a power amp clip led and other's don't?
How do you know if a amp is clipping (without the clipping led)?
Click to expand...

Clip L.E.D.s add more cost to the design. The less expensive amps eliminate it for that reason. Without that feature, you have to use your ears to listen for distortion. Use caution and make sure the speakers can handle the max power that amp puts out. Most SWR amps that I've owned would start to clip with the master around half way up with the preamp gain control set correctly for the bass used.
 
#25
Suppose that you need 300 watt power for a gig; with the 4 ohm cab you don't have to push the master volume so high as you did with the 8 ohm cab.
So I'm assuming that (with an 8 ohm), to get the same volume that you would get with the 4 ohm, you will have to push the amp harder (and hotter)

Is this thought right?

Another one: Do you know why some swr amp's have a power amp clip led and other's don't?
How do you know if a amp is clipping (without the clipping led)?
Click to expand...
i think you´re right about the ohm issue
i have some wonders about the clippings myself
why does the swr clipp so early, with gain and master at 12 that i dont think is so hard
is it dangerous to keep pushing it with the powramp clipping(at least the led, not hearing any sound problems)?
i think it sounds better when it gets a bit pushed!
 
#26
Originally posted by Scotius2001

The loss in power output is made up in the form of heat.


In a normal situation It would be expected that half the load in an amp should double the power (ex.: 8 ohm=400 watt / 4 ohm= 800 watt).

The loss in power output is not only made up in the form of heat.

This is a quote from Terry Buddingh in BassGear March 2001:
"your amp doesn't quite deliver twice the power into half the load. It tries, but the power supply's own resistance limits capacity. Voltage drops across a resistance when current is increased. So when the power amp tries to draw more current, the power supply's voltage decreases - reducing the power amp's ability to produce maximum power."



My problem is that i only have money to buy one cab and maybe i need the extra 100 watt. What do you think? Is 400 swr watt enough?
I ask because one brand's 400 watts it's not the same that other's 400 watt.

I have a warwick pro tube IV head (which delivers 400@4 ohm) and a warwick 4x10 @ 8 ohm. I hardly have the power that i need. Also, the volume knob only increases power up to half way. From half way to maximum there's a little difference in power. Is this because of the 8 ohm load?

Thank you
Click to expand...
 
#27
Hey Warwick !!!, stop hijacking pedroferreira's thread.

Do a search on 8x10's here or start you're own thread.

ps. I had an SWR SM-900 that got wicked hot and activated its protect circuit two times while playing live (shut down the power section so it could cool off). At the time I was playing bridged through a Mesa Diesel 6x10 4 ohm cab.

I really dislike the fact that most rack-mount heads have the fans on the side (facing the rack wall) and their cooling characteristics leave something to be desired. Plan on carving a big hole where your fan is.
 
#29
Mo'Phat: Warwick may have posted in the wrong thread. Its not the end of the earth if someone posts another question in a thread. We're are all big kids here, so if he doesnt get his question answered, so be it. Theres no need to be so harsh either, a simple reminder is all it takes.

Warwick: Name calling isnt aloud here, espcially to that callibre. no need to be so angry when it comes to replying. sure, it may have been uncalled for, but take it like a man.

Why does everyone get upset so easily now-a-days :rolleyes: PM me if your not happy kiddies.
 

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