I suppose this question could go in an amp or speaker forum, but I'm hoping that PA guys will have experience of "funky" wiring configurations...
I have two subwoofer cabinets, each containing two 4 Ohm drivers. Each driver is rated at 150W RMS continuous, 300W max.
I can change the internal wiring of the cabinets, in order to make them either an 8 Ohm load (internally serial), or a 2 Ohm load (internally parallel). In both cases I understand each cabinet should then be rated at 300W RMS continuous and 600W max.
I have a Crown XLS2500 amp, which claims:
I assume that option 1 wouldn't be advisable as 440W is well under the max capability of the drivers.
Option 3 appeals, as each cabinet would be 8 Ohm (so easier/safer to drive if they were needed with a "lesser" amp). Both subs would play the same material, so having the amp bridged (with a single input) seems sensible.
Or would I be better off with the amp "seeing" each cabinet as a lower impedance load (i.e. option 2)?
I have two subwoofer cabinets, each containing two 4 Ohm drivers. Each driver is rated at 150W RMS continuous, 300W max.
I can change the internal wiring of the cabinets, in order to make them either an 8 Ohm load (internally serial), or a 2 Ohm load (internally parallel). In both cases I understand each cabinet should then be rated at 300W RMS continuous and 600W max.
I have a Crown XLS2500 amp, which claims:
- 2x 440W into 8 Ohm
- 2x 775W into 4 Ohm
- 2x 1200W into 2 Ohm
- 1x 1550W into 8 Ohm (bridged)
- 1x 2400W into 4 Ohm (bridged)
- Wire each cabinet in series internally (8 Ohm loads), and connect one to each amp channel (440W to each cabinet).
- Wire each cabinet in parallel internally (2 Ohm loads), and connect one to each amp channel (1200W to each cabinet).
- Wire each cabinet in series internally (8 Ohm loads), and connect them in parallel to the amp as a single 4 Ohm load (2400W bridged => 1200W to each cabinet)
I assume that option 1 wouldn't be advisable as 440W is well under the max capability of the drivers.
Option 3 appeals, as each cabinet would be 8 Ohm (so easier/safer to drive if they were needed with a "lesser" amp). Both subs would play the same material, so having the amp bridged (with a single input) seems sensible.
Or would I be better off with the amp "seeing" each cabinet as a lower impedance load (i.e. option 2)?
If you want 2 1/2 kW then a 4R load in bridge is your answer. Option 3.
Power the amp as near as you can get to the speakers to avoid loss in speaker cable.
If you are using the subs in a room, keep them together to avoid phasing issues as you move around the room.
Power the amp as near as you can get to the speakers to avoid loss in speaker cable.
If you are using the subs in a room, keep them together to avoid phasing issues as you move around the room.
I assume I want the ability to get 600W max into each cabinet - so options 2 and 3 would allow that.
It will be set up in a room. The plan would be for the subs to be about 2 meters apart, with the cable lengths likely something around 4 and 6 meters respectively (though I guess I could use 6 meter lengths for both, to keep things identical for both cabs).
It will be set up in a room. The plan would be for the subs to be about 2 meters apart, with the cable lengths likely something around 4 and 6 meters respectively (though I guess I could use 6 meter lengths for both, to keep things identical for both cabs).
With a 150w continuous rating, I'd put the drivers in series and one cabinet per channel on the amplifier.
Keep it simple. The amplifier will have an easy time, and the red lights will show when you're in danger. If you wire for 2ohm use, the amplifier will happily melt the speakers without getting close to the clip lights. Typically, amplifiers don't sound great when driven down at 2ohm, too. They can "handle" it, but that doesn't make it optimum.
Remember, +3dB is 2x the power.
Chris
Keep it simple. The amplifier will have an easy time, and the red lights will show when you're in danger. If you wire for 2ohm use, the amplifier will happily melt the speakers without getting close to the clip lights. Typically, amplifiers don't sound great when driven down at 2ohm, too. They can "handle" it, but that doesn't make it optimum.
Remember, +3dB is 2x the power.
Chris
+1 for all the reasons mentioned. The only time low frequency drivers should be powered to their peak rating is with classical music, for any popular genre you would be well advised to ignore this number. A 150w continuous rating means these drivers have a 75w rms rating so from a practical standpoint the 8ohm single channel output of this amp is more than sufficient.
chris661/conanski: thanks. I've not come across talk of impedance vs sound quality before (at least not with loudspeakers; though sometimes with headphones).
I understand that a low impedance load can cause issues for an amp; and of course the actual load impedance changes with frequency, so I assume a parallel wired cabinet (nominal 2 Ohm) may well drop below that for some frequencies. Are the sound quality issues purely because the amp is being forced to put out a high current?
Would there be any benefit to option 3 (two 8 Ohm cabinets, in parallel, for a 4 Ohm bridged load on the amp) vs option 1 (two 8 Ohm cabinets, one on either channel)? Or is having the amp bridged with a single 4 Ohm load effectively like having two 2 Ohm loads? Certainly the rated power output is the same: 2x1200W into 2 x 2 Ohm vs 1x2400W into 1 x 4 Ohm.
EDIT: Dammit. Lost a fairly long edit... short version: conanski; the drivers are rated 150W (IEC 268-5 18.1); which I understand to mean they'll take 300W RMS for short peaks.
I understand that a low impedance load can cause issues for an amp; and of course the actual load impedance changes with frequency, so I assume a parallel wired cabinet (nominal 2 Ohm) may well drop below that for some frequencies. Are the sound quality issues purely because the amp is being forced to put out a high current?
Would there be any benefit to option 3 (two 8 Ohm cabinets, in parallel, for a 4 Ohm bridged load on the amp) vs option 1 (two 8 Ohm cabinets, one on either channel)? Or is having the amp bridged with a single 4 Ohm load effectively like having two 2 Ohm loads? Certainly the rated power output is the same: 2x1200W into 2 x 2 Ohm vs 1x2400W into 1 x 4 Ohm.
EDIT: Dammit. Lost a fairly long edit... short version: conanski; the drivers are rated 150W (IEC 268-5 18.1); which I understand to mean they'll take 300W RMS for short peaks.
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Yep, the sound quality issues will be from the amplifier having to supply a lot of current. All a driver cares about is the voltage at its own terminals.
Your drivers are rated for 150W continuous. ie, it can survive (not necessarily sound good with) that power level for a time period of the order of hours. The "peak" rating is relying on the crest factor of the program material.
With drivers rated for 150w continuous, and 4ohm, putting them in series for an 8ohm load and connecting them to an amplifier which would produce 440w per pair of drivers (220w per driver) seems pretty ideal to me.
Clipping the amplifier occasionally would be fine, but if the red lights went up and stayed on, it's time to back off as the amplifier is still capable of burning the drivers.
If you went for option 3, you're still presenting the amplifier with a 2ohm load on each channel.
When you bridge an amplifier, it sets one output as positive, and one output as negative, with the speaker connected across the two. You've effectively doubled the available voltage swing.
If you imagine the 4ohm load as a pair of 2ohm loads in series, you'll see that at the connection between the two loads, the voltage is always zero. You could connect that to the negative terminals of the amplifier (which is also at 0V), and then it's pretty obvious that each side of the amplifier is seeing half of the load impedance when the amplifier is bridged.
If you did go for 2ohm use, you would be reaching the thermal limits of the drivers when the amplifier is still at -6dB.
While amplifier headroom can be good, it can also result in lots of power compression and lots of burnt drivers.
Chris
Your drivers are rated for 150W continuous. ie, it can survive (not necessarily sound good with) that power level for a time period of the order of hours. The "peak" rating is relying on the crest factor of the program material.
With drivers rated for 150w continuous, and 4ohm, putting them in series for an 8ohm load and connecting them to an amplifier which would produce 440w per pair of drivers (220w per driver) seems pretty ideal to me.
Clipping the amplifier occasionally would be fine, but if the red lights went up and stayed on, it's time to back off as the amplifier is still capable of burning the drivers.
If you went for option 3, you're still presenting the amplifier with a 2ohm load on each channel.
When you bridge an amplifier, it sets one output as positive, and one output as negative, with the speaker connected across the two. You've effectively doubled the available voltage swing.
If you imagine the 4ohm load as a pair of 2ohm loads in series, you'll see that at the connection between the two loads, the voltage is always zero. You could connect that to the negative terminals of the amplifier (which is also at 0V), and then it's pretty obvious that each side of the amplifier is seeing half of the load impedance when the amplifier is bridged.
If you did go for 2ohm use, you would be reaching the thermal limits of the drivers when the amplifier is still at -6dB.
While amplifier headroom can be good, it can also result in lots of power compression and lots of burnt drivers.
Chris
Is there a difference in connecting drivers (A) 3 in series first and then 3 strings parallel or (B) first 3 in parallel and then 3 strings in series?
My guess is no difference until 1 driver fails. With option B all other parrallel drivers will fail until the series connection is broken.
With option A you might lose 3 drivers as well, but then 1 from each series and only when driven hard.
Is there a difference and why?
My guess is no difference until 1 driver fails. With option B all other parrallel drivers will fail until the series connection is broken.
With option A you might lose 3 drivers as well, but then 1 from each series and only when driven hard.
Is there a difference and why?
At low impedances the loss of amplifier control over the driver becomes audible.. output becomes muddy, dynamics less crisp. This is particularly noticable at low frequencies.
Yes, and the big danger with that config is that you have enough power on hand to literally launch the cones across the room with a big bass hit so the amp would have to be limited to at least 3dB under full output.
You are mixing up terms here, you can't have peak and RMS at the same time.. it's one or the other. Peaks are very short duration.. on the order of miliseconds, the RMS level is more or less continuous. The IEC 268-5 signal is pink noise with a 6dB crest factor, so those peaks are 6dB above the continuous(rms) level. If we work backwords from the peak rating for your speakers 6dB down is 75w, that is the amount of power they can be expected to handle indefinitely with a steady state signal like a sine wave. As power levels go up from there the duty cycle of that signal must decrease proportionally or the drivers won't survive.
Thanks. I'm sure I read an article where the IEC 268-5 level was listed as RMS rather than Peak; but that does make sense.
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