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How to bridge a macrotech 9000i amp
Dan Johnson:
--- Quote from: Geoff Doane on January 24, 2011, 10:39:27 AM ---Second, there's something wrong with those amp specs. I have a hard time believing that the 8Ω power is considerably less than half the 4Ω power.
--- End quote ---
I found the same specs that he posted on Crown's website but then there were another set of specs in the manual (both shown below).
I don't understand why the 8 ohm bridged rating is higher than the 4 ohm bridged rating.
ThomasKielhofner:
Geoff
It's already been stated by Tim Mc that Crown optimized these amps for 4 ohm loads, that is why they are spec'd at more than double their 8 ohm power rating into 4 ohms.
Dan
Again, these amps (and the I-tech) are optomized for 4 ohm loads. When the amp is bridged into 8 ohms it's the equivalent of running it in stereo with a 4 ohm load on each channel.
Geoff Doane:
OK, let me try this again. We've long since swerved off-topic, but I think the OP's question did get answered.
--- Quote from: Thomas Kielhofner on January 26, 2011, 03:21:04 AM ---Geoff
It's already been stated by Tim Mc that Crown optimized these amps for 4 ohm loads, that is why they are spec'd at more than double their 8 ohm power rating into 4 ohms.
--- End quote ---
I have no problem with the 2Ω/4Ω discrepency. The amp is simply going into current limiting, and the maximum output is throttled back depending on the duty cycle of the signal, the amplitude, and the impedance of the load.
However, there is no need to artificially limit the output voltage at lower load currents (8Ω), but that is what the specs imply.
Let's apply some numbers (and assume we're dealing with sine waves):
3500W into 4Ω is 118.3 Vrms
1500W into 8Ω is 109.5 Vrms
The amplifier is working half as hard, yet the maximum voltage available has gone down.
Maybe there is more to the specs than Crown is telling us. Maybe the 8Ω spec is for a one second burst, while the 4Ω spec is only 100 mS. It's a pretty safe bet that neither one is continuous, since a 120V, 20A circuit can't supply even 3000W (8Ω rating, both channels) for very long before the breaker protecting the circuit trips.
GTD
Fernando Lopez:
Yes my question has been answered
Thanks to all who contributed!!
Regarding the image if you refresh it will come out small
Todd Rasmussen:
--- Quote from: Geoff Doane on January 26, 2011, 08:18:03 PM ---...since a 120V, 20A circuit can't supply even 3000W (8Ω rating, both channels) for very long before the breaker protecting the circuit trips.
GTD
--- End quote ---
Right, but nothing says the rated power is with respect to a 120V 20A circuit. In fact, it's not. 1/3 power is roughly 28 amps @120V according to the specs. Full power would be more, much more.
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