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How to bridge a macrotech 9000i amp

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Fernando Lopez:
Hi, some help here please!!!!

I recently upgraded to a crown macro tech 9000i amp to power my 2  (4 Ohms) Danley TH-118s

My previous amp experience was with the EV CP4000s which I figured out. But I am having a hard time with my new amp.

I have 2 questions

1) Should I power one sub from each channel or should I bridge the sub to power the subs?


2) If bridge is the answer how do I do it?



Anyway this is the back panel:



and here are the amps specs:


Power Output
Guaranteed minimum power in watts at 20 Hz-20 kHz with 0.35% THD
    
 
4-ohm Dual (per ch.).................................3,500W
8-ohm Dual (per ch.).................................1,500W
4-ohm Bridge.............................................5,600W
8-ohm Bridge.............................................7,000W
2-ohm Dual (per ch.) / 20 mS BURST.......4,700W
2-ohm Dual (per ch.) / 20 Hz - 20 kHz......2,800W
2-ohm Dual (per ch.) / 1 kHz.....................2,800W



Here are the subs specs:

 
Operating Frequency Range ........................ 40 Hz -250 Hz - 3 dB
 .................................................................... 28 Hz 300 Hz -10dB
Sensitivity @ 1M ............................................................ 108 dBSPL
 .............................................................. 112 dBSPL @ 100 Hz max
 ........ (Referenced to 2.83V @1M space, measured as 28.3V @ 10M)
Maximum Output ................................. 137 dBSPL/143 dBSPL Peak
 ............................................. 143 dBSPL/149 dBSPL Peak @ 134 Hz
Input Power Ratings ................. 1800 W continuous, 3600 W program
Nominal Impedance .................................................................. 4 ohms
Minimum Impedance ................................................. 3 ohms @ 67 Hz
Recommended Processing ................ 25 Hz HP @ 24 dB/Butterworth
Drivers ......................................................... LF 1 x 18 Long excursion
Input Connections ................................................................. 2-NL4MP
Enclosure Material ............ 13ply, 18mm Baltic Birch, polyurea coate



Thanks for your replies!!!!!

TJ (Tom) Cornish:
You can't bridge this amp (or pretty much any other amp) into a pair of 4-ohm boxes, which present a 2-ohm load to the amp in this configuration.

Power one speaker on each channel.

Geoff Doane:
First of all, you've really got to work on re-sizing those images, so we don't have to do a whole lot of horizontal scrolling to read this post.

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.

And lastly, the specified 4Ω/channel power would seem to match the speakers pretty closely, and you wouldn't be able to run both 4Ω speakers on the bridged output anyway.

GTD

Tim McCulloch:

--- Quote from: Geoff Doane on January 24, 2011, 10:39:27 AM ---First of all, you've really got to work on re-sizing those images, so we don't have to do a whole lot of horizontal scrolling to read this post.

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.

And lastly, the specified 4Ω/channel power would seem to match the speakers pretty closely, and you wouldn't be able to run both 4Ω speakers on the bridged output anyway.

GTD

--- End quote ---

The Macro-I and I-Techs are optimized for 4 ohm loads.  There was a fair bit of discussion about this when the original I-Techs came out.  You can probably find it on the PSW FUD forums with a search.s

Geoff Doane:

--- Quote from: Tim McCulloch on January 25, 2011, 02:25:41 PM ---The Macro-I and I-Techs are optimized for 4 ohm loads.  There was a fair bit of discussion about this when the original I-Techs came out.  You can probably find it on the PSW FUD forums with a search.s

--- End quote ---

I went back and searched. The discussion mostly revolved around the fact that the 2Ω rating was nowhere near twice (and sometimes even less than, depending on how it was measured) the 4Ω rating.  What I am questioning is is the assertion that the amp will put out considerably more than twice the power into 4Ω than it will into 8Ω (all other factors presumably being equal).  With one 8Ω load per channel, the amp will deliver 1500W per channel.  With 2 8Ω loads per channel (equivalent to 4Ω), it claims total power of 3500W per channel, or 1750W into each 8Ω load.

Where did the extra 500W per channel come from?  Has Crown discovered "negative resistance", and incorporated it into their amplifiers?

GTD

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