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Amp for Subwoofer



 
 
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  #1  
Old November 21st 19, 07:02 PM posted to rec.audio.pro
Bob Simon[_2_]
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Posts: 14
Default Amp for Subwoofer

I have some spare audio components and plan to modify a stereo system for biamp operation to add a subwoofer. The room is 22’ x 24’ and the existing amp and speakers are Adcom GFA-545 II driving Polk 10s (re-coned). I have available a Rane AC22 crossover, a second amp and an NHT passive subwoofer.

I’m thinking about using a Crown D-75A (which can be set up to operate in bridged-mono mode) to drive the sub. Here are the specs:
Dual mode (both channels driven):
55 watts into 4 ohms.
40 watts into 8 ohms.
25 watts into 16 ohms.
Bridge-Mono mode:
110 watts into 8 ohms.
80 watts into 16 ohms.

I’ve read that some applications require high current. Due to its light weight, I doubt this amp can source a lot of current. Does a subwoofer require a lot of current? If so, I’m wondering if this amp would not be suitable for this purpose.
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  #2  
Old November 21st 19, 09:31 PM posted to rec.audio.pro
John Williamson
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Posts: 1,660
Default Amp for Subwoofer

On 21/11/2019 18:02, Bob Simon wrote:
> I have some spare audio components and plan to modify a stereo system for biamp operation to add a subwoofer. The room is 22’ x 24’ and the existing amp and speakers are Adcom GFA-545 II driving Polk 10s (re-coned). I have available a Rane AC22 crossover, a second amp and an NHT passive subwoofer.
>
> I’m thinking about using a Crown D-75A (which can be set up to operate in bridged-mono mode) to drive the sub. Here are the specs:
> Dual mode (both channels driven):
> 55 watts into 4 ohms.
> 40 watts into 8 ohms.
> 25 watts into 16 ohms.
> Bridge-Mono mode:
> 110 watts into 8 ohms.
> 80 watts into 16 ohms.
>
> I’ve read that some applications require high current. Due to its light weight, I doubt this amp can source a lot of current. Does a subwoofer require a lot of current? If so, I’m wondering if this amp would not be suitable for this purpose.
>

What power is the speaker rated at? I used to have a subwoofer that was
rated at 300 watts RMS, 1200 watts peak. At 8 ohms, that is just under
40 amps RMS at rated power, 150 amps at peak.

The situation is actually a lot more complicated, as speaker impedances
are reactive, depend to a degree on cabinet design and vary with frequency.

Your amp is rated to supply up to 15 Amps into a bridged mono 8 ohm load.

--
Tciao for Now!

John.
  #3  
Old November 21st 19, 09:55 PM posted to rec.audio.pro
Phil Allison[_4_]
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Posts: 457
Default Amp for Subwoofer

John Williamson wrote:

----------------------
>
>
> What power is the speaker rated at? I used to have a subwoofer that was
> rated at 300 watts RMS, 1200 watts peak. At 8 ohms, that is just under
> 40 amps RMS at rated power, 150 amps at peak.
>


** Fraid your math is waaaaay off.

Power = "I squared R" or I = sq.rt P/R

So 6.12Arms or 8.6A peak.


> Your amp is rated to supply up to 15 Amps into a bridged mono 8 ohm load.



** No way:

I = sq.rt P/R

110/8 = 13.75 so I = 3.7A rms


...... Phil



  #4  
Old November 21st 19, 11:22 PM posted to rec.audio.pro
Bob Simon[_2_]
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Posts: 14
Default Amp for Subwoofer

On Thursday, November 21, 2019 at 2:31:11 PM UTC-6, John Williamson wrote:
> What power is the speaker rated at? I used to have a subwoofer that was
> rated at 300 watts RMS, 1200 watts peak. At 8 ohms, that is just under
> 40 amps RMS at rated power, 150 amps at peak.
>
> The situation is actually a lot more complicated, as speaker impedances
> are reactive, depend to a degree on cabinet design and vary with frequency.
>

NHT SW2: 10" woofer in vented enclosure. Frequency response: 21Hz-350Hz, ±3dB direct in. Crossover: 130Hz (passive version, built-in). Sensitivity: 89dB (2.83V at 1m), 200W maximum. Impedance: 8 ohms nominal, 6.2 ohms minimum.

I'm going to go ahead and configure the amp (which does NOT have a beefy power supply) for mono mode and try it out.
  #5  
Old November 21st 19, 11:28 PM posted to rec.audio.pro
Scott Dorsey
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Posts: 16,656
Default Amp for Subwoofer

Bob Simon > wrote:
>
>I=E2=80=99ve read that some applications require high current. Due to its =
>light weight, I doubt this amp can source a lot of current. Does a subwoof=
>er require a lot of current? If so, I=E2=80=99m wondering if this amp woul=
>d not be suitable for this purpose.


Try it. Does it clip? Does it overheat? If not, go with it.

The D-75A is not exactly the best sounding amplifier of all time, but
putting it on a subwoofer is likely to avoid most of the sound issues
with it, and that NHT subwoofer isn't a very demanding load.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
 




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