2. amps-preamps
  3. 130048-79

Can This Amp Power A 50 Foot Speaker Cable Run?

I'd like to run 50-60 foot speaker cables of 12 AWG cable to a pair of 6 ohm speakers for the rear channels in my home theater.

Would 10 AWG be better?  The specifications on the amp says 6 ohms is the minimum impedance that it will play safely.  Do you see any issues with this?  Does the amp below seem to be up to this task?

Stereo Amp Specs are as follows:

Dynamic Power Output: 2 × 140 Watts at 8 ohms
Total Harmonic Distortion: 0.08 % at rated power
IM Distortion: 0.08 % at rated power
Damping Factor: 100 at 8 ohms
Input Sensitivity and Impedance: 1 V, 50 kohms
Output Level and Impedance: 1 V, 10 kohms
Rated Speaker Impedance: 6 ohms MIN
Frequency Response: 10 Hz – 100 kHz, ±1 dB
Signal-to-Noise Ratio: 110 dB (IHF A, 0.5 V input)
____________________________________

Infinity Kappa 7.1 Speaker Specs are as follows:

Nominal Impedance: 6 ohms
Power Rating: 30 to 250 watts
RMS Crossover Frequencies: 500Hz, 4.5kHz
Frequency Response: 39Hz-35kHz +/-2dB
Sensitivity: 89dB 2.8V/1 meter

128x128mitch4t
11 responses Add your response
erik_squires
16,056 posts
 
I used to work in theaters, and 60-100 ft runs were typical.

12 gauge is just fine, unless you plan on powering a clothes dryer or electric oven.

Have you seen some of the flat cables out now? Very convenient for hiding under rugs and carpets.

Alternatively, if your inputs are truly balanced, run a balanced line instead, and put the amps near the speakers.

Best,


E
zavato's avatar
zavato
1,399 posts
 
A 50 foot speaker cable run should be ok, but I do wonder how robust a power supply the amp has if it can’t handle less than a 6 ohm load

erik_squires
16,056 posts
 
The longer the cable, the thinner it is, the higher the impedance will be at the end.

Best,

E
imhififan's avatar
imhififan
2,181 posts
 
I ’m with zavato, the cable should be ok, most important thing to consider is the amp has enough power for such a big theater room without clipping and destroy the speakers!
http://myhometheater.homestead.com/splcalculator.html
atmasphere's avatar
atmasphere
11,794 posts
 
Alternatively, if your inputs are truly balanced, run a balanced line instead, and put the amps near the speakers.

+1

@mitch4t
The amp won't have a problem driving the distance, but I think you will find that really long cables will rob the signal of detail and impact. In the case of cables that long, the difference between running a balanced line to the amps and then running really short speaker cables will be instantly obvious.
mitch4t's avatar
mitch4t OP
1,610 posts
 
It is a single_ended multichannel amp.

No option to run XLR cables.

Speakers will be rear/surrounds.

Amp cannot be placed near speakers.
georgehifi's avatar
georgehifi
10,312 posts
 
Speaker cable if they have capacitance get get higher in capacitance the longer you go, an amp "if bordering" on becoming unstable, "can" go into oscillation with the higher capacitance of long cable runs.
To cite an amp that was bordering on being unstable, the original Naim 250 in fact went into heavy oscillation and blew up as soon as it was turned on, when it saw the capacitance of Quad ESL 57's presented.

Cheers George      
mitch4t's avatar
mitch4t OP
1,610 posts
 
Admittedly, the amp that I was considering using is questionable for such a task (see the specs in my initial post).  I'll just bite the bullet and get a more robust amp to run those rear channels.  

Thanks to all of you for your input.
atmasphere's avatar
atmasphere
11,794 posts
 
@mitch4t you can still run balanced lines if you want. For something like this I’ve run the preamp into a set of line transformers at the preamp end, run the balanced cables can converted back to single ended using line transformers at the other end. You get a lot more resolution than you do running long speaker cables!

Of course if all the amps are built in to the same box this means you will have to get an additional set of amps for the rear channels.

Since that may not be practical there is another option which is often used in public address, which is to use transformers at the output of the amplifiers to convert to a much higher voltage. Then you run the speaker cables and convert back at the speaker end to the regular voltage. Take a look at this link:

http://www.belden.com/blog/broadcastav/All-About-70-volt-Speaker-Systems.cfm
kalali's avatar
kalali
1,977 posts
 
Quick side question if I may, would there be as noticeable difference in SQ between balanced and single ended ICs if the distance were 20' instead of say 50'?
yyzsantabarbara
4,811 posts
 
My understand from the Bryston reps is that for long distances only use balanced interconnects, not RCA. The longest RCA should not be more that 2 meters. The balanced can be 100+ feet.

Have you ever considered putting the amp near the rear speakers? You can run a long run of balanced interconnects to the rear amp(s) and then have a short speaker cable to the speakers. My understanding is that this is the best setup.
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