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710 posts

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# 95968 17-Jan-2012 19:58
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Hi there,

I've just bought a second hand sub woofer, Looking at the connections it has two RCA inputs on the back of the sub. But my AV receiver only has a single rca sub woofer out.

Am I right in thinking I can pick up an adapter from DSE to merge the two channels together. And is there any loss of quality for doing so?

Another question is What should I set the crossover to? My Kef C5 floor speakers aren't big on bass, so I would like most of it to go to the sub woofer.

TIA

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  # 570117 17-Jan-2012 20:12
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Yeah you can use a Y cable as you suggest, no problems doing that really. Many subs don't require you to do this as they merge both signals inside the sub itself anyway, given there's only one speaker in it.

Typically these days you set the sub crossover very high, even fully round as far as it goes, and use the internal electronic crossover of the receiver. This obviously depends on your receivers capabilities.

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Ultimate Geek


  # 570118 17-Jan-2012 20:12
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Do the RCA inputs have labels?
On my sub one RCA input is a direct input that bypasses the crossover in the sub, the other RCA input uses the subs variable crossover control.

 
 
 
 




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Ultimate Geek


  # 570126 17-Jan-2012 20:19
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kendog: Do the RCA inputs have labels?
On my sub one RCA input is a direct input that bypasses the crossover in the sub, the other RCA input uses the subs variable crossover control.


On the sub, An infinity BU80 it has two inputs labeled low level input Left and Right channels.





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  # 570127 17-Jan-2012 20:23
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Jaxson: Yeah you can use a Y cable as you suggest, no problems doing that really. Many subs don't require you to do this as they merge both signals inside the sub itself anyway, given there's only one speaker in it.

Typically these days you set the sub crossover very high, even fully round as far as it goes, and use the internal electronic crossover of the receiver. This obviously depends on your receivers capabilities.


Thanks for your reply. The receiver is a Sony STR-DH520 7.1

With the addition of the sub it will now be a 2.1 system. I'm pretty green when it comes to home audio and electronics.

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  # 570159 17-Jan-2012 21:33
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Typically (and there are exceptions) you take a digital coax cable and plug it into the left hand input on the back of the subwoofer. It's a pretty easy test to muck around with - so go nuts.



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  # 570254 18-Jan-2012 09:09
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Dunnersfella: Typically (and there are exceptions) you take a digital coax cable and plug it into the left hand input on the back of the subwoofer. It's a pretty easy test to muck around with - so go nuts.


Are there any differences with cable types? Is there a difference between a standard rca cable and a digital coax cable?

I have a twin monster cable 2 x male to 2 x male connectors I was planning to use. I pick the Sub up today. Just want to make sure I have exactly what I need to make it work when I get home.

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  # 570272 18-Jan-2012 09:48
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Wills1:
Dunnersfella: Typically (and there are exceptions) you take a digital coax cable and plug it into the left hand input on the back of the subwoofer. It's a pretty easy test to muck around with - so go nuts.


Are there any differences with cable types? Is there a difference between a standard rca cable and a digital coax cable?

Digital Coax cables typically have an impedance of 50 or 75 ohm and are not the ideal thing to use for low level audio, but will work at a pinch.  Shielded audio cable is what you should be using for analogue signals like this.

Wills1: I have a twin monster cable 2 x male to 2 x male connectors I was planning to use. I pick the Sub up today. Just want to make sure I have exactly what I need to make it work when I get home.

If the monster cable you are referring to is shielded (with one conductor wrapped around the outside of the other), then it should be fine.  But if it's twin-core speaker cable with the conductors laid side by side, then it won't be fine, because it has no shielding.





 
 
 
 


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  # 570281 18-Jan-2012 10:04
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What's it all sounding like now?

Easy cross over test (before you get too technical) is to download some test tones on CD.

Start with the really low frequencies and see how the volume/response behaves as you go up the scale. It will be quiet down low and then the subwoofer will start to kick in. Ideally you want a similar volume from all tracks from then on.

If you have a hole in the middle, where it's quiet then you may be in that zone where the subwoofer has stopped outputting but the main speakers can't go that low. In which case you need to raise the subwoofer cut off frequency. And vice versa, if it gets really loud then both the subwoofer and the speakers are contributing that frequency.



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  # 570400 18-Jan-2012 14:42
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Just got it home and it won't work with my monster cable. I've enabled the sub on the amp, but the sub doesn't seem to work.

I will go and buy 1 male to 2 male RCA and see if that works. I've tried using a single cable in both the left and right channels with no luck.

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  # 570403 18-Jan-2012 14:48
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That doesn't sound right.  Are you sure you have:

a) A source that has some .1 / sub woofer bass component to it

b) Selected a play mode on your receiver that actually includes the subwoofer.  Stereo for instance often is only front left and right, not the .1 sub channel.  If you are on some direct or pure mode then this is often just stereo only.

c) Checked the cable in some other way to ensure it's still conducting properly and isn't faulty.

Banana?
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  # 570419 18-Jan-2012 15:04
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Jaxson: That doesn't sound right.  Are you sure you have:

a) A source that has some .1 / sub woofer bass component to it

b) Selected a play mode on your receiver that actually includes the subwoofer.  Stereo for instance often is only front left and right, not the .1 sub channel.  If you are on some direct or pure mode then this is often just stereo only.

c) Checked the cable in some other way to ensure it's still conducting properly and isn't faulty.


+1

It sounds like you are playing a CD, which the receiver picks up as 2 channel, thereby not using the .1 Sub channel. Your receiver should have some sort of test tones (for calibration) that will tell you if you have connected it correctly.   



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  # 570429 18-Jan-2012 15:13
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I was playing the music channels on sky.

I enabled 2.1 on the amp and tried pII music and movies. I can see the subwoofer light on the amp but nothing coming from the sub

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  # 570450 18-Jan-2012 15:50
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Try a CD with some bass content instead initially.

What are your receiver subwoofer crossover frequency settings?  Try 120 Hz initially if you can adjust this sort of thing.

Do you know that your sub actually works?

Is the sub volume right up?

For a short test you can even use a Headphones jack to RCA cable from an mp3 player etc.  Just some audio to see if it actually does anything.



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  # 570462 18-Jan-2012 16:08
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Ok I tried changing the musky setting from PCM to Dolby and the sub has sprung to life. But now I can only change the volume with the amp remote? Really weird

Does the PCM setting not output for a subwoofer?



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  # 570463 18-Jan-2012 16:09
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Jaxson: Try a CD with some bass content instead initially.

What are your receiver subwoofer crossover frequency settings?? Try 120 Hz initially if you can adjust this sort of thing.

Do you know that your sub actually works?

Is the sub volume right up?

For a short test you can even use a Headphones jack to?RCA cable from an mp3 player etc.? Just some audio to see if it actually does anything.


I've got the sub crossover set to max. But can't seem to find out how to change it through the amp

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