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Connecting a subwoofer

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Re: Connecting a subwoofer

Postby engrssc » Sun Dec 16, 2018 5:52 pm

"Y' (parallel) connections deteriorate the audio quality due to impedance mismatch. :(

Rgds,
Ed
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Re: Connecting a subwoofer

Postby ludu » Sun Dec 16, 2018 6:29 pm

RichardW wrote:Looking at the card and the sub, what is wrong with two "Y" adaptors to split both the "front" soundcard outputs into two?

Indeed, it’s the cheaper solution. I’m also wondering why a "Y" connection is so often discouraged. I know this kind of cable is inappropriate merging sources, but here we’re splitting.
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Re: Connecting a subwoofer

Postby engrssc » Sun Dec 16, 2018 7:02 pm

Your call.

Rgds,
Ed
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Re: Connecting a subwoofer

Postby 1961TC4ME » Sun Dec 16, 2018 8:15 pm

engrssc wrote:"Y' (parallel) connections deteriorate the audio quality due to impedance mismatch. :(

Rgds,
Ed


And, not saying it's gonna happen but an impedance mismatch could cause damage to something in the audio chain. I wouldn't risk that happening.

A couple other thoughts..... How content are you to stick with 4 audio channels and will / does it suffice? A new soundcard with more channels would be a straightforward solution plus open up additional options for you.

If 4 channels does the job then my question would be, what do you have invested in your current sub? Generally speaking, subs without audio outs usually fall into the lesser expensive category (I had one like this myself). And again, if the 4 audio channels is all you'll ever want and a new soundcard doesn't make sense, then if it were me I'd be out sub shopping.

Marc
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Re: Connecting a subwoofer

Postby jkinkennon » Sun Dec 16, 2018 9:33 pm

There is an impedance mismatch with all the audio circuits we customarily use. When using a 'Y' splitter to drive two loads the source impedance will be relatively low and the load a much larger impedance just as is the case without a splitter. Think of a 200 ohm source (higher or lower) driving perhaps a 20k ohm load. Insert the splitter and the 200 ohm source is driving a 10k load. Nothing really changes except for a minute level drop. In telephony it's quite another matter with miles of cable and matching impedances where echo suppression due to reflections and duplexing make for huge issues.
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Re: Connecting a subwoofer

Postby ludu » Mon Dec 17, 2018 5:25 am

1961TC4ME wrote:A couple other thoughts..... How content are you to stick with 4 audio channels and will / does it suffice? A new soundcard with more channels would be a straightforward solution plus open up additional options for you.

My current sound is a RME HDSPe AIO (http://www.rme-audio.de/en/products/hdspe_aio.php). It has only 2 stereo analogue outputs, but many digital outputs: one AES pair, one SPDIF pair and 4 ADAT pairs. I have recently understood what do with the ADAT output, using a converter like the Behringer ADA8200, for example. But I still need help for the AES and SPDIF outputs. Which converters are required?
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Re: Connecting a subwoofer

Postby magnaton » Mon Dec 17, 2018 10:22 am

Ed has posted and given a link to a cost effective S/PDIF digital to analog converter. This will give you the 2 additional audio outputs you are looking for. The ASIO driver for the RME should list these in the drop list when assigning output channels. Many audio interfaces offer an digital output (and input) for an S/PDIF or ADAT connection. On my setup, I'm using the S/PDIF output for may surround (rear) speakers. Works great!

Danny B.
Last edited by magnaton on Mon Dec 17, 2018 1:07 pm, edited 1 time in total.
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Re: Connecting a subwoofer

Postby sjkartchner » Mon Dec 17, 2018 10:59 am

RichardW wrote:Looking at the card and the sub, what is wrong with two "Y" adaptors to split both the "front" soundcard outputs into two?

The subwoofer could then be connected to, and in parallel with, the front channels.


Splitting an output line-level signal with a passive "Y" adapter may or may not (depends on a variety of factors) affect the signal level and/or tone. Only experimentation can determine if either is a factor.
Stan Kartchner, Tucson, AZ USA
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Re: Connecting a subwoofer

Postby RichardW » Mon Dec 17, 2018 8:48 pm

Has anyone who has mentioned the "impedance mismatch" issue checked to see what the various input and output impedances actually are and noted how many of those are mismatched even without any parallel connections?

One of the HDSPe AIO outputs has an impedance of 50Ω and the phones output is 30Ω. My guess is that the active speaker inputs will be much higher and so a mismatch will already exist. In fact, I would expect that putting the speakers in parallel will reduce the mismatch. https://www.manualslib.com/manual/45840 ... =71#manual

Sorry, I still can't see anything wrong with using "Y" connections.


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Richard
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Re: Connecting a subwoofer

Postby jkinkennon » Mon Dec 17, 2018 9:28 pm

Input impedance is often not specified for audio interfaces and amps precisely because it's not a terribly relevant spec as we don't attempt to match impedances. The Crown XLS amps specify 20k ohms for a balanced input and 10k for unbalanced. I threw out an output impedance or 200 ohms as an example but that is likely on the high side as I've just checked a couple of interfaces that are about 50 ohms. Again, this specification will be missing for many audio interfaces as it is not relevant for real world operation. Thus 'Y' cables just work correctly as signal splitters. It's possible to imagine poorly designed input circuits that might interact when fed with a 'Y' cable but that hypothetical possibility shouldn't prevent their use.
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Re: Connecting a subwoofer

Postby engrssc » Mon Dec 17, 2018 10:12 pm

Sure wish someone would have pointed out Y cables before I spent all those thousands of USD on all those audio DA's in my production truck. Looked in my interface box, no Y cables. Hmmm. :o

Seriously, there is always the issue of s/n and hum without any isolation. And an aside, we use all balanced audio in the truck and are in the process of going with fiber, no more copper (for audio or video). Exception, the 3 ph power mains. :roll: Can't push many hundred amps thru fiber. Too much of a load. :wink:

Plus impedance isn't just resistance but combined with the effects of reactance as well. Then there's lead length and routing assuming shielded/screened. Thought as long as the sound card has extra outputs available for a few bucks, why not use them and keep everything nice and clean?

Why don't we let Luc hook up his sub (quite a few options presented here) while we commiserate over some spiked cider or eggnog? 8) A little early, but Happy New Year. Imagine twenty nineteen already.

Rgds,
Ed
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