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Is it worth using a Subwoofer Splitter Y-Adapter Cable?

TK4535

Standard Member
I am looking for a bit of advice,i have just ordered a mordant short 309i and i was just wondering if its worth using a Subwoofer Splitter Y-Adapter Cable to coonect both left and right ins on the sub?.A freind of mine has a kef psw 2000 and uses a splitter on it but i just wondered on the performance benefits using one has.

many thanks for any replies
 

chrisgeary

Member
This gets asked quite a lot. The answer is that it makes no difference whatsoever, unless you are feeding it a stereo signal in the first place - usually its a mono signal from the sub output.
 

MikeK

Novice Member
It depends on the design of the sub and the amp in the subwoofer.
With both inputs driven you'll get more input signal when the amp sums the two inputs together - then there are the more esoteric designs, multiple woofers, dual voice coil woofers.......and so on.

Bottom line is to try it and see.
The cables are or should be, just a few quid - don't fall for any snake oil here!

In average use (or what I would call averade use), you'll probably find Chris is right and it makes very little, if any, discernible difference, but if you drive your sub hard, then you may well find it does!
 
A

amigaone

Guest
No do not think about connecting that way, better to use a L/R phono if twin drive from amp, subwoofer have level control on panel so i would only use one lead.
 

Soundoctor

Novice Member
Sorry, but it the answers abov are a bit on the vague side; here is the whole story:

If you are using a HOME THEATER receiver wih bass management, and have ONE [mono] sub out connector, then run ONE RCA---RCA wire. The sensitivity of the sub, its panel markings, the settings in the receiver and so on all should properly track together to give a pretty close correct level in the room when everything is set to its relative "0" positions.

IF at this point you put a Y cord at the sub you are doing exactly the same thing as raising the level 6dB; this is because you are summing 2 coherent inputs (voltages).

IF you have a 2-channel setup, i.e. a "stereo", Then you would typically want to use 2 RCA--RCA wires from the preamp outs to both the sub inputs; then you have the stereo summing taking place inside the sub which gives you mono bass while preserving the stereo signal separation going into the main amps.

IF you only have one set of PREAMP OUTS in the abovementioned STEREO setup, you may want to use 2 separate Y-cords and effectively "MULT" the left and right outputs; one set goes to your power amp; the other set goes to the sub.

Regards,
Barry
(former Senior Engineer, M&K)
 

Member 96948

Distinguished Member
IF at this point you put a Y cord at the sub you are doing exactly the same thing as raising the level 6dB; this is because you are summing 2 coherent inputs (voltages).
Clarify this for me. Whether one input or two via a Y lead, the voltage applied by the LFE output across the inputs will remain the same. Connecting to two inputs in parallel, will halve the impedance seen by the amp which would double the current required. I also thought doubling a signal results in a 3dB increase, with 6dB requiring a quadrupling?

I'm quite happy to be wrong, I just need this clearing up.:)

IF you have a 2-channel setup, i.e. a "stereo", Then you would typically want to use 2 RCA--RCA wires from the preamp outs to both the sub inputs; then you have the stereo summing taking place inside the sub which gives you mono bass while preserving the stereo signal separation going into the main amps.

IF you only have one set of PREAMP OUTS in the abovementioned STEREO setup, you may want to use 2 separate Y-cords and effectively "MULT" the left and right outputs; one set goes to your power amp; the other set goes to the sub.

Regards,
Barry
(former Senior Engineer, M&K)
I know the OP doesn't address this point, but what are your thoughts on high/speaker level inputs as an alternative for the stereo boys? I can't remember seeing them on any of the M&Ks I've had dealings with.

Russell
 

TK4535

Standard Member
Thanks for the advice guys :thumbsup:
 

Soundoctor

Novice Member
Clarify this for me. Whether one input or two via a Y lead, the voltage applied by the LFE output across the inputs will remain the same. Connecting to two inputs in parallel, will halve the impedance seen by the amp which would double the current required. I also thought doubling a signal results in a 3dB increase, with 6dB requiring a quadrupling?

I'm quite happy to be wrong, I just need this clearing up.:)

I know the OP doesn't address this point, but what are your thoughts on high/speaker level inputs as an alternative for the stereo boys? I can't remember seeing them on any of the M&Ks I've had dealings with.

Russell
Woohoo! Let's start ALL over.

First before we go any further is the LFE issue: THE SUBWOOFER OUTPUT IS NOT LFE !!!!!!!!!!!!!
Again: THE SUBWOOFER OUTPUT IS NOT LFE!!!

To absolutely clarify:
LFE is an effects channel used in the optical track in movie theaters because there is not enough dynamic range in the optical channels for Low Frequency Effects. Movie theaters usually have 5 channels plus a sub channel PLUS an LFE channel. A theater can get away with multiple bass sources because the room is so big - typically much larger than the wavelength of the lowest frequency of interest, i.e. 55 feet at 20Hz.

The actual LFE channel itself may go down to almost DC and up to 120 Hz (it's -3db point) and in the beginning (that would be 1996 or so) there was consternation about what happens to the "lost" area between 80 and 120 Hz when this stuff is summed to the subwoofer out jack, and it is that level of audio nitpicking which busy's people's brains and allows such things as republicans to slip into the white house.

You might enjoy my freq to wavelength chart here:
http://www.soundoctor.com/freq.htm

On DVD's released for home use, most MOVIE soundtracks have 5 full freq channels of surround info (L C R Ls Rs) and one channel called the "Boom" track; this is the LFE in a movie theater.

The bass management circuit in every (Dolby / THX) receiver strips everything below 80 Hz off of each of the 5 channels, sums it into mono, adds the LFE channel (if any) and THAT is what comes out the subwoofer jack.

[[ I have a WHOLE other tirade about 5,6,7,n.1 misinformation, but I'm still working on that for my website & book]]

As far as the levels go, These are not lightbulbs drawing current. An audio SOURCE is low impedance driving a very much HIGHER impedance load, or if your'e using a Y connector, loads.

At the input to a sub each input is buffered an then summed into mono. They are buffered so that the actual RCA connectors are not shorted to mono in case you are simply parallelling the inputs to your stereo power amp... otherwise everything in the room would be summed into mono.

If you take ONE RCA cable and plug it in and measure the output you get a 0dB reference. If you take a Y cord and plug in the 2nd input you get 6dB more. That's VOLTAGE. (that also is 4 x the power)
When you change ANY signal 3dB, (you are adjusting a volume control or gain control) that doubles or halves the power... going from 1 watt to 2 watts is 3dB; going from 10,000 watts to 20,000 watts is 3dB.

In the old instances of broadcast devices, they were balanced 600 Ohms on BOTH the inputs and outputs. When you terminate any given source impedance / resistance with the equivalent load impedance/resistance the voltage on that line will halve, i.e become 6dB less.

Nowadays, the source impedance of nearly any output is low; ideally as low as possible (0 ohms) but of course this is not possible so a buildout resistor is usually used to present a source Z of 50 to 200 ohms to the outside world. The input Z of the next stage is typically 10k, 20k, 25k, 50 k ohms for solid state equipment and often higher, 100k - 500k for tube equipment. Therefore, practically speaking, the input stage does not "load" the previous output stage.

In the case of line level equipment all we are really doing is generating a VOLTAGE and then MEASURING that voltage at the next succeeding stage or stages.

In the case of SPEAKER level equipment, we are mostly transferring POWER from the amp to a load (the speaker) so there ARE higher currents that we are dealing with and the impedances are somewhat more important.

Again, in the days of tube amps, you had an output transformer with taps to match the load impedance so that all the available POWER was transferred fom the amp to the load.

Nowadays with solid state amps the source impedance is very low (oh, perhaps from .1 ohm down to .001 ohm) and when this source impedance is divided by the load impedance (typically 8 ohms) that gives you the damping factor.

When the amplifier pushes the speaker cone in a direction then the elasticity of the mechanism attempts to move the c one back to the center position. During this time the speaker acts as a generator. The voltage it is generating has to go somewhere... where it goes is back into the power amp (we could hope back into the storage caps) and the entire output circuitry of the power amp acts as an "active load" But not to digress too far...

Since the human perception of hearing roughly follows a log pressure relationship, a +6dB change is twice the voltage, twice the air pressure, and to most trained ears is "about" twice as loud, although strictly speaking there IS NO SUCH THING as twice as loud, just as there is no such thing as "twice as beautiful". Once you study audio levels with a calibrated attenuator you can just about discern a 1dB change; you can "just" easily discern a 1-1/2 dB change; and a 6dB change "seems" like twice, although to most people not familiar with audio, they think that a 10 dB change is "twice" or "half". It is a very interesting phenomena, also dependent upon the range of frequencies present while the attenuator change is taking place. I have discerned that the wider the frequency range present, the more level change it takes to affect the human perception, and this is oppositt to what logic or a "mental" experiment dictates! Try it!

As a suggestion, get yourself a 27 or 31 band graphic eq and learn each frequency (and level change). :smashin: It's like playing a piano or a saxophone - at first it seems impossibly hard and then it just pops into place in some alloted slot in your brain, and you simply "feel" it.

Barry
 

Member 96948

Distinguished Member
Cheers for taking the time to type that lot. Very informative and obviously sourced from a far greater depth of knowledge than my own. Indeed, I do know that the SW channel contains the LFE channel as a subset and you were quite right to point out my laziness. It may be semantics, but it prevents the spead of disinformation. I'll clean my act up forthwith!:)

Two quick questions.

When you say "everything below 80Hz", do you really mean everything? That implies brick wall filters.

Whilst chuckling at your Republican gag, I almost forgot that you raised a point thats been confusing the crap out of me. Where does the 80-120Hz info in the LFE track go? My current receiver allows me to set a number of different crossovers for the 6speaker channels and a separate crossover for the LFE channel. This crossover is labeled 'LFE' and not 'SW', just to be clear.

Owing to the Denon manual being in 'Engrish' and poor Engrish at that, you're pretty much out on your own. I'd decided to leave the speakers set to 'Small', the speaker crossovers to 80Hz and the 'LFE' crossover to 120Hz, which is the maximum.

When running the test tone sweep from my SMS-1 (which outputs a stereo test signal), altering the 'LFE' crossover seems to have no noticable effect, whereas altering the speaker's crossover does. I had come to assume that setting the 'LFE' crossover to max only affected the LFE track and could see no sense in curtailing it's output.

Am I about to find out I'm wrong?

Cheers,

Russel
 

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