LFE vs. R&L line level

[wafflebird]

I did a search and did not find specifically this question although I am sure it has been asked.

I just picked up yesterday a Martin Logan Dynamo sub , I am extremely impressed with it to say the least. I had a Velodyne VX-10 in my bedroom before and was un-impressed with it as I always had to have the gain maxxed out, and (due to furniture constraints) I had it sitting catty-cornered in a corner behind a chest-of-drawers. It was rear ported and I just was not happy. Anyway on to the question, in the (very detailed) owners’ manual it states the frequency response @ 25 Hz "When using the LFE input". It states this over and over again. Now I have it hooked up Sub-out (coax cable) of the receiver (Pioneer VSX-816) then into a Y and in the R&L of the sub. In the manual it says that the low pass filter is bypassed when using the LFE. Now even though that is said I still have my receiver set-up @ 100 HZ as the crossover, so regardless how I have it hooked up, the sub is not receiving anything other than that. Am I benefiting in anyway running the splitter or would it be better to lose the Y and run it straight to the LFE on the sub. It seems to me that the sub is set up for this for a receiver / pre-pro etc. I know this may seem like a simple question, but I just want to be able to get the best out of this awesome sub.

Just in case any of you are wondering about the sub itself it is phenomenal. We were watching a regular TV show and there was music in the background, I could here each individual bass note with clarity I have not experienced before. It was packaged extremely well with high quality packaging, and the bottom dense insulation had a piece of dense fiberboard for a solid base. I could say more but I won't probably not the place for it, I may make another post on it.

Thanks for your help folks in advance.

 

[MDS]

Subwoofers often have both regular 'line-level' right and left inputs in addition to a dedicated input labeled 'LFE'. This is purely for convenience so that the sub may be used in many different configurations.

Both the R/L inputs and the one labeled 'LFE' are low level (line level) inputs. The only difference is that the LFE input bypasses the sub's internal xover (as the manual states) whereas the R/L inputs do not. If you use the bass management of the receiver, you would want to use the LFE input so that the receiver is controlling the xover frequency and not the sub. However, if you use the R/L inputs, you can still use the receiver's bass management - you would just have to set the xover dial on the sub to a number that is higher than the frequency set in the receiver to get it out of the way.

Using a Y splitter to feed R/L inputs does nothing more than double the voltage going to the sub and that increases the gain. It sometimes helps to make the 'auto-on' feature of the sub work better because the signal strength is higher, but you can accomplish the same thing simply by turning up the level on the sub.

 

[BigGuy]

Does it really double the signal? One cable going in has X volts, use a Y splitter and that's X/2 volts for each. Attatch to the L+R inputs, Subwoofer combines x/2 and gets X voltage. Are all these assumptions correct, or am I missing somthing?
Brian

 

[MDS]

Does it really double the signal? One cable going in has X volts, use a Y splitter and that's X/2 volts for each. Attatch to the L+R inputs, Subwoofer combines x/2 and gets X voltage. Are all these assumptions correct, or am I missing somthing?
Brian

You're missing something.

The splitter doesn't divide the voltage - the signal will travel down both legs of the splitter (minus any mostly inconsequential loss caused by the splitter).

A subwoofer is mono and will sum the inputs. Say the voltage is 1 volt (the typical line level). You have two inputs, each at 1 volt. The sub sums them to mono and 20 * log (2/1) = +6.02 dB. In other words, the difference between 1 volt and 2 volts is ~6 dB.

 

[BigGuy]

Interesting, Why does a y-splitter work different then let say a satellite TV splitter\combiner? With a splitter\combiner there is a -3.5db attenuation on each output for a 1 to 2 splitter. I never exactly understood this, but the Low Voltage class I took said that even if you use only one of the outputs, the signal will still be -3.5db. If you take apart all the different steps, then using a y-splitter and then a y-combiner will double the signal? How does it double the signal without a external booster? Not trying to be difficult, just trying to grasp as much information as possible!

Brian

 

[MDS]

A Y adapter cable is not like a cable/sat splitter - it's just one wire split into two and the signal will travel down both sides. The doubling of voltage comes from the sub, not the Y cable, because it sums a stereo signal into mono.

 

[wafflebird]

So at the end of the day the Y is better?

So at the end of the day the Y splitter will get me more "Volume i.e SPL" than the straight single LFE correct? The sub should play a little louder at lower voulume with the Y right? Because of it esentially doubling the input as stated above? So leave it the way I have it would be best if I am reading correctly.

Thank you.

 

[sivadselim]

So at the end of the day the Y splitter will get me more "Volume i.e SPL" than the straight single LFE correct? The sub should play a little louder at lower voulume with the Y right? Because of it esentially doubling the input as stated above? So leave it the way I have it would be best if I am reading correctly.

Thank you.

No.

You were told that using the Y-splitter is the same as running the subwoofer at a higher volume setting. Unless you are already running the subwoofer at or near it's maximum volume (which you shouldn't be doing; if you are, your subwoofer isn't powerful enough for your space and you should consider another identical one or, better yet, a more powerful one), or if you have some problem with the auto-on function that the splitter resolves, you should NOT need a Y-splitter.

The same volume increase that is obtained by using the splitter can be attained by setting the subwoofer at a higher master volume setting. The amp will still work the same amount to provide the same output, either way.

 

[brendy]

I would go with what Martin Logan recommends.

 

[wafflebird]

Thanks for the input.

I have e-mailed Martin Logan but it was late Friday night. I expect a reply from them shortly.

Believe me I do not need any more power, this thing is literally incredible, and for a bedroom it is over-kill, but man-o-man what clean detailed over-kill it is.

The main reason I am asking is laid out above, the manual states the frequency response is 25-120 Hz then right after this it always says "When using LFE input". So I am led to ask what’s the difference? Why do they say that each time, is it set up internally to work differently i.e. lower when using LFE? I would not think so but they sure do say that every single time they mention frequency response, so it does beg the question.

 

[sivadselim]

The main reason I am asking is laid out above, the manual states the frequency response is 25-120 Hz then right after this it always says "When using LFE input". So I am led to ask what’s the difference? Why do they say that each time, is it set up internally to work differently i.e. lower when using LFE? I would not think so but they sure do say that every single time they mention frequency response, so it does beg the question.

The sub, when using the R+L inputs, has a variable low-pass filter from 30-80Hz.

The reason the frequency response is stated as being via the LFE input, is because that gives you the full, "unrestricted" frequency response of the subwoofer when using the unfiltered LFE input.

The frequency response of the sub if using the R+L inputs is going to depend upon the particular setting of the variable low-pass filter. But it will not be more than (around) 80Hz, as that is the maximum to which the variable low-pass filter can be set.

The reason they state the frequency response via the LFE input as the frequency response of the subwoofer is because that gives you the true, full range of the subwoofer when used with a surround processor that is providing the bass management crossover (as opposed to when using the sub's low-pass filter).