Why have the sub volume control at halfway? (1 Viewer)

[DaleI]

Why should the sub's amp volume control be at the halfway point or higher and the sub level control on the receiver be in the -6 range or thereabouts?
Currently, I have my Sony SA-WM40's volume control around 8-9 o'clock. What am I losing by NOT doing the above?
Thanks-
Dale

 

[Neil Joseph]

I kept my sub's knob at the halfway point also. You can adjust higher but I would not crank it to the maximum level to introduce any unwanted distortion into the soundstage. At halfway or slightly higher, you then calibrate the sub to get the proper level and adjust the level using your receiver.
orangeman
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[Steve T]

Awhile back there was an article in one of the audio mags (Sound and Vision I think) about measured distortion on the subwoofer output of several popular receivers. With the sub output set @ 0db, distortion was quite high on some models. It was suggested that lowering the sub output level would lower distortion levels. I tried to do a search to find the thread related to this, but the search function is not available.
It has also been said that raising the sub amp volume level is good, but I think this is more opinion than anything else.
[Edited last by Steve T on September 27, 2001 at 03:48 PM]

 

[DaleI]

I know how to set-up the levels; I was just wondering why so many advocate turning the level up at least halfway and operating in the minus range on the amp. Something about getting the cleanest signal???? What's that about?

 

[Neil Joseph]

Dale, I think Steve just answered that question. I have to find that thread but Steve is saying that operating at 0dB and higher on your receiver's sub out, introduces unwanted distortion on many receivers. It stands to reason then that you would want to lower your receiver's sub out so it is operating in the "-" range. As it turns out in my setup, at the sub's halfway point, my receiver is set to -6dB in order to achieve the desired level I want.
orangeman
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[brucek]

Dale,
With respect to the other posts, I highly doubt that any receiver or preamplifier distorts the sub-out line level signal when the level is increased, any more than they would distort any other line out signal. Why would they. This is an operating range provided for you to use.
Generally, a preamp can pass signals from 20 to 20K fairly easily within their given THD specification. Why would the sub out line signal be any different. It has an adjustment range for balancing its level against the other speaker line output levels that can be set from minimum to maximum depending on the amount of control the receiver manufacturer has allowed.
These outputs are usually driven from an op-amp or similar device, and have an associated noise floor and signal component that increases and decreases with the settable output level.
Unlike the power amp in your receiver, or even an external power amp (both of which are usually and desireably physically close to the preamp), a sub is generally located quite a distance away in a corner using a very long interconnect. Even though single ended interconnects are shielded, this distance is a recipe for the introduction of external noise being picked up and sent to the power amp of the sub. By allowing you to dial down the level at the input of the sub, you can eliminate some of the effect of noise caused by this long interconnect run. If you had the input level control at max on the sub and had the preamps line output dialed down low to compensate, then any noise on the interconnect line will be a larger portion of the entire signal in relation to the original signal from the preamp as it enters the subs power amp.
This is why it's a good idea to leave the level on your sub at about half and adjust the receivers output to match accordingly.
brucek

 

[James Edward]

brucek- Long but wrong.
It IS because of a measurable increase in distortion of the sub output level at 0db or above in many receivers and processors that it is recommended that the level be backed off. I will quote the 'in the lab' section of a receiver review this month in Sound and Vision:
"The subwoofer output will not overload as long as it's trim control is set to -10db. Compensate for this by turning up the level on your subwoofer." The levels for overload vary from receiver to receiver, so others might only need a -3db or some other setting.
There was also a thread a while back indicating that a low gain setting on a sub amp might also act as a limiting factor in it's output.

 

[brucek]

I usually avoid telling people they're dead wrong, it tends to stop further discussion.
I also usually avoid placing any stock in what the mainstream audio magazines have to say about electronics. I've read far too many incorrect statements from these "reviewers" when they draw on their vast knowledge of english literature where their backgrounds and training tends to be rooted.
It's fairly easy to design a line output stage that doesn't distort signals at frequencies from 20Hz to 100Hz. There would be no reason for receiver manufacturers to do otherwise.
Certainly the subs level control can be a limiting factor on its output if set too low. This level control allows compensation for various levels of different systems and must be adjusted to allow for full volume of the subs output. This could be at quarter or half or even full clockwise position depending on the receivers line output level. Unnecessarilly adjusting it too high will just increase noise.
We'll have to agree to disagree on this one and let Dale decide.
brucek
[Edited last by brucek on September 28, 2001 at 12:29 PM]

 

[Todd Hochard]

Bruce,
You speak of what CAN be done, but look at what was MEASURED. How can one argue with that? Others besides Sound and Vision have come to the same MEASURED conclusion.
I've got mine set at -8 on the receiver, and +3 on the sub's volume.
Todd

 

[Mariusz Filonowicz]

I own Denon 3802 receiver and SVS 20-39PC sub. I calibrated my set up using Video Essentials, setting sub level to 81-82 db, which is equvalant to a level on a receiver of 0. The rest of the speakers is set to 75 db, with the receiver setting of -3, -4. If I follow some of your advices then I would have to set a sub level on the receiver in the + range as the volume on the sub is set to the maximum and I would have to compensate lower volume on the sub's amp with increased level on the receiver, which is already =0 (distortion ?). Does it mean that there is a problem with the output on the receiver or an amp in the sub?

 

[Steve T]

Sound and Vision publishes subwoofer output distortion for most, if not all, of the receivers they review. Here are a couple of examples:
JVC RX-1028V Dolby Digital Receiver
Subwoofer distortion (from 5-channel 30-Hz 0-dBFS signal; volume at 68, subwoofer trim set to -6).....0.8%
Denon AVR-3801 Dolby Digital Receiver
Subwoofer distortion
(5.1-channel, 31-Hz, 0-dBFS signal played at reference level; subwoofer trim at 0).... 1.9%
As you can see the distortion is rather high for both.

 

[Jeff_Krueger]

I would have to agree with most eveything said here as both Bruce and Todd are correct in a manner of speaking.
The recomendation from the magazine articles does serve an important purpose, which is to inform people that many recievers will not put out a completely distortion free unclipped signal at maximum output. The level at which a reciever or preamp will start to clip/distort will vary between different makes/models. The components outputing the preamp signals have an upper limit as to how much voltage they can put out and most will distort when the controls are set to maximum. To completely optimize setup of preamp levels it is important to find out at which exact control settings the signal will start to distort. Once you find at which settings you reach the upper limit of your reciever/preamp make a note of them. When it comes time to set up your sub-amp set your reciever to the settings at which you determined distortion began to set in, and then back it off a slight bit. Then turn the gain control on your amp up until it starts to clip and or it is too loud, then back the gain control off a little and leave it set there and never touch it again. By doing it this way you will be able to use the maximum clean output from your preamp without setting the amplifiers gain too high.
The level control is not actually the best name for it, as it is actually a GAIN control. The amplifier requires a certain amount of voltage from the signal source to put out full power, this number regardless of all other settings is fixed and will not change. The purpose of the gain control is to match the voltage of the input signal to the ammount that is required by the amp for full power. If you hook up a component that can only put out 2.5V and the amplifier requires 5V for full power then the input portion needs to apply enough gain to boost that 2.5V up to 5V (i.e. double). The problem you can run into is that any noise that is picked up in the interconnect on it's way to the amplifier was also just doubled along with the singnal. So you see that by using the lowest possible amount of gain you reduce your chances of amplifing extra noise along with the original signal. If your preamp cannot output a high enough signal and you use to little gain you will never get full power out of your amp. So it is a delicate balancing act.
The settings advised in those articles are just a general area that will work well for most people's equipment, but will not be optimized for each person's combination of components. There are several different methods to go about finding out at what levels your preamp will start distort/clip that doesn't require expensive equipment. Though after typing all this I can't think of any.

 

[DaleI]

Thanks for all the input to my initial question. My amp's sub setting can go as low as -20. Right now I have it at
-13 and the sub's volume control at the halfway mark. that gives me 75db.
Final question: If someone were to set the amp's sub setting to -20(and calibrate the volume control to 75db) would that necessarily produce a "cleaner" sound?

 

[John Morris]

I calibrated my sub to my system with my amp set slightly higher than half way. At that setting, my sub output is at 0. If I turn my sub amp up higher than that, my output signal cannot go low enough to match my other channels and my taste for music playback. So, I use my sub amp level to bump up the thump when I want it. BTW, my amp puts out alot of watts into 4 ohms mono.
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Take Care,
merc
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God Bless America!!!
[Edited last by John Morris on September 28, 2001 at 10:57 PM]

 

[DaleI]

Thanks for all the replies.