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The volume control on a subwoofer means nothing

Discussion in 'Subwoofers' started by Smurfin, Jun 26, 2004.

  1. Smurfin

    Smurfin
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    There seems to be a common misconception when people talk about how powerful subwoofers are, as many seem to base comments on where the "gain dial" is set on the back of a subwoofer.

    Someone mentioned in a recent SVS thread about the dial being recommended to go no further than "1/3", and there are similar comments along the lines of this:

    But what many people seem to ignore (or aren't aware of) is that there are an awful lot of factors which govern the output of a subwoofer, and the "gain" is only a small part of it. And in reality, where the gain dial is set is NO REFLECTION on how good a subwoofer is, nor any indication of how loud it can go before clipping (and I've not even mentioned distortion).

    The factors - as far as I'm aware - which govern the SPL of a sub is as follows:

    1. The subwoofer gain control.
    2. Processor trim
    3. Subwoofer placement.
    4. Frequency response (linked directly with 3, for obvious reasons).
    5. Size of the listening room

    Discussions on the gain dial on the back of a sub are largely meaningless, because the output of a sub is the sum of all of those things listed above, all of which can have a major impact on the SPL. And in the majority of cases, driving the gain up to silly levels will simply induce distortion and bottoming out of the driver.

    The bottom line is, the subwoofer needs to be positioned right (for the flattest response), possibly with EQ introduced (I know it's a last resort, but let's be honest, how many people can put their subwoofers in the optimal position?), and then CALIBRATED with an SPL meter and your own ears.

    If the above sounds patronising then I apologise, but I thought it was worth mentioning for those people who are new to subwoofery and are likely to fall for the "volume" pitch that can sometimes be heard (and I've heard this often from dealers selling subwoofers to people who know no different). Unless me myself has it all wrong :eek: :suicide: :zonked:
     
  2. ~Kev H~

    ~Kev H~
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    Also.. are the pre-out voltages of Hifi equipment all a standardised level?

    I ask this because with the Head-units in cars you find that some have say a 2V pre-out, some are around 4V and i think they can go upto 6Volts. Thus you essentially use the gain dial on an amplifier to calibrate the amplifier to the signal it is receiving.

    Is it not the same in home hifi? If two people both had exactly the same sub but were connecting it to different stereo or AV equipment i wouldnt be surprised to find a different gain was required to produce the same level of bass in the two systems... ??
     
  3. Smurfin

    Smurfin
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    I think you're right, yes, although I'm a simple fool so couldn't say so definitively:)
     
  4. karkus30

    karkus30
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    that would be me then :hiya: Thats wrt that particular sub woofer, no others. The Ultra is definitely louder at a 1/3 than a 1/4, tested with an SPL meter. It was'nt distorting, but the room definitely was. Your right to point out the issue, up to a point, the position of the volume control has very little to do with the direct output of any amplifier.
     
  5. karkus30

    karkus30
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    Quite right. In most older amplifiers that dont have input adjustment, the phono output is a much lower signal than CD. Usually means turning the amplifier way up for records (a point which would be causing clipping and distortion with the cd source). All things are relative.
     
  6. micb3rd

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    Gain controls are there for input level matching.

    To put it simply a gain control is *not* a volume control, it is input sensitivity control to be matched with the input level going into the unit.


    Check it out out I was giving this same advice back at the start of 2003...


    http://www.avforums.com/forums/showpost.php?p=447970&postcount=6

    ;)
     
  7. Nimby

    Nimby
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    SVS recommend that the gain control be set betwen 1/2 & 3/4 to produce the cleanest bass without overload distortion of the sub's amplifier.

    If you set the sub's gain control low & then calibrate with the receiver. You are more likely to overload the sub's amplifier. Reducing headroom and increasing distortion.

    If you take their advice and set the gain much higher. You won't overload the sub's amplifier.

    By setting the sub's gain higher you are feeding the sub with a lower signal from the recieiver. Which the sub amplifier can use to obtain maximum headroom with lowest distortion.

    Nimby
     
  8. sticker

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    Matt,
    I would add a number 6 to your list..........The quality of the processors/amp subwoofer output. This is certainly what I found when I got my servo 15's and the were linked to a Sherwood reciever. I was very underwhelmed by the Servo's but when I got the AV8, it all changed. I think Beekeeper has mentioned in the past that low cost/quality processors/amps introduce a lot of distortion into the sub output.

    Regards
    John
     
  9. Smurfin

    Smurfin
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    Can anyone else comment on this please? I thought that regardless of where the gain is either on the sub itself or where the LFE trim on the processor is set, it's the actual output which would dictate distortion not where it's being controlled from? Or does that stand, especially given Nic's comments on lower end processors/amps introducing distortion?
     
  10. rd350ypvs

    rd350ypvs
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    So basically, the lower the gain on the sub, the harder it is for the amp to drive it ?
     
  11. karkus30

    karkus30
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    Are you sure this is right ?

    Ive never read anywhere in the SVS manual about turning it up to 1/2 to 3/4, mine mentions 1/4 to 1/3.

    Im really struggling with this gain matching thing. The av amp feeds a variable pre amp signal to the sub. The subs amp is therefore a power amp with a variable gain input. So why does it need a control, why not just hardwire it full on and use the av amp to control the output ? Im missing something here.

    My Yamaha sub would bottom out at anything above about 1/10 th on the subs controls, leaving it turned up to 1/2 would have resulted in total destruction during noisy parts of a film.
     
  12. Nimby

    Nimby
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    Actually the reverse. The lower the gain: the lower the distortion and the higher the headroom. :)

    Though you are not talking about driving a loudspeaker in the convential sense. Because the subwoofer is active.

    Being fed a lower level (distortion free) signal is better for the subwoofer's amplifier than being fed a higher level signal.

    Whether the processor's sub control is turned up and the sub gain down. Or the sub control is turned down and the subwoofer gain up. The subwoofer output level remains the same when you calibrate. Only the distortion and headroom levels change.

    The "loudness" of the sub remains the same during calibration. Leaving you free to choose what gain setting you like on the sub. If you are wise you will set sub gain high and turn down the sub control on your processor to match.

    Nimby
     
  13. Nimby

    Nimby
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    Turning down the sub output on your processor/receiver would surely have reduced the sensitivity to control on the Yamaha? It may not have been able to cope simply because you were feeding it too high a signal. :blush:

    Regarding the SVS subs I can only quote the PCi manual. It clearly states receiver/processor master volume control to 00dB. Sub gain 1/2 to 3/4. No more than -5dB on the processor. LFE trim to 0. These are preliminary settings prior to calibration.

    Ok. I had a quick check on the Ultra instructions manual (on the SVS website) and you are quite correct regarding sub gain between 1/4 & 1/3. I don't know why there should be such a difference to the PCi. Except for the higher sensitivity of the Ultra input. You'd have to ask Tom about this.

    Nimby
     
  14. Andywilliams

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    Hi Nimby
    My 20-39 pc+ gain is set at a third of its volume from speaking to tom your best having the processor output low mines at -3 db for movies and -6db for music if the output from the processor is high it will introduce distortion in to the signal.
    I must be doing somthing right because my system sounds very balanced to me.
    It would be impossible to turn the gain past half because i wouldnt have enough trim left on my processor to compensate the increase in sub volume. Like whats already been said everybodys situations are unique and will require different set up to each others .The main thing is to keep the processor output below oodb and the signal should be clean to the subs amp.
    Cheers Gonzo. :)
     
  15. Nimby

    Nimby
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    Gonzo

    I think we're talking the same languge. :)

    Nimby
     
  16. karkus30

    karkus30
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    Right. Ive adjusted the Denon amp to -6db (1/4 setting by Denons standards), the sub needed to go to between 1/3 an 1/2 volume to keep balanced with music (after reading the SVS manual it says that 1/4 to 1/3 is the starting point, so I dont think there is any conflict with your manual, it just reads differently). So I shall give it a go with films tonight. Its all interesting stuff.
     
  17. davehk

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    There is no one answer for this. As well as everything already mentioned, it depends also on the input circuitry of the sub.

    If the gain control is a simple passive attenuator placed directly after the sub input, before any active circuitry, then its position will have no effect on the distortion from the sub. eg, if feeding in a 1volt signal with the input gain set to unity does not cause distortion, then neither will a 2volt signal with the input gain at 0.5 - the signal into the active stages of the sub will be exactly the same.

    If, OTOH, there is an input buffer amplifier before the gain control, then you have to take into consideration the possibility of overloading it. If you have the gain control too low, you will have to feed a higer level input into the bubffer amp, which may then distort. Such a sub should have the maximum input level stated in its spec sheet.
     
  18. Andywilliams

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    Hi Karkus
    Ive found when setting the svs up with music it needs more gain with movies ie now youve set the sub up with music it will probably not be enough output with movies.When i had the nad t752 you could adjust the sub trim easily on the remote to compensate for either music or movies.On the harman kardon avr8500 you have to set each input individually so no probs with different sub levels.Thats why ive got a 3db difference between music and movies on the processor output.
    Cheers Gonzo. :)
     
  19. micb3rd

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    Oh and if any of you are curious.

    One of the reasons it is often worth dropping the sub level down then calibrating the subwoofer amplifier gain is becuase when AV recievers subwooofer level is at 0 some AV recievers can clip the subwoofer level output when the amp is turned up close to reference levels.

    This would mean no matter who low the gain on the subwoofer amplifier is you could still introduce nasty distortion.
     
  20. karkus30

    karkus30
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    Having readjusted the settings as my previous post, played a couple of films, I noticed that the bass is far more subtle. In essence it would appear that the amplifiers output is a coarse control (very much a pure volume control), it doesnt really matter where the subs gain setting is (to a point), if you have it at the reference setting of 0 db its loud.

    The subs setting has less of an effect on the overall volume, just gives a bit more body and drive, so you can use this to trim the sub in a more accurate way.

    Thats the findings of professor Karkus anyway :lesson:
     
  21. cosmic023

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    The volume on my Rel Q100E is around the 1 o'clock position, and the amp trim / level is on 0.

    Any less than the 1 o'clock position, the sub seems very flat. Any more seems too much.

    Everything is calaibrated to 85dB @ 0 (Reference Level) on the amp, but prefer to listen to films @ 18dB - 25dB as this is loud enough for me & the neighbours :laugh:

    So is this an average setting, because as already stated by micb3rd.

     
  22. krusty

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    i too have found that quality of amp/ reicever can determine the sub,s sound quality. i was using a denon avr 1802 with a velodyne vx10......now im using a yamaha dsp A2 with a velodyne vx10 and there is a marked improvement.....in fact a 100 percent improvement.
     
  23. Nimby

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    Well that explains why some people thought I was exaggerating about the bass from my 16-46PCi. :laugh:

    Unfiltered high level connections and a Naim 72/180 pre-power will blow all of your wimpy AV receivers/amps & processors clean out of the water!

    A nuclear SV Sub! :D

    Shame it doesn't do surround though. :blush:

    Well, nothing's ever perfect. :devil:

    Nimby
     
  24. Ian J

    Ian J
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    There was an interesting article published in Hifi Choice a couple of years ago about bass management which seemed to be contrary to accepted wisdom on setting "large" or "small" on AV amps.

    The author suggested that bass management was a far from tranparent process as apart from the phase shift that accompanied digital filterering, the redirection often caused big changes in both the levels and distortion of the signal.

    Comparative tests were carried out on several mid price AV amps with the speakers set to small and large comparing the amount of distortion measured on the bass signal which showed very little added distortion if there was no additional LFE signal being fed to the subwoofer but considerably more (dependant on amp) if there was LFE in addition to the redirected bass signal.

    Two of the amps tested showed an increase in distortion of up to 12% with speakers switched to small and LFE signal present over the comparative distortion with the speakers switched to large.

    A further two of the amps tested showed that the subwoofer feed increasing by 8dB just by switching from small to large which would either make a mockery of A/B testing or clip the subwoofer.

    According to the author the moral of the story was to set speakers to large regardless of the size of the speakers and avoid any bass management, thus avoiding any additional phase shifts, changes in level or unwanted increases in distortion.

    So the amplifier and bass management settings have quite a bit more to do with the end sound than we may realise.
     
  25. karkus30

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    Ah ha now I understand. I dare not even contemplate lashing the Ultra to my HiFi set up. The bass from the speakers already bottoms 20Hz and its really revving at 25Hz. It would mean putting the bass plugs in and going for the low Hz tune :eek: now that would be scary. But its not going to happen, not even as a trial , "they shall never mix, we will keep them in their rooms, in separate systems and we shall never surrender".
     
  26. karkus30

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    Ian, what setting are you using ?

    On older AV amps you had to switch to small so you could get a sub woofer feed, but these newer fangled devices allow the sub feed regardless.

    If you have set 'em large did you notice the difference ?
     

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