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Amp crossover and sub recommendations

Discussion in 'Subwoofers' started by Mr Incredible, Sep 12, 2005.

  1. Mr Incredible

    Mr Incredible
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    When setting the amp/sub as far as crossover is concerned, how do you determine what crossover frequency to use, whether to use LARGE or SMALL and whether if using LARGE would you have the sub on LFE only or would you have LFE + Main?

    As far as my limited understanding of "Large" vs "Small" speaker and subs are concerned, this is what I make of the options available:


    [​IMG]

    AFAICT the setting of the crossover is crucial in any set up, but much depends on the performance/capabilities of the speakers WRT to producing a flat enough response to the crossover frequency.

    Are there any magic formulae / guidelines as to best determine the optimum? What do you have set up on yours?

    BTW, note my updated new sig....... 1 x SVS sub in the kit. Nice one Rob!! :thumbsup:
     
  2. Ian J

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    There is no magic formula at all and it is just trial and error as the individual circumstances of each room and equipment can alter the optimum.

    I always recommend that people start with all speakers set to small, the crossover facility on the SVS switched off and the crossover in the amp's speaker setup menu set to 80Hz.

    I think that the above gives an excellent starting off point for fine tuning and may also be the optimum for many people. Start by reducing the crossover (if possible) to see whether a lower crossover gives better integration and overall sound.

    When you've found the optimum sound, switch the speakers to large and start again and when you have found the optimum sound you can compare that with the optimum setting for small speakers and see which you prefer.

    Welcome to the SVS club and hopefully you will soon be seeing what all the fuss is about
     
  3. Mr Incredible

    Mr Incredible
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    Potentially faced with a number of hours with the SPL meter, reference tones etc, I was itching to see how well the PB12-ISD would be "out of the box" so to speak. :eek: I think I felt a bit quesy at one point with all the LF it was pumping out (only about 1/2 gain on the sub). :smashin:

    Without any SPL adjustments, but a few amp speaker config and crossover changes, the sub did appear to swamp the B&W's 604's at 80Hz. I tried 60 and 40 and found 60 to be pretty good. Perhaps I should spend my time calibrating at that crossover setting? Then again it may all change when I get any phase adjustments and levels properly set up. Who knows, 80Hz may be the best.

    I had hoped that someone with more hands-on experience than me may have had a few pointers to save me time in the calibration process.

    It isinteresting to note that if anyone could have provided a magic formula for this then Denon probably could, but as people may know, the auto calibration on the 3805 does not adjust crossover. You have to do that manually BEFORE any auto or manual level settings.

    Thanks for the reply Ian.
    :thumbsup:
     
  4. binbag

    binbag
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    When I set my speakers to small (which seemed wrong as the fronts are floorstanders) and the sub to LFE there was a noticable hole in the response. I had to use the Xover on the sub to get a smooth sweep on the Avia test tone; but I know my Marantz SR4200 amp is not rated as great with bass.

    There is a school of thought that says if you take the lower frequency duties away from your mains they reproduce the other notes better as they have less to do and less movement when they do need to move. How true this is I don't know - but the whole system sounds a lot better on this setup than it did before.
     
  5. kbfern

    kbfern
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    What is your gain set at on the sub,SVS recommend you start with gain set at around 10 o'clock.
    What's your sub output on the Denon,SVS recommend -6db.If you have higher settings than these,it may be why the sub is swamping the speakers.

    The above settings are whats recommended for starters before tweaking.

    Dont forget to set the crossover on the sub to bypass.
     
  6. Troon

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    The SR4200 is just fine. You won't hear any anomalies in its frequency response: the room and speaker curves will be orders of magnitude larger. Its only problem is the fixed 100Hz crossover point if you use it for bass management.

    You cannot set small fronts / sub to LFE, as that gives nowhere for the mains' bass to go. You will have set small fronts and sub to LFE+bass, and you'll need to tweak the sub's gain to match the roll-off of the mains. With bass management being handled by the amp, you should set the sub's crossover to maximum, or bypass it altogether if possible, otherwise you will get a hole.
     
  7. Mr Incredible

    Mr Incredible
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    It's about 11 oclock, amp is 0 dB for the sub (other speakers are set up to +4db for ref levels, so 0db seemed reasonable for a test. :rolleyes: Sub is set to Crossover : Disabled. Me thinks its time to :rtfm: and start from scratch.

    The swamping may also be due to some phase differences which I haven't yet attempted to address.
     
  8. kbfern

    kbfern
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    If you are running the sub output at 0db,I think you are probably running it too hot.Remember for every 3db you are either doubling or halving output.

    A few people who have bought SVS's have said on here recently that they have initially set receiver output at 0db and one person had theirs running at +6db and then stated the sub was boomy.When they cut their receivers output back to around -5db there was a much improved sound.

    Regards setting up go to SVS website and download your subs operating/setup instructions if you don't have them.
     
  9. binbag

    binbag
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    Is it me....

    When I set my speakers to small (which seemed wrong as the fronts are floorstanders) and the sub to LFE there was a noticable hole in the response. I had to use the Xover on the sub to get a smooth sweep on the Avia test tone.


    ....or is there an echo in here? :rolleyes:

    Expect more posts when I connect up the Hi Level.
     
  10. Mr Incredible

    Mr Incredible
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    Does anyone know how much lower frequency (not LFE) is present in DVD's for the channels? With all my speakers I can hear an audible difference in them between the large setting with full frequency and the small setting with the crossover at 80 Hz (and 40 Hz TBH).

    That being the case, by routing 5 x channel frequencies below the crossover point, is the channel steering / focus of the 5 channels being compromised because their lower frequencies are now routed to a single speaker (sub)?
     
  11. Nimby

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    I don't know what the problem is here. I took my SVS out of the box. Moved one set of my biwire cables over to the hi-level sub terminals. Switched it on. Played a CD and adjusted the bass by ear. That was it. It was weeks before I even bothered to wheel out the old SPL meter. The SVS just fitted into the system so effortlessly. :D

    Later "messing about" with the Yamaha rear surround processor I quickly discovered that small was not beautiful and always set my fronts to large.

    Now I whack up the gain on the sub by +3dB for films but leave the sub "flat" for music.

    Hope this isn't too technical for you? :devil:

    Nimby
     
  12. Mr Incredible

    Mr Incredible
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    I'm with you on the whacking off bit....... :D :devil:
     
  13. Troon

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    The receiver sub output is totally meaningless unless you also factor in the on-sub gain setting.
     
  14. kbfern

    kbfern
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    This is untrue,if you cut or boost your receiver sub by 3db you will get a doubling or halving of the volume of your sub whatever the sub gain in set at.But if the sub is set to hot you risk bottoming out and distortion.

    Of course the sub gain setting will also increase and decrease output and should be set in conjunction with the amp sub output level,but what i was saying is that at 0db (amp sub output level) I think malice is running his sub to hot and this is probably why his sub is swamping his other speakers.
     
  15. Sniper

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    Not really - as was said so many times - bass is pretty non directional at anything under 100hz (depends on ears, sub design & position), BUT....

    ... this all depends on your speakers too. There will be some designs which allow setting fronts to large (centre - I always reccomend SMALL - but there are some rare cases!). Having said that, I think that setting fronts to Large only makes sense to music, movies will have better bass uniformity (SFX & stuff) if all speaks are set to SMALL. As for music, there are too few fronts with any decent bass @ the 40hz (min -6db) - so i would say set fronts to Small with xover set to 40hz. Some amps/processors (eg. Rotel) allow different xovers per channel group.
     
  16. Mr Incredible

    Mr Incredible
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    Mmm, I can see me drawing my old age pension before I manage to test the variations!! But then again, that's not too far away. :(

    When I did a sweep with the Avia disc, I could still hear the Fronts at 26 Hz. Granted I didn't check the SPL to see if it was within -6dB, but I tell you, at 40 Hz the 604's were performing very nicely. According to the B&W site they perform at:
    "Freq Response 39Hz - 22kHz ± 3dB on reference axis"
    "Freq. Range -6dB at 30Hz and 42kHz"

    So on that basis perhaps a 40Hz crossover may be an option. My only concern would be matching the roll-off at this level with the Sub which I have no doubts would perform really well up to that frequency.

    What is the preferred sequence of setting up and calibrating a sub?

    Do you get the position sorted first by using frequency test tones to assess the frequency response/phase optimisation, and then run the SPL ref level tests for all speakers and sub? Or the other way around? Or doesn't it make much difference?

    Or am I becoming too anal about this? :suicide: :D
     
  17. Nimby

    Nimby
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    Sniper

    I am running a high quality stereo system using a Yamaha rear surround processor (for film only) just to get some rear channel information. Using the processor to provide a "small" setting on my 40Hz speakers emasculated the sound on film and music. The loss of sound quality using the processor made it a non-starter for music and compromised film sound to a point I wasn't willing to accept with the fronts set to "small".

    It is an unusual set-up these days but I don't like the sound quality of surround receivers when I can have the best of both worlds in high quality stereo + 2.1. :devil:

    That said, I doubt I get perfect surround from such a simple system. But my room layout makes it very difficult to use "rears" properly anyway. It is a compromise I'm more than willing to put up with.

    But I/we are wandering slighty from the subject matter of this thread.

    Regards
    Nimby
     
  18. Mr Incredible

    Mr Incredible
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    Well, last night I made a start on calibrating my system with the sub. As recommended I set speakers to small and had a crossover set at 80Hz. Amp Gain @ 0 dB

    (1) I ran the Denon 3805 auto calibration and EQ set up with the Sub crossover disabled and Gain set between 10 'o'clock and 11 o'clock position (just over half way between the two). The Denon produces 75 dB levels and from the set up it set the following:

    FL +5.5
    FC +3.5
    FR +5.5
    SUB -4db
    SR +2
    SL +3

    I then used the SPL meter and ran through the Denon test tones and did a manual adjustment to get 75dB. NO EQ applied. Result in levels:

    FL +2.5
    FC +1
    FR +2
    SUB -5db
    SR -0.5
    SL 0

    Which by all accounts infers I had my sub gain about right with -5db on the Amp.

    Then I ran the AVIA test disc which produces 85 dB levels and I did a manual meter set up again. The results on the levels:

    FL +6.5
    FC +4.5
    FR +6.5
    SUB -2db
    SR +3
    SL +4

    So having done all that I ran the test tones from 120 Hz down to 15Hz to measure the response of the sub. I had to disconnect/disable the other speakers as it was an audio CD which does not have channel encoding.

    I started logging the results and it slowly became clear that the levels on the CD audio were much higher than 85db, because my meter started cranking above 115 db :eek: I decided discretion was needed and turned the gain on the amp. So by making adjustments for this in a spreadsheet for the readings affected to normalise the results, I got this result:

    SPL vs Frequency SVS PB12-ISD


    Room size layout

    Since making that picture I moved the fronts in a bit to get the sub in the corner to the right of the TV.

    Would anyone like to make any observations about my room acoustics/amp settings/ sub position?

    :thumbsup:
     
  19. kbfern

    kbfern
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    What does your ears tell you?

    Do you like the sound or not.

    You can rely too much on meters/computers/etc.
     
  20. Mr Incredible

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    Being a n00b in this I was following the general concensus that using a meter was the preferred method for calibration.

    With a crossover at 80Hz (I set it at 200 for the test on the sub only) I found the LF soundstage a bit "woolly". This improved with 60 and 40 (but no measurements taken) but then the LF (what there was) appeared to disappear as far as integration with the mains. Which I find suprising given the measured results. So on balance I'd say I was a tad disappointed with the end result.

    Ron @ SVS had recommneded a sub position next to or behind the seating position. Perhaps he knows something I don't!! Back to the drawing board I think.
     
  21. kbfern

    kbfern
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    I am not saying that you do not need to use a meter and set up disc.I am just trying to point out that those dustbin lids either side of your face are the most important measuring instruments, in that if It don't sound right it ain't right.

    I still have not set my 20-39PC plus up with any spl meter,(I can't find mine its up the loft somwhere).But whilst it may not be set up perfectly as far as measuring instruments are concerned, to my ears is sounds fekin fantastic.

    By the way due to room constraints my sub is positioned at the rear of the room in a dormer window bay and works just fine.It may work even better in an alternative position but who cares, for the momment I just keep watching my movies and just can't get rid of that big grin of pleasure I get every time I switch it on.
     
  22. kbfern

    kbfern
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    I am not saying that you do not need to use a meter and set up disc.I am just trying to point out that those dustbin lids either side of your face are the most important measuring instruments, in that if It don't sound right it ain't right.

    I still have not set my 20-39PC plus up with any spl meter,(I can't find mine its up the loft somwhere).But whilst it may not be set up perfectly as far as measuring instruments are concerned, to my ears is sounds fekin fantastic.

    By the way due to room constraints my sub is positioned at the rear of the room behind the seating position, in a dormer window bay and works just fine.It may work even better in an alternative position but who cares, for the momment I just keep watching my movies and just can't get rid of that big grin of pleasure I get every time I switch it on.
     
  23. Mr Incredible

    Mr Incredible
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    ... and as an additional thought, if the calibration was for an even-as-possible 85db (AVIA) across all the speakers, sub included, is it the case that for movies most people's experience is to run the sub +3 to +4 db higher than the rest? If so, would that mean I turn up the wick on the amp by 3 db or the sub gain? As the amp is currently -2 db for a 85db SPL at 0 dB on the amp gain, I'm not sure if raising the amp by 3 db would be a good thing or not.
     
  24. Ian J

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    I prefer my sub at the same level as the main speakers whereas others prefer their sub to be louder.
     
  25. eviljohn2

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  26. Mr Incredible

    Mr Incredible
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    Following kbfern suggestion of letting my ears take the lead in determining levels, I revisited my settings.

    I tweaked the phase on the Sub from 0 to about 40 (AVIA sub and speaker test), set crossover to 80Hz, Mains to Large, Centre to Small, Surrounds to Large, Sub = LFE+Mains. Sub position remained the same.

    I have no doubt in my mind that the best sound field is with the mains/surround set to Large. The ambiance seems to wither when set to Small and the crossover @ 80Hz.

    I just had a quick test f a DVD and all I can say is that I was constantly grinning at what I was hearing. It's interesting that the Mains and Rears are set at the same level as I had without a sub, and therefore are operating with just the same frequencies, but the SVS sub has just added a whole new layer to the lower end dynamics. It's extended, tight and appears to pull together all the other speakers and makes for a coherent reproduction of material.

    I don't think I'll even try to reposition the sub nearer to the seating position.

    1 x happy bunny.

    :) x 10
     
  27. Nimby

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    Malice

    Being set to large I expect your mains are now filling out the chasm at 40Hz. This is the most important area in the frequency range for powerful sounding bass.

    Nimby
     
  28. Mr Incredible

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    Because I had made adjustments in the testing of the amp (just got too damn loud with amp on 0 dB playing the test tones I downloaded off the web here ) I thought representing the results as a curve (to see troughs and peaks) would have been good enough to determine where I could improve. In practice I was seeing SPL levels at 18 dB higher than the graph actually shows. I presumed the tones were just too hot on the CD I burned and to represent the results as if they were "less hot" is perhaps an error/oversight?

    The graph actually looks like this.

    As I appear to have some headroom available to me, would you think it would be worth getting a BFD to calm the peaks at 28 and 46-54 to the level of the 40 hz "chasm" (relatively speaking) and then run my crossover at 60 Hz (to avoid the real chasms at 63 and 73)?
    :smashin:
     
  29. Mr Incredible

    Mr Incredible
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    Perhaps I should also test my Main speakers for room response to see if the chasms still appear. According to room mode calcs, the room has axial modes at 26 Hz, 32hz, 52hz, 79Hz, and tangential modes at 41Hz, 73 Hz. I've added these as overlays to the graph
     
  30. Mr Incredible

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    Question:

    If the accepted concensus is to run everything "small" with a sub in place, why would my Denon run its auto set up routine and set them all to Large, excepting the centre? Sure, give the listener the option of setting to large if they want, but surely an auto setup is mor elikely to get it right that wrong?
     

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