Confused about slope steepness

Discussion in 'AV Receivers' started by PaulDA, Oct 27, 2004.

  1. PaulDA

    PaulDA Cinematographer

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    Last night, while moving my sub around the room to find the best sounding bass, I tried something for the first time and I am confused as to the meaning of the result. A while back I plotted my bass response curve using only the sub (had to disconnect the front mains) but I used a series of test tones and it sounded like what I expected. Last night, however, I disconnected the mains and ran music through the sub only. I did this in two ways. My main CD player is my Cambridge Audio 540D DVD player. It allows me to set the mains to small, sub on and applies the crossover/bass management to two channel regular CDs. The manual (which is pitifully thin on info--my biggest complaint about Cambridge (Arcam is also thin on info in their manuals--must be a Brit thing) doesn't state the crossover frequency but after some exhaustive research I've learned that it is supposed to be at 80hz. I have no idea what the slope is. In my receiver, I can set it anywhere from 40, 60, 80, 100, 120, 150 (globally for all speakers) and the slope is said to be 12dB high/ 24dB low pass. My player is connected via analogue cables to the multichannel input of the receiver, where I engage "Pure Audio", which completely avoids DSP and lets the player's signal through. The player is also connected via toslink to the receiver so when I select the CD input on the receiver, I can use any DSP setting I want, should I wish to (sometimes I use Pro Logic II music mode for some of my two channel CDs). By switching from the M/C input to the CD input on the receiver (each input remains in the last setting used, so M/C was in Pure Audio and CD was in Stereo (which uses the receiver's crossover and activates the sub), the difference in sound from the sub with no mains was both startling and not at all subtle. In each case the xover is supposed to be at 80 hz. With the player doing the xover, the sound was articulate, one could clearly identify the bass guitar and the kick drum as separate instruments and there was more information coming from the higher frequencies (I don't have the instrumentation nor the knowledge to measure actual vs stated crossover frequencies and slopes so I'm going with the settings as stated). With the receiver doing the xover, a lot less higher frequency info was heard clearly, and the lower frequency info was muffled, inarticulate and boomy. The sub was in the identical spot throughout (all I did was toggle back and forth on the remote). My friend and I preferred the player's xover management for music, by a long shot, both with the sub alone and later with the mains engaged as well. We were trying to figure out which unit had the steeper (or shallower, I suppose it depends on your point of view) slope. Neither one of us is an engineer or physicist and we reasoned that the player's slope was steeper because the area under the curve was larger and thus contained more information than a shallower slope. I'm curious if we are correct (it's a fifty-fifty chance, the way I see it). Regardless of steeper or shallower, I know that I prefer the player's management. I'd like to know if the player has the steeper or shallower slope, though, as in the future, I would likely prefer a replacement machine (should the need arise) that gives me the more articulate, cleaner sound.

    Of course, another possibility is the player's xover is not 80 hz, but something else entirely, but I have no way of checking that myself. I compared the player to the receiver set at 100 hz, to kind of explore this hypothesis, but found the player's sound preferable and more articulate. I'd love any thoughts or explanations on the subject.

    Thanks.
     
  2. ScottCHI

    ScottCHI Screenwriter

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    oy.

    [​IMG]

    then again, it could be something completely different that you're completely overlooking. [​IMG]
     
  3. Lewis Besze

    Lewis Besze Producer

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    It's obvious that the palyer uses a shallower slope[lowpass] maybe like 2nd order[12db/oct],which will yield more upper bass to go to the sub,however that is not neceserally a good thing,as it's purpose is to ensure a better blend with the mains.So running the sub alone will defeat that purpose,and you might wanna engage the mains and then do your switching[A/B]
     
  4. PaulDA

    PaulDA Cinematographer

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    I did also listen to the music with the mains on and still preferred the player's xover to the receiver's xover. I was just curious about which one had the steeper slope and whether my friend and I's reasoning was correct. I guess we were wrong. Does anyone know a good place for me to get more info on this subject so I can understand the error in my reasoning?
     
  5. oliverLim

    oliverLim Agent

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    You can also try having a different crossover of the mains and sub. I found that in my case, a 60hz crossover on the mains with a 80hz crossover on the sub resulted in a much smoother Freq Response for me. Part of the reason was a dip near my crossover of 80hz no matter the phase or what I did.

    Oliver
     
  6. PaulDA

    PaulDA Cinematographer

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    I wouldn't know how to implement this as my crossover control is in the receiver and I can't select separate frequencies for each speaker.
     
  7. oliverLim

    oliverLim Agent

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    PaulDA,

    Then unfortuntely you cannot try that. I guess if both the player and the reciever has the same crossover point, the slope of the crossover is making the difference. Most players has a shallower slope such as 6db/octave. While recievers typically use a 12 or 24db/octave crossover. What this means in layman terms is that in a 6db/octave, if the crossover point is at 80hz, it is 3db down at the crossover point and a additional 6db down an octave below it which is 9db at 40hz. The downside to this is that your mains is only playing 9db less of bass at 40hz but a 12db/octave(2nd order) crossover slope will mean the mains is 15db down at 40hz. Considering 3db down uses twice as little power, your mains will have to work a little less.

    Now if you took my earlier note that the player usually uses a shallower slope, how can it sound better as both the sub and mains has to work much harder as both the mains has to work a little harder compared to the typical recievers crossover slope? Thats where there are some that says that a 6db/octave crossover results in less phase shift(1st order) and is time coherent. That could result in better sounding music. So there is no hard and fast rule in HiFi. Your own ears and testing will tell you which config works best in your own room in your own setup! :)

    For me? I am a believer of 1st order crossover. As I like the sound of all first order crossover speakers such as Thiel, Meadowlark & Vandersteen.

    Oliver
     
  8. Brian L

    Brian L Cinematographer

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    Given the large perceived SQ difference you are hearing, I would be inclined to suspect that maybe the slope AND the frequency are different.

    But rather than guessing, how about this...

    If you have an SPL meter and a set of discrete test tones, you could do a crude map the FR of your sub alone using the players crossover vs. the receivers.

    At the end of the day, it matters not because you know which you like best, but perhaps such a test would help explain WHY you like one vs. the other.

    BGL
     
  9. Wayne A. Pflughaupt

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    I don’t think that’s the best approach between subs and mains, though. Using shallow 6dB slopes you’d have to low pass subs really low to keep unwanted stuff like voices out of them – a 30Hz filter would only be 12dB down at 120Hz.

    On the high pass side, a shallow slope would certainly stress a large percentage of the HT speakers on the market. And having so much low frequency information duplicated by both the sub and mains would introduce phasing (time alignment) problems if its own.

    Everything I’ve seen indicates 24dB/octave slopes with Linkwitz-Riley alignment has excellent phase characteristics.

    Regards,
    Wayne A. Pflughaupt
     
  10. PaulDA

    PaulDA Cinematographer

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    Thanks for the information and explanations. I will plot some curves as soon as I can (am getting ready for a trip overseas next week, so I have little time to experiment--not that I'm complaining [​IMG] ). So to make sure I understand: the player has a shallower slope because the sub is able to play frequencies well above the xover and since I hear more of the higher frequencies clearly, the attentuation of the slope is more gradual than with the receiver (which is THX certified, so it HAS to have a 12/24 slope, right?). Okay, I understand that and I should have been able to reason that out myself. However, is the fact that the bass sounds cleaner and more articulate with the player rather than the receiver a consequence of the xover slope (assuming unless I establish otherwise that both xover points are 80hz) or would the player's DACs just be "better" than the receiver's (to mine and my friend's ears)? I know better is usually a subjective term but the difference in clarity between the player and the receiver was quite evident. If it's a consequence of the slope, then I guess (at least in this room with this speaker set) I prefer the gentler slope. If not, then I will continue to explore this issue.
     
  11. Brian L

    Brian L Cinematographer

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    Regardless of what one reads in certain hi-end publications, your DACs, unless one or the other is very, very broken could not impart the kind of difference you are hearing.

    Its slope, turnover frequency, or both.

    IMHO, AFAIC, YMMV....!

    BGL
     
  12. Wayne A. Pflughaupt

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    I’ll vote with Brian here. The DAC would have to be pretty pathetic in order for you to attribute the difference to that – especially when you consider that bass frequencies are not the best thing to use for evaluating the SQ of DAC’s to begin with.

    Bottom line, you can’t really do a good A/B comparison unless the two have the same slopes and crossover frequency.

    Regards,
    Wayne A. Pflughaupt
     
  13. PaulDA

    PaulDA Cinematographer

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    I didn't really think the DACs could be the issue, but I did want to make sure (I'm no engineer or expert). Still haven't had time to make measurements, but I've had to move the primary seating position in the room a bit forward from it's initial placement (about a foot or so) and after doing that, I re-listened to the same tracks under the same conditions and now it seems the better bass is with the receiver doing the work, not the player. At this rate (inches at a time), it will take months before I get this right (of course even then I'll be wanting to add traps and/or EQ into the mix--not to mention taming the higher frequencies--whole other issue but if I understand correctly, easier to fix than the bass issue). Does this tweaking ever end?[​IMG]

    The good news is, although I know I can tweak it some more, my setup is already far better than anything I've had before and the sound is very good already (keeps me from spending every minute in there fretting about these issues, I already get to enjoy the tunes). Thanks for all the info so far, everyone.
     
  14. Brian L

    Brian L Cinematographer

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    Only when you die......[​IMG]

    BGL
     

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