Confused about sub crossovers

Discussion in 'Archived Threads 2001-2004' started by Ashford Little, Mar 8, 2002.

  1. Ashford Little

    Ashford Little Stunt Coordinator

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    My sub has a variable crossover while my preamp's sub out is permanently set to 100hz. I fail to understand the relationship between the two pieces. Can someone educate me?
     
  2. Evan S

    Evan S Cinematographer

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    Ashford, the Sub's crossover is used in situations when you run speaker wire directly into the sub, then out of the sub for Satellites. Some receivers have one fixed crossover point and people prefer to use the variable crossover in the sub, or some people like me have SACD capability but there is no bass management. So, I run a full range signal into my receiver and have the subwoofer's crossover perform that duty for me.

    If you have a crossover in your reciever/processor set to 100htz, you need to keep the variable crossover in your sub set to AT LEAST 100htz or you will attenuate the frequencies below 100htz and there will be a frequency gap in your spectrum.

    Hope that helps.
     
  3. Ashford Little

    Ashford Little Stunt Coordinator

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    Thanks for your response, but I need further remedial education. If I raise my sub's crossover above about 60hz then the sound gets muddy. Why?
     
  4. ColinM

    ColinM Cinematographer

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    What kind of system are you running?

    Some subs naturally sound muddy above 50 - 75 Hz.

    There could be some overlap between the top of the sub's response and the bottom of your mains. Playing with a phase control could help, but this may / may not be audible immediately.

    Perhaps the mains are set to large?

    - CM
     
  5. Ashford Little

    Ashford Little Stunt Coordinator

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    Thanks Colin for your reply. My system is a smorgasbord right now, but my main speakers are B&W 602S2's and my sub is a B&W ASW1000. The preamp is a Rotel RTC 970 that crosses the sub at either 100 or 120, I can't remember.

    Can't wait to upgrade the preamp, but this whole Firewire & SACD vs. DVD-A battle has to work itself out until I upgrade.

    Thanks and looking forward to your response.
     
  6. ColinM

    ColinM Cinematographer

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    Nice Stuff...

    I'll cover a few things, chime back in to let us know if you find any answers...

    How to you feed signal to the sub? Speaker wire or RCA?

    Do you return the signal from the sub to anything? Like pass thru the RCA's/speaker wire back to another peice of equipment?

    Quote from B&W:

    Low-Pass Filter Active 4th-order, variable cutoff frequency 40-140Hz

    High-Pass Filter Line level: active 3rd-order at 80 Hz

    Speaker Level: passive 1st-order at 80Hz into 8 ohm resistor (response using speaker level connections dependent on satellite impedance)

    If you don't cut-off the bass to the main LR pair, you will likely get 'muddy' bass. The sub should then only be used to augument the bottom octave only by keeping the crossover down as much as possible....

    If you ARE indeed able to limit the bass to the mains, you may have to set the crossover on the sub to about 60 - 80, as the slopes of each crossover will combine to fill in any gaps. Tweak as necessary.

    The general rule of thumb is that if the bass is too muddy or boomy, drop the crossover and up the volume a bit.

    If mid bass is lacking, open the crossover a bit and reduce volume.

    Let us know what you think..

    - CM
     
  7. Ashford Little

    Ashford Little Stunt Coordinator

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    Thanks Colin, the sub is connected to the preamp via coax cable and connected to the preamp via the sub out connection.

    I don't lack mid-bass at all, but if I raise the sub's crossover to anywhere near 100hz then it gets muddy. I currently have the crossover set to around 55-60 which gives excellent bottom end.

    The preamp is a bit dated and the crossover is fixed as I mentioned before at somewhere around 100 hz.

    In the future I will upgrade the preamp, but am waiting until there is the availability of a digital connection from a universal SACD/DVD player and a preamp capable of handling IEEE1394.

    BTW, I don't understand what a high pass filter is. Sorry for the naive question.
     
  8. Evan S

    Evan S Cinematographer

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    A high pass filter is another name for crossover. It simply tells the pre-amp at what frequency signal to "pass" onto the speakers. Or vice versa, it "filters" out the high frequencies and sends only the low ones to the sub.
     
  9. BruceD

    BruceD Screenwriter

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    Ashford,

    Critical question,

    What are your speaker setup settings?

    Main=Large

    Center=Small

    Surrounds=Small

    Sub=Yes

    If this is the case, then you probably want to set your main speakers to;

    Main=Small

    and make sure you don't have a Mains+Sub bass output setting turned on.

    Mains=small is supposed to be the basic idea behind a prepros xover. In this case you ideally want the xover in the sub itself turned off. If you can't turn it off, then try setting it to the highest setting of 140Hz.

    This lets the sub handle all frequencies below 100Hz, but like you said this may not sound as good to you (100Hz is a little high for many subs).

    high-pass is all the frequencies above the xover eg. >100Hz

    while low-pass is all the frequencies below the xover eg.
     
  10. Ashford Little

    Ashford Little Stunt Coordinator

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    OK, I'm still confused. Sorry, but the quote from B&W has the low pass filter variable from 40-140hz while the high pass cuts off at at 80hz. What am I missing here?

    As for the speaker settings I am using, I'm afraid that my preamp doesn't have that capability to set the speakers. It does have a 5.1 inputs so I have a Technics SHA-C500 which handles the DD & DTS decoding. It's setting is fixed at 100hz.

    Bruce: If I set the sub's crossover at a level higher than about 60hz then it sounds too muddy.

    Basically, I'm dealing with two different systems here; one for cd listening and one for DVD's. The CD player is connected to the Rotel RTC970 using analog outputs from the player and I suppose all frequencies below 120 are routed to my subwoofer. I'm not 100% certain since the manual is one of the lamest I've ever seen.

    While watching a DVD, the SHA-C500 decoder routes frequencies below 100 to the subwoofer if the main speakers are set to small. However, I set them as large.

    Settings:

    Main: large

    Center: small

    Surround: small

    Sub: yes

    As you can see this system, while working fine, has some limitations, but I'm reluctant to upgrade at this point due to the inevitable IEEE1394 issue.

    Thanks
     
  11. Chris Zell

    Chris Zell Stunt Coordinator

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    I'm still not clear where the inputs to your main speakers comes from. Is it wired from the high pass output of the sub?

    Id that is the case, if you set your sub lowpass to 100 Hz, then all the stuff between 80 and 100 is going to the mains AND the sub - you have a humpo, and it can sound muddy. Crossovers are not just on/off things either. If a highpass is set at 80 Hz, there is still very significant output at 60, 40, even lower.

    It also depends on the order of each. If the high pass is first (or even second) order, then it drops off VERY slowly below the cuttoff point, and it can be difficult to mate properly with a different order Lowpass crossover to the sub.

    For the above reasons, I often have the best luck with the lowpass point not exactly at the same point as the high, making it seem like I have a gap. For example, I had one setup that worked great with the High pass at about 80 Hz, and the lowpass at about 70. The highpass was only 2nd order (12 dB/octave), so If I moved the lowpass up to a matching 80 Hz, there was too much at that point, and it started to sound too thick.

    Sorry if some of this does not apply directly to your setup, but I was having a little trouble figuring out esactly how you had things connected, your settings, and how the gear is designed to work.

    Cheers,

    Chris
     
  12. Ashford Little

    Ashford Little Stunt Coordinator

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    Chris, I'm sorry if I was not clear. The main speakers are connected directly to the amp and are not connected to the sub.

    I hope this answers your question.
     
  13. Ashford Little

    Ashford Little Stunt Coordinator

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    see below reply. Initially there was something wrong with the posting.
     
  14. BruceD

    BruceD Screenwriter

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    Ashford,

    I also use the Technics SH-AC500D DD/DTS processor, as you can see by clicking on my equipment list below.

    Here is part of the problem. You have mains=large which means most of the bass goes to your mains, not your sub. Only the bass from center, surrounds and LFE goes to the sub. What is the low frequency response for your mains?

    Like you. I didn't like the Technics 100Hz-120Hz xover so this is what to do:

    1) Disconnect the sub-out cable from the Technics sub-out and put the sub in the main L&R signal path with your main speakers - can your sub be connected this way? This means main L&R out from Technics SH500 to the Rotel 970 L&R ins, then the Rotel 970 L&R outs to the sub's L&R in, then the sub's L&R out to the amp's L&R ins for the L&R main speakers. I bought a separate electronic xover for this myself.

    2) In the Technics speaker setup, set sub=NO

    3) Now you can set the xover on the sub for the main L&R/sub at say 80Hz.

    I'm assuming the high-pass xover @80Hz you were talking about on the sub, is specifically for main speaker/sub connections like I described above.

    This also means your sub will be active when listening to 2-channel music from your CD player which is connected to the Rotel 970 with analog L&R interconnects.
     
  15. Ashford Little

    Ashford Little Stunt Coordinator

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    Bruce, thanks for your reply. Since you also have the Technics decoder then I need to ask you a couple of questions; I'll follow them up with those pertaining to your post later if that's alright.

    I have a DISH satellite system and recently noticed that while listening to music from Dish I have no bass via the sub at all; this is contrast to listening to CD's (which don't go thru the decoder) and getting sub response. I do get low frequencies thru the sub while watching a DVD so I am confused.

    What to do?
     
  16. BruceD

    BruceD Screenwriter

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    Ashford,

    I assume your DVD is connected to Digital 1 on the Technics.

    Is the DISH connected to Digital 2?

    Do you have a toslink output connection on the DISH for DD?

    Is the DISH audio connected to the Technics with L&R analog?

    If you are connecting the DISH L&R audio output to the 5.1 L&R analog inputs on the Technics, then this Technics "LINE" pass-thru mode doesn't support the sub connected to the Technics sub-out jack (another reason to use the sub on the L&R main channels as I described above).
     
  17. Ashford Little

    Ashford Little Stunt Coordinator

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    Thanks Bruce and sorry for not being clear.

    Digital 1 is the DVD player connected optically.

    Digital 2 is the Dish PVR also connected optically.
     
  18. BruceD

    BruceD Screenwriter

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    When Digital 2 is being played from the DISH for music, what do you have the mode selected for on the remote?

    Surround?

    DTS?

    Stereo?

    What shows up in the little red light on the Technics?

    Surround?

    Stereo?

    If Stereo shows up, then I don't think the sub is part of the output stream and sound only goes to the the L&R.
     
  19. Ashford Little

    Ashford Little Stunt Coordinator

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    I use the stereo selector for audio playback from the Dish PVR. Hmm, that's interesting that is doesn't route anything to the sub.

    I did not see any light "light" up other than the stereo script. The other lights only indicate either ProLogic or Digital. Still since this is a digital input (Toslink) I thought I would regard it as digital.

    I guess not.
     
  20. BruceD

    BruceD Screenwriter

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    Ashford,

    It is digital (PCM) just like your CD. It's not a digitally compressed signal like DD or DTS.

    Therefore it is only a stereo signal just like your CD with only 2 channels (no bass management involved) even though it comes from the DISH as a digital signal.

    The digital formats for CD-PCM and HT-DD-DTS are completely different.

    Just an FYI, I don't like the way the Technics sounds with PCM, which is why my CD player is connected to a separate stereo preamp. A digital connection between my CD player and the Technics (using the Technics DACs instead of the CD player's DACs) sounds less than desirable to me.
     

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