Active vs. Passive Subwoofers & connection

Discussion in 'Archived Threads 2001-2004' started by Stasulos, Oct 4, 2002.

  1. Stasulos

    Stasulos Stunt Coordinator

    Joined:
    Sep 9, 2002
    Messages:
    50
    Likes Received:
    0
    What's the difference in running a passive subwoofer using receiver's amplifier or an active subwoofer?

    If the LFE output gives only low frequency signals do you really need a crossover on a passive subwoofer?

    Thanks
     
  2. John Garcia

    John Garcia Executive Producer

    Joined:
    Jun 24, 1999
    Messages:
    11,571
    Likes Received:
    24
    Location:
    NorCal
    Real Name:
    John
    Most passive subs I've ever seen do not have line level inputs, so you can't send an LFE signal to them.

    The difference between using the receiver's amps and a dedicated amp for the sub is the fact that the receiver now has to do that work as well as drive the other speakers, and a sub will often draw more current than most other speakers. A dedicated amp for the sub means the receiver doesn't have to work as hard.

    The crossover on a passive sub usually has a low pass for the sub, and a high pass output for the other speakers. With this arrangement, you would connect via speaker level inputs, set the mains to large, and then run the main speakers from the high pass output of the sub. Since these x-overs are commonly adjustable (not always, some have fixed high pass), this allows you to fine tune the x-over point between the mains and sub.
     
  3. Dustin B

    Dustin B Producer

    Joined:
    Mar 10, 2001
    Messages:
    3,126
    Likes Received:
    0
    Not much. The biggest difference is that rarely will the receiver be able to supply as much power as a seperate or plate amp. Also having a seperate or plate amp will relieve the receiver's power supply of the hardest frequency range to amplify. Allowing more power and headroom for the other speakers.

    If the bass management of the processor is being used then you don't need or even want another crossover between the processor and the sub.
     
  4. Joe Szott

    Joe Szott Screenwriter

    Joined:
    Feb 22, 2002
    Messages:
    1,962
    Likes Received:
    0
    Stas,

    I'm a newb, but here's my 10,000 ft view of subs.

    The difference is the active sub plugs directly into the wall and has it's own 1 ch. amp built in. The passive relies on the power of the receiver/main amp to drive it (just like a normal speaker).

    In general, I would go with an active sub as it lets the main amp focus on driving the speaker set and not be bogged down by the wongo-sized woofer in the sub. It also allows you to adjust the amount of bass (volume) independent of the receiver volume, which is good for fine tuning your bass preference. If the amp/receiver is driving the sub, it usually needs to drain some power from the other channels to do it (unless it's a beastly amp system.)

    Also, not 100% on this info, but I believe 5.1 audio receiver usually means that 5 powered outputs are for FR, FL, C, RR, RL speakers and the .1 (LFE) part is just provided as a signal (usually unpowered.) So you would need a powered sub in such an instance to hear any of the LFE at all.

    Most receivers and pre-amps these days have a crossover setting that helps with the sub. They sometimes call this 'Bass Management' or 'LFE Control' in their marketing media. What it means is that you can set the frequency that the receiver switches from the main channels to the sub output. A few examples: If I had bookshelf/sattelite speakers I might set the crossover to 80 Hz. If I had larger tower speakers, I might set it at 40 Hz to just give that extra rumble at the low end. The crossover adjustments on the sub do the same thing, they just have to be set manually for your specific system.

    Hope that helps...
     
  5. John Garcia

    John Garcia Executive Producer

    Joined:
    Jun 24, 1999
    Messages:
    11,571
    Likes Received:
    24
    Location:
    NorCal
    Real Name:
    John
     
  6. Stasulos

    Stasulos Stunt Coordinator

    Joined:
    Sep 9, 2002
    Messages:
    50
    Likes Received:
    0
    Ok, I see, thanks a lot everybody.

    I'm still slightly confused with the connection though.

    If I have a passive sub and want to connect it to the main L and R channel, how do I do that? Presumably that's the case when the sub should have a crossover?

    If I connect the sub to L and R receiver outputs and then the sattelites to the subwoofer outputs wouldn't that mess up the channels?
     
  7. John Garcia

    John Garcia Executive Producer

    Joined:
    Jun 24, 1999
    Messages:
    11,571
    Likes Received:
    24
    Location:
    NorCal
    Real Name:
    John
     
  8. Lew Crippen

    Lew Crippen Executive Producer

    Joined:
    May 19, 2002
    Messages:
    12,060
    Likes Received:
    0
    Based on the prior posts, I assume that we are not discussing a passive sub to which an amp is later added turning it into an active sub, but a true passive sub. Given that one way to configure your speakers is:
    ·Connect the subwoofer’s R/L inputs to the R/L outputs from the receiver.
    ·Connect the R/L, front speakers to the R/L outputs of the sub.
    ·Connect all other speakers (center, R/L surrounds and any rear speakers) to their respective receiver outputs.
    ·Set the receiver ‘subwoofer’ option to ‘No’ or ‘none’ or whatever is appropriate.
    ·Set the receiver speaker option for the front speakers to ‘large’.
    ·Set the other speaker (center & surrounds) options (at least to being with) to ‘small’.
    ·If your receiver has an option to select frequencies for small/large, set it in accordance with your speakers (most would choose 80hz–100hz).
    ·All frequencies will now be sent to the sub/front speakers.
    ·Frequencies above the small/large option selected in the receiver will be sent to the center/surrounds.
    ·The passive sub’s crossover will strip off the lower frequencies and pass the rest to the front speakers. A good many passive subs won’t allow this crossover to be changed.
    ·Using this approach the sub gets all the lower frequencies and all other speakers get the rest.
    ·There is no way using this approach to allow the sub and the front speakers to get the low frequencies.

    The classic problem with passive subs is that the sub is powered from power the amp supplies to the front speakers, and in many cases it is the front speakers that should have the most power.

    Hope that this helps.
     
  9. Stasulos

    Stasulos Stunt Coordinator

    Joined:
    Sep 9, 2002
    Messages:
    50
    Likes Received:
    0
    Ok, I see. Things are much clearer now. Thanks a lot guys.

    Last question: what about connecting a passive subwoofer with only one input (+/-)?
     
  10. Lew Crippen

    Lew Crippen Executive Producer

    Joined:
    May 19, 2002
    Messages:
    12,060
    Likes Received:
    0
    You should ignore my prior post, if you only have one input on your passive sub.
     

Share This Page