Hi Level / Lo Level

Discussion in 'Subwoofers' started by SDH, Feb 7, 2009.

  1. SDH

    SDH
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    Hi
    I currently have an Rel Q150E connected to an Onkyo 605 via both Hi Level and Lo Level as instructed in the REL manual.
    I have just bought the cable to Bi Amp the 605 and was wondering how I set up the Hi level now as it will send seperate feeds for the woofer and tweeter?
    Any help would be gratefully received
     
  2. William YZF-R1

    William YZF-R1
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    I believe it will be fine as it was. The biamped channels will have identical output to the front channels. Its still down to the speakers crossovers to eliminate the unwanted frequencies. ie The amp does not send high in one channel and low in the other.
     
  3. PSM1

    PSM1
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    I have my Arcam amp biamped and have my high level inputs from my T1 connectted to my centre speaker. This means do not have to worry about which to connect it too. Also since around 60% of all sound goes to centre speaker then sub is backing up more signal.
     
  4. William YZF-R1

    William YZF-R1
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    Could someone please explain to me what the benefits of connecting a sub by high and low level. I only have mine connected by low level.

    TIA.
     
  5. Nimby

    Nimby
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    High level connections usually have a more gentle crossover in the subwoofer which greatly increases the overlap with the speakers. The speakers still have to play their own bass to their best ability and do not enjoy the relief from this task when using high level connections. So the amplifier has to work hard and the speakers have to work hard. Distortion will be much higher with 90% of speakers compared with many larger subwoofers. You cannot use a BFD to equalise the subwoofer on high level connections. Using high level connections is the only way you can use a subwoofer in most simple stereo audio systems unless a line level (Pre-out) sockets are provided by the stereo amplifier. The speakers will still have to play full range unless you split the line level (Pre-out) stereo signal with a line level active crossover and then biamp the Main speakers above the chosen roll-off point. (~80Hz)

    Low level connections allow the speakers to be set to "Small" which rolls off the bass to the speakers in the AVR. You can set bass to subwoofer AND Mains in your AVR for ordinary stereo listening, or not. Using the Centre channel to provide a bass source for your subwoofer might deny you the full bass potential. With the speakers freed from bass reproduction duties they tend to sound cleaner because the amplifier is freed of the heavy loads involved in reproducing bass. This may or may not provide a cleaner, more dynamic sound quality depending on the quality of the amplifiers involved. Low level connections provide all the digital audio bells and whistles your AVR can provide. You can also equalise the subwoofer's in-room response with the inexpensive BFD. Allowing the subwoofer alone to manage the bass much higher levels are usually possible without introducing a bass-heavy quality to the SQ. A good subwoofer usually has a much wider dynamic range than most domestic loudspeakers because they have massive power and (usually) very much larger drivers to move a lot of air. (drivers = loudspeaker units in Olde English)
     
  6. missinglink

    missinglink
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    I don't quite follow some of the descriptions mentioned above. You don't biamp an amplifier; you biamp speakers using amplifiers?!

    Biamping refers to sending the same amplified signal from different amplifiers to the two separated (electronically) speaker parts - treble (tweeter) and mid/bass (woofer). In some amps a stereo 'second room' or zone B can be wired up to become this second amp; but you have to have speakers with two sets of input terminals.

    Low level inputs are typically via one RCA lead from the AV's subwoofer output. This is usually the way a specially designed subwoofer channel (the LFE channel or .1 channel) is tranmitted to a sub. The sub's crossover is usually bypassed and therefore acts at full range but is only fed the frequencies as set on the AV sub crossover value.

    Low level needs amplifying by the sub.

    If you connect a preamp output from a stereo amp as above you will likely run the sub at its full range as stereo amps have no facility to control the outgoing bass spectrum.

    High level or speaker level into a sub will now go through the sub's own crossover as the entire signal will be incoming. The crossover will be set to match the main speakers it is working with. The signal will have already been amplified.

    The schools of thought about using a sub - apart from lower frequency extension - is that the main speakers can sound better if they do not have to strain to produce their lowest bass. However, getting two different speakers - one main and one sub - to work as a team and sound smooth and seamless is not so easy. It is probably less noticable on movies soundtracks compared to music.

    Finally, biamping can often improve the performance of speakers as the separate tweeter and woofer sections get their own power - woofer needs more of the lion's share of power - and they both get the full signal from which they reproduce their part. The internal crossover is bypassed. But the differences usually depend on how well the speaker and its tweeter and woofer were designed and voiced in conjunction with its crossover i.e. the crossover may be better engaged rather than bypassed.
     
    Last edited: Feb 8, 2009
  7. Nimby

    Nimby
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    Odd, I don't remember mentioning bi-amping an amplifier and still prefer my own description. ;)

    In the case of Pre-out connections the signal can be re-inserted into the power amp section of the same stereo amplifier after the frequency split using an active crossover.

    Or the speakers can be driven by a completely separate stereo amplifier and only the preamp section is used. A passive subwoofer can then be driven by a separate power amplifier.

    I think of any system as bi-amping where a full range stereo signal does not pass through the same power amplifier. There always have to be at least two (i.e. bi) power amplifiers.

    Biamping can also mean that two stereo power amplifiers are used to drive the same pair of speakers after a frequency split via an active crossover. Or via the speakers' own internal crossovers. In this case the speakers play full range but the top end gets its own stereo amplifier thereby avoiding the heavy loads placed on the bass stereo amplifier. A sort of bi-wiring writ large. The downside with crossovers is that they use passive components which mean that series resistance often intervenes in the drivers' rigid control by the power amplifier.

    I would be loath to attach quality speakers to the high level out terminals of any subwoofer.
     
  8. missinglink

    missinglink
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    Apologies Nimby, by 'mentioned above' I meant the original post.
     
  9. m4rky_m4rk

    m4rky_m4rk
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    :lesson:
    Is that true? I thought it was the highest frequencies that required the most power, current, to reproduce. Its a basic law of physics isn't it?. Put another way. To move a mass backwards and forwards 10's of thousands times a second requires a lot of energy. To move a similar mass only 10's of times a second is much easier. Woofer's have higher mass than tweeters thats true, but they are on the same scale when compared to hi vs low frequencies. Or have I missed something in my understanding? The missing link could be the speakers built in crossover network. I guess this wasts a lot of power but is it worse for woofer than tweeter?

    If you turn the volme up to the max I think its more likely that you will blow the tweeter due to over heating than the woofer. My mate did excactly that whilst showing off his new speakers with Pink Floyds Time on the Darks Side Of The Moon album. When all the clocks started chiming a nice little puff of smoke arose from his tweeter, like they had inbuilt josh sticks -- his tweeter was a bit crispy after that. :devil:
     
    Last edited: Feb 9, 2009
  10. m4rky_m4rk

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    True Bi-amping is really quite a complicated and expensive option. In its simplest form it's as missinglink says above. I am not sure if its done this way that you will really hear any benefits! Its easy to try though if your amp and speakers allow it.

    This link explains some more quite nicely

    Bi-Amping: Pleasure or Pain?
     
  11. Nimby

    Nimby
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    Tweeters are fried by over-driving an amplifier into distortion. Meaning that the amplifier can no longer provide a smooth waveform as its power supply reaches its limitations. The pretty sinewaves become ever more distorted by clipping the tops off to produce nasty square waves. The even nastier sound produced is usually very audible and should prompt to the user to reduce the volume immediately to save the tweeters from overheating.

    I believe the power required to drive a loudspeaker unit at any particular frequency is related to the amount of air being moved. Not only does the woofer cone inertial mass need to be accelerated hard but air resistance is also involved sine it is air movement which produces sound. The amplifier must also provide electromagnetic braking on the voicecoil to avoid overshoot. The lower the frequency the more air has to be moved and the greater the excursion required to reproduce VLF at high levels. Under-powering a woofer cone will often result in resonances and even hitting the end stops. In fact one uses a small amplifier with series resistance to confirm the natural resonances of a driver by plotting impedance against frequency.

    Over-powering a woofer is likely to be much less harmful than under-powering it. Since the crossover may have passive series resistance in line with the drivers then under-powering is worse than keeping an iron grip on the voice coils. Only the resistance of the suspension and finally the end stops can limit cone movement. The more powerful amplifier can accelerate the cone viciously hard but will also stop it just as quickly. Producing an exciting, dynamic and hard hitting performance. The big amp never runs out of steam thanks to a massive power supply. So the ideal waveform remains clean and healthy for all the drivers.

    Having said all this.. in the very strange world of Naim forums you will sometimes see the most powerful amplifier recommended for the tweeter section of a bi-amped or tri-amped system containing fairly large woofers. I have no reasonable explanation other than the poster assumes that the more powerful (therefore more expensive) Naim power amplifiers will provide the most transparency. Some A/B/X blind listening tests might be worthwhile here but I wouldn't mention mention A/B/X over there. Or subwoofers for that matter. Quickly scanning their thread titles in their AV section I reached page 8 before subwoofers were mentioned and then only a member seeking advice on connection. Thank goodness I was dragged screaming over to the dark side by AVF's Subwoofer forum and SVS. :devil:
     
  12. missinglink

    missinglink
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    If you consider active loudspeakers, you will find that the amplification apportioned to the woofer is considerably greater than that for the tweeter.
    e.g. ATC active speakers typically have low frequency to high frequency amplification of 4:1.

    Considering the size of woofers and the amount of movement (cone excursion) needed to reproduce bass (shift air) then the physics is on the side of the woofers when it comes to power requirements.
     

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