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  1. #1
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    Default A different slant on subwoofer connection

    Hello,
    Here is an interesting article from Paul McGowan's (PS Audio) daily blog on his favorite method of connecting a sub:

    "In yesterday?s post I discussed the fact that there are basically only two ways to connect a modern powered subwoofer: with a high level or a low level input. The vast majority of subwoofers today no longer offering a high level input because Audiophiles are probably ok adding another cable and with the rise of home theater applications as the primary market for subs, which require a low level input from the surround processor, the fate of the high level input has been sealed.

    But what advantages did that high level input offer? Plenty and, to this day, it is still my favorite for integrating a sub with a system.

    Let?s review what the differences between the two inputs are first. Fact is, both inputs actually go to the same place on a powered sub ? they just take somewhat different routes. The high level input is designed to come from the main power amplifier?s outputs ? which is typically 20 to 30 times louder than its inputs. Subwoofer designers merely take a couple of resistors and reduce this very loud signal down to match the main power amplifier's input levels. If done properly the result is that there is no loudness difference between the low levelor the high level input signal that feeds the subwoofer's internal power amplifier.

    There is one big difference, however, and that?s the effect the main loudspeaker?s power amplifier had on the signal we reduced in level. Remembering that all power amplifiers affect the sound of the music that passes through them (phase shift at the lower extremes, tube amps with their output transformers, solid state amps, vs. class D amps etc.), we'd be much better off using the already-amplified output of the power amp to feed our sub because that output will be much closer matched, sonically, to what's being fed to our main loudspeakers.

    If we use, instead, the low level input directly from the preamplifier's output we have not only lost the advantage of matching the amplifier's sound but we risk the possible degradation of adding another length of interconnect to the preamp?s output which, in many cases, can do a lot of sonic damage (depending on the interconnect's length and the preamp's design).

    So with all this in mind here?s my advice. If you?re forced to connect the subwoofer with its low level inputs, use a Y connector at the end of your interconnect cable feeding the power amplifier if the run is more than 2 meters.

    If you?re handy with a few tools and want a better DIY path, just make a 30X resistive divider (use a 30K resistor and a 1K resistor) across the output of your power amplifier and feed the subwoofer's low level inputs from the junction of the two resistors (the 30K going to the + output of the amp and the 1K going to the - of the amp).

    Either way you go, you?ll be delighted you have a sub and connected it right."

    Regards, Ken
    Last edited by Kenneth Swauger; 08-28-2012 at 10:08 PM.

  2. #2

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    Used high-level inputs when I had a sub in my two-channel rig. Don't any more, but I may go back to it.

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    I noticed improved sound using high level on many subs I have tried for 2-channel. H/T I still use the LFE. Thanks Ken.

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    Polk subwoofers have both inputs, so trying the idea should be fairly easy.

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    So dumb question of the month, but when he keeps saying "High Level Input" does he mean the line in RCAs (using my PSW125 as an example)?
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    High-level is speaker-level, RCA is low-level.

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    For the same reasoning REL and previously Mirage have touted using the speaker ( high) level connection.

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    I've also used High Level in a two channel system. But I have a question there. What I did is use and integrated that had A/B speaker terminals. I hooked the B terminals to the HLI on the sub and the A terminals to the speakers directly. The reasoning is that I thought, running my speakers from the subs High Level Outs would also add more wire and more items between the amp and the speakers. (Obviously I ran the amp in an A&B configuration.

    Was/am I wrong in thinking that?

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    I believe you are correct, use the connection method that requires the least amount of speaker wire.

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    Quote Originally Posted by Syndil View Post
    High-level is speaker-level, RCA is low-level.
    Then next stupid question, how would that work with say LSi's or inefficient speakers? Wouldnt they present too much a load?
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    Not a stupid question. The connection to the sub's bass amplifier doesn't change the load the speaker gives the amplifier, since the input impedance presented by the bass amplifier is very high compared to the much lower impedance of the speaker.

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    So using a dedicated amp it would look like this: Pre to Amp via RCA, Amp to sub via speaker cables, sub to speaker via speaker cables?
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    That is correct, assuming this connection method uses less speaker wire than connecting your speakers directly to the dedicated amp would require. In other words, if the sub is located between the dedicated amp and your speakers then use the method you've described.

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    Quote Originally Posted by cnh View Post
    I've also used High Level in a two channel system. But I have a question there. What I did is use and integrated that had A/B speaker terminals. I hooked the B terminals to the HLI on the sub and the A terminals to the speakers directly. The reasoning is that I thought, running my speakers from the subs High Level Outs would also add more wire and more items between the amp and the speakers. (Obviously I ran the amp in an A&B configuration.

    Was/am I wrong in thinking that?

    cnh
    When you do this you are also sending the full range of bass to your mains (bypassing the sub's crossover), so you would need to be very careful about setting the upper cutoff on the sub or you would end up with a peak or valley in your overall bass response. When I had a sub in my two-channel I ran it with the sub in the chain to my mains and it produced no audible degradation in my mains. Of course that probably has a lot to do with the quality of the sub. This also gives you the flexibility of setting the crossover point between the sub/mains where you want it to be for the best sound rather than being forced to choose a setting based on your mains' specs, which IMO is a much more important issue.

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    Nice thread Ken,
    Very informative and you guys provided me with answers I needed regarding my thread about bridging 2 subs for 2 ch. I will be making the following connection for 2 ch.

    Amp left ch output to left sub (high level input) then left sub (high level out) to left main...then
    Amp right ch output to right sub(HLI) then to right sub (HLO) to right main

    What's your thoughts on that connection
    PS: I'm still kinda new in the hobby, but my wallet has been around the block a couple of times.

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    If I had two subs in a 2-channel system, that's the way I would do it.

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  17. #17
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    Look's fine, dhart86

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    I have used this method often for both 2 channel (that's how my office rig is set up right now) as well as the ht rig, which is usually dual-purpose anyway. Sometimes it helps solve a dilemma. For instance, I have for some time run my center channel through a small front-ported 8 in sub using the speaker level inputs/outputs. This allows me to run my center full range, which makes a HUGE difference with movie and hdtv soundtracks. I couldn't believe how hard that little sub was pounding the first time I played The Dark Knight on bd through it. But recently I downgraded receivers, and it will not allow me to run my center large and my mains (which are now in ceiling) small. So I am running my mains through the LFE sub, and using the subs internal crossover. And once again everything is right in the world (well, at least the world of small children and in-ceiling speakers).

    Anyway, I didn't know about the difference in signal. very informative. Thanks Ken.
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  19. #19

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    Quote Originally Posted by Kenneth Swauger View Post
    That is correct, assuming this connection method uses less speaker wire than connecting your speakers directly to the dedicated amp would require. In other words, if the sub is located between the dedicated amp and your speakers then use the method you've described.
    Gotcha, makes sense.

    I might give this a try someday in my 2 channel rig. I am hoping to run some Maggie's with a sub (since they have bass but not the punch you in the face kind I like) and this would allow me to do so. When that day comes I hope to be lucky enough that I can put the gear into the wall in the middle of the room (so nothing between the speakers but the sub) and will try that method.
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    Quote Originally Posted by Syndil View Post
    If I had two subs in a 2-channel system, that's the way I would do it.
    Very cool, thank for the feedback Syndil
    PS: I'm still kinda new in the hobby, but my wallet has been around the block a couple of times.

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    Quote Originally Posted by Kenneth Swauger View Post
    Look's fine, dhart86
    Thanks
    PS: I'm still kinda new in the hobby, but my wallet has been around the block a couple of times.

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    Thanks for this post Ken. I've been championing this for years, as well.
    It's funny, I recommended using high level inputs on subwoofers when available, here on the forum, and invariably I would get chastised for the methods "inferiority." I should say, however, many of those criticisms were from the same crowd who say there is no need for subwoofers in 2ch stereo.

    Good information here. Amplifier tone matching goes a long way to promote coherence.
    design is where science and art break even.

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    My pleasure, I'm glad the information was useful.

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    Quote Originally Posted by newrival View Post
    Thanks for this post Ken. I've been championing this for years, as well.
    It's funny, I recommended using high level inputs on subwoofers when available, here on the forum, and invariably I would get chastised for the methods "inferiority." I should say, however, many of those criticisms were from the same crowd who say there is no need for subwoofers in 2ch stereo.

    Good information here. Amplifier tone matching goes a long way to promote coherence.
    I heartily agree......I run my 2ch system with 2 small subs....Balance of the 2 subs is critical,but once you dial it in,it sounds wonderful,imho.....peter

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    Ken, that article appears to be somewhat flawed in its reasoning. Even accepting for purposes of discussion the proposition that the amplifier for the speakers has some unique sound characteristics which should be "matched" for the sub-woofer, simply using the speaker level sub inputs can't do that. The internal sub amplifier remains the component which actually is powering the sub driver cone and any sound characteristics it supposedly has will be reflected in the sound of the sub, and not, of course, in the sound of the speakers. If someone considers this to be a significant problem, a passive sub without an internal amplifier would have to be used, and a separate external amplifier would be needed to power both the sub and the speakers.

    The use of the speaker level sub inputs has the significant disadvantage of not having the benefit of the bass management available with a line level sub output in a receiver or pre-pro, so that the speakers would be forced to play full-range, including low bass they may not handle well. There's still a misunderstanding around that a sub has an internal "crossover" which can be used as a substitute to provide for bass management; it doesn't, despite the control on the back of the sub which is often (mis)labeled as such. This is simply a variable low-pass filter which affects only the sub itself and has no effect on the speakers, even if they're connected through the sub. The speakers are still forced to attempt to play full-range, including the lowest bass. A very few subs have a separate high-pass filter on the speaker outputs, commonly fixed at about 100Hz to limit the bass load on the speakers, but this has nothing to do with the sub's low-pass filter and its control knob.

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    John, I reject the assumption that the bass management offered by a pre/pro or a receiver is a superior solution to utilizing the bass management of the sub. I understand the appeal as it may seem like a more elegant solution, but it is actually a more complex solution, and complexity in the signal chain is the enemy. Many serious 2-channel rigs won't have built-in bass management for that reason. If you're using a pre/pro or a HT receiver in a 2-channel system, it's already a compromise.

    In my case, my 2-channel rig has always consisted of a CD player with variable outputs and an amplifier to drive my speakers. Nothing more. I have auditioned numerous stereo preamps in my 2-channel rig, but I would always go back to hooking the player directly to the amp. Simply could not be beat, convenience be damned. Obviously when I was running a subwoofer in that setup I had to rely on the bass management offered by the sub, and I got the best sound quality out of the sub when I was running it with speaker-level connections rather than RCA connections.

    Using RCA in to the sub and out to the main amp might have seemed like a more elegant solution, but in the end the sound quality was better with the down-and-dirty speaker level connections. I assume it's because any coloration/degradation done by the sub's crossover was less evident in the higher-power speaker-level signal than it was in the low-power line-level signal.

    I agree that the notion of your main amp's coloration making its way into the subwoofer's output is questionable, but in the end I still feel that--for stereo listening--speaker-level is the way to go when adding a sub.

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    You've missed the point regarding bass management: a sub has no crossover which limits the bass sent to the speakers; it's only a low-pass filter on the sub.

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    By allowing the mains to play full range along with an additional sub, or preferably subs, will help smooth out bass response even further.

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    Hello John,
    While I'm not trying to explain someone else's theory, I imagine Paul is of the opinion that using the high level connection method results in aligning the most troublesome aspects of getting convincing blending between main speakers and subwoofers. Granted there are many other factors (high pass filtering reducing bass distortion in main speakers) which could tip the balance in another direction, but trying another approach should always be considered. From reading Paul's blog I have the impression he prefers fairly full-range main speakers and values a blending where the subwoofer disappears from obvious hearing. For him the high level approach gets what he's after.
    Good discussion.
    Ken

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    I have my twin Velo subs connected from my Yamaha RX-A3010 via LFE & then I use Cat5 wire (only 2 strands) from my Rotel amp main speaker posts to the Velos speaker input. It really like the way it adds a bit more punch to the mix. A long time custom installer told me about that little tweak & it sure does work nicely. Both 2 channel & HT have awesome bass.
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