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Adding a sub to Bookshelf setup. Does it make sense?

Discussion in 'Sound Science' started by russdenney, Aug 13, 2016.
  1. russdenney
    I have a new pair of Bowers & Wilkins 805D3 bookshelf/monitor speakers that are awesome--and they damn well should be at $6000 for the pair!
    My question is this...
    Due to location and size constraints,  I need to stick with a bookshelf. I happy very happy with the 805D3s, but they are a bookshelf, and I would like something to get me a little more oommppff in the lower mids and bass. I am thinking about adding a sub to this mix.
    I am a 2 channel music listener....not using for movies at all. Do you think a high quality sub will give me more in the mids and bass if it has a adjustable crossover and  I set it as such? I know it may seem silly to some, but I like a little more kick than most in the music, but I don't want to go to a full floor standing speaker.
    A) Will it work for my requirements?
    B) Is using a sub in a 2.1 channel configuration that common?
    C) Any downside?
  2. PurpleAngel Contributor
    Assume you have a stereo amplifier or receiver with a sub-woofer output?
  3. ProtegeManiac Contributor
    Are they on your shelf? Because if they're on stands in a generally normal size (ie non-nearfield) listening area, then the space occupied by some towers wouldn't be that much more than what a standmount on stands would occupy. The difference in size will come only really be a factor if:
    1. You have too many drivers on the tower and you can't sit far back enough for the difference in pathlengths from your head to each driver to be effectively neutralized
    2. You have to move out and you can't get help. A fat 800-series tower will be a PITA to move compared to bringing on standmount down with the box waiting in the truck/car and then the stands.
    That said, unless you're going from a 2-way to a 3-way with a huge bass driver - the low frequency extension isn't going to be a lot deeper. Maybe lower by another 20hz to 35hz.

    I don't see what's silly about it, this is fairly common. Just not as common as relying on LFE channel (ie the ".1" on an HT system), which is why most subs - and all the cheap ones - don't have inputs that can send out a high pass instead of fullrange signal after taking a signal for the sub.
    For the most part, yes. You just need to find the right kind of sub with the crossover features you'll need.
    Alternately, you can get a receiver with digital input and a subwoofer output. Not a surround receiver - most digital stereo receivers from mainstream brands like Onkyo. The NAD D3020 and D7020 have such a sub output too.
    Not as common as 5.1, which is why cheap subs don't have the bypass output much less a matched high pass output.
    That said, for other applications, it's fairly common. Car audio typically uses 2.1 systems since you have two front speakers, rear speakers disabled in serious non-surround set-ups because all they do is screw up imaging, and then a subwoofer or two. My car has such a system, although if you're looking only at the number of channels of music that's played on it; if you looked at the actual channels of amplification, it has five. Why? Because I apply digital crossovers before the analogue line level output, and the amps come after that, just so I can add customized time delays (think of the Audyssey DSP on some receivers) to the two tweeters, two midwoofers so they're all synchronized with each other and the subwoofer when the sound reaches my head. From the driver's seat, ocals are dead center and high up on the dash, everything else spread out around it like a nearfield set-up at home.
    First thing you have to think about is how to get the signal to the subwoofer and how to control the output level easily: moving your amp's volume knob should be all that's necessary, as opposed to perpetually matching the sub to the mains. If you're using a fantastic amp right now, but it doesn't have a dedicated subwoofer output nor an external preamp to power amp stage connection (like on NADs), then you're restricted to using a sub that has high level input and output. Also, check with the sub manufacturer to make sure the variable filter still works with the high level input, just to be certain.
    Second problem: the room. If apart from the roll-off on those the real problem is actually the room, adding a bass driver isn't the solution on its own because the room will still act on the subwoofer's output, making it inarticulate or outright bloated. At the same time if you can't sit far back enough then you increase the likelihood that you might localize the location of the subwoofer way down to the floor, even without you being consciously aware of where the sub is, because of reflections or rattling on the floor.* Ive seen a set-up where he built a pedestal to elevate the sub close to the height of the main speakers, but then it needs to be in the center, and your equipment rack might be there, so putting it ahead of the rack will block access including visual to the source unit, or when placed behind the rack, the bass output can rattle your CDP or TT. If you're using a music server, you can use LAN to access an HDD in another room, or SSD local memory.
    *In cars this is solved by cutting the sub low and have more of the bass coming from the midwoofer up front, and then using time alignment to polish it by delaying the output in front to sync with the sub, that way barring loud sub gain levels that pound on your seat, the sub is harder to localize. In my car the bass drum sounds like it's coming from the windshield.
    LajostheHun likes this.
  4. russdenney
    So, here is a pic of the setup...
    A Marantz PM-11S3 2 channel integrated amp (which is heavenly--nothing like their run of the mill stuff) and speakers sitting on a credenza on my home office:
    As you might see, going to the left/right with a floor stander is not my first choice. My amplifier does have a pre-amp out which can feed any decent subwoofer with a built in crossover/line level in. I have a corner in the room to place the sub. I am considering the B&W PV1D subwoofer or their DB1 (most likely overkill).
    The room is 12 foot by 12 foot with 12 foot ceilings (approximately). I don't have a lot of room to get far away from the sound as a result.
  5. ProtegeManiac Contributor
    Well that's why I asked if they were on stands or on a desk. Now that we've established which it is, and you really can't use stands farther out from the wall, you should address the acoustic environment first.
    One thing you can do, with a sub or not, is line that back wall with some sound absorbing panels. You're too close to the wall and that's probably affecting the bass, and if you put the panels in there, they'd still be useful if you still get a sub. And keep the window closed and covered by that acoustic panel - humidity from outside can adversely affect the wood and metals in the amp and speakers. Just make the panel that goes over the window easy to move, ie mostly just pushed in place by the desk, that way you can more easily inspect it in case there's enough moisture coming from even a closed window and you're getting mold in the back side of the panel. DIY panels would be best for controlling the cost as well as conforming to the specific needs of the room.
    Also, I'd decouple the speakers from that desk - get some cone feet that can be attached to the speakers without compromising the finish, and that also come with matching "shoes" so if they have sharp spikes they won't dig into and scratch the glass. That might not help as much but you never know, considering that desk has panels and large hollow areas unlike a filled, and weighed, proper speaker stand. I think Vibrapods might work but double check on how they can mount to these speakers.

    You might want to read Page 19 of the user manual - it states there that use of the preamp output is with a power amplifier. It isn't a dedicated subwoofer output and since it was intended to be used with a separate power amp, chances are the signal will all be routed to the preamp output, with no signal going into its own amplifier stage. Basically, chances are it will not have any signal going to the speakers if you enable the preamp output. At the very least, unless you already know someone else using it that way, contact Marantz and ask if it can work with just a sub without cutting the signal going into the power amp stage for the speakers.
    What I was describing were either the dedicated subwoofer preamp outputs on 2ch network receivers, or the likes of the NAD 304. The preamp board (which has the inputs, potentiometer, and line level outputs)  and the amplifier output stage board are not internally connected (even though only the inputs are on a physically separate board) as far as the circuit is concerned, they're connected through the line level output from the preamp on the rear to the line level amplifier input into the amplifier by a metal rod. This allows this amp to be used purely as a preamp or as a power amp (whichever you use), but alternately, you can pull out the metal bridge and replace it with cables, including a Y-connector from the preamp output so you can connect one to the power amp input and the other to a subwoofer.
    Here's a Marantz HD-AMP1, a 2ch network receiver - it takes digital inputs and has a DSP that can direct low frequencies to that mono subwoofer preout (lone black RCA).
    Here's the NAD 304 - the connectors I'm referring to are on the right of the zoomed view. The preamp and amp aren't wired internally hence the bridge on those sockets, and that's where you can use a Y-adapter plug to split the preamp signal between its own power amp stage and a subwoofer with line inputs.
    Given the size of the room I'd much rather put the sub in that space under the amp. Maybe DIY some kind of platform to raise it as much as you can without hitting the panel under the amp so as not to scratch nor transfer more vibrations, that way you minimize the difference in distance from your head to the speaker vs from your head to the sub.

    LajostheHun likes this.
  6. russdenney
    Thanks for sharing your extensive input here.
    I have confirmed with Marantz the preamp output is in conjunction with the signal to the speakers. So good news there...
    Interestingly enough, I am pretty happy with the bass on the setup (amazing really for a bookshelf!)...some of the tom toms (mid sized drums) in rock tracks have a thud sound to them I find less than optimal. Would moving to a proper stand help in this regard?
    Perhaps mistakenly so, but I was hoping that getting a bigger driver (via subwoofer) and setting the crossover as such might also help with that thud by bringing up some brute force in that frequency range.
  7. spruce music

    I think what you wish to do would work fine.  It won't be a problem.  Looked at the back of your Marantz.  Now optimally I might want to roll off the low end of your bookshelf speakers.  But even if you don't plenty of good subs would have adjustable crossovers.  You use the extra outputs to feed your sub off the amp.  Just use speaker output B for that.  Feed into a sub and you will need to set sub volume and crossover point on the sub.  That would be simplest. I would suggest Rhythmic subs as a good quality sub without being too horribly expensive. 
    Now on the other hand, with a square 12x12x12 room you might be better off without the extra low end.  It will be hard to tame the basic room resonance in a square room like that.  So simply not exciting it might be the better route.  A sub would excite those room modes.
  8. russdenney
    Thank you for your input.
    I took the plunge and picked one up today...and what a heavenly difference. It took a little tweaking to get the little extra "kiss" of sound I was looking for without overdoing it.
  9. ProtegeManiac Contributor
    Yep that makes using a sub a heck of a lot easier.
    This is why I was saying you need to deal with the acoustic environment first - everything in your set-up right now is just getting in the way of the sound and adding a sub might not even deal with the problem, whereas the acoustic treatments are still going to be beneficial when you do add a sub. For starters, the speakers are on a desk. Even if you filled up the drawers with sand all that will do is keep them from rattling once you have a sub (which is another reason why I didn't recommend starting with the sub - any rattling there will just inhibit properly hearing the bass), but it doesn't help much in making that desk a more stable platform for the speakers to work on. Get some cone feet with matching shoes for the speakers to decouple them from the table (nearfield set-ups more typically use the angled anti-vibration stands to point them up to the user's head), and when you add a sub, they'll still be working to decouple them from the desk. Sound absorbing panels to minimize reflections especially when you want non-nearfield speakers that close to the wall will still be helping out the speakers and the sub when you add one.
    To fill in the very low frequencies that the speakers cannot do properly, or if the sub has a high-pass output, you can have the sub do more of the work (this however increases how much more likely you can localize the location of the sub, which is why I said keep it in the center and elevated as high as possible). In the case of the other drums, and even most of the sound for the bass drum, it's more a matter of managing the reflections than adding a sub that will barely play any of the frequencies to reinforce those instruments in the first place.
  10. jazzwave
    Have try to use speaker stand?
    Yes, it will not add bass immediately but it will refine sound better when you put speaker on stand correct placement.
    room treatment
    I'm stereo lover as well, I don't like to add sub bass speaker into my stereo system. For stereo set, adding sub bass speaker need more parameter to be considered ; phase, position etc
    When I feel the bass not good enough , I check speaker position and room acoustic  first ,
    if that solution not help  I  prefer to change to better bass bookshelf speaker or floorstand
    Good luck
  11. ProtegeManiac Contributor
    He already mentioned it's a 12ft x 12ft room (too lazy to put that in meters but that's small) and he can't move the speakers farther from the wall as he cannot move his seat farther back than where they are now.

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