[roymail]

Subwoofer or "bass module"?

OK, it's common to see 2-way monitors sitting on top of  matching bass modules on each speaker.  In some cases the bass speakers are powered internally, others are designed for bi-amping.  This seems like a more elegant solution than using an add-on powered subwoofer, but I may be wrong.  I've been wrong before? 

Anyway, I've been using some diy 2-way monitors with an older Velodyne sub, but I'm thinking about building some bass modules.  Is this a good idea, and what are the pros and cons that I should consider?

I was thinking about using a single 10" driver in approx 1.5 cu it cab, or I could use two 8" drivers in the same size enclosure.  I'm not sure about the best xover frequency.  Feel free to comment, advise, etc.

Thanks! 

[srb]

One possible reason that one might choose separate powered subwoofers rather than bass modules as stands for monitors is that sometimes the ideal location for generating low bass is not the location of the monitors.  This would assume that the crossover between them would maybe be 80Hz or less.  Higher crossover points would probably dictate that the bass module or subwoofer be located close to the main monitors for coherence and lack of localization.
 
As others have found, and well as my own personal experience, raising subwoofers off the ground by a foot or so often results in tighter, less boomy bass.
 
Steve

[rollo]

One possible reason that one might choose separate powered subwoofers rather than bass modules as stands for monitors is that sometimes the ideal location for generating low bass is not the location of the monitors.  This would assume that the crossover between them would maybe be 80Hz or less.  Higher crossover points would probably dictate that the bass model or subwoofer be located close to the main monitors for coherence and lack of localization.
 
As others have found, and well as my own personal experience, raising subwoofers off the ground by a foot or so often results in tighter, less boomy bass.
 
Steve

 Wonderfull advice. Try raising that sub 22% of your room height to the centerline of the driver as per ASC sound traps recco. Works very well.


charles

[eclein]

I raised my 10" POLK sub up off the floor about 8 inches and it was like getting a new subwoofer...try it.

[srb]

Wonderfull advice. Try raising that sub 22% of your room height to the centerline of the driver as per ASC sound traps recco. Works very well.

Based on my 8ft. ceiling height, that would be 21 inches.  I need more concrete blocks!
 
Steve

[roymail]

Thanks guys, very good comments and suggestions, much appreciated. 

[James Romeyn]

Forget placing subs under the monitors.

Get two more powered subs (any type, type is close to irrelevant) for three total.  Read about multiple subs for flattening modes (my website or search Earl Geddes, Duke LeJeune/AudioKinesis here at AC). 

Spread the three subs throughout the room, near the walls.  One sub must be sited above ear level.

Stagger the three LPXO frequencies.

The only caveat is that you must not use two or more subs with identical high-Q box tuning.  If that is the case, on one one sub add mass to a cone with clay or putty, on the other sub add stuffing to the port.  This will stagger the tuning and allow the disparate placement of the multiple subs to flatten the room's modes.

There's more to read about it.  It's well proven to flatten modes and achieve the sound quality of bass in a large commercial space.

Benefits will accrue by HP filtering your mains. 

With four subs all could remain on the floor and none need be elevated above ear level. 

I'd avoid corner placement.  Use my Golden Ratio formula at my website to assist with placement. 

Mono is fine.       

[ctviggen]

What website?

I'm going to put one sub in/near the corner and a second sub in the "middle" of the long wall, as this is the easiest placement for my particular room.  I also have two stands the subs will sit on; they are slightly (a few inches) different heights.  Same subs and amps, though.  The amps have a single notch filter, which I'll use to filter out the largest peak.  If this works well, I may purchase a third, smaller sub for placement elsewhere in the room.

[EthanH]

I don't know if this is off topic, but isn't the advantage of bass modules a higher crossover point rather than just an increase in low end extension?  In my limited experience it seems like much of the power and drama in music is located between 50-200hz.  Could a quad of 8" subs paired with two-way mini-monitors ever produce an upright bass comparable to a pair of three-ways anchored by 15" woofers, or even a three-way anchored by a pair 8" woofers per speaker? 

Interesting topic.  If I could figure out a way to make my 7" monitors sound like much larger speakers I'd be a happy camper.

[ctviggen]

What's a "bass module"?  Is it really a separate bass "speaker" placed under monitors?

I believe that multiple subs can make up for the low frequencies not produced by monitors.  The issue will be at what frequencies do you crossover the subs?  If your monitors only go down to 200 Hz, do you want the subs to go up to 200 Hz and can they integrate well with the monitors?  And can the subs play that high?  Most subs these days seem to made for 20 Hz and not 200 Hz. 

8 inch subs, though, should be able to go to 200 Hz with relative ease.  Another issue, however, is what does it cost to buy four subs with the capability of going to 200Hz?  Or do you take that money and upgrade the fronts to larger speakers?  If you're buying "nice" subs at 4-600 each, that's 1,600-2,400 dollars.  You're getting into the range where you could buy a nice set of speakers for that price.

[EthanH]

Most subs I see are meant to be crossed over at 50hz or lower, but I think a lot of monitors, even relatively robust ones with 7" drivers, would be better served with a higher crossover.  By "bass modules" I assumed the OP meant something like the "Puppy" in the Wilson Watt/Puppy or the lower cabinet in a Von Schweikert VR4 or VR5, for instance.

[ctviggen]

Hmmm...This thread seems to imply that cheap subs might do the trick:

http://www.audiocircle.com/index.php?topic=65562.0

[roymail]

By "bass modules" I assumed the OP meant something like the "Puppy" in the Wilson Watt/Puppy or the lower cabinet in a Von Schweikert VR4 or VR5, for instance.

That's right, and I'm not suggesting that they can duplicate the low hz of a 12" sub.

Yes, they would have to cross over somewhere around 200hz.  I'm just looking for greater output than a small monitor can deliver alone without bringing in a bunch of big boxes.  Keep in mind this is our home living area we're talking about, WAF must be considered, too.

[Quiet Earth]

If I could figure out a way to make my 7" monitors sound like much larger speakers I'd be a happy camper.

  I'm just looking for greater output than a small monitor can deliver alone without bringing in a bunch of big boxes.

Try placing your speakers very close to the back wall. If you have two symmetrical  corners available, place the speakers in the corners. They don't necessarily have to be right in the corner, mine work better closer to the side walls than the rear walls of the corner. The idea is to use the room boundaries to support the sound coming out of the speakers. Adjust the toe in to recapture the center image.

I realize this is considered improper speaker placement, but if you really want to know what your speakers can do from 50-500Hz, you should at least experiment with it before you buy a sub. You might be surprised that you don't need to buy anything at all. Unless you need longer speaker wire  .

[James Romeyn]

What website?...

You can click on the little globe under my avatar or just read here http://jamesromeyn.com/home-audio-gear/dsa-1-0-distributed-subwoofer-array-5-pieces-4k-usd/

[drew54]

My 2 cents,
based on my system.
mid bass couplers could be 2 high quality 8 inchers in a box underneath your monitors as you describe.  Lets say 200Hz x-over. 

V important to high pass your monitors to increase power handling.

Then separate corner loaded good quality sub (2 would prob be optimal). X over at 50Hz to the mid bass system.

The key for my system is digital eq on the bass systems.  I use 3 amps, and the eq goes only to the bass.  Roll off the mid bass woofers at about 3db/octave and adjust the sub for proper fill.

Its complicated, and thats half the fun. 

[JLM]

Definitions get us in trouble.

Subwoofers go below woofers so should cross below 40 Hz.  (What kind of self respecting woofer can't reach 40 Hz?)

I had bass modules 30 years ago (passive woofers in separate cabinets that supported the small 2-ways).  These bass modules crossed overy around 100 Hz and were rated down to 17 Hz at 114 dB, so they provided serious bass (some are fairly wimpy).  But they also needed some EQ as they could easily overwhelm nearly any residental room.

I agree that ideally subs shouldn't be used as stands and mostly certainly should be free to be located differently than the main speakers.

[James Romeyn]

...I agree that ideally subs shouldn't be used as stands and mostly certainly should be free to be located differently than the main speakers...

For multiple reasons I tried so very hard to get good sound using four small subs (2 per monitor) as stands under the monitors.  It failed miserably, even firing the four subs in every conceivable combination of directions.  The modes are awful in this room even though it's larger than many listening rooms.

It's not too far fetched to view all domestic listening rooms as two rooms, the acoustic space below 200 Hz and the space above 200 Hz, such is the huge difference in the way the room reacts to music above vs. below 200 Hz. 

This sounds bold but it's not necessarily meant to.  With maybe one exception of architecture every single so-called full range speaker is inherently flawed because of the way that rooms react to sound.  The best place for bass reproducers is completely different from the mid-treble ideal location.  You can see this in every professional review, it's right in front of your eyes.  The rep from the speaker company first sets up the speaker for ideal bass, then they fine tune other secondary parameters for the best possible mid/treble.  But this obviously means that no matter where might be the best location for mid/treble, the person setting it up has already acknowledged they are stuck at the location minimizing the worst damage that is caused by the room's bass modes. 

It's so obvious it's almost silly.  A loudspeaker should ideally be two completely separate entities, one section for the bass, the other for mid-treble.  The emperor has no clothes, but don't tell him because he'll have your head on a platter!

Really, within about 10-15 years, IMO, there will be no such thing as a super high end full range speaker with the bass section setup next to the mid-treble section.  That entire philosophy is incorrect.   

I heard Carver is working on a sub system with many itsy-bitsy subs spread throughout the room. 

[chlorofille]

Roymail,

What drivers are used in your 2 way ? If a 6.5inch or inch midwoofer is used, then all you need is a good ol single 12'' subwoofer placed in a corner. Bass modules reduce WAF tremendously. Even if a 2 way bookshelf on a stand occupies the same space as a floorstander, WAF is still higher for the 2 way bookshelf.

IMO bass modules are not needed. You might as well save up for a well designed 3 way as the bass can integrate much better through the midrange. The woofer of a 3 way can also play the "power region (70-200Hz) much better than a 6.5inch midwoofer in a 2way. (assuming that the woofer is at least 8'')

[Quiet Earth]

Bass modules reduce WAF tremendously.

They don't want to see our speakers out in the middle of the room either.  Maybe they know something that we don't?