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Speaker placement, or how I learned to stop worrying and love the bookshelf.

post #1 of 6
Thread Starter 

Posted here because I like the discussions here better than in the speaker forum.

 

So, I've had these Boston Acoustics VR-M60 bookshelf speakers kicking around for years. I bought them new in 2003 when I still had a real job and they did HT front duty. I went to grad school and they sat in their box for awhile, got set back up for a 2 channel HT setup that I promptly downsized (and sold my TV - moving it sucked) and nearly forgotten.

 

A few years ago I purchased some woodcraft stands and placed them on a desk with some solid two channel power, and purchased a pair of Polk Monitor 70's for two-channel HT duty (I'm just not that discriminating with TV and Movies, and they do a great job without having to futz with a sub).

 

I had an old Klipsch KSW-12 paired with the Bostons because, frankly, they sucked in the bass dept. I often left the sub off because I lived in an apartment, and in my mind a pair of booshelves should be "enough" in a nearfield setting. For those not familiar, these are rear-ported bookshelves, and the manual recommended very generous wall spacing which I tended to follow. They sounded very nice in the store (don't they always), but never really captured the impressive bass extension at home.

 

 

So, I pack up and move again (cross-country this time, woo!). In this new scenario I downsize again - gone is my office space (only a 1br), but there is a desk "nook" with some shelf space above it. While smaller than my old 6' table, There's enough room for my 30" display and my Bostons and some healthy space around each speaker. They're around 8" from the wall, but each rear port now essentially points to a double corner - wall, desk, back wall, and upper shelf (source is a EMU 0404 USB, not pictured):

 

 

(The laptop isn't always there, the stand tucks away when it isn't). Hard to tell from the image, but the Bostons are around 3-4" from the side walls, 8" from the rear walls, 6" from the upper shelf, on 8" stands. Both toed-in maybe a couple degrees.

 

They're being powered by a Pioneer Elite A-35R rather than my Yamaha RX-797. Theoretically half the power, but the Pioneer fits the space better and the Polks are thirstier than the Bostons anyhow. The polks sound fine in this configuration, and the Yammy provides the thump they're capable of, so the issue isn't with the previous amp. People might describe both the Yamaha and the Pioneer as bright, but they're SS amps so I'm sure any differences here are minimal compared to speaker design and placement and room treatments.

 

So, I listened to them briefly at my old place with the Pioneer and recall thinking they were even brighter and less bassy than with the Yamaha (the Pioneer probably doesn't manhandle the drivers as well as the Yammy, either). Anyway, I plug everything up and power things on, prepared to be underwhelmed. I wasn't. I got all the bass I felt they lacked in a more spacious arrangement. Really, a huge difference - bassy stuff like 90's trip hop has a satisfying thump and is rather enjoyable to listen to where before I needed to go to headphones to enjoy bassy textured music. Not chest pounding bass, but you can tell its there.  I think these things really needed to be placed in a bookshelf. I've done some testing with a tone generator, and I'm really not hearing much under 50hz (their +/-3 dB lower limit), nor are there any crazy humps between 80-120 hz. Pioneer set to bypass tone controls or tweaked to take a 2db edge off the treble. Bass transients in particular are just delightful now, provided the source material doesn't brickwall them away.

 

Now, this isn't my first rodeo, and I've had small bookshelf speakers before. In the past, placement never really seemed to have this drastic effect - what else might account for it? Could I have been wiring them out of phase all this time? Interference from rear wall (behind the listener) reflections? (This room is a bit larger)? If anything I sit a tad closer to the speakers, but the enhanced low end is audible as I walk around the room, too.

post #2 of 6

That upper shelf is probably acting like a horn.

post #3 of 6

I don't know what this is called in technical terms, but since lower frequencies are less directional than higher ones, they tend to bend around to the back of the speaker. If you put the speaker up against a wall these lower frequencies will be reflected back towards the listener (bit like a large baffle), and will be perceived as a gain in low frequencies.

For all I know (which is scant, I've never owned a set of decent speakers), this might be what bigshot is alluding to; that a horn also is in a way just a big baffle with a funny shape.

post #4 of 6

But if the speaker is all the way flat against the wall, it couples with it and the bass isn't as pronounced. That upper shelf is turning the waves around and projecting them forward.


Edited by bigshot - 2/8/14 at 12:22pm
post #5 of 6
Quote:
Originally Posted by bigshot View Post
 

But if the speaker is all the way flat against the wall, it couples with it and the bass isn't as pronounced. That upper shelf is turning the waves around and projecting them forward.

 

Yes, the fact that there are five walls surrounding the speakers that can reflect/channel the sound amplifies the effect, but it's still based on the fact that the reflected sound is low-passed, so that the net effect is an increase in low frequency, compared to the speakers free-standing.

post #6 of 6

Ported speakers are notoriously more critical with respect to placement relative to the walls.

 

Personally I am baffled as to why a rear-ported speaker would be marketed as a bookshelf speaker.  Placement too close to the wall (esp. when surrounded by books :rolleyes:) would turn it more into a "reverse" bandpass enclosure, with the port as a Helmholtz resonator coupling the air volumes inside the cabinet and that enclosed behind it.  Placement flat against the wall would make the bass very poor (boomy with very little deep extension).

 

Interesting that the manual recommends generous wall spacing for these bookshelf speakers.  Boston Acoustics must be using unusual bookshelves :D)

 

Just be happy your current arrangement seems to work and don't wonder too much as to why that is...

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