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Rear ported bookshelf speakers: Question?

74.108.123.127

Posted on January 10, 2010 at 14:20:40
2-ears
Audiophile

Posts: 79
Joined: January 19, 2003
Is it just trial and error, or is there some general guidance as to how much distance there should be between the speaker and the rear wall?

 

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RE: Rear ported bookshelf speakers: Question?, posted on January 10, 2010 at 15:20:53
R6Bears
Audiophile

Posts: 5
Joined: January 7, 2010
I've been researching bookshelf speakers myself. I just read a review on Polk Audio Tsi series and it was reported that placing the speakers at least 8 to 10 inches from the wall produces much better sound. If you find a bookshelf speaker that you like, please post back.

 

So-called bookshelf speakers., posted on January 10, 2010 at 16:28:01
Kal Rubinson
Reviewer

Posts: 9841
Joined: June 5, 2002
Most all are designed for use on stands and away from walls and floor. The term "bookshelf" is an anachronism.

Kal

 

RE: Rear ported bookshelf speakers: Question?, posted on January 10, 2010 at 18:03:02
Ron Oehlert
Audiophile

Posts: 5109
Joined: December 18, 2003
General guidance is to not use Rear ported speakers on bookshelves, but rather use Front ported or Sealed speakers there instead.

 

None the less, thousands of people put speakers on bookshelves.*, posted on January 10, 2010 at 19:07:05
Mali
Audiophile

Posts: 1700
Location: Wyoming
Joined: June 12, 2003
*

 

Indeed. Unfortunately. (NT), posted on January 10, 2010 at 19:23:20
Kal Rubinson
Reviewer

Posts: 9841
Joined: June 5, 2002


 

RE: Rear ported bookshelf speakers: Question?, posted on January 10, 2010 at 20:51:21
Rick58
Audiophile

Posts: 901
Location: No. California
Joined: January 24, 2001
I would think a foot or so should do the trick ... but mine are 5' out into the room, with a sub to augment the low end. Soundstage city!

 

RE: Rear ported bookshelf speakers: Question?, posted on January 11, 2010 at 00:30:51
Bill the K
Audiophile

Posts: 5378
Joined: June 3, 2006
How will it affect the sound if a lump of sponge is glued to the wall right behind the port? Will it adversly affect the bass?

 

General? Many (most?) front ported or sealed speakers do not do well stuck close to walls, posted on January 11, 2010 at 07:17:07
Frihed89
Audiophile

Posts: 13921
Location: Copenhagen
Joined: March 21, 2005
This may be a necessary condition, but is not sufficient. My LS3/5As are sealed. They sound OK a foot or so away from walls. They sound very good, if you make that distance a meter. If you make the distance even larger, they begin to sound like a symphony.

This weekend, a guest at our flat, asked me what subwoofer I was using!
"What did the Romans ever do for us?"

Observe, before you think. Think before you open your yap. Act on the basis of experience.

 

If they are reasonably good stand mounts, they will never know what they are missing, posted on January 13, 2010 at 04:27:16
Frihed89
Audiophile

Posts: 13921
Location: Copenhagen
Joined: March 21, 2005
Good monitors excel in sound staging and smoothness on integration, no matter how they are voiced.
Observe, before you think. Think before you open your yap. Act on the basis of experience.

 

RE: Lump of Sponge Question, posted on January 13, 2010 at 18:46:24
roblistens
Audiophile

Posts: 60
Location: Midwest US
Joined: December 11, 2009
Is this natural sea sponge, or cellulose sponge from the grocery?

I could see how some sponge might spread out the resonance and lower the peak. Like when they put fiberglas inside the port, as in the Dynaco A25. It ought to prevent the wall from reflecting sound energy directly back into the port, as well.

 

It depends entirely . . ., posted on January 13, 2010 at 21:29:53
caspian@peak.org
Audiophile

Posts: 1043
Location: Oregon
Joined: January 12, 2008
. . . on how the designer intended them to be placed.

Many small speakers are intended to be placed on stands, well away from walls. These are designed with up to 6dB of baffle diffraction step compensation (look it up), so they will not sound thin and anemic when so placed. They will sound thick and muddy when placed too close to a wall -- ESPECIALLY if they are rear-ported. (If they must be placed within a foot or so of a wall, then some big pads of sound-absorbent material behind them would definitely help. 2x2 foot slabs of 4"-thick rockwool, covered with sculptured acoustic foam, would be about the minimum necessary acoustic treatment.

A few small monitor speakers (see North Creek for some excellent kits) are designed for near-wall or bookshelf placement. These, by contrast, WOULD sound thin and anemic if placed out in the room on stands.

Define your placement limitations/purpose, and then shop for appropriate speakers.

 

Yes and no…, posted on January 13, 2010 at 21:46:46
David Aiken
Audiophile

Posts: 5858
Location: Brisbane
Joined: September 25, 1999
Yes re it all depends on how the designer intended them to be placed.

No, or at least a very big maybe about the foam on the wall.

Most acoustic foam products placed directly on the wall aren't particularly effective at bass frequencies so they'll do little to help the excessive bass reinforcement that proximity to the wall produces. You can improve the bass absorption of such products by increasing their thickness and/or spacing them out from the wall but the more you increase the thickness of the foam and the bigger the air space you leave behind it, the further away from the wall the speaker is going to be and the less need you have to use such techniques.

Anyone trying to get effective absorption below 100 Hz by using foam placed on the wall is virtually doomed to failure, even with foam that's 4" to 6" thick. It will absorb at higher frequencies and reduce the reinforcement there, but that's only likely to make the bass reinforcement even more noticeable.

You can probably get better results with some rear ported speakers by using a foam plug in the actual port, and many speakers come with just such plugs for just such a purpose but even then you probably still need to place the speaker a reasonable distance from the wall.

If you want a speaker that can be placed very close to a wall, the best option is to buy a speaker that has been designed for just such placement. They do exist.


David Aiken

 

RE: Lump of Sponge Question, posted on January 14, 2010 at 02:25:40
Bill the K
Audiophile

Posts: 5378
Joined: June 3, 2006
Thanks for the feedback.

I was thinking of the sponge from the grocery.

I tried some in the port once but did not notice any difference.

 

RE: Lump of Sponge Question, posted on January 14, 2010 at 09:32:29
plantsman
Audiophile

Posts: 4790
Location: Maine
Joined: April 4, 2002
Assuming normal port tuning a sponge a couple inches thick stuck to the wall is likely to be nearly acoustically invisible relative to the port output. It shouldn't make much difference no matter what type of sponge it is and it won't make the speaker sound as though it is much farther out from the wall.
"There are political consequences to remembering things that never happened and forgetting things that did." Ariel Levy

 

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