Rear port distance from wall - AVS Forum
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post #1 of 26 Old 11-23-2009, 11:08 AM - Thread Starter
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OK, I have it now pinned down to two speakers to get. Both Energy. Either the C-200 or the RC-10 (I will post something on that in a bit)
But, since it is a rear fireing port, Energy recomends putting two feet of space between the back of the speaker and the wall. I can't do that due to space limitations. What do I do? The best I can do is maybe four inches. Help!

Sounds good!
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post #2 of 26 Old 11-23-2009, 11:16 AM
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Quote:
Originally Posted by karlsaudio View Post

OK, I have it now pinned down to two speakers to get. Both Energy. Either the C-200 or the RC-10 (I will post something on that in a bit)
But, since it is a rear fireing port, Energy recomends putting two feet of space between the back of the speaker and the wall. I can't do that due to space limitations. What do I do? The best I can do is maybe four inches. Help!

You need at least the distance of the port width away from any object. That will ensure the ports aren't constricted. This is a known in the DIY subwoofer building realm, but I'm sure the same applies here. The recommendation to pull two feet in has more to do with bass response and imaging due to room placement.
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post #3 of 26 Old 11-23-2009, 12:34 PM
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I had always thought the rule of thumb was three times the diameter of the port.

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post #4 of 26 Old 11-23-2009, 01:07 PM
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You need to rethink your speaker choice. Look for either front posted or sealed speakers.
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post #5 of 26 Old 11-23-2009, 02:23 PM - Thread Starter
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Oh boy

Sounds good!
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post #6 of 26 Old 11-23-2009, 02:40 PM
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??? rethink your speaker choice?? If you like the way they sound keep'em. Just make sure you're not restricting air flow.. 4" should be fine, I doubt your mains have a port bigger than 2 inches anyway. The only time it really matters is when your bass drivers are reaching X-max (their full potential to move) and that's something you don't have to worry about at all with Amps designed for HT or an AVR. If you roll off to a sub you wont be moving much air through the port anyway so a wall even 2" away wont be a factor and probably wouldn't matter even if you ran them large and didn't roll them off.

I wouldn't worry about it. Now proper speaker placement in relation to the way the "room" will effect bass response and imaging may be something that your location could effect.
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post #7 of 26 Old 11-23-2009, 02:47 PM - Thread Starter
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On that note, I have three other choices I am going to look at. All have front ports. The B&W 685, Focal 706V, and the monitor BR2. I have listened to and liked the Focals. I just have to listen to the B&Ws and Monitors. Luckily, the A/V place near me has both!

Sounds good!
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post #8 of 26 Old 11-23-2009, 03:06 PM
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You should be fine with the RC-10's, they also come with port plugs for situations like yours. Their use does not adversely affect their sound.

Chris
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post #9 of 26 Old 11-23-2009, 03:20 PM - Thread Starter
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I will look into that. The local Energy dealer has four left! Other than that, I think I am going to listen to the Monitor BR2s. Of the three I listed earlier, these look the best to me. B&Ws have that yellow cone. The Focals, at least on paper, don't go low enough on the bass.

Sounds good!
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post #10 of 26 Old 11-23-2009, 04:24 PM
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Quote:
Originally Posted by cdepaola View Post

You should be fine with the RC-10's, they also come with port plugs for situations like yours. Their use does not adversely affect their sound.

Be aware that plugging the port changes the tunning of the box, the speakers won't go as low with the port plugged but it will tighten up the bass a little, they're probably added for personal preference. But it will most definately change the sound of the lower frequencies.

There are subs on the market that do this as well, some with multi-ports, the more ports you plug the subs low end goes higher but tigher.
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post #11 of 26 Old 11-23-2009, 05:59 PM
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Quote:
Originally Posted by cdy2179 View Post

Be aware that plugging the port changes the tunning of the box, the speakers won't go as low with the port plugged but it will tighten up the bass a little, they're probably added for personal preference. But it will most definately change the sound of the lower frequencies.

The the plug does not let any air through at all, then it will also cause a rise in the bass response somewhere above the port tuning.

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post #12 of 26 Old 11-23-2009, 06:21 PM
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Quote:
Originally Posted by cschang View Post

The the plug does not let any air through at all, then it will also cause a rise in the bass response somewhere above the port tuning.

Exactly, the box becomes a sealed enclosure.
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post #13 of 26 Old 11-23-2009, 06:36 PM
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The slug of air in a tuned vent is just that - a slug of air oscillating at great relative velocity and very low frequency. It's not directional and it isn't particularly sensitive to moderate proximity, at least not as sensitive as the speaker itself would be at similar distances to boundaries.

Give the port mouth a few diameters or more from the nearest large boundary. Since the expansion around it at that distance is so radically greater in area and volume (here the air mass effectively turns into a much lower velocity donut of air fanning out radially all around the port mouth) you won't adversely rearrange the bass tuning. You'll have more issue with the entire speaker being four inches from the wall than the air in the vent tube.

On the other hand, vents emit midrange energy across a very narrow band, so be careful to keep a rear-ported design far enough away from reflective surfaces to avoid bouncing that energy back into the front field.

As for stuffing the port, bass reflex drivers naturally tend to have Q's suitable for bass reflex systems (roughly under 0.4) and if you seal their vented alignments typically the driver will see a much larger air volume than it "wants". The end result is that our sealed-off bass reflex box probably turns into an overdamped system, and rolls off very prematurely. You'll get less bass under the previously usable curve both in terms of extension and sensitivity, plus an unfortunate lowering of maximum bass output owing to no restoring force imparted by the previously tuned vent.

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post #14 of 26 Old 11-23-2009, 07:03 PM
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Quote:
Originally Posted by cdy2179 View Post

Exactly, the box becomes a sealed enclosure.

Right, but not tuned/sized properly.

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post #15 of 26 Old 11-23-2009, 08:02 PM
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Quote:
Originally Posted by cschang View Post

Right, but not tuned/sized properly.

exactly! unless they sized the enclosure to work both ways, which is very easy to do.
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post #16 of 26 Old 11-23-2009, 08:58 PM
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I just got my RC-10's for my room today and they have about 5 inches of clearance from the walls and they sound great. I think they are just to small for it the effect the sound noticeably. Now my Klipsch RF-7's with two 10's in each speaker, thats a different story, but with one 5 1/4, it sounds good. And they sound realllllly good, very happy with the purchase, and their sexy
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post #17 of 26 Old 11-23-2009, 11:36 PM - Thread Starter
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I re measured and found I can get up to six inches of space between the back of the speaker and the wall. Not a problem.

Sounds good!
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post #18 of 26 Old 11-24-2009, 06:39 AM
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If you plan on running them "small" and crossed @ 80Hz or higher, a few inches will be adequate in my experience




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post #19 of 26 Old 11-24-2009, 10:47 AM - Thread Starter
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Would some kind of felt or fabric behind the speaker help any? To kind of "soften" the wall?

Sounds good!
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post #20 of 26 Old 11-24-2009, 11:35 AM
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go listen to the front ported models you listed. The B&Ws are pretty good (not heard the others). Front porting is a better solution that playing games in back all things being equal. You will likely note a difference in the base if you have too little room but that does not mean that you will hate it. You may actually like it better? Listen to all your options but a front port (or sealed) is a better choice in general for 4" of space if all else ifs equal.
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post #21 of 26 Old 11-24-2009, 01:15 PM - Thread Starter
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I just wish more manufacturers made sealed enclosures. It would make life much more simple.
I do remember something that involved front ports and the woofer canceling out each other to some extent. Picture the the driver moving out and the air next to it being sucked in. I was going t ostart a thread on that alone but, it is probably something too minor to make a difference.

Sounds good!
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post #22 of 26 Old 11-24-2009, 01:23 PM
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Quote:
Originally Posted by karlsaudio View Post

Would some kind of felt or fabric behind the speaker help any? To kind of "soften" the wall?

You can get acoustic panels or just get the acoustic panel material and wrap it you're self, I built my panels for around $18 a panel.

http://www.atsacoustics.com/cat--Fib...ards--106.html
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post #23 of 26 Old 11-24-2009, 01:32 PM - Thread Starter
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When I get my speakers, I will let you all know what happens. Thanks all!

Sounds good!
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post #24 of 26 Old 11-24-2009, 05:44 PM
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Quote:
Originally Posted by karlsaudio View Post

I will look into that. The local Energy dealer has four left! Other than that, I think I am going to listen to the Monitor BR2s. Of the three I listed earlier, these look the best to me. B&Ws have that yellow cone. The Focals, at least on paper, don't go low enough on the bass.

What is wrong with the yellow cone? Pretty big difference between Monitor's Bronze & Silver line IMO - the silver series competes against B&W's 600 series btw.

Have fun - the RS line is half price right now...

Ron
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post #25 of 26 Old 11-24-2009, 10:26 PM - Thread Starter
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I am heading to the B&W dealer tomorrow. They also carry Monitor. I will let you all know what I think. I guess the yellow cone won't bother me that much if the sound is right.

Sounds good!
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post #26 of 26 Old 01-22-2014, 06:52 AM
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4" is a bit tight, can you get 8"?     It won't be a 'disaster' for home theater but will be less than idea for two channel listening.

 

Another thought is to experiment with dampening foam on the back wall to reduce reflections/cancellations.

 

The issue is that the rear firing wave might add to the bass or cancel it depending on the resulting phase.  You can eliminate the randomness by experimenting with foam and also slight angles.

 

Are you well away from side walls?

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