Sub placement decided by frequency wavelength

[ThA tRiXtA]

<font color='#000000'>Well since I am not getting any responses in the speaker placement forum I'll try this speaker forum!

Reading the speaker pleacement guide on the audioholics website and taking note of the subwoofer placement article (as listed below) I have a question. Seeing my diagram below as well, when they mention that a sub with a hi frequency cut off of 80 hZ should be placed 1 foot 9 inches from the wall, do they mean from both walls in the corner or just from the back wall where my sub ports fires in that direction? The driver faces out towards the couch, same as the tv, and the port fires towards the rear wall.

D: Subwoofer placement and number of subwoofers

This can be the most difficult speaker to place. There are a variety of reasons for this, but in general, bass frequencies are most affected by their placement in the room. First let's examine placement with one subwoofer. This is actually the most difficult. Subwoofers can either be placed in corners, where they have the benefit of sound reinforcement from adjacent walls. This means less amplification is required and less distortion on the sound the woofer is producing. However, this comes at a price. While many subscribe to the thought that bass is omni directional, a woofer placed in one corner can usually be detected as being in THAT corner. Omni-directional does not necessarily mean it can not be detected as a sound source. The other expense is that corner placement excites room modes and generally delivers less than a flat frequency response.

When we calculate room response curves theoretically, we do it to find out how flat a response we can achieve. This usually yields a subwoofer placement that is slightly off center in the room and fairly far out into the room. This gives us a good idea of how flat we are able to achieve, but inevitably this is not the best overall sound for the subwoofer. It is for this reason that we do not even specify subwoofer placement, rather we give a location where we found the flattest frequency response.

There really are two potential locations, near center and near the rear wall (within 1/8 of a wavelength of highest frequency the subwoofer is set to produce*), or in a corner and within 1/8 of a wavelength of that corner. We recommend that you try both of these locations. If you can not distinctly detect the subwoofer when it is in the corner, then this is a good place for it. Otherwise, move it to the center.

If you have two subwoofers, corner placement behind the main speakers is almost always the best placement. These should be within 1/8 of a wavelength to the corner they are placed in. If you can afford a second matching subwoofer, this is generally preferred to a single more expensive subwoofer.

Getting the subwoofer in phase can be a little tricky for a novice. The best way is to use a test tone at the crossover frequency of the subwoofer. Play this tone and adjust the phase so that the tone is the loudest at the listening position. Using an SPL meter can be a great help here. When it is at the loudest the subwoofer is in phase.

* Note: 1/8 of a wavelength (in feet) = 1130/wavelength * 1/8

Thus for a 80 Hz wavelength = 1 foot 9 inches

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[Sounds Simple]

<font color='#000000'>A somewhat simple approach to help make sub placement decisions is to place the sub at the listening position and then walk around the room to find where it sounds best. Move the sub to this location and then start your tweaking for best-possible bass performance.

Bob</font>

 

[ThA tRiXtA]

<font color='#000000'>thanks man

no comment on the positioning from either wall though? does it only have to be away from the wall where the driver and port is, or even on the side where the box is?</font>

 

[Sounds Simple]

<font color='#000000'>The closer you get to walls (allowing breathing room, of course), the greater bass reinforcement is; that is why many consider corner placement optimal (two walls). That said, I think the best thing to do is too find a suitable spot to start with and start tweaking by moving the sub around that location including trying different angles. The idea is to produce a well-blended extended bass that integrates well with your speakers and without fairly specialized equipment (why do you think that those high-end custom installers charge so much? they have expensive toys to buy) you need to just sort of play with it.

Bob</font>

 

[ThA tRiXtA]

<font color='#000000'>great thanks</font>

 

[annunaki]

<font color='#000000'>If well blended response is the goal, a corner is usually not the place for a sub.  Corner placement tends to amplify peaks that already exist (due to room dimensions). Corner placement also tends to work for people trying to get the most output from a woofer. Not for the person looking for well integrated smooth response.Check out http://www.guidetohometheater.com  
Go to past issues and check out Jul./Aug. 2003 - Jan 2004 in the &quot;Home Theater Architect&quot; section. The Jul./Aug. 2003 issue has a great formula that works for any room to find out what frequencies your peaks occur, just plug in your dimensions. They did an excellent piece on subwoofer placement and what causes poor response in rooms.
The best way to balance out peaky response in a room is to place the woofer in a null to reduce the peaks to acheive a smoother response. Also, the lower you can keep the croosover on the sub (50-60hz seem to be quite good) the easier it is to integrate into the system, and its position to &quot;disappear&quot;. However, this only works if you have speakers capable of playing that low at a decent volume level.</font>

 

[ThA tRiXtA]

<font color='#000000'>wow thats a great site thanks man

cheers</font>

 

[bob griffiths]

<font color='#000000'>this is a good link to simple to understand sub placement

http://www.smr-home-theatre.org/Sub-woo....on.html</font>

 

[ThA tRiXtA]

<font color='#000000'>cool! good link</font>

 

[RLA]

<font color='#000000'>Hi
Standing waves are created and are a direct result from room dimensions
Mode overlap &nbsp;is a result of the ratio of the room dimensions &nbsp;
and the impact of room modes will be determined by how dense the wall are &nbsp;You have three types of wave modes
Axial, Tangential and Oblique &nbsp;Axial are the most important and occur &nbsp;between two opposite walls Tangential occur between two pairs of walls Oblique &nbsp;occur between all room surfaces
When the frequency increases the room modes smooth out and become more evenly distributed &nbsp;135Hz is generally
the frequency where the FS becomes diffusive. Room Modes
can't be eliminated so you have to work around them to try and minimize standing waves &nbsp;There are a few ways to do this
#1 Move Listening position #2 Move Subwoofer Location
#3 Use Absorption #4 Active EQ
Subwoofer placement is the easiest solution &nbsp;as a general rule placing the subwoofer 1/3 in or along a wall will give you the smoothest response these are generally the Low relative Pressure locations in a rectangular room another consideration is to find out where the subwoofer drives the positive and the negative areas of the wave between your listening position and the subwoofer place the subwoofer in-between the positive (hump) location of the wave and the negative (dip) location and this will reduce resonance &nbsp;Or get two subwoofers and place one at the positive location of the wave and one at the negative location and drive the positive and negative locations of the wave equally. Moving your seated listening position is another way to minimize the modes placing the seated location between the positive location of the wave and the negative location of the wave will reduce resonace.Absortion is another way to reduce standing waves however you would need very thick absorptive material &nbsp;absorption at 90Hz would take approximately 4 feet thick absorptive material. Active Equalization is &nbsp;another way to reduce standing waves but formulas and room calculations are complex &nbsp;and you may end up minimizing standing waves at the expense of creating other problems in the room This should not be done unless you are qualified to do so
Hope this helps
RLA</font>

 

[MarkOcena]

<font color='#000000'>RLA,
This probably seems like like a dumb question, but I'm curious about how these standing waves are formed in home listening rooms. &nbsp;I've read that strings in musical instruments are the host of standing waves, and these vibrations give us the sound/music. &nbsp;In these cases, the string is a medium for the standing wave. &nbsp;Can standing waves exist without a physical medium like a string?

Thanks,
Mark</font>

 

[ThA tRiXtA]

<font color='#000000'>Hi Mark

I believe when he mentions the term &quot;standing waves&quot; it is referring to a wavelength of a frequency that is reflected over and over and is not being absorbed by a medium to make the wave dissipate.

This then causes issues of that particular wave conflicting with other waves and frequencies.

Even further, when one has a certain frequency of wavelength that won't die down easily, that frequency tends to become overbearing and can cause large humps in the response of the room

The same goes for certaim room dimensions or speaker placement can nullify or reduce certain frequencies, so this is where you get a dip or void in your desired linear response.

(PS: this is a rough and amateur take on the situation. Perhaps some one with more knowledge could take a better approach to this question.)</font>

 

[ThA tRiXtA]

<font color='#000000'>One other thing - I believe the reason for why these standing waves are such an issue in home listening rooms is that because the rooms are so small, and the sound waves are so long in size that they don't have ample space to dissipate naturally...

Yes / no anyone?</font>