Room Acoustics, Speaker Placement

[phillihp23]

How close or far should the back of your speakers be to the wall? Same question for ported subwoofers? Also,
What are opinions on acoustic panels behind speakers and if so how close / far should the panels be from the back of the speaker/sub?
I am gradually working on improving my room acoustics. I will be acquiring more panels this weekend and looking to tweak things the best I can.

 

[ddude003]

You might start off with looking into this information about speaker placement...

Room Setup Calculators

Generally speaking, speakers need to be _in_ the room not against the walls... Acoustic absorber and diffuser panels are usually against or near the walls and ceiling... For bass absorbers corners are most important...

 

[phillihp23]

You might start off with looking into this information about speaker placement...

Room Setup Calculators

This is in inches. That don’t work....

 

[Adhoc]

I general: The closer the main speaker's baffle is to the wall behind them, the higher up in frequency you will get the SBIR null from the frontwall reflection. This is good as it takes less thickness for a resistive absorber to absorb that reflection resulting in the null. Try placing the sub closer than 1/4 wave length of the crossover frequency, from the main speaker, that way the main speaker and sub will play more in phase. An air gap to the wall about the same as the diameter of the port should be enough "breathing space". Avoid having the same distance from woofer / midbass to the closest sidewall, wall behind, floor and ceiling. If same distance, the deeper the null at a certain frequency. Nulls can't EQ:ed, placement versus reflecting surfaces rules.

Some good advices from an acoustician (Jens Eklund) at another forum. Advices are for a control room, but just about all of it is applicable also for a dedicated listening room. Take special notice of actual suitable thickness of resistive absorbers. Post #11 and forward, the other llinks in the post from him are good stuff to read as well: https://www.gearslutz.com/board/stu...-s-additional-bass-trapping.html#post14291770

 

[JStewart]

Avoid having the same distance from woofer / midbass to the closest sidewall, wall behind, floor and ceiling.

Same for seating distance to rear wall.
This is all in an effort to not have the same SBIR induced cancellations at the same frequencies. For an explanation of SBIR see http://arqen.com/acoustics-101/speaker-placement-boundary-interference/

That said, I have always agreed with @AudiocRaver ’s advice to place speakers for best sound stage and imaging first. This always made sense to me because you can use eq or panels to address response issues to varying degrees, but outside of placement what might affect SS&I?

 

[MeJ]

How close or far should the back of your speakers be to the wall? Same question for ported subwoofers? Also,
What are opinions on acoustic panels behind speakers and if so how close / far should the panels be from the back of the speaker/sub?
I am gradually working on improving my room acoustics. I will be acquiring more panels this weekend and looking to tweak things the best I can.

You haven't told us about the speakers - or the dimensions of your room. So the answer is "it all depends". It always is!

Assuming normal style hifi speakers designed to operate into half-space or thereabouts, good positions are very close to the wall or some way away.

If they are small, close.

Look at the section titled "Wall Reflections and Cancellations" in...

Although it addresses studio monitors, audio physics is the same for all speakers and listeners!

It also discusses sub-woofers.

Myself, I much prefer sealed subs in a small room - though they they need a lot of power. It's harder for reflex systems to drive a pressure wave below the lowest eigentone.

But if you have ported sub-woofers, give them help by approaching the corners. Two or more is best, but if you have one then you have one! And they are fine in a big room (>20m /70ft)

An old trick for sub-woofer placement is to put it in the listening position and move your head around to see where there is smooth bas without peaks - this is easier than doing it the other way round

The latest REW has a much-improved room simulator which with my measurements very accurately predicts the measured room response as per speaker positioning, so this is another tool to use.

Apart from that, all predictions for good outcomes can fail in the face of practical reality, but usually theory and simulation predictions can give a good starting point or two...

Re panels. it depends on the room. Where I am right now, adding panels behind the speakers (small studio monitors) made the upper mid response give a distinct dip - so they are gone. In another room I have, they convert it from unlistenable to OK.

Panels can be very useful placed where in a mirror on the wall or ceiling, you would see your speaker cabinets. Also can kill any flutter echo.

YM *will* V.

Measure at the listening position using REW or similar and a calibrated mic (But REW is really very good).

MeJ

 

[MeJ]

It would not let me post the URL - said I was posting spam. Good quality filters there! The URL is www dot genelec dot com slash monitor-placement

Sigh.

 

[MeJ]

...and Earl Geddes has good arguments for multiple sub-woofer placements, which I have adopted in my studio (5 subs)...

mehlau dot net slash audio slash multisub_geddes

and

gedlee dot com slash Papers

Good grief? Spam? Sigh.

check multiple subs.

Works For Me.

 

[DanDan]

Speakers are normally towed in enough to allow free passage for a rear port even when one edge is kissing the FW. There is a widespread believe that Speakers need to be distant from the Front Wall. It had some validity back in the day of large speakers. Due to LF room gain, things could easily become boomy in an untreated room. So SBIR punching a hole in the excess bass could be welcome. Indeed the relief from that tilted tonality is often misinterpreted as 'better imaging' 'soundstage' and so on. Apart from the also popular 'Bookshelf' speakers which led to the NS10, these mores were ubiquitous, to the extent that BBC standard monitori was a self standing Spendor BC1 on a stand. Their rooms were probably mostly wider than the typical domestic. In our typical rooms here, there are additional nulls at half height and half width at frequencies close to the typical FW SBIR null.
So.... theoretically, and when done well, flush mount obviously wins hands down. Including imaging and soundstage, but let's stick to LF here. Assuming that most people can't or don't want to impose a 2.5M or more distance between speaker and FW, many of us recommend as close as possible as the next best thing. With modern small efficient speakers, and the increased amount of LF which Digital has promoted, excess LF is unlikely. If it does occur it is easily mitigated by blocking ports, or by using onboard speaker controls, or Dirac Live, Sonarworks, etc.
There is a newer ubiquitous belief that an absorptive trap behind the speaker will eliminate SBIR. Maybe a test I posted decades ago on NorthSlutz encouraged that. it showed a single MiniTrap pretty much nuking a null.
However, the test was illusory. I 'idealised' by placing the Speaker and Mic on the carpeted floor. PZM style.
In the real world, those pesky side and ceiling and floor SBIRs coalesce with the FW ones and the Modes.
More often than not testing will show no improvement or as below, deterioration, when inserting a single small trap behind a speaker. I can only suggest an object of 0.6M x 1.2M may not be significant to wavelengths of 3-4M.

Ultimately, Testing Trumps Theory. Optimising locations is the single most powerful, and free, treatment technqiue at hand, try it. Touching and kissing can be beneficial.
A

 

[phillihp23]

Thanks DanDan...some very helpful guidance and measurements to support it.

 

[DanDan]

Mod Hat on for the first time. I am trying to increase/stimulate activity here. So welcome new members and thank you all for posting irrespective of what I am about to say. Linking to other Fora, publications, calculators, can be an 'Echo Chamber', confirmation bias. e.g. Some of the links posted seem to add to or support the two substantial myths elucidated in my above post. That's a dead duck as there is no debate between a link and a live post. I would rather see new, here, now, rather than sustain historic or overturned rote assumptions. That is the stuff of life here. Fresh individuaisedl posting with salient content, test data, images, by all means referencing certain and conclusive research.

 

[ddude003]

No "echo chamber" here... The OP posted a general question without much information to go on like room size, shape or current acoustic treatments... I responded with some "general" information and a link to a place that could provide more information about speaker placement and a "handy" calculator...

Why do the various speaker manufactures "suggest" placing their speakers in various ways which, in my experience, "mostly" appear to be away from the walls? I am guessing that most of them have experience and insight into their own product designs and where, generally speaking, they might sound the best... Both of the OPs speaker Polk RTi A9 Front, Polk RTi A7 Front Wide manuals show a diagram that to me, shows the placement somewhat away from the front wall...

Also consider that there are many various speaker and subwoofer designs that are not your "standard" speaker in a box design... Think electrostatic hybrid like Martin Logans, Magneplanars, Open Baffles, Line Arrays, Horns etc.. Should we consider speaker enclosure geometry? Rectangle vs curvature... And not all speaker designs have all the drivers firing forward... How well do you think these other designs sound against the wall?

I do agree with you "Ultimately, Testing Trumps Theory. Optimising locations is the single most powerful, and free, treatment technqiue at hand, try it."... Because not every speaker, system, room or ear/brain is the same...

Cordially...

 

[DanDan]

"Generally speaking, speakers need to be _in_ the room not against the walls..."
I used to accept that Myth until I became an Acoustician and found the tested reality to be generally the opposite. Here is a pair of Celestion Ditton 66 kissing the Front Wall Blue, vs about 1M distant Red.

"No "echo chamber" here... The OP posted a general question without much information to go on like room size, shape or current acoustic treatments... I responded with some "general" information and a link to a place that could provide more information about speaker placement and a "handy" calculator..."

I am afraid this is exactly what I was talking about. Cardas have their own unique and aberrent views on optimum placement and terminology. e.g. Their Front Wall is probably our back wall.

Some Calculators predict an identical null when the woofer centre is equidistant to the Front and Side Walls.
But given a central listening position, there would be a different length of path from woofer to ear and thus a different nulling frequency at the ear.
So that prediction, that Calculator is incorrect.
Unless of course one considers the null to occur at the speaker rather than the listener.

"Why do other manufacturers state otherwise?" Ask them perhaps or take a poll of how many say one thing or the opposite. I am not really up for first or second guessing or he said she said here.
Most of these recommendations are simply wrong acoustically, both theoretically and as measured by those of us that do this professionally.
However the incorrect or vague recommendations do seem to appear more in the Hi Fi Market rather than the Pro.

"Why do the various speaker manufactures "suggest" placing their speakers in various ways which, in my experience, "mostly" appear to be away from the walls? I am guessing that most of them have experience and insight into their own product designs and where, generally speaking, they might sound the best... Both of the OPs speaker Polk RTi A9 Front, Polk RTi A7 Front Wide manuals show a diagram that to me, shows the placement somewhat away from the front wall..."
Who knows? Perhaps they are afraid the Hi Fi world would be upset to read a decades old more was and is nonsense. Are you again suggesting a Poll of sources of myths? Does every manufacturer get an equal say irrespective of whether they present their reasons or not? Does the majority win irrespective of acoustic reality?

"Also consider that there are many various speaker and subwoofer designs that are not your "standard" speaker in a box design... Think electrostatic hybrid like Martin Logans, Magneplanars, Open Baffles, Line Arrays, Horns etc.. And not all Speaker designs have all the drivers firing forward... How well do you think these other designs sound against the wall?"

I think anyone using a Dipole would be well aware that none of the above applies to them at LF. Line Arrays tend to be HF only, horns usually ditto, why do you mention them? I think anyone using Bass Horn or Cardioid LF would also be well aware of the benefits of the diminished outputs to the rear and sides.
In the spirit of new and adding, do you have recommendations of why Dipole and indeed where to place them?

 

[MeJ]

DanDan is right on: unless the speakers can be well away from the wall, close is best, as Genelec describe rather clearly. Here's some measurements in the different conditions in a small 4x4x2.5m (about) room, no subs:

Note that first, the predicted LF response from the room model by REW very closely matches the measured response below 200Hz. Changing this (much) requires a builder And an architect, probably.

Then see how adding absorbent panel behind the LS makes the response - in THIS case not generally - worse.

With speaker only 30cm from the wall there's (in this case) a noticeable - and audible dip - just above 10K, as well as an enhanced bump @ ~160Hz

Final adjustment with midrange set down 2dB is the green line. No EQ except that built-in to the monitors.

It's always best to measure, but the principles of acoustics are a guide to where to start

Also in this room there's no eigentone below 44 Hz or so, so any sub working below that will be working in semi-pressure mode: semi, because rooms unlike cars/autos, are pretty leaky. Still, sealed subs will help... I think. Installing them tomorrow.

MeJ

 

[phillihp23]

My room is about 14.5’ x 15.5’.
Recently I was reading a rather lengthy thread on acoustics, both panels and speaker placement. It appeared as I read through the lengthy posts there were strong advocates for speakers close to the wall or a decent distance from the wall. Post sides, some acoustic experts, appeared to back up there statements. Which leads me too believe that this is still a highly debated matter. I also agree that based on varying environment some sort of reading in that environment is really the only way too see what is happening in that environment. Like wise when it comes too acoustic panels there seems to be differing opinions. Some say the whole front wall should be treated. Others say in most home theaters there isn’t a very confident way to determine if the front wall treated makes a difference, it’s hard to record the difference on equipment in such a setting. A lot of us have the front wall covered with a screen so it’s difficult to treat anyway. Some treat 90-100% of a room, some treat 50%.

So as a generalist, which I am, and not as any sort of expert the following is what I have concluded best for myself. I don’t really have the space, and acoustically to my ears the speakers sound fine close too the front wall. I will treat the bottom 2 feet of the wall on both sides with 5” 244 panels 1” air behind, the 2-4 feet level of the wall on both sides I will treat with 2” thick panels 4” air behind for the first four feet, then 4” thick panels 2” air behind for the rest of the length of the side wall going toward the back of the room. On the ceiling I will add two panels going the width of the ceiling for first reflection point. Partially because these are the panels I have acquired for a reasonable price.
Already installed are tri-traps floor too ceiling in the front corners, 244 on the ceiling running center screen back too MLP ( the ceiling peaks in the middle), tri traps back corners floor halfway too ceiling.

The surface of the panels on the walls will be even to appearance.

This should treat the first 4 feet of the walls and the ceiling for reflections. I also have a handful of 24x24x2 panels that I can place if needed in higher areas if I see reflections. Find attached my expert rendering

 

[Adhoc]

MeJ; (If I don't misunderstand what you wrote) the broad dip in response you get at around 10 kHz cannot be SBIR or because you put an absorber behind your frontwall speaker. It is something else. Why? A 10 kHz tone has a wavelength of 3,4 cm / 1 3/8", your speaker baffle is a lot wider than that I presume, so the tweeter can be seen as installed "inwall", just like the picture from Genelec's manual which DanDan posted above in #11.

Phillihp23, It would be good to install your absorbers in pairs on each side wall. 1 pair at a time with measurements in between so you know what is happening due to the addition. -As they are rather thin they will be efficient in absorbing from upper bass / lower midrange to high frequencies but not very efficient for low bass. Keep an eye on the Spectrogram i REW and RT, how this range changes. In general; you wish to keep the energy in midrange - high frequencies intact and not absorbed. Too much of absorbtion there and the rooom turns out sounding dead while at the same time being boomy in the bass.

The attacehment can be used to figure out in advance SBIR due to different path lengths for reflections compared to the direct sound. 1/4 and 3/4-wavelength for the wall behind the speaker, 1/2 wavelength for side walls, floor, ceiling and wall behind the sofa.

 

[DanDan]

Nice one Adhoc. We have seen a few examples of traps between the speaker and Front Wall doing nothing or worse.
Previously I have noted that 0.6M x1.2M is not very big as seen by LF Waves.
Today I have also noticed that three different speakers here place the Woofer 28-30cm from the Front Wall.
I wonder if that distant also overwhelms any contribution from a typical 10cm trap?

 

[Adhoc]

From the chart; if the speaker baffle is 30 cm / 1' from a solid front wall one can expect the bottom of the SBIR-null to be at around 280 Hz. For a frequency where 30 cm is between 1/4 to 1/6 of its wave length one can also see that as "part of" the null and less bas at LP because of destructive SBIR. For frequencies where 30 cm is about 1/6 wave length it goes towards a +/- 0 change in the frequency curve. As the distance 30 cm becomes less than about 1/6 wave length, the reflection comes more and more in phase with the direct sound wave = room gain in the bass. -The frequency dips because of SBIR from front wall, floor and ceiling can be quite wide in range.

So, as I see it: If the speaker is "far away" from the side wall and 30 cm from the front wall a 0,6 x 1,2 m absorber is not large, -as the wave length of 280 Hz is about 1,2 m = larger than the absorber width of 0,6 m. (And even less sufficient for lower frequecies where the null starts to form)

 

[DanDan]

Indeed