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Bass trap placement - high or low? Does it matter?

52K views 109 replies 19 participants last post by  phazewolf 
#1 ·
I got a set of 4 Acoustimac 48x24x4" corner traps, and I'm wondering where to put them. Should they go up near the ceiling or down by the floor or in the middle? Or does it make any difference? I don't want them right on the ground because I don't want my cats mistaking them for scratching posts, but I don't have to put them right up against the ceiling to keep them out of claw range.
 
#45 ·
You're right, my mistake.

First rekman wrote about reflections then you also wrote about reflections, cancellations and using absorbers against the reflections.

Point given.

Nevertheless the other points are still valid.

Are there any factual topics or do you prefer to write about me and what I wrote wrong?

Cheers
Babak
 
#46 ·
Babak, I'm ecstatic to see someone here paying attention.:T
You're right on the money.
Perhaps Sanjay can explain how a 4" thick pillow surgically "traps" 20-50+ foot wavelengths, much less having no effect on spatial perception and timbre? I don't see how that's possible. So your info is completely relevant.
Anyone here have measured effects of 4" pillows vs 20-50' waves? From a physics standpoint, I'd be fascinated to see the results.
And yes, it's much more difficult (if not impossible) to perceive dips (cancellations) of pressure if the Q is high. Despite what your eyes "see" your omni mic measuring as pressure.

cheers
 
#51 ·
Perhaps Sanjay can explain how a 4" thick pillow surgically "traps" 20-50+ foot wavelengths, much less having no effect on spatial perception and timbre? I don't see how that's possible.
Where did I tell liteglow to use 4" thick pillows for his dip between 20-50 Hz? I explained why bass traps are placed at boundries (or where boundries meet). For his low frequency dip, I asked if he could move his sub.
 
#48 ·
I recommend products by Vicoustic.

One can use the Wave Wood panels over the room corners. They then work down to about 100 to 125 Hz.

Then there are the Super Bass Extreme elements for getren frequencies below that.

And there are the Vari Bass Pro elements that can be tuned to specific frequencies to address room modes.
 
#55 ·
If truly bass traps, then best practice is 1st location placement, at the tri-corners near the ceiling and at the tri-corners near the floor. everyone needs bass traps and plenty of them, for proper mode reduction. Bass modes pile up in the corners. Their are some great room mode calculators out there that can graphically indicate the modes in your room based on dimensions and give you relative placement of the traps and the required trapping frequencies.
Ultimately, it would depend on the type of trap construction as to placement. then measure measure measure.
Bottom line is, no matter where you put them, it will help the room. The question is how many do you have room for, and are you willing to incur the associated cost of treating the room. It is my opinion, that it is one the best investments you can make for your theater or listening room.
JMO.
 
#66 ·
My 4 foot high Bass Traps sit vertically on the floor behind the speakers up against the corner. I have Corner Traps mounted in all 4 ceiling corners. Is this the optimal placement? I dunno, but logistically wise, it was the only place I could put them and it definitely made a difference. If you don't have a dedicated room for your audio setup, you make do as best you can.
 
#68 ·
My 4 foot high Bass Traps sit vertically on the floor behind the speakers up against the corner. I have Corner Traps mounted in all 4 ceiling corners. Is this the optimal placement?
"Optimal" for what purpose? What are they "trapping" (besides space) in those corners?

I dunno, but logistically wise, it was the only place I could put them and it definitely made a difference.
I'm sure they did make a difference. But did they solve the specific set of perceptual issues you had prior to placing them there? Did any others subsequently arise?

If you don't have a dedicated room for your audio setup, you make do as best you can.
I'd suspect most don't....and yes, always do the best you can.

cheers
 
#71 ·
So, let's see if I can get the posting thing right...

It seems as if the same questions is being asked without a direct answer and that is "where should I place my bass trap" so I will jump in with both feet with a direct answer to that basic question - while most people want to place a "bass trap" in the corner of a room where the "cumulative" effect seems most noticeable or against a boundary when in actuality it is the least effective placement for a trap. The corner has the maximum pressure but low particle velocity therefore corner traps are less effective. The most effective place for placement of a bass trap is when the trap is placed a quarter wave length from the nearest boundary. For 100hz that would mean approximately 1m from the boundary.

So I will duck back in the fox hole now....

Gordo
 
#73 ·
AJ,
I agree with your ascertain that one of the best ways to deal with small room modes is through multiple subwoofers and proper placement throughout the room. There have been numerous white papers and such written about this topic due to the problem that room modes cause in a small room and the difficulty in absorption due to the size of the wave length and the limitations of room size. And unfortunately, this problem probably causes more impact to the listening environment then others and it is the most difficult to solve.

Gordo
 
#74 ·
Bass traps can do one thing a extra sub can't and that is help with the decay times in the bass region. That said I think in the case of this room there maybe something else going on think about it.

If he moved the sub all over the room and still has the same issue at the same frequencies then it could be several issues combining to cause the dip. Not using that line of thought maybe just maybe a trap could help more then a sub.

I am not a pro at this so take what I say with a grain of salt but this issue just screams no quick fix sense I feel it is several issues at once.

My room had a 30db peak at 57hz that could not find a way to fix with moving stuff around. When I started adding traps it helped it a lot but then show other issues that were being masked. The bass traps took care of son of the peak and moving stuff fix a lot of it too. But I ended up with a few large deep nulls that when I remove the traps are not there.

Have you thought about the mains and how they interact with the sub? Could be the two are causing the null. Phase issues are not fun.
 
#76 ·
Yes I do and the width is 23.8 so from about 52 to 58 or so was a huge peak. Traps and 2 subs both helped a lot. Plus I ended up moving where I sat by 6 inches which made a world of difference too.

There now is a huge dip at if I recall 107hz that was not there before traps. As of now I have no idea where the room is at as I now own a new pair of speakers that are placed different and respond totally different then my old pair.
 
#78 ·
Well this room is the only one I can use. They are on the 24' wall but only half that wall is usable 12x20 is kitchen and the other half is liven room. So basically I sit on one half of the room. The right of me us kitchen and the left wall is a door wall and fireplace.

Now to make it even worse and yes it can be worse the half of the room I am in is not drywalled it has the cheep fake wood paneling that was all the rage in 1970 loosely nailed to the 2x4 studs the kitchen is plaster. Also half the room on the right side of me has kitchen cabinets both top and bottom. Oh the kitchen is over a basement the half I am in is a cement slab.

Fun times for sure
 
#79 ·
Tough situation for sure. For the moment it's probably best to do what you did by moving your seating out of the null. Down the road, if you can put one of your speakers at the location of the 107Hz null, you might be able to reduce the mode that is causing it.
 
#80 ·
The null goes away if the speakers are flat against the wall at least with the old ones. The new Legacy focus se who knows what is going on as I have not run REW as of yet.

When I have time I will and slide them around to find the best compromise and then place what bass traps I own back into the room and find the best locations for them. Really I only have 2 floor for ceiling corners but lots of wall to ceiling that I can use. That will allow 3 2x4 traps on the front and rear wall ceiling and I can use the the floor also on the back wall. The left wall also has 8 feet along the ceiling I can use.

So there is a fairly good amount of area I can use for trapping. Once that is done I can play with sub locations once again.
 
#82 ·
Not disagreeing with anything being said here - i kinda think that this problem is being over thought a little....

He already stated that the null went away when he placed the old speakers against the wall.... hence he moved the source to change the wavelength location in the small room, hence room mode.......

If when the new speakers are looked at and the problem comes back, location could then be checked and then the crossover points between the subs and the mains (and phase).

Knowing the problem is half the battle.

Gordo
 
#86 ·
For the measurements I used REW with a calibrated mic. I don't have any of the files anymore they were not recovered when the hard drive crashed so I am only going by my memory which is poor a lot of times.

The hole at 107hz was about 35db deep and if I recall went down to 103 and upto 111hz but I can't be sure.

I have no issue using a eq to fix a peak I just prefer moving everything I can first to make things as smooth as I can first.
 
#88 ·
Hi

For the measurements I used REW with a calibrated mic. I don't have any of the files anymore they were not recovered when the hard drive crashed so I am only going by my memory which is poor a lot of times.

The hole at 107hz was about 35db deep and if I recall went down to 103 and upto 111hz but I can't be sure.
Thanks for the details.
Do you remember which kind of measurement you performed using what kind of signal?
Do you remember the position of the mic in the room, that means in relation to all room boundaries (floor, ceiling, walls)?

Those distances could give a hint, whether the hole was caused by interference of the direct sound with the sound reelected by one of the boundaries.

As written before...
In my opinion one gets a better idea of the room response and room modes by measuring the reverberation times (RT60 or RT30) and a waterfall diagram of the room response curve and it's decay.

Cheers
Babak
 
#89 ·
The mic was at ear height 38" from the ground the location is 8' from the rear wall this had the best sounding bass other locations has large drops in bass and you could hear things missing. From the left wall I am 70"

As I have said the room is split into 2 half's so very limited placement.

When I get time I will measure more but what I knew of of the room was with my old Polk SDA speakers which needed to be placed with in 6 to 12 inches of the front wall to work correctly. The new speakers are placed completely different.

The sweeps were made with REW as I said and it was a normal sweep I can't really recall the rest of the details anymore.
 
#91 ·
How would adding more subs to a room deal with a room that has very slow decay that makes bass muddy? If just adding a few subs to the room was the answer then there would be no need to have traps and yet many of us use them to great effect.

Have you even been in a treated room before?
 
#92 ·
How would adding more subs to a room deal with a room that has very slow decay that makes bass muddy?
It's not just "add subs". It's add subs, apply eq. Fixing the frequency domain, the "mud" goes away.
Can you show me a "trap" that affects time domain and not frequency? You are "fixing" amplitude with absorption, just in a less efficient manner.

If just adding a few subs to the room was the answer...
It is the answer for smooth amplitude (and resulting perception), greater output/headroom, lower distortion and better power efficiency. All actively adjustable, not passively fixed.

...then there would be no need to have traps and yet many of us use them to great effect.
Well, perhaps those that do have different needs than above. To each their own if the methods gets you where you want to be.

Have you even been in a treated room before?
Many, including the iso-wards studiophile types like to hang out in.:)

cheers
 
#94 ·
Trust me I run a pair of subs and it helped to smooth out the bass quite a bit
Two are insufficient for spatially averaged smoothing. Three would be a minimum.

but I also found that adding traps helps the room quite a bit.
In terms of amplitude? Any EQ? Does that mean you didn't try more than 2 subs? What was the cost of the traps? How big are they?

I however did not trap to the point to where the room is dead.
Well, your perception and preferences are what matter most here. It may not be "dead" to you, but I doubt they had no effect on spatial reproduction and spaciousness. That's why I ask people what they hear...and what they prefer.
I know fully well that 99% do not attend symphony's/live acoustic music and may judge by unknown to me references. Their local movie theater? A high end stereo shop? Who knows?
So I ask.:)

cheers
 
#95 ·
Let me put it this way. The room is a audio nightmare, it sounded like a ecco chamber. You could clap your hand and hear the sound bounce around the room.

The floor is a slab of concrete and there is no carpet on it so it reflects everything more of less. The one wall is concrete with fake wood panel on it for show the kitchen wall is plaster and the other walls are wood studs which sit in front of brick outer wall and on the studs there is loosely tacked on 1/8 inch 1970's fake wood panel.

The couch is leather so that does not soak up much and there is a nice door wall that messes up things as well.

As for the panels I have they were grabbed used off of Craig's list for $150 and I got 5 GIK 244 and 1 GIK 242 for that amount so not bad.
 
#107 ·
Let me put it this way. The room is a audio nightmare, it sounded like a ecco chamber. You could clap your hand and hear the sound bounce around the room.

The floor is a slab of concrete and there is no carpet on it so it reflects everything more of less. The one wall is concrete with fake wood panel on it for show the kitchen wall is plaster and the other walls are wood studs which sit in front of brick outer wall and on the studs there is loosely tacked on 1/8 inch 1970's fake wood panel.
That seems atypical of most living rooms I've been in. Bare concrete floor?

The couch is leather so that does not soak up much and there is a nice door wall that messes up things as well.
Well, actually it does, though it will be slightly more reflective of HF. What about the loveseat, chairs, ottomans, rugs, drapes, media storage, wall art, etc, etc, etc??
Or is this a leather couch in bare concrete floor room?

As for the panels I have they were grabbed used off of Craig's list for $150 and I got 5 GIK 244 and 1 GIK 242 for that amount so not bad.
Not bad, but a $150 PE 3rd sub may have yielded as smooth (or smoother), over a wider area (if important), bass. With more output/headroom and lower distortion.
Of course it wouldn't function as an absorber.

Different strokes for different folks.
I did check out the GIK site and they are very reasonably priced. Must have been on sale when you bought though.:)

cheers
 
#97 ·
Name a full range speaker that can do want sub can do in a room when placed where it will image and have good overall balance to the sound that can play down to 20hz or less when also placed on the nulls of a given room and cost under 10k

The best place for the speakers to image may not be on a room null and how often is the best most even location for bass in that spot?

And when I am talking full range I mean tested to be flat to 20hz or less without room gain being added in and not can play down to stuff that some company say but by time it is at 20hz it is down 25db
 
#104 ·
Hi



20 Hz or less, flat?
Where does the specification come from?

The frequency range of musical instruments very rarely reaches down to 20 Hz or even below.

You will know the frequency charts like this one from gearslutz.com:

They have left out the lowest tone of the pipe organ, the subcontra c at about 16 Hz (in German it's called the humbleness pipe).
Only some pieces use that pipe, for example Richard Strauss' "Also Sprach Zarathustra".

Also room responses of concert halls don't include frequencies that low.
The famous Golden Hall of the Vienna Musikverein (if you are watching the New Year's concert of the Vienna Philharmonic Orchestra, you will know it) has a well known mode at 21 Hz. But you don't hear that as strong as a room mode in a home theater.

------------

If you read the papers by Floyd Toole and Sean Olive on loudspeaker evaluation, you might know that they also determined how listeners rated the bass response of loudspeakers.

The found out that there was no real correlation between listener preference and the "flat" bass extension (the usual -3 dB limit).

But they found a correlation of listener preference with the -10 dB point. The lower that was, the better were the ratings.

That means tha speakers don't really need a deep flat bass responde (@ -3dB), but a flat roll-off in order to reach a deep -10 dB point.

------------
There are several speakers with those specifications, also at lower prices than 10k U$.

I'm using Shahinian Obelisk peakers, they reach 28 Hz @ -3dB and have bass roll-off of -6dB/octave.

------------

Regarding the placement.

If one is really serious about good sound reproduction, he won't make any coompromises.
So he would first place the speakers (e.g. onto the nulls) and build up his equilateral stereo-triangle from that.

But I'm aware that in most cases one needs to make compromises in regards of the placement.

------------

I think it is also important to note, that only looking at what frequencies can be resproduced at which levels is not really the correct way to estimate how well the result will be for the listener.

The human ear does not work that way.
It analyses the complete sound patterns, i.e. the enevlope curves consisting of a mixture of many frequencies.
One of the important elements of that envelope are onsets. Those consist of different frequencies rising at the same time.

If one places a subwoofer far away of a speaker, the low frequency onsets arrive at different times than the higher frequency onsets.
That diminishes the onset of the envelope cuve.

Even worse, if one uses one sub that is closer to one speaker and further away from the other.
This results in different envelopes from the left and right signal, making the bass "slow".
So, if using one sub, one should place it symmetrically between the two speakers.


Cheers
Babak
 
#98 ·
Maybe, maybe not. Personally, I don't need to get down to 20 Hz for audio only purposes. Not sure if I need it for HT. Some speakers have plenty of extension to satisfy me in their optimum placement for imaging. Most of the speakers in the last review session we did were fine without a sub IMO. You might want more extension, and a sub is needed for that, but not everyone does.
 
#99 ·
But there is a difference between a speaker and good sub and how deep it can dig. A good speaker can did deep for music we both know that but with home theater the lfe channel can have effects down to 5hz I don't think I want my mains trying to deal with such things.

My friend tried to run a book shelf speaker set to full range with no sub. Played fine at reference volume until a nice loud bomb went off in the movie and popped a driver.
 
#100 ·
No one is denying that there is a difference in what subs can do and what most speakers can do. The point is that many full range speakers CAN be satisfying to many people. The amount of actual signal below 30 hz is minimal actually, and not of great importance to most people.

Don't confuse your own priorities with those of others. They may not have any connection.
 
#101 ·
What I am saying is with no sub all of it is sent to your mains and that may not be the best idea even a small sub can be helpful.

Not everyone want the low frequency information but they should also be shown what they are missing by giving up it too. I am still unsure if the lfe channel is redirected to the mains or not when there is no sub. Some say yes some no I would need to use a scope and take a look at what is going on I guess.
 
#102 ·
I don't disagree. I am just saying that for many, if not most people it probably is meaningless. I have done thousands of demos and installed and calibrated hundreds of systems. Most people just don't care. Even among those that care a lot about sound quality, for many purposes they don't need a sub. With my Arx A5 I am just on the edge with music of needing more extension. I don't use them for HT at this time. In my HT I certainly do want a sub, but I don't need much below 30 Hz, certainly not below 20 Hz, to be satisfied.
 
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