Concave ceiling corner traps - suggestions please.

[Heifetz]

Hello,

I would like to reduce some of the bass echo/reflections to the ceiling corners. The challenge is to make it aesthetically pleasing and subtle for WAF.

So I would like something approx 30cms-40cms each side with concave outer face that attaches to the ceiling corners. 

 I would also like to be able to paint it to match the wall colour (sort of yellow - I think its called 'blond').

 

I did some experiment with a regular grey  sponge bass trap that seemed to improve the listening. 

Does anyone have any suggestions? May be you know of a product or a DIY solution or someone who make it to order. 

 

Your help and suggestions would be very welcome.

 

Kind regards, 

 

[Audiophile Neuroscience]

Hi

Judging by your fairly large room and subs you are likely going to get axial mode resonances extending down below50Hz. For physical treatments you need very large traps. Either velocity type traps which need to be out from the wall (where motion of air molecules at 1/4 wavelength) or better, bass pressure traps placed in the corners There are some commercial products that may go down this far and some DIY instructions on the web for cylinders. Both are large.

 

WAF may be a problem. Have you thought of Eq software bass management ( I prefer acoustic treatments).

[Heifetz]

Hello David,

Thank you for your reply.

Actually my room set up has just changed so i need to update my ID pic.

Attached is a photo.

no more subs. Speakers are Tannoy Kensington's.

Bob

 

[Heifetz]

Would something like this be effective?

https://www.primacoustic.com/cumulus/specifications/

 

 

[Hipper]

1 hour ago, Heifetz said:

Would something like this be effective?

https://www.primacoustic.com/cumulus/specifications/

 

 

No! The spec shows it absorbs to 100Hz. The suspicion is that your problem is lower then this.

 

Sponge (foam?) doesn't go very low unless you have extremely large sizes. Most bass traps are also large (40cm square).

 

In addition it's not a good idea to paint the surface of any absorber as that will affect its absorption. The best you might be able to do is find something with a cloth covering that matches, or contrasts nicely, with what you have.

 

You have an attractive room and it certainly would be a shame to damage that with lots of room treatment even though that is probably the best solution.

 

The first thing you really need to do is identify exactly the issue - which frequencies are boomy, or not heard at all. That can be done by measuring. The simplest way but not the most accurate is to use your ears and a set of test tones (the most accurate way is to use software and a microphone and many on here do that but it gets complicated). You can download a free set of test tones here which is ideal:

 

https://realtraps.com/test-cd.htm

 

(This site also has lots of information to help you understand what is going on)

 

There will be some frequencies that sound louder, others quieter.

 

It may help repositioning your speakers and listening chair, using the test CD to find what's best. DSP/EQ is the other obvious solution. You could also try using a number of subwoofers. There is also a product like a subwoofer that uses a microphone to hear the problem and counteract it as you listen (no experience of either and can't remember what the latter was called).

 

There are tuned bass traps like this:

 

https://gikacoustics.co.uk/product-category/tuned-membrane-bass-traps/

 

You need to know the target frequencies to use these effectively. I have no practical experience of these either.

 

Solving bass problems, whilst not the whole story, is the major part. It will clear the sound so you can hear the mid and highs much better.

 

[Audiophile Neuroscience]

2 hours ago, Heifetz said:

Would something like this be effective?

https://www.primacoustic.com/cumulus/specifications/

 

 

I doubt it. Even their spec sheet only rates to 125Hz and the absorption coefficiient is maybe a bit sus ? random incidence rather than a percentage ?

 

To get really serious something like

https://www.gikacoustics.com/product/gik-acoustics-soffit-bass-trap/

 

or a DIY version of a ASC tube trap

http://www.acousticsciences.com/products/tube-trap

 

It also obviously depends on how low the speakers go and where you place the speakers in relation to which resonances get excited

 

will post again tomorrow

 

 

 

 

[Audiophile Neuroscience]

So, to do the job properly you need to have bass traps physically capable of dealing with those large energy, big wavelengths in the bass.

 

Bass resonances are maximum at the tri-corners (where walls meet ceiling and floor). It makes sense to place traps there. The smaller, thinner traps will most likely only absorb highs and mids. Exactly what you dont want.

 

It may be preferable to go with a software solution?

 

here is my room

 

 

That gives you an example of what is required for acoustic treatment of bass resonances. Cylinder bass traps have been around for many decades and refined by various acoustic/audio engineers and a physicist.

 

I got mine made after doing the research and as supervised by Barry Diament of Soundkeeper recordings. here is a good article http://barrydiamentaudio.com/monitoring.htm

 

[Edit; 90% of good sound is in the recording. Barry is a master recording and mastering engineer. Check out his recordings]

 

This is a DIY link.

http://www.teresaudi...raps/traps.html

I used reflective foil on half the circumference, not plastic, plus other refinements.

 

Definitely a WAF challenge!

Good luck

David

Edited July 25, 2019 by Audiophile Neuroscience

[Marco]

I’m just an enthusiast not an expert.

But my first thought seeing the photo;
Those curtains do very little for absorbing sound.

You can have your WAF go all out on larger curtains, with pelmets and thick velours fabric etc.
If these are oversized left and right you might also be able to hide a wide strip of sound absorbing material behind it (not blocking the window).

Not sure if it helps the bass a lot, but it could make her happy and improve the sound reflections from the rear.

Just a thought.

[Audiophile Neuroscience]

3 minutes ago, Marco said:

I’m just an enthusiast not an expert.

But my first thought seeing the photo;
Those curtains do very little for absorbing sound.

You can have your WAF go all out on larger curtains, with pelmets and thick velours fabric etc.
If these are oversized left and right you might also be able to hide a wide strip of sound absorbing material behind it (not blocking the window).

Not sure if it helps the bass a lot, but it could make her happy and improve the sound reflections from the rear.

Just a thought.

Hi Marco

The problem with using curtains and soft furnishings is they suck up the high frequencies (and no bass) so they’re great to put at the early reflection points. Elsewhere it is usually recommended that you diffuse reflections in order to keep the sound lively.

So the curtain should be placed ideally on the wall behind the speakers but in between the speakers to catch the first reflection from the rear wall.

A large pelmet spanning across the top could be used to conceal a soffit style bass trap ie a large thick trap spanning from corner to corner where the ceiling meets the wall.

Cheers

David

 

 

[Heifetz]

@Audiophile Neuroscience

David, Thank you so much for your advice.

I am learning heaps and @Marco is also prompting more understanding for me.

Right-Side

I usually open up the right side of my room (big bifold doors - see pic) so that I have little/no first reflections from that right side of the room.

 

Left-Side

On the left, I have a mirror and window. Sometimes I just throw up a foam-type light weight absorber onto the mirror and on the window sill. These, however, are not the first reflection points. There is some angled bits & pieces that I think, deflect the sound into different spots in the room i.e.. not my ears. 

 

I always thought the glass framed pictures in my room added to the pleasant amount of 'liveliness' and they are above my ear level too. 

 

Back wall

On the back wall I have nothing (walls are just by-rock type sheet) except some photos hanging up that are above ear level. 

At ear level I have put some cushions on a music stand about 0.5m behind my listening chair. This definitely improves the sonic experience and tells me that I need something to absorb/deflect the sound on the back wall. Is that a correct assumption? My listening chair is 3.5m from the back wall. Maybe if I rearrange a little higher the pictures on the back wall it may help and/or substitute a nice absorber/diffuser like the viacoustic at approx. ear level?

 

Front Wall

The front wall you have already commented on from the picture earlier in the thread. 

David, thank you for your suggestion. I have the two bamboo plants for aesthetic purposes but i thought they also help little for deflection. There is only space for a 20cms wide deflector that would sit immediately left of the window that would also keep it symmetrical and central behind the turntable.  I'm not sure whether 20cm wide deflector exactly behind the turntable would make such a difference. What do you think? Perhaps, together with the plants it would be worthwhile.

The proper bass trap would make the largest improvement.

 

Ceiling

The first reflection points from the ceiling would be quite straight forward to solve. 

 

Thank you again. Bob

 

 

 

 

 

[Audiophile Neuroscience]

3 hours ago, Heifetz said:

@Audiophile Neuroscience

David, Thank you so much for your advice.

I am learning heaps and @Marco is also prompting more understanding for me.

Right-Side

I usually open up the right side of my room (big bifold doors - see pic) so that I have little/no first reflections from that right side of the room.

 

Left-Side

On the left, I have a mirror and window. Sometimes I just throw up a foam-type light weight absorber onto the mirror and on the window sill. These, however, are not the first reflection points. There is some angled bits & pieces that I think, deflect the sound into different spots in the room i.e.. not my ears. 

 

I always thought the glass framed pictures in my room added to the pleasant amount of 'liveliness' and they are above my ear level too. 

 

Back wall

On the back wall I have nothing (walls are just by-rock type sheet) except some photos hanging up that are above ear level. 

At ear level I have put some cushions on a music stand about 0.5m behind my listening chair. This definitely improves the sonic experience and tells me that I need something to absorb/deflect the sound on the back wall. Is that a correct assumption? My listening chair is 3.5m from the back wall. Maybe if I rearrange a little higher the pictures on the back wall it may help and/or substitute a nice absorber/diffuser like the viacoustic at approx. ear level?

 

Front Wall

The front wall you have already commented on from the picture earlier in the thread. 

David, thank you for your suggestion. I have the two bamboo plants for aesthetic purposes but i thought they also help little for deflection. There is only space for a 20cms wide deflector that would sit immediately left of the window that would also keep it symmetrical and central behind the turntable.  I'm not sure whether 20cm wide deflector exactly behind the turntable would make such a difference. What do you think? Perhaps, together with the plants it would be worthwhile.

The proper bass trap would make the largest improvement.

 

Ceiling

The first reflection points from the ceiling would be quite straight forward to solve. 

 

Thank you again. Bob

 

 

 

 

 

First reflections are basically where soundwaves become directional and they bounce off surfaces like billiard balls off the side cushions, angle of incidence equals angle reflection.

 

Soundwaves become directional more or less above the Schroder frequency about 300 Hz. This is approximately the whole top half of a piano keyboard or treble clef in music. Frequencies below that, the whole bottom half of a piano keyboard for practical purposes can be called the bass .

 

Bass frequencies are more omnidirectional and do not bounce off surfaces the way that higher frequencies do.

 

Obviously we have missed out classifying the mid frequencies in that description which are roughly in the middle of the piano keyboard, straddling between the bottom half of the top half of the piano keyboard.

 

Remember that each speaker will send out soundwaves in the treble range which will bounce off, for example, both the side walls. So the left channel speaker will have a first reflection point on the left side wall as well as the right side wall.

 

 

This diagram shows reflection points for left and right speaker with respect to the side walls and the rear wall (labelled c in the diagram). There will also be reflection points from each speaker from every other surface including the wall behind the speakers, the floor and ceiling.

 

It easy to find the reflection points from your seated position by having someone carry a mirror along the wall or surface and when you can see the tweeter of each speaker, that is a reflection point which needs to be treated.

 

So on the rear wall behind your couch you would probably need to place an absorber around the middle of the wall where the reflection points are. The other photos with glass surfaces are probably not doing much harm but in theory you would want diffusers here not reflectors. The bookcase off to one corner is likely doing some absorption as well some diffusion, but my biggest gripe would be that it is asymmetrical placed

 

still looking at that rear wall behind the couch you have curtains on one side and a glossy door on the other side, again asymmetrical. Then you have a bookshelf on one side and a piano on the other side, again asymmetrical.

 

To be honest they may be only making tiny differences but I am just pointing out what I see. One simple solution might be just to get rid of the pillow on the music stand and shift your bookcase on the rear wall to the centre location. You could open the curtains so that it matches the reflectivity of the glossy doors.

 

You have carpets and a rug covering the first reflection points on the ground.

 

I can't see any treatment on the ceiling for reflection points but usually this is impractical in most listening rooms.

 

Looking at the side walls I see you have some foam atop the piano and a bit further down, which I presume you have mapped to the reflection points.

On one side of the speakers you have the large window with curtains and on the other side a large opening, again this is very asymmetrical. The opening will help prevent bass pressure from building up, but only on that side. I'd be tempted to close those doors and the glossy surface will tend to match the shiny surface of the glass on the other side. At any rate it is very easy to experiment to see which give you the best sound.

 

Looks like you've got records stacked in both corners behind the speakers and these will be providing some kind of combination of absorption and diffusion, but if I have the locations right at least it will be symmetrical

 

so overall I would go around strategically treating the first reflection points and attempting to make everything else diffuse and scatter the higher frequencies/late reflections as well as making everything as symmetrical as possible.

 

Where possible bass traps need to be in the corners from floor-to-ceiling and if you were limited to only two traps to place in the entire room you would put them in the corners behind the speakers.

 

Not sure what you mean by the 20 cm deflector. You either try and absorb or diffuse/scatter sound (maybe diffract/bend it) but not deflect/reflect it. I'm guessing the 20 cm location is on the front wall in between the speakers and behind the equipment rack but I'm not sure why you only have 20 cm of wall space. You could put an absorber along the wall where the reflection points are. The same could be achieved by putting up dummy curtains behind the equipment rack. This may be more acceptable to your wife. When listening to music I would close the curtains i.e. bunch them up from the right side so that you only have curtains immediately behind the equipment rack. You don't want to deaden huge amounts of real estate on the front wall. There was a school of thought back in the day about "live end, dead end" but I don't recommend it.

 

Anyway none of this is written in stone just my thoughts

Cheers

David