The 'Dark' Art Of Room Acoustics!

[ajay124]

My 'Jalsaghar' is undergoing changes.

Over the past 15 months as I acquired and tweaked my stereo system,there were two aspects of my 'music room' that defied a solution.Namely,a dining table plumb in front off,but mercifully between the speakers.And a side wall opening where I wanted a solid wall.With the help of a cousin who is an architect,I finally found a solution for removing the dining table from the music room.I also sealed the side wall opening near the speakers with a solid wall.In a couple of days the old 'undulating' marble flooring is going to be replaced with (hopefully) a dead level,vitrified tile flooring.The choice of vitrified tiles is for practical reasons.The rest of the renovations,including a medium sized carpet,are partly for audio and partly for aesthetic reasons.

Having removed the dining table and sealed the side wall I settled down to audition the 'new' room.To my horror,I discovered that the earlier,magical sound was gone.Room acoustics is indeed a 'dark' art.You don't know where you are going until you are actually there.I am sure many audiophiles have been through a similar experience,where a carefully considered and executed tweak or upgrade,yeilds disappointing results :sad:

Apparently,the dining table had been acting as an absorption panel.Soaking up undesirable sound reflections.Secondly,sealing the opening in the side wall may have created more sound pressure inside the room.As I cranked up the volume the music revebrated,bounced and boomed.I cringed when I remembered the tight,focused,detailed,intimate and precise SQ from 'happier' times.Since then the sound has improved considerably,with adjustments in the placement of the speakers and the minimal furniture that I prefer having in a room.

My technical knowledge of standing waves,reflections from the walls/floor/roof,room treatment,bass traps,etc. is zilch.Which is better absorption or diffusion?Does too much absorption deaden the sound?My speakers have a provision for filling sand in the base.Should I give it a try?I tried plugging the bass reflex ports with an old pair of cotton socks.It instantly reduced of the boom and reverb,but it also did something that I did not like.SQ became leaner,more compressed and less open sounding.Somebody seemed to be gently strangling the speakers

I would appreciate if the audio engineers on the forum could shed some light on these mysteries.

 

[vivek.saikia]

Having removed the dining table and sealed the side wall I settled down to audition the 'new' room.To my horror,I discovered that the earlier,magical sound was gone.Room acoustics is indeed a 'dark' art.You don't know where you are going until you are actually there.I am sure many audiophiles have been through a similar experience,where a carefully considered and executed tweak or upgrade,yeilds disappointing results :sad:

tried plugging the bass reflex ports with an old pair of cotton socks.It instantly reduced of the boom and reverb,but it also did something that I did not like.SQ became leaner,more compressed and less open sounding.Somebody seemed to be gently strangling the speakers

I know exactly how you are feeling This feeling is very similiar to loosing something/someone very close to your heart :sad:

To reduce the boom maybe you should try a tweak by simply inserting some cold drink straws into the bass port of your speakers. Might tune the bass to your liking.

 

[prem]

Hi Ajay 124

If there is a bass boom, you will need absorption.
If you put the dining table back do you get the earlier magic?

I feel the closing of the side wall opening could be the main reason. Because of the opening there was 100 % absorption happening there.

If you have a window behind your speakers try opening them and see what happens?

Try putting up two small pillows on the top 2 front corners of the room behind your speakers where the ceiling, front wall and side wall meet.

If these simple solutions do not work, then try some bass traps

 

[mandeep]

There are three types of treatments:-

a) Pure Reflected sound creates--->standing waves--->Standing waves tend to collect near the walls and in corners of a room, these collecting standing waves are called room resonance modes----->these modes distort lower mid frequency and bass ranges---->Move chairs or sofas away from the walls or corners to reduce standing wave effects as these cause lot of reflection due to their hardness, better to put lots and lots of absorbing material in the corners.

b) Absorption---->Different materials absorb different amounts of acoustic energy at different frequencies---->result of this indifferent absorption is "flutter echoes" -----> "flutter echoes"can color the sound in the room and cause an emphasis at frequencies whose wavelengths correspond to the distance between the walls, and between the floor and ceiling------>midrange and high frequency absorption helps minimize echoes----->the most effective absorber for midrange and high frequencies is rigid fiberglass.

c)Diffusion--->Diffusion is often used in addition to absorption to tame the echoes

 

[viren bakhshi]

Hi Ajay,

Sorry to hear about your problems with the room. Removing the table from in front of the speakers was absolutely the right thing to do (for imaging). However, filling in the opening in the wall has probably added a reflecting corner to the room, and brought in some bass boom.

Acoustics is a "dark art" , not in itself, but in how it is promoted by its practitioners. Too much obfuscation, especially by people who are not clear of themselves.

Acoustics principles are clear and scientific. Enclosed spaces, which is what we live in, reflect sound. Reflected sound builds up in intensity unless it is absorbed. All solid, closed surfaces are reflective to sound - that includes wood, styrofoam. Probably the most efficient absorbers are fibrous materials, such as fibreglass matt, and open cell foams. These act only in the mid to high frequencies. Efficient bass absorbers are actually lossy mounted, thin solid panels. The art of acoustics is to balance the reflection and absorption of sound across the frequency spectrum, to provide a conducive environment for humans in that space.

Smaller rooms do tend to have bass resonance problems. The resonances are higher in frequency, actually midbass, that tend to cloud the entire midrange. Because of the corner reinforcement, your problem has increased. Stuffing the port is one option, to reduce exciting the low frequencies. Play with speaker location to reduce the room interaction somewhat. Move speakers further from the corners; change location to the adjoining wall; locate speakers facing diagonally across the room. Try these first.

Regards,
Viren

 

[mandeep]

Hi Ajay,

Sorry to hear about your problems with the room. Removing the table from in front of the speakers was absolutely the right thing to do (for imaging). However, filling in the opening in the wall has probably added a reflecting corner to the room, and brought in some bass boom.

Acoustics is a "dark art" , not in itself, but in how it is promoted by its practitioners. Too much obfuscation, especially by people who are not clear of themselves.

Acoustics principles are clear and scientific. Enclosed spaces, which is what we live in, reflect sound. Reflected sound builds up in intensity unless it is absorbed. All solid, closed surfaces are reflective to sound - that includes wood, styrofoam. Probably the most efficient absorbers are fibrous materials, such as fibreglass matt, and open cell foams. These act only in the mid to high frequencies. Efficient bass absorbers are actually lossy mounted, thin solid panels. The art of acoustics is to balance the reflection and absorption of sound across the frequency spectrum, to provide a conducive environment for humans in that space.

Smaller rooms do tend to have bass resonance problems. The resonances are higher in frequency, actually midbass, that tend to cloud the entire midrange. Because of the corner reinforcement, your problem has increased. Stuffing the port is one option, to reduce exciting the low frequencies. Play with speaker location to reduce the room interaction somewhat. Move speakers further from the corners; change location to the adjoining wall; locate speakers facing diagonally across the room. Try these first.

Regards,
Viren

very well said and nice suggestions Viren:signthankspin:

 

[ajay124]

Viren
You are absolutely right.Dark arts are probably borne out of ignorance and superstitions.I have never been particularly bright in matters of science,therefore for me,audio tweaks will remain a hit or miss affair.But I trust my ears and have the time and inclination to keep pushing for higher fidelity .I would really appreciate if you could suggest some inexpensive absorption and diffusion options.

I packed up the system after an extended session yesterday because the work on the flooring has begun.The room is 14x25 feet.Fairly big.It will take at least 3 days to finish laying the floor.

Yesterday's audition was far more satisfactory.I suspect that the freshly erected,semi-complete brick wall may have been playing 'dirty tricks' on Day 1.Sound quality improved noticeably after the wall was finished and plastered.I moved the speakers further away from the sidewalls (from 2.5 feet to 3.25 feet), and extended the furniture a little closer towards the speakers.A carpet in front of the speakers completed the scenario.The set up looked very nice because the 'view' was no longer marred by the dining table.The music sounded more like old times.Almost.

I am looking forward to further experiments once the flooring is done.I now have the liberty of moving the speakers around significantly.Will also try out a few amateur bass traps recommended by friends.I do not like the idea of stuffing the reflex ports.I would only do so as a last resort,as an act of desperation,because nothing else is working.I have three sets of power cords to play around with.The Volex,a gift from Prem.The XLO Reference 2,a loan from Sid and my generic cords.Both with US plugs.I would like to try Furutech (European) Schuko plugs with 230V cables before I upgrade my power cords.

 

[arj]

I am looking forward to further experiments once the flooring is done.I now have the liberty of moving the speakers around significantly.Will also try out a few amateur bass traps recommended by friends.I do not like the idea of stuffing the reflex ports.I would only do so as a last resort,as an act of desperation,because nothing else is working.I have three sets of power cords to play around with.The Volex,a gift from Prem.The XLO Reference 2,a loan from Sid and my generic cords.Both with US plugs.I would like to try Furutech (European) Schuko plugs with 230V cables before I upgrade my power cords.

Hi ajay, as rightly put by viren, acoustics is a science and very easily explainable in terms of diffusion/absorbtion/reflection and wave mechanics....but for a layman it can be pretty daunting..and hence i have always found it to be a combination of magical/logical/explainable all at once

Also get to powerchords et al only after you have set it up well...else it will give wrong results.

personally,I really am not a favour of bass traps unless it is after a proper study. As all work across a frequency range , unless you are sure as to why you are damping it, you will only suck out the life from the sound room here

check this link out Test: Stereoplay, Englisch

Try modelling your room and choose any speaker which best represents your room extension. you can play around with your speaker position and listening position and the graph above will give you the frequencies being impacted by your room node. typically in the 40-60 Hz range . this can give you an indicator of the frequencies causing the problem...interestingly if you move the listener you can see how the SPL changes. this way you can choose a good enough location with the most even response

After setting up the speaker most optimally (like Cardas/Audiophysic methods) , identify the first reflection points on both wall for both the speakers (ie ach wall can have a first reflection point for each speaker) and put a diffusor there. also in the rear wall between and behind the speakers (you may need to think of the ceiling too)

Regarding diffuser vs absorber, diffusers IMHO are better options but absorbers are more easily available.While it can be a topic in itself, typically you diffuse higher frequencies and aborb low frequencies. While the idea of a diffusor is to improve imaging etc by ensuring reflected waves do not reach the listener. Absorbers reduce sound levels in their operating region


Interesting Links here http://www.rivesaudio.com/resources/links/frame.html

 

[captrajesh]

Apparently,the dining table had been acting as an absorption panel.Soaking up undesirable sound reflections.Secondly,sealing the opening in the side wall may have created more sound pressure inside the room.

The room is 14x25 feet.Fairly big.

The room is fairly large. IMHO, the room needs to have sufficient furniture to break propagation of sound waves in undesirable directions (towards walls) which could be reflected around to distort the imaging and built up standing waves at corners.

My living room, which doubles up as my listening room has a lot of furniture and doesn't have any echo problem. My neighbour's similarly sized living room only has a sofa set and there is perceptible echo even during conversations.

 

[Bluu]

I've heard that potted plants act as excellent absorbers since the leaves do not provide a flat surface for the sound waves to bounce off of. Plus, they may add to the decor of the room itself.

 

[ajay124]

The room is fairly large. IMHO, the room needs to have sufficient furniture to break propagation of sound waves in undesirable directions (towards walls) which could be reflected around to distort the imaging and built up standing waves at corners.

My living room, which doubles up as my listening room has a lot of furniture and doesn't have any echo problem. My neighbour's similarly sized living room only has a sofa set and there is perceptible echo even during conversations.

Rajesh
I too think the problem is,that there is not enough furniture in the room.After removing the dining table, the only furniture left in the room is the seating arrangement at the other end of the room.Wooden sofas with a total seating of 8 and two small side tables.One half of the room is bare except for the audio rack and speakers.Looks like a shrine or a temple!Which it actually is

Once the flooring is done,I intend to spread the sofa sitting over a larger space,add two small carpets and potted plants/bass traps fashioned from one inch foam,in the corners behind the speakers. I am also looking for a good sitting option for the sweet spot.The sofa is not very comfortable for long sessions.I would prefer a single seater in rich leather
on which I could sit or recline with ease.Any suggestions?I had earlier come across the website of an audiophile furniture
supplier in Gurgaon,but I can't locate it at the moment

 

[iaudio]

One of the rooms in my apartment where I have kept my Mission speakers in has a loft with a whole lot of empty cartons. Once due to water percolating the walls, I had to remove all the cartons. The sound took a major blow with substantial echoing and bass boom! On the plus side, it didnt cost me anything to 'treat' the room and solve the problem!

 

[arj]

The room is fairly large. IMHO, the room needs to have sufficient furniture to break propagation of sound waves in undesirable directions (towards walls) which could be reflected around to distort the imaging and built up standing waves at corners.

My living room, which doubles up as my listening room has a lot of furniture and doesn't have any echo problem. My neighbour's similarly sized living room only has a sofa set and there is perceptible echo even during conversations.

hi Captrajesh. the job of furniture is primarily as an absorber. it will not really "break propogation" effectively as that needs a lot more high furniture and is better done by On the wall hangings. apparently Coir+Cardboard in a wooden frame does that well..egg cartons do a better job but look very ungainly.

 

[arj]

I am also looking for a good sitting option for the sweet spot.The sofa is not very comfortable for long sessions.I would prefer a single seater in rich leather
on which I could sit or recline with ease.Any suggestions?I had earlier come across the website of an audiophile furniture
supplier in Gurgaon,but I can't locate it at the moment

Ajay, a good plush seating can just improve the experience a great deal..it could just improve the sound as well if it acts as a good absorbant of SPL !

if you upto it one of the Lazyboys are amazing but not exactly cheap ... Also personally i prefer fabric over leather

 

[ajay124]

Ajay, a good plush seating can just improve the experience a great deal..it could just improve the sound as well if it acts as a good absorbant of SPL !

if you upto it one of the Lazyboys are amazing but not exactly cheap ... Also personally i prefer fabric over leather

Lazyboy! Thanks Arj. This was probably the website I had come across earlier. I am willing to consider other fabrics too,but would prefer leather,as long as it is good quality,and not the squelchy,squishy,sticky variety generally encountered in India.

 

[Asit]

A lot of good suggestions have poured in. I just like to share one small thing. My wife , my son and I myself are big readers, as a result we have accumulated a lot of books. In spite of me keeping all books related to my profession in my office, we still have a lot of books at home in each of the bedrooms and the living/dining area. I never really had a serious bass boom problem. For example, in the current configuration, the speakers (about 3' away from the backwall) face a 3 seater sofa (+3 small coffee tables) and a small divan some 10-12 feet away and behind those on the wall there are shelves keeping books upto about 10 feet height. One of the speakers has a 12'(length)x9'(height) drapes on the side about 2.5 feet away, behind which there is a sliding door opening up to a balcony, and the other speaker has an open side.

Keeping books in the room always helps.

Regards.

 

[vinay]

Engineer

Ajay,

Do you think such engineers exist on this forum? Would they help you to solve the mysteries keeping in mind that this is their source of income?

V.

I would appreciate if the audio engineers on the forum could shed some light on these mysteries.

 

[arj]

A lot of good suggestions have poured in. I just like to share one small thing. My wife , my son and I myself are big readers, as a result we have accumulated a lot of books. In spite of me keeping all books related to my profession in my office, we still have a lot of books at home in each of the bedrooms and the living/dining area. I never really had a serious bass boom problem. For example, in the current configuration, the speakers (about 3' away from the backwall) face a 3 seater sofa (+3 small coffee tables) and a small divan some 10-12 feet away and behind those on the wall there are shelves keeping books upto about 10 feet height. One of the speakers has a 12'(length)x9'(height) drapes on the side about 2.5 feet away, behind which there is a sliding door opening up to a balcony, and the other speaker has an open side.

Keeping books in the room always helps.

Regards.

hi Asit,that is a really great point. In fact when I build a house..plan to have a library+audio room with bookshelves lined up on the side walls to act as diffusers/absorbers and potted plants in the corners ! prefer natural rooms to heavily" Audiophile" treated ones

yup books are great..cardboard boxes with books in corners are also great for reducing room boom.

 

[ajay124]

Re: Engineer

Ajay,

Do you think such engineers exist on this forum? Would they help you to solve the mysteries keeping in mind that this is their source of income?

V.

Vinay
This forum has passionate and talented amateurs.I would rather seek their advise than that of mammon worshipping professionals.

I believe you are one of the most experienced 'room specialists' on the forum.I would be happy to learn something from your experiences

 

[iaudio]

hi Asit,that is a really great point. In fact when I build a house..plan to have a library+audio room with bookshelves lined up on the side walls to act as diffusers/absorbers and potted plants in the corners ! prefer natural rooms to heavily" Audiophile" treated ones

yup books are great..cardboard boxes with books in corners are also great for reducing room boom.

Arj, I am so with you on that!:clapping:

Asit da, Yes newspapers and books have helped in my case too.

And yes, Vinay and Santhosh are guys who are as good an authority on this subject as any engineer/ acoustics expert.