Page 1 of 5 123 ... LastLast
Results 1 to 15 of 65

Thread: Room Treatment Impressions

  1. #1
    Senior Member
    Join Date
    Apr 2003
    Location
    Australia
    Posts
    7,942

    Room Treatment Impressions

    I have opened this new thread to describe the acoustic transformation of my primary listening room.

    Room influences and issues of colouration have been discussed at length else where.

    The intent is not a blog but to oultline some of the issues I have in my room and the practical measures that I have decided to implement and the reasons behind the treatment..

    Everyone’s room is different and in no way is the information discussed here to be taken as a solution for a generic listening room.
    There are hundreds of references in the www and consultants eager to discuss your specific needs.

    Background.
    What started this off was an email response from an associate when I was enquiring about building a parametric equaliser. And my question was would it help with room modes below 300 hz as I can hear some clouding of the midrange on certain types of program material. It varies with listening position

    The response was:



    Theprimary purpose of the equaliser is to linearize the frequency characteristic of the loudspeaker. Optionally and less advisably, it may also be used to correct room response. However, where the room effect is particularly pronounced, there is not much the equaliser can do to fix the problem. In such cases, a proper acoustic treatment of the room (with respect to standing waves and reverberation time) will be required to improve the overall listening experience. For instance, if we wish to adequately suppress the standing waves effect of the listening room, we may have to use acoustic elements (such as diffusers, provided that the reverberation time is OK). The main problem with this approach is that it requires significant room adjustments, which may be rather costly, have low WAF and still not guarantee a perfect result.

    So I sent some diagrams and some photos and we looked at the basic issues of the room and how to deal with them. The inside of the Tardis is particularly boring although it is dimensionality transcendental . So sorry no pictures.
    A quick analysis reveals that the distribution of your room modes is such that it should not impact the sound of your system audibly/significantly in the centrally placed listening-chair position. For illustrative purposes, I have modelled your room as a 4-metre by 4-metre square room with parallel walls. Picture 1 shows the axial mode at 86Hz. The blue lines in the picture represent standing wave minimum’s whereas the red lines are standing wave maximums. The crosses are critical (worst) listening positions.


    At 86Hz, the critical listening position is the centre of the room. At a frequency of about 175 Hz, you have a standing wave minimum intersecting with a maximum at the spot where your middle chair is positioned, which should not pose any listening difficulties. However, the neighbouring two seating/listening positions (i.e. the chair on the left and the one on the right) are compromised because they happen to be at the intersection of two standing wave minimum’s. Likewise, at circa 258Hz things look pretty good at the middle-chair position as there are no standing wave collisions there. Again, it is the other two chairs which are in sub-optimal listening positions because they are relatively close to the standing wave maximums.The above are only case studies for the three most important axial modes and they should be taken with a pinch of salt because other room modes may also have an impact to a certain degree. Having said that, I do believe that in your case room modes may be corrected by the right placement of the speakers against the rear wall. Thus, if you pull them away from the rear wall by 20 or 30 centimetres, you may be able to reduce standing waves at critical frequencies.

    As I see it, a far more serious issue here is the room's reverberation time at midrange frequencies (the most critical band to our ear), which is too long due to lots of bare spots on the walls and a number of glass surfaces. On top of that, I suspect you may also have a problem with the so-called "early (or first) reflections" bouncing off the side walls, glass windows/coffee table, TV screen and the rear wall (paintings), which must be avoided as they can obscure the sound quite a bit, imaging and clarity in particular.

    I've been told that acoustic engineers make appalling interior decorators but here's what I'd do with your place just in case you ever feel like living on the edge :

    Put a 1.5-metre by 1.5-metre diffuser behind the TV set.Mount another diffuser onto the rear wall above the bookshelf, covering the entire width of the rear wall.

    Diffusers are used to reduce early reflections and reverberation time (to a certain extent).

    The ideal position for the paintings is to the left and/or to the right of the front diffuser (i.e. the one behind the TV set).

    Put some absorbers onto the left side wall above the bookshelf. They should be 1.5 metres in width and 1 metre in height.
    Hang some drapes (heavy curtains) to cover the windows and the balcony door.If required, put bass traps in the front two corners of the room.

    I believe these room adjustments would make a significant difference to the quality of the sound you hear, particularly when it comes to the midrange band which is currently greatly troubled by reverberation, reflections and all kinds of resonances.
    If you decide to have a go at this, there are some good web sites about how to build your own absorbers and diffusers plus a few tips of my own that I'd be happy to share with you.


    Well that was a lot more than I expected.
    Attached Images Attached Images      

  2. #2
    Senior Member
    Join Date
    Apr 2003
    Location
    Australia
    Posts
    7,942
    At this stage I have put in the wall treatment panels. The other recommendations will be implemented over the next few weeks.

    This consists of (8) 24 x 24 x 3 inch broadband foam absorbers tiles on the upper left wall and a heavy curtain covering the right wall windows.

    The audible changes are quite interesting.

    There is a lot more tonal color and richness to the sound. Voices are wamer and more natural

    Even more interesting is the depth or blackness of dynamic contrasts. I also seem to be able to drive the system to much higher levels without it sounding blaring loud. The impression is a more solid sound but not muffled or dead sounding.

    The apparent imaging is also what I would call richer and more opaque whereas before there was a tendancy for a planar or comb filter type quality on some pogram genres.

    While it could be said this is all subject there is no doubt its a change for the better.

  3. #3
    Senior Member
    Join Date
    May 2006
    Location
    Ireland
    Posts
    1,232
    Thanks for posting that....any pictures.

    I think you have done the right thing treating the side wall reflections first. They are most likely the strongest and therefore have the most potential for creating comb filtering effects as you say.

    Your comment re. transients is very interesting. Too many people get hung up on the Frequency Response of their system and ignore the Time Response. That's one of the reasons 1/3 octave equalisation common in the 70/80's has been dropped now...because it creates way too many problems with a systems time response.

    The other thing to remember is with room modes, you are dealing with reflected energy interacting with itself (and not with the direct energy from the source as with comb filtering). That's why they are most effectively dealt with by room treatments as apposed to active equalisation. What I mean is, if you try to actively attenuate a room mode, you have to attenuate the direct source level first and that will not sound right to your ears in the Time Domain even though it may look better in the Frequency Domain. Room treatments is the only effective way to treat the Time response. Also, measurements gear is way behind the ear brain mechanism and will be for a long, long time.

    People say acoustics is a black art...it actually isn't in many ways....at least with relatively small rooms that are slightly easier to pin down.

  4. #4
    Senior Member
    Join Date
    May 2006
    Location
    Ireland
    Posts
    1,232
    Another thing I noticed is you have bookshelves behind the listening position. They don't offer true "diffusion" as such but they do help to break up the strong specular reflections that are at the root of comb filtering.

    You may find that diffusers have less of an effect compared to the side wall treatments.

  5. #5
    Senior Member
    Join Date
    Apr 2003
    Location
    Australia
    Posts
    7,942
    Andy,

    Your input is highly valued.

    I have edited the post with some graphics.

    Milan did a great job, particuarly as he is so busy with AES conferences at the moment.


    Milan Uskokovic (Master M) has a bachelor's and master's degree in electrical engineering and over 15 years of experience as a licensed designer of professional broadcast and PA systems. He currently serves as the Chief Technical Officer (CTO) for Radio 101, Zagreb, Croatia.

  6. #6
    Senior Member
    Join Date
    Apr 2003
    Location
    Australia
    Posts
    7,942
    Yes,

    The book shelf is only 1 metre high. The rear wall is relatively bare otherwise.

    The bookshelf in the corner is 2 metres high.

    I suspect the diffusers will be the icing on the cake but not before some real effort on the bass traps. Those diffusers are the most intriguing contraptions. Weird as they may appear these new age diffusers are apparently optimised designs for more even scattering.

    In terms of product all these are available locally.

    http://www.soundseasy.com.au/v3/prod...?productID=451

    These bass traps look interesting. I am not sure about the Purple though. I can also buy ex factory a local product that is similar. http://www.soundacoustics.com.au/150Brochures.pdf

    http://www.majormusic.com.au/products/auralex_lenrd.php

  7. #7
    Senior Member
    Join Date
    May 2006
    Location
    Ireland
    Posts
    1,232
    I like his method for plotting the room modes...I might pinch that myself!

    The front wall diffuser treatment is interesting. I have seen that quit a bit but struggle with the reasoning. QRD diffusers normally start working at around 500Hz (unless they are very deep). The direct level from the speakers incident on the front wall will be lower in level due to directivity effects and that will only be more evident as frequency rises. The rear wall diffuser will get the full bandwith of direct sound. I guess the closer proximity of the front wall diffuser is the reason for it to be considered as useful as the rear wall diffuser??

    I would be interested to hear how it sounds with and without the front wall diffuser as I have never had a chance to hear that myself.

  8. #8
    Senior Member
    Join Date
    May 2006
    Location
    Ireland
    Posts
    1,232
    Quote Originally Posted by Ian Mackenzie View Post
    These look interesting. I can also buy ex factory a local product that is similar.

    http://www.majormusic.com.au/products/auralex_lenrd.php
    I personnally don't like them.

    The problem is they have tried to apply the same type of absorption to low frequencies as would be used for mid and high frequencies.

    For room modes, the most effective absorber works off pressure and not particle velocity (your mid/high freq. side wall absorbers are designed to convert particle velocity sound "energy" into heat). By that I mean, they need to be "driven" by pressure maxima in the room and those always occur at room surfaces/junctions. By the way, your ear is sensitive to pressure and NOT particle velocity and they both represent sound energy but in different forms.

    RPG's Modex Corner is more effective and works in a completely different manner to the Aurelx product.
    http://www.rpginc.com/products/modexcorner/index.htm

  9. #9
    Senior Member
    Join Date
    Apr 2003
    Location
    Australia
    Posts
    7,942
    Well,

    This was his quick look.

    I was wondering as well. Particularly if I go the home builder route on the diffusers.

    It appears to be a means of creating depth in the sound stage. I read about that on Decware.com. My only thought is the return wave, partially diffuse off the rear wall will also bounce in a diffuse manner across the room rather than spectrally like a reflector back to the front.

    What I am not sure about is the design of the rear diffuser if I go diy QRD? Shallow, deep, wide or narrow wells or partially absorbtion / diffusion...and close to my chair. It will be about 3 feet wide and 4 feet high. The front one is 6 fee square

    The blades might bite me! Imagine a big diffusor crashing down on a JBL nut!
    This is a modified QRD, no blades.

    http://www.srlaudio.com/product_pdfs..._6fft_wide.pdf


    I have read you have to be 3 wave lengths from the diffuser for it to work correctly. That means 1000 hz is the lower Fr for near field. As mentioned above it might not be relevant if the intent is to scatter the wave evenly and not back to the front wall.

    Interesting puzzle. But Milan nailed the side wall treatments. I am really pleased with the result.

  10. #10
    Senior Member
    Join Date
    May 2006
    Location
    Ireland
    Posts
    1,232
    When in doubt probably model something similar to the RPG type 734 diffuser and maybe bump up the design frequency a bit. That's "prime seed" 7 in the calcs.

    I wouldn't add absorption personally.

  11. #11
    Senior Member
    Join Date
    May 2006
    Location
    Ireland
    Posts
    1,232
    Quote Originally Posted by Ian Mackenzie View Post
    The blades might bite me! Imagine a big diffusor crashing down on a JBL nut!
    This is a modified QRD, no blades.

    http://www.srlaudio.com/product_pdfs..._6fft_wide.pdf
    Sweet

  12. #12
    Senior Member
    Join Date
    Apr 2003
    Location
    Australia
    Posts
    7,942
    To Steve,

    Thankyou for the ideas!

    In reference to the room construction it appears to some sort of hard paster board over double brick.

    Right wall had 2 metres of glass with door to the skywalker.

    The floor is carpeted wth a large rug over the carpet. The ceiling & floor are 12 inch concrete, quite plastic at low frequencies. Furniture is leather. Various art works on walls at the moment

    I wrote to RPG about diffuser options late last week. I suspect the Bad panels will be very expensive and long lead time. The T'fuser and Metro fuser are interesting devices.

    There may be a requirement for more important issues at the rear of the room..I am not sure. But there definately needs to be something on that rear wall and (the front). There is some flutter and slap off the front and rear walls. Perhaps some low frequecy treatment.

    There are other options, a patterned array of small tiles. It will need to be rationalised down to what is acceptable in terms of decor and cost.

    The early reflections off the side walls will also need to be look at. At the moment the sound stage is quite broad. The side treatment has improved this no end.

    Two channel stereo is the primary listening, sometimes 5.1 DVD. I do have a large vinyl and DVD music collection.

    Various testing facilities on tap, access to CNC and router equipped trade shool. But unless I know specifically what I need to make I don't want to embark on that road at this stage.

    Fibre type absorbers are virtually out..I suffer allergies terribly.

    Ian
    Last edited by Ian Mackenzie; 05-19-2007 at 02:21 PM. Reason: place marker

  13. #13
    RIP 2009
    Join Date
    Feb 2004
    Location
    Rohnert Park, CA
    Posts
    3,785
    Quote Originally Posted by Ian Mackenzie View Post
    I will delete the fine detail now because these forums represent what the cops would refer to as as a lot of under age drinkers on what they do and dont have to say.
    But it makes it a real drag to talk about pics and other things and then delete them so the rest of us have no idea what you're talking about... It's like you two are carrying on a private conversation, or like listening to someone else on a cell phone when you only hear one part of the conversation.

    John

  14. #14
    Senior Member richluvsound's Avatar
    Join Date
    Dec 2006
    Location
    london england
    Posts
    2,060

    Cheers !

    Hi Ian'
    well done for starting this thread . Its really interesting that you mentioned the cloudy mid-range thing (Maybe the Bryston was not to blame after-all) As were are both members of the 45's Your experience will help me no-end.Any pictures and dimensions of the room would be really helpful too !

    Rich

  15. #15
    Senior Member
    Join Date
    Apr 2003
    Location
    Australia
    Posts
    7,942
    Quote Originally Posted by johnaec View Post
    But it makes it a real drag to talk about pics and other things and then delete them so the rest of us have no idea what you're talking about... It's like you two are carrying on a private conversation, or like listening to someone else on a cell phone when you only hear one part of the conversation.

    John
    We have been.. . The thread is about impressions. Not design as such but it make interesting discussion.


    Ian
    Last edited by Ian Mackenzie; 05-19-2007 at 07:01 PM. Reason: update

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. The Perfect Room: Spaces
    By mikebake in forum General Audio Discussion
    Replies: 41
    Last Post: 03-29-2008, 03:50 PM
  2. Quick & Dirty Room Treatment
    By lfh in forum General Audio Discussion
    Replies: 3
    Last Post: 05-01-2007, 01:41 PM
  3. Room Placement and Bass LSR32 or LSR6332?
    By Minatogawaman in forum Lansing Product General Information
    Replies: 37
    Last Post: 02-24-2007, 04:44 PM
  4. Room treatment??
    By Hornblower in forum General Audio Discussion
    Replies: 20
    Last Post: 04-19-2006, 04:39 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •