Room Treatment Impressions

[Ian Mackenzie]

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.

[Ian Mackenzie]

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.

[Andyoz]

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.

[Andyoz]

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.

[Ian Mackenzie]

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.

[Ian Mackenzie]

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/product_detail.php?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

[Andyoz]

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.

[Andyoz]

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

[Ian Mackenzie]

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/4ft_tall_X_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.

[Andyoz]

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.

[Andyoz]

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/4ft_tall_X_6fft_wide.pdf


Sweet :)

[Ian Mackenzie]

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.:eek:

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

[johnaec]

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... :biting: 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

[richluvsound]

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

[Ian Mackenzie]

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... :biting: 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

[Ian Mackenzie]

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

Hi Rich,

Yes. Any given loudspeaker will couple and react with a room in all sorts of funny ways. Because of the size and location of the woofer it will undoubtably have issues. I am confident they can be addressed to some extent with some broadband absorbers. More on that later.

But as has been said the 4345 still works.

I could say that about the room actually.;) At a glance on paper it should not work but it seems to even under the worst circumstances.

[Ian Mackenzie]

I was browsing the WWW and found this mutifunction device.

http://www.innovativemusic.com.au/Polyfuser.htm

[richluvsound]

Hi Ian ,

thanks for posting the diagrams. Not being an engineer, the diagrams really do help.

Thanks again, Rich

[Andyoz]

I was browsing the WWW and found this mutifunction device.

http://www.innovativemusic.com.au/Polyfuser.htm

We have used that type of product before as a "poor mans" replacement for QRD's. I tend to call them a "deflector" instead of a diffuser as they don't diffuse sound in the true sense. They are effective none the less.

One thing to watch out for if you attempt to make them yourself, you can get a VERY strange (upper) low-frequency absorption performance. One client made up some of his own and covered 50% of the ceiling with them. This resulted is a very strange RT profile in the room as he was losing a load of energy out of the room at around 200-300Hz. Everests book has some sound absorption data for these and from the RT's we measured, they fitted the profile in the book perfectly. It didn't sound too good TBH!!

So I would be careful making your own. I imagine the proprietary ones are designed to offer absorption over a broader range of frequencies. I still woudn't buy anything without seeing test data as this "peaky" absorption performance around 250Hz appears to be inherent in that type of design.

Having said that, if I was dsigning my own listening room, I would still seriously consider those poly's myself. I think they look much better than QRD's in a domestic setting. I just wouldn't go overboard with the area of treatment!!

[Ian Mackenzie]

Thanks Andy,

There is a paper I have somewhere by Dr Cox on curved diffusers.

I will have a read.

The profiles of some of the more advanced diffusers are apparently optimised designs using a computor that don't necessarily use prime and primative root numbers.

On construction I think even the type of timber is probably important in a true wood QRD

But I won't being doing anything until I get some real clarity around the application.

The intent of the these poly types incl the Q'Fuser, Mini and Metro'Fuser and the Primacoustic curved one is that you can buy a pack and try them at critical points in the room until the desired result is obtained.

I doubt if diffusers are a good thing for home theatre with 5 speakers splaying sound in every direction. Easy, just take the poly Fusers them off the wall.

I would probably put one on the flat screen or end up mounting it flush to the wall. Flat screens are a bit of a problem for two channel stereo imaging according to the experts.

The Decware.com 2x prime 13 wood diffusers look quite smart. They are 61 x 61 cm and only 7.5 cm depth.

They appear to be ambience phase graters because they operate only over the upper mid range and high frequencies. 1100-10,000 hz

Building a wood QRD to size is the right design approach but is a lot more limiting. A modular array like the Decware approach with be flexible but that has technical limitations of periodicity if used in numbers as you know.

From what I have read higher prime numbers tend to work better at high frequencies and are more aggressive if depth is not a major issue.

The rear wall has a usable width of 100 cm, So a potential QRD design would be . 2 x prime 17 or 19 with a theoretical depth of 14 cm. I would look at prime 38 for the front wall like the SRD designs. But it will be costly to make, heavy and a permanent fixture.

Installing a solid wooden QRD does not have the same flexibily.

But for pure two channel stereo they no doubt have a play.

The more immediate requirement is the bass traps.

Ian

[Andyoz]

If you have a pdf of that Cox paper I'd like a copy..:)

I would agree that the bass traps will give more noticeable benefits than diffusers and seeing as we are dealing with JBL's here...you gotta get the bottom end right!

You can half solve your rear diffusion issues by careful placement/filling of those bookshelves.

Have you got access to any gear for measuring the changes. It isn't that expensive to get into it really compared to 15 years ago. EASERA is a great bit of software and can be run off a moderately priced soundcard. We use some nice Bruel & Kjaer mics but a £100 Behringer mic is more than adequate for this type of stuff.

[lfh]

Sorry about the TLA:s ;)

Fraunhofer Institut für Bauphysik (FhG IBP) has developed and patented a membrane type bass absorber called Verbund-Platten-Resonator (VPR).

From a reliable source I have heard that they work very well (as opposed to some crap that's out there...).

Given that the design is patented, you should be able to find a nice design manual ;) (Building clones should be fine as long as it's not done an a commercial basis, in which case, of course, it would be considered a patent infringement.)

Here are two links (in German, sorry), the first to the research institute, the second to the patent licensee and manufacturer.

http://www.ibp.fhg.de/akustik/ra/vpr/index.html

http://www.renz-akustik.de/page/index.php?id=46

[Ian Mackenzie]

If you have a pdf of that Cox paper I'd like a copy..:)

I would agree that the bass traps will give more noticeable benefits than diffusers and seeing as we are dealing with JBL's here...you gotta get the bottom end right!

You can half solve your rear diffusion issues by careful placement/filling of those bookshelves.

Have you got access to any gear for measuring the changes. It isn't that expensive to get into it really compared to 15 years ago. EASERA is a great bit of software and can be run off a moderately priced soundcard. We use some nice Bruel & Kjaer mics but a £100 Behringer mic is more than adequate for this type of stuff.

I have a Behringher mic and all sorts of software inc Sound Easy..complicated bastard to drive ..written by a Nerd but it does a lot......

Might be worth a trip to office works or Ikea. If the book shelves dont help I can wripe out the shelfs and convert to a quick and dirty QRD.:D.

Will try and sort the bass traps this week. The QRD's do make a nice discussion though on a cold winters day!

Thanks again for yout tips.

Ian

[Ian Mackenzie]

Sorry about the TLA:s ;)

Given that the design is patented, you should be able to find a nice design manual ;) (Building clones should be fine as long as it's not done an a commercial basis, in which case, of course, it would be considered a patent infringement.)

Here are two links (in German, sorry), the first to the research institute, the second to the patent licensee and manufacturer.

http://www.ibp.fhg.de/akustik/ra/vpr/index.html

http://www.renz-akustik.de/page/index.php?id=46

Thanks IFH,

I will check it out.:)

Ian

[Andyoz]

I have a Behringher mic and all sorts of software inc Sound Easy..complicated bastard to drive ..written by a Nerd but it does a lot......

If you already have a decent mic and soundcard, download the 30 day demo version of EASERA.

It the easiest package I have seen. You will be doing measurements within 15mins :).

[Steve Schell]

Hi Ian, great thread. I generally go off the deep end with room treatment, loading in huge amounts in an attempt to create a quasi-anechoic environment. Maximizing the ratio of direct to reflected energy at the listening chair sounds good to me, but freaks out some people.

One thing I have found is that one can DIY nice looking panel absorbers for about 10% of the cost of commercially available ones. I have built over thirty 2' by 6' absorbers using 1.5" compressed fiberglass, an exterior frame made from 1 x 2s and burlap covering. Cost was just a few hundred bucks for all of these.

Apparently one goal is to achieve a fairly short RT60 time in the room that is as consistent with frequency as possible. Controlling low frequency hangover is perhaps the toughest problem once the recycling of midrange energy has been tamed. I learned a lot from Per A. Hellstrom's U.S. Patent #4,362,222. He found that placing baffles across the room corners at 45 degrees offers a lot of bang for the baffle in absorbing low frequencies. After reading the patent I placed several of my older 3' by 8' baffles across the corners and noticed an immediate improvement in bass smoothness, clarity and apparent level.

A couple of Harry Olson's patents are also worth a look, #2,502,016 and #2,502,020. It looks like he used perforated masonite and Kimsul paper padding (or similar) in the construction of his diffraction type sound absorbers.

Our first sale of a complete Cogent horn system was to Chris Brady of Teres Audio in the Denver area. When we loaded the system in there, Chris had just completed an overhaul of his listening room. He has recently updated his personal web site to reflect the changes to system and room. This page contains a link to an article detailing the construction of his homebrewed tube traps.

http://www.teresaudio.com/haven/index.html

[lfh]

an attempt to create a quasi-anechoic environment. Maximizing the ratio of direct to reflected energy at the listening chair sounds good to me, but freaks out some people.

Right, such a setup is certainly not everybody's cup of tea. I think Earl Geddes summarizes this nicely (from http://www.gedlee.com/downloads/Audio%20Acoustics%206%2012%2005.ppt):

"
Moving forward [higer direct to reflected ratio (my remark)]*creates a subjective effect that I call “in the recording”
Backward [lower direct to reflected] - “in the room”
The former gives the subjective impression of “being there” – you are moved into the recorded space
The later gives the impression that the musicians have been transported into the room with you

Some like the “in the recording” effect, but I find it unnatural - precise imaging beyond reality, no spaciousness, a kind of headphone effect"

Of course, with a "nasty" power response (non flat off axis FR) it is harder to achieve an uncolored reflected sound field, whereby the straight forward approach is to dampen the early reflexes as much as possible.



I learned a lot from Per A. Hellstrom's U.S. Patent #4,362,222. He found that placing baffles across the room corners at 45 degrees offers a lot of bang for the baffle in absorbing low frequencies.

As to cheap (but bulky) friction-type corner absorbers (I didn't check the patent yet), see the two popular DIY designs discussed at Studiotips:

Studiotips Corner Absorber (http://forum.studiotips.com/viewtopic.php?t=534)

and

Studiotips SuperChunk (http://forum.studiotips.com/viewtopic.php?t=535)

[Ian Mackenzie]

Hi Steve,

Thanks for your input.

"Controlling low frequency hangover is perhaps the toughest problem once the recycling of midrange energy has been tamed.".

Yep,

On a movie with sustain LF this is a definate build up.I played The Matrix last night and you can can really hear the overhang now I have damping the HF and mids but only down to 200 hz..or there abouts.

On typical music its not so bad but I am sure it will make a marked improvement if I can damp the overhang.

I do have a plan after looking at the Studio tips.
http://forum.studiotips.com/viewtopic.php?t=534


I can buy "a good" foam studio corner trap about 1 foot corner x 2 foot for a really good price and a 6 inch thick x 2 foot square broad band absorber. They are only $35 and $45 respectively if I pick up for cash (usually double that)

Using the Studio tips approach I want to first try 2 corner traps in each corner and then place 2 the 6 inch slabs with an air gap across each corner. That would be a serious amount of absorber.

Moving the 45's just a little bit makes an audible change and I ssuspect once I have done some damping it will be a case of finding the best overall compromise.

Ian

[JBL 4645]

I was looking at the diagram and it would help if the loudspeakers where all built into a baffle wall with treatment placed over it this will minimize reflections in the front and help the sound focus just that bit more extra into the room or over the listen position.

I agree with treatment on the sidewalls and at the back.

Typical music is mixed slightly different from a motion picture soundtrack. The Matrix I’m familiar with the whole soundtrack in each film I find the blend of midrange slightly laid back in, The Matrix reloaded on the JBL control 5 as it needs a little more turned up on the fader.

Caution of warning! The lows now they are spread deeply over the three screen very deeply like when the glass melts and buckles there’s a deep cracking sound that you think, at any moment the low frequency driver is going bust! The lows are down to 25Hz and they peak very high really there made for the big screen JBL loudspeakers but if you can find ways of taming the low end so it wont get out of control and damage the loudspeakers the (DCX2496) might be a perfect affordable answer.

Knowing what your loudspeakers are capable off what they can and can not do within there technical tolerances within the rooms confines, there’s plenty of magical electronic devices that work extremely well with some of the above issues. But room treatment is paramount in dealing with it in more natural way where the bass traps make some huge differences in frequency responses and when using the RTA its proof shows on the display where some of the dips and have been increased and peaks smoothed out, yeah it’s a kinder magic.:)

[Ian Mackenzie]

JBL4645,

Unfortunately I am unable to build the enclosures into a wall cavity.

I had thought about briing the flat screen forward 500mm and adding side wings for a resistive bass trap but that would be extreme.

The intention is to arrange practical treatments that will make a reasonable difference. Two channel stereo being the main consideration.

I quite like the Matrix sound tracks.

The amp did not leave class A (35 watts /channel) when the floor turned to jelly.

Strange as it may seem concrete floor slabs are easy to shake.

I have never seen the meter move out of class A with the 45's using the Passlabs X250.5.

The amp is rated 250 into 8 and 500 watts into 4 ohms. The 45's are largely a 4-6 ohm load in the bass and midrange so there is plently of headroom. Biamping is particularly perilous in such a modest room although there is no doubts it does improve the bass end. In the colder months I will engage more class power to warm the room!

The other thing is that some sound waves will move into other areas via wooden doors and the glass 6 x 6 ft frontwindows. So the theoretical modes will possibly be a bit different in reality. But I can voucher for the centre seat being the best postion for smoothest bass.

2010 is under audition tonight.

The aero-braking as quite spectacular. One of the panels fell off the wall! That was a sign!

I think the wall panel array has really helped a lot of the issues. The system can be driven the a much higher ambient level.

Ian

[Ian Mackenzie]

http://www.soundscapes.nu/rb_prd.htm
http://www.soundscapes.nu/rb_dif.htm


Here is something to checkout!

I did a seach tonight in google on QRD diffuser and found the above site.

Despite not being in English it is by far the most comprehensive coverage of diy diffusers I have seen.

Ian

[Hoerninger]

Great!
Thank you.
__________
Peter

PS:
Just "coming back", a listening room for your DD66000 or other speakers:
http://www.soundscapes.nu/!gallery/design/index.htm (http://www.soundscapes.nu/%21gallery/design/index.htm)
And more foto-galleries ("A picture says more than a thousand words"):
http://www.soundscapes.nu/!gallery/

[Andyoz]

I really can't stand the "look" of the 2D diffusers.

For domestic use, I would just stick with 1D diffusers and alternate the orientation.

[Ian Mackenzie]

Yeah,

They are a bit technical. Nice for a ceiling application though.

It is entertaining to see what he has been up to..a diffuser farm!

I will try and scan that doc for you Andy.

Ian

[Andyoz]

Some of those 2D diffuser installations on that Soundscabes website appear to be more to do with "willy wagging" for audiophiles! I mean, painting them in yellow for Christ's sake.

Due to the hearing mechanisms higher sensitivity to lateral reflections. I would concentrate on 1D diffusers in the lateral plane and leave it a that.

[Ian Mackenzie]

Some of those 2D diffuser installations on that Soundscabes website appear to be more to do with "willy wagging" for audiophiles! I mean, painting them in yellow for Christ's sake.


I am surprised some of our Yanky friends have not chimed in on the color. Yellow I mean. In any case it would clash badly with the JBL Blue

One of the images is of a the Harman testing room with 2 D diffusers:eek:.

My understanding is its a case by case thing and these devices should be used in critical locations.

That said most of the primitive Root 2D diffusers seem to be used in roof locations and that makes a lot of sense to me when you think about the angle of the incident rays.

The real benefit is they throw off only about half the energy in the same plane as the classic 1D QRD. That in fact could be real plus on the rear wall where they are used as a passive suround sound ambience.

There are some interesting applications using the Omidiffusers in that situation.

The idea of controlling the absorption by using a binary code for applying some absorber material (J Angus) to the 1D QRD does have some merit.

[Andyoz]

Yes, I woud agree re. your comment about placing them on the ceiling (if you can stand to look at them!!).

I like the idea of using a limited area of polycyndrical 'deflectors' though. Not as good as the diffusers, but even the missus would like them :). After all, were're not trying to mix super critical music recordings here, just after some happy enjoyment of music playback in the home environment.

[Ian Mackenzie]

I'm having a close look at the Bad panel scrim 12 x 12 bad panels for the rear wall.

This or Arch is RPG's recommendation.

http://www.rpginc.com/residential/pdfs/CineMusic-2007-MSRP-Catalog.pdf (http://www.rpginc.com/residential/pdfs/CineMusic-2007-MSRP-Catalog.pdf)

A 1D amplitude phase grating QRD could be fabricated but for the equivalent cost of 9 square bad panels I doubt the result would be a good.

""I like the idea of using a limited area of polycyndrical 'deflectors' though""

Yes they are an interesting creature. I think that might be the way to go on the front wall if I decided not to make a lot a saw dust!

[Ian Mackenzie]

The lead time is months on the Bad panels so I have opted to have a go at the 1 D QRD 17 diffuser for the rear wall.

I did some research during tonight and called up Primacoustics regards their Polyfusers and they are true diffisers except the Minifuser. The reason I called however was to discuss my application. Apparently the diffuser really needs 12 feet from the source for it to work properly. My room just meets that requirement taken from the baffles. The effect of the diffuser can be detected from the rear listening position but the effect is more so on the room overall according to the applications specialist. Similar feedback was obtain from SRL who make a whole line of modified Schroeder diffusors.

My design is based on the Prime 17 Schroder diffusor and has 2 inch wide wells.

In my inital design I took into account the coverage area of the rear wall, about 3 ft wide x 4 1'2 high. The maximum depth is a theoretical 8 inches.

The working range is 798 - 3390 hz although the practical frequency range is about 1/2 an octave above and below these operating points. The design frequency is about 930 hz.

The higher prime number designs have better high frequency characterictics. The prime 17 design suited my rear wall coverage area better than the QRD7 design for the same bandwidth. The important bandwidth from what I have read is 800- 4000hz. The width of the wells does not want to be any narrower than 2 inches in practice to avoid absorption.

I basically decided not to use blades because of construction issues and because at a normal angle of incidence the effect on the diffuser is un important. At wide angles the blades have an effect. Given the location of the diffuser on the rear wall and distance from the source I hope it will not be an issue.

After reading a google translation of the Soundscapes design notes it is apparent that solid construction is critical to correct operation. Given the side walls/blades and have to be ideally thin this makes them mechanically weak while if they are too thick this impairs the diffuser operation.It will also be an order of magnitude easier to make without the blades.

Below are details of the design.

It is essentally very similar to the SRL audio design. Depending on what happens I will consider a similar (larger) version for the front wall.

Ian

[Andyoz]

Excellent work there!

I would take issue with Primacoustics statement that their Polyfusers are a "true" diffuser. I don't think that is really correct under the strict definition of what a diffuser is. The true diffuser scatters sound over a broad area, for a broad range of frequencies and these affects should be (relatively) independent of the angle of incidence.

Cylidrical type "diffuser" also scatter sound but they are sensitive to the angle of incidence and don't have the abandwidth of properly designed QRD designs.

I still like them though.:)

[Cyclotronguy]

Hey Ian;

You gotta come back over for a visit, listen and some adult audiophile approved beverages. I've set up the listening room with active bass traps.... damn but they are impressive. Will get you some jpgs.

Build as follows:
Ten inch (sorry 3.9 cm) floor to ceiling concrete form tubes, covered with layer of spun glass and linen "socks" to keep the glass fibers out of the air.

At top and bottom are 8" car audio subwoofers looking into the corners of the wall floor and wall ceiling. Looking back at the room are microphone capsules.

Inside the tubes are electronics; Mic preamps, crossovers and chip amps; in addition to twin drivers.

Woofer output the antiphase of any signal the microphones sees below 100 Hz. Gain is set just below where they go into feedback.

Works like glue!

Cyclotronguy

[Ian Mackenzie]

That is one of the reasons I wanted to try this out>

Having printed, read and researched over 100's pages I wanted to see what all the fuss was about.....If something happens...Look , "its full of stars".

I may look at a Diffractal just for grins!

If it clashes with the JBL decor there is always the option of putting some acoustically transparent fabic over it.

[Ian Mackenzie]

Hey Ian;


Gain is set just below where they go into feedback.

Works like glue!

Cyclotronguy

Sniff! Active absorbers..Love it!

"You gotta come back over for a visit, listen and some adult audiophile approved beverages."

I think so.... and catch up with the Diva.

[Hoerninger]

When reading here I got in mind some pictures with details I did not pay attention first.
At the launch of the new Everest in Tokyo there was quite a usage of diffusors. The pictures will show you.
___________
Peter

[Ian Mackenzie]

Making it is not easy...:hmm:

Using discrete MDF sections and joining is quite complex and difficult assembly..for a prototype.

I will thereforelook at solid timber construction using 2 x 2 and 2 x 4's. The profile will be 4 inches thick in some places so heavy is only downside but has advantage of being solid and no resonance.

Timber will be cut in workshop and then assembled on site like a model plane.

[JBL 4645]

I wonder if you can make a skyline diffuser with Lego? :D

[JBL 4645]

JBL4645,

Unfortunately I am unable to build the enclosures into a wall cavity.

I had thought about briing the flat screen forward 500mm and adding side wings for a resistive bass trap but that would be extreme.

The intention is to arrange practical treatments that will make a reasonable difference. Two channel stereo being the main consideration.

I quite like the Matrix sound tracks.

The amp did not leave class A (35 watts /channel) when the floor turned to jelly.

Strange as it may seem concrete floor slabs are easy to shake.

I have never seen the meter move out of class A with the 45's using the Passlabs X250.5.

The amp is rated 250 into 8 and 500 watts into 4 ohms. The 45's are largely a 4-6 ohm load in the bass and midrange so there is plently of headroom. Biamping is particularly perilous in such a modest room although there is no doubts it does improve the bass end. In the colder months I will engage more class power to warm the room!

The other thing is that some sound waves will move into other areas via wooden doors and the glass 6 x 6 ft frontwindows. So the theoretical modes will possibly be a bit different in reality. But I can voucher for the centre seat being the best postion for smoothest bass.

2010 is under audition tonight.

The aero-braking as quite spectacular. One of the panels fell off the wall! That was a sign!

I think the wall panel array has really helped a lot of the issues. The system can be driven the a much higher ambient level.

Ian

Ian

What are you saying its impossible I bet your room is a whole lot larger than mine a whole lot larger and you can’t construct a baffle wall just a few feet in front of the room and then place the loudspeakers into it? Wow.:blink:

This is practical, its part of the THX formula that works with even out reflections where most cinemas have some type of absorbent on the front wall but still the sounds waves are going in-between them. A false baffle wall shouldn’t cost you know more than $100.00 of your dollars not for a small room that is.

[Ian Mackenzie]

Skyline Lego.

It would absorb to much energy.

Just to be clear I am not attempting to re engineer the listening space, only modify the acoustics.

There is not enough room for that proposal and there are other domestic considerations. ie Where would I put all the remotes...LOL

[Ian Mackenzie]

Waiting for bass traps on order.

[readswift]

today I had this crazy idea of covering walls (no thin walls=80 cm)
with Icynene open cell foam sprayment almost entirely and use sheets of speaker grill cloth in front of it so it stays "open" as well
http://www.icynene.com/

absorption ratio is measured here: http://www.bobgolds.com/AbsorptionCoefficients.htm

though my plan is to defeat early reflections of 2344 horn :)
new room shape instead of square shape room becomes easy task. Of course I also plan bass traps.
madness?:bs:?

[hjames]

Be careful -
I did check your URL and that product apparently does NOT give off formaldehyde when curing or afterwards ... (excess formaldehyde is one of the causes of "sick building syndrome") ... so thats a real plus for it.

But I didn't find any info about flammability. I'm not sure about that foam, but some of the spray in foams can be flammable unless covered with gypsum board (sheet rock) or a similar inert material. Open foam covered with cloth may be more flammable than you'd like - please check first.

be careful ...


today I had this crazy idea of covering walls (no thin walls=80 cm)
with Icynene open cell foam sprayment almost entirely and use sheets of speaker grill cloth in front of it so it stays "open" as well
http://www.icynene.com/

absorption ratio is measured here: http://www.bobgolds.com/AbsorptionCoefficients.htm

though my plan is to defeat early reflections of 2344 horn :)
new room shape instead of square shape room becomes easy task. Of course I also plan bass traps.
madness?:bs:?

[readswift]

its free of formaldehyde.. its written in their faq, also
http://www.icynene.com/assets/Products/InsulationComparisonChart.pdf

'It contributes no fuel in the event of fire and it will not sustain flame upon removal of the flame source. However, like fiberglass, it will be consumed by flame, and gypsum board or other acceptable thermal barriers are required by applicable building codes.''


looks green to me...
http://www.icynene.com/FAQs.aspx

"STC Sound Transmission Class - 37
Hz. Freq. ____125 250 500 1000 2000 4000
ASTM E90___ 19 30 31 42 38 46
NRC Noise Reduction Coefficient - 70
Hz. Freq. ____ 125 250 500 1000 2000 4000
ASTM C423 ___.11 .43 .89 .72 . 71 . 67
Actual performance is superior than
reported test results because of Icynene®’s
ability to control air leakage."

[Andyoz]

today I had this crazy idea of covering walls (no thin walls=80 cm)
with Icynene open cell foam sprayment almost entirely and use sheets of speaker grill cloth in front of it so it stays "open" as well
http://www.icynene.com/
madness?:bs:?

Yes....madness unless it's for 5.1 cinema as all the audio directional cues are in the mix and you can "lose" the room acoustic. But the room will be way too dead for 2-channel as that relies on some room response to create ambience. I would have only covered the rear wall (not 100% though) and maybe a small area of the side walls.

Interesting idea though. Looks like a padded cell :blink:

[richluvsound]

Andy,

where do I start ? I'm thinking that room treatment will lessen the need to use the PAR.

I have a serious LF issue @ 66.97, gain is -10.9 and Q 7.35. Is there a bass trap that will do it . I would prefer to make it ;)! Then Diffusers, it would make an interesting project to post if you have the time .

What information do need to make a diagnosis ?

Rich

[Andyoz]

Rich, you can do tuned absorbers...sure. I'll try to find some links as the theory is really simple actually.

I thought you were moving anyway??? I'm damn busy with work at the moment.:)

[grumpy]

This kind of thing?

http://www.ethanwiner.com/basstrap.html

http://www.runet.edu/~shelm/acoustics/bass-traps.html

60Hz might be pushing the region where these are effective...

-grumpy

[richluvsound]

Hi Andy,

moving ? yeah at some point ! Plans have taken a turn for the better . The Germans like TAX records:( I have taken a full time job to get me back into the system.... I spent a year pissing away my savings on this obsession.:D

I have looked at these things a lot - not that hard to make . The theory is where I need to concentrate my efforts . Its a shame Gabriel ain't playing.

If I cant grasp the basics I can use the knowledge anywhere !

Cheers for the links Grumpy .

Rich

[Andyoz]

Rich,

Basically, these things work on sound wave pressure and not velocity. Pressure is at a maximum near room boundaries. Whereas velocity is at a minimum, and that's why normal foam/mineral wool absorption won't work at low-frequencies when simply mounted on the wall.

The trick is to mount a "membrane" panel so that it resonates at the required freq. range. When the panel hits resonance, it vibrates like crazy and this extracts sound energy out of the room (converts it to heat as the panels flexs).

So you basically build up a panel on the wall (or corner) with a plywood outer sheet and air-cavity behind that is sealed off by a perimeter timber surround. The resonant frequency is defined by the surface mass of the panel (kg/sq.m) and the depth of the cavity. You can control the Q by the type and amount of absorption in the cavity.

To get you 67Hz, I roughly calc: 10mm plywood panel on 150mm air-cavity. You will need to experiment with the mineral wool infill but start at 50mm.

To test it, play some sine waves through you 4345's and feel the surface of the panel - you'll know when you hit resonance (trust me!)

[cooky1257]

Rich,
Here's another good link;http://www.mhsoft.nl/Helmholtzabsorber.asp
Cooky

[Andyoz]

Cool link...I haven't seen that one before :)

[cooky1257]

Hi Andy, yeah there's great useful stuff on there.
I like the helmholtz resonator ideas, be it timber slats or perforated(radiator covers?)hardboard as having more domestically acceptable hidabilty.
My better half will never know I'm treating the room....in fact I may get some brownie points.
Cooky

[Hoerninger]

http://www.mhsoft.nl/Helmholtzabsorber.asp

Thank you!
And more interesting links down there.
May I call it link-hopping?
__________
Peter

[readswift]

http://www.bobgolds.com/AbsorptionCoefficients.htm


check out the BBC pdf for heimholtz stuff.

[richluvsound]

Ian,

Be is best ! anything else is a fools overture ;)


Andy,

can I go lower , say 38 and up to around 70 htz. the rear wall behind my babies.

So the larger the panel the lower the frequency ? the same principle as enclosure design ? sorry for being such a novice !

Rich

[readswift]

its all there in that BBC pdf, look:
http://www.bbc.co.uk/rd/pubs/reports/1992-10.pdf