Room Treatment Impressions

[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..

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/Audi...012%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

and

Studiotips SuperChunk

[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