Interesting article on Room Effects

http://www.regonaudio.com/The GREAT Divide.html

 

Interesting article. I've read a few similar pieces on room interaction. I still have a dozen more to wade through, if I get time. Although you have reminded me to get some acoustic foam ordered, so I'll dig about in my saved links this morning and get it sorted.

Interesting point with regard to eq-ing the room (above bass frequencies), whereby you compound the room errors if you move your head too much! This is where the high tech approach fails to impress me. A perfect soluton for recording, but quite lame for playback to multiple people. Simple acoustic foam placement sounds like a better idea by far.

 

Bought some absorbers for my room which has slight echo's, from this cheap studio supplier. Some other places only sell them in vast quantities. I'll try a couple of panels on the wall, using the mirror placement technique.

"465-040" is the product code to search for in this website...

http://www.studiospares.com/mac/category.asp?gid=15&gtitle=ACOUSTICS


(Looks like everyone's too busy with sweedish baby food to comment)

 

Its a nice article and shares many of the same views I have regarding how to get a good sound.

The one thing I disagree on though, is that for the bass, he seems to ignore (unless I am missing something, I read it pretty quickly) the listening rooms RT60 (reverb time).

It is all very well using corner placement and EQ to get a smooth frequency response but in my experience the frequency response is really only half the issue with bass. What is of great importance is the sound after the speakers have stopped playing. No amount of EQ can change the fact that after the speakers stop making sound, one will hear coloured room resonance for a time afterwards causing overhang and boomyness. If you go for corner placement these resonances will be pretty strong and can continue for quite a few milliseconds, although they will be more even than if the speakers were placed say, 2 or 3 feet from the wall.

 

It is an interesting article....I've used systems for yrs without any form of EQ,until moving to our current house,which is rather old and timber framed,and had no end of problems with room interactions.

My current pre/processor is a TAG AV32R Dual Processor,with TAG's own room correction software,set up with a PC and RTA software to look at the in-room response,and then uploaded to the AV32R after calculating the filter settings.

Perhaps a bit complex,and not as easy as I might prefer,but the results have been one of the most obvious improvements in sound quality in yrs of listening....no more nasty mid-bass boom,far better LF extension,and much improved midrange.

 

The RT60 parameter isn't actually of relevance at low frequencies.
Have a search for Schroder Frequency and you'll see what I'm getting at. It's the frequency defining the boundary between diffuse and non-diffuse sound fields. RT60 relates to diffuse sound fields.

 

Sorry I know it's not the exact correct term (is simply 'decay' better?), but my point was the existence of stored low frequency energy in the room that can be heard after the sound from the loudspeaker has stopped. To me this has as great an effect, if not more, on the quality of sound reproduction as the frequency response.

 

Yep, low-frequency decay is one hell of a problem. One I found when I moved into a new house with blockwork internal walls instead of plasterboard. The lack of low-frequency absorption was clearly audible.

 

Alex2, sounds like you've had some success. However, what does the sound do when you change seats in the room? Does it get markedly worse as this and other articles suggest?

Tenson, havent really felt the need for those bass traps yet. It turned out tighter than I thought it would be.

I'll let you know if my £30 foam experiment does anything to my tiny room echo next week.

 

Good luck, I think you should notice a difference if you have audible echo. Don't forget other first reflections from the back wall and ceiling.

Also try clicking your fingers at your listening position. If you hear a flutter echo then its worth putting some foam on the walls either side of your head as well as the ones at the first reflection points.

 

Still looking for something acceptable for the ceiling. It must be white. I've found a few things online, but they want to sell me a dozen mega size sheets. I only wat 2! If anyone else knows a link or wants to split a box let me know.

 

How about the RPG Skylines? Or for white foam it'll be melamine foam which is the fireproof acoustic foam. Melamine is a bitch though as it's fragile and tears easily.
Contact Matty at RPG Europe he'll try and help with small quantities and can be found at Hifiwigwam, AVforums and rpg-europe. Soundwave is the melamine foam I got as it's discontinued so was cheap, then I had it fabric wrapped which wasn't.

 

In my experience £30 won't get you very far.I do also recommend speaking to matty at RPG,he has been very helpful to me in trying to sort out my room even from afar.As Andyoz said,if you have brick construction instead of plasterboard then the results are very poor with alot of boom around the 60Hz area,I've found it very very difficult to erase completely,I've bought the RPG procorners for the corners,and profoams for the wall,plus made them thicker.Also the melamine foam aswell,so most usable walls are coverd,but still have some really nasty modes that are hard to erase.

Room acoustics seem simple,but in reality are very difficult,even though the foams arn't too atractive the benefits sonically outweigh most other changes.

 

Not only that: you compensate the longer decrease of energy due to the room characteristics with turning down the energy from the beginning on (for those specific frequencies which were corrected by means of an EQ).
The first impact (first ms) is therefore not at all linear! This is though one of the most important moments for our ears.

 

I believe it really doesn't make much sense just choosing one of the different diffusors any company makes without having a precise idea which frequencies have to be more or less diffused and also how much absorbtion you need. I for example had to get the Omnifusors. Not anything else but another room may need something totally different.

 

Why not just choose any company's diffuser? Unless you need a pretty low frequency (much below about 1KHz say) diffused you should be alright as most are made to work over a pretty board range.

What are the ones you have at the back there? They look very similar to the ones they have at SAE's main studio.

The idea behind very close corner placement is that you get a pretty smooth response. This is because the gap from the speakers to the wall and back is so small that the phase isn't messed up very much, you just get an increase in amplitude. Though its not perfect like this.

The best way is with the speakers in the wall so the drivers are in line with the reflective boundary. This way all reflected energy from the wall is in phase with the direct sound and you simply get an increase in amplitude, no suck outs or peaks.

By doing this you can reduce each frequency by about the same amount and the direct sound is still pretty linear.

I feel the best route to go is heavy room treatment, in this case bass trapping and then experiment with speaker placement and EQ. Move them right into the corner and then gradually move them away as far as you can while keeping a pretty even frequency response. After this you can EQ the bass down to the correct level as it is likely to be too strong.

The speaker placement is tricky. Close corner placement gets a more even frequency response in the bass, but having them further away helps the decay time due to the reflections being lower in energy.

Of course... close to corner placement means the speakers are also near the side wall and this excites a few other issues such as stronger first reflections and laminar flow, but these can be quite easily controlled.

Sorry I'm waffling, I'm a bit tired.

 

Paul...the TAG can be set up to have 2 configs for different positions in the room,but we tend just to use a nice soft settee facing the gear,and anyone else can simply sit elsewhere!

Seriously though,it's not a cheap option,and the similar designs from TACT and Meridian bear that out as well,but in terms of results,and the fact it can work in your next house etc etc,makes it a very worthwhile addition.

It managed to cope with some huge dips and peaks in the room response,which our rather old house is very prone to,no doubt as a result of the timber frame,and lath/plaster walls.

As with any significant change in furnishings etc,you will notice a difference,but any such changes can be pretty much smoothed out again.

The effects of the filtering are very obvious when you use a PC and RTA to analyse the effects of what's going on before and after applying the filters,and when the major LF room modes are sorted out,a lot of the associated mid-band anomalies go with them.

 

I have very good experience with Auralex, for which I am a dealer since a few months. It is cheap (relatively), very high quality and they have a big range of products.

http://www.auralex.com

 

Aside from the tact, what other high end EQ's exist which won't harm the audio signal?

 

TAG,TACT(as mentioned),Meridian,and I dont know about Lexicon etc.

There are a lot of pretty low-end digital EQ devices about,such as the Behringer,and similar products,but these do tend to be fairly cheap,and aimed at the studio/club markets,and I have no idea of their effects on sound quality in general.

I would say from my experiences of the TAG system,and very limited exposure to Meridian,that these will not degrade the signal quality,but they DO have huge effects on the room/speaker interactions,and can clean up the modes very effectively.

Of the stand-alone stereo preamps with room EQ,the TACT is probably the best current model,with the obvious recent demise of TAG.