Room Acoustics Guide.
Posted by: 911gt3r on 15 December 2018
Dear Forum.
I have used the Search Function here to learn about room acoustics, but found that previous posts on the subject are both scarce and with very limited interest strangely. Having also read ongoing posts and forumers replies to various issues people suffer with their speaker/ room interaction has made me realise, that there are clearly people here that know, what they are talking about. I am hoping that this thread could serve as a comprehensive guide to Naimees, who are in the need of help with their listening room issues and who can be bothered about using the search- function in the future.
I myself was lucky with speaker placement in my previous house, as it literally turned out to be plonk and play. I lived with my relatively big listening room ( 4.7x 7.8) very happily with Naim SL2 speakers which were ultimately replaced by PMC Fact 12 speakers, as I found the SL2s sounding a bit to lean simply because the space was too big for them firing the long way down the room. The PMCs very much have the qualities of the SL2s ( transparency, speed) , but additionally can produce some earth shakingly deep and clean bass being a front ported transmission line design.
As I recently retired my wife and I decided to move to a smaller new build house, where I was lucky enough to have a didicated listening room ( for clarification my avater should give you an idea of layout).
Now this is where my problems started ????. The room is 3.5Wx6.0Lx2.4H. Speakers are placed 1.6 mtrs in front of bifold glass doors. Listening position is 3.2 mtrs from the Facts. Walls is a particular low density plasterboard drylined ie a 20mm gab to solid wall behind them enabling some bass absorption. Floor is suspended concrete and although feeling very solid it has got a slightly boomy sound to it when you jump up and down ( and that I have been in sheer frustration and Interspersed with foul language). Due to being a low energy modern construction having to comply with modern building regs the plaster board ceiling has 200 mm of rockwool battens placed between the wooden joists above it. This means on the old clapping test, that the room is far from bright. However on the flip side the room has proven not to be able to absorb the pressurisation/ energy induced by my much loved Fact 12s this resulting in too much bass/ bass boom.
Beyond head scratching and throwing all my the toys out of the pram the last couple of weeks has given me an opportunity to read up on room acoustics and watching a lot of Dennis Foley’s videos @acousticfields.com. These very instructive short videos explain the fundamentals of room and speaker interactions and have helped me a lot to in simple terms understand, what is at play in there. Essentially you don’t have to have an engineer’s grey matter to understand, what he is talking about ( suits my little brain to a T).
Initially the sound was literally so bad I could have cried and ‘ The baby nearly got flushed out with the bath water’. Reassurance was on tap from other Forum members and Foottapper’s suggestion as to using Gaia III feet elimated 90% of the vibrational influency from the floor.
An intesting observation was the influence ( or not as case ended up) of the bifolds behind my speakers. I essentially opened them right up to work out at what point the didn’t interfere with the sound from my speakers. This probably also helped by the Facts being front ported turned out to be 1.5 metres in front ( measured from front baffle) and at that point the sound evened out to also produce a fine tonal balance.
I initially used Dynaudio’s rule of thumb namely dividing the room square up into 1/5th as a good starting point. Ie neither listening position nor speaker placement baffle to rear wall and side wall within the 1/5th distance. This will ofcourse mostly apply to a floorstanding design I guess. It certainly worked well. My speakers drive unit- centre is now an equal 85 centimetres from the side walls and with a 20mm toe in to establish a good soundstage but also to reduce the impact of first reflection. In addition I am using 2 GIK Acoustics panels to dampen first reflection. These particular panels both diffuse and absorb at the same time to prevent mid/ highs loosing too much energy and actually even look nice.
I have managed to even out most of the excessive bass by literally standing in each corner of the room and listen ( YEP, bonkers hobby this ????). I found that keeping absorption at the listening end to a minimum served the mids and highs not to loose energy- otherwise the overall sound became flat and lifeless without sparkle. This could ofcourse in most cases be achieved by soft furnishings/ curtains etc. In my case this wasn’t sufficient, so I installed 2 GIK Acoustics tri trap absorbers on top of each other in the corner behind my listening position, but strangely only had to do one corner- use your ears for where you feel the need to reduce bass lift/ boom. ( even get down on your knees and listen- at that point my dear wifey was beginning to fear for my sanity admittedly)
The speaker end ( dead end rule literally ruled in my case) proved to be the biggest challenge beyond moving the speakers round first in big chunks ( a foot) and then in the end literally millimetres at a time. Once you find the best compromise in the first place for placement, make sure to mark that point say with decorators tape on the floor. It is actually difficult to remember how something sounded half an hour ago. I found that I always managed to end up at that same place again, so there must be something to be said for going with your first instinct
After having achieved a very good bass reponse for both overall resolution and decay a 100 hz mode decided to pop its ugly face up. This is a distinct lift from the deepest string on an acoustic guitar or say a double bass being played. To this effect I have experimented with Hofa bass traps from Thomann.de. These are specifically tuned to be most efficient at around a 100 Hz and after having realised , that they need to fill in the corner full height floor to ceiling stacked on top of each other to work properly, I am now receiving 2 more on Monday. They are very heavy and slightly cumbersome, but really work in the speaker end corners ( Check my profile for pics).
I shall report back next week, but after the last couple of weeks desperately hoping that I would achieve the best compromise with my somewhat tricky new listening space , I really hope it will be mission accomplished . It would great if you guys would chip in, so maybe we can tap into each others experiences with the for most of us tricky speaker/ room interaction and viable solutions. In my case I never imagined it would so difficult to eke out my issues, but on the flip side I am chuffed to have persevered instead of of chucking my speakers in the skip.
Thanks Fellas ???????? ATB Peter