Room acoustic case study part 1

Recently I was involved in a project to try and improve the acoustic of a very challenging listening space. The goal here was to see whether a top quality hi-fi system could be reasonably deployed in such a bad sounding space.

The room is quite small with parallel reflective surfaces and to start with was not a very flattering listening environment.

My first subjective impression when listening to music in the space was that reflected sound and room characteristics were very dominant resulting in very poor fidelity. The tonality was characterised by a lack of bass energy and chaotic mid-range which was quite disconcerting to listen to. An interesting listening observation was that at first the musical presentation was severely lacking. However after a while the ear brain system can adjust to this new reality and make more sense of it. This is due to a human ability called binaural unmasking where due to the advanced abilities of our hearing system we can choose what we want to listen to with complex signals from varying angles. So in effect we focus on the music coming from the loudspeakers and can negate the impact of the troublesome room reflections. However this only works for a limited amount of time as it does require more brain processing power which means that listening fatigue kicks in. The last thing anybody wants when listening to their hi-fi is to experience listening fatigue.

Its this sort of scenario which can often get audiophiles onto the upgrade merry go-around. System gets installed in less than ideal listening environment. User adjusts to this new reality. Over time the issues become more apparent. The band aid is to buy new cables, or change a piece of electronics, which doesn’t fix the problem and can be very costly.

Thankfully at Ultimate Resolution we offer room acoustics consultancy and remedial design so people can get off the upgrade merry go-around for once and for all.

So it was clear that this space needed some help and that measurements were required to pin point the problems.

I began by placing a measurement microphone at the listening position with the usual listening chair removed to avoid reflections into the microphone.

Alternating between the left and right loudspeakers allowed impulse response measurements to be taken individually from both speakers. With a small adjustment the microphone was positioned equidistant from each speaker which means that it is in the middle of the stereo field. The first measurement which provided useful data was the waterfall plots.

Please see below for the left speaker waterfall measurement:

Waterfalls show dB level on the vertical colour scale on the left as well as decay time in milliseconds on the scale to the right. Both level and time are plotted against frequency so that the all important decay time in each octave can be observed. With excessive decay time across a wide range of frequencies it was clear that remedial treatments were required.

In order to be able to objectively quantify the effect of acoustic treatments I decided that acoustic treatment installation should be done in 2 phases. The first phase would involve broadband treatments to address the bulk of the issues, with another round of measurements to follow, in order to asses the impact and to give guidance as to whether further remedial work was required.

Please see below for right speaker waterfall measurement:

The following acoustic treatments were installed as part of phase 1.

GIK acoustics broadband absorption panels.

2 were placed on the side walls at the first reflection points. 2 more went on the ceiling first reflection points. 1 went on the rear wall behind the listening position.

GIK acoustics tri-trap corner bass traps.

2 were placed in the left corner behind the loudspeaker and 2 more in the right corner. The tri-trap bass traps were custom built to run from floor to ceiling.

GIK acoustics monster bass trap.

1 was placed on the rear wall behind the listening position.

Once the treatments were in place the first test was a subjective listening test. Immediately the improvement was very clear. The bass player had suddenly arrived at the party! The out of control mid-range was tamed and I could hear aloft more of the loudspeakers and alot less of the room.

The improvement in soundstage width, depth and height was particularly impressive.

So the question was would the measurements reveal similar improvements?

Please see below for the left speaker waterfall measurement:

This measurement show alot less decay time overall which is helping to get the environment under control.

Please see below for the right speaker waterfall measurement:

Once again a significant reduction in decay time.

For the sake of comparison please see below for left speaker before and after waterfall plots:

For the sake of comparison please see below for right speaker before and after waterfall plots:

This project has shown how some careful analysis and proper consideration can take even the most challenging space and transform it into an acceptable environment in which to deploy a high quality audio system.

The before and after measurements show marked improvement and more importantly the before and after subjective listening tests take the listening space from being unusable to being a relaxing space where fatigue free music listening can be enjoyed.

All that is remaining now is to consider how the post treatments 50Hz resonance could be tackled which will be part of phase 2.

Stay tuned as there is more to come.

If you have a room acoustics project which we can help with please do get in touch using the details at the bottom of the page.

All the best,

Oran Burns

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