Room Measurements and treatment advice

[DANOFDANGER]

This was posted as a follow up on another thread of mine, but i relay it here for its own exclusive thread for others to see as its somewhat unrelated to the previous thread.

So i have done several measurements with different room furniture configurations and extended mattress treatment testing. All with interesting results. I even went as far as to remove all furniture except for my audio equipment and bed. Lets dive in.

Room dimensions 5.3m x 3.65m x 2.7m. Here is my modal simulations.

Ok so these are the measurements with all furniture removed except of course for my audio and video equipment. Also my bed remained.

These were the first measurements i made before i moved anything. Including draws on both side walls and various draws on the ends of the rear wall.

This is a comparison of with and without draws on the sidewalls (purple is draws removed, brown is with draws). Without any side furniture, the clarity and soundstage from doing this was much improved. Waterfall plot and spectrogram showed no real difference.

With and without my bed (brown is with, green is without bed). Without my bed was another nice change in clarity and take a look at the reduction in bass energy with the green (no bed), which shows some interactions with room modes going on. Waterfall and spectrogram showed no real difference.

Now on to the interesting part. Using my mattresses as acoustic treatment. These mattresses are heavy duty pillow top, not cheap old ones.

Using mattresses as side wall treatment at main reflection points. With and without (Pink is with treatment, Green is without). This offered the best quality improvements out of all the tests. Soundstage increased, imaging was noticeably improved. But the dynamic range was better. Hearing subtle sounds that were otherwise unnoticed previously. I attribute all this to the improved decay shown in the waterfall plot. Which was vastly reduced above 500hz.

Sidwall Treatment Waterfall Plot

Sidewall Treatment Spectrogram Plot

Next is using mattresses for rear wall treatment (green without, red with treatment). This had a similar increase in areas much like the sidewall treatment, but not nearly to the same degree. RT60, waterfall and spectrogram showed similar decreases in decay but again not nearly as well as the sidewall treatment.

Last is pushing the mattress into the front wall corner to act as a bass trap and also covers for sidewall treatment (Purple corner + sidewall and green without). But this lead to lower quality. I can only guess this was due to not a complete coverage of the sidewalls as when they were primarily placed as such. RT60 also showed worse results in comparison to only sidewall treatment.

To conclude, this allowed me to asses the differences that acoustic treatment would provide, both from measurements and audible differences. Sidewall treatment seems to be what will offer me the best audible improvements. Without any treatment. My room has excessive decay issues above 500hz and excessive bass energy below 100hz. I did not and will not be moving my speakers positions which could ultimately change some of these things, as their current position places them in the best possible configuration for soundstage (equilateral triangle) and imaging. The angle is unchanged also to allow the best on axis frequency response (moving off axis would only lower the high frequency rolloff).

Plan of action for treatment.

Because of the low decay in the high bass and low mid area, I am contemplating on using panels that are less effective below 500hz and primarily focus on energy above this frequency. So as to balance the decay as best as possible. I will place these panels on both the sidewalls and rear wall for a balanced effect. Even though when i used the mattresses as bass traps and found little effect. I believe that this doesn't mean bass traps dont work. It just means a mattress is not the best for this. So i intend to get some GIK soffit bass traps or tri traps with the optional range limiter to focus on bass energy only and a scatter plate fitted to keep the room as lively as possible.

Of course i invite anyone to look at the measurements i have made and offer any further advice as to the direction i should take with respect to acoustic treatment. I found it very interesting how much energy the mattresses could actually absorb (down to 60hz) when used as acoustic panels. Although an unrealistic solution for actual application. Thanks to those that insisted for me to get measurements done, it definitely has allowed me to make decisions on what and where.

 

[Hipper]

Very interesting. Thanks for taking the trouble to post all that.

I started preparing a thread for adding GIK Soffit Traps and other treatment in my room, from no treatment to full treatment, then adding EQ. It ended up as a long treatise, far to big to post. However I offer these images that may help you but I've become a bit of an extremist in most eyes I would think - I now have 21 Soffit Bass Traps! Some will say that's too many. Oh well, I like what I hear!

This speaks for itself. Green before, purple after all treatment - no smoothing.

The extended noise at 40Hz is road traffic.

These are with EQ. I ran out of Parametric EQ filters so this is only up to before 200Hz. I haven't done anything about the higher frequencies because I'm enjoying the music!

Not only is the lower range frequency response smoother but perhaps even more interesting is the reduction in decay times. I can't help thinking that it is the latter that has had the biggest impact on what I'm hearing.

 

[cooky1257]

So just how much eq are you applying at 50hz to flatten that huge dip?

 

[ToTo Man]

@DANOFDANGER, are those measurements for one speaker only or both speakers playing at the same time? IME, if you measure both speakers together, the results (especially the frequency response) become less accurate as the frequency increases due to the two sound fields causing dips at peaks at the single point mic source (AIUI our ears do not hear in this way):

Measuring both speakers together for bass response is ok for lower frequencies as this does not cause the same pattern of cancellations at the microphone location. In fact evaluating the bass response of both speakers together can be very helpful because one speaker's bass response might be helping to smooth out the other, so you may not require as much low frequency EQ as the individual measurements might suggest.

PS - Your results from experimenting with room treatment mirrors my own, i.e. that it has a much more profound effect on reducing reverberation times than smoothing out the frequency response. Luckily though, improving the reverberation time has a much more positive impact on improving the imaging, focus, speed and dynamics of an in-room replay system than the far difficult and far less effective approach of trying to iron flat the frequency response.

 

[Hipper]

So just how much eq are you applying at 50hz to flatten that huge dip?

10db.

I've made lots of effort to locate the problem - moving speakers, chair, checking speaker drivers, gear, and using test tones to find the peak somewhere in my room but had no luck. I know you are not supposed to feed nulls but I thought I'd try at first with a 5dB addition with a wide spread - the null reduced by 5dB. So I added the 10db and don't have any issues resulting from that.

In fact to get that curve I used REW to find the filters then manually added them to the ten (per channel) parametric filters on my equaliser (Behringer DEQ2496).

I don't understand it but it works.

 

[DANOFDANGER]

Very interesting. Thanks for taking the trouble to post all that.

I started preparing a thread for adding GIK Soffit Traps and other treatment in my room, from no treatment to full treatment, then adding EQ. It ended up as a long treatise, far to big to post. However I offer these images that may help you but I've become a bit of an extremist in most eyes I would think - I now have 21 Soffit Bass Traps! Some will say that's too many. Oh well, I like what I hear!

This speaks for itself. Green before, purple after all treatment - no smoothing.

The extended noise at 40Hz is road traffic.

These are with EQ. I ran out of Parametric EQ filters so this is only up to before 200Hz. I haven't done anything about the higher frequencies because I'm enjoying the music!

Not only is the lower range frequency response smoother but perhaps even more interesting is the reduction in decay times. I can't help thinking that it is the latter that has had the biggest impact on what I'm hearing.

Thanks for posting this. There is not a lot of easy to find material out there showing how acoustical treatment performs. I would be curious to see if you had any measurements with only two or so traps installed. As i will only be able to get a few in due to the high cost of importing (around $1500 for just two soffit traps). Id also be curious to know how much the traps affect higher frequencies in the corner positions. Appreciate any additional data you can provide. Im sure my data will help you in the future with treating reflection points.

Yes i believe that the reduction in decay of bass energy would be whats providing a great deal of the improvements for you. I have moved equipment around my room where bass energy was higher in fft measurements but yet sounded cleaner and less boomy compared to other locations that measured less. When looking at the spectral decay characteristics, this showed me potentially why with it showing a lower decay.

As you can see in my waterfall data, i also have excessive decay in the bass region which i am hoping to reduce with two soffit traps. Combined with side and rear wall treatment to bring the decay into a fairly even balance.

The treatment of early reflections is something that makes a big enough difference to warrant an investment. More than i initiallly thought. The clarity of low level sounds and imaging is vastly improved and the sense of differentation of spaciousness of sounds in rooms or voices is huge. At least in my experience. I do like a nice spacious sounding room thats not overly dead though so i have to be careful treating these early reflections while keeping the reverb at the right level.

 

[ToTo Man]

These are the stage-by-stage before and after results of my installation of GIK broadband treatments at the first reflection points on the side walls and corner spaces (measurements taken in 2013):

Legend:
red = no treatment,
blue = two GIK 244s on each side wall,
green = two GIK 244s on each side wall + one GIK tri-trap in each corner,
yellow = two GIK 244s on each side wall + two GIK tri-traps in each corner.

In 2016 I then made some DIY wedges out of RS45 to extend the GIK tri-traps all the way to the floor and ceiling, yielding a small but audible further reduction in reverberation times, helping to tighten up the low end even more. My reverb times below 90Hz are still higher than I'd like but I do not have much physical space left to accommodate tuned traps.

 

[DANOFDANGER]

@DANOFDANGER, are those measurements for one speaker only or both speakers playing at the same time? IME, if you measure both speakers together, the results (especially the frequency response) become less accurate as the frequency increases due to the two sound fields causing dips at peaks at the single point mic source (AIUI our ears do not hear in this way):

Measuring both speakers together for bass response is ok for lower frequencies as this does not cause the same pattern of cancellations at the microphone location. In fact evaluating the bass response of both speakers together can be very helpful because one speaker's bass response might be helping to smooth out the other, so you may not require as much low frequency EQ as the individual measurements might suggest.

PS - Your results from experimenting with room treatment mirrors my own, i.e. that it has a much more profound effect on reducing reverberation times than smoothing out the frequency response. Luckily though, improving the reverberation time has a much more positive impact on improving the imaging, focus, speed and dynamics of an in-room replay system than the far difficult and far less effective approach of trying to iron flat the frequency response.

Initially i ran all my measurements with speakers independantly. But i found that they were indifferent or near enough indifferent from measuring at the same time. I attribute this to my very symmetrical room and furniture layout which the waterfall plots of both the left and right speakers are virtually identicle. So i figured i was safe with stereo measurements.

 

[DANOFDANGER]

These are the stage-by-stage before and after results of my installation of GIK broadband treatments at the first reflection points on the side walls and corner spaces (measurements taken in 2013):

Legend:
red = no treatment,
blue = two GIK 244s on each side wall,
green = two GIK 244s on each side wall + one GIK tri-trap in each corner,
yellow = two GIK 244s on each side wall + two GIK tri-traps in each corner.

Absolutely fantastic, thanks for that. It does seem that bass trapping has very minimal effect to the actual bass response as you pointed out before. But still has some effect. If you have frequency overlay plots to show this i would be appreciated. Harder to see on waterfalls.

Im curious to know, after seing your decay times of around 200, down from 400ms. Has this made things sound too dead ?. Or about right.

 

[Hipper]

I do have such information.

Below is no bass traps, then two, one in the left and one in the right front corners (behind the speakers), then four, two in each corners.

Adding the base traps from none to all twenty-one.

Another bonus is phase improvements. Apparently a smoother phase response is preferred listening if anyone actually does hear it.

 

[ToTo Man]

Absolutely fantastic, thanks for that. It does seem that bass trapping has very minimal effect to the actual bass response as you pointed out before. But still has some effect. If you have frequency overlay plots to show this i would be appreciated. Harder to see on waterfalls.

Im curious to know, after seing your decay times of around 200, down from 400ms. Has this made things sound too dead ?. Or about right.

My before-after frequency response measurements aren't very helpful because I think something went wrong with the 'before treatment' measurement as it shows a much steeper HF roll-off than the 'after treatment' measurements. I think this might be because I was measuring as a stereo pair instead of each speaker individually (I had only been using REW for a day or two when I took those measurements so didn't rally know what I was doing!). You can see my full write-up here (note my hifi kit has changed a lot since then!): https://www.pinkfishmedia.net/forum/threads/results-of-my-acoustical-room-treatment.146435/

About the decay times, these depend on where I'm sitting. If I'm sitting in a nearfield arrangement it's around 200ms, if I'm sitting in a farfield arrangement it increases to around 300ms. They're probably a touch on the low side, and if I were doing things again I'd probably choose corner traps faced with a membrane or diffuser panel to reflect more secondary reflections. I think a reverb time of around 350ms-400ms would be the sweet spot to aim for.

PS - An interesting side note, I've recently been to two concerts (A Tribute To George Michael - at Glasgow Royal Concert Hall) and (The Eagles - at the SSE Hydro), and in both cases I really struggled to get to grips with the sound of the kick drum reverberating around the venues like a ricochet. It makes me laugh when I read about pfm'ers wishing to make their systems sound like a live music venue, each to their own I suppose!...

 

[Hipper]

And some full range results.

Blue - no treatment, turquoise - two soffits, red - four soffits.

No treatment

There seems to be a difference down to 3kHz but not much after that. These are GIK soffit bass traps without limiters - they weren't available when I bought them.

Where do you live that GIK is not easily available? There may be other options. It is possible to make these things yourself. All they are is a wooden frame with mineral wool inside and covered in a certain type of cloth. They don't look too difficult to make providing you have the space and protections against the unpleasantness of working with mineral wool. There's plenty of advice if you go down this road.

 

[ToTo Man]

I do have such information.

Below is no bass traps, then two, one in the left and one in the right front corners (behind the speakers), then four, two in each corners.

Adding the base traps from none to all twenty-one.

Another bonus is phase improvements. Apparently a smoother phase response is preferred listening if anyone actually does hear it.

Do you have a pic of your room on the Systems Pics thread, Hipper? I'd love to see how you've laid out your 21 traps. I'm assuming a lot of these
are reflective to mid and high frequencies, or else you'd be listening in an anechoic chamber?! I think I've been pretty conservative with my treatments (13 traps in total, 8 of which are corner traps), yet my RT60 has dropped to below 300ms, and it's not even as if my room is filled with lots of soft furnishings (carpet, rug, fabric reclining chair, that's basically it).

 

[DANOFDANGER]

About the decay times, these depend on where I'm sitting. If I'm sitting in a nearfield arrangement it's around 200ms, if I'm sitting in a farfield arrangement it increases to around 300ms. They're probably a touch on the low side, and if I were doing things again I'd probably choose corner traps faced with a membrane or diffuser panel to reflect more secondary reflections. I think a reverb time of around 350ms-400ms would be the sweet spot to aim for.

This has been exactly my experience, around 300-400. I do intend to get the range limiter and scatter plates with my soffits to reduce what you mentioned.

PS - An interesting side note, I've recently been to two concerts (A Tribute To George Michael - at Glasgow Royal Concert Hall) and (The Eagles - at the SSE Hydro), and in both cases I really struggled to get to grips with the sound of the kick drum reverberating around the venues like a ricochet. It makes me laugh when I read about pfm'ers wishing to make their systems sound like a live music venue, each to their own I suppose!...

I could not agree more. Its never computed for me. I love a good soundstage and ambience as the next guy. But id rather the reproduction system play back what was intended by the engineer. Whether thats a dead but clean sounding source or spacious reverb. The same happens with video reproduction and everyday TV filters. Where many want to see the jaw dropping peak brightness and colors by using dynamic picture filters. But realistically and ideally you want the most accurate, naturally reproduced filters.

 

[DANOFDANGER]

And some full range results.

Blue - no treatment, turquoise - two soffits, red - four soffits.

No treatment

There seems to be a difference down to 3kHz but not much after that. These are GIK soffit bass traps without limiters - they weren't available when I bought them.

Where do you live that GIK is not easily available? There may be other options. It is possible to make these things yourself. All they are is a wooden frame with mineral wool inside and covered in a certain type of cloth. They don't look too difficult to make providing you have the space and protections against the unpleasantness of working with mineral wool. There's plenty of advice if you go down this road.

Thanks so much for this, its exactly what i need to asses this for. I am in NZ and everything we import is much more expensive than the rest of the world. My note 9 which would cost around $1350 in the states. Cost me $2000 for me. Half the cost of getting the gik soffits for me is in shipping and exchange rate difference (damn you guys "shakes hand").

 

[Hipper]

As well as the twenty-one Soffit Bass Traps, in the four wall-wall corners and the four ceiling -wall corners, four Monster panels on the front and back walls plus two 242 panels that are meant to stop side wall reflections, which I've found I don't like.

As I said, probably over the top but I like it. This evolved over fourteen years!

 

[Hipper]

Thanks so much for this, its exactly what i need to asses this for. I am in NZ and everything we import is much more expensive than the rest of the world. My note 9 which would cost around $1350 in the states. Cost me $2000 for me. Half the cost of getting the gik soffits for me is in shipping and exchange rate difference (damn you guys "shakes hand").

Have you got no NZ producers. I believe there are some in Australia - might that be cheaper?

This is an Aussie forum that seems friendly:

https://www.stereo.net.au/forums/forum/222-room-acoustics-construction-and-design/

I could not agree more. Its never computed for me. I love a good soundstage and ambience as the next guy. But id rather the reproduction system play back what was intended by the engineer. Whether thats a dead but clean sounding source or spacious reverb. The same happens with video reproduction and everyday TV filters. Where many want to see the jaw dropping peak brightness and colors by using dynamic picture filters. But realistically and ideally you want the most accurate, naturally reproduced filters.

Unfortunately there are inconsistencies in the production of music recordings, both in the equipment they use, their studio performance, and their own preferences, especially it seems with pop music. So as far as I can see there isn't an ideal arrangement that suits all music. My aim is to get some sort of basic standard, then perhaps using an equaliser like tone controls and just make two other settings that deal with those albums with weak bass, and those with weak treble.

 

[ToTo Man]

As well as the twenty-one Soffit Bass Traps, in the four wall-wall corners and the four ceiling -wall corners, four Monster panels on the front and back walls plus two 242 panels that are meant to stop side wall reflections, which I've found I don't like.

As I said, probably over the top but I like it. This evolved over fourteen years!

I was going to say.... I'd need to take out a bloody mortgage to afford 21 Soffits in a single purchase! Were GIK around as long as 14 years ago? I thought I was a fairly early adopter in 2013!

Would you might uploading an RT60 graph of your system post-treatment? I'm not used to the spectrogram format, - why is there a negative time axis?

 

[Hipper]

I've no real understanding of RT60 plots.

Here are the before and after graphs: green - Totp, turquoise - EDP, black - T20, purple - T30:

The negative on the Spectogram is noise from road traffic - I live on a High Street. Any sound produced before the REW signal will show up. If you have a hum in your system it will also pick that up - I had one a while ago which was clearly at 150Hz.

Actually I have exaggerated. I've just looked things up and this is my history. I bought some good gear in 2004, then in 2006 I wanted better speakers. They sounded good round my dealers house but were awful here no matter what we did. He suggested room treatment, so he's the cause of all this activity ever since - measuring, positioning, more measuring etc. etc.. First I got Auralex foam and thought that did the job. I also got interested in equalisers and eventually bought the Behringer DEQ2496. Realising foam wasn't good enough (only going down to 125Hz) I first bought GIK stuff in 2013.