Room Treatment Advice

[elangoas]

I am in no hurry. Would like to figure out and cut/ make holes in walls once.

Provisionally I think that tube traps to cut the lowest of my length/ width modes, (probably placed in the corner behind either speaker, they are velocity absorbers after all ) is what think will be my most productive option. If I can cut this modal frequency I will be able to reduce the amount of attenuation that Dirac has to put in and get slightly higher listening levels (which I miss occasionally)

Practically, you may not be able to tame below 80Hz with absorption, but may be some treatment can reduce the level of the peaks.. I was referring to the same idea, few posts back.. Having abt 3ft thick trap for the width of the room, high on front wall near ceiling..

My issue right now seems to be tacking the fundamental modes with trapping if that is possible

From the images you have shared of your room, possible areas places where you can have treatment at the same time aesthetically and not eye sore..

1) The wall behind the speaker and above the door, until ceiling.. Guess you must roughly have 3ft height, if you are able to utilise that area with thick traps, should help..

2) If you can make a look-alike of the whole TV unit table and fill with absorber?.. I guess it should be abt atleast 2 (H) x 2 (D) x 6 (W) ft..

Also I cannot have a rug/ carpet in my room

@sud98 I think the rug, carpet treatment will not help much as they absorb the high freq and does nothing to the bass (Bcoz of wavelength theory)..

 

[elangoas]

I never said that, what i said was do not directly suspect the room and start treating the room. The problem could be elsewhere - viz.amplifier, IC, speaker cables and speakers. Once you have ruled out everything finally comes the room treatment.

He already has some niche gear at the moment.. I think, even if he changes the whole set-up and get fresh equipmet and put the speakers at same location, the bass issues will remain the same..

If you are 80% satisfied with the setup, then only balance 20% can be achieved only by understanding your speaker and proper placement of the speakers in the room. Check if some other speakers sounds ok in the room.

I too was of the same understanding until sometime back, that change of speakers might do the trick.. But I guess not.. This is something related to room resonance and will be identical for most speakers..

I think in addition to the reading, practical approach of measuring and listening and correlating the findings are more easy than just reading and digesting.

yes.. You are right.. I missed to add these points..

In an ideal speaker, the SPL phase will vary from say around 20Hz to 20KHz from +180 deg to -180 deg and 0 deg will be around 1KHz. The minimum phase of such a system will vary from +180deg and around 300Hz onward till around 15KHz stay at 0 deg without any phase shift inbetween. The gated response of such a system will show the excess phase at exactly 0 deg throughout.

If in the above speaker you happen to add a subwoofer to take care of freq below 80Hz, but this subwoofer is not a minimum phase design, then it will interfere with the low frequency of the full range driver and cancel out the bass respsonse. Hence its very important to know the minimum phase response of your front speaker to integrate it effectively with the subwoofer. If your front speakers are having a minimum phase of around 40 deg, then it will be wise to have your subwoofer phase control also set to 40 deg so that cancellation of common frequency is minimum at the sweet spot.

Thanks for the detailed explanation.. I will need your help/inputs, with my room response where i have subs.. I don't want to barge his thread..

Ears can easily diffrentiate beween 80Hz and 40Hz. You can try playing a 40Hz and a 80Hz single sine wave and check out for yourself. When you check the FR curve you need to check at which frequency there is a room gain and correlate with the larger room dimension. Most standing wave frequency can be attributed to the larger room wavelength (atleast in my room). Checking spectogram can also be useful here to check the frequency where the room dictates the boom.

What i meant was, when music is palying, it is hard to differentiate between bass on which is resonating..

Isn't taking a single measurement easier than playing multiple sinewave and analysing by ear?.. At the end of the day, measurement is ideally needed to correlate..

 

[sound_cycle]

Practically, you may not be able to tame below 80Hz with absorption, but may be some treatment can reduce the level of the peaks.. I was referring to the same idea, few posts back.. Having abt 3ft thick trap for the width of the room, high on front wall near ceiling..

From the images you have shared of your room, possible areas places where you can have treatment at the same time aesthetically and not eye sore..

1) The wall behind the speaker and above the door, until ceiling.. Guess you must roughly have 3ft height, if you are able to utilise that area with thick traps, should help..

2) If you can make a look-alike of the whole TV unit table and fill with absorber?.. I guess it should be abt atleast 2 (H) x 2 (D) x 6 (W) ft..

I have a different philosophy / angle of attack. I can only do velocity based treatments with my DIY skills/ budgets. The positions where these would work best to combat LF are in the corners. All the ceiling corners in my room are load bearing beams. I don't want the onerous and possibly futile chore of explaining holes in concrete to a prospective buyer some years down the road, and would rather live with somewhat poor audio, instead.

The other issue is that Chunky traps would need to be quarter wavelength at their thickest and my problem frequency - the modal ones you pasted - are too low to do anything meaningful about. These were the reasons why I was completely convinced to pony up for a rather expensive Dirac license even though the wife thought (past tense ?) me to be completely bonkers.

I can do tube traps that I place on the floor and worst case throw away if it does not work. I sadly cannot do a false ceiling

I did not show it in the pictures but I have foam diffusion that covers the TV and also the space above it. In yesterday's listening session we were running Roon remote on a phone/ laptop and not using the display for much of the time. All three of us noted the difference the diffusion made to focussing the sound stage

ciao
gr

 

[sud98]

What are the alternatives you suggest ?

I have no possibility (no funds to change house , no know how or DIY ability to get tuned membrane traps and no space if I did get past that)

My major tools (cheap and easy) is absorption.

Consider now that 94 Hz problem. Let's say the speed of sound is 340 m/s. The wavelength is 3.6170212765957 m.

ciao
gr

Would you be open to have a diffusor in the back of the wall? Since you are facing a null, my guess is that its caused by the back wall reflection for which a diffusor may be more effective than adding bass traps.

 

[Hari Iyer]

Room dimensions, 24 x 10.5 x 10 feet

calculated from dipole calculator
Dipole speaker (center front) to a side wall: 35.88 " actual is different (I have to re measure), I could not have them that far out from the side walls in my room, it is the max practicable at the moment
Dipole speaker (center front) to rear wall: 74.16"

I have my listening position ~.38 of room length from the back wall ~ 9'

I have cross checked the "eared" best position for bass with REW/ RTA (and also around the listening position). The null is there before correction. An exercise to be completed is to verify at the wall behind the speakers. At the moment I am convinced that it is not something that I can solve with positioning. But conviction does not mean a closed mind

will see if i can figure out and improve the graphs

ciao
gr

Thanks for the details.

As can be seen from your Dirac measurements, the boom at 48Hz can be correlated to the room length of 24 feet (Wave length 731cm). Nothing much can be done about this other than absorbing them boom.
The distance of 74.16" from the rear wall gives us a frequency of 182Hz below which will hit the rare wall and add up with the front. You need not do anything to this too.
The distance of 35.88" to the sidewall is a bit of concern to me as frequency above 376Hz gets cancelled from the front and the rear. You can try avoiding this by reducing this distance to almost "Zero" for testing. Yes - you need to move both the left and right speaker very close to the left and right wall (as close as 1") to prevent the cancellation of front and back wave. This will reinforce the critical mid-bass which is missing in your Dirac measurement. Post a measurement once you have done this.

Cheers,

 

[elangoas]

I can do tube traps that I place on the floor and worst case throw away if it does not work. I sadly cannot do a false ceiling

Ok.. Understand the limitations of Living room treatment..

 

[sound_cycle]

As can be seen from your Dirac measurements, the boom at 48Hz can be correlated to the room length of 24 feet (Wave length 731cm). Nothing much can be done about this other than absorbing them boom
<snip>
The distance of 35.88" to the sidewall is a bit of concern to me as frequency below 376Hz gets cancelled from the front and the rear. You can try avoiding this by reducing this distance to almost "Zero" for testing

I agree with the first one, the second I missed. The maggie guideline is that the between tweeter distance should be .6 to 2/3rds of the distance to the LP. I might just have wiggle room to move a foot or so back. This suggestion is easily implemented and tried out, will do this in the evening.

Would you be open to have a diffusor in the back of the wall? Since you are facing a null, my guess is that its caused by the back wall reflection for which a diffusor may be more effective than adding bass traps.

Behind the speaker you mean ? People use diffusion between the speakers to improve dispersion and have a level of liveliness in the room. I have foam diffusors there.

My understanding is that when low frequencies are attenuated in a room, the cause is (always ?) canceling reflections. The easy fix, DIYable and effective solution is squashing with absorption - if one can have the space for quarter wave thickness. It that is realizable the frequency response within the room improves. Diffusion redistributes the energy, will not solve this issue. Let's say we can have a well depth of about 40 cm (that's alreay a foot deep!!) it would be ~800 hz. Lower requires a lot of diffusor depth, and diffusing bass frequencies may not be so useful anyway. You need to be 1.5x away from the largest wavelength for a diffusor to be effective. For the frequencies such as the null causing ones in my issue, I would be halfway across the neigbours living room

ciao
gr

 

[sud98]

I was actually referring to the space behind your listening area.

See if these two links help you
https://danylastchild07.files.wordp...r_j-_cox_acoustic_absorbers_and_diffusers.pdf
http://arqen.com/sound-diffusers/

 

[sound_cycle]

Thanks for the details.

As can be seen from your Dirac measurements, the boom at 48Hz can be correlated to the room length of 24 feet (Wave length 731cm). Nothing much can be done about this other than absorbing them boom.
The distance of 74.16" from the rear wall gives us a frequency of 182Hz below which will hit the rare wall and add up with the front. You need not do anything to this too.
The distance of 35.88" to the sidewall is a bit of concern to me as frequency above 376Hz gets cancelled from the front and the rear. You can try avoiding this by reducing this distance to almost "Zero" for testing. Yes - you need to move both the left and right speaker very close to the left and right wall (as close as 1") to prevent the cancellation of front and back wave. This will reinforce the critical mid-bass which is missing in your Dirac measurement. Post a measurement once you have done this.

Cheers,

Cardas (the arrangement I had posted earlier (the centre is 25" from the side wall, that's 10" less than the Cardas recommendation)
The zero distance from side wall

Sticking it to the side wall did make the two channels very much alike. The measured null, as you predicted, is gone.

The tweeters were now an additional foot apart. the phantom centre was okay, the LEDR over track behaved fine, the sound stage had moved further back. But the son and I both subjectively felt that the Dirac-ed Cardas arrangement sounded better. The sound and tonality is somehow fuller, nicer. This does not make sense, we should like the zero distance arrangement per the measurement, what else besides Dirac is to be considered ? Intriguing.

A thing to try, is to flip the panels ie, get the tweeters "outboard". That would get the tweeters against the wall. Will do that this weekend.

ciao
gr

 

[tuff]

Magnepan recommends tweeters on the outside to widen the sweet spot. As far as rugs/Carpets go, they don't work for planar speakers well. Also there is not much side reflections as they radiate sound straight forward compared to dynamic speakers that radiate in a cone shape. Most conventional dynamic speaker treatments do not work on Magnepan. From everything i have read on various forums about Magnepans, the less you have the better results one gets. To improve imaging , skyscraper diffuser's on the front wall work really well. I am planning on making one using balsa wood.

 

[sound_cycle]

@tuff I've tried having the tweeters outboard in the first arrangement iterations. not by design, I must admit I was in such a hurry to get feet on and hear them that I neglected to look at serial numbers. Presently I find having them on the inside is nicer imagingwise. I would love to have skylines, on the wall between and behind the panels. The cost and a 4K TV come in the way. I've kind of fixed that with some foam diffusion, which is way better than flat shiny glass (ofc it would pale to nothingness in relation to a proper 2D QRD). However my problem frequencies are in the lows and if I had a QRD it would have to have Antilla sized skyscrapers.

I spent some more time scouring the 'net and found this thread. The problem is very similar to what I face. The cause is the room mode. The fix was in tweaking position to Limage/HK and DSP. I have not figured a way to get REW to measure with Dirac running. I cannot pull out the speakers much more into the room.

@Hari Iyer It is a modal issue. Bringing the panels closer to the walls substantially changes the reflection pattern. I've just pulled them into a different orientation heard two tracks "cottage for sale" (Flack) and "ride across the river" (Straits) and am gobsmacked. Not enough time for a measurement as I rush headlong to show shave and shove myself into 47130 @ 0740, maybe I will even make it. I will get REW and measurements later this evening. Thanks though, that idea will get me somewhere, even if my post just before this one had not quite realized it

ciao
gr

 

[sound_cycle]

Per the quarter wavelength calculation, the trap has to be 4ft thick.. Ofcourse 4ft traps in a living room isn't possible and wouldn't look good.. But a 2 ~ 3 ft thick trap might be able to help to an extent, somewhere where the frontwall meets the ceiling..(Entire width of the room)

https://www.acousticfields.com/schroeder-frequency/

Schroeder tells us that the room is really two parts, and that the energies, the problems and the issues that each part has are completely different. These two parts are the resonator and reflector.

For small rooms it is typically between 100 and 200 Hz (can be calculated using amroc for example) Implications, anything less than 200 Hertz has to have one kind of treatment and above that another type of treatment. The solutions lie in figuring out where in the room are we going to have our high pressure and where we are going to have our reflection issues? Tech for the resonator part or the wave part or the low frequency part of our room: Diaphragmatic, membrane, Helmholtz. Diaphragmatic. For reflections absorption and diffusion.

FM Hari's solution was redirecting the energy from the back of the planars into the side wall, causing it to bounce elsewhere and not excite the room modes. What I heard this morning had the ooph and depth - without DRC, so I am quite eager to get home this evening and see if my measurement match my listening impression

Then there are tube traps or DRC

What I did with the low end was the DRC bit. But here is the physics as to why, beyond thickness and practical considerations, absorption is not always the answer, true it is easy and at hand.

Will see after the REW measurement session this evening.

https://www.sonible.com/blog/room-modes/ has a nice calculator and some tips on finding the listening spot. What I did with REW/ RTA was just this with a screen and no assistant


PS: Mods, I could not multi quote this because I answered it much later than my previous post on this thread


ciao
gr

 

[elangoas]

https://www.acousticfields.com/schroeder-frequency/

Schroeder tells us that the room is really two parts, and that the energies, the problems and the issues that each part has are completely different. These two parts are the resonator and reflector.

For small rooms it is typically between 100 and 200 Hz (can be calculated using amroc for example) Implications, anything less than 200 Hertz has to have one kind of treatment and above that another type of treatment.

Looks like smaller rooms have more room modes.. My room has 147 all possible modes .. Also Schroederfrequency is at 238Hz.. (freq range is higher compared to bigger rooms)..

Interesting above links, with 3-D illustration of room modes.. Helps to perceive the room modes..

Absorption area required for my room is approx 125 Sqft Sabine, which i think am fairly close to what i planned for..

I think this resonators are basically absorbers and for full problematic freq absorption without using any EQ.. They are huge in size due to dimensions..

An absorber before any room boundary seems better.. Ofcourse the thickness, area differs based on one possibility and the problematic freq in the room..

Will see after the REW measurement session this evening.

So you are trying for speakers best possible location in the room for improvement in response and then approach treatment..

 

[sound_cycle]

I think this resonators are basically absorbers and for full problematic freq absorption without using any EQ.. They are huge in size due to dimensions..

An absorber before any room boundary seems better.. Ofcourse the thickness, area differs based on one possibility and the problematic freq in the room..

No.

Below the Schroeder frequency absorption may not be a good fix for a number of reasons including that it might be the wrong thing to consider.

For reflections broadband panels are a good (but not the only) fit. For resonant low bass it would be either velocity- or the pressure- based treatment. The pressure based treatment solutions would need much thinner panels compared to their absorption cousins for the frequency they are targetted at. They are not easily DIYable and are also fairly narrow in the range of frequencies they address. These "resonant absorbers" are vibrational system that “runs” on sound pressure. So you use tar paper inside a cabinet (interesting aside this was apparently developed at AIR - or so the BBC write up i found on the 'net says). This works like mass vibrating against a spring. The mass and stiffness of the spring, are the controls to tune the resonant absorber to the desired modal/ resonant frequency to squash. Treatments with Helmholtz and membrane are effective, useful and expensive. Trained, sexy looking assassins if you will

The velocity ones are the cheap, easy, Gorakhpur ka katta things which are rather indiscriminate in what they do. It works but is certainly not the best. And sadly it kills friendlies in blue too - the shimmer you spent your money to get, the "air" we want to hear will all get sucked out if you over do it. And it is very easy to overdo.

So you are trying for speakers best possible location in the room for improvement in response and then approach treatment..

Yes ofc.
Once banged in and fixed, treatment is not easily (or cheaply) reversible and the time to regret errors is long and the reminders frequent.

I tried this

You can try avoiding this by reducing this distance to almost "Zero" for testing. Yes - you need to move both the left and right speaker very close to the left and right wall (as close as 1") to prevent the cancellation of front and back wave. This will reinforce the critical mid-bass which is missing in your Dirac measurement.

out last evening. And thought it through a little better this morning just before leaving for work and posted

FM Hari's solution was redirecting the energy from the back of the planars into the side wall, causing it to bounce elsewhere and not excite the room modes. What I heard this morning had the oomph and depth - without DRC, so I am quite eager to get home this evening and see if my measurement match my listening impression

That arrangement is rather unusual. Being that close to the wall (6" was the mornings expt) is what every Maggie placement advice thread warns you against. I did not even consider anything within 18" of the wall in my previous arrangements, and I did not think I'd need somewhat drastic toe-in. It sounded rather good with the two tracks I heard, I would like to see how it measures.

ciao
gr

 

[elangoas]

Below the Schroeder frequency absorption may not be a good fix for a number of reasons including that it might be the wrong thing to consider.

I guess thickness of the absorber required must be one of them ( i mean for freq below 80hz freq)..

When reading thru once of the threads on gearslutz, one member mentioned that Peak absorption for a frequency happens at 1/4th of wavelength thickness.. But, absorption starts to happen when the thickness of the absorber is 10% of the wavelength of the freq.. No idea if this a validated claim, but just though of sharing this..

Treatments with Helmholtz and membrane are effective, useful and expensive. Trained, sexy looking assassins if you will

Ha ha.. Good name..

I would like to see how it measures.

Hope for the best.. Please share the graphs one below the other to relate the difference that the speaker-positioning brings in..

 

[Hari Iyer]

Cardas (the arrangement I had posted earlier (the centre is 25" from the side wall, that's 10" less than the Cardas recommendation)
The zero distance from side wall

In my recommendation the hole from 75Hz to 100Hz is better controlled

 

[sud98]

Looks like Hari's recommendation worked for you atleast from the null perspective. BTW, what smoothing are you using to those graphs? Plus are you measuring it at a very high SPL?

 

[Hari Iyer]

This is how i approached my speaker positioning problem with REW,

Initial position:
40" from front wall, 18" from both left and right side wall, speakers around 6.5 feet away from each other.

https://imgur.com/a/ApnKPzG

You can notice the dip in the mid-bass from 75Hz to 200Hz. This was clearly because of acoustic short circuit from the front and back side of the speakers.

2nd position:
72" from front wall, 2" from both left and righ side wall, speakers around 8.5 feet away from each other.

https://imgur.com/J5xV3Uk

You can again see the dip in the mid bass from 75Hz to 200Hz and the boom at 40Hz and 75Hz.


This made me investigate further if there is anything wrong with the speaker design as the acoustic short circuit was removed by moving the left and right speaker very close to the wall. I did one more measurement with microphone at 1 meter distance and at 45 deg off-axis and this is what i got.

https://imgur.com/6I1vbj8

Analysis of the above gave me an indication that the dip from 75Hz to 200Hz was not because of speaker design but the position of the speaker in the room. After doing some Wavelength and front wall distance calculation, i noted that the dip was maximum at 120Hz and i will need to move the speaker at a distance twice the octave of that ie.240Hz. This gave me a distance of around 52" and also i now moved the left and right speaker just 8" from the left and right side wall, which is also the size of my full range driver. This was decided because at 1028Hz, the full range driver will start beaming and below this frequency it will not. The measurement gave me the below final result at listening position,

https://imgur.com/bETZNEI

 

[sound_cycle]

Looks like Hari's recommendation worked for you atleast from the null perspective. BTW, what smoothing are you using to those graphs? Plus are you measuring it at a very high SPL?

I did not apply any smoothing.

No, to the high SPL.

Last night I flipped the tweeters to the outside and did not like the results, and then could not get back to the "What I heard this morning had the oomph and depth - without DRC". I had not marked them carefully enough (had misplaced my sticky tape and used a less reliable method Will be back to dancing around with the tall thin beauties this evening.

This is how i approached my speaker positioning problem with REW,

Thanks for this illustration.

Will repeat and update

ciao
gr

 

[elangoas]

This is how i approached my speaker positioning problem with REW,

Initial position:
40" from front wall, 18" from both left and right side wall, speakers around 6.5 feet away from each other.

2nd position:
72" from front wall, 2" from both left and righ side wall, speakers around 8.5 feet away from each other.

72" from front wall?.. That is 6ft.. What are your room dimensions?.. Where is your listening position in the room ?..