REW Graph analysis

[pseud]

Thanks for the detailed analysis and suggestions.

I have contacted GIK even when my house was constructed, unfortunately, their local distributor is not too keen on home setups and keeps suggesting the same options irrespective of the room and the issues.

For the bass traps, I do have someone who has the skills to build it for me. So a separate thread would be great, but I would anyway update myself with the threads in various forums. I have seen the generic bass trap DIY threads in other forums. But not sure how to build it with a specific frequency or a range to be trapped.

 

[pseud]

Also, do you have any suggestions around PEQ?

 

[Matthew J Poes]

Thanks for the detailed analysis and suggestions.

I have contacted GIK even when my house was constructed, unfortunately, their local distributor is not too keen on home setups and keeps suggesting the same options irrespective of the room and the issues.

For the bass traps, I do have someone who has the skills to build it for me. So a separate thread would be great, but I would anyway update myself with the threads in various forums. I have seen the generic bass trap DIY threads in other forums. But not sure how to build it with a specific frequency or a range to be trapped.

There are methods to calculate a tuned bass trap to a specific frequency, however it is tricky to get right. A lot of people who have built these haven’t had a lot of success. This is why I usually suggest buying a tuned bass trap, a theater least you can be sure of its tuning and effectiveness. None the less if you are willing to take the risks, I can try to help with specific tubes trap designs.

Broadband bass traps that rely on a frequency attenuated velocity absorption method are much easier to build. They are basically large rectangular boxes filled with dense fiberglass or minerwool and with a membrane of low density attached to either a face or internally. The placement of the membrane impacts the absorption response in the mid/high frequencies while the membranes density and stiffness effects the boost in LF absorption.

Here’s a picture of a box type bass absorber sometimes referred to as a soffit trap. They are usually used in corners.



The chamber style used in this trap was done because the trap is so deep at 24”. Solid 6lb mineral wool would become reflective to even upper bass frequencies and so not provide much absorption benefit.

 

[pseud]

Thanks MJpoes.

I realised some errors in my setup and switched to getting them right from the driver to win 10 setup. Here is the individual speaker guide. Overall, seems similar, but there are a few differences.

 

[pseud]

Actually, GIK has stopped selling in India and they said they couldnt supply it for individuals. So will have to get it done locally or check for other vendors, although 37hz is far too low for most people. Is it possible that this is a floor reflection and if I raise the speakers, the effect would be reduced?

 

[Matthew J Poes]

Actually, GIK has stopped selling in India and they said they couldnt supply it for individuals. So will have to get it done locally or check for other vendors, although 37hz is far too low for most people. Is it possible that this is a floor reflection and if I raise the speakers, the effect would be reduced?

37 hz is too low to be a floor reflection. It also shows up on the subwoofer yet I assume the subwoofer is not on a stand. Floor reflections typically only show up on your speakers sitting on stands, they are a boundary interference related to the distance to the boundary.

Do you have or can you obtain an eq device? The very low resonances should be addressable with eq.

What kind of materials are used in your house in India? Being in the United States I know what we use here. Those resonances look nearly totally undamped which implies really hard surfaces. It seems like that room just needs some damping more than anything.

 

[pseud]

Do you have or can you obtain an eq device? The very low resonances should be addressable with eq.

What kind of materials are used in your house in India? Being in the United States I know what we use here. Those resonances look nearly totally undamped which implies really hard surfaces. It seems like that room just needs some damping more than anything.

Can you suggest some EQ devices? Also, will software based tools like Dirac also work?

The room is in my basement and built with solid concrete slabs. The side walls are totally bare and half of the back wall, so they would probably the first cause of the issues.

 

[Matthew J Poes]

Can you suggest some EQ devices? Also, will software based tools like Dirac also work?

The room is in my basement and built with solid concrete slabs. The side walls are totally bare and half of the back wall, so they would probably the first cause of the issues.

Minidsp should be available for you. I would check that out. The 2x4hd can be upgrades to include dirac.

Dirac should work well. I have sometimes found that some IIR peq at low frequencies does a better job, but dirac is nearly fool proof and offers great improvements in the upper range too.

If the space has bare concrete slab walls that would explain everything. The room is probably suffering back echo, no? Can you share your RT60 graph. I suspect the room needs some treatment to be improved. Dirac can only do so much.

 

[pseud]

Minidsp should be available for you. I would check that out. The 2x4hd can be upgrades to include dirac.

Would this be the right device https://www.minidsp.com/products/ht-series/nanoavr-hd

I suppose I still need to treat the walls, So while adding corner traps is given, would I need to cover the entire wall with panels or only the early reflection ones.

 

[Lesmor]

Have you considered using an Anti-mode and then running EQ on top of that
I had a 26Hz mode that Audyssey always failed to fully address
I also have a well treated room but it cant really touch the Low end
I bought an Antimode which hit the 26Hz I then ran Audyssey on top I now have the best bass I have ever been able to achieve in my room

 

[pseud]

I am not sure how much the anti mode costs. The ones I googled are as expensive as the minidsp one I put in the link. I would think the PEQ can handle a bit more than the anti mode unless my understanding is incorrect.

 

[Lesmor]

Here in the Uk the antimode costs £304..95 complete with microphone
The mini DSP £102.00
You would need to also add the cost of a UMIC-1 but you might already have that
Its down to preference
For simplicity I chose the antimode and it has performed as advertised

This is my untreated room response

And after adding an Antmode

Finally after Audyssey

 

[Matthew J Poes]

The antimode finds the modes and automatically applies peq filters to knock down the peaks. Because of this it's able to improve the time domain as well as modes typically lie in a minimum phase region and this a reduction in amplitude will also lead to an increase in decay (reduction of ringing).

For someone looking for the simplistic approach a antimode is great.

For someone looking for the best performance and most flexibility the minidsp would offer greater capabilities. It's a manual process however and our need to know what you are doing to use it effectively.

 

[pseud]

I ran REW multiple times in the last week. Initially to test the mic position at 3 feet, but then ran it at the default 1 feet and yet the 37db peak is not prominent (except in the sub) and instead there is now a dip at 55hz.

I tried with different things to understand the issue but cant find the root cause of the change.

Here is the mic with various distances from the back wall

The speakers with mic at 1 feet from back wall

The mdat file with the current drawings
https://drive.google.com/open?id=1zXXi3LwX220_akGskpPQH-5FfOZC41CO

Not sure of the cause and how to handle these dips and whether this is the right measurement.

 

[Matthew J Poes]

All of the peaks and dips are reflections of the low frequencies off of barriers causing interference with the direct signal and other reflections of the bass. The closer you are to a wall the higher bass levels will be but also often the more messy.

Unless you sit against a wall don't worry about the measurement by the walls (unless I'm misunderstanding what you are doing).

I'm not sure I understand how you got these new response curves? The slope from 20khz to 20hz would typically be undesirable for most people. The exact opposite slope is what most people find most compelling. Is this a Dirac corrected response?

 

[John Mulcahy]

Those measurements are from "HD Audio mic input 1", were they meant to be from a UMIK? Appear to have a UMIK cal file loaded. Worth making sure the input signal is actually coming from the UMIK, looks like it may not be.

 

[pseud]

In order to treat the issues in my room, I got some broadband absorbers. Built them around 8 feet tall with 1 feet*1 feet filled with rockwool 48 kg/m3 at the two front wall corner. Also got 4 inch thick panels of 3.5 feet by 2 feet for the front wall.

Post this the new measurements are as below (compared to the old ones)

and the waterfalls

Do I need more absorbers?

For the longitudinal room mode at 37hz, I can build a helmholtz trap or use the minidsp (which I have bought).
Let me know your views.
The full mdat is below
https://drive.google.com/open?id=1SKkeIrOw0PhGVqIPb9_A04BVODuE6AZR

 

[Lesmor]

My first observation is that your speakers appear to be toed out
if so is there any reason for that?
The trends also seem to indicate that there is no room EQ in play?

 

[pseud]

My first observation is that your speakers appear to be toed out
if so is there any reason for that?
The trends also seem to indicate that there is no room EQ in play?

Seems like that in the photos, will check.
I wanted to first check without room EQ and then do the EQ.

 

[pseud]

After PEQ

The waterfall

and the spectrogram

I am sure there would be better filter coeffecients I can use to improve this further.

 

[acangialosi]

Pseud, Matthew, Lesmor, Earl, and of course John, thanks for the really useful discussion and explanation. I’m a complete AV newbie learning REW on my existing Sonos TV setup ahead of purchasing a new home theater. This thread was very helpful at tying together the concepts in the REW getting started docs and other REW tutorials. Thanks!