Ran REW, now what?

[sud98]

I ran the REW with the attached mdat. Can anyone help me analyse the same and give me inputs? Would I need specific room treatments?

https://drive.google.com/open?id=0B8SRo782zUzxVzlQeHF1YldGRnM

I ran it using a laptop HDMI output and a kind FM's UMIK-1 USB microphone.

I have thick carpet on the floor and acoustic tiles in the ceiling and heavy duty recliners on one end.

The side walls are bare and the space behind the speakers also bare.

Not sure if they need just bass traps or absorbers so if you can understand the reading and analyse, it would be of help.

 

[Hari Iyer]

Can you copy the image and upload, the attached file cannot open in a mobile device unless you have a mobile app for REW.
Thanks

 

[sud98]

Below are the readings of each speaker



and the waterfall of the same.


There is a sharp rise in 37Hz which I will need to handle through bass traps.

The dips are also a problem which I will need to handle through some eq or treatments.

 

[Hari Iyer]

For frequencies below 100 Hz you will need to treat the front or the rear wall to prevent room modes and the associated standing waves with a thick absorbent/ bass trap.

For mid-bass, mid and higher frequency try using a diffuser or adsorbed only in the early first reflection points using the mirror technique from your usual listening position.

Imo, the peak at the high frequencies seem to be more of a resonance issue in the speaker than a room issue. If you can also measure the speaker impedance then it can be further scrutinized.

 

[elangoas]

Below are the readings of each speaker

View attachment 24213

and the waterfall of the same.
View attachment 24214

There is a sharp rise in 37Hz which I will need to handle through bass traps.

The dips are also a problem which I will need to handle through some eq or treatments.

Am novice to measurements & room treatments.. A learning experience for me here..

i believe you have a single subwoofer..Placement of subwoofer might change the peak at 37Hz ? Where have you placed the subwoofer in the room?

For frequencies below 100 Hz you will need to treat the front or the rear wall to prevent room modes and the associated standing waves with a thick absorbent/ bass trap.

I have read bass trap would need to be in the corners of the room & would be huge to accomodate in a room..

Would a 2nd subwoofer help him in this regard..

 

[sud98]

Am novice to measurements & room treatments.. A learning experience for me here..

i believe you have a single subwoofer..Placement of subwoofer might change the peak at 37Hz ? Where have you placed the subwoofer in the room?



I have read bass trap would need to be in the corners of the room & would be huge to accomodate in a room..

Would a 2nd subwoofer help him in this regard..

Actually if you see the first graph it has the graphs with and without the sub and the 37db bump is there in all cases. So its a room mode and not linked to the sub or speaker placement.

The second sub will help in the subsequent dips and evening out the graph. The second sub could also help in lowering the bump but the room mode being that strong I will need to use traps.

 

[elangoas]

Actually if you see the first graph it has the graphs with and without the sub and the 37db bump is there in all cases. So its a room mode and not linked to the sub or speaker placement.

If you were to use a crossover in your AVR say 80hz/100Hz for all channels, that should get directed to sub..Which then, you can try re-position in your room for a better response (if possible)..

The second sub will help in the subsequent dips and evening out the graph. The second sub could also help in lowering the bump but the room mode being that strong I will need to use traps.

If you could take measurement after re-positioning the sub, i think you will have more clear picture whether bass trap/ 2nd sub will help..

 

[Hari Iyer]

IMO, I doubt if adding a 2nd sub would resolve the issue as this is room mode that needs taming. Careful placement of the Speakers can help reducing the effect. Bass traps are good if there are boom, but room modes will require absorption in either one of the rear or front wall corners or wall to cut the standing waves. As per calculation, for getting a room mode at 37 Hz require the room to be atleast 30 feet long.

I would suggest, you should now try to place the speakers and try listening to them from your usual listening position and adjust for no boom. You can use the one-on-one third rule where the speakers can be placed in the first half i.e. 1 to 10 feet, you can listen from 11 to 20 feet and from 21 to 30 feet should be for rare wave reflection. Pls. Confirm the area of your room too.

 

[sound_cycle]

I have read bass trap would need to be in the corners of the room & would be huge to accomodate in a room..

Would a 2nd subwoofer help him in this regard..

You would need to be 1/4th the thickness of the frequency you are trying to address. Below ~ 400 Hz in an average room that is usually not acceptable But that does not mean all is lost, you have other options. DRC, membrane traps and others I don't know about. IMHO adding additional energy to the room is hardly a solution.

I will try and redo the plot at home. From what I see all the "hills" are marching upto 300ms and beyond, which suggests that there is way too much energy bouncing around in the (completely untreated ?) room.

The 37Hz is ***probably*** spurious unless the speakers have that bass extension (and I ofc do not know what they do). If they were like my speakers which go down only to 45Hz, I'd think that it would be something else, a refrigerator or some other appliance.

Now I don't claim ***any*** expertise in this but I will try and regenerate the waterfall plot from the .dat OP had posted. I think there should be a better view of things from that data.

Very curious. Why do you think an additional sub would help here ? (I know tastes vary but I would also ask why even a sub at all but that is not the OPs question)

ciao
gr

 

[elangoas]

IMO, I doubt if adding a 2nd sub would resolve the issue as this is room mode that needs taming.

Am guessing a 2nd sub might help to reduce the peak fairly without bass traps..

Pls. Confirm the area of your room too.

Room dimension & his present sub-woofer location should give more insights for further re-positioning (if that might help)..

 

[elangoas]

You would need to be 1/4th the thickness of the frequency you are trying to address.

37/4 = 9.25.. Does this mean the bass trap has to be 9.25 inch thick?

Very curious. Why do you think an additional sub would help here ? (I know tastes vary but I would also ask why even a sub at all but that is not the OPs question)

From the dual subwoofer articles that i have read, i was saying a 2nd sub in a different location in a room would help bring down the peak..

A measurement after re-positioning the 1st sub should give a better view..

Would you share your room response say below 200Hz.. Just to get an impression of bass in your room..

 

[sound_cycle]

37/4 = 9.25.. Does this mean the bass trap has to be 9.25 inch thick?



From the dual subwoofer articles that i have read, i was saying a 2nd sub in a different location in a room would help bring down the peak..

A measurement after re-positioning the 1st sub should give a better view..

Would you share your room response say below 200Hz.. Just to get an impression of bass in your room..

Umm, Hz is a unit of frequency (cycles per second) and not wavelength.

I've been meaning to do that REW through DIRAC measurement someday.

The dual sub is not always a solution - I don't have a sub, what should I do about room modes ? Are there no issues above the range you are run your sub in.

ciao
gr

 

[elangoas]

Umm, Hz is a unit of frequency (cycles per second) and not wavelength.

Sorry, if i didn't get what you were conveying.. Approx, what should be the size of bass traps to address 37Hz peak issue...

I've been meaning to do that REW through DIRAC measurement someday.

room measurement before Dirac, should help identify the bass behavior..

The dual sub is not always a solution - I don't have a sub, what should I do about room modes ? Are there no issues above the range you are run your sub in.

Based on the above, you can then consider workable solutions..

 

[Hari Iyer]

The absorbing material needs to be thick enough for absorbing the LF energy. Around 2" to 4" high density should be good enough. It would be needed in almost the entire front or the rear wall to cut-off standing waves. Not required in both the walls but only one.

 

[sound_cycle]

Sorry, if i didn't get what you were conveying.. Approx, what should be the size of bass traps to address 37Hz peak issue...



room measurement before Dirac, should help identify the bass behavior..



Based on the above, you can then consider workable solutions..

My apologies for being blunt, but what really is the point you are making ? And to whom.

If you want to discuss absolute basic physics ie the relationship between frequency and wavelength may be a separate thread or some basic reading is in order.

Dirac correction is based on multiple measurements.

But these are not OPs interests.

Thanks

Ciao
GR

 

[elangoas]

My apologies for being blunt, but what really is the point you are making ? And to whom.

If you want to discuss absolute basic physics ie the relationship between frequency and wavelength may be a separate thread or some basic reading is in order.

I repeat, am a novice with room measurements & treatments..

You had mentioned this in your post..

You would need to be 1/4th the thickness of the frequency you are trying to address.

I was trying to interpret it..1/4th thickness of the frequency..The OP measurements had a peak at 37hz.. So was doing the math (37/4= 9.25) and seeking clarity if the thickness of the bass traps should be 9.25 inches.. If my interpretation is wrong, help me correct it..

Dirac correction is based on multiple measurements.But these are not OPs interests

Agreed.. Since you have microphone to take measurements, was requesting you to share room response before Dirac correction, to see untouched bass response only as information..

Share, only if you like to, else please disregard my request..

 

[sound_cycle]

Below are the readings of each speaker

There is a sharp rise in 37Hz which I will need to handle through bass traps.

The dips are also a problem which I will need to handle through some eq or treatments.

Redid your waterfall plot. That does not look too bad to me.

https://photos.app.goo.gl/iaQgudkVz3NnFn9y2

I've scaled it to about 30 db below the max, and that is probably not loud enough to be heard.

Having said that, the worst issue - the hill that marches right up to all most 450ms is at ~ 60 Hz and by 120 Hz or so the ringing seems to be below 350 ms.

ciao
gr

 

[sound_cycle]

I was trying to interpret it..1/4th thickness of the frequency..

Thanks for pointing out that brainfart. Wavelength not frequency

ciao
gr

 

[sdurani]

Actually if you see the first graph it has the graphs with and without the sub and the 37db bump is there in all cases. So its a room mode and not linked to the sub or speaker placement.

Room modes can be cancelled by sub or speaker placement, so they are linked. So is listener placement. Can you measure a couple feet forward and rearward of your listening position to see if the large peak changes in size or frequency? Also, what are your room dimensions and where are you sitting relative to the front wall?

 

[sud98]

Room modes can be cancelled by sub or speaker placement, so they are linked. So is listener placement. Can you measure a couple feet forward and rearward of your listening position to see if the large peak changes in size or frequency? Also, what are your room dimensions and where are you sitting relative to the front wall?

I tried to change the position, checked each speaker at a time still the same. I even ran Dirac, with similar results.

The room dimension is 15'2"*11'10"*8'9"

The 37hz approx. To a wavelength of 30feet which I thought should be altered if I change the placement but no luck.

The only thing that helped is loading the filters onto Dirac processor and then running rew. It then controlled a major amount of the dips and peaks.

Does that mean I need to use parametric eq to manage this besides traps and diffuser?

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