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Treat ringing at 37Hz with Helmholtz absorber?


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looking for info/experience with Helmholtz absorbers and treating ringing. Is it the right absorber for the job? will it work? 

 

this it the fr decay

image.png.84dad6c1f00f858d6c6e8348b33d0b60.png

 

this is the room from https://amcoustics.com/tools/amroc?l=570&w=440&h=270&re=EBU listening room

 

image.thumb.png.f36086014b83fa7342ffc6038d0a1020.png

 

and potential designs for helmholtz from http://www.acousticmodelling.com/helmholtz.php

 

 

 

image.thumb.png.f57f021944df8d3c39070815364aeb62.png

Edited by frednork
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5 hours ago, frednork said:

looking for info/experience with Helmholtz absorbers and treating ringing. Is it the right absorber for the job? will it work? 

 

this it the fr decay

 

image.png.84dad6c1f00f858d6c6e8348b33d0b60.png

 

 

 

Wow!  That indeed is a troublesome spike!  :o

 

Can you tell me how you generate the 'Spectral Decay" plot?

 

In the REW version I'm running, I only see these plots:

 

360661931_REWControls.JPG.8dafa35afad7d168c9ccd909aa9f1b48.JPG

 

Thanks

Andy

 

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42 minutes ago, andyr said:

 

Wow!  That indeed is a troublesome spike!  :o

 

Can you tell me how you generate the 'Spectral Decay" plot?

 

In the REW version I'm running, I only see these plots:

 

360661931_REWControls.JPG.8dafa35afad7d168c9ccd909aa9f1b48.JPG

 

Thanks

Andy

 

Andy, its the decay tab

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42 minutes ago, frednork said:

Andy, its the decay tab

 

Aah, thanks fn.  :thumb:  (I don't get a 'Spectral Delay' heading.  :( )

 

Actually, here is mine:

 

 

1600723683_SpectralDecay.thumb.JPG.87a93a0277053ccda6afd5040146efb5.JPG

 

 

Very different to yours ... and my room is a similar size:  5.8 x 3.6 x 2.7m.

 

I have no idea whether the above shows me I have any issues!  :(  (Whereas your Decay plot clearly showed the large anomaly at 37Hz.)

 

Andy

 

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Your obviously a pipe organ music fiend as that would not present as an issue for the majority of regordings I reckon. My 50hz issue on the other hand dangled beneath the dog so bad that as your aware (and have observed) necitated radical changes to tame.

 

 

 

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1 hour ago, andyr said:

 

Aah, thanks fn.  :thumb:  (I don't get a 'Spectral Delay' heading.  :( )

 

Actually, here is mine:

 

 

1600723683_SpectralDecay.thumb.JPG.87a93a0277053ccda6afd5040146efb5.JPG

 

 

Very different to yours ... and my room is a similar size:  5.8 x 3.6 x 2.7m.

 

I have no idea whether the above shows me I have any issues!  :(  (Whereas your Decay plot clearly showed the large anomaly at 37Hz.)

 

Andy

 

look ok above 1k but what about below 1k which is where problems occur, would be good if you can  adjust the scale to show from 10-20hz up to 20k and on the y axis to show down to about 30db

Edited by frednork
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55 minutes ago, Tubularbells said:

Your obviously a pipe organ music fiend as that would not present as an issue for the majority of regordings I reckon. My 50hz issue on the other hand dangled beneath the dog so bad that as your aware (and have observed) necitated radical changes to tame.

 

 

 

Cant say I notice it that much but the objectivist part of me thinks it might  better if  I fix it!

 

This is yours when on the long wall

 

image.png.cc863a532495285fff709b729d555e2b.png

 

and mine with a similar scale

 

image.png.5cf6ada71984c7e0202287c4aa887168.png

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1 hour ago, andyr said:

 

Aah, thanks fn.  :thumb:  (I don't get a 'Spectral Delay' heading.  :( )

 

Actually, here is mine:

 

 

1600723683_SpectralDecay.thumb.JPG.87a93a0277053ccda6afd5040146efb5.JPG

 

 

Very different to yours ... and my room is a similar size:  5.8 x 3.6 x 2.7m.

 

I have no idea whether the above shows me I have any issues!  :(  (Whereas your Decay plot clearly showed the large anomaly at 37Hz.)

 

Andy

 

Ahh I see you have shown from below 1 k but we just cant see it. you need to change from linear scale to logarithmic on the x axis

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45 minutes ago, frednork said:

Ahh I see you have shown from below 1 k but we just cant see it. you need to change from linear scale to logarithmic on the x axis

 

Sorry about that!  :(

 

I think this is it?

 

 

938883752_SpectralDecay.thumb.JPG.49316abf8ef03a6eb437d9814a304219.JPG

 

 

Looks a lot worse!  :o

 

Andy

 

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8 minutes ago, andyr said:

 

Sorry about that!  :(

 

I think this is it?

 

 

938883752_SpectralDecay.thumb.JPG.49316abf8ef03a6eb437d9814a304219.JPG

 

 

Looks a lot worse!  :o

 

Andy

 

 I could be wrong but it looks like the slices are too short . try to set it up like below for a good comparison to mine  and zoom out  the y axis  till you can see 20 dB.

 

if you hit the controls icon the popup screen on the right top side it will pop up  just copy the settings as on mine.

 

image.thumb.png.79af109bbb53046b13e285c3bb41f2ed.png

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19 minutes ago, Ittaku said:

I have the tunable helmholtz resonators in my room. They do not go down to 37Hz. Lowest setting is 56Hz. So for that particular type of resonator, the answer to your question is no.

yes have looked at those  but alas too small for that design to go that low

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8 hours ago, frednork said:

 I could be wrong but it looks like the slices are too short . try to set it up like below for a good comparison to mine  and zoom out  the y axis  till you can see 20 dB.

 

if you hit the controls icon the popup screen on the right top side it will pop up  just copy the settings as on mine.

 

Thanks, fn.  How about this?

 

29446797_SpectralDecay.thumb.JPG.1fcdcd8e8ea2b9d78c7b7dfd90db6db1.JPG

 

 

Andy

 

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3 hours ago, frednork said:

@andyr looks a bit too different . The whole decay is only about 30db and should be around 60+. Did you hit the default settings button by chance? settings are time slice 50ms window 500, rise time 100 smoothing 1/12

 

Yes, had those settings - as you can see from the below graph.  However, it's possible the smoothing in my previous graph was 1/48?

 

 

 

1715177968_SpectralDecay.thumb.JPG.1af3843494aba5e19e73dc9546609394.JPG

 

 

Andy

 

Edited by andyr
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8 minutes ago, andyr said:

Yes, had those settings - as you can see from the below graph.  However, it's possible the smoothing in my previous graph was 1/48?

Geez you're measuring it loud! You're game.

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20 minutes ago, andyr said:

Yes, had those settings - as you can see from the below graph.  However, it's possible the smoothing in my previous graph was 1/48?

 

14 minutes ago, Ittaku said:

Geez you're measuring it loud! You're game.

Ok   def looks better than mine! but still some ringing at 50. regarding loudness it doesnt make sense. It actually looks to me like  you measured at pretty low volume and then somehow the levels got pushed up to 100. if you look at decay for yours at around 2k over the 500ms its about 45db on mine its about 55db, on dougs its about 65db.

And ambient noise at around 50db thats a noisy room!

 

Edited by frednork
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38 minutes ago, frednork said:

 

Ok   def looks better than mine! but still some ringing at 50. regarding loudness it doesnt make sense. It actually looks to me like  you measured at pretty low volume and then somehow the levels got pushed up to 100. if you look at decay for yours at around 2k over the 500ms its about 45db on mine its about 55db, on doug's its about 65db.

And ambient noise at around 50db thats a noisy room!

 

 

Thanks, fn.  :thumb:

 

Aah, OK - now I see how to interpret the graph.  I presume my decay of 45dB (at 2kHz) instead of yours at 55dB ... means my room is 'livelier' than yours?

 

But which is 'better' - 65dB of decay ... or 45dB?

 

Yes, mine is a noisy room - your level (of 20dB?) is much better!

 

Andy

 

Edited by andyr
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4 minutes ago, frednork said:

good thought but sealed cabs

Fair enough. Mine does a huge jump from when the (closed) sub kicks in at 35Hz and remains high below that. Given the nature of ultra low frequencies I'm not sure it's much of a problem, but sure anything can always be improved upon.

Edited by Ittaku
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2 minutes ago, Ittaku said:

Fair enough. Mine does a huge jump from when the (closed) sub kicks in at 35Hz and remains high below that. Given the nature of ultra low frequencies I'm not sure it's much of a problem, but sure anything can always be improved upon.

yes not the end of the world but just rethinking my treatment and how this might fit in and is it likely to work and worth the effort

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36 minutes ago, frednork said:

yes not the end of the world but just rethinking my treatment and how this might fit in and is it likely to work and worth the effort

For what it's worth, I have a (main driver related) peak and ringing at 56.6Hz and have tuned the varibass helmholtz resonators to that frequency and found their effect to be about 3-4dB attenuation of ringing.

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