How to treat nulls

[Jens Eklund]

Originally Posted by Jens Eklund

A dip can be caused by SBIR, a mode (if source and/or receiver is in a node), or simply by the lack of modal support. The first two are quite easily dealt with but the last one is somewhat trickier. If you treat other modes surrounding this gap, the situation will improve since the Q of the other modes will be lower and hopefully fill the gap.

Making sense of modes, standing waves and bass traps

A modal null caused by speaker and/or receiver in a node, is due to destructive interference, so in order fix it; you need to absorb the interfering energy.

[boggy]

Originally Posted by Aaron Rash

........
So in my case the peak at 67hz needs to be treated to fix the null at 90hz. ....

No, if you treat only peak at 67Hz, but nothing else (highQ resonant method) , null at 90Hz will still exist.

[Jens Eklund]

Originally Posted by boggy

No, if you treat only peak at 67Hz, but nothing else (highQ resonant method) , null at 90Hz will still exist.

+1

(Assuming modal null. If due to SBIR, the situation can be quite complex).

[onceagain]

Originally Posted by Jens Eklund

in order fix it; you need to absorb the interfering energy.

So, in Aaron's case, what would be the interfering energy?

[George Necola]

Originally Posted by onceagain

So, in Aaron's case, what would be the interfering energy?

I don't know.. maybe a NASA space satellite.

try to move the speakers around in your room.

[boggy]

Originally Posted by onceagain

So, in Aaron's case, what would be the interfering energy?

It's sound pressure energy bounced from boundaries (walls, ceiling, floor) back to the room.

[Karloff70]

Originally Posted by George Necola

I don't know.. maybe a NASA space satellite.

try to move the speakers around in your room.

It's the cigar. Remove the cigar and it will sound pristine.

[seen-da-sizer]

Originally Posted by boggy

No, if you treat only peak at 67Hz, but nothing else (highQ resonant method) , null at 90Hz will still exist.

Love this subject so far! Here is my followup question for clarification: I can address the 67Hz peak with a tuned trap. Could I address the 90Hz null in addition with something like a Helmholtz Resonator?

[Jens Eklund]

Originally Posted by onceagain

So, in Aaron's case, what would be the interfering energy?

Check out the post I linked to for further reading on the topic.

[Jens Eklund]

Originally Posted by seen-da-sizer

Love this subject so far! Here is my followup question for clarification: I can address the 67Hz peak with a tuned trap. Could I address the 90Hz null in addition with something like a Helmholtz Resonator?

As long as the treatment is placed at relevant surface, any absorber effective in the frequency range of interest is a solution.

[boggy]

Originally Posted by seen-da-sizer

Love this subject so far! Here is my followup question for clarification: I can address the 67Hz peak with a tuned trap. Could I address the 90Hz null in addition with something like a Helmholtz Resonator?

There isn't an easy answer. In some situations you can address 90Hz with tuned trap if source of 90Hz interference is at different boundary (surface). It is all depends of particular situation. If you are unsure, use only broadband pressure based or porous methods.

[Mctwins]

Originally Posted by Aaron Rash

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Hello everyone,

Just to make sure I'm correct, in order to treat a null you must absorb the opposing peak. So in my case the peak at 67hz needs to be treated to fix the null at 90hz. Just want to make sure I treat this the right way

You are on the right track(thinking). What the opposing peak are has to be determind first.

I know the right way to fix your problem but I can't tell you this because I am afraid to be accused for shilling.

You have lot's of experts here that can help you with the practical solution and not only by talking(write) about it.

So go ahead and help Aaron know and fix his room so he can get +/-3dB without any resonances from 20-200Hz.

[Mctwins]

Originally Posted by boggy

There isn't an easy answer. In some situations you can address 90Hz with tuned trap if source of 90Hz interference is at different boundary (surface). It is all depends of particular situation. If you are unsure, use only broadband pressure based or porous methods.

I have the answer to his problem but to use any broadband pressure based or porous methods is not the way to go.

[Jens Eklund]

Originally Posted by Mctwins

I know the right way to fix your problem but I can't tell you this because I am afraid to be accused for shilling.

As you did here you mean:

Use EQ for the final peaks?

?

[boggy]

Originally Posted by Mctwins

I have the answer to his problem

Great! What prevents you to help him?

Originally Posted by Mctwins

but to use any broadband pressure based or porous methods is not the way to go.

Do you know any better method which you will to share with other forum members/visitors?

[Jens Eklund]

Aaron:


A +/- 7-8 dB response at 1/12 oct resolution is not bad. Very expensive builds in large rooms are considered excellent if +/- 5 dB at 1/24 octave (which b t w is the normal resolution we use).

Unsuccessful Bass traps... Need advice


PS:

You seem to be using a diffuse field mic aimed towards the speakers. If diffuse field type (or even if called "free field" but behaving as a diffuse field mic); aim it at the ceiling or approx. 70-80 degrees (or whatever the manual states).

And: Before posting your measurement results

[Tom Higgins]

Originally Posted by boggy

Great! What prevents you to help him?

Do you know any better method which you will to share with other forum members/visitors?

He's holding back because he knows he'll get slated for recommending his incomparable 'Varitunes'

[DanDan]

Aaron, you can tell modal nulls from BIR nulls using Waterfalls.
Moving the mic and listener positions can refine this further. Quite often a particular null can e directly associate with it primary causal boundary.
(Jens please do not comment on or reply to this, your contrary view on this is well known)
Here we see how the Back Wall BIR is more significant than modes.
http://recording.org/studio-construc...en-matter.html

And here you can see Front Wall BIR entirely removed using a 3.5 inch fibre panel. SBIR
This test in another room also showed BWBIR to be more significant than modes.

So it would seem wise to be clear whether your nulls are modal or BIR.

You can often identify the primary causal boundaries by movements, as in both those tests. It can also be useful to calculate their likely frequency.
Here's a useful Single bounce calculator.
SBIR & Floor Bounce calculator

DD

[Mctwins]

Originally Posted by boggy

Great! What prevents you to help him?

Do you know any better method which you will to share with other forum members/visitors?

YES, I know a better method but I wish not to share this method due to risk of accusation. Sorry.

[Jens Eklund]

For a full explanation of SBIR, see this thread (yes; it´s a long one, start at about post 250 if in a hurry):
SBIR

[boggy]

Originally Posted by Mctwins

YES, I know a better method but I wish not to share this method due to risk of accusation. Sorry.

There are other possible ways to help people without risk of accusation...

McTwins, one of basic functions of my MyRoom design principle is a (big) Helmholtz resonator, integrated and not that easily recognizable to everyone. But I never spread "tips" that some "mighty" Helmholtz absorber, may solve all people's problems. Why? Because not all Helmhotz absorbers works, and only some of constructions really works. You can find many threads on GS where people argue because their (ordinary, textbook) Helmholtz absorbers don't work (anything).

So if you tell someone to use Helmholtz absorber you cannot help him, if you don't tell him, how actually he must build his absorber which will really work in his room (which you can usually see only on photographs).
My experience tells me that Helmholtz absorbers can help, but people must be experienced (and very enthusiastic, mistakes may be expensive...) to design it to work.
DIY people needs something that will "just work" without maths, without measurements, and Helmholtz absorber does not belong to easy ways to treat room.
Wideband methods are acceptable to non-skilled people and this is a reason why I recommend this.

When recommending Helmholtz absorber on public forum, without (design specific) details, I actually push people to hire a professional, at the very end, but after they spend money and get angry....
Why we need this?

[Mctwins]

Originally Posted by boggy

There are other possible ways to help people without risk of accusation...

McTwins, one of basic functions of my MyRoom design principle is a (big) Helmholtz resonator, integrated and not that easily recognizable to everyone. But I never spread "tips" that some "mighty" Helmholtz absorber, may solve all people's problems. Why? Because not all Helmhotz absorbers works, and only some of constructions really works. You can find many threads on GS where people argue because their (ordinary, textbook) Helmholtz absorbers don't work (anything).

So if you tell someone to use Helmholtz absorber you cannot help him, if you don't tell how actually he must build his absorber which will really work in his room (which you can usually see only on photographs).
My experience tells me that Helmholtz absorbers can help, but people must be experienced (and very enthusiastic, mistakes may be expensive...) to design it to work.
DIY people needs something that will "just work" without maths, without measurements, and Helmholtz absorber does not belong to easy ways to treat room.
Wideband methods are acceptable to non-skilled people and this is a reason why I recommend this.

When recommending Helmholtz absorber on public forum, I actually push people to hire a professional, at the very end, but after they spend money and get angry....
Why we need this?

I understand what you are trying to say here but why DIY when one can buy it.

It is not so difficult to work with HH if proper one is used and properly placed in a room. It's a piece of cake.

[boggy]

Originally Posted by Mctwins

I understand what you are trying to say here but why DIY when one can buy it.

Because they love to DIY, and I understand them...

Originally Posted by Mctwins

It is not so difficult to work with HH if proper one is used and properly placed in a room. It's a piece of cake.

(bolded by me)
"Proper one" is a keyword!

[DanDan]

Modes may not be the biggest issue at all.
Curing BIR nulls will need a large surface area. The narrow VariTunes will not work for this unless in large quantity.


P227 -229 Master Handbook of Acoustics shows a single Helmholtz Tub completely curing a 49Hz mode.
I duplicated the device as best I could, but made it tuneable over a small range. This worked fine. But one of these had absolutely no impact on my small room. Acoustics Forum • View topic - Helmholtz formula, is this incorrect? Subsequent research indicated that Helmholtz devices need as much surface area as other LF treatments.
Inappropriate advertising for VariTunes aside-
Buying and shipping such large heavy products, would be hugely expensive.
In which case why not buy the seemingly best product on the market, which is much thinner. http://www.rpginc.com/product_Modex_Plate.cfm
Easy to DIY by the way.
The Helmholtz story goes on. Primacoustic brought a tuned trap to market. Gone very quickly. One or two of them did nothing, similar to my device.
Another GS appeared here some years ago. He suggested Helmholtz was the way to go in pretty much every post he made. This was singular to the point of absurd. He has now moved on to other singularities.

James T Quirk-

To boldly go where everyone has already been.....

DD

[Mctwins]

Originally Posted by DanDan

Modes may not be the biggest issue at all.
Curing BIR nulls will need a large surface area. The narrow VariTunes will not work for this unless in large quantity.


P227 -229 Master Handbook of Acoustics shows a single Helmholtz Tub completely curing a 49Hz mode.
I duplicated the device as best I could, but made it tuneable over a small range. This worked fine. But one of these had absolutely no impact on my small room. Acoustics Forum • View topic - Helmholtz formula, is this incorrect? Subsequent research indicated that Helmholtz devices need as much surface area as other LF treatments.
Inappropriate advertising for VariTunes aside-
Buying and shipping such large heavy products, would be hugely expensive.
In which case why not buy the seemingly best product on the market, which is much thinner. http://www.rpginc.com/product_Modex_Plate.cfm
Easy to DIY by the way.
The Helmholtz story goes on. Primacoustic brought a tuned trap to market. Gone very quickly. One or two of them did nothing, similar to my device.
Another GS appeared here some years ago. He suggested Helmholtz was the way to go in pretty much every post he made. This was singular to the point of absurd. He has now moved on to other singularities.

James T Quirk-

DD

BIR won't solve first axiell resonances. If you can't fix a HH resonator how can you fix this only with BIR.

About the rest you wrote, whatever.

[Aaron Rash]

Originally Posted by George Necola

I don't know.. maybe a NASA space satellite

Funny you say that. I actually live across the street from NASA, ha! Thanks for all the great info guys. Doing lots of reading now... Quick question what does SBIR stand for? and also what is a BIR Null?

[Mctwins]

Aaron..

It is very simple to fix this room.

Just download testtones from SMT homepage.
Run one at a time and at the same time the person takes notes and what freq is the most dominated in all corners of the room, floor-wall and wall-ceiling corners.

For the freq that is most dominated above 60Hz, use a V4

For the freq that is most dominated below 60Hz, use a V6

Start with the lowst dominating tone and adjust the hatch on the varitunes until the selected tone goes down in level.

After that, just continue with next hotspot and do it in the same manner.

You are done and finished in couple of hours.

[Glenn Kuras]

Originally Posted by Aaron Rash

Funny you say that. I actually live across the street from NASA, ha! Thanks for all the great info guys. Doing lots of reading now... Quick question what does SBIR stand for? and also what is a BIR Null?

Learn what is SBIR (Speaker Boundary Interface Response)

[DanDan]

BIR won't solve first axiell resonances. If you can't fix a HH resonator how can you fix this only with BIR.

About the rest you wrote, whatever.

Could you try that again McT, in a known terrestrial language.

DD