Help. 120hz Drop out in my room.

[Mpr_65 115]

I am hoping to get some advice from the well informed members here regarding a significant frequency drop out from my speakers in my listening room / lounge room.

I recently purchased a pair of Revel Salon 2 speakers from a fellow member of SNA.  While I am very happy with the speakers and the amazing sound they produce I was a tad disturbed when I ran 

Dirac and looked at the measurements (below). Approx 10 - 8db drop at around 120hz both sides L and R.  The rest of the frequency band I can live with as I generally only apply Dirac correction below 250hz.

As shown, my room is less than ideal with regard to speaker placement and acoustical neutrality however I have to live with this for the time being.  I'm wondering what mechanisms I can use to offset the 120hz issue.

A few come to mind

1.  Isoacoustic feet (GAIA 1's) for the speakers

2. Some room treatment. (what will be the most effective and achievable in a shared space)

3. Bigger rug - already on order

4. Professional assessment and advice (Red Spade Audio).

 

Suggestions welcome.  Cheers

 

Edit:  Sorry, some measurements might help.  The speakers are about 2.5 M apart measured from centre of drivers.  Listening position about 3.5 M from centre of drivers to ears.

 

Edited February 11 by Mpr_65

[Mpr_65 115]

For the sake of completeness I've added a photo of the open left hand side of the room.

The pink line in the graph represents the Left Speaker the green is the Right

[sakabatou 308]

how far from the rear wall is your listening position?

[Mpr_65 115]

22 minutes ago, sakabatou said:

how far from the rear wall is your listening position?

 

Rear wall is 2.8 metres from listening position

[Bunno77 1,559]

What is the after Dirac measurement?
Is that a sub in the corner? It may help

Probably only placement is going to fix it but understand might not be possible

Edited February 12 by Bunno77
.

[andyr 6,089]

14 hours ago, Mpr_65 said:

I am hoping to get some advice from the well informed members here regarding a significant frequency drop out from my speakers in my listening room / lounge room.

I recently purchased a pair of Revel Salon 2 speakers from a fellow member of SNA.  While I am very happy with the speakers and the amazing sound they produce I was a tad disturbed when I ran 

Dirac and looked at the measurements (below). Approx 10 - 8db drop at around 120hz both sides L and R.  The rest of the frequency band I can live with as I generally only apply Dirac correction below 250hz.

As shown, my room is less than ideal with regard to speaker placement and acoustical neutrality however I have to live with this for the time being.  I'm wondering what mechanisms I can use to offset the 120hz issue.

A few come to mind

1.  Isoacoustic feet (GAIA 1's) for the speakers

2. Some room treatment. (what will be the most effective and achievable in a shared space)

3. Bigger rug - already on order

4. Professional assessment and advice (Red Spade Audio).

 

Suggestions welcome.  Cheers

 

Edit:  Sorry, some measurements might help.  The speakers are about 2.5 M apart measured from centre of drivers.  Listening position about 3.5 M from centre of drivers to ears.

 

 

 

 

Surely a drop like that (at 110-120Hz) is related to your room dimensions - ie. a 'room null'?

 

So what are your room dimensions?  (Someone a bit more clued up than me can then tell you what null frequencies these dimensions imply!   )

 

One thing you might like to try is moving your listening position (and therefore microphone position) and re-measuring.  Move the lp/mp:

• firstly 0.5m closer to the spkrs; this may require you to adjust toe-in and their distance apart
• and then 0.5m to one side - which will require you to move one spkr's position, plus their toe-in.

Andy

 

[sakabatou 308]

38 minutes ago, Mpr_65 said:

 

Rear wall is 2.8 metres from listening position

I think that could be your issue. A 120Hz sound wave is 2.8m long. 

 

http://www.mcsquared.com/wavelength.htm

 

although being a full multiple, I think it should be summing - but I'm no expert

 

try moving the mic back or forward maybe 0.5m and see what happens the the waveforms

 

 

Edited February 12 by sakabatou
grammar

[Mpr_65 115]

12 minutes ago, Bunno77 said:

What is the after Dirac measurement?
Is that a sub in the corner? It may help

Probably only speaker placement is going to fix it but understand might not be possible

Thanks for the tips Bruno.

After the Dirac measurement?  Do you mean the corrected curve?

Sub is only for the soundbar linked to the tv.  It can be moved but can't be incorporated.  Given most subs operate up to 80hz I didn't think adding one would help much.

Yes speaker placement is a big issue.  They're too close to the front wall and the one on the left is way to close to that corner.  I've tried moving them closer together (2 meters) however the sound stage pretty much collapses as well is the imaging.  

[Mpr_65 115]

13 minutes ago, sakabatou said:

I think that could your issue. A 120Hz sound wave is 2.8m long. 

 

http://www.mcsquared.com/wavelength.htm

 

try moving the mic back or forward maybe 0.5m and see what happens the the waveforms

I'll give that ago.  Moving forward not so bad but back is an issue.

[Satanica 1,655]

Also, can the speakers be moved forward at least a bit (30cm) ?

[Mpr_65 115]

22 minutes ago, andyr said:

So what are your room dimensions? 

Its a big room.  It incorporates the lounge (shown), kitchen and dining 

7.4 X 6.6 M give or take.  

Theres also a stairs leading down to the ground floor behind the listening position.

 

I've read that 110 - 120 hz is a resonant frequency of wooden flooring which might effect the drivers hence the GAIA's in the suggestion box.

4 minutes ago, Satanica said:

Also, can the speakers be moved forward at least a bit (30cm) ?

I wish!!  I've got about another 5cm before the Mrs really cracks it!  lol

[Satanica 1,655]

3 minutes ago, Mpr_65 said:

I've read that 110 - 120 hz is a resonant frequency of wooden flooring which might effect the drivers hence the GAIA's in the suggestion box.

 

I doubt it.

 

3 minutes ago, Mpr_65 said:

I wish!!  I've got about another 5cm before the Mrs really cracks it!  lol

 

Yeah, moving forward is your best option but what does Dirac indicate as the predicted corrected response now?

And you can use Dirac to measure the actual corrected response.

[Mpr_65 115]

8 minutes ago, Satanica said:

 

I doubt it.

 

 

Yeah, moving forward is your best option but what does Dirac indicate as the predicted corrected response now?

And you can use Dirac to measure the actual corrected response.

The predicted corrected response -

[Satanica 1,655]

1 minute ago, Mpr_65 said:

The predicted corrected response -

 

And that of course looks excellent, so is there really an issue you think?

[Steffen 1,238]

A null associated with a room mode should be at the same frequency for both speakers, only dependent on the listener position ad room dimensions.

 

It looks as though both speakers are about 60-70cm from the front wall (measured from the front of the speakers, where the drivers are). If so, it could be SBIR dips. This is easily confirmed – if you move a speakers back or forth by 10cm, and the dip in the Dirac graph moves along with that, it’s SBIR.

 

The dip around 70Hz could also be SBIR from the right side wall (assuming the magenta curve is the right speaker).

 

These things are easy to predict/check. To confirm a suspicious distance associated with a frequency dip, calculate:

343/freq/4 (e.g. 343/120/4 -> 0.7)

 

To find the frequency corresponding to the distance of a nearby surface (wall, floor), just do:

343/dist(m)/4 (e.g. 343/0.7/4 -> 122.5)

 

Remember to measure from where the bass drivers are (front baffle, centre line).

 

 

 

Edited February 13 by Steffen

[Mpr_65 115]

 

5 minutes ago, Satanica said:

 

And that of course looks excellent, so is there really an issue you think?

It's only that in a few of the Dirac (training) videos it's suggested that Dirac shouldn't be used to correct greater than 4-5bd either way.  Not sure why but that's what they say.  I guess I was looking for a solution to augment the 10db loss.  Eliminating it all together given the constraints would seem impossible.

[Satanica 1,655]

Just now, Mpr_65 said:

 

It's only that in a few of the Dirac (training) videos it's suggested that Dirac shouldn't be used to correct greater than 4-5bd either way.  Not sure why but that's what they say.  I guess I was looking for a solution to augment the 10db loss.  Eliminating it all together given the constraints would seem impossible.

 

I think I have the best bit of a 20db peak at 50Hz in my room and Dirac treats it well.

 

Yeah I think you'd have to move your seating position substantially forward to be within 2m of the speakers to make any large improvement and even then it might still need quite a lot of correction.

[Steffen 1,238]

10 minutes ago, Mpr_65 said:

The predicted corrected response -

 

 

This is another way of confirming the nature of the dips:

 

If the measured response agrees with the predicted one, then those aren’t SBIR dips. If the dips remain, it’s SBIR. EQ is powerless against SBIR, the stronger a signal you put out, the stronger the reflection will be, and the extinction remains.

[Mpr_65 115]

Just now, Steffen said:

 

This is another way of confirming the nature of the dips:

 

If the measured response agrees with the predicted one, then those aren’t SBIR dips. If the dips remain, it’s SBIR. EQ is powerless against SBIR, the stronger a signal you put out, the stronger the reflection will be, and the extinction remains.

Thanks Steffen, I'll remeasure with Dirac operating and see what happens.  

[Mpr_65 115]

26 minutes ago, Steffen said:

If the dips remain, it’s SBIR. EQ is powerless against SBIR, the stronger a signal

And they do!  Remeasured with Dirac running and low and behold the 120hz dips still there.

SBIR it is.

 

[Steffen 1,238]

7 minutes ago, Mpr_65 said:

And they do!  Remeasured with Dirac running and low and behold the 120hz dips still there.

SBIR it is.

 

 

Just shift a speaker back or forth a bit, and watch the dip move, for confirmation and nerdy gratification

 

[Mpr_65 115]

27 minutes ago, Steffen said:

 

Just shift a speaker back or forth a bit, and watch the dip move, for confirmation and nerdy gratification

 

For the nerds!  LOL

Moved the speakers forward about 30cm...dip seems to have gone to below 100hz.....

 

Edited February 12 by Mpr_65

[Satanica 1,655]

28 minutes ago, Mpr_65 said:

For the nerds!  LOL

Moved the speakers forward about 30cm...dip seems to have gone to below 100hz.....

 

 

Hmmm, in some ways better and in some ways worse.

[davewantsmoore 6,741]

2 hours ago, Mpr_65 said:

I've read that 110 - 120 hz is a resonant frequency of wooden flooring which might effect the drivers hence the GAIA's in the suggestion box.

 

Yes.... but the vibration of the floor doesn't result in 10dB missing.

 

10dB is much to big to be caused by that.   Such a "big" hole is caused by sound cancelling out itself.

 

 

Almost certainly due to the distance from the speaker baffle to the wall behind the speaker.... and then reaching you.

 

An approximate path length difference of 120cm would cause what you are measuring.   Meaning the baffle of your speaker would be ~60cm from the wall.    Which looks about right from the photos.

 

Quote

1.  Isoacoustic feet (GAIA 1's) for the speakers

As above.   No.

 

Quote

2. Some room treatment. (what will be the most effective and achievable in a shared space)

It will need to be very thick... and be behind the speakers.     This won't pass your WAF restrictions.

 

Quote

3. Bigger rug - already on order

No.   This will do nothing for this issue..... although might generally improve the sound (but at much higher frequencies).

 

 

Quote

4. Professional assessment and advice (Red Spade Audio).

The issue in play here is quite simple.   I'd highly recommend RSA, but for this issue.... there's no need.

 

Like all acoustic cancellation issues.... You have the following choices.

1. Move the speakers
2. Move the listener
3. Add more sound sources (eg. a subwoofer)

 

 

 

1 hour ago, Mpr_65 said:

For the nerds!  LOL

Moved the speakers forward about 30cm...dip seems to have gone to below 100hz.....

 

Right... I should have read the whole thread before writing my last post. 

 

 

As you make the distance longer...... the cancellation freq decreases.

[davewantsmoore 6,741]

Typically what you would do it move them out far engouh to get the issue into subwoofer frequencies (Eg. << 100hz) and then add a subwoofer, located somewhere that doesn't have the cancellation.

[Mpr_65 115]

7 minutes ago, davewantsmoore said:

Like all acoustic cancellation issues.... You have the following choices.

1. Move the speakers
2. Move the listener
3. Add more sound sources (eg. a subwoofer)

 

 

Thanks https://www.stereo.net.au/forums/profile/108814-davewantsmoore/some pretty succinct and valuable advice there.

Appreciate the feedback from yourself and https://www.stereo.net.au/forums/profile/107174-satanica/, https://www.stereo.net.au/forums/profile/105652-steffen/ https://www.stereo.net.au/forums/profile/109073-sakabatou/. Much appreciated.

 

[davewantsmoore 6,741]

For now, just correct it with Dirac... and be happy.

 

 

The only thing which will solve it, really.... is, as mentioned... move it low enough (it almost is, but not quite) and add a subwoofer.

 

The reason "not quite" is that if you added a subwoofer that you were going to play up to well over 120Hz .... then you would need to position it close to your main speakers..... and you are right back at your original problem.

[Mpr_65 115]

Thanks Dave. Bit of a learning  curve but I’ve got it now (I think) 😀

Good news is Mrs gets a new rug and I get a new house!  One day. 

Cheers. 

[DrSK 463]

Others are already on it, 

SBIR. 

 

As soon as you said 120Hz I calculated 70cm and saw your speaker distance to the wall. 

 

Take 343/120 gives wavelength. SBIR is a quarter wave issue, so divide wavelength by 4.

 

Others have given suggestions. 

 

Another thing to remember is that base is relatively omni directional. 

 

The effect can be largely tuned out if space permits by adjusting speaker placement to control side wall reflection. The side wall reflection will again have a timing delay relative to the direct speaker signal and can either make the dip worse or resolve it somewhat depending on how you space things.

 

Many technical combing effects are actually resolved by good side wall reflections, especially within our auditory system. 

 

For example the spacing between my speakers is purely about controlling timing delays of my side wall reflections relative to the direct signal at the listening position. With the aim to optimising and controlling base response and imaging. After speaker width I made small adjustments to seating position to tune effects of a room mode. Then speaker toe to compensate for width of speakers as was a bit out of the equilateral triangle rule of thumb. 

 

Edited February 12 by DrSK

[Mpr_65 115]

1 hour ago, DrSK said:

 

The effect can be largely tuned out if space permits by adjusting speaker placement to control side wall reflection.

Sadly space is the issue here. I don’t really have much room to move. Initially I thought some absorption/reflective panels might help placed behind the speakers. However this does not appear to be a solution. 
I actually quite like the sound with Dirac running however chasing rainbows 🌈 seems to be the audiophiles lot.  

[DrSK 463]

15 minutes ago, Mpr_65 said:

Sadly space is the issue here. I don’t really have much room to move. Initially I thought some absorption/reflective panels might help placed behind the speakers. However this does not appear to be a solution. 
I actually quite like the sound with Dirac running however chasing rainbows 🌈 seems to be the audiophiles lot.  

Yep, chasing rainbows! I'm an audiophile and acoustic engineer. Sometimes I have to invite mates over just to enjoy and stop analysing. 

 

At 120Hz your only hope potentially without use of a sub to fill may be a helmholtz resonator panel behind it. Note box behind panel needs to be sealed. 

 

The theory works well for design. Use a model for panels with multiple holes. 

 

Could home build and cover in speaker cloth to hide the drilled hole spacing imperfections. Covering will slightly broaden the tuning. 

 

If worried about tuning error, could screw together multiple thinner layers before hitting with holesaw and remove a layer to increase resonant frequency. 

 

I haven't built one for 16 years. 

Edited February 12 by DrSK

[Decky 1,335]

Manage those corners somehow. 

[davewantsmoore 6,741]

5 hours ago, DrSK said:

helmholtz resonator panel behind it

IME they need to be waaaay too big to be effective...

 

6 hours ago, Mpr_65 said:

seems to be the audiophiles lot.  

 

I think the best advice short of adding another source, is to say that it's not as bad as the "giant chasm" in your response might make you think.

 

Most system measurements look a lot worse.

 

Let dirac do it's thing and sleep easy.

Edited February 13 by davewantsmoore

[btiltman 11]

'What does it sound like? If you don't hear anything obviously wrong don't worry about it.

 

ie If you didnt look at the graph would you have felt there was an issue?  🙂

[davewantsmoore 6,741]

11 minutes ago, btiltman said:

'What does it sound like? If you don't hear anything obviously wrong don't worry about it.

 

ie If you didnt look at the graph would you have felt there was an issue?  🙂

 

In most ways I think this is terrible advice.    Most things I fix in audio systems, I wouldn't be able to "pick out" with my ears.... but one the thing is fixed, and you (if you have the opportunity) switch back and forth, the difference is well audible.

 

 

But... the opposite (agonise over every wiggle in the response), can be problematic too.

 

The perhaps obvious thing is that the solution is knowing what in a chart is problematic, and whether it can be solved (with practical / available options).

 

In this case (like many/most) the chart makes it look worse than it is.... and it isn't easily fixable.    In short it's why a decent sized room, and multiple subwoofers (or at least one) are a good solution......   but that's impractical for lots of people as you can't (always) just go get a new house and / or a new wife, because of your audio setup.

[Mpr_65 115]

20 hours ago, davewantsmoore said:

The perhaps obvious thing is that the solution is knowing what in a chart is problematic, and whether it can be solved (with practical / available options).

 

In this case (like many/most) the chart makes it look worse than it is.... and it isn't easily fixable.

I think you’re spot on,  hence the reason I started this thread. 

Thanks to all that have contributed. The advice/feedback I’ve received has saved me $100’s possibly $1000’s in products which would have had a negligible impact correcting this issue. Additionally I’ve learnt a few things along the way. 

As for the sound?  The Revels Sound great!  Easily the best speakers I’ve owned. Could they sound better in a different room without the need for Dirac? .....probably/maybe.   Either way its not an option for now. 
 

Thanks again.