Why is REW not correcting these two big dips?

[C0mbat]

Hi all,

I've produced the created some EQ filters for both my left and right speakers (on both occasions I had the sub on as well so happy to discuss if I'm doing that wrong) but for some reason it's not correcting a couple of really big dips in my right speaker. Why is that when it does correct smaller dips and peaks? Is there something wrong with my settings?

 

[diablo]

You'd need to increase the 'overall max boost' and 'individual boost' settings. Though getting rid of the dips by boosting will get you some distortion.

Usually better to lower the target level.

 

[C0mbat]

You'd need to increase the 'overall max boost' and 'individual boost' settings. Though getting rid of the dips by boosting will get you some distortion.

Usually better to lower the target level.

Thanks for this. Are you suggesting that I leave it as is? I did increase the max boost and individual boost to 10db and it does create an eq filter for it by boosting it 10db at 82hz.

Out of interest, that dip at 82 hz occurs no matter whether whether I'm using speakers on their own or with a sub. It's both the Kef LS50 Meta and Kef R7s. And it doesn't matter what crossover I choose. So I'm assuming that's a null being cause at my listening position?

Just one thing. I've currently got my sub crossover at 75hz. Is that the best place to have it in terms of using that 10db boost eq filter? It means that the sub and the speakers (the 6.5" woofers on the Kef R7s that deal with anything below 400hz) will be working together to boost that 82hz region. Or should I leave it more to the sub (Kef KC62) or the speakers? Is one more likely to distort than the other? I'm assuming that I could play around with it, post PEQ fitler change in my WiiM, and use the Distortion readings in REW to determine whether the speakers or the sub distort the most and then adjust the crossover accordingly?

 

[diablo]

In my lounge I get a dip at 70Hz near the speakers, either the mains or sub, so clearly a room problem. So probably similar to what you get at 82Hz. I cheated by setting the crossover to 80 and moving the sub elsewhere - which doesn't get the dip. Though more of a problem at 82.

Everything tends to be a compromise of some sort. I'd probably try setting the target 4dB lower and seeing if the smaller dip is still audible.

 

[JeffS7444]

That 80 Hz dip ought to be sonically benign, but attempting to boost that region might not be. If you're able to invert woofer phase, perhaps that would help?

 

[ernestcarl]

Besides time and phase alignment adjustments between speakers, the overlapping frequencies need to sufficiently complement each other in the first place. Although, that’s easier said than done since speaker-listener positioning is quite constrained in many cases.

 

[TurtlePaul]

It looks like your trying to generate more than 10 filters. If you are making a filter for a MiniDSP or similar, it runs out of filters at 10. You can try to set some of the filters to the preamp if this is the case. If nothing else, kill the filter at 1.8 khz to make the 82 hz filter.

 

[kemmler3D]

Out of interest, that dip at 82 hz occurs no matter whether whether I'm using speakers on their own or with a sub. It's both the Kef LS50 Meta and Kef R7s. And it doesn't matter what crossover I choose. So I'm assuming that's a null being cause at my listening position?

This is probably it. Peaks are correctable because if you have 2+2=4, and the intended volume is 2, you just change the gain so you have 1+1=2. A null is considered "uncorrectable" in theory, because 2-2=0, 3-3=0, 4-4=0, etc. Because the signal is subtracting from itself, increasing or decreasing the volume doesn't get you where you want to be.

I've currently got my sub crossover at 75hz. Is that the best place to have it in terms of using that 10db boost eq filter? It means that the sub and the speakers (the 6.5" woofers on the Kef R7s that deal with anything below 400hz) will be working together to boost that 82hz region. Or should I leave it more to the sub (Kef KC62) or the speakers? Is one more likely to distort than the other?

If you are boosting (esp. with these relatively small and high-excursion KEF drivers) you'll probably want as many speakers working as possible.

You might try flipping the phase on the sub and/or moving the sub to see if it helps the null.

 

[TurtlePaul]

Just one thing. I've currently got my sub crossover at 75hz. Is that the best place to have it in terms of using that 10db boost eq filter?

Is your sub all the way in the corner of the room? You may be able to fix the 82 hz dip by moving the sub against the wall if it is caused by speaker boundary interference response.

 

[TurtlePaul]

Because the signal is subtracting from itself, increasing or decreasing the volume doesn't get you where you want to be.

This is BS that other audiophile sites say. Adding +4 dB will in-fact correct his 4 dB null. The reason not to correct deep nulls is power. A 10 dB null is corrected with 10x the power, and that is why you can’t do it - your speakers or amps will break if you try to fix one of those at reference listening levels. Correcting 4 dB is about 2.5x the power, which should be manageable.

 

[kemmler3D]

Adding +4 dB will in-fact correct his 4 dB null. The reason not to correct deep nulls is power.

If it's a true null, no it won't. Real nulls in real life are rarely perfect or "true", and I do boost a bit when I correct in my room also. But I've also run into nulls that really don't respond much to gain.

A 10 dB null is corrected with 10x the power,

Yes, worth noting.

 

[Jim Taylor]

This is BS that other audiophile sites say. Adding +4 dB will in-fact correct his 4 dB null. The reason not to correct deep nulls is power. A 10 dB null is corrected with 10x the power, and that is why you can’t do it - your speakers or amps will break if you try to fix one of those at reference listening levels. Correcting 4 dB is about 2.5x the power, which should be manageable.

Please read this:

So, if your direct and reflected sound waves are similar in strength, and half a wavelength out of phase, the waveforms mostly annihilate each other.

This is called speaker-boundary interference response (SBIR), listener-boundary interference response (LBIR) or the boundary effect. All these terms boil down to the same thing: boundary-induced comb filtering.

SBIR causes deep dips in the bass response below a certain frequency, and it can affect your low frequency response even more than room modes.


Frequency response measurement at the listening position showing a dip / null caused by the speaker-boundary effect.



Unfortunately, you can’t correct for SBIR using EQ. If you apply a correction filter to try to boost the signal at a cancellation frequency, you will also boost the refection that’s causing the interference!

To address SBIR you have only two weapons in your arsenal: speaker placement and acoustic treatment.

I hope this clarifies the matter somewhat.

Jim

 

[Jim Taylor]

Hi all,

I've produced the created some EQ filters for both my left and right speakers (on both occasions I had the sub on as well so happy to discuss if I'm doing that wrong) but for some reason it's not correcting a couple of really big dips in my right speaker. Why is that when it does correct smaller dips and peaks? Is there something wrong with my settings?

This thread may give you some useful information:

What is the cause of this room null on Room Sim?

I can't work out what the cause of this null is on the REW Room Sim. I think it is something "room length" related, because absorption on the other surfaces doesn't affect it. As the screenshots show (taken from this thread/discussion), the frequency decreases as you move away from the back...

www.audiosciencereview.com

Jim

 

[C0mbat]

That 80 Hz dip ought to be sonically benign, but attempting to boost that region might not be. If you're able to invert woofer phase, perhaps that would help?

Yeah I tried that but it didn't work. That dip exists even without the subwoofer. I've taken measurements with the Kef R7s and the Kef LS50 Metas without a sub and both show that dip.

 

[C0mbat]

Besides time and phase alignment adjustments between speakers, the overlapping frequencies need to sufficiently complement each other in the first place. Although, that’s easier said than done since speaker-listener positioning is quite constrained in many cases.

Yeah, unfortunately, I'm really limited in my speaker positioning. I'm in a small room and they have to be close to the back wall. You could say that the Kef R7s definitely shouldn't be close to the back wall but the dip also exists with the LS50 Metas and they are far more friendly close to the wall. I'm also very limited in terms of being able to put any sort of bass traps behind the speakers due to their location. So it's REW or nothing really. Not ideal.

 

[C0mbat]

Is your sub all the way in the corner of the room? You may be able to fix the 82 hz dip by moving the sub against the wall if it is caused by speaker boundary interference response.

I can't put the sub in a corner as the left speaker is already in one and the door is in the other. I have the sub right in front of the left speaker, 2 inches from the side wall and 3 feet from the back wall. I tried moving the sub just to test it and it weirdly does very little to that dip.

 

[C0mbat]

Please read this:

So, if your direct and reflected sound waves are similar in strength, and half a wavelength out of phase, the waveforms mostly annihilate each other.

This is called speaker-boundary interference response (SBIR), listener-boundary interference response (LBIR) or the boundary effect. All these terms boil down to the same thing: boundary-induced comb filtering.

SBIR causes deep dips in the bass response below a certain frequency, and it can affect your low frequency response even more than room modes.


Frequency response measurement at the listening position showing a dip / null caused by the speaker-boundary effect.



Unfortunately, you can’t correct for SBIR using EQ. If you apply a correction filter to try to boost the signal at a cancellation frequency, you will also boost the refection that’s causing the interference!

To address SBIR you have only two weapons in your arsenal: speaker placement and acoustic treatment.

I hope this clarifies the matter somewhat.

Jim

Thanks for this. As per my other message, I'm limited in speaker placement. I'm not sure if I can do much about room treatment either as the speakers are too close to one back wall corner and the door blacks the other back corner.

 

[C0mbat]

This is BS that other audiophile sites say. Adding +4 dB will in-fact correct his 4 dB null. The reason not to correct deep nulls is power. A 10 dB null is corrected with 10x the power, and that is why you can’t do it - your speakers or amps will break if you try to fix one of those at reference listening levels. Correcting 4 dB is about 2.5x the power, which should be manageable.

@TurtlePaul and @kemmler3D

This is interesting to note. Can I check whether a 10db correction draws more power (i.e. x10 power) than doing no correction and just playing my speakers 10db louder? I'm assuming the 10db correction is better as it's only drawing x10 power at that particular frequency range? The reason that I ask is that I did manage to play with the REW filter settings and get it to correct that dip for the right speaker. It didn't do it for the left. So one of my PEQ slots has a +10gb boost with a q factor of 5.67 at the 83hz Freq. Should have reset things so that REW ignores that dip?

I'm worried I'm going to blow something now lol. The only thing that might make it ok is the fact that the Kef KC62 is sharing the load with two Fosi Audio V3 Mono amps because I'm crossing over at 75hz. Plus my listening volumes in this small room are at about 60-65db. However, I do have two other PEQ slot at almost +7db and two slots at nearly +5db, at high frequencies where only the speaker will be doing the work.

 

[TurtlePaul]

10 dB of boost cost 10x the power relative to whatever volume you are playing the rest of the material in room.

82 dB for a SBIR frequency corresponds to speakers being 3.4 ft. away from the wall. You are using the crossover and high pass on the sub? What happens if you move crossover frequency up to 82 hz or up to around 100 hz? Also, no way to put the speaker in front of the sub?

The good thing is the KC62 has a limiter so it is unlikely to destroy itself. The +5 dB stuff is fine. It is typically only the SBIR related stuff which is 10-20 dB where the power changes orders of magnitude.

Also, if you look at filters 8 & 9 in your plot above, there are two filters close in frequency with opposite sign (one cut and one boost) so the result is the boost isn’t actually the full magnitude of the boost filter. That is why programs like REW let you set individual filter max boost and overall max boost.

 

[Sokel]

@TurtlePaul and @kemmler3D

This is interesting to note. Can I check whether a 10db correction draws more power (i.e. x10 power) than doing no correction and just playing my speakers 10db louder? I'm assuming the 10db correction is better as it's only drawing x10 power at that particular frequency range? The reason that I ask is that I did manage to play with the REW filter settings and get it to correct that dip for the right speaker. It didn't do it for the left. So one of my PEQ slots has a +10gb boost with a q factor of 5.67 at the 83hz Freq. Should have reset things so that REW ignores that dip?

I'm worried I'm going to blow something now lol. The only thing that might make it ok is the fact that the Kef KC62 is sharing the load with two Fosi Audio V3 Mono amps because I'm crossing over at 75hz. Plus my listening volumes in this small room are at about 60-65db. However, I do have two other PEQ slot at almost +7db and two slots at nearly +5db, at high frequencies where only the speaker will be doing the work.

Drawing x10 the power means that if it needed 100W before correction for peaks (not unusual at all) it will need 1000W after the correction.
Make sure your amps and speakers can handle that or else you'll end up with severe distortion,clipping or damaged drivers.