Why is REW not correcting these two big dips?

[Koeitje]

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.

Ok, then add a small boost and see if it does anything. If it doesn't then you can't fix the dip.

 

[C0mbat]

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.

@TurtlePaul - Sorry, those eqs in the original post have changed. See the new ones. The R one has the 10db boost. However, it's inbetween two filters that are cutting dbs. So its it really boosting 10db? Because in reality that dip is actually only 6db from the target line.

I don't really get your above explanation as I'm not technical explanation. I could increase the crossover up to 85hz without making much difference to the sound. Are you suggesting letting the KC62 taking the brunt of the power at that 83hz PEQ boost slot? Given that the WiiM has 24db slope settings by default on the Ultra, I'm guessing the sub is already taking some of the load. If I move the crossover to 85hz then it will take a small majority of the load.

For some more information, I'm 2m from the speakers, so very close. I'm typically playing at 60-65db from my listening positioning. My thoughts was that by boosting the 83hz Freq on the right channel by 10db then it's the same as playing my right channel at 70-75db at certain times? Surely that's no issue at all? The sub, speakers and amps and all capable of being driven above 100db. So I was thinking this narrow freq 10db boost was no issue. Or does it not work that way?

 

[C0mbat]

@TurtlePaul - Further to the above, here are two new measurements with both the L + R and the sub on at the 75hz crossover. One is post eq and the other pre-eq (the WiiM allows you to toggle easily, which is nice). While nowhere near perfect, it looks better across the whole freq range.

I've also attached the measurements for the L+Sub and R+Sub post eq. Again, they look better.

Should I be aiming for better than this as I definitely wouldn't call it flat. The only thing I do want to change slight, and it's noticable during listening, is that I want a curve slightly sloping down from left to right with a slight boost in the lower frequencies. At the moment I would say the midrange is slightly boosted.

 

[AdamG]

A picture of the room and the speaker/sub location layout can sometimes reveal little movement tweaks that might be of some improvement. If that is possible it can’t hurt to give some of these very smart guys more data to work with in helping you improve this situation.

Good luck. You are getting excellent advice and feedback.

 

[ernestcarl]

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.

You'd need a heck of a lot more of acoustic treatment before you'd even begin to see a flatter bass response. So EQ is kind of obligatory.

Look at distortion plots as you incrementally increase the SPL -- boosting EQ will have an effect there as well.

Should I be aiming for better than this as I definitely wouldn't call it flat. The only thing I do want to change slight, and it's noticable during listening, is that I want a curve slightly sloping down from left to right with a slight boost in the lower frequencies. At the moment I would say the midrange is slightly boosted.

Detailed EQ (besides broader tone controls like HF shelving EQ) above a few hundred hertz -- e.g. 500 Hz -- based on an in-room steady-state frequency response plot is somewhat questionable at this point in your journey... Quite a bit more data is really needed to justify these decisions. A very extreme example that should at least help illustrate the point: https://www.fulcrum-acoustic.com/wp-content/uploads/2019/09/Prod-Spec-P-v15.pdf

 

[TurtlePaul]

I think that if you have 6-7 dB of total gain at that frequency and listen at 70 dB and below you will be fine.

 

[kemmler3D]

I'm assuming the 10db correction is better as it's only drawing x10 power at that particular frequency range?

Technically yes, but actually not really.

Since the frequency is quite low (80hz) it's drawing a lot of power already. Bass inherently takes more power to generate, so saving the 10dB at 1khz is a relatively trivial savings.

Since you're using the KC62, it has protection built-in, so you probably won't really damage it nor will you probably hear much clipping, but you might hear dynamic compression, i.e. the sound getting quieter in an unexpected or annoying way.

 

[DonH56]

The biggest reasons for narrow dips are room modes and SBIR as already said. And already said was the reason they are considered uncorrectable by EQ: You have signal - reflection = null, so if you increase gain (EQ) then you have 10xsignal - 10xreflection = null. The usual solutions are to move the speakers for SBIR and/or treat the first reflections, although treatments are physically too large for low bass in most rooms, and for room modes move the listening position or move the sub(s) to counter the null.

Throwing power at the problem is usually a no-win scenario at best and at worst damages speakers and perhaps other things (ears, the room...) Note when you move out of the null the sound will be very loud with so much boost. For a single listening position, moving the seat out of the null usually works best if at all possible, though moving a single sub around can help if you can place it appropriately. Otherwise, and for multiple or broad listening areas (e.g. across a couch or more than one row of seats), the practical solution is usually multiple subs placed and aligned (delay/phase and volume) to counter the nulls across the listening space.

Todd Welti subwoofer placement presentation: https://www.harman.com/documents/multsubs_0.pdf

HTH - Don