Giant SPL Dip from 70-105hz... Most effective way to correct?

[Audio Joe]

Hello!

I have a giant SPL dip from 70-105hz. It bottoms at 88hz at -20 SPL. I'm using a Dayton UMM-6 and REW to measure this and looking at the SPL graph.

My system: Tidal hifi> schiit modi 3e > schiit rekkr or fosi V3 > Kef R3. I use windows volume control when using the rekkr.

I tried using parametric filters in eAPO to boost up that range and it basically did nothing no matter what I tried.

What is the best way to correct this dip in the frequency response?
-Huge bass traps?
-Adding 1x or 2x subwoofers?

Thanks,

Joe

 

[SDC]

I suggest placing main speakers in different position to move the dip first.

Lower the frequency and add multiple subs to cover it

Increase the frequency and add absorption.

I personally like the former method as it makes not only FR but also decay extremely clean.


If moving the mains is not an option, I'm afraid the problem won't be fixed as it is too high for sub and too low for absorption.

 

[AnalogSteph]

It's probably a problem relating to SBIR. Back wall distance would be a common culprit but multiple paths might be at play here.

Monitor Placement - Genelec.com

To create the ideal listening experience, several aspects need to be taken into account when placing the monitors within the listening space. First, you need to identify the listening area within the space and consider where the listener will be placed in relation to the space as well as the...

www.genelec.com

 

[DVDdoug]

You can't really boost with EQ to fix standing wave nodes (where the waves cancel). Boosting by 20dB requires 100 times more power!

Multiple subs in different locations can sort-of "average out" standing waves.

Bass traps can also help by absorbing waves before they are reflected. That helps with with the nodes (dips) and antinodes (peaks).

 

[Cbdb2]

Yea room modes can be a real pain. What are your room dimensions? Can you move your listening position and speakers? If yes try measuring other spots you can move to.
More info hear.

Room Modes Theory - What are Room Modes?

Explanation of room modes written by the author of the room mode calculator amroc. What are room modes? Why are they so bad?

amcoustics.com

 

[boxerfan88]

Try moving the speakers closer to the front wall. The dips will shift, hopefully the dips won’t be as bad.

Using EQ to boost frequency wont work when the dip is caused by cancellations. Double/triple the power at the problem frequency, the more powerful signal will still get canceled by the more powerful reflected wave.

 

[Audio Joe]

Thanks for the helpful replies.

My room dimensions are: 18' Long x 13' Wide x 7.5' Tall. I have a sloped ceiling where the sidewalls are 4' tall before sloping up to meet the 7.5' flat portion.

Based on your suggestions, I moved the speakers closer to the front wall by a few inches at a time, taking measurements each time. The back of the speakers started about 3' from the front wall, now they are about 1' from the front wall. This increased bass spl generally and shifted the dip higher in frequency.

The dip now starts at 90hz, bottoms at 105hz at -12SPL, and recovers by 135hz.

My plan is to order 2x GIK Monster Bass Traps with Range Limiters and place them in my front corners. They look very effective at absorbing frequencies above 80hz.

Thanks again! Will continue to monitor the thread for any new thoughts and ideas.

 

[RayDunzl]

I have a giant SPL dip from 70-105hz. It bottoms at 88hz at -20 SPL.

I've got a big cancellation dip around 48Hz due to asymetry in the back of the room, left corner is open to other areas.

Don't notice it.

Didn't know it was there until measured.

If the bass is stereo (different signal/phase from each channel) the measured defect goes away.

I still don't notice it, and quit worrying about it.

Left, right, and both speakers unsmoothed, playing a test sweep:

The waves at the listening position, centered around 48Hz, from left and right speakers, go 180 degrees out of phase.

 

[kemmler3D]

Thanks for the helpful replies.

My room dimensions are: 18' Long x 13' Wide x 7.5' Tall. I have a sloped ceiling where the sidewalls are 4' tall before sloping up to meet the 7.5' flat portion.

Based on your suggestions, I moved the speakers closer to the front wall by a few inches at a time, taking measurements each time. The back of the speakers started about 3' from the front wall, now they are about 1' from the front wall. This increased bass spl generally and shifted the dip higher in frequency.

The dip now starts at 90hz, bottoms at 105hz at -12SPL, and recovers by 135hz.

My plan is to order 2x GIK Monster Bass Traps with Range Limiters and place them in my front corners. They look very effective at absorbing frequencies above 80hz.

Thanks again! Will continue to monitor the thread for any new thoughts and ideas.

Welcome to ASR!

Looks like you're on a reasonable path. I would definitely suggest buying a sub or two in addition, if you can swing it. Even adding one sub in my (much smaller) room and doing EQ with REW / EQAPO made a huge difference.

The conventional wisdom is "You can't EQ a null". This is true. 100 - 100 = 0, Boost it 10x, and you get 1000 - 1000 = 0.

However, in the real world (and especially if you have 3 or more sources at a given frequency) A null is actually more like 100 - 100 + 20 (or something like that). True, complete nulls won't happen nearly as often. If your 3rd source has enough SPL you CAN EQ a null by filling it in with the 3rd source. Of course this might require an excessively high SPL and still make things bad around the room away from the MLP, but the notion that you ABSOLUTELY CANNOT EVER boost nulls to fix them isn't 100% true.

 

[ozzy9832001]

Hello!

I have a giant SPL dip from 70-105hz. It bottoms at 88hz at -20 SPL. I'm using a Dayton UMM-6 and REW to measure this and looking at the SPL graph.

My system: Tidal hifi> schiit modi 3e > schiit rekkr or fosi V3 > Kef R3. I use windows volume control when using the rekkr.

I tried using parametric filters in eAPO to boost up that range and it basically did nothing no matter what I tried.

What is the best way to correct this dip in the frequency response?
-Huge bass traps?
-Adding 1x or 2x subwoofers?

Thanks,

Joe

Do you mind posting the response? REW can take a Screenshot of it. Will give us some visual aid.

Moving the speakers closer to the FW will increase the frequency at which the SBIR becomes problematic. It's the preferred method because an issue at 150 or 200hz or what have you is much easier to treat then one at 60hz.

Multiple subs is always an option for me, I think they provide the best experience for the low end. 90hz-130hz is an important region of the bass, especially for guitars.

In order to get the benefits from the bass traps, you'd need quite a few of them and they'd have to be thick. Otherwise, they won't even come close to denting the lower frequencies. At 12" thick, you're probably barely even tickling 60hz.

 

[Audio Joe]

I attached screenshots of no EQ+ no smoothing, and no EQ+ 1/6 smoothing.

Maybe a lot of my problems are related to that 40hz mode and its harmonics? Peak at 40, null at 120, peak at 160, peak at 240, null at 440 etc... All multiples of 40hz.

I'm now considering getting 2x GIK soffit bass traps because they are 17" deep and more effective at low frequencies.

Thanks

 

[MAB]

Thanks for the helpful replies.

My room dimensions are: 18' Long x 13' Wide x 7.5' Tall. I have a sloped ceiling where the sidewalls are 4' tall before sloping up to meet the 7.5' flat portion.

Based on your suggestions, I moved the speakers closer to the front wall by a few inches at a time, taking measurements each time. The back of the speakers started about 3' from the front wall, now they are about 1' from the front wall. This increased bass spl generally and shifted the dip higher in frequency.

The dip now starts at 90hz, bottoms at 105hz at -12SPL, and recovers by 135hz.

My plan is to order 2x GIK Monster Bass Traps with Range Limiters and place them in my front corners. They look very effective at absorbing frequencies above 80hz.

Thanks again! Will continue to monitor the thread for any new thoughts and ideas.

Hi, have you tried to calculate your room's modes?
Your room will have primary modes at 31Hz and 43Hz for the length and width, and 75Hz for the height. Plus all of modes between the corners.
Here is a handy online room-mode calculator (I ignored the sloped areas, may or may not be a good approximation depending on how chamfered your ceiling is!):

amroc - THE Room Mode Calculator

HTML5 room mode calculator. Read and hear the tune of axial, tangential and oblique modes. Scientific sources included.

amcoustics.com

And this very detailed thread:

Analytical Analysis - Room Gain

-Introduction- The term 'room gain' is often seen used when the topic of subwoofers and the low frequency sound reproduction comes up. As I see many explanations that are lacking or incorrect, I thought I might try and clear up the topic once and for all. In all rooms there are so-called...

www.audiosciencereview.com

REW has a flexible room simulator with speaker and main listening position. I don't know what arrangement you have, but you can explore actual speaker and listening position within a room. Certainly the L/R separation will also have a big impact. I'm guessing at your speaker and listeniing postions.

To do the sim, would need to know speaker positions, and your listening position. I would do all this before ordering traps. You may end up still getting the traps, but REW is free and you might get a better handle on where that dip at 100Hz at your listening position is

 

[kacos]

What is the best way to correct this dip in the frequency response?
-Huge bass traps?
-Adding 1x or 2x subwoofers?

I tried the SubZone app to help me figure out the best position for a sub in my office.
I suggest you give it try ..

Here's what it suggested: for my room:

and the combined result:

Edit: Forgot to also mention that my speakers go down to 45Hz but I set the crossover at 60Hz and the sub crossover at 85Hz - so they overlap between 60-85Hz smoothing out the curve .. Look at the blue line (farfield/seating position):

 

[ExPerfectionist]

Can you move your seating at all, even 6-12" ? That will change the acoustics as well, not just the speake /sub locations.

Do you have a dip in that range, or do you have peaks at 40Hz, 175-375Hz, 525-800Hz, and so on? Meaning...could you use your DSP to tame the higher peaks and ranges under 1KHz? Bring it back to around 82-85dB range on your graph? Right now you have a 10~15 dB difference between 200Hz and 10KHz

Yes integrating a sub could potentially help fill in some of that dip under 100Hz, depending on room acoustics.

 

[ozzy9832001]

I attached screenshots of no EQ+ no smoothing, and no EQ+ 1/6 smoothing.

Maybe a lot of my problems are related to that 40hz mode and its harmonics? Peak at 40, null at 120, peak at 160, peak at 240, null at 440 etc... All multiples of 40hz.

I'm now considering getting 2x GIK soffit bass traps because they are 17" deep and more effective at low frequencies.

Thanks

Your mid range seems to be fairly bright relative to the rest of the curve.

Can you post the REW .mdat file in .zip format, so we can look at the other graphs.

 

[Eleo]

I had a similar problem - a large dip between 60 and 90 hz, see my posts in other threads - I added a small sub close to the wall, at the middle of the lenght of my room and the dip went away