Cab someone explain what is going on here? Strange room measurements difference

[Mentalrudy]

Hi everyone,

I'm mystified by the measurements I've added here.
Some context: I've had horrible bass response in my room and consulted a professional accoustical firm (that works for studio's, broadcast stations etc) to fix it as much as possible with room treatments. Now, pic 1 & 2 are the result of the professional measurements after the treatment. Seems perfect, but alas: I still hear huge bass dips, confirmed when I run a bass sweep and check with a spl-db meter.
Now, since I'm not technically adept I haven't tried working with REW myself and I don't own a calibrated usb mic, I can't really verify his measurements. But when I tried a Elac sub which has autoEQ, the measurements (via Iphone mic) showed up in the app as you can see on pic 3, where blue is the nearfield response of the sub and the red line is the response at listening position.
This graph resembles more what I'm hearing.

This looks to me as if someone is fraudulent. Or could it be the case that the large difference in the two graphs are explained by teh first being a easurement with calibrated mic, pink noise and rew and the second is just a phone measurement with the elac app? Seems unconvincing.

 

[Philbo King]

Any FR measurement graph can look amazing with 20 dB/div scaling and excessive smoothing.

 

[dshreter]

You need to spend the money on a UMIK-1 and just measure it yourself. You’ve had professional work done and you have concerns it was not a proper job - and there’s really only one way to properly know.

By the way, what sort of treatments were put in?

 

[KxDx]

I hope your consultation and bass traps were cheaper than buying a MiniDSP with Dirac license.

That first graph looks like it was smoothed out quite a bit.

 

[Mentalrudy]

You need to spend the money on a UMIK-1 and just measure it yourself. You’ve had professional work done and you have concerns it was not a proper job - and there’s really only one way to properly know.

By the way, what sort of treatments were put in?

A lot, 6 bass trap modules (2 of each at 40, 70 and 130 hz) hidden behind a fake wall of Wood-upp akupanel on the one side and acoustic cloth on the other side. The details of the traps are in the attachment. it's very nicely done and absolute professional craftsmanship in the installation, but the effect in sound is unsatisfying. Bass response still very uneven, dips at all practical listening positions and - at elevated volume - excessive high frequency energy. Maybe my expectations were too high to start with.

 

[howdomagnetswork]

If you are hearing dips in a simple bass sweep, yeah, confirm with a UMIK-1 mic + REW (which is honestly pretty easy following YT tutorial) and potentially get your money back if the consultation/fix was not up to the agreed result.

For the part of you not being technically inclined, it's simple with well-documented steps (youtube). Getting UMIK1 would be an immeasurable benefit to validate your setup to quantifiable values. Without much fuss, REW most importantly just gives you the readout of your frequency response. Yeah, there are other things, but to start using it, almost anyone can do it.

 

[Mentalrudy]

I hope your consultation and bass traps were cheaper than buying a MiniDSP with Dirac license.

That first graph looks like it was smoothed out quite a bit.

I whish! I could by a truckload of minidsp's for that amount!

 

[Mentalrudy]

If you are hearing dips in a simple bass sweep, yeah, confirm with a UMIK-1 mic + REW (which is honestly pretty easy following YT tutorial) and potentially get your money back if the consultation/fix was not up to the agreed result.

For the part of you not being technically inclined, it's simple with well-documented steps (youtube). Getting UMIK1 would be an immeasurable benefit to validate your setup to quantifiable values. Without much fuss, REW most importantly just gives you the readout of your frequency response. Yeah, there are other things, but to start using it, almost anyone can do it.

I was thinking of going that path, but you know, it's a professional studio biulding firm. I woulnd't stand a chance.

 

[Inner Space]

it's a professional studio biulding firm

Couple random questions, based on experience of a similar problem:

Did they do acoustic measurements in the "before" state, i.e. sweeps and mikes, etc? Or just physical feet-and-inches, as if they were going to rely on software simulations?

The similar problem I saw before was caused by the latter. The tape measure said the room was a certain size, but the bass waves said it was a different size. Happens all the time. What looks like a wall to us might be the back of a closet opening on a hallway with a solid outside wall twelve feet away. The bass waves pass through the drywall and take notice only of the distant brick. The same can happen vertically, with cellars or basements. Always better to measure with actual sound, rather than just input dimensions into a computer.

 

[dshreter]

It’s hard to even correlate what is in the Elac measurements with the first full frequency range measurement. I think it’s a leap to say anything is fraudulent for know so you’ll have to further investigate.

One of the other challenges is it’s hard for you to even know what your own expectation is for what good bass sounds like unless you have an authoritatively known good reference room. It’s entirely possible you don’t like what you’re hearing because the response is now less peaky. Or maybe the room is actually still setup poorly. Or maybe the subwoofer EQ is screwed up… who knows?

It would surprise me if a professional firm installed tuned absorbers and completely botched the job. But if they did, they are absolutely on the hook to correct the work. For you to address that confidently though, it will help so much to have your own measurements you can refer to with conviction.

Members here can probably help with the small handful of measurements you need to build out a picture.

 

[Sokel]

The measurements don't look THAT different in comparison,they both are between an 10db range.
Lowest end can be deceiving.

 

[Mentalrudy]

Couple random questions, based on experience of a similar problem:

Did they do acoustic measurements in the "before" state, i.e. sweeps and mikes, etc? Or just physical feet-and-inches, as if they were going to rely on software simulations?

The similar problem I saw before was caused by the latter. The tape measure said the room was a certain size, but the bass waves said it was a different size. Happens all the time. What looks like a wall to us might be the back of a closet opening on a hallway with a solid outside wall twelve feet away. The bass waves pass through the drywall and take notice only of the distant brick. The same can happen vertically, with cellars or basements. Always better to measure with actual sound, rather than just input dimensions into a computer.

Well, they did extensive measurement. A whole study actually, prety thorough

 

[Mentalrudy]

Thanks for joining the conversation. It’s indeed hard to correlate the graph from the firm with what showed up in the elac sub app. Especially since the elac data corresponds more to what I’m hearing when playing a bass sweep, or even good old music (imagine that, just playing music through our installations!)

What you wrote in your second paragraph is what the firm told me when I adressed them with my reservations. But, sitting at the listening position, definetly texture is missing from bass drums, male vocals, and many basslines I know are there are hust missing or uneven.

I agree I should take matters in hand and perform measurements.

 

[Mentalrudy]

The measurements don't look THAT different in comparison,they both are between an 10db range.
Lowest end can be deceiving.

I can see your point, scale is different. A reassuring thought, but as I wrote in other replies, when sitting down at LP sound is very thin, bass lacks or goes missing.
However, when standing up, things get a lot better. Bass returns, still sooewhat uneven but acceptable. That, to me indicates a vertical dip. I told them all this at the beginning. He dismissed my idea of looking at ceiling treatments

 

[OldHvyMec]

I've seen friends spend a fortune because they had the money. I've used the same rooms for over 40 years. Below 300hz is as simple as fixing the peaks
with helmholtz tunning traps. The dips will be seen for what they are. Speaker placement and full length heavy curtains that you can retract.
You will never get it right by using DSP. I don't care who wrote the code. There are different options, but all are a crock. Sorry. It's a poor way
to correct an easy issue. The problem is understanding what you hear vs what a program can measure.
Few programs work in the bass region. It's a guess. You have your own experience to at least give yourself a big ol ?

What do I know, I'm just an old beat up mechanic with very nice sounding (OLD) systems that you can change main monitors in 10 minutes.
DSP. It's a 1/2 ass way of saying your hard headed and lazy to boot. There are TWO types of boxes. The room and the rest of the boxes inside
your BOX, speakers. Most people leave out the biggest BOX, THE ROOM.

HT is sound affects, nothing more, nothing less. I concert often. I haven't listened to TV more than 5 minutes in 35 years.

Stereo is still king.

At least the OP gave it a shot. Happy hunting.

Regards

 

[KxDx]

I can see your point, scale is different. A reassuring thought, but as I wrote in other replies, when sitting down at LP sound is very thin, bass lacks or goes missing.
However, when standing up, things get a lot better. Bass returns, still sooewhat uneven but acceptable. That, to me indicates a vertical dip. I told them all this at the beginning. He dismissed my idea of looking at ceiling treatments

Oh yeah, “sitting bass” and “standing bass.” I’ve dealt with that too.

Put your room dimensions into amroc and you can see vertical modes too. That’s why final tweaks have to be done at the listening position, because you could literally have the best bass a foot above your head.

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

 

[Chrispy]

Hard to know what you're hearing particularly. Where are the consultant's graphs of before and after?

 

[alex-z]

6 bass traps is not much for a typical room. Especially if they are not located optimally in relation to the problem room modes. Keep in mind that Helmholtz resonators are relatively inefficient, when comparing surface area to absorbed energy.

The SPL graph from REW looks terrible. Your system is not outputting enough energy below 100Hz. The bass region should at minimum be equal in level to your mid-range, most people actually prefer an elevated bass response. Instead, your bass is 6-10dB lower than your mid-range. So raise your subwoofer level. Ideally you would add a second sub, which will also help smooth out the frequency response.

Also, you have a random 6dB dip around 1900Hz. I would 100% fill that with EQ.

 

[Mentalrudy]

6 bass traps is not much for a typical room. Especially if they are not located optimally in relation to the problem room modes. Keep in mind that Helmholtz resonators are relatively inefficient, when comparing surface area to absorbed energy.

The SPL graph from REW looks terrible. Your system is not outputting enough energy below 100Hz. The bass region should at minimum be equal in level to your mid-range, most people actually prefer an elevated bass response. Instead, your bass is 6-10dB lower than your mid-range. So raise your subwoofer level. Ideally you would add a second sub, which will also help smooth out the frequency response.

Also, you have a random 6dB dip around 1900Hz. I would 100% fill that with EQ.

Thank you for this interesting answer. Of course, being a living room, there had to be compromises. If they had gone all out without esthetic or budget constraints they would have covered 45% more surface area than is actually the case. It is a very large room for European norms. So maybe I'm too harsh on the firm.
All the REW measurements were performed without sub, btw. I thought that you can't fill up dips and nulls because it acts like a black hole: you can put as much energy in as you will, it'll still be cancelled out. I tried the elac sub, but I didn't have actual bass management on my stereo amp so that didn't work out very well.
So you think getting an amp with bass management and room correction, and adding one or two subs could solve this situation? Maybe the new NAD 389 amp is an interesting path...

 

[alex-z]

All the REW measurements were performed without sub, btw. I thought that you can't fill up dips and nulls because it acts like a black hole: you can put as much energy in as you will, it'll still be cancelled out. I tried the elac sub, but I didn't have actual bass management on my stereo amp so that didn't work out very well.
So you think getting an amp with bass management and room correction, and adding one or two subs could solve this situation? Maybe the new NAD 389 amp is an interesting path...

With a measurement mic, DSP, and 2 subwoofers, you should be able to dramatically improve your bass response, and therefore the overall quality of your system.

UMIK-1

The UMIK-1 is an omni-directional USB measurement calibrated microphone providing Plug & Play acoustic measurement. From speaker & room acoustic measurement to recording, this microphone provides low noise and accurate results you can rely on.

www.minidsp.com

You can add bass management by using something like a miniDSP 2x4HD, or miniDSP Flex. Both can act as a DAC with individual DSP for each output, or as an analogue pass-through. I never recommend stereo amps with integrated DSP, they tend to be overpriced, offering less functionality than similarly priced AV receivers.

Nulls can be filled, but it comes at the cost of peak output headroom. Nulls are caused by reflections having different phase than the direct radiated sound. The on-axis sound is usually stronger, so if you raise the on-axis response through EQ, eventually the null can be filled despite the phase summation issue. Of course, if the dipped area is a result of the speakers themselves, EQ works better because you aren't fighting room acoustics.