Room bass measurements

[nzlowie]

Hi all, I'd like to get a better idea on how to better measure the bass response in my room so I can optimize it better.

Do I put the mic (REW ) where my head would be or do what I've been doing and that take 4-5 measurements at the corners of my chair and then average these?

 

Either way there are always big swings in the response levels, everywhere you place the mic we get a different response. Yea I know they're room nodes and whatever else the room does, so what's the best way to take and interpret these measurements? My bass amp has DSP so i can tweak as required.

 

Cheers Dave 

[Snoopy8]

Have a read of this

http://www.hifizine.com/2011/06/bass-integration-guide-part-1/

 

[Keith_W]

Hi Dave, as a guide, a 50Hz wave has a wavelength of about 7m. You only need 1/4 wavelength (about 1.8m) to hear a difference. In midrange and higher frequencies, comb filtering makes much more of a difference. If you want a wider sweet spot, I would take measurements from a wider area and average them. 

 

This has been discussed quite extensively in the Acourate forum and it seems to be the consensus. 

[almikel]

Hi Dave,

it's always the interpretation of REW measurements that is the tricky part, and if you only have 1 main listening position I would recommend only measuring from that spot (ie where your head is), only to reduce the number of graphs you're trying to get your head around.

 

On 04/05/2018 at 8:12 AM, Keith_W said:

If you want a wider sweet spot, I would take measurements from a wider area and average them. 

 

This has been discussed quite extensively in the Acourate forum and it seems to be the consensus. 

I agree with this - but having spent hours trying to "interpret" squillions of REW graphs trying to make some sense of all of them, you can end up in "analysis paralysis"...measuring with REW is so easy - interpreting the measurements and implementing changes based on the interpretations and measuring/hearing a positive improvement is the hard part!!!

 

Averaging over multiple microphone positions would be preferable for smoothing bass across multiple seating positions, but if there's only 1 position you want to tune for, give yourself an easier time interpreting fewer graphs.

 

Be cautious of the EQ/DSP you apply if it relates to a single mike position though.

The narrower the EQ applied, the more position dependent it will be - try to keep EQ broad, and use cut rather than boost as a preference.

IMO I wouldn't use EQ at all above about 200Hz

 

Some check measurements after DSP is applied in a few different mike positions is useful to see if the EQ you've applied creates worse issues elsewhere - you may accept that with only 1 primary listening position.

 

IME getting the room bass right requires treatment 1st then EQ after.

If applying EQ as the first solution to fix room bass, then expect the EQ solution to be quite position dependent, but the broader the EQ, the less position dependent it will be.

 

cheers

Mike

[Keith_W]

 

2 hours ago, almikel said:

Be cautious of the EQ/DSP you apply if it relates to a single mike position though.

The narrower the EQ applied, the more position dependent it will be - try to keep EQ broad, and use cut rather than boost as a preference.

 

Yes, I agree. With Acourate it is possible to force the software to correct every peak and dip so that a repeat measurement (with the mic not moved) looks impressively ruler flat with a variation of +/- 1dB. But this is only in one mic position. All you need to do is move the mic a couple of cm to the left or right, and suddenly the corrected response is all over the place, perhaps even worse than before. 

 

You have to be careful that you are not correcting for comb filtering. Comb filtering should be corrected with room treatments and not DSP. The reason? Because correction for comb filtering in one position will exacerbate filtering in other positions. 

 

You could also try a pseudo-anechoic measurement technique, but this requires that you are able to center the mic between your speakers consistently. The technique goes like this: center your mike between the speakers from 1m behind the listening position and take a sweep of left and right. Then move forward 20cm, re-center your mic, and repeat the sweep. Keep repeating until you have 10 measurements (i.e. a distance of 2m). If you have a large room, take 15 measurements (i.e. 3m). The theory is that the room response changes with the mic position, but the direct response from the speaker does not. You then average these out. I have found that this gives you a cleaner, more reliable measurement than taking a reading from a single position. 

[nzlowie]

Today I had a look at room acoustics today, I ran a 100hz tone and moved around the room. WOW I never realised how much the volume changed as you move around! A real eye  (ear?) opener. So do we place our listening spot to where the bass null is or where? If we move to a null is it a cancellation null or?? Or do we move to the spot where the level matches the average level across the rest of the FR. But then I suppose this changes for each freq we check......  Not sure about the ringing at 16k, don't believe this is that bad... HF horn issue?

  

Edited May 11, 2018 by nzlowie

[almikel]

17 hours ago, nzlowie said:

 WOW I never realised how much the volume changed as you move around! A real eye  (ear?) opener.

yes the bass changes lots around the room. If someone is sitting in the main LP in my room sometimes I'll go stand in the corner for the extra bass just for fun.

 

17 hours ago, nzlowie said:

So do we place our listening spot to where the bass null is or where? If we move to a null is it a cancellation null or?? Or do we move to the spot where the level matches the average level across the rest of the FR

are you running a sub or subs or just stereo speakers?

you definitely don't want the LP in a bass null - that's no fun at all

Best would be where the bass level matches the average - BUT only if that LP was good for imaging etc.

 

IMO that's why subs are good - you can position main speakers and the LP for good imaging and shift the sub/s around for smooth bass at the LP.

From there you can move the LP forward or backwards to tweak bass response depending on the off axis response of your horns.

 

The baseline FR in your graph is great - does it have smoothing is applied? 

 

18 hours ago, nzlowie said:

Not sure about the ringing at 16k, don't believe this is that bad... HF horn issue?

Could be.

No decay at all - if it was at 50Hz or 100Hz it would be power supply hum for sure, but it's not...

...young ears would be able to hear it.

Take some more measurements just focussing between 10KHz and 20KHz at different volumes.

Does the ringing stay the same level or increase/decrease with volume?

When you move the mike, does it change in frequency?

 

Do kids and dogs run screaming from your room?  this could be a good thing provided you can't hear it 

I recall running some test tones through my setup in the 15kHz-20kHz range with kids around and it was exactly like that - the adults couldn't hear anything and the kids were holding their ears yelling "stop that"!!

 

There's an argument that says if you can't hear it it doesn't matter - but it's definitely worthy of further investigation - especially if that energy is heating tweeter voice coils.

It could be an acoustic issue in the horn and some damping of the horn itself may assist?

 

My knowledge of horns is extremely limited - my current setup being the first time I've owned any horns (PSE144s, and tapped horn sub).

 

cheers

Mike

 

 

[nzlowie]

Hi Mike, thanks for your thoughts.

3 hours ago, almikel said:

are you running a sub or subs or just stereo speakers?

 

No subs just the mains. Been thinking about subs to tidy up the bass.

3 hours ago, almikel said:

The baseline FR in your graph is great - does it have smoothing is applied? 

Yea plenty of smoothing , read to use 1/3 octave when looking at bass responses. Very peaky response at 1/6th. (Below) Yet pretty much flat at close range.

 

 

The horn response in reality is a lot flatter than this sweep as normally it uses the JRiver EQ, below is the before JRiver and after filters are applied. Close range..

3 hours ago, almikel said:

There's an argument that says if you can't hear it it doesn't matter - but it's definitely worthy of further investigation - especially if that energy is heating tweeter voice coils.

It could be an acoustic issue in the horn and some damping of the horn itself may assist?

Come to think about it there was a bit of noise introduced when I plugged it the bass amp dsp to do some tweaks, some random noise so could have an HF component thats causing this. Will try again without this unplugged. Also should try dampening the horn and see if there are any changes there.

 

Anyway once again thanks for your thoughs, appreciate it.

Edited May 12, 2018 by nzlowie

[almikel]

2 hours ago, nzlowie said:

Very peaky response at 1/6th. (Below)

looks pretty smooth to me - that's an impressive graph...

 

2 hours ago, nzlowie said:

No subs just the mains.

Ok - sneak your LP forward or back to tweak the bass - accept it won't be perfect at all freq...

...rigidity of walls/room modes/SBIR all contribute to less than ideal "in room" bass...

...but who wants to live in a tent?

 

cheers

Mike

[nzlowie]

Yea I did move the LP back a bit once I heard just how much the pressure changed within the room. It was the combination of this and a video from Paul McGowan of PS Audio about his listening room.

 

All these little bits of info add to our overall understanding of how the whole thing comes together.

 

Even though it does sound pretty good, still keep looking for any improvement. More bass trapping to help tame the lower bass? I know it's hard to control things at those lower frequencies.

[Primare Knob]

Yea I did move the LP back a bit once I heard just how much the pressure changed within the room. It was the combination of this and a video from Paul McGowan of PS Audio about his listening room.
 
All these little bits of info add to our overall understanding of how the whole thing comes together.
 
Even though it does sound pretty good, still keep looking for any improvement. More bass trapping to help tame the lower bass? I know it's hard to control things at those lower frequencies.

When you don't use subs I would start with moving the listen position in good pressure zone. Away from 1/2 and 1/4 room dimensions. The best pressure zones to sit in can be found at 0.2, 0.32, 0.45, 0.55, 0.68, 0.8 x room dimensions.

If you sit at 0.45 room width you will need to setup your speakers asymmetrical, which isn't bad for the bass response but your stereo image can suffer.

Try to find out which things are related to room modes and which to near room boundaries. The first one can be helped by EQ to generate a smoother response, the other cannot. EQ won't help, dealing with ringing, which is mostly the domain of acoustic treatment.

[almikel]

20 minutes ago, Primare Knob said:

EQ won't help, dealing with ringing, which is mostly the domain of acoustic treatment.

I've found EQ very helpful to reduce ringing below 100Hz or so where treatment becomes impractical.

This is in a lightly constructed room with lots of absorption already.

YMMV

 

cheers

Mike

[Primare Knob]

I've found EQ very helpful to reduce ringing below 100Hz or so where treatment becomes impractical.
This is in a lightly constructed room with lots of absorption already.
YMMV
 
cheers
Mike

If you EQ the peak, it would output less pressure/power, which would influence the ringing as well. In my concrete and brick room it shows very little effect.

How much effect does it have in the decay time with your room?

[almikel]

25 minutes ago, Primare Knob said:

If you EQ the peak, it would output less pressure/power, which would influence the ringing as well. In my concrete and brick room it shows very little effect.

How much effect does it have in the decay time with your room?

lots - significant enough not to require further treatment - the benefit of my lightly constructed room.

 

Rigid walls make good "in room" bass a challenge.

 

Mike