Measurement of room acoustics (for the layman)

I've read a lot about measuring rooms with sound pressure meters to identify problem areas.

I do understand the principle, but it always leaves me a little bit confused as to what I should be looking out for in terms of measurement.

Is anyone.able to provide a description of what I should be looking out for in the measurements in easy to understand terms?

For example, I should take measurements from all corners of the room, should I be hoping for the same reading in all corners meaning my room is perfect?

Or if I measure a low / high reading, what does that mean? And how does it translate into a bass problem or the terminology of room acoustic treatment speak?

I know ones own transducers are the most reliable, but I'm curious to map out the listening room.

Any guidance would be much appreciated.

Original Post

I urge you not to do this unless you specifically have a big problem with the room acoustics that is noticeable when listening to music. I say this because no home room is perfect and you are going to find fault if you measure the room. If you don't hear a problem then don't look for it otherwise you may find yourself spending a lot of effort and money correcting it!

I had a big issue with my room that I could easily hear. Certain bass frequencies would excite the room and make the bass way too exaggerated. When I measured the room I realised why, there was a massive hump around 45Hz.

I used Room EQ Wizard (free) with MiniDSP UMIK-1 microphone ($75), they both work very well and should be all you need to take accurate measurements.

I'm still waiting on my solution to arrive - a set of four RPG Modex Plates (Type 2) - one placed in each corner of the room. Why these? They are the only product on the market that are effective at low frequency ranges whilst being relatively small and thin and therefore room friendly.

Hope this helps and good luck!

Wise words HM!

I hear what you say and I understand why you say it. I don't believe I have big problems even thoigh i I know my room is far from ideal

 I am alqays inyeresyed to learn though so im still curious.

So when you say you had a hump around 45Hz, how did you see this present itself, and was it measured in all 4/corners?

 

There's an excellent piece of software called REW - room equalisation wizard, which is available  free of charge (donations suggested if you find it useful). However a decent microphone is required (iirc they make some suggestions if you don't have a suitable one).

with it you can check resonances, also things like decay, which can help you decide what room treatment might be approriate to improve sound in your room. Significantly, the software includes detailed information that explains what the measurements mean, so I would suggest starting be downloading the software and reading the information given in the help section.

Chris,

Don't measure the corners of your room: Measure at your listening position - the corners will give a distorted frequency and time response.

I also use REW and a miniDSP UMIK-1, and crafted my own system that's a combination of bass absorbers and DRC that's only applied to the sub I use.

Huge,

Granted you ultimately want to measure results at the listening position, but if you want to identify the best placement for treatment don't you need to measure throughout the room identify where? For example, bass traps. Wouldn't I want to measure various locations - ceiling versus floor junctures in all four corners to see where modes are collecting and bass traps would be most effective? The RPG Modex Plates (Type 2) suggested by Halloween Man are quite expensive and I'd want to be certain I was getting best use of these assuming I couldn't afford top-to-bottom treatment of all four corners in my room. It also gets into the question of how much treatment is necessary and at what point does "over treatment" become a detriment.

Okay Chris, since you asked the question I will answer it to satify your curiosity and it may help others.

I used REW and umik-1 mic (placed at listening position) and did a room measurement. its very simple to do with REW and umik-1 mic. The spl graph generated showed a 12db increase in level around 45hz. This is huge and effectively meant that when listening to low bass in music the room is in effect making it louder by about 12db, so quite significant. The waterfall graph generated by rew showed that these bass waves are hanging around in the room way too long causing standing waves. I needed something in the room to absorb the low bass waves.

After some research I realised the only effective and acceptable room solution was RPG modex plates. These need to be placed in high sound pressure points in the room. To find these pressure points I simply played 40-50Hz test tones and went around the room with the mic using rew level meter. The highest levels were in the corners and some room boundaries. The levels were lowest in the middle of the room.

I have not yet got the modex plates so unable to say how effect they are at the moment.

atb

Halloween Man posted:

Okay Chris, since you asked the question I will answer it to satify your curiosity and it may help others.

I used REW and umik-1 mic (placed at listening position) and did a room measurement. its very simple to do with REW and umik-1 mic. The spl graph generated showed a 12db increase in level around 45hz. This is huge and effectively meant that when listening to low bass in music the room is in effect making it louder by about 12db, so quite significant. The waterfall graph generated by rew showed that these bass waves are hanging around in the room way too long causing standing waves. I needed something in the room to absorb the low bass waves.

After some research I realised the only effective and acceptable room solution was RPG modex plates. These need to be placed in high sound pressure points in the room. To find these pressure points I simply played 40-50Hz test tones and went around the room with the mic using rew level meter. The highest levels were in the corners and some room boundaries. The levels were lowest in the middle of the room.

I have not yet got the modex plates so unable to say how effect they are at the moment.

atb

My result was very similar - and of the commercial products the RPG flat panel sounded best and would be the only shape that could be accomodated. However I understand that each panel might make only 1-2 dB difference, so multiple panels needed to make a significant difference. I decided to leave till I have time to try making my own panels.

however one other thing I used REW for was to compare different speaker positions, measuring at the listening position, and varying the listening position and mic. My original listening position was defined by the room and its alternative use as a home cinema, the seat being a sofa roughly in the middle of the room with no its only flexibility being maybe a foot further forward or back, which I tried.  But investigating further with REW I found that positioning an easy chair directly in front of the sofa got rid of the major hump in the response curve, though needing repositioning of the speakers. So for critical listening i do just that, putting the easy chair right in front of the sofa and moving the speakers. Interestingly that positions my head  about 40% of the room width from the front wall, and I seem to recall from somewhere that optimum may be about 38%. It's a bit of a hassle moving my current speakers, 'walking' them on their spikes because they're too heavy and awkward to lift and carry, but it works (My previous speakers had castors, which made it easy!)

Hi ib, I was under the impression a single panel was the equivalent of 4 modex corners so could offer up to 4db reduction if placed correctly. It will be interesting to find out.

im limited with where I can move sofa and speakers. The movement I have doesnt make much difference unfortunately. I also don't like to be too close to speakers, like to be 6-7 foot away.

Btw what is an easy chair?

 

HM, no comment!   

It took 6m² area of LF wideband (40-200Hz) absorbers and a -10dB cut at 42Hz on the sub to control the 40-45Hz resonances.


A single Modex panel has about 4 times than absorbing area of a Modex corner, so you you only need 1/4 the number (they both have peak absorption coefficients of about 0.9).

Halloween Man posted:

Hi ib, I was under the impression a single panel was the equivalent of 4 modex corners so could offer up to 4db reduction if placed correctly. It will be interesting to find out.

im limited with where I can move sofa and speakers. The movement I have doesnt make much difference unfortunately. I also don't like to be too close to speakers, like to be 6-7 foot away.

Btw what is an easy chair?

 

Easy chair is another name for armchair etc. in my case it is a swivel reclining leather chair that is light enough to manouvre easily. 

My sofa that I had intended also as the listening position on the other hand is very heavy requiring two people to move, so practicality means it stays at the position optimum for a variety of uses, hence putting a different listening seat, or two if desired, in front of it.

the optimum listening position in my room as untreated does place me closer than is my natural inclination, with ears only about 7ft from the front plane of the speakers, 

The effect of the Modex panel was advised to me by the manufacturers, however it will depend very much on the room, and they were careful to be non-committal. Great if you can try before you buy, but if not it is an expensive punt.

Innocent Bystander posted:
Halloween Man posted:

Hi ib, I was under the impression a single panel was the equivalent of 4 modex corners so could offer up to 4db reduction if placed correctly. It will be interesting to find out.

im limited with where I can move sofa and speakers. The movement I have doesnt make much difference unfortunately. I also don't like to be too close to speakers, like to be 6-7 foot away.

Btw what is an easy chair?

 

Easy chair is another name for armchair etc. in my case it is a swivel reclining leather chair that is light enough to manouvre easily. 

My sofa that I had intended also as the listening position on the other hand is very heavy requiring two people to move, so practicality means it stays at the position optimum for a variety of uses, hence putting a different listening seat, or two if desired, in front of it.

the optimum listening position in my room as untreated does place me closer than is my natural inclination, with ears only about 7ft from the front plane of the speakers - though from a different angle itis good for the other occupants of the house, as for any given level at the listening position the overall sound level is lower!

The effect of the Modex panel was advised to me by the manufacturers, however it will depend very much on the room, and they were careful to be non-committal. Great if you can try before you buy, but if not it is an expensive punt.

 

 

I do admire you guys ... sounds like a whole new hobby

 

I'm delighted that my listening room is my living room and I know its totally weird for sound - L-shaped for a start!

... but there is no way I can do anything about it other than make sure my chair is the one in the middle of the speakers;

... so I'm happy

... and I won't read any more of this thread because I can feel twitching around the idea of how much a mic would cost on Amazon

... no no no, going to eat now and try to forget all about this

 

Allan

Halloween Man posted:

I urge you not to do this unless you specifically have a big problem with the room acoustics that is noticeable when listening to music. I say this because no home room is perfect and you are going to find fault if you measure the room. If you don't hear a problem then don't look for it otherwise you may find yourself spending a lot of effort and money correcting it!

I had a big issue with my room that I could easily hear. Certain bass frequencies would excite the room and make the bass way too exaggerated. When I measured the room I realised why, there was a massive hump around 45Hz.

I used Room EQ Wizard (free) with MiniDSP UMIK-1 microphone ($75), they both work very well and should be all you need to take accurate measurements.

I'm still waiting on my solution to arrive - a set of four RPG Modex Plates (Type 2) - one placed in each corner of the room. Why these? They are the only product on the market that are effective at low frequency ranges whilst being relatively small and thin and therefore room friendly.

Hope this helps and good luck!

I think I have a very similar problem, bass guitars sound somewhat exaggerated , probably some where around 45-100hz; while the top end is slightly muffled IMO. Need to do these measurements though interestingly I'm not able to find this mic UMIK anywhere in my country. Until I can solve this major issue, I feel it doesn't make sense to invest further into better equipment.

Thanks HM, the problem is I don't know whats going to happen at the customs as the price of the item with the courier exceeds the threshold for customs exeption; so I backed out of ordering at the last moment. I may purchase it while abroad within the next few months or ask someone to bring it with...

So got hold of the UMIK-1 mic, now what? I am finding it hard to find a configuration video to get going. I understand that I need some kind of cable to connect my laptop to the preamp (NDX)? I have a standard laptop so will be using the headphone out connection but what kind of connection should I have on the NDX side?

Hi Tariq,

I assume you mean for the sweep output of REW or whatever other software you are using?

For that you can use a 3.5mm to DIN (or phono as appropriate) cable and connect to your preamp, or use a USB->S/Pdif converter and take the output of that to one of the digital inputs of the NDX (that's what I did, as then it includes the FR of the DAC you use in playback).

There may well be other solutions as well.

Tariqv posted:

Will try to find a 3.5mm to DIN (or phono) and connect to the digital input of the NDX, would a 3.5mm to RCA work? 

No, that won't work.  The 3.5mm headphone output from the Laptop is an analogue signal and must go to the preamp, not the NDX.

Some laptops (principally Macbook Pros, but also a few others) have an optical digital output combined with the 3.5mm headphone jack.  IF you have one of these you can use a miniToslink to Toslink optical cable to connect the laptop to the optical digital input of the NDX.

You need to know what you're trying to fix.

Tariqv posted:

I think I have a very similar problem, bass guitars sound somewhat exaggerated , probably some where around 45-100hz; while the top end is slightly muffled IMO. Need to do these measurements though interestingly I'm not able to find this mic UMIK anywhere in my country. Until I can solve this major issue, I feel it doesn't make sense to invest further into better equipment.

The bass guitar problem is probably the upper bass boost from 100Hz - 350Hz.  As HM says, you need the waterfall plot to see why it's there.

Room acoustics is a minefield.  I too looked at this but to make an effective change you need to add quite a few products, whether it be absorbers or diffusers, and generally the cost / wife factor makes it unachievable.  I'd look at moving the system and fettling speaker and listening position first.  The listening position in my own room suffers from a slight lack of bass which is restored when I stand up (i.e. I need bass traps in the corners of the room where it's in excess) but I don't really have the space to install them so I make do with it and just try to enjoy it as it is.  Sounds great ether way, but n a perfect world the bass frequency within the room could do with being addressed.  Most modern living envirnoments aren't really optimised for acoustics so unless you have a specific listengin room that you can design from the ground up it's a tricky one to attack.  It can be done though, it just depends how much time and effort and money you wish / can afford to invest.  Good luck!

Halloween Man posted:

The graphs won't tell you that. Have you tried the waterfall graph? That's useful for seeing how long problem frequencies are hanging around. Overall your room doesn't look too bad, you're lucky!

He is the waterfall graph, as well as the average of the SPL responses with "Var Smoothing" applied. Does it still look good; what are the downfalls of my room and any ideas how to treat?

[img]http://i.imgur.com/KdoGYsX.jpg[/img]

[img]http://i.imgur.com/qcNiHjg.jpg[/img]

 

 

To my untrained eye I can see you have a strong resonant point at about 39 Hz and it has its first harmonic at obviously around 78 Hz .. this to me will give difficult boomy bass... and possibly quiteuneven bass... i would try adjusting speaker positions bringing into room slightly and away from corners and/ or moving soft furnishings around to see if those resonance points decay better. I sus

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