John Sayers' Recording Studio Design Forum

hello everybody,

i relocated my mixing room from the city to our house upstairs.
The room is very small and some problems have been affirmed that my feeling predicted...
I think the problems are cause the roommode that is not easy to calculate but seems to be around 62hz after frequency measuring and listening tests. I´d like to get out the best of this room to use it as mixing and mastering room.
The room has wooden wall carpeting all around yet.

The floor exists of:
- carpet
- timber floor board
- light plaster
- top of the next room

The right site and front is made of massive 30cm bricks
There are two pitched roof areas that consists of roofing tiles->insulation->OSB-> and the inner wooden wall carpeting.
Also the left wall and the back wall from the sitting position is made of some kind "light bricks"-> inner wooden wall capreting.
One plus is that i do not need to isolate the room to other rooms cause of sound pollution.

After listening i find out that there is a bass drop somewhere unter the kickdrum frequency. PinkNoise and frequency meter sayd 62hz. All the other frequencys seems to be fine. I do not have a bass boost problem (might be the pervious/light room construction).

Strange to say the bass in the corners is perfect so I thought building a massive mdf cloude on top ahead the speakers and adding drywall mass to the left wall to shift the roommode.
Do you have any other idea getting the 62hz -6db drop problem handled?

The attachement is the room with the original measuries sketchup file:
http://www.file-upload.net/download-3791681/upstairs-mixing1.skp.html

Any comments, suggestions are welcome and appreciated very much.

might it be a good idea or possible to shift the 62hz room mode maxima from the corners to the listening position with massive clouds?

22mm osb
22mm mdf
100mm rockwool

Hi there,
are there any opinions about rebuilding the back site of my room?

I would have some space behind the rear wall to move the sitting position and the speakers more back in a diagonal place to the corners. Maybe i recieve a better listening position within the room modes as it is at moment. The most problems are in the upper midrange. The walls on the left and the rearwall is very thin and not clothed with any absorber yet.

On the pic you can see i skizzed the new rear wall a little bit angular (right-bottom). The reason for that is there is an opening were stairs go down behind. So i can not enlarge the room more with this wall.

I would be very happy for any opinions, absorber suggestions, idieas before i change walls or building absorbers to decrease the midrange reflection.

Hi Aaron, and welcome!

I don't know why I didn't see your thread before!

There is a program called REW that you can download for free, and is excellent for diagnosing problems like this. Test your room, then post the results here, so we can help you analyze the problem. The room is a very strange shape, with all those angles, so there is no easy way to predict the response. Measuring is the only possibility.

What treatment do you have in that room already?

If you already have a lot of bass trapping, then your best option might be a panel trap tuned to 62 Hz. If you don't have much bass trapping in there, then that is your problem: you will need LOTS of bass trapping in such a small room.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Hi Stuart,

thank you a lot for your response and discovering my thread

I downloaded REW, a very great software.

The room is only treated with an inner layer of wood paneling/timber lags all around fixed on 2cm thick wooden slats that are screwed to the walls (so there is a cavity behind the panels).
I did not do any acoustically treatments yet.
The floor exists of hardwood and wall-to-wall carpet.

Do you think do i need to add basstrapping in this room? Especially the left thin wall and the angeled roof wall is very thin too (panels->osb->roof tile).
If this is the case these walls act like bass traps i don´t think i need more bass traps or am i wrong?
The only bass problem i figured out with REW is a 3-4db phase issue on 62-65hz. The other bass frequencys seems to be even flat.
Bigger issues start at 172hz, 278hz, 480hz and the most phase issues i did not (recognize that is is so heavy. but it is) start at 1000hz.

To flaten this high frequency range, do you think does it make sense to remove the panels of the sitewalls and adding a 15cm/6Inch thick frame construction filled with rockwool and fabric covering or is 15cm thick rockwoll to thin for 600hz upwards?

I also could build in a framing construction onto the front window-wall to get in a 20cm/8Inch Rockwool trap?

What do you think of enlarging the room to the back site?

This came out after calibrating and measuring:

Here are two further pics. Measured with a cardioid characteristic MKH40 mic on two positions 20cm/8Inch displacement difference to show phase issues.

Some of those graphs look rather suspect to me! I'm very suspicious that they are showing the true response of the room and your sound system: I find it VERY hard to believe that you are getting flat response down to 12 Hz.!

So let's start with the system: What speakers are you using to do these measurements? What else is in the signal chain? What interface? Did you measure with just ONE speaker on, or did you have both on?

One thing I did notice, is that you seem to be doing your measurements at very low levels, around 55 dB. It needs to be much louder than that to ensure accurate readings. You need to measure at levels more like 85 dB. There's no way you can get RT-60 measurements with an average intensity of 55 dB.

The only curve that looks believable is the gray dotted curve on mkh40.jpg How did you get that one?

So please check your setup, measure again at a level of at 85 dB, and what I'm most interested in is a waterfall plot.

If mkh40.jpg is correct, then you clearly have what seem to be modal issues in the low end, which is very normal for an un-treated room.

Oops! So all of your walls are resonant cavities???? That is going to be a big part of your problem...

OK, you mentioned that there is a 2cm air gap, but I also need to know about that wood paneling: How thick is it, and what type of wood? (I mean, is it plywood, MDF, something else). Also, is there any insulation in side the cavity, such as fiberglass or mineral wool?

OK, so that is also a big part of the problem! It is a small room, so it will need lots of treatment.

YES! No doubt at all: it is a small room, so it needs LOTS of bass trapping.

Well, the walls are probably acting as panel traps, but that doesn't mean they are HELPING! They are tuned to very specific frequencies, which is NOT what you need right now. What you need is broadband bass trapping, that covers a large range of frequencies. Your "panel trap" walls are most likely seriously degrading the room acoustics, as they are sucking out one specific frequency all around the room. Most likely, it isn't even a frequency that you need to treat! That's why I need to know the thickness and exact type of wood that the paneling is made of, so I can calculate what frequency the walls are tuned to.

That might be a possibility, yes, but first let's try to figure out if you are getting accurate readings from REW, and what the room walls are doing.

Those are other possibilities. But the basic idea is first to figure out what you have right now, then add normal bass trapping, then measure the room again with REW to see what else needs doing.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

oh sorry, i think the program used my calibration-point as master-file and substracted the abnormalitys from the further measuries i did (good to know for the future).
So i did just some more calibrations and no further measuries to archive the diagram that looks more real. I also send a tune up and down and realized that there are heavy drops that agree to the black dotted diagram ->
The volume output should be fine. I checked it twice with an spl meter t.bone meter (C Mode) and recieved 75dB output PinkNoise- Tested with both speakers/Stereo.

- Speakers: are b&w 800 -> Lynx16 -> RMEAES32
- Monitor controller: dangerous monitor
- Mic(s) used for measuring: MKH40 / tlm 170 omni -> gr me1nv to adjust the input volume -> Lynx16 -> RMEAES32

> The only curve that looks believable is the gray dotted curve on mkh40.jpg How did you get that one?
With -> preferences -> calibration

> Oops! So all of your walls are resonant cavities???? That is going to be a big part of your problem...
yes, i think they are

> but I also need to know about that wood paneling: How thick is it, and what type of wood?
This wood paneling is 1,3cm/0,5Inch thick and hardwood -> European spruce

> Also, is there any insulation in side the cavity, such as fiberglass or mineral wool?
no this is a hole cavity without any insulation between.

I could remove it.

> YES! No doubt at all: it is a small room, so it needs LOTS of bass trapping.
Where do you think is the best place to build a huge bass trap (Front-wall, cloude on top of the front above the speaker, sidewalls or behind the rear wall if i remove the rear wall) ?


>as they are sucking out one specific frequency all around the room...
i suspected it, thats what it sounds like if you sweep a sinus up and down...

What bass trap do you think i should start with or should i remove the panels first to see what happen?

Still not loud enough. In order to calculate the RT-60 time and the waterfall plots (and even to get the impulse response correct), REW needs to do just what "RT-60" implies. It needs to look for and measure a decrease of 60 dB in the signal, from the peak value. In reality, it doesn't actually look for 60 dB, but rather looks for 30 dB, and extrapolates from that. If you are only peaking at 75 dB, then it needs to measure the decrease accurately down to 45 dB, but I'm betting that 45 dB is probably below the noise floor (ambient sound level) for your room, or very close to it. REW will not be able to detect such tiny signals in the room. That's why you need to peak with AT LEAST 85 dB, so that the 30 dB drop will be at 55 dB, which should be well above the noise floor for most rooms.

So you need to erase all your measurements so far, and start again, using the correct level. Also, you need to do it with only ONE speaker at a time, not both at once. There will naturally be interference patterns (peaks and dips) caused by the interaction of the two sound fields. So set up your system to produce at least 85 dB from ONE speaker, and re-measure.


OK, so your signal path should not be doing any bad stuff! That's a nice setup, by the way. So if REW is calibrated correctly, that path should give you really accurate picture of what the room is doing.

OK. Great! Spruce is around 450 kg/m3, and theory says that 1.3 cm of that over a 2 cm air gap with no damping is going to resonate at around 397 hz. Not exactly doing much bass trapping!

So at least that isn't causing your bass problems, so my guess would be that you are seeing a room mode at aprox. 65 Hz. Since the room is not a rectangle, there's no way to predict which mode is causing that. All that can be said is that somewhere in that room is a path that is a multiple of 5.45 meters long, and that there is a standing wave forming around that path. You also have several other peaks and dips in the low end, so there seem to be several modal issues going on.

It would be good to confirm this diagnosis with a waterfall plot, and I'd expect to see a really long tail at around 65 Hz., another around 48 Hz, and probably one or two more a bit higher up.

But regardless of the confirmation, you still need a lot of bass trapping in there!

Wow! Good question! The shape of your room is so strange that I'm really out of my depth trying to understand what is going on! I wish Eric Desart was around! I'm sure he could figure out it.

But I'll go way out on a limb here, and say this: If that were my room, I would take off all the paneling, put a horizontal superchunk wrapped in plastic under the front window, put very deep bass traps in the front corners of the room (in the very tight angles at the left and right, perhaps with 4" 703 against the walls there, hangers in front of that, then a cloth-covered frame to hide it all), open up the rear part of the room (take out the wall behind the sofa, like you show in "upstairs mixing-deconstructed.png", but leave the sofa and speakers where they are now), put deep absorption on the new rear wall (maybe 4" of 703, spaced 16 inches away, or at least 8 inches away, and maybe angled slot walls on the sides of the room. The ceiling is really hard to figure out: I think I'd put absorption on the front section, directly above the video monitor and on the angled side pieces above the speakers: All of that looks like potential first reflection points.

I also noticed that the room is not symmetrical: the left part is wider than the right part, and the angles are way different! I'm really not sure if it is worth trying to fix that, as building a walls to make it symmetrical is going to remove so much volume from the room.... Two minds.... Probably not worth it.

Wow! I can't believe I said all that, based on so little information, that is self-conflicting anyway! I must be a little crazy... (but everyone already knew that! )

I have to be really honest, and say that I don't think that room can ever be made to sound good: there's just sooo much strange stuff going on there, and the lack of symmetry is a big issue. I don't think you'll ever be able to get an accurate stereo image in there. It might be OK as a home theater, but I can't see it working as a studio.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Thank you very much I bought the n800 this year from a friend for a very low price i could not say no to that but i recognized the same time that i hardly can recieve the sound these speakers can do in a perfect room.


Yes, i did the waterfall (attached) and especially 48Hz seems to have a long tail



I love this! It sounds like a plan and i need to ensure if the effort is worth. It is mostly building Frames and filling with rockwoll so it is not very expensive
and i think i should give it a try. The room will not be perfect but if i can mix my songs for the next 2 years with much less reflections, i can live with some problematic bass frequencys.


it might be the corridor section behind the room/ behind the rear wall. This is 3,16m long till the massive outer wall (40cm brick) of the house ends.
If i remove the wall behind the sofa and build a very deep rockwool trap. Maybe it could improve the standing wave situation.


Yes, i thought about deconstruction the top roof and making the angled walls straight but this afford is to huge for this room size.
The angle of the left and right "angled-roof-wall" is the same angle. I did not get the inner angle of these walls done perfect in sketchup but they are the same. The left wall is deeper. There is standing a "studio"-rack If i would put in a second wall on the left site the room would be symmetrical (but where to put my rack? )


I must laugh about this but you throw out very good points that are damn right .


well, but i´d be happy if i can make something better than it is at moment cause i have no other room i can put the gear in at moment.

I calibrated the left and right speaker to 85db and did the measuring again with each speaker. Here are the results (Yellow is the left speaker and Green the right one):

Hoooo boy! That's an ugly waterfall!

OK, it's more or less what I expected, but you have some surprisingly long tails in there, even in the mids Everything below 1.5 kHz. has RT-60 times exceeding 250 ms! I was expecting the large bass build up below 200 Hz, but the area above that is a little unexpected. I guess it must be due to the strangely angled ceiling. Either that, or you speaker/amp combo is doing strange things on the mids, but I doubt that. So I definitely think that you'll need slot walls on the side to help out with the mid range problems.

It would be interesting to extend the time window of that waterfall plot, out to about 500ms, to see just how bad it is, but that's not imperative right now: the evidence is glaringly clear that you have major bass problems, and will need major bass trapping to deal with it.

Did you notice that you have a large 30 Hz peak from your right speaker, but a large 30 Hz dip from your left speaker? This is why it is important to use only one speaker at a time for the tests! That just was not visible at all in the other tests, since the two sides were canceling each other out, but that most likely represents a mode going across the room somehow, where one speaker is located in the null and the other at the peak. (Your speaker and mic setup easily get down to 30 Hz, so that most likely is real: normally I'd be hesitant to think that 30 Hz details are accurate, since most home setups can't get down there, but in your case it is probably fairly realistic). You have the same issue at 60 Hz. (which is most likely the second harmonic of the same mode), and at 70 Hz (which is a different mode). There might be several more, too.

One good thing: Your room seems to be fairly flat from 1.5 kHz to at least 8 kHz! So this is important: When you build your bass traps, put thick plastic sheeting in front of most of them, to reflect high frequencies and only absorb lows. You don't want to mess up the highs in your room by absorbing too much. So especially the bass traps on the rear wall will need plastic over them, mostly but not completely. Maybe cut wide strips of plastic, and leave narrow gaps between them, so that you still absorb some highs. You might have to experiment a bit to find the right percentage of "gap vs. cover".

I suspect that you will also need some type of tuned device for that 48 Hz problem

Finally, it's hard to tell from the graphs, but it looks like you might have something in the room making a noise at around 750 Hz??? I doubt that that's an acoustic issue, as it seems to be leveling out on both speakers (would be good to see a longer time window), so I'm suspecting maybe a fan or motor in the room, or close by? Air conditioner maybe? Fridge? Just a wild guess, and maybe I'm wrong, but that doesn't strike me as being part of the room acoustics. (Then again, it MIGHT be acoustic: There are similar signs at around 320 Hz and 160 Hz... all harmonics? Hard to say...)

I don't think that is it. In a room that shape, there really aren't any axial modes, except maybe some very weak ones, due to the multiple hard angles. I reckon all of your modes are tangentials and obliques. hitting multiple surfaces.

Exactly! You could even do hangers in there, if you want to go to all that effort, but just thick rockwool covered in plastic is going to make a bog difference. But you also need to do the front, sides and ceiling. Some of your modal issues might not even involve the rear wall, in which case bass trapping there won't have much effect on them.

On the other side of the wall? It would be outside the room, but would that be so bad?

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Yes this all nice gear is eleminated by analysing this waterfall, thats very true but what i did so far is finding a european
supplier for rockwool that is similar to 703 from specs. It is called "Termarock 50" Do you know this product?
http://produktwegweiser-rocknavi.rockwool.de/produktwahl-nach-name/innenausbau/termarock-50.aspx
There is also an acoustic mineral / glaswool that is called Knauf TP 440 that seems to be similar:
http://www.knaufinsulation.de/de/products/Akustik-Daemmplatte_TP_440

I think i should try to put some big packages to the front and top of the room temporary -> measuring again to see if there is an effect that is worth to remove the wall.



this is my computer fan



I should also say there is a mid traveled road around 66feet away from this house. I made the measuries when it was quiet for a while but almost measure a 30hz / 30-40db noise if trucks drive trough sometimes. So i guess this could be a resonance frequency of our house.



I begin to understand this waterfall diagram and see how bad it is too
(The waterfall with 800ms attached below)


Yes i noticed it before. This was the reason i started the thread cause of the leak in this bass range. The bass range of the right speaker does sound fine or even better than the left position. I thought it is cause of the massive outer wall. The 60hz seems to be cause the different corner positions of both speakers / -> bigger distance to the left wall.



I might better mix with my laptop speakers



Very nice point. What thickness of plastic sheeting do you think is fine? There are 0,3mm tick plastic construction foils or better using >0,5mm pond foil? By the way i did see the SAE studios germany in construction phase and i am sure they used pond foil on their walls too.


This is important, so i should start with the other walls definitely.




It would be in my bed and this would be bad ... I´ll gonna think about it if i can recieve some better results with temporary placed rockwool.

I have learned so much this day from you, I appreciate it very much. Many thanks.

Here are the measuries with 800ms:

Ahhh! OK, now it's more clear: the stuff above 250 Hz is mostly just noise, so that can be ignored. Slot walls on the side will still be good, though.

I looked at the link you sent, about the substitutes for 703, but I don't read German very well! And the only one that I could see with any acoustic data at all, is "Knauf Insulation Akustik-Dämmplatte TP 440". That data is OK, but not as good as 703. It would be good if you can get proper acoustical specifications for the "Sonorock Akustik" and also for the "Termarock 50". The information on their web site is not useful for understanding the acoustic properties: Maybe if you call them, they can send you detailed acoustic data?

Unless you do it like this:



The SKP is here:
http://digistar.cl/aaronsommer/upstairs-mixing1-2.skp



Finally, it would be good to have some photos of the room! Very useful.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Termarock 50 seems to be similar to oc703 from weight (50kg³) and flow resistance (kPa s/m²) > 16.
I gonna ask them tomorrow for acoustical specs.


WOOOW Thats a pretty good idea!

Here are some pics to get a view in my room that is not tidy at moment.

Here i gonna type the informations i found so far for mineral wool and Europa substitutes for OC 701 and OC 703.

Product Type________(mm)___125___250___500___1000___2000___4000___NRC___kPa s/m²___kg/m³

OC703, plain_________51____0,17___0,86___1,14___1,07___1,02___0,98____1_______16______48kg
OC701, plain_________51____0,22____0,67__0,98___1,02___0,98___1______0,9______8

ISOVER SSP2/1________50___0,26_____0,6___0,95___1,07__1,01___1,04____________11
ISOVER Ductliner 602__50___0,19____0,56___0,94___0,98__1,02___1,13____0,9
KNAUF TP 440________50___0,25____0,59___0,95___1,06___1_____1,03_____________10
Termarock 50________50______________No Data available_______________________16______50kg
Rockwool Sonorock____________________No Data available__________________________6
URSA AKP 2/V________50___0,22____0,53___0,99___1,05___1,03___1,04_____________5

OC703, plain_________25____0.11____0.28__0.68___0.90___0.93___0.96___0.70
Rockwool RAF_________30___0,05___0,34___0,81___0,99___1,06___1,07
Rockwool RAF 30mm(+20cm air)_0,34_0,73___0,93___0,81__0,92___0,94
KNAUF TP 120 A_______20___0,11____0,26___0,52__0,70___0,84___0,95_____________10
KNAUF TP 120 A_______30___0,11____ 0,28___0,61__0,86___0,97___1,04_____________10


Awaiting a call-back on monday to (hopefully) get acustical informations from "Rockwool" for "Termarock 50" and "Sonorock".
I was researching for Termarock 50 and Rockwool Sonorock and saw many people using it instead 703 in European region.
But there are no acustical informations to find online so far so i gonna wait for the call-back from "Rockwool" (I guess the kPa Data and weight is not enough to assume this material acts similar like one with the same air resistance and weight?)

In other threads people building deep >20cm superchunks and bass traps using lighter material like 701.
The price with regard to the same or better effect was the reason.

Can i use for ceiling bass traps that are 30-40cm thick lighter material similar to OC 701 too or should i use 703 (or an alternative) everywhere?

Aaron