Ground floor studio in Derbyshire, England - first REW test!

I will do the string test later, and the walking test once I've put this round of treatment in.

Better to do those NOW, before putting in the treatment! How will you know what to treat, if you don't first do the tests? :) Also, treatment will "dilute" the visibility of the real problems in the room that the "walking mic" test would otherwise reveal clearly. Since treatment lowers the Q, the problems will spread out more broadly and be less intense, thus harder to identify accuratel in the data...

I'd not spotted the 500Hz bump - the speakers are in theory +/-1.5dB between 39Hz and 20KHz, but anything's possible!

Yep.... but that's when you measure them in a perfect anechoic chamber, in a carefully calibrated test in a proper acoustic laboratory! When you put speakers in a real room, the room itself affects their performance. The room "loads" the speakers acoustically. Just like your car will perform nicely on a dead flat road that is perfectly smooth and dry, but will not even go in a straight line if the road is tilted to one side, angled upwards, with two wheels running on hard concrete and the other two in wet sand, with a strong wind blowing from one side, and rain... The car might be in perfect condition, with brand new, top-quality tyres, but it still wont go straight or accelerate the same way it would when tested under perfect conditions. The same happens to your speakers in a real room. Most people don't realize that the room itself places an unbalanced load on the speaker, just like those driving conditions place an unbalanced resistance on the movement of the car. There's an "impedance" imposed by the air and treatment in the room, that causes the response to be different from what it would be under those perfect laboratory conditions. So it's quite possible that the 500 Hz. "hump" is caused by the room, not the speakers. It can be fixed, but I'll PM you about that.

Any ideas why some of the frequencies have got worse since adding the wall/ceiling super chunks?

Because you are tightening up the room response! So now you are starting to see things that were hidden in the "mush" of the loose, incompletely treated room previously. It's normal, and it's a bit scary, which is why you need to start identifying individual issues now, and dealing with them individuality, instead of taking the "shotgun" approach of treating everything at once. Think of it like a patient arriving at a hospital after a car accident: he's covered in mud and blood and dirt and oil and shredded clothing, and you can't really see what's wrong with him. You know he's injured, but you don't know where or how bad. You do some tests, clean him up a bit, and now you can see the REAL wounds that were hidden under the grunge before. Since you can see them now, you can treat them now. They look uglier than before, because they were hidden in the fact that EVERYTHING looked ugly, so nothing was in focus as being worse than anything else, but now that he's cleaned up and you did the tests, you can see just how bad the really bad bits are. So you sew up the really bad wounds as you come across them, then keep cleaning and testing ans sewing up more and more, until he's fixed. That's the point of doing early REW tests, then treatment, then more REW tests. You are peeling off layers and cleaning up stuff that needs to be cleaned up, so you can see where the more ugly, underlying acoustic issues are. Each round of treatment cleans up some acoustic "wounds", and each additional REW test reveals "new" stuff that was actually there before all the time, but you just couldn't see it because of the mud and dirt and blood and tattered cloths. Once you "clean off" the superficial problems, you start seeing the real problems more clearly, so you can then deal with each of those individually, one by one, doing what is needed for each "new" problem you find. So just like a doctor will first do general typical tests and clean off the worst grime in general, he'll then focus on the actual real issues. He won't use a cotton ball and alcohol to fix a deep gash! It needs suturing. And he won't use sutures to fix a broken bone: he'll use a splint or plaster cast. And he wont use a plaster cast to fix an infection. Each problem needs its own specific "fix". That's where you are getting to now. You've cleaned off the general grime and muck, and now you are seeing specific problems, so you need to treat those individually, and stop treating the muck! You might still need to treat more "muck" later, but you first need to deal with the deep gashes and broken bones that you have found, as they are the most important things in sight right now. Excuse the analogies and allegories! But acoustics is so non-intuitive that it sometimes helps to put things in a more every-day understandable perspective.

I'll add some treatment to either side of the glass door (thanks for that tip) - we don't get OC703 in the UK - would RWA45 be as good?

I would go with something a little lighter and softer for there. What can you get in fiberglass insulation?

Between the door on the front wall - I was thinking of putting another super chunk there at that wall/ceiling intersection - the GIK panel won't fit.

That would be fine, but once again I'd go with something lighter than the mineral wool for that one.

Finally, I'm not sure how best to achieve -6dB reduction on the speakers - a picture of the rear panel switches is above. Maybe I'll go for Quarter space (A) and 47Hz? Currently set to Half Space (B) and 37Hz..

Don't cut back on the low end response! You want to roll it off a little, not kill it entirely! Keep it at 37 Hz, but set it for Quarter Space. I PM'd you about that, and some other stuff we can do if you really want to get your room as good as it can be. - Stuart -

Thanks again Stuart, and I'll reply to your PM shortly. I took your advice and did the walking mic test before adding any more treatment. Results for that are: https://www.dropbox.com/s/v6ftkoqtrtgi8 ... .mdat?dl=0 and https://www.dropbox.com/s/zg9udj85n3o2c ... .mdat?dl=0 Interestingly, the massive dipper at 136Hz is only so pronounced at my intended mix position. Something's obviously gone wrong either with the measurement, or the impact of the other changes on the room. It looks like the response would be quite a bit flatter 12" further back. Hang on, I've just realised, I put the mic where my head would be, not where the speaker axes intersect, which is... wait for it.... 12" behind my head. DOH!! I also did the string test: - 3.6ms, which works out to a bounce length of 125cm = the side wall nearest the speaker - 1.74ms, 59.6cm = not really sure! - 188cm = the side wall furthest from the speaker (opposite) - 259cm = seems to be the glass door? I then added three of the GIK 'bass trap' panels to the ceiling, and two of the thinner ones to left and right of the mix position. These should help cater for some of the above identified reflections. I took further REW readings, then set the speakers to quarter space and took readings again. These are all in: https://www.dropbox.com/s/h1fsf1qs93tlk ... .mdat?dl=0 SPL comparison between yesterday and end of today, so the addition of ceiling and wall treatment, and changed speaker settings: I am much happier with the sound of the room now as the ceiling and wall treatment has got rid of the flutter echo. I experimented turning the HRV on and off and can confirm it is this unit generating the 100Hz hum you see. Not sure if the hum is in the power line/coming out the speakers, or actually an audible noise in the room. I'll test for this somehow soon. Knocking back the bass a bit on the speakers has made a visible difference of a couple of dB at the bottom end, and adding the extra treatment has made the RT60 more even. Waterfall plots: NB all the above readings taking in the same place as before for consistency. I will sort out some softer insulation and add it to the insides of the doorway, and to a small super chunk above the door/between speaker soffits. You say I need something other than RWA45 - would this be OK? http://www.knaufinsulation.co.uk/produc ... nifit-slab ?? Thanks! Gareth

Interestingly, the massive dipper at 136Hz is only so pronounced at my intended mix position. Something's obviously gone wrong either with the measurement, or the impact of the other changes on the room.

... or maybe with your interpretation of the data? :) Here's a small part of the results of your walking-mic test, which clearly shows what the real problem is at 136 Hz! Take a close look: You can clearly see how that issue occurs for different frequencies at different mic positions. Here's the Impulse Response for the mix position mic location (0 inches), showing the large reflection I mentioned yesterday, measured more precisely with a delay of 3.630 ms: Do the math on that, and you have a path length difference of 106.5 cm. Do the math on that, and you have a half-wave cancellation frequency of 137.7 Hz. Check the frequency response graph for that mic position, and see what you see at that frequency: Well gee! Look at that! There's a practically perfect match for your null at 136 Hz. To confirm, let's check again, at a different location. Let's say 6 inches behind the mix position. The impulse response shows a strong reflection... At 3.463 ms. That works out to a frequency cancellation of 144.4 Hz. The actual graph for that mic locations shows a frequency cancellation here: 142 Hz. Pretty much spot on! Repeat the above for several more mic locations, reflection times, and frequencies, and you come to the conclusion that this is a floor bounce! So your conclusion that something went wrong with the measurement, or with the treatment, is not correct. The measurement and the treatment have helped to HIGHLIGHT the problem! And the problem is floor bounce. You can easily confirm this by putting the mic back at the mix position (0 inches), and putting a large thick pad of insulation on the floor, half way between the speaker and the mic (for both speakers), then running some more REW tests. Do a few, such as +3", +6", -3" and -6", to check that the problem really did go away. Don't forget to check that the insulation remains at the mid point between speaker and mic for each of those tests.

It looks like the response would be quite a bit flatter 12" further back.

You need to stop looking at the frequency response so much! It's NOT the most important indicator of what's happening at this point in the process! It is one factor, yes, but focusing only on FR will only give you a small part of the big picture. If you look at the IR graphs, you'll see that -12" is no better than 0". In fact, the reflection is LARGER at -12 than it is at 0". It's 37.7% FS, at 12, vs. only 27.9% FS at 0"... :)

I put the mic where my head would be, not where the speaker axes intersect,

If you put your mix position at the point where the speaker axes intersect, then your ears will be off-axis for the speakers! Your EYES will be on-axis, but your ears will be off. So if you want to get your ears surgically transplanted onto your eyeballs, that would be fine... but you might find it hard to see the DAW with your ears in the way! :)

- 3.6ms, which works out to a bounce length of 125cm = the side wall nearest the speaker

Either your SketchUp model is grossly wrong, or you did something wrong with the string test. It should have clearly shown the floor bounce... I checked on your SketchUp model, and I can't make any triangle from the speaker to the mic at 0" that touches the wall. But I certainly can make one that touches the floor!

SPL comparison between yesterday and end of today, so the addition of ceiling and wall treatment, and changed speaker settings:

Once again, FR is only a small part of the equation. Take a look at the OTHER stuff that changed. At this point, you won't be getting more large changes in FR from adding absorption to the room. But you will in other areas, which clearly shows up elsewhere in REW. And the conclusion there is that the room is now too dead. There's too much bare face of absorption in the room. You will need to put strips of thick plastic across some of your bass traps, tuned to the right frequency ranges, to keep the room live. The decay times are even, yes, but too short. - Stuart -

Ah OK this is vey helpful and insightful. I'll try dropping some treatment on the floor as you suggest to confirm it is a floor bounce. So, if that is related to the floor - what's the solution? I don't think I've seen many studios with soft treatment in a specific floor location? Made a desk and open cupboard thing today for my gear, and did the last bits of painting so my floor can be finished this week.... Thanks Gareth

Work still continues... I have installed the remaining bits of treatment: a panel of 2" insulation either side of the corridor, and a small super chunk between the soffits, above the corridor. I've almost finished the fabric covers for the other super chunks but these are velcro'd in place so can be removed to add plastic, to bring back a bit of life into the high end. I've got to get the floor finished, then make two final fabric covers, then it's very nearly done for now!! It already sounds great... Gareth

Here is a long overdue update. I've been busy using the room because it feels, and most importantly, sounds great! I've recorded acoustic guitar, electric guitar and vocal in there, all of which have sounded good. Moreover, the mixes I'm currently working on are sounding great and it's fantastic being able to hear all the low end extension. I finished the treatment of super chunks across the long wall/ceiling intersections and made some furniture - as small as possible. Since then, I've been working offline with Stuart doing some digital tuning to help even out the response, as I'd kinda maxed out on treatment for the space. Stuart will hopefully be able to explain the work we've been doing and show with some nice graphs the improvement it's made to the sound of the room. The only problem I faced is there are some more vibrations in the right hand soffit wall then the left, and I also noticed that the pretty purple covers I made for the speaker air vents were vibrating at certain frequencies, because bass from the 'passive radiator' at the back of my Mackie monitors is also coming out of the air vents. I've removed these purple covers for now. I'm very pleased with the outcome. It took about 3 months of mainly evenings and weekends, and about £3000, much of which went on rebuilding and upgrading the door to outside. Looking forwards: Looking backwards:

Wow, it looks great. Nice work!

This was all a very motivational read

Thanks Jeremy. I've realised I didn't add my final graphs. I've not added any plastic to the traps as I feel the high end is good as it is. I've just got the first tracks back from mastering that I recorded and mixed in this room as it is (with the exception of the drums) and I'm really pleased with the results. The mixes translate to other systems so much better than ever before...! SPL all frequencies: SPL up to 200Hz: Waterfall plot: Spectrogram - note how even it is: I think this pretty good for a room with two identical dimensions!

I've been meaning to do this for a while, Gareth, but kept forgetting. But it's done now! viewtopic.php?f=10&t=5842&p=40923#p40923 You are at the top of the list at present! :thu: Job well done! (Let me know if you like the title I gave your place...) - Stuart -

That’s fantastic Stuart!! Thank you so much. I’m still loving using the room - mixes translate brilliantly, imaging is awesome and it works great for tracking guitar and vocals too. A house sale could be on the horizon so there could well be a two room project in the future!! Thanks again for all your help Gareth

Great! So glad it worked out for you in the end. I must say you did a great job building it.

A house sale could be on the horizon so there could well be a two room project in the future!!

Cool! That would be fantastic! I'd really like to see how that works out, and follow the process! I'm certain that it will be even better than this place. - Stuart -