Here’s a spectrograph of the impulses so you can kind of see what effect it has where, at least in that room. They don’t seem to have had any affect below 1k.
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makes sense, they would need to be pretty deep to handle those. I doubt styrofoam, even with a feet deep would have the desired effect. The sound may not even reflect far enough from those trenches 
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I wrote about it before, but my DIY broadband absorbers changed my room from nasty echo chamber into a brilliant place to record voice. I can’t speak to drum recording or even recording anything with a mic apart from voice, but just capturing the errant soundwaves is going to make your room sound so much better. I have room which is roughly 5m x 6m or so. All wall and window, plus on end has a built in closet. Before treatment, and depending on where you placed your head, you would either get zero bass, loads of reflections from the high end, or loads of reflections and bass twice as loud as you thought it was. It was comical.
I’ve ended up with 8 absorbers. I experimented with their placement quite a bit, so I have two between front wall and ceiling, two in each corner on the front wall (stacked up to cover about 90% of the corners, and then the rest are either on walls or ceiling wall corners. Although I haven’t got an LA studio sound, I sometimes do pat myself on the back when I hear the quality of the voiceovers I do!
I did also cover the front wall of my studio with those soft foam panels, which got rid of 95% of all the flutter echoes I was hearing in my room.
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I know you didn’t ask about the vocal room, so ignore this if you want.
However it seems like you threw this in as a must without considering the cost. Treating the whole room might eat up more of your budget than you are thinking.
A good way to keep the costs down and still get good results.
Drop in an Aston Halo behind the mic. Yes, a good condensor mic will cut out much of the room noise from behind the mic, but the design of the Halo also cuts out a lot of floor and ceiling reflections, saving you a lot of treatment from that aspect. (Other reflection shields I’ve tried don’t do much for cutting reflections from up and down, the Halo is curved for this function.)
But what a lot of people forget is to put a curtain behind the vocalist. Because the reflection from behind is most of what is going to get into the mic.
And considering you cement floor, make sure you have some sort of floor underlayer beneath the mic stand.
Should be able to do for around 400€ to get you started, and then you can add improvements later.
The guitar aspect, there is always the option of Rivera Silent Sister Isolation Cab, but that will run you about 800€. Not cheap, but it will take room treatments out of the equations.
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update: the “Attack Wall” tube trap system costs around $10,000 and using the tube traps randomly isnt as effective as the attack wall based on the feedback from the person who uses it.
However he does swear by the attack wall and its effectiveness but the price tag alone is most of your budget.
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Thanks for all the insights guys ! Its very helpfull in shaping my understanding of these things !
I’ve been watching these video’s the last couple of days, and sort of got an idea because of this that I’m currious to hear you’re thoughts on.
Something like this. Its the basic idea. THe way it would actually be made needs to be thought of more.
For the back wall, I have space enough to even make 2 yton walls. Of make slanted walls with the yton blocks.
Dennis is well known in the acoustic fields, he is mostly on point. The only thing I do disagree with him in the first video is that diffusion isnt as distance dependent on the frequency bands it mostly operates on. Most diffusion deals with frequencies over 1000 hz and which is merely a distance of a couple of feet for the wave to fully form. Most reflected waves from the diffusive surfaces will be fully formed by the time they reflect back to the mic or the listening area.
Personally I have not seen a diffuser that works on lows like 90 cycles as dennis says, the diffuser would have to be 4-5 feet deep which would be impractical. Impossible … maybe not but practically if anyone has seen it work on 90hz it would need some testing. Thats where @bozmillar comes in 
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It’s still not clear to me what you are trying to accomplish by building the walls in. The very fact that you are using the term “Isolation foam” is a pretty strong indicator that you are intertwining two completely different concepts as if they were the same thing.
Isolation and room acoustics are completely separate and nearly unrelated things.
Isolation exists to keep outside sounds out (and inside sounds in). Are trucks driving by, or kids playing outside, or neighbor’s vacuuming causing you issues? If so, then you need to think about isolation. If not, then you can scrap isolation from your vocabulary because you don’t need it. You already have it. Being underground is a great way to create isolation. You already have thousands of miles of dirt to isolate you from the outside world. a couple inches of drywall isn’t going to make it much better.
What you need to be worrying about is the internal acoustics. This has nothing to do with isolation and everything to do with how you control the sounds bouncing around inside your room.
Building non-parallel walls will definitely have an effect on the internal acoustics of the room. It will help to reduce flutter echo. But there are other simpler ways to do the same thing, mainly through absorption and diffusion. I think you could easily get a great sounding room in your budget by using just absorption and diffusion.
I think you are far better off starting with the basics: Bass traps and broadband absorbers. Put those up, measure your room and then figure out what it still needs. It may need more absorption, it may need diffusion.
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Even in that video he talks about how deep the diffusers have to be in order to work on low frequencies. It’s completely impractical for most small to medium sized rooms.
If you are too close to a diffusor, it is possible that you can hear some of the ringing from it. But you have to be super close for that. Step back a little bit and the ringing goes away, and you may not have “true” diffusion, but I don’t see why that’s such a big deal. True diffusion will give you a flat response while being too close for the diffusion to be “true” diffusion may add a little color to it. But even then, nothing compares to the nasty coloration of straight up comb filtering. I’d still rather have “untrue” diffusion than a flat wall.
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I’m trying to interpret hte video on diapragmatic absorbers.
He works with multiple “walls”. He talks aobut how important the air between the layers are important so that the absorbtion material can absorb all around.
Btw, I probably just mispkoe when using isolation. Just a way of talking here in Belgium I guess.
So the Yton block would be one of the porous materials that absorbs a part of the waves. So instead of making multiple units like they make, I could do the same principles with these “walls”. At least if it would work.
Before I actually start building I’m going to a professional btw to get some advice on my speciffic advise.
ah, you are trying to build walls that are diaphragmatic absorbers? He’s not talking about building a wall that is an absorber. These are diaphragmatic absorbers: https://www.acousticfields.com/product/acda-12-activated-carbon-diaphragmatic-absorber/
They are standalone units that are calculated both in size, density and thickness. You can’t just take the general idea, build a wall out of it, and expect it to work.
These things are basically bass traps that are tuned to be more effective. But you have to know what you are doing both on the acoustics and the mechanical side to actually design one that works.
wow, according the the specs, those things have a 100% absorption coefficient at 50Hz. If that’s true, that’s pretty amazing. I guess that’s why they sell for $1000 a piece.
Ah, I looked a little deeper. These things are tuned to absorb ONLY 50Hz. Here’s the spec sheet: https://www.acousticfields.com/wp-content/uploads/2012/01/ACDA-12.pdf
By the time you get up to 63Hz, it’s not really absorbing much any more. These things are designed to kill specific frequencies, and you shouldn’t even think about using them until you’ve done everything you can and figured out exactly which frequencies are still causing issues.
which brings us back to the beginning. You need bass traps and broadband absorbers.
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So if I where to hire a guy to calculate exactly that on how to do my design, this would be a great choice or ? If its manageble within the budget ofcourse. I don’t realy want to spend too much money on accoustics after this for a couple of years also.
I think Boz is saying the other way round and I agree. These would not be a good choice since they only operate on 50hz and some on 250 per the sheet. Even a 2 inch owen’s corning fiberglass has better response in the 150 to 250 zone than the diaphragmatic absorbers. These are sort of like just a cherry on top of an already treated room
From what I’ve read on the Acoustic Field’s stuff that you pretty much need an engineer to place it and determine if the sound is useful or detrimental. It sounds good in theory but likely not a good choice for DIY on your build.
I think their target for DIY is people that design rooms for living.
Also, another recommendation I have for planning your build. Not sure if you know about this:
https://www.roomeqwizard.com/
Use the room wizard and a simple Measurement Microphone to help you make changes to the EQ of your room in software. Or figure out your best areas to change.
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Nice mate ! I’m gonna check that out for sure. I was thinking of using something like that to figure out what to do when treating the room. This might come in handy.