Hello,

I am planning a new room and want to flush mount the first time. I still planned a few rooms with the LEDE principle and they worked quite fine. But this is new.
The room has 2.85m x 6.63m x 5.61m and is totally empty right now. I am at a starting pont of my measurments /plans and want to build up the acoustics suitable for the flush mount and now i have to decide where to put the speakers. So I had a few measurments and as expected a good listening position is in the first third of the room. The speakers ageled 30 degrees to the sweet spot don´t allow many positions. the only question for me is a good heigth form the floor. do you have a good idea how to calculate well? Are there any good tutorials for proferssional flush mounting in the web? i hope you can understand my bad english




the speakers should be the Neumann KH420 btw

Thank you very much!

For monitor height the recommendation is 1.2 m for the acoustic centre of the speaker. If that places the woofer at the mid point, flip the monitor.

Andre

Thank you very much for your help!
Tell me if I am thinking wrong:

-Avoiding the mid Point of the Room with the woofer is because of the risk of inducing energy to the vertical room modes...am I correct?

-1,2 Meters is because of the height from the floor to the ears?



i took 1,41 m for the mid of the room and 1,25 m for the height of the ears (I am quite a tall person)


My current height of the room is 2.85 m. It will be partly lowered because of minimizing flutter echos and get a little bit of the RFZ design. So i take the center of mass of the lowering and half the way is my middle. correct?

The maker should have centre in its docs.

Yes 1.2 m as being the height of ears when seated.

The vertical midpoint is not an issue with your room. Avoiding the vertical midpoint is to avoid the woofer working into the null at the mode.

Andre

Actual point where the "equilateral triangle" meets should be around 30cm behind the actual sweet spot as there is a distance between your ears and it's usually recommended to sit forward a little.

Don't angle your speakers in the vertical axis unless absolutely necessary. If so, keep the angle at 5° max.

Make sure you can remove the amplifiers from the KH420 using a remote amp / extension kit. Otherwise they will overheat and their reliability will be problematic very fast. They also have a ton of settings that you would not be able to reach once the speakers are permanently set in the wall. That's no good.

Unless K&H can provide you with a remote amp kit, it looks like they are not suited for in-wall mouting at all.

Make sure your wall construction is based around a very rigid and solid structure whose modal response is known and controlled ( https://en.wikipedia.org/wiki/Modal_analysis ) and is also highly damped, broadband. You can achieve that by using materials with a high damping factor layered within the mass and structural layers. These walls are always heavy.

Calculate the acoustic behavior of the cavity (ex: what kind of resonator it is) make sure it has a very low resonance frequency and very wide Q. Filling it with rockwool of the right density will help achieve that for ex.

Make sure your speakers are fully decoupled from the wall structure at a low natural frequency (<8Hz, aiming for 5Hz is better) also making 100% sure there are no possible nasty mechanical interactions with the front wall structure or cavity at said natural frequency. This also concerns the floating floor natural frequency (if there is one). Also make sure the wall cavity remains air tight.

Most importantly: do not mount in-wall unless you know you can control the rest of the room properly. If the rest isn't really tight, you're in for a lot of LF issues.

Proper in-wall mounting isn't a trivial thing to design and implement at all.

thank you so much for your sharing your valueable knowledge! i really really appreciate this!

And yes, there are Remote Electronics Kits for the KH420. I will work on the rest of the room the next days/week and will post the progress of the plan/sketch then.
Here in Austria/Tirol it is not easy to find someone who is familiar with flush mounting and so I am very happy to talk with specialists who have this experience to help.

cu later

Hello again

I am happy to be back again. I was quite busy the last days and finally I did some drawings with sketchup. I had been at the Messe in Frankfurt and had some interesting conversations and I was even able to listen to the Neumann KH420 and also to some Genelec Speakers. I really liked the 8351A btw. They told me that there are Flush Mount Kids for the speakers so maybe I will also think about that also.

Hopefully the pictures can show my concept.











listening position:

-moved back a little (thx again)

speaker wall construction + mounting:

-my thoughts are to make a complete massive brick wall construction
-straight wall with the Bass Cone under the middle of the room
-leave left and right some space for big hybrid bass/broadband corner traps (filled with 6000 Pa.s/m2 Sonorock)

hybrid corner trap

-i wanted the low frequencies to absorb but did not want to affect the higher frequencies to much
-except in the area of the reflection back to the couch / near speakers to sweet spot

angled Walls

-try to lead the sound above the Schroder frequency to the QRD in the back
-minimize flutter echos
-use the material plasterboard (still not quite sure about the material) and make a solid stiffened construction without empty holes
-integrate broadband absorber on the ceiling

back wall

-fill the whole wall with a 1D QRD diffuser. (not calculated yet)

ceiling (first half) :

-angled ceiling
-integrated braodband absorber with rockwool termarock 50 (16.000 Pa.s/m2)


still missing:

-back half ceiling (want to integrate a 2D diffusion for the couch position)
-a fitting cover for the remaining bass traps that let me absorb only the deeper frequencies (maybe it´s better to wait for the first measurements with the first built)
-concept of the ventilation

I am happy to hear about your thoughts about this concept
if there is anything where you would say: STOP, don´t do it, then please tell me. Thank you!

Your rear wall is a big problem here. You've done nothing to deal with the front to back room mode. I'd recommend making the entire rear wall absorptive with a thickness of no less than 0.5m. Although, this is typically where a layered combination of broadband in front of membrane traps (wall to wall, not a few little devices) are a better choice, particularly when the room is concrete or multi-layer drywall. Add any diffusion in front of that, but you should plan that part carefully. While turning the entire rear wall into a diffusor may be great for a live room it's not a good idea for a control room. People always love the idea of diffusion, but more often than not have bad ideas when it comes to implementing it! Also keep in mind that sitting on a couch directly in front of a large diffusor array as you've pictured will not sound good at all.

okay, thx for your input, nms! So I am going to plan a multi layered limp membrane absorber for the back wall... My target will be the 51Hz Mode in this case. I still think about a good material for this... I am looking for something with 5kg/m^2 or above...I think it could be hard to get MLV from a local dealer(Austria)... i have to look more on this and alternative materials... I think it is also good to have measurements with the brick wall built up to find out the exact room mode frequency

diffusion couch problem

-maybe i make something like a variable part in the QRD where you can replace this part with a broadband absorber. or are there other ideas to solve this?

speaker wall construction

-is there something i should change or do you think that I (my friends) can start building up the brick wall in the meantime?

Thank you very much

Membrane yes, limp no. Forget the MLV and think thin hardboard or plywood.

Evaluate the need to actually have a diffusor that size there.

Since you're DIY , first fix the LF properly then make sure that by adding the large diffusor you're not going to mess up the LF by reflecting energy again before it hits the bass trap.

You need to revise your front wall geometry (ratio between side walls and center area). As such, you're going to have issues.

Avoid the forward pitch too if possible.

Incorporate speaker decoupling in the front wall design from the get go and not as an after thought - otherwise you should expect issues and to have a real hard time getting it 'right'. Build around the decoupling system, not the opposite.

I will be very careful with this and I will build the diffusor at the last step, thank you for this advice! I will do some membrane absorbers on the Side walls also...

do you think a 1:1:1 geometry will be fine like on the picture now? There is no more pitch now. Just a straight wall from the floor to the ceiling....


Thank you again, I will plan it like the pictures below if this is okay...




I thought of using shock absorbers like this one for the speaker ground: DRD45 45 Shore High Deflection Rubber Flange Mount | IAC Acoustics

Do you think this is okay?

You have to calculate that geometry (ray tracing, & behaviour @ LF.) vs speaker dispersion etc.

1:1:1 is unlikely to be it.

No angle is better yes

You will never load these properly following this diagram (Old Genelec Drawing IIRC). Sadly your speakers wouldn't load even one sufficiently.

Even if you dummy load the system, then these will remain very soft and the whole speakers will move/shake. Which is not good.

Think out of the box

I Wouldn't base decoupling scheme on these old drawings. I think they are technically misleading: there is no way this is going to work well. They describe pretty much one of the worst possible way to do it. :(

knightonabicycle, you are being given very good free advice by Northward, who has more experience building walls with flush mounted speakers, than anybody who is likely to contribute here. You are lucky. I strongly suggest you go back and read every word of his posts in this thread over and over again.

This is a good point. I am sure that I am missing sth basic or interpreting sth wrong... I feel really happy about the support i get here and I really try hard to understand it.
Maybe I have found to much outdated information or even misinformation in my former studies about building up a flush mounting system. I really have to rethink things new... it is hard to get out of old thoughts

As already correctly mentioned the base of my informations was the old Genelec Drawings and this video (last part)...



The reason i had chosen the "brick solution" is because of the easier decoupeling. But to be honest I am not able to calculate the modal response of a "curved" brick wall and i always thought that the modal resopnse of a wall like this is deep enough... (about 10 Hz below...) I talked to a friend of mine who had studied physics and he said that this calculation ("curved brick wall thing") is not an easy thing to do...it is even more complex when the construction of bricks is also connected with a heavy concrete room....

Back again...

Maybe I come closer to a good concept now... I have read everything over and over and I really hope that I don´t misinterpret something.

Geometry:

First I moved the Speaker a little and redesigned this RFZ Concept. The brick wall is now smaller (height and with) and above the wall there is some space left for more LF absorption (part of the ceiling).

I also planned more LF absorption in the rest of the Room. I will do this with multi layerd porous absorbers and membrane traps with a HF reflecting surface. The surface (just a random layer from sketchup) in the picture is not the final thing. I will try to do it like my former "hybrid bass trap"

My plan is to create the brick wall first (I really hope it is fine now ) and then I make the suited membrane traps for the right position in the wall after the first measurements. I think this is a quite safe way...

I will also do a quite massive ceiling multi layered bass trap (not planned yet)



Position of the speaker:

-I had a closer look @ ray tracing of the KH420 and I think it looks quite fine. (check?)
-The recommended listening distance (1-3 Meters) to the speaker is also good (check)
-remote electronic kits available (check)
-about 1/3 of the room is the sweet spot + 30cm to target the aiming of the speaker (check)
-60° between left and right speaker (check)
-center of the room for the stereo imaging(check)
-woofer not in the middle (check)
-height of the ears in listening position (check)
-no forward pitch (check)

Ray tracing:



am I missing anything?

decoupling from the wall:

I was thinking about this a long time and I think the "out of the box" was meant like this... I took a layer of Silomer for the first cover of the speaker. then I wrap some wood structure around it to keep it in place...

For the cavity of the speakers i had 2 Ideas...

-Idea one, also Silomer

-Idea two, stiff PU foam, the stuff that looks like yellow bubble gum but is quite hard, and fill the cavity and then cut out the hole for the speaker thing

-put the cover around the speaker and have it flush with the wall








what are our ideas about it? do you think this could be a way to be decoupled from the wall?

Going on Getzners diagrams the common 12 mm thick sylomer gets down to about 17 Hz natural resonance if properly loaded. It should then isolate from 17 x (root 2) = about 24 Hz and upwards and start to amplify vibrations below 24 Hz, with roughly 18 dB amplification at 17 Hz. If the speaker load is too light on the sylomer the natural resonance goes up, giving a poorer isolation frequency wise. Too heavy a load and the rubber "bottoms out" giving a stiff(er) connection instead of a floating one.

To reach a very low natural resonance with the sylomer, you have to go for a thicker version than 12 mm.

Northward / Thomas: Could you please explain a bit more about what you wrote? Right or wrong, I presume you mean the vibration damper in the link is much too stiff with its max load of 20 kg/pcs versus a light full range speaker. A too light speaker on top will give a too high natural resonance in the vibration damper so lower frequencies will not be isolated to the surrounding / shelve where it is positioned. (Also, I feel that kind of vibration damper (a “rubber ball” type) is not the best with a down angled speaker, there is a risk it might topple over.)

I have installed the very same kind of vibration damper on my speakers and I feel they work well in my case. As a free standing speaker, it certainly wobbles back and forth if I give it a push. But playing at 95 dB / 1 m, only a very, very slight vibration can be felt with fingertips on the baffle. On the surrounding “baffle wall” the vibration is extremely small, hardly noticeable and I cannot say if these minimal vibrations come from connection through the vibrations dampers or from airborn noice.

(As side note: I use a version for max load 9 kg/pcs versus 44,5 kg speaker weight, so 5 pcs are used which should give a natural resonance of about 14 Hz according to manufacturers diagrams. Mounting is horizontal as in the picture and the room is a basement concrete bunker, partly below ground, with surrounding noice levels at around 15-20 dB. The room is meant only for entertainment / listening room. The dog house / “baffle wall” is not solid concrete / brick but still fairly stiff and heavy. The grey / black wood around the speaker sides are 132 mm / 5,2” thick solid particle board, behind and to the side inside concrete as well as the floor. The speakers are only meant to play down to about 110 Hz where separate subs will take over. So there should be good margin between the vibration dampers resonance of about 14 Hz and the frequency range the speaker shall play. Gaps to the sides are 5 mm, gap at the top about 15 mm. Ratio of speaker weight versus cone weight is quite high, 890:1, so the speaker should not move much back and forth with cone movement / acceleration. Still I will insert some pieces of viton rubber hose of suitable diameter at the top to stop any rocking motion.)

Yes, yes and yes + the differential in loading due to speaker's weight being offset towards the front and eventual angle. The differential in frequency created between the units can potentially add other periodic vibration cycles too. Their shape and the way they are to be installed also creates a fairly large cavity (and de facto tuned) around the speaker, which should be avoided.

Sure, that stuff always works at least to a certain extent. And certainly a lot better than any of these so called Iso stands. For a fraction of the price.

My question back to you is: that slight vibration felt with fingertips - how does that compare in terms of physical displacement to the vibrations/oscillations from a tweeter or mid range driver?

Devil is in the detail.

Ah, thanks. You point out two things which are probably overseen and forgotten by most, me included. If the cavity behind is sealed, the gaps around the speaker should result in a Helmholtz resonator at some frequency. (I believe it is good then when I have 10-30 cm of fiberglass insulation in the cavity between cabinet and the outermost concrete wall. Should provide some damping anyway.)

The second one; cabinet vibrations versus mid / tweeter driver, was given some thought in the construction of the DIY cabinets, though not as part of a flush mount detail with immobile cabinets. Thanks for pointing it out. I have no means of really measuring it but made the same crude “experiment” again and played at 95 dB / 1 m. With fibertips slighltly touching the aluminum waveguide for the mid / high, vibrations are hardly noticeable. I can only say they are lower than the cabinets. (A reason may be the use of viton o-ring seal between aluminum frame and the cabinet. I went through some headaches when the DIY cabinets were made and when I came across a NASA report saying viton tops neoprene for damping vibrations of audible frequencies at room temperature, I decided to go for viton as sealing element between driver frames <=> cabinet and machine screws through slightly oversized holes. The cabinet baffle is a 2 sheet constrained layer damping construction. On the aluminum wave guide, inside the cabinet, 4 mm adhesive bitumen sheeting was applied as vibration damping.)

Successfully decoupled- Can you hear it? Measure it?
Or is it imagination? (Which is a powerful beast )

- How much isolation is needed? Is my decoupling successful?

Intuitively (to me at least) you have to measure vibration levels because it’s difficult too measure acoustically.


Is 10 dB isolation enough (or maybe difficult to reach?

Wobbling speaker cabinet? E.g rhythmic kick drum @ 120 BPM How to measure that? (IM dist?) I dont know…

To me the challenge when flush mounting speakers are:
At the same time soft decoupling (large static deflection), increase resistance to cabinet movement (inertia/ extra load) and then ruin the whole idea with a too stiff trim sealing the gap around the cabinet.

Best

And if you like to change loudspeakers at a later date...

Yes, absolutely. You can feel it as well, as in nothing vibrates in the studio. Some engineers can react to this and find it strange at first that nothing vibrates when they are used to coupled main systems shaking the shell and floors at higher SPL.

You can easily measure it with an accelerometer on site. Though to tune and check decoupling nacelles systems before install, you need a test rig system.

Usually a test rig will consist of a very heavy slab base, many times the weight of the speakers (ours is 960kg) decoupled on Springs & Sylomer for efficiency at a very low natural frequency and across the full spectrum, based over a very solid/rigid foundation (concrete) so it does not suffer from outside vibrations. This is the "clean slate".

Over this you first install the test speaker in a rigid mock-up frame as if in wall (so not decoupled from heavy slab base) and measure how much coupling you get with the slab using an accelerometer.

You then switch frames and insert the one that holds the tested decoupling nacelle system over the slab, measure the difference with the accelerometer and tune the system so it reaches its optimal behaviour.

In the studio, good decoupling is heard pretty easily having the following effect:
- Much tighter and clearer mono & stereo image
- Better depth perception
- Easier to hear fine details
- LF are clearer, especially textures
- Better ability to work at low levels (also a factor of room noise floor)
- Total lack of parasite vibrations (unless playing back at insane SPLs, usually 110dB+, which will excite surfaces nonetheless by the means of speaker -> Air -> solid)

When using good speakers, a side effect that is not evident at first is also that engineers do not have as good an idea of the actual SPL of the playback in the room as it stays very clean no matter what the level is.

In our show room and on construction sites when we test the speakers for the first time or go through extended listening tests, it's not uncommon after a while that we have to tell Engineers that they're listening way over 100dB. The level creeps slowly over time as they go through tracks and play with the volume but they don't realize.

Well, we have to scream or wave at them - which is usually enough, they suddenly realize and turn it down.

So that needs some getting used to and for some a SPL meter during the first days.

We reach -32/34dB with the nacelles only, broadband. Then shell and structure damping further pushes it well under -40dB.

Wobbling cabinet results in lack of detail in HF and MF. Less defined sound. Lack of depth.

You can measure speaker displacement with an accelerometer by measuring speaker front baffle behaviour when hard mounted and when placed in a woobly decoupling system. You will see the amplitude shift a lot.

Well, not saying it's easy, but we have a good system here. Works really well so we can even use it in glass (thick glass). Using dummy loads and pre-constraint parts, you can create a high tension system which will be stiff.

Change of speakers is indeed a problem. That's why clients need to very carefully evaluate their options and think long term. Better wait than invest in a system you're not 100% sure of or of inferior quality because of budget reasons.

+1
Thomas, thanks for this detailed tutorial! I am delighted!

I have a suspicion
that we are so used to vibrating floors, panels racks we will find it strange to hear music without these vibrations.

Best

Ake

Well, I went along with Northwards advice, to kill another one of those devilish details and stop any rocking from the cabinet backwards-forwards when music is playing. Not as elegant a solution as Northwards design where tensioned wires are compressing springs versus the cabinet, flush mounted in a glass wall (if I remember correctly). But, …, it seems to work quite well.

The first two pictures show a mock up of the idea and the 3rd when the device is in place between cabinet and the structure of my doghouse opening. It is a quite simple solution to install: An Allen screw of appropriate length goes through the doghouse structure and into a kind of hurricane nut which is forced into the wood from beneath when the Allen screw is tightened. There is about 10 mm / 3/8” of free screw length down towards the cabinet underneath after tensioning. On the free length, a washer and a nut is threaded on. The nut can then be tensioned versus a piece of rubber which is placed on top of the cabinet. To check for a correct compression of the vibration dampers under the cabinet and reach optimal lowest resonance, a calipers was used to measure the compressed height between cabinet and the structure (shelve / floor).

I didn’t have an accelerometer / contact microphone or stethoscope, so I used the old foreman trick. –A wooden dowel pressed to the ear, the other end of it first on the cabinet and then the doghouse structure. Not much noise from the cabinet itself really and substantially less, next to nothing, from the doghouse structure. So, the rubber shims between cabinet and tensioned nut seem to work well to prevent transmitting cabinet vibrations. There is one on each upper corner of the cabinet and the cabinet does only move ever so slightly if I push on it with substantial force with both hands now. The air gap between cabinet and the structure will be closed off with some cell foam later on.

For once, this is an old habit that dies quickly and painlessly. I don't think any of our clients would enjoy going back to the rattly version.

Any audible difference when playing music? (beyond imaginary ones )

It is not easy to say something for certain at this stage. It is not worse with those devices in place, I can say that. But if they make for a substantial improvement, compared to without, is harder to say as there weren't any loud irritating rattling before they were installed. As they cannot be taken away instantly, sound memory is generally short and it wouldn't be a blind test, this too makes it harder for quick dependabale comparisons. Also, as the wife is home I cannot play at very loud levels where differences could be more noticable.

My imagination is of course 100% positively certain though . Placebo can be a potent medicin!

(It think it might be easier to determine after some prolonged listening with and without them.)

Great thread with lots of useful info!! I'm just about to install my flush mount speakers in the coming couple of weeks and this thread has given me some great ideas!!

I've got some AMC springs to mount my speakers on (AMC100 x 4 for ATC SCM100A with 220KG dummy load). I did a test today with just a dummy load of approx. 240KG and the whole column moved about when touched! Glad I tried it out as I had no idea what to expect with the springs...Hence finding this thread (I've looked high and low about this rather specialized area).

Now I'm thinking I'm going to have to constrain the movements of the cabinets from above like you've done Adhoc. I've got some spare AMC 50 springs with sylomer bases which I think I can rig up similarly to how you've done it with the bolts and stuff. I've no clue on how to calculate screw force etc so I'm going to rig up a little test tomorrow and measure the deflection.

Any more info/ideas on this subject would be great.






Ok so I did a quick test this morning and managed to achieve about 10mm of deflection of the AMC 50 Spring. According to their charts that should equal approx 25KG of load and isolate down to just over 5Hz (inline with the isolation from the 4 AMC 100 springs underneath). The tension/clamping created in this rudimentary test started to pull apart my unfinished mitre saw station so I'm pretty sure it'll stabilise the speakers if built solidly enough. I'm building my studio full time currently and hoping to be hearing the speakers within the next 10 days...I've got a ton of pics and will start a separate thread once I've got time (I've got a thread on John Sayers Forum but haven't updated much).

I think I've got really lucky having these spare springs and I can rig up a frame easily, thanks Adhoc, Northward /Thomas, and akebrake for the inspiration and solution to a problem I only just realised I had!

Some things to keep in mind and think through beforehand could be:
Needed opening height and width before and after the speaker are put in place in your flush mount. To push it in isn’t necessarily the biggest problem. To get it out again, for whatever reason, can be. Figure that out before you construct final baffle wall opening. (My speaker weighs “only “ 44,5 kg / 98 lbs and there is small distance between speaker bottom and the floor where a ”rake” can be inserted to pull it out. Easy to write, harder to do ... An “oversized” opening makes it easier of course but the gaps around should be covered up.)

It might be a good idea to have the baffle wall hole opening up at an angle backwards, instead of a 90 degree corner. -In case you find out you need to rearrange the speaker angel inwards / outwards towards listening position. Change of listening position length wise in the room would probably need some adjustment for the speaker angle.

Thanks Adhoc, I'm adding a bezel with sorbothane to seal the gap round the speaker once in position so the opening I have should alright. In sketchup it looks perfect, in real life I'm sure its probably going to be a real pain, dreading it and excited at the same time! Most of my engineer friends think I'm mad using springs but I think I'm on the path to sonic nirvana and if it doesn't work I can always remove them.

Do you think the speakers would benefit from being clamped using the same system from the sides as well or does the top system eliminate all noticeable movement?