Gavin's DIY Home Theatre (Hardcore)

Wechnivag · 29 July 2023 14:03

Talking about SBIR, take a slight detour to explore what it means.

Floyd Toole’s incredible book has a section on it.

https://www.amazon.com/Sound-Reproduction-Psychoacoustics-Loudspeakers-Engineering/dp/113892136X

Here’s an extract from the book. Anechoic response (left) what we see with the klippel NFs, vs in wall - flush mounted (right). The boundary gain reinforces the low end very nicely. Free bass boost.

When the speaker is against the wall but not flush mounted (on wall), SBIR rears it’s ugly head.

Next is something that unfortunately happens quite often, sometimes due to unavoidable constraints, sometimes because of lack of information. Stuffing the cavity mitigates it slightly, but not completely. Avoid as far as possible.

My speakers are currently ~ on wall ish. Talk about breaking rules…

When come time for the final setup of acoustic panels, hope to mitigate it somewhat…

Wechnivag · 18 August 2023 14:40

It’s been a while since the last update. Next item is the screen.

For me it is a foregone conclusion to go with AT screen. I will take my chances with a bit of image quality, in order to have the center channel behind the screen. AT screens not too common as they require basically a dedicated setup, but I don’t think any else comes close to the natural presentation of cohesive sound with the image. Many here have experienced Bryan’s top notch screen and center channel experience.

Size wise, I basically went with the largest screen I could possibly fit. THX maximum is about 45 degrees, I’m at ~50 deg which is common for hardcore setup on Avsforum.
Erick_Garci_diagram

The logical screen size for my room I think is 135in. With the common saying that you wished it was one size bigger, I skipped 135in and went to 150in. It’s XY Screen, 4k material, got it through Earth Sound.

By my calculations, I had 10cm each between screen and floor / ceiling on the front right corner with the low ceiling.
Guess what - the first time I had the screen up and fired up the image, I thought I could have gone 160in…. Just kidding. This is plenty fine… Or is it?

I use this screen size calculator, very useful.

I just saw another thread asking about mains placement. I prefer to keep the mains outside of the screen, both for a wider front stage, as well and avoid the screen HF loss on the mains. With the screen about 50deg, the mains are roughly 55deg apart.

I always wonder why are movies still in scope 2.35. Everything should just be standardized in 1.85 as all TV are that ratio. With imax enhanced, I hope most agree that movies are more immersive with that taller vertical image. For me, it is always a thrill when I fire up a movie and it’s 1.85 with full image height.

It was a great milestone to clear out the room and have enough space to start assembling the screen frame. I actually had no idea how I was going to mount the screen, needed to have the hardware in front of me to strike the inspiration. Luckily Murphy didn’t give me too much of a hard time, maybe just 2 curveballs.

First, due to the size of the screen, they included a couple of struts to brace the span near the middle. Here’s one of the struts being installed.

The problem is, I guess the good people at XY don’t expect their AT screen to be used with the JBL 4722 speaker, because the struts block and will cause diffraction on the center channel…

Thankfully, it wasn’t to difficult to shift the struts to a wider position to clear the center waveguide. Drill a couple of holes, buy some extra nuts and washers.

Next, was realizing that the screen didn’t come with a black backing cloth. This is important to reduce the light reflection, and raising the black floor level. However another layer does mean more HF attenuation on the screen channels. A quick trip down to Chinatown people’s park, level 2 above the hawker center. Got some stretchy black spandex that did the job.

I may have underestimated the amount of stretch needed on the spandex. It was literally a stretch to get it onto the frame. The idea was that more stretch = more acoustically transparent

I used the existing screen fabric mounting hooks to secure the spandex. I also added some led strip lights around the back of the screen frame, but these turned out really quite dim.

Similarly, I added lighting to the manifold subs, hoping that they would be visible behind the screen with lights on. I think this was one of the last time I have seen them…

After that, it was truly a milestone to mount the screen and see the vision take shape.

Unfortunately, the back lighting didn’t really work so well… This is the best I can capture with the camera… Can also see the stretched out black spandex. Actually, it would probably be much more visible without the black spandex.

I wasn’t quite sure what to expect with the very large screen size. Surprisingly, it was a very natural and comfortable feel. I wonder if it is the lower down placement, as the viewing is straight ahead, not looking slightly upwards.

This is only possible with single row seating. Typically the screen height is a compromise for multi row. It has to be raised to maintain line of sight for the back rows. Also the reason for the risers on the back rows.
In this example, the 3rd row is actually still blocked by the 2nd row. And the screen is quite high for the front row.

Wind · 19 August 2023 00:46

I’ve got the honour to be invited (self invite actually lol) by @Wechnivag to visit his den, which is still a work in progress. I can feel SO MUCH dedication into his built upon stepping into the room

I’ll break my experience into 3 sections in brief

Screen and prj
Unlike my prj screen, it’s a little high up since it’s ceiling mount motorized, plus not to compromise my center spk height, there is a limit in how low I can set my prj screen.

His place is the 3rd or 4th place I visited that have full length ceiling to bottom screen size. Definitely an advantage when comes to viewing comfortably plus having center spk behind the acoustic transparent screen. It’s eye leveled without tilting the neck, very nice and relax feel. Can’t really see what’s behind but he showed a very cool jpeg pic on his screen on what’s behind it which is cool! Uncalibrated prj out of the box, definitely can improve in this aspect. *Can borrow you my meter to try out before you looking into a new purchase.

Sound
No heights, only bed layers, the over feel did however gave me a slight hint of height as well, could be the works of the ceiling panels or prolly due to the horn spk. I rem I experience this as well at bro @kennyluck2000 place.
Sound is dynamic, is clear, not to extend of fatigue. Do note that ALL spk are DIY and a huge thumbs up on this aspect. Perhaps shifting the LR surround spk a little back would be ideal for a better steering experience… need to try this out

Bass
Low end is power! Definitely natural rumble I can feel. Very powerful bass considering the room volume to be filled. Only front subs behind screen and the bass just fills the room! The mids is still a work in progress but considering what has been done till date, the bass will still bring a smile to anyone’s face I’m sure. A very interesting concept in achieving this kind of bass and I’m glad I’m able to experience them

Encore before I took leave
One needs to experience the bass at his living room. With ONLY just 4 x 10" sub in wall, I’m very surprised the bass is extremely evenly distributed. No crazy low rumble compared to the ones in the attic, still can feel a little though, but you’ll be suprise how well it worked! The bass comes from the front to the back, no localisation since it’s room filling. Moreover the room volume is even bigger than the attic. It’s very well built and I love it!

Am lucky to have experience this kind of bass and concepts at his place. We’ve discussed about his next idea of going full range for all his spk with bass not only you can hear, but also feel from the heights! Extremely intriguing on the outcome when the day comes!

I had an enjoyable afternoon at your place bro @Wechnivag. Thank you very much for your time I would love to visit again after you’ve completed your work!

Wechnivag · 19 August 2023 03:14

Yes, both you and Ralf pointed it out, definitely something I’m thinking about. The gap between side surrounds to back surround is quite large. Really ‘kiang’ ears all can pick out these areas for improvement.

Likely once the new LR mains are built, I can shift the current mains to the front wide, at the current surround LR position, and move the coax side surrounds to just back of MLP.

Or perhaps different layout and tweaking of the acoustic panels as well on the side walls, shift a bit here and there.

Thanks for the kind words and feedback, always helpful to get a new perspective to point out different areas, as I’m too deep into it myself and will miss some things.

Wind · 19 August 2023 05:23

Not kiang la… … Well at one point in time when i started, my surround placement is like near to surround back lol

Welcome. Just helping each other to make things better. Really happy to get to hear such setup. Really ear opener and admire your work/dedication on the diy

Wechnivag · 19 August 2023 05:39

I have a post covering this bass array in a separate thread.

I was really lucky that the open area to the rest of the house dissipates the bass energy enough that there is no first modal dip from the bass array, unlike in my attic room.

Suspect that modal dip is the cause of the ‘hole’ in the middle. The mid-upper bass above it, and the low bass below it seems good like you noticed.

Now currently working on the low bass diaphragmatic absorber for the back wall to try and tackle this dip. More on the theory and design later, provided it works…

You mentioned Trinnov waveforming. Bro Wong also just shared this link with me, looks like trinnov is also developing in this area, not unlike Dirac ART.

Wechnivag · 19 August 2023 06:23

Next, talk about the room construction. In a nutshell, used the room - in - room approach as much as possible, working with my contractor, without any expert design and construction input from professional acoustic consultants. Definitely a scenario of blind leading the blind, and I truly appreciate the patience and accommodation from my contractor.

Many of the construction techniques and principles for sound isolation are the absolute direct opposite of what the contractors are used to doing, for ease and speed and convenience. Even for professionally designed room, the construction is the absolute Achilles heel. One single, innocent, even well meaning deviation can compromise the sound isolation by 6-10dB.

The main thing I chose to go all out was to have all the walls on resilient mounts. These provide a elastomeric layer between the wall and structure and are the most crucial element in isolation builds.

They are used to hold the ‘hat channels’ and the wall layer is mounted onto the hat channel.

Here’s a better view of how the assembly is done. The studs are stuffed with rockwool. The resilient clips are mounted on studs, hat channels in the clips, and the final wall layer on the hat channels.

For my room, the objective was two fold. First was to keep the outside noise out of the room. The tile roof was the weakest link for this.

Now I realized that one layer is not enough isolation - fighter jets going for landing are very audible…
In hindsight, it is also the weakest link in isolating the low bass from my neighbors.

The 2nd objective is to prevent the HT sound from affecting the rest of the house. The entire left wall is a new construction wall, and it’s performance will be key.

However, I also did not want the wall to be too perfect. Imagine an absolute stuff 12inch thick RC wall. Yes that blocks the sound, but that also gives me the most peaky bass reflection and modes inside the room… So in a zero sum scenario, I tried to find the best compromise between sound isolation and less ‘hard’ bass reflection within the room…

The highest isolating walls are done with dual layers, which is what I did.
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In fact, what I did was a combination of the double stud wall, with the quiet clips, hat channels and double layer sandwich with green glue.

Except, instead of green glue, I used bitumen sheeting that is easily sourced by my contractor, also cost effective. Instead of double layer Drywall sandwich, I used drywall-bitumen - 18mm plywood sandwich.

The innermost layer is plywood for ease of mounting of stuff, but most importantly wood is acoustically the most friendly and benign sounding surface.

More layers of wall doesn’t mean better. There is this thing called triple leaf effect, and it can compromise the isolation significantly due to internal resonance in the internal later. Needless to say I steered clear of it.
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Wechnivag · 19 August 2023 06:48

Some of the construction pitfalls.

I saw the builder driving screws through the hat channel, through the rubber and into the stud. I asked why are you doing that, it short circuits and defeats the rubber isolation.
His well meaning reply was that it would be stronger, as the hat channel felt ‘wobbly’ in the rubber slots.

Corner joints where walls meet walls, or walls meet floors or ceilings are another tricky area. For isolation, there should not be contact. The wall should be shimmed off the floor, and the gap filled with acoustic sealant.

Next is the wall /wall and wall/ceiling joints. Since all walls are isolated on the rubber mounts , they are very flexy and have a lot of movement. Any contact between these perpendicular or angled meeting walls will cause a lot of creaking noises. All must be gapped, and later filled with sealant.

For everyone’s sanity, I didn’t ask them to try and stagger the joints like the illustration. Gap is enough.

Also, the joints between the first and 2nd layers should be staggered, so that there is not a weak area with aligned seams through both layers.
Also note the gap off the floor.

The clips are also not installed at every location. There is staggering involved, and this was also tricky to implement, and took a few tries and rework to get right.

Wechnivag · 19 August 2023 06:59

The whole construction process was extremely challenging. Just installing the studs, resilient mounts and hat channels, we had a few rework.

Then the rockwool stuffing went in and the first layer of drywall went up. Then I did full inspection which involves me banging on all the wall panels and looking for any rattling and creaking sound. All these are marked and investigated and fixed. Typical causes are incorrect mounting with some metal to metal or hard to hard contact.

This part was the most challenging and as had to remove drywall, reposition clips several times.

Then the bitumen layer went up, and finally the plywood layer went up. Finally was the final wall banging inspection to chase down the last of creaking and rattles sound…
Once again I thank my contractor and project manager for their infinite patience in accommodating what must absolutely look like ‘insanity’ on my part…

Wechnivag · 19 August 2023 12:01

With that, here’s some photos of the most difficult part of the room build.

Adding the studs on the front wall. The right wall is brick, so i didn’t use the clips on that wall. Also visible the resilient clips and furring strips (hat channels) on the low ceiling extension on the right.

Some rockwool, clips and furring strips in on the front wall.

Building the ceiling frame structure to support the ceiling panels. Can also see the LH wall separating the HT from the rest of L3. My Project Manager Barry!

The back left wall area. Can see the resilient clips and furring strips on the ceiling part on the left.

First layer of drywall going up. You can just see the gaps between all the angular joints. The gaps are intentional to avoid creaking noises when the walls move with the resilient clips.

The clips and channels behind the front wall. Stuffed with rockwool. Use 100kg for mass and isolation

Looking towards the left wall.

Bitumen layer on and some of the plywood on. Back looking towards screen wall.

Front looking towards back of room. Plywood installed onto bitumen for the low ceilings, the right an back wall extensions.

Looking towards LH wall. Bitumen pasted onto drywall. Plywood to go up over it.

Looking towards RH wall. Plywood not up on the vaulted higher ceiling areas.

Plywood up on all the ceiling areas. Painted the plywood black.

Framing up the baffle wall for the IB. Basically this entire space is the ‘cabinet’ volume for the subs.

Closed up and painted black!

A view of the front wall and ceiling

Carpenter help me head start by cutting out the center and manifold openings.

Can see all the electrical wirings coming into the room. One of the key decisions was to run all wiring externally. After all that effort to build strong wall structures, the last thing i wanted was to cut it full of holes to run wiring… This is not typical of most dedicated HT constructions i’ve seen… they have to work around cutting holes for all the outlets…

I got a regular carpentry outer door. Inner door is from Fascina, together with the windows.
Added a layer of bitumen and ply on the outer door for more mass and isolation.

Screwing onto the door. This is a way to improve the isolation of existing doors. Together with batwings seals all round. I opted for full 360deg seal on both doors, so will have to step over the doorway floor sills. Hardcore, after all haha.

And that completes the recap of the room interior walls construction. I think those who have visited and experienced the bass hopefully can understand the reason for going to these lengths.

Foodie · 19 August 2023 13:12

Power la bro. U are the man!

kennyluck2000 · 19 August 2023 14:10

Awesome work

Wind · 19 August 2023 15:09

Wechnivag · 20 August 2023 02:06

Just want to clarify the room build wasn’t my diy hor…built by the contractors workers… I just help ‘supervise’…

But it’s really not easy. These type of dedicated acoustics construction really needs specialized builders, and they are going to be extremely expensive.

Next, I’ll gather some thoughts of my experience with the room isolation so far. What went well, what didn’t go so well.

First the floor. For full room in room build, the floor is raised and isolated from the structure. This is something that I just don’t have the height in room to afford. I just kept the existing Parquet flooring, no additional lining, nothing. For the 2 bedroom below the HT, I did stuff the ceiling with rockwool. Standard structure, standard ceiling board, just stuff with rockwool. This has been a good compromise. It has not been the weakest link of the sound isolation. Nothing is audible from the bedrooms below. Quite remarkable…

I’m sure this is helped by my fully isolated subs. There is no vibration energy transfered into the structure by mechanical connection. Any energy transfer is only by air pressure.

The weakest link is really the air pressure energy transfer. I guess I was optimistic that the double wall, and the isolated baffle wall and subs would be enough on the front wall, which is party wall with my neighbor. The son’s room is on the other side of the HT, and in the strongest low bass demo scenes, his room shakes… Everything shakes…
Actually let’s be honest, I don’t think some half passed build diy like mine has any chance of containing that kind of low bass energy. Not sure that anything could…

The left wall is really quite flexible in terms of low bass energy. I realized after the fact, the STC ratings are never meant to deal with bass below 100hz.
A friend helped sim this. A wall with STC 48 at 900hz, only has STC 18 at about 60hz, and even lower below that.

STC 12 at say 20 Hz means a 100dB bass inside the room is only attenuated to 88dB on the other side of the wall…

That certainly feels like what the bass sounds on the other side of the left wall. The wall surfaces move with the bass, both inside and outside.
The good thing is, this means the bass is less peaky and some energy is removed by the wall motion. The bad thing is, there is not much bass isolation on the other side of the wall.
The worse thing is, depending on the damping (you hear me talk a lot about damping) the wall can oscillate with the stored energy, cause very long decay tails. So far, I think between the rubber in the resilient clips, and the bitumen sheet sandwich inner wall, the stored energy ringing hasn’t been too much of an audible problem.

I have read comments about drywall ‘roar’. I guess that is related to the resonant and stored energy of typical drywall structures.

I always see the construction threads on avsforum. Full studs, fully stuffed with rockwool. Then the drywall goes up and I feel such a pity. If plywood is used instead of drywall, it would just sound immediately so much better.

When I first completed the room, bare with no acoustic treatment, not even first sidewall reflection, I listened in the room testing the coaxial surrounds. And the sound was just natural, not echoey or offensive as one might expect of a bare room. That’s imo is the difference with the wood vs drywall. The natural internal damping of wood is just acoustically more pleasing that most other material - drywall, glass, stone etc.