Odd Shape HT build

I am in the process of constructing a new Semi-D. TOP is about Mid June.

I decided to build the HT room as much as possible by myself. It is more of a journey that I want to take as a hobby.

The HT room is on the 3rd level and I have a carpentry room on the 2nd level.

The HT room is 5m high on one side and slope down 45 deg to 1.6m on the other side.
On the higher 5m side, it is 3.8m wide and on the lower 1.6m side, it is 6.2m wide.
The length is 7.2m on one side and 9.9m on the other side.

This is the plan. Initially I put the screen on the 3.8m side that I can put my existing 3 x 90mm King Cloud III in a single row. At the advice of Pete and Wiz of Oz on site yesterday, I put the screen on the 6.2m side. But I split the King Cloud into 2 rows.

This is the doll house view, I cut the wall off at 2.4m.

My build plan is

  1. The floor is built with a drop of 180mm. I will build the raised floor. The purpose of the raised floor is to do sound absorption for both acoustic and prevent too much noise to flow down to the dining room below. As I plan to squeeze in golf simulation in the future, the raised floor is also for golf ball return and to do a tiltable hitting platform.
  2. The equipment and speakers buffer wall.
  3. Absorbers and diffusers

I Will be using existing speakers and equipment that I have except for a new AT screen ( can as big as 5m x 2.13m for 2.35 ratio) and a new 4K projector. Current JVC X7900 will be moved to master bedroom.

Will appreciate comments on layout and bass management.

My humble view, leaving aside the acoustics .

  1. Will it be better to have a wall build at the back to make the room more rectangular or trapezoidal. I believe that will make it easier for acoustics.

  2. WIth it, that area could be considered to be used for
    a. Having the projector install there, possibly reducing the noise impact and also not having it hung above the sitting area
    b. to house the equipment, golf clubs etc…making the main area cleaner
    c. refreshment area
    d. Having options for floorstanding back surrounds or heights to be at both ends. Maybe access to that area could be at the centre via sliding door or just open cover with thick curtains. If sliding door is used, maybe can then mount treatment onto it, too

Also, maybe can buffle the toilet flushing noise haha, I have a toitlet inside my HT room too, can be irritating. hahaha

I agree - try to square off the back - it will help with speaker placement, and ease the acoustics issues…
Maybe you can show the pic of the ceiling too and the shape?
Use some custom cabinetry to square off the back, and use it for storage of gear and discs?
The atrium volume ceiling is something amazing and you can also dangle speakers from the top or use a lattice structure with wooden beams for a open ceiling look…

I cannot move the 2 rows nearer to the screen because I plan to put a golf hitting area between the front row and screen. The golf hitting screen is in blue.

So I can put a wall immediately after the 2nd row.
Which means 5.1.4 if 2 rows. And 7.1.4 if one row. Have to look for a AVR that support multiple configurations. I think Anthem can do that?

BTW, I might need to put a loft above the 2nd row when I ran out of storage space. To put seldom use light items. Or the loft can act like a circle seat hahaa…

Difference 3D perspectives

Bro, do you need some soundproofing from the vibrations / noise from your compressors?

Yes. Definitely. Any suggestions?

Asphalt layer on the roof
Rock wool in the rear baffle and in a air / wool / air then plaster configuration
But firstly measure the frequency to kill at your workplace first and see which frequency we’re dealing with…

The entire floor is dropped by 180mm. I intend to level it up with Plywood and carpet which will take up about 25mm. The rest of the 150mm, should I fill all up with 3 layers of 50mm rockwool?

Good resource on baffle walls.

A lot of the Avsforum home theatre of the month builds are also baffle walls.

For your main floor, I’ll avoid plywood since there may be spills and if it soaks through, you can’t get rid of the odor and the wood will rot…
Unless you have removable boxes + carpets that can be cleaned?

I will use marine plywood will reduce the amount of water that can be absorbed but not totally.
Will be using 500x500mm carpet tiles.
The plywood will be 500x1000mm. Screwed down. Can be removed if required.
What other option I have to raise the floor?

You could lay a layer of vinyl etc over the plywood, before the carpets. That should take care of any liquid spills.



Does it mean the GXC300 also required 90cm of space behind?
The AT screen will need to be about 1.3m from the wall.

There are two ways to this,

If you have a very large space, you can place the speakers away from the boundary, 2.2m, ie 1.3+0.9m location .

They will be ideal and free from boundary interference. Boundary interference is a result of the bass frequency energy reflecting off the back wall from your speaker, and causing a cancellation with the direct sound .

Another methodology is placing the speakers as close to the wall, or flush mount it to avoid the existence of a boundary. That way there is no energy reflecting off the back wall.

The rule of thumb is the closer your speakers are placed against the wall, the higher the null frequency/ cancellation frequency/ Null is. You then have less distortion and higher output from boundary gain, getting the phase & timing correct is a lot easier

Doesn’t mean the cancellation won’t happen , it’s just that we are now shifting the cancellation frequencies to a higher frequencies so we can use effective absorption panels to handle the bass

When you do that and you now have a crossover of 100hz, sending all those energy to the subwoofers, you now possess the capability to place the subwoofers in any part of the room to handle these cancellation frequencies

When you go full range, You cannot move your main speakers. Because u need to maintain the stereo imaging and balance. But you will suffer from these room modes. Hence I would advise you not to go full range.

Since you have the same speakers, it’s a lot lot more easier… when I get home, I’ll pull out the data I have on this…

I’ll explain here, exactly why one should not go full range , but instead use the subwoofers to handle Low frequencies where you have tons of options for subs placement and acoustic treatment to bring your system to nirvana

On how much toe in and how u intend to bring the best out of the MA, there is a strategy to doing this, using the Schroeder integral. It is pretty complex if you are not familiar with REW.

Everything will play a part, from your placement, to your room to acoustics to the degree of toe in and finally using sound test patterns to dial in the imaging

Then we have vibration control and how to prevent things from rattling in the room etc etc

It’s a lengthy process but u will need someone to help u if you are to bring the set up up to nirvana stage

There are just too many stuff on the internet, sometimes it can be time consuming , but it’s fun.

In short the fundamentals of this is , you gotta get these right.

  1. Room acoustics
  2. Noise , electrical , internal, external
    3, vibration control
  3. Placement
  4. Integration

Happy to host you one more time, to explain in detail the things you can try and should avoid.

If at the end of the day, you liked what u hear, you should follow that path to nirvana. If on the contrary, if you get the chance to listen to a set up that does full range and love it, take that path instead.

At the end of the day, there is no right or wrong, just preference.

But one thing I’m certain, the numbers don’t lie. I have accumulated enough experience to tell instantly how the room is gonna sound just by looking at the numbers.

We can’t defy physics

Ronildoq, Great Thanks for the detailed advice.
Most certainly delighted to go to your den again. That is a reference setup!

I have decided to switch the layout 180 deg.

  1. Now there are 0.6m to 1.8m behind the front speakers.
  2. The screen size is reduced from 4.6m wide (200") to 3.5m (160") at advice by wechnivag via a long and detailed whatapps. great thanks!
  3. The wider side will give 1.5m space between the wall and edge of sofa. Now I can use MA Gold 100 as he surround side speakers.
  4. The in wall 380 will be moved to use as surround back speakers
  5. Will put front sofa on slider or wheels. to move away when doing golf simulation.

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Bro, you’re the expert here, but maybe I can ask if it’s a better idea to do the room treatment after he moves in, since the room is a more peculiar shape?

Courtesy of Gavin:

Some diagram and response plots to illustrate the effect of baffle step and benefits of a baffle/screen wall design.

Effect of the baffle step

Mounting the speaker in a cavity causes some pretty nasty problems

It can be done after he moves in, no problem.

There is no other way if the shape is odd, we need to measure since the room simulation will no longer work

It’s gonna be challenging and we will need to find the spot where the multiple subs are helping each other

Try and cater for a spot for subwoofers at diagonal front back positions . Take advantage of the boundaries, where the subs can be placed at trihedral sections of the room.

Over the years, I’ve tried many different approaches, from “Geddes technique “, to ‘welti” approach , “parham” approach and when I finally got the lyngdorf, I see clearly why methodology from lyngdorf works best. In their videos and interviews, they advocate having subs at corners and boundaries, with 1 main advantage in mind, Timing. That’s what they strive and advocate . Because in their approach, the explanation is very simple . I explain in layman terms

The claim is, like it or not, the room is always a part of the equation for us. We have to work with the room, there is no two ways about it . We cannot escape the room. Then peter lyngdorf explains it further, he said, when you place the subwoofers at the corner of the room, the SPLs go up as a result from boundary gains. When u place it in the middle of the room, you may get a smoother response at the listening position, but notice that your SPLs are lower, compared to the subwoofers placed corners of a solid wall.

We were puzzled, so we thought, hey, we want a smooth frequency response ! Don’t we all strive for that ?

He says, when the subwoofer energy radiates in omnidirectional frequencies, when it sums in phase, do you get a gain in SPLs ? The answer is yes, you have a gain when the frequencies sum in phase. When there is a cancellation, the SPLs reduces, that means there is a lot of frequencies having cancellations and the results are you have phase issues at other frequencies.

This makes perfect sense to me, because what we are after, is not the subwoofer decay time, but the decay time in the room itself. When most of the energy in the room is combining and in phase, they rise fast, they also stop fast

This is why I can tell u, a solid boundary is where you should place the subs, ideally 1 front 1 back.

This is just one small part of the story…

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