Arcam_Boys Home Cinema mk2 - JBL 3677's

[Arcam_boy]

Hello,

Thought I'd create a little thread on my second incarnation of my home cinema as I feel I'll need a bit of help/advice to get it to the next stage and my own thread is the best place to ask the questions...


So two years ago we moved to our new house and I soon took over one of the spare bedrooms. It measured approximately 14ft long and 10ft wide with 8ft ceilings.

I went for a 7.1.2 set up which consisted of...

Front LCR - JBL LSR 305 active speakers
Subwoofer - SVS PB12/2 + subwoofer
Rears - MK 150T's
Surround Back - MK CS29's
Atmos - Monitor Audio CD 265 IDC

NAD T778 Amplifier

JVC 350 Projector

Spitfire 100" AT Sceeen

xBox Series X / Sky Q / Custom Built PC

This was pretty much the end result...

 

[Arcam_boy]

Continued...

I only have two seats in the room as 99% of the time its just for the wife and I to retreat to and watch a film of some sort and so I opted on buying two stressless recliners for the room which are absolutely amazing to sit on and really pleased with them!!

I also changed the projector as the JVC couldn't quite fill the screen with my throw length and developed a slight magenta tint on the right hand side and when an Epson LS10500 turned up on here with 3 hours on the clock I jumped at the chance to buy it...however it transpired after a few days it wasn't quite what it seemed and I'd be done!!

Its still in my set up and produces a decent picture but its been clocked somehow and has way more hours on it than 3....how many no one knows so my love for it isn't really there!

We've really enjoyed it for the last 12 months or so and the only other change I've made along the way was the screen material from Spitfire to some of the XY 4K sound max stuff which was a nice upgrade on the brightness of the screen!!

For the last few months I've hankered after a set of JBL 3677's for the front, don't ask me why as the little active JBL's I had were absolutely brilliant, they went as loud as I ever needed whilst remaining smooth and fit behind my screen without taking up too much room!

I'd always wished I could of hidden the subwoofer out of view in my room but its absolutely ginormous - stood in its correct orientation its approx 3ft tall x 2ft x 2ft (off the top of my head) so I laid it flat and put it as close to the wall as I could but it still stuck out around 2 foot in to the room!!

I was also at the max throw again with the Epson so ideally I needed a longer room!!!

Anyway pretty much out the blue someone contacted me saying they were selling their JBL 3677's and moving on to some DIY speakers so I jumped at the chance - hired a van and went off to collect them!

This then triggered mk2 of the cinema room....

 

[Arcam_boy]

On the bottom floor of the house was a double height room which was approx 11ft x 10ft and what we use for the Peloton stuff - its always been a bit of a strange room being double height and seemed a but of a waste. Due to the design of the house we have limited loft space as so we decided (much quicker than expected) to turn the room in to a single height space with the space above split in to a 'loft/storage' room and the other part as an extension to my cinema room as fortunately for me it backed on to that room on the first floor!!!

So I managed to find a reputable builder / carpenter and the ball was in motion...

First side of the wall (plasterboard) removed from in the cinema room...

Hole cut....no going back now

 

[Arcam_boy]

False floor going in...

Once that was all finished I took the rest of the wall down which now opened up the cinema room by another 10 foot so it was now 24ft long - I was tempted to keep it like this but had promised the wife some much needed storage

I then laid a layer of 'acoustic foam' on all the joists and topped with 22mm loft boards so get it as solid and resonant free as possible...

 

[Arcam_boy]

I then set about building a false wall and frame. I probably went a little OTT and used 95mm x 45mm C16 timber for the frame - double boarded acoustic 12.5mm plaster boarded at the rear and 18mm MDF on the shelf with 12mm rubber underlay and 20mm rubber matter for the speakers.

I foam taped every joint between the wood/walls etc to hopefully stop any rattles / vibrations etc so we'll see!! In the end I've gained approx 3 foot back in to the room although I've gained foot in the room as my previous screen wall stuck out 1 foot in to the room to accommodate the speakers behind and I've also managed to get the subwoofer hidden!!

Unfortunately I didn't get many pictures at this stage as I simply forgot

And this is pretty much as it looks today (13/03/22) although I've added two more bales of 100mm rockwool in the bit to the left of the sub and a couple of panels stood up the sides / rears of the speakers...

 

[Arcam_boy]

As you can see still lots of work to do but at least they're out the lounge!

I also purchased a new frame / screen from XY and went for 110". I'm hoping/praying I'll have enough throw to fill the screen but my main reasoning was to give me a little more width to space the speakers out as I think the 110" gives me 28cm of extra width over the 100" frame which allows just a little more spread across the front.

I really don't know what to do with regards to finishing off the frame now....

Do I build a full baffle wall with MDF / Plaster board or would I achieve the same (very similar results) with a load of 100mm rockwool??

Should I board the rest of the dividing wall up with 18mm MDF or leave it open like that so the rockwool acts as an absorber, as such???

I had a quick (5 hour) play yesterday afternoon whilst the wife was out and was slightly underwhelmed but I'm 99.9% sure it'll come together eventually and I really really need to get my head around DIRAC / REW....I'm not sure how to 'tame' the JBL's on -40db they were ridiculously loud and the sub wasn't really doing much and sounded a bit flat! The DIRAC graph shows a massive null at 50 - 60Hz so hopefully I can improve that before the rooms finished...but as I say its a long way from being finished

 

[Peter Parker]

The rockwool alone will absorb high frequency reflections, but not stop the bass from wrapping behind. The baffle wall pushes all the bass forward and gives you an extra 6db of bass. That's why THX spec a BW and not just rockwool with a cloth covering.

THX baffle walls - design, build and benefits - Acoustic Frontiers

What is a THX baffle wall and why do I want one in my home theater?! This article explains what a baffle wall is, covers the acoustic and audio benefits and finally provides tips on how to design and build them. A baffle wall is essentially a false wall into which the screen speakers (i.e. [...]

www.acousticfrontiers.com

You can toe in the L&R speakers along with the BW if you like as well.

You can use REW's room simulator to work out where to put the subs. It's easy enough to use and will get you in the ball park. I think most people end up increasing the subs output as many EQs seem to run them a lot lower than most people would like. It can also help identify nulls etc and multiple subs can help with that. I also usually check the dB output from all speakers afterwards with a test disk as well to see if they need tweaking.

With Atmos, I found that if your L&R speakers are near the walls, don't run the height speakers in line with them - that just gives the impression the sound is moving up and down the wall, instead place them at the centreline between the left and centre, and right and centre as done in commercial theatres - it puts the sounds more above the seating/listeners and works more as intended. Otherwise they're too near the walls and firing down into the floor either side of the seats. Angling them towards the listeners helps too.

 

[IWC Dopplel]

nice project and use of space !

 

[LittleNipper]

Good Man, always good to see someone having the balls to rip their house to bits a little !! That double height thing is a tad odd, you've certainly taken advantage of the space !

 

[Arcam_boy]

@Peter Parker

Do I need to put any rockwool in the void between the backwall and the baffle wall?

I'm guessing if I build the baffle wall correctly then no sound waves should be able to get in this area and I'll only need to put some foam on the front of the baffle wall to stop reflection off the speakers with the screen up etc?

Many thanks

 

[Peter Parker]

Yes, I would fill the cavity to stop the void acting like a drum and prevent any resonance. Some add some gaps in the wall to allow it to act like a large bass trap.

 

[LittleNipper]

@Peter Parker

Do I need to put any rockwool in the void between the backwall and the baffle wall?

I'm guessing if I build the baffle wall correctly then no sound waves should be able to get in this area and I'll only need to put some foam on the front of the baffle wall to stop reflection off the speakers with the screen up etc?

Many thanks

@Arcam_boy that's a really good question as it has also gone around in my head also !

This is my understanding of the situation. War And Peace coming ...

You create a baffle wall by essentially having the face of the speaker drivers inline with a false wall you construct. This wall needs to be non-flexing and solid. As such two or three layers of different materials. The different materials so they do not resonate at the same frequency. This needs to be made as solid as you can. Overlapped materials and screwed.

However, as you have now created a large void behind where these speakers are, why not then go ahead and take advantage of this space by turning it into a base trap by filling it with 'stuff', prob. Rockwool. Which makes sense, but i messy.

Equally, if you're making a solid wall with two or three layers of, let's say, plasterboard ( dense ), ply and perhaps MDF. Is stuffing the rear really any use ? My gut feeling is, perhaps. Look at the inside of speakers, they are usually lined with insulation. So, it's kinda the same as doing that I think.

I've seen a lot of baffle walls where holes have been drilled into the 'solid structure' and this allows some of the sound to pass through and get 'trapped'. Which makes sense. I think this would work but you must ensure the baffle wall is really rigid.

The final thing I've noticed is where, on top of the rigid baffle wall more insulation is placed to reduce the effect of sound bouncing back off the AT screen.

What am I going to do in this situation ( as I'm using the same as you ).

1. Construct Baffle wall out of two or three layers of 'stuff' probable a mix of plasterboard and ply. Depends what I can get second hand a decent price ( seeing as new ply is £40 a sheet ). Perhaps Shuttering ply as that should be down around £25 a sheet.

2. I will back fill with Rockwool or similar. I've just found a place not too far away from me selling RWA45 at a pretty darn good price. Two reasons. One, to reduce noise coming into the room. Two, if it helps then the front wall is a large area that is not seen that allows me to chuck a load of sound absorbing materials.

3. I also have 4 purpose built subs I am installing in the wall, these I will build in 'tight' so I have no ability to perhaps twist a little ( as I might want to with LCR to get the 5% gradient to MLP ).

4. Drilling holes to assist the baffle wall do it's thing. Ok, look at all the sound defusors / absorbors that are custom made, they have gaps / slits / holes. Brains greater than mind have decided this works. As I know where all the vertical / horizontal structural timbers are for my baffle wall, I can put these in later, when I am convinced of it. I will have to ensure they are aligned ect. I have also seen, where people have done this they have had black material behind the baffle wall infront of the insulation, so in the hole it looks black.

5. The absorption material ON the baffle wall also makes sense. I need to research this a little more, however quite a few people have opted for the black foam egg cup stuff. Simple. Helps absorb / diffuse. And most of these people are brighter than me ... Oh and you can buy it in the colour black !

Hope my thoughts help or perhaps help cement your thoughts ?

 

[LittleNipper]

On some of my walls I will be creating Panel Sound Absorbers that I can sit behind / in my fabric walls.

Basically a wooden frame with MLV ( Mass Loaded Vinyl ) inside. This link shows you what these are and how to determine what freq. they will effect. As such. Easy to make them, do a freq. response on REW or similar then put them in place and see what occurs.

Panel Sound Absorber

www.mh-audio.nl

As I will have some TecSound left over I will try a few. Personally I think this will work better than the RockWool. Pretty easy to make, don't need to look pretty ( if hidden behind fabric wall ).

 

[LittleNipper]

If you have a look at these acoustic calculators it gives a good idea of how to build stuff for handling different frequencies also how to build them. Took me a while to find this but I thought quite usefull.

I prefer a most scientific approach to just, yeah, should work. Doesn't mean these will work, but gives me warm fuzzies !

Acoustics

www.mh-audio.nl

 

[LittleNipper]

Came across this also, if you are making panels. It's a really good demo of how to do 'em. The main thing I took from this is use GOOD ply to build the frame from rather than timber. You could use the same technique for building the panel suggested above.

The staple gun looks good too. You should be able to purchase a battery nailer.



And this technique ( 5mins in ) to do the cloth is super fancy !

 

[Arcam_boy]

Thanks for all your replies @LittleNipper

I think I'm a little like you trying to get my head around it all and what to do best.

Cost of materials is ridiculous I reckon if I'd done this whole thing 2 years ago it'd of been a good £1000 cheaper than what I've paid already! 18mm MDF is costing me £40 a sheet - the acoustic 12.5 plasterboard is £20 a sheet. However I don't really want to skimp and then regret it for the next 5 years so guess I'll have to grin and bear it!!

I've been playing mainly music for the last week or so in the room at silly levels with plenty of bass to test for any vibrations/rattles and so far not a rattle anywhere but I've literally gone belt and braces with everything!!

Anyway I've made a start on the baffle wall today

I've used C16 38mm x 89mm to construct the frame....

I've decided to go with 12.5mm acoustic plasterboard - heavier than normal board on the back and used foam tape between the frame and board and screwed it in.

I'm going to green glue 18mm MDF on the front which should hopefully make a nice solid wall. I'm using 100mm rockwool around the speakers in the void area.

I've left around a 3mm gap between the speakers and wall. The speakers are very solid/secure so don't think they'll move. I'm going to stick some foam tape around the opening too.

I didn't realise the size of the tube for green glue so had to order a new applicator gun which is due to turn up tomorrow so I can properly secure the MDF on the front.

I'm pretty much out of materials now so will have to order some more plasterboard/MDF/rockwool this week and hopefully get the main part of the wall built. I'm probably going to go for the foam 'egg' material on the front too then cover it all up with MVEL!!

@Peter Parker or anyone else in the know....I'm using plasterboard / green glue / MDF. Do I just use the green glue to secure the wood or do I use the glue and screws?

A few pictures from today it is still W.I.P and it'll probably be a week before I make any progress now whilst I await for wood/plaster!!

 

[Arcam_boy]

Just watched the video on the GG web page and they glue and screw the panels so that should give me a nice secure fix!

 

[Lesmor]

Just watched the video on the GG web page and they glue and screw the panels so that should give me a nice secure fix!

link?

 

[Arcam_boy]

skip to 2 minutes if you don't want to watch it all...

 

[LittleNipper]

Thanks for all your replies @LittleNipper

I think I'm a little like you trying to get my head around it all and what to do best.

Cost of materials is ridiculous I reckon if I'd done this whole thing 2 years ago it'd of been a good £1000 cheaper than what I've paid already! 18mm MDF is costing me £40 a sheet - the acoustic 12.5 plasterboard is £20 a sheet. However I don't really want to skimp and then regret it for the next 5 years so guess I'll have to grin and bear it!!

I've been playing mainly music for the last week or so in the room at silly levels with plenty of bass to test for any vibrations/rattles and so far not a rattle anywhere but I've literally gone belt and braces with everything!!

Anyway I've made a start on the baffle wall today

I've used C16 38mm x 89mm to construct the frame....

I've decided to go with 12.5mm acoustic plasterboard - heavier than normal board on the back and used foam tape between the frame and board and screwed it in.

I'm going to green glue 18mm MDF on the front which should hopefully make a nice solid wall. I'm using 100mm rockwool around the speakers in the void area.

I've left around a 3mm gap between the speakers and wall. The speakers are very solid/secure so don't think they'll move. I'm going to stick some foam tape around the opening too.

I didn't realise the size of the tube for green glue so had to order a new applicator gun which is due to turn up tomorrow so I can properly secure the MDF on the front.

I'm pretty much out of materials now so will have to order some more plasterboard/MDF/rockwool this week and hopefully get the main part of the wall built. I'm probably going to go for the foam 'egg' material on the front too then cover it all up with MVEL!!

@Peter Parker or anyone else in the know....I'm using plasterboard / green glue / MDF. Do I just use the green glue to secure the wood or do I use the glue and screws?

A few pictures from today it is still W.I.P and it'll probably be a week before I make any progress now whilst I await for wood/plaster!!

View attachment 1670324

View attachment 1670325

Yep, that ply looks like a good tight fit. It will be interesting to hear your thoughts on your bottom shelf, where you are putting your equipment / sub ?? Do you feel it obstructs / hinders your view of the main screen ? Or if you were able to would you prefer not to have it present if you could fit your equipment / sub without having to have it ?

 

[Lesmor]

skip to 2 minutes if you don't want to watch it all...

thanks for the link
wouldn't you only need green glue if you wanted to soundproof the room?

other than sound propagating into other rooms
if you were building a baffle on an exterior wall with no close neighbours or had a detached house I don't really see the need for the expense?

 

[Peter Parker]

GreenGlue is viscoelastic and when correctly applied it turns vibrations into heat, reducing their effect, so in a baffle wall it makes the wall more dead and less likely to resonate/vibrate while in close proximity to sounds. Although it is sticky, it's not really a glue (in the same way toffee or honey isn't), so you have to use fixings/screws to hold the plasterboard into position, or it will move/sag/come apart over time.

 

[Romey]

Nice progress - saw your posts in the XY Screen thread. Following with interest. I'll also be constructing a partial baffle wall.

 

[Arcam_boy]

Yep, that ply looks like a good tight fit. It will be interesting to hear your thoughts on your bottom shelf, where you are putting your equipment / sub ?? Do you feel it obstructs / hinders your view of the main screen ? Or if you were able to would you prefer not to have it present if you could fit your equipment / sub without having to have it ?

The bottom shelf is a bit of an 'annoyance' really and I've still not quite decided how I'm going to finish it all off - planning isn't my forte

With the extra length I've created in the room I've managed to move the sub back around 3 foot and out the old room as such. I couldn't go any further back as it would have made things way to awkward in the room we've built behind as a 'loft room' with the ladder and shelving to put stuff.

The speakers obviously had to sit on a shelf to get them at ear height and I wanted the sub at the front still out the room. I don't think it'll effect the screen in anyway as most of the front end will be covered in MVEL. I just need to decide if I'm going to attach the screen to the baffle wall and have a 10" shelf along the front of bring the screen forward and have a completely flat wall with the screen but then may have an issue with my throw length still as since doing the build I went from a 100" screen to a 110" as it then gave me that bit extra width to space the speakers as I wanted to have a little bit of a gap between them rather than 'shoulder to shoulder' but whether it'll make much a difference I'll never really know.

I know we all say it but I genuinely want to keep these speakers for the next 5+ years and so anything I'm doing now I want to do the best I can. The green glue / foam tape etc etc maybe OTT but if it stops a rattle/vibration then it'll be worth it for me.

I've just spent another £272 at Wickes on MDF / Plaster / Rockwool but hoping this will let me finish the baffle wall! Then I'll get some foam ordered to cover it all in!!

 

[Peter Parker]

The shelf isn't ideal, but I guess we could look at it as a kind of stage if it stays (many have speakers on the floor with a stage). I would try and reduce or remove it to get the most benefit from the baffle wall though.

The shelf may cause some bass bounce and will be reflective to the screen, so it might help to treat it like the baffle wall (layer of acoustic foam - you can get flat unprofiled AF which is easier to cover with MVEL, ask if you need a source) and should at least be covered in black MVEL so it's not visible during a movie.

If you bring the screen forward to reduce the shelf and leave the speakers where they are (I believe there may be some small audio benefits with respect to the screen for doing that), you then have the speakers in a box so the sides and top also need to be treated as some audio that bounces back from the screen can then bounce around inside the box. Toe the speakers in to the seating position helps reduce the impact of the walls on the sound. It may even help to cover the speakers with some acoustic foam as well (you can get sheets of glue backed AF of varying thickness)

Without measuring, we won't really know how much the shelf will affect the sound, or even if it measures a difference would you hear it during a movie. The shelf may be outside of the effect on the tweeters due to the waveguides so might even be acoustically invisible to higher frequencies. It's a pity we can't measure a with and without to see.