Garden mix room near Nottingham, UK

#136

Thank you for the insight to your thought process on those soffits. I'm trying to wrap my head round building some, and building them quickly, so it is inspiring to witness you doing the same.

Cheers!
Jennifer

#137

Great! The hangers don't seem to touch each other so there shouldn't be a problem. Their motion is certainly not visible!

Cheers,
Dio

#138

endorka wrote:Thank you for the insight to your thought process on those soffits.

I’ve been mulling over what Jennifer said, so here is my thought process around building these soffits. Of all the stuff I’ve done so far on this build, this is the third time I’ve soffit mounted monitors whereas most other things have been first or second time.

What I learned from building before that I applied this time:
- it’s easier to build something level and straight if it’s done in sections. So I built the floor to shelf bit first, followed by mounting the box that holds the speaker, followed by the framing for the soffit face. This meant shorter pieces of wood and enabled easier checking and adjusting of each bit to ensure level
- I spent a while calculating and writing down the best position for the soffit face so that each dimension was 20% more than another from the acoustic centre of the speaker
- clamps are your friend. I have four clamps and often used one to hold the spirit level to the piece of wood I was installing.
- I used the spirit level to line up the acoustic centre of the speaker (according to what a very helpful tech support person from Neumann’s UK distributor told me) with the previously marked correct location
- plastic shims are also your friend. I bought a couple of packs of shims for installing the UPVC door and window but they’ve come in super handy for getting the soffit walls to be level and true. Even though I took my time measuring and cutting carefully, these were needed to help push some of the bits of wood back to level
- Sorbothane is expensive! I spent £100 on the hemispheres to hold my monitors in place. The people I bought them from were a Uk seller/distributer and they helped me choose the right items to hold my monitors in place
- despite calculating the right size for my speaker box, based on 20-30% compression of the hemispheres, I found the gap at the top was too big so had to add a layer of 9mm ply to decrease the gap. Not sure what happened there
- I made a template out of strip wood for the holes in the soffit front, that I then clamped and used my trim router bit to cut the holes in the soffit face
- symmetry was proven because once I’d made one soffit face I was able to fit it to both sides!!!! Amazing! This meant I was able to use that as a template for trim routing the other one

So as of this evening, after two days at it, I have the soffits done except the second layer (ply) on the front, and the cupboard in the middle. I reckon I’ve deserved my beer.

Pictures aren’t uploading so will add tomorrow

#139

Thanks for that Gareth. Like yourself I used shims for doors a few months ago, and have found several uses since then. These are the wooden wedge types, and for example were invaluable to ease the silencer into plumb vertical recently. Just gently hammer them in until the spirit level is correct.

Your tip about clamping the spirit level to a workpiece is genius!

#140

Here are the pictures of progress last Friday and over the weekend.

My rudimentary plan for the soffit face. I've ensured that there is at least 20% difference in the distance from acoustic centre of speaker to each edge of the face, according to Stuart's general rules for soffit design.

Power and signal cables clipped to frame.

All hangers in underneath, spaced apart to coincide with equal divisions of the room width.

Bottom of 18mm MDF speaker box screwed to the shelf (which is 2 layers of 18mm OSB). Four hemispheres sat on there calculated to deflect by around 20% with the weight of the speaker. Calculations done in collaboration with hemisphere supplier.

Speaker being positioned with a spirit level so that the acoustic centre (according to the manual) lines up with the mark on the framing measured according to my design. The speaker location is determined by a list of things to avoid, like avoid a line 45 degrees from the corner of the room, avoid placing it on a quarter of the width etc. This was designed in sketchup.

Smaller hemispheres used on the box sides: the box had been designed to account for 20% deflection of these hemispheres. The box side panels were screwed to a piece of 3x2 and the 3x2 then screwed to the shelf, as I couldn't screw up from underneath.

Second side added, as above.

Top of box with hemispheres same as the sides. Something had gone wrong in the measurements meaning I had to add a layer of 9mm ply on the inside of the MDF to get the hemispheres to touch the top of the speaker.

Looking down from above to show the speaker's amp heatsink and through to the cavity below with the hangers in.

List of the hemispheres I bought, if it's useful for someone!

Spirit level and clamps used to get the framing level before screwing the top shelf above in, which held it all in place and true.

Framing for one side finished. Hopefully its strong enough!

Chicken wire metal to create a path for the warm air from the back of the speaker to exit. Managed to fix to the box with a few staples and twist it to itself.

The chicken wire wrapped in felt like fabric (left over from the window gap), held in place with cable ties around the outside.

Lots of insulation cut to fill the cavity around the speaker box.

Insulation in cavity.

Second side box complete and 3x2 screwed to shelf to attach upright supports to.

Plastic packers used to fill gaps between wood to ensure front uprights level. This one is particularly bad just because I didn't give any thought to where I was attaching the 3x2 to the speaker box sides. This has been a bit of design as you go!

#141

They are really helpful photos, both to see what you have been working on, and also because I am starting to think about the flush mounting of monitors and whether I would need to extract the amplifiers or whether sufficient cooling airflow can be provided. I see your funnel above the air hole for hot air rising, Gareth; where will the air supply enter under the monitors?

#142

Thanks Starlight. Hopefully even more helpful now I've added comments to the post. I have some more pics to add in a bit.

The air supply comes from the cavity underneath with all the hangers in, which will just be faced with cara fabric.

Cheers
Gareth

#143

This is superb Gareth, thank you.

I've just posted Stuarts rules for soffits in the reference area, viewtopic.php?f=12&t=912

One thing I can't quite wrap my head round is the cooling duct coming in and out of the speaker enclosure. I understand it is necessary to cool the speaker, but won't it let some of the "SBIR stuff" out that we're trying to keep in?

Apologies for the colloquial language, I'm sure there is a good explanation

It's particularly rattling around my brain at the moment because I'm trying to figure out how this will affect a rear ported speaker.

Cheers,
Jennifer

#144

Hi
Yeah I'm not sure about that either, but I should imagine that most of the SBIR issue is caused by the front facing plane of the speaker. In the case of these Neumann monitors they are a closed design with no ports, so there shouldn't be too much sound coming from the rear. I have tried to get the air vent as far up (and therefore away from the speaker) as possible. I'll report back on how much sound comes out when I can.

However my previous build used Mackie HR824 which have a passive radiator on the back, responsible for considerable low end output. I did the same thing with the air vent out the back and did find that I got sound coming through the air vent - so much so that the fabric trim I initially put over the air vent hole had to be removed as it vibrated audibly. I suspect I'd therefore ended up building some kind of port that was in fact tuned?

However, despite the above, the sound I had in that space was a million times better than I'd ever had with the monitors on stands.

I can already report that music played with the soffit fronts on in my new room sounds loads better than without. What they do to stereo imaging is hard to put into words. I would never go back from soffit mounting now.

Cheers
Gareth

#145

Follow on post:

Cavities filled with insulation (a mix of lighter "fluffy" and rock wool rwa45):

Template made out of batton type wood:

Template clamped to OSB - rough cut with jigsaw then trim routed.

OSB layer up on one side - the template worked well! I was able to mount this piece of OSB to both sides, so then used it as a template to route out the OSB for the other side.

OSB layers up on both sides

Plywood up on one side. I had to re-do the template for this as this layer goes around the edge of the speaker, rather than around the speaker box. The hole for the air vent will be cut once the grille for it arrives. I've gone with some softwood ply for now and may well replace it with baltic birch ply in the future so it looks nicer, or alternatively I'll stain this a light grey.

#146

endorka wrote:Source of the postI've just posted Stuarts rules for soffits in the reference area, https://www.digistar.cl/Forum/viewtopic.php?f=12&t=912

Thank you, Jennifer.

garethmetcalf wrote:Source of the postPlywood up on one side. I had to re-do the template for this as this layer goes around the edge of the speaker, rather than around the speaker box.

Just a question to check my logic: the OSB can touch the speaker box because it is isolated from the monitor by the sorbothane. The plywood, I guess, cannot touch the monitors as that would be a flanking path. Does that mean there is a gap between the plywood and the monitors?

#147

garethmetcalf wrote:Source of the postHowever my previous build used Mackie HR824 which have a passive radiator on the back, responsible for considerable low end output. I did the same thing with the air vent out the back and did find that I got sound coming through the air vent - so much so that the fabric trim I initially put over the air vent hole had to be removed as it vibrated audibly. I suspect I'd therefore ended up building some kind of port that was in fact tuned?

However, despite the above, the sound I had in that space was a million times better than I'd ever had with the monitors on stands.

And that is what I needed to hear, thank you.

Presumably the sound coming out of the speaker enclosure holes is attenuated by bouncing about off the absorbant walls soffit, a bit like a silencer.

And perhaps it would only be a big SBIR problem if the SBIR frequency coincided with the dominant frequencies of the tuned speaker port? Usually the speakers in soffits are very close to the front wall of the room, so the front wall SBIR dip should be up in the midrange, and might not affect the frequencies coming from the tuned port at all? Just ponderings.

Magic to hear that your soffits sound awesome. They are going to look totally boss too.

Cheers!
Jennifer

#148

Starlight - that observation is very astute and has made me realise I probably need to widen the hole around my monitors on the plywood - it’s quite likely touching.

This realisation alone just demonstrates how useful this forum is, Thankyou!!

Jennifer - your musings are beyond my subject expertise so I’m not able to comment, but they do make sense!

Edit.. made the hole bigger so it doesn’t touch the speakers and finished the second front. Also doubled lined/layered the cupboard between the speakers. No idea if this will become a resonant box but I read Stuart say somewhere that a cupboard between the speakers is doable so thought I’d do it! Will make double thickness cupboard doors tomorrow. Once that’s done I should be able to think about another REW test, but I might try cutting wood for my desk furniture first so I can then throw away all the offcuts and clear the room.

#149

Day 164. I’ve been on it in my evenings this week in the desperate quest to get to the end of the heavy duty and incredibly messy woodwork.

This evening I cut the double layer cupboard doors to size and they are glueing overnight. I also fitted the grilles for the air vents then sanded down and screwed the plywood soffit fronts in properly. For cheap ply once sanded it actually looks OK.

The picture below shows the cupboard doors temporarily in place too. I’ll fit the hinges tomorrow night and some kind of gap for my fingers to get in to open them.

I also cut the top for my desk. My design is based on Stuart’s low profile desk, although smaller and less fancy. It will have 4u of rack space each side on the top, at a shallow angle and 4u of rack space underneath on each side as well as a drawer, I think. Again I’m making it out of cheap softwood ply for now and will likely replace it with a birch ply version in the future. So in a sense this is a draft version of the desk. My screen will be mounted off the back of the desk, low down and angled up to get and minimise it getting in the way of sound from the speakers.

#150

garethmetcalf wrote:Source of the post... cupboard doors ... some kind of gap for my fingers to get in to open them.

Have you considered kitchen cupboard push-push latches? Here is an example on amazon.co.uk.

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