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PostPosted: Sun Jul 15, 2018 4:10 pm 
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Waka wrote:
Gregwor wrote:
Innovative design! The size of these things make fitting them anywhere so difficult. I'm re-designing mine right now and it's proving to be a nightmare, just like yours :-(

Have you checked the specs on that register grill? Make sure it's quiet enough!

Greg

They are indeed a pain!

I phoned them before I bought it. It has 50% free area, and is 450mm x 450mm. This allows quite alot more than the flow in the silencers, so it looks good to me. Silencer cross section is 37500mm2 and flow through diffuser is 50625mm2.


Is the diffuser supposed to reduce the noise of airflow? Is there a reason why you chose to use this as opposed to a normal grille?


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PostPosted: Sun Jul 15, 2018 4:58 pm 
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Quote:
Is the diffuser supposed to reduce the noise of airflow?

The opposite actually. It disturbs the laminar air flow and it shoots the air in different directions around the room. No matter what, the change in air direction will cause some noise. Each diffuser will have an NC rating based on CFM passing through it. Here's an example:

Nailor Catalog

You can see the specs of the different types and the more CFM passing through them, the louder they are. You should be picking a register/diffuser that maintains the quiet operation we've all struggled so hard to achieve in our HVAC designs!

Greg

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PostPosted: Sun Jul 15, 2018 6:03 pm 
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Hi Greg,

I wasnt aware of an NC rating. The company I got these from doesn't list anything on their website for it. Looking at the same design at another company shows it achieves 15-18 NC when below 300fpm. So I'm hoping mine will be the same! I might phone them Monday and ask for a datasheet.

Dan


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PostPosted: Sun Jul 15, 2018 6:22 pm 
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Looking at the same design at another company shows it achieves 15-18 NC when below 300fpm.

At what CFM? 10 CFM or 1000 CFM? To put that into perspective, 10 CFM @ 300 FPM is a lot less air moving than 1000 CFM @ 300 FPM.
Both values matter when it comes to achieving low NC levels. I hope the one you picked up works out! Keep us posted.

Greg

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PostPosted: Sun Jul 15, 2018 9:46 pm 
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Gregwor wrote:
Quote:
Looking at the same design at another company shows it achieves 15-18 NC when below 300fpm.

At what CFM? 10 CFM or 1000 CFM? To put that into perspective, 10 CFM @ 300 FPM is a lot less air moving than 1000 CFM @ 300 FPM.
Both values matter when it comes to achieving low NC levels. I hope the one you picked up works out! Keep us posted.

Greg


My fan draws 410m3/h. The diffuser I'm looking at is the same size listed as I have, with the neck area listed as 0.192m2. Giving a velocity of 410/0.192 = 2139m/h or 0.59m/s. The datasheet says 16NC at 1 m/s.

So seems to be looking good to me (Assuming my diffuser is in anyway comparable to the the one that looks exactly the same and is the same size)


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PostPosted: Sun Jul 15, 2018 9:58 pm 
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buttermuffin wrote:
Is there a reason why you chose to use this as opposed to a normal grille?


They are mainly used on the room supply vent and aren't really required on the extract vent (I'm using it on both for cosmetic reasons). A grille on supply would cause a big draft right near it, that will be cold especially in winter. The diffuser takes the air and distributes it more evenly in the room to reduce the draft and improve the oxygen distribution. The extract side is less of an issue though.


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PostPosted: Tue Jul 17, 2018 4:26 pm 
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Waka wrote:
buttermuffin wrote:
Is there a reason why you chose to use this as opposed to a normal grille?


They are mainly used on the room supply vent and aren't really required on the extract vent (I'm using it on both for cosmetic reasons). A grille on supply would cause a big draft right near it, that will be cold especially in winter. The diffuser takes the air and distributes it more evenly in the room to reduce the draft and improve the oxygen distribution. The extract side is less of an issue though.


Maybe someone else can read this and tell me if it is right. I thought that by having the return and supply registers on opposite sides of the room you would create a distribution of air around the room as it creates a pathway of airflow.


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PostPosted: Tue Jul 17, 2018 5:24 pm 
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buttermuffin wrote:
Waka wrote:
buttermuffin wrote:
Is there a reason why you chose to use this as opposed to a normal grille?


They are mainly used on the room supply vent and aren't really required on the extract vent (I'm using it on both for cosmetic reasons). A grille on supply would cause a big draft right near it, that will be cold especially in winter. The diffuser takes the air and distributes it more evenly in the room to reduce the draft and improve the oxygen distribution. The extract side is less of an issue though.


Maybe someone else can read this and tell me if it is right. I thought that by having the return and supply registers on opposite sides of the room you would create a distribution of air around the room as it creates a pathway of airflow.


They are still on opposite sides of the room.

From Wikipedia:
Quote:
Diffusers are very common in heating, ventilating, and air-conditioning systems.[3] Diffusers are used on both all-air and air-water HVAC systems, as part of room air distribution subsystems, and serve several purposes:

To deliver both conditioning and ventilating air
Evenly distribute the flow of air, in the desired directions
To enhance mixing of room air into the primary air being discharged
Often to cause the air jet(s) to attach to a ceiling or other surface, taking advantage of the Coandă effect
To create low-velocity air movement in the occupied portion of room
Accomplish the above while producing the minimum amount of noise


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PostPosted: Tue Jul 17, 2018 7:17 pm 
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Waka wrote:

They are still on opposite sides of the room.


You said:

Waka wrote:
A grille on supply would cause a big draft right near it, that will be cold especially in winter. The diffuser takes the air and distributes it more evenly in the room to reduce the draft and improve the oxygen distribution


So I was trying to say that just by having the exhaust vent on the other side of the room should help with distribution of air right? Because of this I don't understand why you need a diffuser to "distribute" the air to other parts of the room. I understand that you also want it for the purpose of not having a draft but the air will circulate to other parts of your room without it too.


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PostPosted: Tue Jul 17, 2018 11:20 pm 
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buttermuffin wrote:
Waka wrote:

They are still on opposite sides of the room.


You said:

Waka wrote:
A grille on supply would cause a big draft right near it, that will be cold especially in winter. The diffuser takes the air and distributes it more evenly in the room to reduce the draft and improve the oxygen distribution


So I was trying to say that just by having the exhaust vent on the other side of the room should help with distribution of air right? Because of this I don't understand why you need a diffuser to "distribute" the air to other parts of the room. I understand that you also want it for the purpose of not having a draft but the air will circulate to other parts of your room without it too.


Diffusers are not required, they simply improve the distribution. The air will circulate with or without a diffuser but a diffuser improves the circulation. The design I'm installing is a 4 way diffuser, it directs the air in all 4 directions. This is better distribution than a grille which sends it towards the ground. With the diffuser the air will be spread across the ceiling in all directions and fall towards the ground as warm air rises mixing with it. A grille sending the air out forwards, will mix too, but not as well.


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PostPosted: Wed Jul 18, 2018 1:58 am 
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Maybe there's a misunderstanding of terminology here: There are MANY different types of HVAC registers.

Here's a couple of simple "grill" type registers, such as the ones that Waka is talking about, that do not direct the air in any way: the air just passes through directly, and carries on straight out:
Attachment:
HVAC-hex-grill.jpg


Attachment:
HVAC-grill-Eggcrate-Grille-Standard.jpg


Attachment:
HVAC-grill---.jpg


Attachment:
HVAC-GRILLS-AND-REGISTERS.jpg


Attachment:
HVAC-decorative-grills.jpg


With the above types, the air just flows through without changing direction. So if you have your duct coming down through the ceiling, those just dump the air directly down on your head.

You can also get a type that changes the flow in to move in only one direction:
Attachment:
HVAC-1-way-register.jpg



Or two opposite directions:
Attachment:
HVAC-2-way-register.jpg



Or two perpendicular directions, such as you would use if your duct comes down in the corner of the room:
Attachment:
HVAC-2-way-corner-register.jpg



Or three mutually perpendicular directions, such as you would use if your duct comes down against the middle of a wall:
Attachment:
HVAC-3-way-register.jpg


Or the four-way "diffuser" type that Waka is talking about using in his case:
Attachment:
HVAC-4-way-register.jpg



In some cases the angle of the vanes and flow rate are fixed: you can't change them. But in other cases, there are controls on the register to allow you to adjust the rate, and also the direction of flow:
Attachment:
HVAC-adjustable-diffuser-s-l300.png


Attachment:
HVAC-adjustable-diffuser-2.jpg


Attachment:
HVAC-adjustable-diffuser-3.jpg


Attachment:
HVAC-adjustable-diffuser-5--three-way.jpg


So choose your register carefully, specifically for the job it has to do! The cheaper registers have a low "percentage open area", and are made with simple flat vanes that create a lot of turbulence in the air flow, thus increasing air noise and also static pressure. The more expensive type have smooth, curved aerodynamically shaped vanes and high "open area", so they are a lot less noisy, and do not increase your static pressure much.

Obviously, the more you change the angle of air flow, the more turbulence, noise, and static pressure increase you get.

So, long story short: choose your registers carefully! They have a surprisingly large effect on the performance of your HVAC system, as well as on noise, and comfort.


- Stuart -


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PostPosted: Wed Jul 18, 2018 6:44 am 
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Thanks for that breakdown Stuart, the pictures really helped clarify the descriptions.

I think in the UK the terms are slightly different than the USA (and other places) and this can cause confusion, for example the word register isn't used here. There isn't an overarching generic term describing them all that we use. They're just, a grille, diffuser or a louvre.


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PostPosted: Thu Jul 19, 2018 1:32 am 
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Thanks Stuart, Thanks Waka.


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PostPosted: Mon Jul 23, 2018 9:01 am 
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Ok, so I've been working on my speaker baffle design properly now. I'm using a design inspired by barefoot's method (that is having a self supporting speaker assembly disconnected from the speaker baffle to avoid direct transfer of vibration).

In my design I use a shelf supported by timber screwed into the back and side wall as well as steel wire attached to hooks supporting the front of the self. The speaker shelf has a 25mm gap between it and the baffle at the closest point, and the speaker overhangs the shelf through the hole in the baffle. The speaker is secured by two flat adjustable straps. Ventilation is achieved through the side of the baffle with a light timber frame covered in wire mesh surround the rear of the speaker guaranteeing ventilation behind the speaker.

The baffle is timber framed faced with thick MDF and possibly a thin plasterboard layer to be painted. It has a removable middle panel that can be unscrewed to allow future speaker upgrades, just requiring the speaker hole to be resized. The speaker cutout in the baffle has a 5mm gap all around the speaker face.

Underneath the speaker shelf (not touching the shelf) is a fully sealed slot resonator. This is tuned to 40Hz to 140Hz, achieved by slats of 200mm depth by 50mm width, with 5 - 15mm gaps between them and it being in a corner with an air space ranging from 150mm to 800mm.

(Quick question: Should this be completely filled with insulation? I see in John's (admittedly old) designs in the recording manual section, that it just features a layer of insulation against the inside of the slats and an air gap behind it)

Behind the baffle in the cavity is filled with insulation to dampen resonance, the baffle stops 500mm short of the ceiling height, with the remaining height faced with fabric and completely filled with insulation as bass trapping.

Here are the sketchup images:
Attachment:
Speaker Baffle Finish.jpg

Attachment:
Speaker Baffle Facing Removed.jpg

Attachment:
Speaker Baffle Framing.jpg

Attachment:
Speaker Baffle Speaker Shelf with straps.jpg

Attachment:
Speaker Baffle Slot Resonator 40 - 140hz.jpg


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PostPosted: Sat Aug 04, 2018 2:41 pm 
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I wouldn't put slats across the bottom of the soffit: you'll be getting reflections down there from the rear of your desk, and everything on it: console, video screens, gear, decorations, etc. The speakers will be "illuminating" those very loudly, since they are very close to the speakers, so there's some pretty serious reflections coming off there and heading forwards again, down to where your slats are. It's better o have absorption down there to deal with that. If you are worried about losing the high end from too much absorption, then cover it with plastic, but that probably won't be an issue.

- Stuart -

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