Re: Please help with acoustic baffle box...
Posted: Tue Apr 14, 2020 4:45 am
I designed/drew these up for him (John, don't worry, I didn't charge him but instead asked him to donate to the forum)
GregA World of Experience
https://johnlsayersarchive.com/
Apologies, I only just saw your post. For the foam, I used a sharp insulation knife I purchased from Amazon - https://www.amazon.co.uk/Connex-COXT670 ... B007HKYCOG in combination with a large metal square to ensure straight edges. It was easy to cut, I just had to measure carefully as I'd built the boxes first, so everything had to fit quite precisely.John Steel wrote:Impressively neat job! Can I ask what you used to cut the foam with? Best wishes, John.
The advantage of having the fan on the supply side is that you can filter the air before it enters the silencers and it will also pressurise your room, which keeps dust out.atomicus wrote:Apologies, I only just saw your post. For the foam, I used a sharp insulation knife I purchased from Amazon - https://www.amazon.co.uk/Connex-COXT670 ... B007HKYCOG in combination with a large metal square to ensure straight edges. It was easy to cut, I just had to measure carefully as I'd built the boxes first, so everything had to fit quite precisely.John Steel wrote:Impressively neat job! Can I ask what you used to cut the foam with? Best wishes, John.
Updated pictures above. The one thing I'm having a bit of a conundrum about now is the airflow. I'd already settled on having the fan as extract - I could still change this to intake as I haven't hooked the fan up yet, but from all my research, extract was indicated to me as the best option. With the passive return though, I'm unsure if I should be using a filter or not on this, and if so, what exactly? I've seen quite a few of the carbon cylindrical types (used mostly for hydroponics), but these seem to be more commonly used for extract, and always seem to incorporate a fan. But because my intake is PASSIVE, I don't know if this is the correct thing to use, not least because it would significantly impact the airflow resistance. Any thoughts? Maybe I don't need a filter at all, just some mesh to prevent any creepy crawlies getting in. I certainly don't want anything building a nest inside my baffle boxes lol!
So if the extract side has the fan (as I had planned), I am more likely to suffer with dust build up in the room and baffle boxes?Paulus87 wrote:The advantage of having the fan on the supply side is that you can filter the air before it enters the silencers and it will also pressurise your room, which keeps dust out.atomicus wrote:Apologies, I only just saw your post. For the foam, I used a sharp insulation knife I purchased from Amazon - https://www.amazon.co.uk/Connex-COXT670 ... B007HKYCOG in combination with a large metal square to ensure straight edges. It was easy to cut, I just had to measure carefully as I'd built the boxes first, so everything had to fit quite precisely.John Steel wrote:Impressively neat job! Can I ask what you used to cut the foam with? Best wishes, John.
Updated pictures above. The one thing I'm having a bit of a conundrum about now is the airflow. I'd already settled on having the fan as extract - I could still change this to intake as I haven't hooked the fan up yet, but from all my research, extract was indicated to me as the best option. With the passive return though, I'm unsure if I should be using a filter or not on this, and if so, what exactly? I've seen quite a few of the carbon cylindrical types (used mostly for hydroponics), but these seem to be more commonly used for extract, and always seem to incorporate a fan. But because my intake is PASSIVE, I don't know if this is the correct thing to use, not least because it would significantly impact the airflow resistance. Any thoughts? Maybe I don't need a filter at all, just some mesh to prevent any creepy crawlies getting in. I certainly don't want anything building a nest inside my baffle boxes lol!
Paul
Yes, dust could be an issue.atomicus wrote:So if the extract side has the fan (as I had planned), I am more likely to suffer with dust build up in the room and baffle boxes?Paulus87 wrote:The advantage of having the fan on the supply side is that you can filter the air before it enters the silencers and it will also pressurise your room, which keeps dust out.atomicus wrote:Apologies, I only just saw your post. For the foam, I used a sharp insulation knife I purchased from Amazon - https://www.amazon.co.uk/Connex-COXT670 ... B007HKYCOG in combination with a large metal square to ensure straight edges. It was easy to cut, I just had to measure carefully as I'd built the boxes first, so everything had to fit quite precisely.John Steel wrote:Impressively neat job! Can I ask what you used to cut the foam with? Best wishes, John.
Updated pictures above. The one thing I'm having a bit of a conundrum about now is the airflow. I'd already settled on having the fan as extract - I could still change this to intake as I haven't hooked the fan up yet, but from all my research, extract was indicated to me as the best option. With the passive return though, I'm unsure if I should be using a filter or not on this, and if so, what exactly? I've seen quite a few of the carbon cylindrical types (used mostly for hydroponics), but these seem to be more commonly used for extract, and always seem to incorporate a fan. But because my intake is PASSIVE, I don't know if this is the correct thing to use, not least because it would significantly impact the airflow resistance. Any thoughts? Maybe I don't need a filter at all, just some mesh to prevent any creepy crawlies getting in. I certainly don't want anything building a nest inside my baffle boxes lol!
Paul
If the fan is on the supply side as you suggest, I assume the extract is then passive? Are there any disadvantages to this?
Paulus87 wrote: Yes, dust could be an issue.
I am not aware of any disadvantages, perhaps it depends on the climate? But, I am also not aware of the advantages of doing it the other way round that Gregwor was talking about.
There's other advantages to positive pressurised rooms; it helps to keep the doors closed up tight against the seals.
and this:
"In reverse flow conditions, when the air flows in the opposite direction of the
sound wave the effective speed of sound decreases slightly,causing the sound to take
a longer period of time to travel the silencer passages. This results in improved low
frequency insertion loss performance.
The opposite is true of forward flow applications. When the air is flowing in the
direction of sound propagation the result is decreased acoustic performance at low
frequencies and increased performance at high frequencies."
This is taken from a quote by Rod Gervais, who was referencing the Price Silencers & Panels Engineering Guide.
Paul
I have put a filter box on my air intake path. It has a replaceable dust filter which I'm told is also insect proof. Some designers also choose to filter both the supply and exhaust paths. Bear in mind that whatever you install, the fan has to be powerful enough to meet the airflow requirements of your room and also overcome the static pressure inherent in your HVAC system. Every component added to the path will add a small amount of resistance to airflow or static pressure. This can be cumulatively significant and is tricky to work out although there is a very helpful app available from ASRHAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) which helps to detail static pressure for specific HVAC components. I'm sure you'll have seen this already, but if not, this thread is a must read. ATB John.Any thoughts? Maybe I don't need a filter at all, just some mesh to prevent any creepy crawlies getting in. I certainly don't want anything building a nest inside my baffle boxes lol!