Silence and ducted vs ductless mini-split

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  #1  
Old 07-02-18, 11:35 PM
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Silence and ducted vs ductless mini-split

I'm trying to get to the most silent A/C in a small 1200 sq ft house (old construction) and am zeroing in on a mini-split system (prob 1x 15k-18kBTU and 1x 9k). I have a 2007 vintage Mitsubishi MSZ09UN wall-mount in a studio and while it's quiet it's not very quiet, e.g., when sitting reading or working silently it gets to our nerves after a while. That unit is rated 22dBA on low. I'm looking for quieter...

Looking at the engineering manual for the MItsubishi slim duct units I see that at first glance they seem to be louder, for example, rated at 23 and 30dBA minimum for the 12k vs. 15k units (SEZ-KD12NA4R1.TH and 15 variant). But then I look at the engineering manual, and I see that for wall mounted units the sound measurement is taken approx 1m down and 1m in front of the unit, i.e., in the direct air flow, while for the ducted units it's taken 1.5m straight under the unit, i.e., away from the airflow. That makes it a bit of an apples vs oranges comparison, plus presumably the ducted unit sits on top of a soffit or ceiling.

Does anyone have experience with the noise level that can be achieved by the ducted vs ductless units?
 
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Old 07-03-18, 09:38 AM
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if 22 DB is an issue then you better get an engineer to design a ducted system for you.
 
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Old 07-03-18, 09:49 AM
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Thanks for the reply! How would you go about finding an engineer that has a clue about such quiet systems?
 
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Old 07-03-18, 10:18 AM
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For such a small house you will be dramatically increasing your HVAC system cost. If building a muli million dollar home a few thousand for an engineer would be a trivial expense but you could easily spending thousands on custom engineering before anything gets fabricated and installed. Since you are familiar with mini split systems I would for quiet ones or get a traditional force air system though I doubt any will be less than the mid-20's db. You are at the bottom of the noise end and at the point of diminishing returns where you will spend a lot of money to get slightly quieter.
 
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Old 07-03-18, 12:45 PM
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Pilot Dane, thanks for your thoughts. I fear you are correct... A trad. forced air system is a bit out of the question due to upheaval in terms of duct construction, but maybe I should see whether I can get a contractor out to even look at our place (not easy due to location).
Where I'm at is that it seems to me that the ducted mini-split if installed with care should be more quiet that a wall-mount unit, but I'm puzzled by the noise specs...
 
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Old 07-03-18, 08:12 PM
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I am sensitive to noise. I have a 12k Daikin 15 SEER in Florida. During the day the loudest it gets is usually covered by the sound of the fridge..

After the heat of the day I put it on the night setting and it is silent.

If you need quieter than what this is I would suggest sound cancelling headphones or a white noise generator. Also might want to look up misophonia.
 
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Old 07-03-18, 10:13 PM
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Thanks for the humor, you got me to laugh :-).
We live in the middle of a national forest and value the silence we have. We value being able to perceive wildlife sounds around us. We notice how our friends have lost that ability: they can physically hear the sounds but their brain is so trained to ignore sounds that they don't notice anything.
The awful thing about A/C noise is that it practically never stops. Our older fridge (which is on the to-replace list) stops every now and then and it's such a relaxing event every time. I used a phone app today to measure & plot the noise level and when the fridge stops the dB(C) noise level drops 15dB and other than some barely perceptible noise below 400Hz it shows nothing.
I'm not about to go off the deep end to try to get a silent A/C, but to us spending 50% more to get something significantly less noisy makes total sense. I wish I could go to a showroom and experience one of the newer super-quiet wall-mount units. I can't tell whether the "22dBA" unit we have is just much noisier than that or whether that level of noise is unsatisfactory if 50% more gets something better :-).
 
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Old 07-04-18, 05:26 AM
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They have DB meter apps for smart phones.

and inexpensive meters.

https://www.amazon.com/Decibel-Meter-RISEPRO-Digital-Sound/dp/B01EZZ8B5Q/ref=asc_df_B01EZZ8B5Q/?tag=hyprod-20&linkCode=df0&hvadid=195451805901&hvpos=1o1&hvnetw=g&hvrand=9124585003934851713&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9012217&hvtargid=pla-312317797099&psc=1[/URL]
 
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Old 07-04-18, 09:54 AM
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jjrbus, thanks for the pointers. I used a phone app and it's very helpful for relative measurements. Where it leaves me wanting is determining how loud on an absolute scale my current appliances and noises are so I can figure out how a new unit would fit in.
WRT the inexpensive meters, none that I saw go below 30dBA, which is the range I'm interested in.
 
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