Home made sound enclosure

[Perdiem]

Hello. I am installing a rebuilt Northern Lights 6kw generator to replace the 43 year old Onan 7.5. I was hoping to find a used sound enclosure off of a generator that was being upgraded but no luck.

Has anyone successfully built their own? I was thinking of using 2x2 quarter inch angle aluminum uprights in the corners and tying the tops together with more aluminum pieces and then bolting the foam covered plywood sides and top to that. I am a bit tight for width.

How much ventilation is needed for air intake and heat dissipation?

Thanks for any ideas!
Gregg

[Chotu]

Originally Posted by Perdiem

Hello. I am installing a rebuilt Northern Lights 6kw generator to replace the 43 year old Onan 7.5. I was hoping to find a used sound enclosure off of a generator that was being upgraded but no luck.

Has anyone successfully built their own? I was thinking of using 2x2 quarter inch angle aluminum uprights in the corners and tying the tops together with more aluminum pieces and then bolting the foam covered plywood sides and top to that. I am a bit tight for width.

How much ventilation is needed for air intake and heat dissipation?

Thanks for any ideas!
Gregg

The factory sound enclosures do not have ventilation. They rely on the cooling from the sea water. So it’s not much of a concern to have openings for ventilation in this. Any openings you have will allow the sound to come leaking out. As far as intake air, that’s a different question. I don’t know the answer.

However, straight plywood is not what you want. It would will resonate. The key to deadening sound is mass. They make mass laden material that you can use on the surface of the plywood. I think Lead sheeting. That absorbs sound and deadens it from being transmitted out of the box.

[a64pilot]

Many generator heads are air cooled and must have a LOT of air cooling, unfortunately it’s not always just put a fan on a box, often times the incoming air is directed to a particular spot where the cooling is needed.

I’d try to find a factory sound enclosure and get a look at how it’s done before I tried building one so you can try to duplicate the ducting.

My little 3.5KW generator has a 150 CFM blower on it and it’s designed to suck hot air out. Personal opinion is the motor would likely last longer if it blew cool air in as opposed of sucked hot air out, but it’s got 800 hours on it, and I believe it has about a 1,000 life

My little Nexgen’s cover happened to be off, on it you can see there is an interior duct wall that directs air and keeps there from being a direct outlet so sound would get out.

The air is exhausted from the top of the other end via a 3” hose, I used aircraft SCAT hose.

[Perdiem]

Thank you for the quick reply! That lead filled foam is what I was considering using. I didn't know there was no ventilation for heat dissipation - that makes it easier and quieter.

[Chotu]

Originally Posted by a64pilot

Many generator heads are air cooled and must have a LOT of air cooling, unfortunately it’s not always just put a fan on a box, often times the incoming air is directed to a particular spot where the cooling is needed.

I’d try to find a factory sound enclosure and get a look at how it’s done before I tried building one so you can try to duplicate the ducting.

My little 3.5KW generator has a 150 CFM blower on it and it’s designed to suck hot air out. Personal opinion is the motor would likely last longer if it blew cool air in as opposed of sucked hot air out, but it’s got 800 hours on it, and I believe it has about a 1,000 life

Please note, I own the generator that he is talking about. And it has the factory sound enclosure. That is what I’m describing. Just to be clear, they don’t have anything you’re talking about. It is just a box. It relies on the fresh water cooling system.

The factory box uses painted metal panels with a metal frame somewhat like OP is describing. Each panel is held on by some clips that allow you to open it easily from all sides. There are no openings whatsoever in the box. They use the lead foam.

Let me know if you need pics.

This is the Northern Lights m753k

[apacit]

We have a Kohler 5kw diesel gen. I built a three sided box around it and it works well. I used 2x2s for the frame of each side. Then used frp sheeting like shower wall panels with Soundown foam. I then used standard door hinges to hold it together. When I need access I pull the pins out of the hinges and remove the panels individually.

[DaleM]

I've built soundproofing for the main diesel engine using hardi cement board and a soundproofing adhesive between layers. There is way more information on the web on generator soundproofing for houses and home theater systems soundproofing than you will find on boats.

Dale

[Crusty Joker]

Sound insulation.
Study the physics. What are methods of energy management relative to NOISE...
US Navy has been exploring and managing sound for many, many years. I learned a little about it from a great US Navy Veteran...

Absorption, conductance, resonance, reflection, and transfer. Do it in layers and trap the energy as much as possible. That is referred to as deadening sound. Muffling... layers of various density. Few cracks to leak the energy to undesirable locations. Modern engine design traps noise in the crankcase as much as possible with internal webbing to help.

I live at a busy intersection near LAX and have used the knowledge the Chief taught me it to reduce street and other noise by at least 70%. I also increased the ability of soil to absorb and muggle rather than to reflect.

I installed an air cooled single cylinder diesel powered generator on a vessel many years ago and that was a very poor thing to be a part of. System worked but the noise was just horrid.

I love opera, classical symphonic music of all ages. Even some contemporary. I also enjoy the rhythm and hum of a good vessel and well synched engines...

UB a winner too!

[mbinns]

Build a box out of marine plywood , have a right angle elbow air intake and exhaust lined with a skin faced foam. Line the inner box with "composite foam" (1/4" foam/ 1 lb vinyl sound barrier 1/8" thickness (( don't need lead))/ and a 1" foam with a protective urathane skin facing or foil. make sure there is no leakage around box. Use closed cell foam edging or a bubble to seal properly. "A 1% leakage around box will reduce effectiveness by 50%." The 90 degree elbow for vents blocks the direct sound path and reduces the indirect sound path; make sure it is a large enough opening for air flow. Go to acousticalsolutions.com and look under composite foams. Sonex brand is a class a fire rated composite foam

[barnakiel]

On the air intake side, I helped building custom housing on a boat and the air was fed with a big tube. The tube was also wrapped in sound proofing material. There was a powerful fan pushing air into this tube at the entrance point.


I could hear the engine while in the cockpit but in a fine muted way - loud enough to know the engine was on, but not more than this.



Later we discovered that replacing the air intake system (assembly and filter) gave us even more 'boost'. Apparently old systems were not designed as good as the newer ones in this respect.



b.

[boatman1]

Well, it is difficult (for me) to accept that forced ventilation to your sound box would be a waste of time. Perhaps the design, engineering and execution will be more involved, but surely all the accessories which are a part of the genset will benefit from the reduced temperature. It may be that the physics of a properly conceived forced air system will increase the sound attenuation. Maybe Mr Bose will offer his thoughts?

[doog]

Yes..the foam lead..but there is also a sound absorbing paint with remarkable effects. Runs quiet or similar..claims to turn sound vibration to heat energy..their demos are amazing.

[a64pilot]

I’d be real tempted to build an aluminum frame out of angle extrusions, and the sides from aluminum sheet, maybe .090 thick and attach the sides with Camlocs.
https://www.aircraftspruce.com/catal...8aAtikEALw_wcB

You really, want to make it so the set is easily accessed for maintenance.
Usually there is one side that just about all maintenance activities are done on that one side

If there is no requirement for forced air, that pretty much means it’s a water cooled generator as well as engine I’d suppose, but even most engine rooms have blower fans to keep the temp down

[Squanderbucks]

I built 2 different gender enclosures for my 8 kw diesel he set. The first out of 3/8” plywood lined with 1” sundowner foam. Made a snorkel with in-line fan yo take the hot air that the electrical generator portion put out overboard. Also installed a continuous duty 120v fan inputting air to the electro unit as well.
Used this arrangement fir 10 years or more until I decided to open things up some and made a sectional 3 sided box out of honeycomb fiberglass panels lined with sundown were once again. Corners of the box are 1” right angle alum stock and the whole thing screwed together so it can be removed in sections. Two access doors allow oil and filter as well access to the start/stop switched. Top of the enclosure is insulated floor hatch.
Use the same fan an snorkel arrangement from the earlier model.

[SV__Grace]

Originally Posted by a64pilot

My little 3.5KW generator has a 150 CFM blower on it and it’s designed to suck hot air out. Personal opinion is the motor would likely last longer if it blew cool air in as opposed of sucked hot air out, but it’s got 800 hours on it, and I believe it has about a 1,000 life.

Are you saying that your generator or your exhaust fan has a life of 1,000 hours?

(I have a NexGen 5.5kw with similar setup)