Roofing lead used for soundproofing

I have small amount of knowledge, I took EE360 Acoustics in electrical engineering, I built a house with the interior walls sound proofed, and I have built allot of loudspeaker enclosures.

1) Don't mount the dog house to the carriage. Mount the carriage with some isolation from the ground, like rubber, tires, or better still: hanging with springs. 2) Go for the layered effect. Walls within walls. A wall made with 2x6 top plate and bottom plate, but 2x4 studs staggered on interior and the exterior and fiber glass wall insulation filling the interior is good, the interior and exterior are still coupled at the top plate and bottom plate. Other walls, such as the sonex or lead, should not be connected anywhere and have their own foundation. Stagger the sound leakage of the top and bottom plate of one wall with the weak spots of the other. 3) Treat the air intake passage as carefully as the exhaust muffler. 4) Get the exhaust stack up high, the further up, the less sound comes back down, and the less you will have to breathe.

Be careful what you pray for, it can happen.

Well, if the redirection of the residual sound that I am hoping for, will indeed occur, the sound will be redirected under the deck.

I absolutely agree with this. It is a point that you and, I believe, someone else made, and I will do my utmost to accomplish that.

My diesel has a certain spec on backpressure, which seems fairly liberal as far as the muffler system that I can put it. I forgot the exact number, but it could be as high as 27 inches. Do not quote me on it. In any case, I already own a tractor muffler with is surprisingly quiet given its price.

Yes, thanks. I already bought lead this morning. :)

Thanks, some of the features of my enclosure parallel, broadly, what you are suggesting. I appreciate your thoughts.

i

Thank you. I, myself, have doubts about sensibility of mounting the enclsure on the carriage. Mainly from the standpoint of surviving long term vibration. Please note though, that when installed as intended, the bottom of the carriage will be supported by something like 2x6s, and will be firmly on the ground. The carriage is double layered, with used tires between the bottom of the carriage and the generator platform. Check out "Carriage" under

i

You want to avoid if at all possible having any mechanical connection between the noisy equipment and the enclosure. It will just form a conduit for the sound to bypass the acustic barrier and turn the whole cabinet into a resonator.

Is this thing supposed to be portable? Ideally I would mount the generator on a slab with flexable mounts. Then bolt the barrier foam enclosure set in heavy mastic to the slab.

The city emergency center is next door to my office. They have a pair of

80KW gensets enclosed that way. Except for a little exhaust noise you can't even tell those monsters are running.

Thanks. I am, generally, not opposed to what you say. Since I already mounted the enclosure on the carriage, I will try how it works the way it is, first. If the result is unacceptable, I will redo it to make sure that the enclosure is supported by the foundation and not by the carriage. It will not be difficult to change and will present other advantages.

i

"Ignoramus13187" wrote in message news:csqpjj$e2k$ snipped-for-privacy@pita.alt.net...

i

I read most of your RCM posts, and consider you to be a bright guy with an interest in learning. I respect that. I dont offer any advice so that it might diminish your plans. I do suspect that the noise from an air cooled diesel generator will be so extreme that there will be no way to quiet it to a level you will be satisfied with. I'm considering that this sound absorbing is done with a limited budget. I think you have already considered the wide bandwidth of the noise spectrum produced by the generator. The highs are something you can absorb in alot of affordable materials. The lows are going to be real difficult to diminish to a level you'll accept (I think). Remember, 5DB and even 10 DB wont hardly make any difference when the level is so high to begin with. I assume you know about "3 DB" as being the least amount of power level change thats agreed to have been adjusted. And, less noise is still too much noise when the noise is so great at the source. The quieter it gets, the more your ears adjust and seem to hear better. I think Alexander Graham Bell had that figured out 'way back when'. I am not qualified to calculate the DB level you'll be trying to acheive. I suspect you are better qualified in than calculation department than I am. I do have some experience with trying to reduce noise levels from noisy machinery and generators. It seems that the the quieter you get it, the more 'quietness' you want. I wouldnt be surprised to learn that you will want to diminish the noise level by 50DB or more when that generator is producing power.

All that said, my advice would be to not spend alot of money on materials till you are convinced you will ever achieve your acceptable goal within your budget.

Jerry

Glen

Are you taking into account that the diesel i is using is air cooled?? I'd be surprised to learn that the 80KW gensets are air cooled. It has been my experience that air cooled diesels are a whole lot more noisy that liquid cooled ones. It has been my experience with air cooled diesels that exhaust noise is trivial compared with clatter and vibration.

Jerry

Thanks.

I have a sound level meter. The noise level from an un-enclosed generator running in the open, at 10 feet, is 85 dB. I believe that it is not so bad.

This is an excellent point. The question is, from the standpoint of not pissing off neighbors too much, is 70 db of 125 Hz noise just as annoying as 70db of 1000 Hz noise. I think that the answer is that lower frequencies might be less annoying.

Well, if I quiet it down from 85 unshielded to say 75 or even (maybe I am dreaming) 70 db, that would be a very big improvement.

I know that I generally do not mind people running a lawnmower in their yard, and those would produce noise comparable to my unshielded generator. Google for lawnmower decibel, the most common number cited is 90 dB for a lawnmower. My unshielded genset is 85. If my generator produces even 80 decibel shielded, I would be basically fine.

I used to have an awful, disgusting 3600 RPM diesel generator that was much, much noisier than my current Onan. Fortunately, I sold that POS and the buyer is apparently satisfied (he left me good feedback).

So, perhaps you are thinking about such very noisy units, but my Onan is a bit better.

This is an excellent point, yes.

Thanks Jerry. The lead purchase was kind of a big leap for me. A big (relatively) expense that is a real gamble. The reason for accepting this gamble is that lead is the best material, and also that other than this, there are no unknowns. The generator runs, and does so quite well.

If I fail, I can always sell this lead on ebay for at least a fraction of my original price.

i

I used to have a 3600 rpm diesel unit that was as terrible as you are describing. This one, is not so bad. 85 decibel at 10 feet.

i

Sure it will be a little better, but only a little bit. The thin stuff will reduce the noise to near zero. The thicker stuff might be available in smaller quantities however so that might be it's biggest point.

Thanks, Roger, and thanks everyone. I will work on soundproofing tomorrow and on Sunday, provided nothing serious happens with one of my sick relatives. I will make photos as I go and will post updates as to the noise level. At least I have a sound level meter, so I can obtain "hard" data.

i

But the buyer better be able to pick it up himself.

Jeff

I would expect it to be noticably better. If the lead acts as the mass in a second-order system, 2.5X the mass per unit area should drop the corner frequency by 2.5 x or 1.32 octaves. At a given frequency above the corner freq, at 20 dB/octave that's 26.4 dB more attenuation. The biggest issue will probably then be muffling the air passage.

Since a genny runs at essentially constant speed, the air vent could greatly benefit from tuned resonators, at least at higher freqs. A heroic solution might be forced-air (a blower) moving air thru the enclosure, with automotive mufflers on inlet and outlet.

I agree on all counts.

I will read on tuned resonators.

That is out of question.

i

There is a program called "silencer" that is mainly for designing the chemer sizes in mufflers. Might be worth a look - a freebie on the Net. Geoff

I understand that this is a fixed position genset so if you could mount it below ground level and reflect the sound upwards you may get about 6dB reduction, similar to bund walls alongside freeways, with virtually no cost. Do not mount your box on the frame, leave it freestanding, then vibration noise will not be transmitted to the box from the frame. If possible, the lead sheet sides should hang from the top of the box , not be fixed to the plywood sides, similarly the top should be fixed only around the edges, with the centre free to absorb sound. Suspending the lead on old carpet can help to stop it sagging.

HTH Alan in beautiful Golden Bay, Western Oz, South 32.25.42, East 115.45.44 GMT+8 VK6 YAB ICQ 6581610 to reply, change oz to au in address