[Amps] Acoustic Noise Comparison

[Jim Barber]

And that's where we have to be careful.

I work on dampening and otherwise normalizing enclosures and spaces for 
artsy designers, so if there's a measurable resonance in a waterfall 
decay display when excited by a high-energy signal, I feel compelled to 
fix it. To me, the 76A cabinet rings like a bell. To someone else it 
might sound acoustically dead. It's a matter of perspective.

Can the "average guy" tell the difference between an acoustically 
treated amp blower/case and an untreated one? Absolutely. Will that same 
"average guy" care, or perceive it as an improvement? That's a different 
question.

My .02,
Jim N7CXI

On 6/21/2012 6:58 PM, Carl wrote:
> My 76PA 3 holer is almost silent, same sheet metal
>
> Carl
>
>
> ----- Original Message -----
> From: "Roger (K8RI)" <k8ri at rogerhalstead.com>
> To: <amps at contesting.com>
> Sent: Thursday, June 21, 2012 9:05 PM
> Subject: Re: [Amps] Acoustic Noise Comparison
>
>
>> On 6/21/2012 2:43 PM, Jim Barber wrote:
>>> Spot on, Jim.
>>> The 76A and the 78 suffer from both vibration and turbulence, with the
>>> effects compounded by resonances in the sheet metal cover.
>>
>> My "old" 76A is almost silent with no vibration in the cover.
>> For those that do vibrate, a simple piece of tape on the top of the
>> center partition should quiet it as it has to vibrate against something.
>>
>> If the fan vibrates bad enough to make the case vibrate enough to make
>> noise I'd check the squirrel cage to make sure there is nothing going
>> for a ride. Those fans are very sensitive to any foreign material...
>> like bugs.  I can lay my hand on the case while the fan is running and
>> feel no vibration and that thing is so old that any rubber is long gone.
>>
>> And for Jim? Mig welding from a spool is often an exercise in futility
>> and frustration.  Heat and speed are critical and I'd not weld anything
>> to the cover anyway.
>>
>> 73
>>
>> Roger(K8RI)
>>
>>>
>>> Better blower mounting and fuzz would help a lot, a scattering of braces
>>> in different lengths (where they'd fit) under at least the cover top
>>> would help them help.
>>>
>>> Some may not believe this, but after bracing, bead-blasting and
>>> powder-coating the top cover with heavy wrinkle-black helps at least a
>>> little with the cover resonance(s).
>>>
>>> My .02,
>>> Jim N7CXI
>>>
>>> On 6/21/2012 9:28 AM, Jim Brown wrote:
>>>> On 6/21/2012 10:12 AM, Jerry Kaidor wrote:
>>>>>       Still playing with my "new" Alpha 78.
>>>> No experience with that amp, but some components of motor noise are
>>>> vibrationally coupled to the desk or shelf that the amp sits on. I've
>>>> reduce that component of the fan noise in my Titan 425 amps by setting
>>>> the RF deck on soft foam padding. There are no vents on the underside of
>>>> that amp, so I'm not interfering with cooling.
>>>>
>>>> I bought all of my 425s used, and one of them came with a power
>>>> transformer that made a lot of noise. The problem was loose windings, so
>>>> I jammed some shims between the windings and the frame to kill the
>>>> vibration.
>>>>
>>>> Another component of fan noise is air turbulence, and the components are
>>>> higher in frequency.  Higher frequency components bounce off of hard
>>>> surfaces (like walls and shelves) and into the room. We can kill those
>>>> reflections (and thus some of that noise)  by placing soft materials
>>>> (what we acoustic consultants generically call "fuzz") on those
>>>> surfaces.  Obviously this should be done in a manner that doesn't
>>>> interfere with cooling.
>>>>
>>>> 73, Jim K9YC
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>>>
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>>
>>
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