ewi shock mount rack cases

mgavin

mgavin

Experienced
is it normal for the shock mount foam not to extend the entire depth of the case?

i noticed that the depth of the foam frame in my ewi case is about 1/2 to maybe an inch deep depth. i bought it assuming that the foam would extend all the way to the other side. is this normal for shock mount rack cases? or is this just because these cases are made in china?



so to be clear there is a shock mount frame, but then behind the foam frame it is hollow to the otherside .....



A3UE-14 Shock Mount Case


thanks, mg
 
I don't own any EWI Shock cases (do have a couple of their non-shock cases tho', and they are AWESOME). I would assume the foam should extend all the way around the inner casing and the entire length of that inner casing too. If not, what's the point? Without pictures of your case, it's hard to fully comprehend from your text, exactly what not right.

However, if you bought it from Audiopile, I'd email Mark/Liz directly and explain the issue. They have always been more than stellar in responding to issues/quesstions I've had.. and I will continue to purchase anything that they carry. All the EWI (cases, cables, etc) products that I own have far surpassed any other in their price range and their quality has been excellent.
 
that's what i'm wondering what's the point? but the foam only extends about an inch in depth. it's not like mark and liz can do anything either, they're only distributors of ewi products.... and it's not like i could take a picture of this problem with out destroying my case. but essentially the two fronts are framed in foam and that's it leaving a hollow gap through the rest of the top and bottom and potentially sides as well. it's definitely a tough ass case. but i'm just saying i would have assumed that there would be sheets of foam inside instead of merely two foam framed openings not even extending half way in. I discovered this problem because when i received my case, it was slightly damaged by ups, leaving a small gap on the top of the foam and i could see to the other side through it. and i noticed that the foam frame DEPTH is like an inch deep. wtf


there are pictures on that link i provided....
 
Here are some thoughts/experience from my military electronic design and shock mounting (including cases):

Any shock isolation system (rack cases included) MUST have both a compliant suspension system and some form of energy damping to provide a reduction in shock load from the external (the environment) to the internal (the protected element).

In order to do this, manufacturers use a compliant element (think of a car suspension spring) and a damping element (car shock absorber). The goal is to reduce the peak shock (measured in G force... example 1000 G's, dropped from 3 feet on plywood) to a lower G (shock) peak value (example 50 G's, common limit for electronics innards). What happens really is that the sharp external G load is converted into a lower peak G shock but also makes the load duration longer (widens the pulse of shock). To accomodate this conversion, the spring element provides the isolation and the damping (shock absorber) converts some of the energy into heat (yup, that is really what happens).

In order to provide the ability for the spring to move, some distance is required between the internal and external surfaces. This is called 'sway space' and is a key factor in the limitation of the shock protection system. Heavier internal loads (mass, i.e. pounds of stuff) require stiffer springs and sufficient sway space so the compliant 'springs' can allow for shock to be absorbed. Stiffer 'shock absorbers, i.e. dampers will raise the internal shock loading but are needed to keep the protected element from just bouncing around on the 'spring system'.

The bottom line is that the design of ANY shock mounting system must consider: The internal mass of the protected stuff, the worst case external shock loading (G load and shock pulse waveform), the requirement for limitation of protected stuff (G load and damped/stretched shock waveform), the repetitive shocks or single event (i.e. airframe crash loading or vehicle transport vibration). These input parameters to the design of the shock mounting system then yield the need for sway space (3 dimensional, i.e. X/Y/Z axis). Other vibrational loads (like aircraft engine vibration isolation, etc.) are also considered (example is an A-10 Warthog GAU-2 gattling gun vibration into the airframe and all avionics).

Specifically on the OP mentioned case, the front and back foam (said to be 1/2" thick) is really the shock isolation compliance (springs) and damping (the foam converts the motion into heat). Normal isolation 'boxes' use shock mounts at all 8 corners (rectangular systems), this is provided in a distributed manner with this foam. There is no need for 'shock mounts' to be located in locations other than these points (or in this case the front/back interfaces).

I hope this helps in shock mounting understanding.. Yes, I'm an engineer (35 years in DOD electronics design including mechanical, thermal, optical, RF, communications, processing and former USAF lab coat guy)... and now I'm unemployed (yes, I watched 'Falling Down' ironically the day prior to the layoff)... Shock mounting is a science but is easily modeled today with common mechanical CAD programs.

Pete
 
thanks for the response pete can you put your next response in laymens terms though pease :D


just so i know you understand pete, the front and back foam is 1/2 thick deep in DEPTH which means that entire top and bottom black wood cover from front to back is hollow. seems kind of crappy to me.... but if you say it's good i believe you. i know this case was made in china and already see a few corners cut in design. and to be fair mark and liz are the nicest people to deal with ever, that being said i just want to get to the bottom of what i want and need from my cases and what i will be buying in the future.

thanks
 
mgavin said:
thanks for the response pete can you put your next response in laymens terms though pease :D


just so i know you understand pete, the front and back foam is 1/2 thick deep in DEPTH which means that entire top and bottom black wood cover from front to back is hollow. seems kind of crappy to me....

thanks
Click to expand...

The foam is only a thin strip because that is how much foam is required for it to act as a shock absorber. If the entire thing was covered on foam there would be too much resistance. Kind of like if you push on a bed mattress it with you hand, you can compress a section of it whereas if you put a sheet of plywood on the mattress and try and push, you wont be able to compress any of it because you are then trying to compress the whole thing at once. (you could go the whole aeronautical explanation but mine is simpler :).

Cheers S
 
What Pete said. What Simon said, too.

The only place where your equipment makes contact with the rack is at the rails. Any impact to the case will be transfered to your equipment at the rails and nowhere else, so that's where you need the foam. It doesn't matter what happens in between the front and the back rails; it's the rails themselves that need the springiness and damping of the foam.
 
so it sounds like my case is built correctly, which is surprising because it's made in china. can i expect every shock mount rack to have the same design as the ewi cases then? are they all built like this is essentially what i'm asking? are the really expensive shock mount cases built just like these then? i don't know the brands but if anyone else could chime in that would be cool....
 
if i designed these cases i would have it be all foam enclosing the entire thing. what if a random heavy ass corner just punctured the top? that's totally possible as it's not that thick... you know it's just going to go right through the top like butter too, because it's hollow.... in my opinion it just seams like crappy build quality but maybe you guys are right....
 
it's heavy duty, but i don't think it's that heavy duty when you take into context the other heavy gear that's going to be around it, especially their corners.... seams like any hollow spaces (like the ones i mentioned above) are just a bad idea.....
 
Mgavin,
I'll spare you the details but there is a definite reason to NOT have continuous foam (compliant) on the sides. Using Simon's matress analogy, pushing down with the hand is like any motion (within reason) to the strips. If you tried to shift the entire matress sideways, the total foam surface would resist (much stiffer spring)..

One note on transport cases and rack mounting, the ability to carry the load of the rear of the individual equipment may require rear rack mounts for the equipment (like an ART SLA-1/2 has). The AxeFX II is likely OK as a 2U component as well as moderate weight (the bulk of which is really just the steel housing, thus distributed).

On the 'made in China' side, they (China) produces most of US electronics (at some level), the real area of importance is the design of the case. I think this case is OK, but I have NOT used one and certainly not designed it.

Sorry for the details however that is the real 'engineering stuff' that makes these systems work..
 
mgavin said:
seems like Soc9 agrees w/ me too any other takers?
Click to expand...
LOL - but that doesn't mean we are both correct :)
Based on 1wheel's explanation, it would seem that this is something of a "standard" with shock mount cases... I don't own any and those I've seen have not had holes punched into the foam, so I "assumed" (as I stated in my prior response) that foam extended the entire length of the outer casing. One sees foam at both ends, a+b=c :)

Regardless of manufacturing source being China, it would appear that my assumptions were not correct.
And, based on other EWI gear I own, I assume what you got is a quality built. ALL my stuff is...
 
hey larbear63 not sure you get the conversation, the question is weather shock racks foam frame depth extends all the way to other side. so that picture doesn't really show anything and to actually take a picture would require destroying a case. anyways i think the theory behind it has been well addressed. thanks for the responses guys...
 
mgavin said:
so it sounds like my case is built correctly, which is surprising because it's made in china. can i expect every shock mount rack to have the same design as the ewi cases then? are they all built like this is essentially what i'm asking? are the really expensive shock mount cases built just like these then? i don't know the brands but if anyone else could chime in that would be cool....
Click to expand...
Whether a shock-mount case is built correctly depends on a lot more than just foam depth. There's foam thickness to be considered, along with the physical properties of the foam itself. Some cases use springs or shock absorbers instead of foam. Then there's case materials to consider, and even the location of the feet on the bottom of the case.

In general, the more expensive cases are built tougher than the less-expensive ones. But as with everything else, when you buy big-name merchandise, part of the price premium goes to pay for the name, not the product.
 
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