auralex mopads - quality control?

[localhost127]

decided to try these out just to test.
can anyone confirm if this is correct or a QA issue?

[localhost127]

by the way they were sold as a pack of 4 (for a pair of speakers - 2per speaker)...but look at the cut / height difference between the pair!

[AlexK]

They also look to be made out of a completely different foam. You can see the difference in consistency.

Is it possible you've got a chinese-knock-off and an original product?

[localhost127]

possible - ill be returning (bought it from a store (guitar center), not an online outlet)

by the way, i like the richard james avatar...have you heard the tuss?
Tuss, The - Rushup Edge (CD, Album) at Discogs

[localhost127]

also, regarding these pads...im still 'feeling' a little bass/vibration on my desk.

im not sure if it's from the speaker transferring vibrations to the desk, or if it's just from the low freq coming from the speaker...

should i still get vibrations from bass? i would assume yes...

i guess my unknown is whether those vibrations are still coming from the speakers themselves or if it's just bass causing that. hmm.

bah, sooner or later im probably just going to get stands, anyways...i should stop messing around and do it right from the start. (stands over pads)

[AlexK]

Originally Posted by localhost127

possible - ill be returning (bought it from a store (guitar center), not an online outlet)

by the way, i like the richard james avatar...have you heard the tuss?
Tuss, The - Rushup Edge (CD, Album) at Discogs

Haha thanks.

I haven't, and I haven't got the inclination to listen properly right now, but I've saved the URL onto the desktop and I'll drop you a PM or something when I've listened. thumbsup Thanks for the heads-up.

[localhost127]

Originally Posted by AlexK

Haha thanks.

I haven't, and I haven't got the inclination to listen properly right now, but I've saved the URL onto the desktop and I'll drop you a PM or something when I've listened. thumbsup Thanks for the heads-up.

yeah - it's rich's best work imho. nutty on the synths. sounds unlike ive ever heard.

[andrebrito]

This product lacks information about what is the weight of monitors that should be used.

Any kind of spring or elastometer has a specific loading weight of what is going to be damped where the behaviour is optimal

[SAC]

Andre is correct!

Besides, as far as their general effectiveness at mechanically decoupling a deriving source from the underlying surfaces, the variation doesn't matter.

What does amaze me is that so many would spend so much for something that is so easily accomplished in more economical alternative ways.

The rest of the argument regarding their effectiveness is spurious, as for the effects of minute group delay due to cabinet movement are ironically actually increased by an elastomer base and diminished by the very tight mechanical coupling to a rigid base they seek to eliminate. But it does make for a fancy glossy brochure.

[localhost127]

Originally Posted by SAC

Andre is correct!

Besides, as far as their general effectiveness at mechanically decoupling a deriving source from the underlying surfaces, the variation doesn't matter.

What does amaze me is that so many would spend so much for something that is so easily accomplished in more economical alternative ways.

The rest of the argument regarding their effectiveness is spurious, as for the effects of minute group delay due to cabinet movement are ironically actually increased by an elastomer base and diminished by the very tight mechanical coupling to a rigid base they seek to eliminate. But it does make for a fancy glossy brochure.

im interested in alternatives...returning these today (because of the mismatched foam)...i know it's highly overpriced for simple foam.

any recomendations?
regarding stands, im finding it a bit difficult to find stands to support my jbl L820s...e.g wide speakers (15") but very slim (5.5")....

[SAC]

If you are interested in high tech energy damping elastomers, Sorbothane excels - but its pricey!

A very inexpensive alternative for mechanical decoupling is neoprene sheet available at almost any industrial rubber and gasket supply house (check the phone book - as they commonly supply material and also fabricate hydraulic and other hoses, etc. for industrial equipment. It is available in multiple thicknesses.

And, if brand names aren't important and price is critical, you might check with local dive shops to see if they have any old torn wetsuits that they are rotating out of rental. Multiple layers can be easily cut and used.If necessary, spray adhesive can be used to 'attach' the layers.

Just be aware that the only benefit will be in the form of mechanical decoupling of the unit from the base.

[RKrizman]

Originally Posted by SAC

If you are interested in high tech energy damping elastomers, Sorbothane excels - but its pricey!

A very inexpensive alternative for mechanical decoupling is neoprene sheet

What about weight loaded vinyl? (I have a bunch from failed bass trap experiments)

-R

[SAC]

That's hard to say, as if it is sufficiently dense, it will serve to mechanically couple the two surfaces, and your goal here is to decouple the mechanical transmission of energy from one surface to another.

My gut says that unless the non-mass-loaded (???) portion of the material is not sufficiently 'lossy', it may it be very suitable.

But then again, if you have a cheap accelerometer such as an ACH-01, you could easily measure the mechanical transfer of energy and see.

But make a few calls regarding neoprene at various thickness and densities (less dense is better here). You may find a few feet is not very expensive.

[localhost127]

i got a replacement pack (opened it in the store), and the 2 pairs in that were different as well! so we just mixed and matched. hilarious.

regardless, back home now. even though the foam is quite sturdy, it still dont like my wide/slim (15.5"wide/5.5"deep) bookshelves resting on the foam as they could be prone to being pushed over.

could i add a layer of wood or something flat/solid on top of the foam, and then place my speakers on top of that? that way the speakers are resting on something more sturdy/dense, and then i'll still have the foam underneath/between the desk.

[localhost127]

Originally Posted by andrebrito

This product lacks information about what is the weight of monitors that should be used.

Any kind of spring or elastometer has a specific loading weight of what is going to be damped where the behavior is optimal

understood. so technically adding a piece of wood (e.g. my above question) could be pushing the total weight on the foam pieces over their limit of absorption or effectiveness? without the proper data...yes, i see the problem.

[SAC]

The irony of all of this is that the variation is likely insignificant from a decoupling POV. It only matters from an appearance perspective.

And from my perspective, if I were to buy a pair, the first thing I would do would be to try to remove the label without damage! But I could imagine that many might be very upset if the labels were not applied precisely! ;-)

[localhost127]

yeah , the labels are ugly/hidden. not a big deal.

my question was more in regards to the speakers resting on something solid.
as the speakers (JBL L820) are very wide/slim..so they could be easily "pushed over" when resting on the foam (and not a hard/flat surface).

it's not like they'll fall over if i breathe on them, but doesn't putting a piece of wood or something between the speaker and the foam make sense?

i thought that's the point of the primacoustic pads that have the steel on top of the foam (to give proper weight, too)...but i understand that goes into the design of the foam as well (weight load, etc).

[SAC]

You voice a very legitimate concern regarding the speaker stability, and one that I don't think has a simple answer - especially if the speaker has a high center of mass.

Experimentation and perhaps some form of attachment such as an adhesive Velcro placed between the speaker & decoupling material and between the decoupling material & rigid surface beneath might work to help stabilize the speaker while still allowing for a mechanical decoupling to occur.

Additionally, whatever you use to decouple the speaker, I would attempt to avoid having any extending surface (including the decoupling support) extending (in front) beyond the speaker face, as it risks becoming a source for an early reflection or diffraction (an ETC can show this).

[localhost127]

thanks.
would adding a piece of wood between the foam and the speaker cause more vibration?

e.g. would the vibrations just go through to the pads themselves (to the desk)...or would i add a *new* problem by sitting wood on top of the foam, and then putting the speakers on top of that (e.g. having the new piece of wood vibrate instead of transferring the vibrations to the foam to the desk)?

[SAC]

Assuming the base of the speaker is essentially the same size (surface area) as the decoupling material itself, I don't think any advantage would be gained.

If however, the surface area of the base of the speaker was significantly smaller than the surface area of the decoupling pad, and the speaker tends to 'rock' on the pad itself, some advantage might be gained by adding a hard layer that fully covered (matched) the surface area of the decoupling pad...as the mass of the speaker would be distributed over the larger surface area.

In this case mass of the hard layer would simply be added to that of the speaker itself in terms of the mechanical compliance of the decoupler to dissipate the transmitted mechanical energy.

In other words, if the mass of the additional hard surface is low, and there is no vibration, etc. between the speaker and surface, that it should be fine to do that...

[localhost127]

exactly.
my JBL L820s are only 5.5" deep...and the pads themselves are 4" deep (8" total when using 2 pads).

i tried like this (how you're supposed to use them for "normal" sized bookshelves):


and didn't feel comfortable.
so i turned them sideways and put them together (like in the original post of this thread) - with no gap between the 2 pads.

so now the speaker sits right where the 2 pads join together...still not ideal in my opinion.

i would like to put a piece of wood or something sturdy that covers both pads (the entire surface area) just so the speaker is actually resting on something uniform and sturdy ... vs resting on the pads themselves which have a bit of "play" and the speaker has more of a tendancy to be pushed over on the pads than say on my desk by themselves.

[localhost127]

here is a view from the side...you can see how it's not idea...

[SAC]

Try it.

If they work as promised, you should still benefit from a degree of mechanical decoupling.

But beware, any 'extending' surface beyond the front of the speaker will result in an early reflection that will be much more detrimental to the speaker response than anything short of catastrophic mechanical resonance!

Be careful you are not treating one minor issue while creating a still larger one.

[Yiannis]

SAC,

is this a trouble even for a couple of cm?

[SAC]

Technically yes. You will introduce an early reflection which will tend to create time smear distortion (per Heyser) and comb filtering in the frequency response which is indicative of polar lobing in the spatial dispersion of the signal that will result from the combining (superposition) of the direct and reflected signals.

Can you place a solid thin panel on the 'blocks' and place the frame of the speaker such that the edge of the solid speaker cabinet base is even with the edge of the base? And also, place the speaker and 'blocks even with the edge of the support shelf?



You might be able to attach a (nonconductive) wire or cord to the speaker back attached to a wall surface (or other secure spot) to prevent the potential for the speaker to inadvertently fall forward should it be bumped, etc..