MuteMat sound absorption kit

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MuteMat is basically a competitor to the likes of AcoustiProduct: Sheets of damping material that can be applied to the inside panels of a PC case to help make it quieter. The big difference is that it’s not foam. Instead, it is an “unwoven micro-fibre that can supposedly absorb more noise than acoustic foam due to its finer underlying structure.” We tried MuteMat on a quiet system and wrote up our findings… along with SPL measurements, sound recordings and descriptions of before and after.

September 28, 2005 by Devon
Cooke

Product
MuteMat Plus
Manufacturer
MuteMat
Price£30

Building a quiet computer begins with selecting the coolest, quietest components
and putting them together in a case that allows efficient cooling with low airflow.
This is the approach most often espoused by SPCR, and it can take you quite far into the realm of quiet.

For many DIYers, there comes a point when a system is as quiet as it can
be without compromising cooling or performance… but it’s still too loud!
This is when some people begin modifying their system. Hard
drives are suspended, fans swapped out, and fan grills removed. Sometimes, the
interior of the case is lined with rubber, foam, or anything else that might
help damp the noise.

By and large, case
damping is a do-it-yourself job. Although several prepackaged damping kits exist,
only one seems to have relatively widespread use:
AcoustiPack, from
the
British company AcoustiProducts
.

MuteMat Plus is also a case damping kit. By an odd coincidence,
MuteMat is also a British company. But unlike AcoustiPack, MuteMat’s product is not acoustic
foam. No, MuteMat thinks they have something
better: An
unwoven micro-fibre that can supposedly absorb more noise than acoustic foam
due to its finer underlying structure
.

At present, MuteMat (the company) sells two versions of MuteMat (the product).
One, which they call the "Universal Noise Reduction Kit", consists
of MuteMat (the material) alone, while the other, called MuteMat Plus, adds
an additional layer of high density foam that is designed as a sound barrier.
Although MuteMat sent us a sample of both kits, we opted to test the product
at its best, so we used the MuteMat Plus.

At present, the basic MuteMat kit costs £16 and MuteMat Plus goes for
£30. This is on par with the current price of AcoustiPack in the UK. However,
I was unable to find any online retailers (or even international distributors)
that carry MuteMat, so if you want it, you need to buy it from them directly.
Fortunately, they accept international credit cards (and PayPal!), and ship
internationally.


Our MuteMat sample arrived in a large flat cardboard box. No retail art
here!

According to the
MuteMat product page
, the following pieces are included in the MuteMat
Plus kit:

  • Two full size sheets (495 x 380 mm)
  • Two half size sheets (495 x 190 mm)
  • One fitting guide

Our own measurements confirmed these numbers exactly. Our samples actually
contained more than is listed on the web site:

  • Six spare sheets (150 x 150 mm)

We’re not certain whether this was a special kit that they put together for
our review or if these extra pieces are just missing from the product description.


All the contents of the kit — minus the fitting guide.

VISUAL INSPECTION

As mentioned, MuteMat Plus is a composite with a base of high density foam
underneath a thick (~2cm) layer of micro-fibre material. The marketing material
also mentions a third layer: Viscoelastic Adhesive, but we’re not sure whether
this is much different from ordinary adhesive. Each layer has a different function:

Layer 1: MuteMat Material

This layer is what makes MuteMat unique: As far as we know, no other company
sells damping material for computers based on micro-fibre material, although the material
is used in the audio industry to damp speaker enclosures. The claim is that
— thanks to its low density and fine pores compared to ordinary acoustic
foam — MuteMat is especially effective at absorbing sound. MuteMat should also help reduce cavity resonance inside the case.

Our experience with other damping materials has indicated that sound absorption
is usually not as important as vibration damping. Damping material work best in a sealed case so that there are no direct noise paths between the
noise sources (usually fans) and the listener. But in almost any fan cooled (or even convection cooled) case, there must be intake and exhaust vents. So, even if
the damping material can absorb some noise and cut down on the noise reflection
inside the case, it can’t stop the noise from getting
out through those vents. This is the fundamental weakness that affects every brand of PC acoustic damping.


The MuteMat layer is soft, white and fluffy, almost the consistency
of fiberglass insulation but finer.
The black layer on top is a tough fabric that holds it all together —
a necessary feature given the looseness of the MuteMat material.

Layer 2: High Density Foam

The layer of high density foam was one of the features that set AcoustiPack
apart from its competitors. MuteMat Plus uses a very similar layer of foam.
The advantage of this extra layer is that is provides what is known as mass
damping.
The essential idea is that a dense material is bonded to
the case panel, increasing its effective mass. This makes
it less prone to vibration, which is often the primary source of noise in
systems that use low-noise components. A side effect of this is that the resonant
frequency of the side panel is lowered, dropping it away from the range of
frequencies that humans are most sensitive to.

A secondary function of the high density layer is to reflect any noise that
makes it through the MuteMat layer back through it again, effectively doubling
the thickness of the material that the sound waves must travel through. Once
again, this is thanks to the increased density that makes it more difficult
for the side panels to vibrate, and thus transmit noise.


The high density foam is the upper black strip. The white layer on top
is a paper backing that protects the adhesive until it is ready for use.

Layer 3: Viscoelastic Adhesive

According to the MuteMat web site, the Viscoelastic Adhesive is meant to
provide a further layer of vibration damping. Personally, I find it difficult
to believe that it’s anything other than adhesive, although it does seem thicker
and more rubbery than usual. If I had to make a guess, I’d say it’s the same
gummy, silicone-based material that is sometimes used to attach extras to
magazines.

Most likely, the vibration-reducing qualities of this layer are minimal.
It’s too thin to be of much help. Still, if the adhesive itself can contribute
even a bit, who am I to complain?


The "Viscoelastic" Adhesive is visible on the surface of the
black foam as a yellowish film.
It’s thicker than standard adhesive, and can actually be peeled away from
the foam.

Standard MuteMat

The basic MuteMat package lacks both the high density foam and the special
adhesive, but is otherwise identical to the MuteMat Plus kit, both in the size
and number of pieces. The most noticeable difference is actually not visible
at all: MuteMat Plus weighs several times the standard MuteMat thanks to the
high mass of the high density foam. This is something to consider when shipping
MuteMat over long distances: International shipping for the basic MuteMat kit
is £3.50, but that cost almost quadruples to £13 for the Plus kit.


The standard MuteMat is missing the thicker dark foam layer.
Be careful: The backing sometimes peels away the adhesive from the MuteMat!

TESTING

The MuteMat Plus was installed in an existing low noise system that happened
to be in the lab. Most of the system components were chosen for
their low noise qualities, and some work had already been done to reduce the
noise further, notably an undervolted CPU fan and a soft-mounted hard drive.
The test represents how we believe MuteMat should most likely to be used: In
a system that cannot be easily improved by swapping out components.

Because the system is already so quiet, reducing the noise any further will
be challenging, and this is how it should be. In a situation like this, the
noise level of the system is near the ambient room noise, and the kind
of noise
it makes, not its volume, will probably be the the factor that
determines whether it is noticed. Although SPL measurements were made of the
system both before and after the MuteMat was installed, these are much less
relevant than the subjective noise description that is given along with them.

Thermal testing to determine what, if any, effect MuteMat has on system temperature
was considered and then abandoned. We do not believe that the material itself
has much effect on system temperature beyond a minimal insulating effect. Heat
transfer through the case walls is only significant in a complete fanless setup
with no airflow, and this is not a configuration that we recommend. Differences
in temperature are much more likely to arise because of how it is installed
than any intrinsic properties of the material itself. Minimizing the impact
on system temperature is simple: Don’t cover up or impede any intakes or exhausts
for airflow.

Ambient noise at the time of testing was ~18 dBA, and ambient temperature was
24°C.

TEST SYSTEM


The test system before MuteMat was applied.

Please read through the details of the test system below carefully. The system
is not simply a collection of stock parts, and a number of modifications were
made to reduce noise before MuteMat was installed. Acoustically important
details are highlighted.

  • Intel P945GTP motherboard
  • Intel Pentium D 820 (2 x 2.8 GHz). This is a hot processor, making it a
    challenge to cool quietly.
  • 2 x 512 MB Corsair XMS2 DDR2 RAM
  • Western Digital Raptor WD740GD 74GB, 10,000 RPM hard drive, soft-mounted
    in a NoVibes III drive caddy from Noise Magic
  • NEC CD-3002A 52x CD-ROM drive
  • Antec SLK3000B case, with TAC duct and hard drive cage removed, and
    stock TriCool exhaust fan set to "L"
  • FSP Zen 300W Power Supply fanless
  • Scythe Ninja CPU heatsink, with 120mm Nexus Real Silent fan, undervolted
    to 5V

There are four main sources of noise in this system: Two slow 120mm fans, the hard drive,
and the optical drive. The hard drive in particular is worth taking a closer
look at, as it is not mounted in a conventional way.


The hard drive mounted in a NoVibes III drive caddy.

The NoVibes III decouples the drive from the rest of the case by
suspending it between two elastic loops. It minimizes the HDD
vibration transferred to the case, almost eliminating the low hum associated with hard drive resonance.

INSTALLATION

Installation was simple but tedious. MuteMat was applied to both
side panels, all of the top and bottom of the case, and as much of the front
and rear as could be covered without interfering with the case airflow. Two
holes were made in the sheet for the door panel to keep the
TAC intake and the VGA vent unblocked.


The side panel, with holes cut in Mute Mat for the two vents.


The thickness of the material is obvious here: It’s almost the same thickness
as the exhaust fan (~25mm)!

The general procedure was simple: The available space inside the case was measured,
the measurements transferred to a sheet of MuteMat, and the sheet cut
using a sharp utility knife and scissors.

Cutting the material proved to be a little difficult at first. The utility
knife I was using did a good job of cutting through the high density foam on
the back of the material, but it was useless for cutting the (extremely
tough) fabric that lined the other side of the sheet, and it tended to separate
the two layers, bunching the MuteMat layer in clumps along the cut. On the other
hand, scissors did a good job of cutting both the MuteMat and the fabric lining,
but could not cut through the foam.


The layers are prone to separating if the sheet is cut from the wrong
side or the wrong tool is used.

In the end I used both scissors and ultility knife. First I slit open the foam using the utility knife and a straight edge,
and then I extended the cut through the lower layers using scissors. Using this
method, I didn’t have to worry about cutting straight with the scissors, since I just had to follow
the knife cut. I also didn’t need to worry about getting the scissors stuck,
since once the foam layer was cut, the cut could be widened at will by folding
the sheet along it.

Applying the pieces once they were cut was a little tricky, but mainly because
I didn’t bother removing the components from the case. The
best approach was to test position each piece with the backing
still on before I actually applied it. A couple times, this saved me from trying
to force a piece that was too large for the intended space.

The top and the bottom required special attention. For the bottom, I needed
to put a piece under the base of the drive cage, which is riveted to the case
and can’t be removed. Fortunately, there was enough clearance to maneuver a
square of the material underneath it without inadvertently touching the adhesive
to the case floor before I was ready to stick it down. The other piece for the
bottom had to be cut in two, as the PCI slots hung over one end while the hard
drive hung over the other, and the piece I was trying to install was too wide
to fit between them.

Fitting the sheet to the top of the case required removing both the power supply
and the optical drive. Fortunately, it was enough just to slip the power supply
away from the back of the case — removing it entirely would have meant
removing both the CPU heatsink and the motherboard!


Tight fit! I had to install the bottom sheet in three pieces: One under
the drive cage, and two under the motherboard.

The front bezel also proved to be a challenge, not because of access problems
but because I needed to decide which holes I could safely block, and which needed
to be left free for airflow. In the end, I just wedged a couple of sheets beneath
the drive covers without removing the backing (against the official fire-safe
advice from MuteMat). This was enough to reduce the rattling of the plastic
covers a bit, although I probably could have achieved the same effect using
tape without blocking so much space inside the bezel.


Deciding which holes were safe to block was a challenge.


Two pieces of MuteMat were wedged in front of the drive bay covers to
reduce rattling, but the front airflow was otherwise untouched.

BEFORE / AFTER COMPARISONS

To determine the effect of MuteMat Plus on our test system, detailed notes
were made about how the system sounded in three activity states, before and after MuteMat was installed:

  • System Idle
  • Hard drive seeking
  • Optical drive spinning

These activity states cover the whole range of noise that the system
can produce. Load testing was not done, as the noise would be the same as in idle; there are no thermally controlled fans.

System Idle

Before: The system measured a respectable 24 dBA@1m: Quiet enough that it
could easily be tuned out, but loud enough
that it was still clearly audible above the low ambient noise level of the test lab. The character
of the noise was fairly benign, with few pure tones. The bulk of the
noise was in the lower frequencies. I would describe it as a low hum or growl.
There was also a significant amount of broadband airflow noise easily
noticed on close listening.

The main source of noise was the Antec TriCool exhaust fan. Stopping it temporarily
made a big difference to the noise level. Aside from that, most of the noise
seemed to be resonance, the source of which could not be easily pinpointed.

MP3:
Test system without MuteMat Plus, Idle (24 dBA@1m)

After: MuteMat had very little effect. Both
the volume and quality of the noise were largely the same as before. The measured
noise level was identical. The balance between the low hum and the airflow may have changed
a little, with the airflow becoming more noticeable and the hum receding further into
the background, but the change was minor if it was there at all. A comparison
between the two recordings confirmed that there was very little change.

MP3: Test
system with MuteMat Plus (24 dBA@1m)

Hard Drive Seek Noise

Before: Seek noise was one of the worst aspects of system noise
during the baseline test. The Western Digital Raptor is a fairly quiet drive
when idling, but its seeks are sharp and loud, and stand out against the otherwise quiet idle noise. Despite
the intrusive nature of the sound, the measured noise level was only 26 dBA@1m.

The noise recording below was done while the drive was being defragmented. This gives a good idea of what the drive sounds
like, but it doesn’t drive home how irritating the seeks can be when they are
intermittent, which is typical during general PC use. For me, variability is the worst part
of seek noise.

MP3:
Test system without MuteMat Plus, HDD Seek (26 dBA@1m)

After: MuteMat Plus made a noticeable difference with seek noise. The noise became much less sharp, more broadband
and muted. Instead of having my attention drawn to the seeks every time Windows
decided to hit the swap file, I had to actively listen to
hear the seeks. The measured noise did not drop by much though — maybe a decibel.

It is possible to get a sense of how MuteMat changed the quality of the noise
by comparing the two recordings, but they don’t quite illustrate the significance
of the difference, perhaps because they are recorded at a distance 3",
while most users will be seated closer to a meter away. Because the muted seek noise became much
more broadband than the original noise, it was harder to distinguish
the seek as you moved away from the source of the noise.

MP3: Test
system with MuteMat Plus, HDD Seek (25-26 dBA@1m)

Optical Drive Noise

When they are in use, optical drives are often the worst noise offender in
a quiet system. Their proximity to the front of the case (and thus the user),
the difficulty of soft-mounting them, the variability of the noise, and the
inherently unbalanced nature of optical disc media all contribute to the loud noise
of optical drives. Because of this, four separate tests were run with the optical
drive to get a good idea of what it sounded like. All tests were done with a
disc in the drive; without any media loaded the drive was effectively silent.

  • Drive idle, case door closed
  • Drive in access mode, case door closed
  • Drive idle, case door open
  • Drive in access mode, case door open

"Idle" and "access" refer to the speed that the disc was
spinning inside the drive. The "access" mode could be reliably induced
by leaving the autorun window that pops up after inserting the disc. "Idle"
refers to the baseline noise of the disc spinning after the autorun window was
closed. Each state was tested with the case door open and closed to determine
what role the door played in damping the noise.

Before: The generic optical drive in this system did not sound nice,
even at the basic "idle" level. This is reflected partially by the
high SPL measurement — 28 dBA@1m — but the recording is a better
demonstration of how the drive destroys the otherwise smooth character of the system
noise. Even at idle, the optical drive added a rough midband clatter to the system. It’s
possible that the drive had a loose bearing, as there is a distinct rattle
that sounded a bit like muted hard drive seeks.

With the drive in access, the midband noise became significantly louder,
and the measured noise went up by 3 dBA to 31 dBA@1m. The spindle motor noise
sounded like heavy machinery operating in the distance. There was a slight
warble or throbbing to the noise that made it difficult to tune out. The
rough rattle at idle was still present, but it did not increase
in volume like the motor noise, so it was less noticeable than before.

Opening the door, at any optical drive speed, made high frequency
noise audible, along with a rough "ch-ch-ch".
In addition, the basic motor noise became louder and rougher in character.
When the drive was spinning, the distant machinery sound became louder, along with the warble, especially in the
lower frequencies.Strangely, the measured SPL did not change with the door open, suggesting that all the heard differences were qualitative.

MP3:
Test system without MuteMat Plus, Optical Drive at Idle, Case Door Closed
(28 dBA@1m)

After: The biggest drop in measured noise came when
the optical drive was tested. With the case door closed, the idle noise dropped
a decibel to 27 dBA@1m, while the in use noise dropped 2 dBA to 29 dBA@1m.
Opening the case door lessened the change, although it still measured slightly
lower with the drive in use — 30 dBA@1m compared to 31 dBA@1m.

The measured noise says
very little about how the noise actually changed. At idle, the roughness of
the noise became smoother, changing from a midband drone to a low frequency
hum, making it more difficult to distinguish it from the rest of the system noise. A slight high frequency buzz was all that remains of the rattle.

The improvement was no less noticeable when the optical drive was in use. It sounded more like a medium-speed fan than heavy machinery. The primary noise
turned into a low drone and a small amount of airflow noise.

Even with MuteMat in place, opening the door increased the noise. At idle, the main
noise was the "ch-ch-ch" described before, perhaps slightly softer in character. Although motor noise was rougher than with the
door closed, it was still better than without MuteMat.

With the optical drive in use and the case door open, it sounded a bit like
distant machinery again, although not as bad as before.
The biggest change was that air turbulence, not motor noise, now
dominated the noise character. The motor noise was not gone, but
not nearly as intrusive.

MP3: Test
system with MuteMat Plus, Optical Drive at Idle, Case Door Closed (27 dBA@1m)

CONCLUSIONS

MuteMat Plus is an interesting product, and a fair amount
of R&D has gone into its development. Like their main
competitor, AcoustiProduct, MuteMat goes to a lot of trouble to explain the science
behind the product, and does a good job of presenting it in layman’s terms.

A damping product like MuteMat Plus is not the place to start when
silencing a system. If your components
are loud to begin with, acoustic damping materials really won’t help much. This can be seen by the marginal difference it
made in the sound pressure level measurements. But, if you’re looking for an improvement in the subjective noise quality with a PC that’s already reasonably quiet,
MuteMat can definitely help. The most noticeable difference
is with noise sources that are rough or sharp — seek noise, for example.

MuteMat cannot
turn a loud PC into a quiet one, but it can improve system acoustics by smoothing the quality of the noise. The overall effect of MuteMat with our test system was to lower the overall frequency balance,
pushing some of the noise out of the more audible midband. It also did
a good job of smoothing out pure tones and changing the noise character towards
a less irritating, more broadband sound. Fans that buzz when undervolted, for example,
may be less of a concern with MuteMat installed.

Is it better than AcoustiPack? It’s very difficult to say without applying the two materials in the same way to two identical system, and having an untreated third identical system as a control. Even then, I’d guess that the differences might be difficult to assess definitively. Suffice it to say that MuteMat seems like a good, viable alternative.

Mutemat is sold only in the UK at this time. The company does ship internationally.

* * *

Much thanks to MuteMat
for the opportunity to examine these vibration-reduction products.

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