Posts Tagged ‘Noise’

Welcome to my round 11 fan testing.  This is a fairly small round of fans from the kits I previously tested.  Rather than do my normal written form, I’m trying to do this more video based.

Before I do that, I would first like to thank my parts sponsors, without their support this test wouldn’t have happened:



Kit Fans Intro

This video does some physical comparisons of the fans and gives you a good close up look of the fan, sleeving, build quality, etc compared with my previous best performing fan the Gentle Typhoon.

Fan Test Rig Description

This video is just a quick overview of the flow bench and meters used in the fan testing to follow.

Individual Fan Tests

The following videos are of the actual test run on each fan recorded with audio and stepping through 50FPM air flow results.  You can now easily adjust two or more fan videos to like air flow numbers and pause them both, then switch back and fort for a direct apples to apples air flow comparison.

Larkooler Kit Fan

Corsair H100i SP120 Kit Fan

Swiftech H220 Kit Fan

XSPC 750 Kit Fan

Servo Nidec Gentle Typhoon AP-15

Extracted Results

These were pulled from the video, by isolating a looped region where air flow was close to the 50FPM increment.  This provides the resulting detail read on the meters and a calculated RPM.  On the right are some subjective noise quality comments I added as I reviewed and extracted the results.


Summary Radiator Noise Level vs Radiator Air Flow

This is the “Meat & Potatoes” result.  While I wish I could measure noise quality in a good quantitative way, that’s really not possible.  The next best thing is to compare noise levels when mounted to a radiator at like air flows through that radiator.  It takes into account the fans pressure capabilities and puts it in a more real world condition.  It’s not perfect, but the best thing I’ve been able to come up with to simplify radiator noise performance.  Fans that extend further right are capable of higher air flow maximum results at 12V.  Fans with lines lower on the Y axis are producing more air flow per noise level.


No real surprise, but the kit fans all tested relatively the same (most within 3dbA or less differences which fall within the “barely perceptible” level).  The Helix fan did for some reason have a bit higher than expected harmonics on the radiator bench which didn’t seem to be as noticeable when actually testing in a case, but it is something I heard a little when trying push only.  In push+pull I noticed most of that helix harmonic disappeared.

I would consider the kit results to be relatively similar, they are like most fans and all perform roughly the same.  The Gentle Typhoon however does seem to retain that unique ability on a radiator and tested upwards to 8-9dBA lower in noise level at 12V than other fans producing the same flow.  The H100i fans and their 2700RPM capability did produce the highest maximum air flow, but it comes at the prices of having a fairly gritty noise quality.  Noise quality isn’t captured well in the graph and really only something you can listen for in the videos.

The other aspect I’m now noticing that is missing from this single fan test bench is harmonics between the two same fans.  In the thermal testing using the kits and earlier noise testing, I had significant RPM harmonics issues with the H100i fans, but a single fans test scenario completely misses that.  This is something I seriously want to consider in fan flow bench future upgrades.  I think it is important to capture the “paired fan” harmonics effects as it can be fairly significant.  The helix H220 fans did really well paired together in the kit testing, but you just can’t see that in a single fan test.

Also as noted some of the pressure harmonics issues can also be mitigated for by going push + pull.  The helix fans don’t show real well in this single push test, but I found when testing four fans in push/pull on a radiator the fans worked very well together.  They are not up to Gentle Typhoon silence or build quality standards, but in use I would say they fair better than what the above chart or single fan test result demonstrates.

I also think the Larkooler fan subjectively sounds quieter than the produced dBA.  I’m not sure how to describe it, but the sound type is more lower in frequency and seem to contain less motor noise and gritty noise that is more prevalent in the other fans.  It has a noise quality that reminds me of the noise blocker series which I’ve always liked.  Noise level doesn’t measure anything special, but I think this fan does have pretty good noise quality particularly at slower speeds.  This is another one where my own ear and the meters don’t really agree all that well..:)

This at least gives you one more perspective on the sound.  I would suggest listening to the fans at like air flow levels and make a decision not based on noise level, but what you perceive as being less irritating.  That is likely a combination of frequency, noise quality, and noise level.  Don’t put too much weight on the noise level, it is important, but it’s not the entire picture and each person and each setup will be slightly different.

So there is another round and the Gentle Typhoon retains it’s low noise/rad air flow ratio crown.  Nothing comes close…

When I stop to think about watercooling for a bit, I see two basic performance reasons why I like it .  One reason is the performance of it, I can overclock higher than with air.  The second and probably more critical to me is the performance per noise level.  Perhaps I’m getting more noise critical in my old age, but listening to a vacuum cleaner in the background is not at all acceptable or what water cooling is really about.

I can test performance and log RPMs, but that’s really not apples to apples either.  Some fans have stronger PQ curves at like RPM levels and there is also a large variety of noise quality differences.  How a fan interacts with neighboring fans can be both good and bad and box specs simply do a poor job at measuring noise levels in an actual case/radiator condition. IMHO, a review of performance without a measurement of noise is no different than testing one radiator with 1800RPM and the other with 2700RPM and calling it a review.  You can compare like RPM levels as a quick and dirty test, but that too is generally a poor measure since fan performance can vary by as much as 400RPM producing the same air flow.  To do a review and comparison correctly, you really need to measure and compare noise vs dT or noise vs Core temp or some sort of constant. That’s what I’m attempting to do with this first noise testing phase.  I am also retesting in a top case mount condition so all kits get a equal and fair condition.

I started this kit testing using the bottom mounting location on my Switch 810 however I encountered a problem when trying to install the H100i….the hoses are about 2″ too short.  I’ve done enough testing to know you can NOT change the condition, no matter how small between tests.  A simple thing like placing the case on carpet vs a hard surface is enough to throw results out by 2C, same goes for noise measurements.

So in an attempt to get a true apples to apples noise vs DeltaT, I first need to compare noise vs RPM and then in Delta T testing I can convert the logged RPM average to noise level.

Unfortunately, Corsair Link is not compatible with Windows 8, so my only means to control the unit at all was to use the PWM fans and control speed via speed fan. Corsair Link simply does not monitor or control anything H100i related if you are running windows 8 as of this testing which was a bit of a surprise to me.  I believe Win8 has been out since last October so a good 5 months later, still no Win8 support.  Oh well, it really didn’t bother me since the new kit fans do have 4pin PWM control. At least I could control fan speeds using the motherboard and speed fan, I just needed to use a PWM splitter.

Corsair H100i VIDEO

Swiftech H220 VIDEO

That is what I have so far, I will let your ears do the talking… As a place holder you may start and stop both videos to match up RPMs if you would like and simply play one, stop, then play the other back to back.

Corsair H100i Chart


Swiftech H220 Chart


RPM Comprarison


dBA Chart

For reference use this to compare to similar daily noise types:

Sound sources (noise)
Examples with distance

   Sound pressure
 Jet aircraft, 50 m away 140
 Threshold of pain 130
 Threshold of discomfort 120
 Chainsaw, 1 m distance 110
 Disco, 1 m from speaker 100
 Diesel truck, 10 m away 90
 Kerbside of busy road, 5 m 80
 Vacuum cleaner, distance 1 m  70
 Conversational speech, 1 m 60
 Average home 50
 Quiet library 40
 Quiet bedroom at night 30
 Background in TV studio 20
 Rustling leaves in the distance 10
 Hearing threshold  0

Using the following chart for perceived noise level differences:

Perceptions of Increases in Decibel Level
Imperceptible Change 1dB
 Barely Perceptible Change 3dB
Clearly Noticeable Change 5dB
About Twice as Loud 10dB
About Four Times as Loud 20dB


Top Mount Noise vs Core Comparison

While I only have the H100i for comparison at this point, this is how that combination of noise testing and thermal testing lays out.  This is the meat and potatoes results as it pulls out all the variables such as fan performance vs RPM differences and compares a direct apples to apples noise vs performance.


And that plots out like this:


I’ve conducted a few different fan polls in the past before moving forward with radiator testing and typically the majority of watercooling users out there were using fans at about 1350RPM with a distribution that predominantly covers the 1000-1800RPM range.  There are a few people that run higher speeds, but the vast majority are more in the 1000-1800RPM range.  That makes sense as those speeds are only producing noise levels in the lower 40s dBA which is acceptable by most.

With that “Silence” preference in mind, the Swiftech H220 did outperform the Corsair H100i by roughly 2dBA at the 1350RPM mark, and about 3-4dBA better at the 1800RPM mark.  The H100i does have higher speed capabilities, but at 60dBA you are approaching vacuum cleaner noise levels (70dBA).  There are some users that don’t care about noise though, so I’ll leave it to you on what’s important.

For me personally, minimum noise level, dynamically throttling the noise and performance, and a smooth noise is priority.  I find the H100i fans (like most high speed fans) to produce quite a bit of motor noise and there was quite a bit of harmonics between the two fan RPMs that generally produces a poor noise quality.  The H220 helix fans are for the most part fairly smooth and the sound quality blended in well with my other fans.  That’s not to say you couldn’t replace the kit fans with something better, but in spirit of testing kit vs kit, the H220 is king of silence (minimum noise level) and better at like performance levels by 1-4 dBA over the H100i.

As part of my radiator testing, I did purchase several sets of fans to experiment with.  Since the Gentle Typhoon AP-15 did so well in a noise/cfm ratio in previous testing I had been curious how the higher speed GTs work in comparison.  The AP-29 differs from the AP-15 in that it only has 7 blades as opposed to 9 and it also has a special and unique stiffening ring.  I tried to make contact with Scythe about possibly sponsoring fans but my request was ignored and I could never make any sort of actual contact.  The Titans are just something I found perusing SVC one day and had to have a set and also picked them for my radiator testing since they were cheap, in stock, and had a good RPM range.

Being without any sponsor, I’ll give myself a special thanks to for sponsoring this test…:)  I ordered the GT AP-29s from an ebay seller as it seemed to be the cheapest price shipped I could find.  I also ordered the Titan’s from SVC myself since they were on sale for $10.99 and I was anxiously crossing my fingers I would find a good alternative to the GTs.

Gentle Typhoon AP-29

First thing to catch my attention is this fan comes only with 4 pin molex connectors, so you will need an adapter or to rewire it on your own if you need 3 pin.  The fan doesn’t come with much more than standard self tapping case screws.  It is built well though and heavy and more industrial in quality than your average 25mm fan.

Gentle Typhoon AP-15

For comparison purposes with the previous 1000-1800RPM winner, here is the AP15.  The king of CFM/RPM from my previous rounds.

Zalman ZM-F3

For comparison with a good but average noise level and more conventional 7 bladed fan, here is the Zalman ZM-F3.  It what I consider a good average noise level fan at a great price.  It also has a pretty good speed range so it’s a good one to compare with as well.

Titan Kukri

These are the fans I’m using for the radiator testing that were attempting to be low cost GTs.  They look nice and actually do better than the Zalman at slower speeds, but things fall apart quickly at the higher speed range.  The sample tested seemed to have some debris in the motor causing a bit of rubbing type noises from 1400-1800 and then a harmonic developed from 1800 up to 2300RPM.  The debris would probably work itself over time and the harmonic may or may not be specific to the radiator test rig, but that’s what I got in this run.

Charted results

The charts above include looking at a few variables independently.

Of primary value is the air flow vs noise level chart which is the most representative of radiator performance.  It’s not perfect nor as good as actual thermal based testing, but I find it good “quick” simulation that allows looking at the full spectrum of possible undervolting conditions very quickly.  It does however only represent noise “Level” and not “Quality”.

Chart 2 is just comparing RPM to noise and plots a similar response.  The GTs are very good about keeping noise “Level” down to a minimum when mounted to a radiator and much the same using RPM between the 15 and 29.

Chart 3 is taking a closer look at how much air they push per RPM.  This is where the GT 15s doing very well having a higher blade count without stiffening ring allows them to produce more air per RPM.  General most fans produce the same amount withing about a 200-400RPM window though.  Somewhat surprising though, the Titan despite it’s similar appearance doesn’t have the same flow/rpm advantage as the GT 15s.  There is quite a bit more gap between fan blade and frame and slightly different blade pitch as well as how the back of the blade curves more than the GTs.  The AP-29s do a bit better than average at slower speeds, but seem to loose all of that advantage from about 2000RPM on upwards which I suspect is mostly due to the stiffening ring causing turbulence.


The higher speed AP-29 does seem to follow in a similar trend (CFM per RPM) as the exceptionally low AP-15 did although I would say subjectively when listening to the videos side by side, the 15 is producing less motor noise and smoother in sound.  The stiffening ring does seem to eliminate the resonance spikes that are present as specific RPM levels of the AP-15, so that’s a good thing although the CFM per RPM level is not quite as good as the 15 which is also probably due to this same ring.  The range is a bit more limited on the lower end were 5V is basically starting at 1200RPM, but it makes up for that in it’s near 3000RPM maximum at 12V.

While it’s hard to find fault in the AP-29, I personally find noise levels beyond 2000RPM still to high for my taste despite the noise levels being significantly lower than your average fan and also find the noise quality of the GT15 better than the 29 at slower speeds so it is a bit of a compromise.  I think more people would be better off with the slower speed 15, but the AP-29 does extend the fan power range for those needing similar GT quality in a higher speed flavor.  As with pretty much all fans, you can’t have it all and extremely high speed fans generally struggle at slower speeds and the AP family is much the same there.  The AP-29s are exceptionally good at 1800-3000RPM, but  the AP-15s are still king of 1000-1800RPM levels.

The Titan Kukri’s do pretty well at slower speeds and they do have a more desirable white blade color, but they are not even in the same league regarding build quality as the gentle typhoons.   On my particular test rig with radiator, I also had high speed harmonics and other not so smooth motor type noises as RPMs increase beyond about 1400RPM and particularly beyond 1800RPM.  Not quite sure why but I suspect it’s the blades flexing since the plastic used is softer than that of the GTs and not as reinforced at the hub either.  Overall a great fan for the price when operated at slower speeds, but the Titans are not at all outperforming or coming close in performance to the GT-15 in terms of noise level or noise quality in the 1400-1800 range.  I would say they are better than average in the <1300-1400RPM level, but average to poor at higher speeds.


Welcome to my very first standardized round of pump noise tests in my continued pursuit of silence (The primary reason I water-cool).  This round will be much more controlled with an emphasis on consistency between pump tests.  Anything with the pump noise Round 1 will have the same test conditions.  Pump noise is normally not a concern for folks with higher speed fans or for installs where the pump is allowed to float freely avoiding vibration transfer.  However,  solid mounts and/or when users begin dipping below the 1000 RPM level are conditions where pump noise can become the primary noise annoyance.  This testing effort is looking at a variety of DDC/D5 series pumps in various flavors and tops measure dbA relatively to flow rate on a low restriction loop.

I want to give a huge thanks to my many sponsors.  Tim at, Gabe at, bmaverick, and have all sponsored in some way.  Without their generosity this test would not have been possible.   Tim from sponsored most of the items in this test including the pump controllers used on voltage regulated pumps.  Thanks!!!

Test Conditions

Test Setup, sorry for the poor phone picture, camera in use.:)

This round will use a low restriction CPU block only type loop that includes the Danger Den MC-TDX, XSPC RS120 radiator, King Instruments Flow meter, 1/2″ tubing, and a custom 3″ ABS reservoir with 5/8″ fittings.  The loop also contains some very low restriction brass globe valves for easier swapping between pumps.  I chose a low restriction loop for this round so I could get a greater number of data points. I may later attempt the same for a more restrictive loop although you could cross correlate with RPM values to PQ pump curves if desired as well.  Some noise is actually generated at the restriction points (blocks) as well, but this will be a good relative test between pumps.

I am also testing in two decoupling scenarios.  The first is a near ideal soft foam free floating type test, the second is direct metal contact.  This gives you sort of a worst/best range of noise.  In my earlier testing I found that thinner foam neoprene would fall somewhere in the middle.  Other options such as rubber washers/grommets would also fall in between and likely a bit more toward the worst case condition.  This best/worst case should give you a sense of possible noise range which is fairly dramatic in most instances.  This will also likely emphasize the importance behind decoupling pumps.

For relative scale, I’m including approximate noise level tests from my Gentle Typhoon fan on the left from my fan/radiator round 6 based testing here.  It was tested at roughly the same distance so I thought it would give some sense of scale to the charts.

Laing DDC-1 + XSPC top

This is the old model DDC-1 pump rated at 10 w and manufactured in 2003.

I think noise level is subjectively higher than average due to a buzz type noise present, but the pump is fairly consistent with very little issue with harmonic spikes even without decoupling.  Fully decoupled at 12V it measures roughly the same noise level as a GT-15 at around 1400RPM.  Noise scales well with voltage and at lower volts is approaching the 940RPM fan mark.  A good performer for it’s age, but not quite as silent as the newer models.

Koolance PMP-400 (DDC3.25) + Koolance COV-RP400 Top

This is the latest PMP-400 pump (18 watt) flavor with a nice thick/heavy acetal constructed top from Koolance.  Being acetal and extra thick, this top will likely provide some improvement to the thin and hard factory top material.

The pump/top combo does very well when completely decoupled.  Even at the extremely strong 12+V mark it’s just a hair more noise than a GT15 at around 1,000 RPM, that’s excellent!  You should however noticed there are two harmonic bumps that may or may not be associated with the simulated test rig.  The metal contact test however was all over the place with harmonics causing increased noise over the decoupled test from 3 dbA to  15 dbA.  This pump & top combo really likes to be decoupled completely if possible, the trick is likely some sort of lift or UN bracket system that will allow cooling and vibration decoupling.

Swiftech MCP-35X

This is the new PWM “Smart Pump” by Swiftech.  One obvious difference is the much larger operating range over voltage control of similar non PWM pumps.

Results are also similarly good when fully decoupled as the Koolance PMP-400 with some slightly higher numbers in some areas by 1-2 dbA.  It does have an extended range and the PWM feature could potentially be scaled dynamically, so those are all details to consider as well.  Overall a good showing that also like to be decoupled for best noise results.  Solid mounting can result in anywhere from 1 to 10 dbA more noise than a really well decoupled installation.  Of course being a DDC series high performance pump, you also may want to consider lifting the pump off the base to provide cooling and decoupling

Koolance PMP-450 (D5 Vario) + COV-RP450 Top

Well how does our larger vario pump model with factory speed controller work, these have generally been popular by the noiseless priority folks as they are factory built with a manual speed controller.  This first test is with the Koolance COV-RP450 top which is somewhat unique in that it includes an aluminum casing for the pump motor.  This serves to mount the pumps, but also to clean up the visual.  In addition, I suspect this help mask motor noises as well…  Let’s take a look:

Decoupled the Koolance PMP-450 with Koolance COV-RP450 top is the top performer, only hitting around 33 dbA at full speed, very good! However, similar to the other pumps when not decoupled, the noise levels climb significantly as RPMs increase creating up to 13dbA more noise than the fully decoupled test.

Koolance PMP-450 (D5 Vario) Sample #2 Stock Top

This is a second sample pump I had hand and initially decided to test it simply because I still had the factory top on it.  My intent was to compare stock top vs aftermarket top, but it turns out I also found some significant sample variance over the first sample.  This pumps had some rather pronounced spikes in noise level in a few places.

Overall this pump sample did good at middle speeds, but had higher than average noise levels at slow and high which I suspect is an impeller that’s slightly out of balance.  Sample variance is obviously a big factor in results so far and is going to make solid conclusions difficult with the low sample quantity being tested.

Koolance PMP-450S (D5 Strong)

The new king of power on the test bench…running with the factory top which it seems to like the best.

The Koolance PMP-450S strong did well, particularly under 14 V with the exception of a blip at 3800 RPM. Very good pump for noise and power.

Laing DDC 3.2

I’ve had this pump for a while, these are the last generation Laing DDC 3.2 series which is being replaced by the DDC 3.25 model.  This one also has the base “Feet” and a solid blue impeller.

This pump did very well and similar to the Koolance DDC 3.25 and only measuring about 1 dbA (less than perceivable noise difference) at full speed.  The thicker Koolance acetal top again seems to help reduce noise levels of the DDC series pumps.  It keeps noise at similar levels to an extremely silent GT fan at 1000RPM which is very good when decoupled.  Loosing the foam decoupler however reveals a similar erratic and harmonic variable results up to 9 dbA higher than the decoupled test.   I’m starting to sound like a broken record here, but decoupling is everything when it comes to pump noise reduction.

Summary Comparison Charts

Noise vs. Low Restriction Loop Flow Rate

First, lets look at the “Best Case” scenario where the pump is completely floating freely on a thick piece of foam.  Note, DDC series pumps should have a stand to allow base heat dissipation.

At the 2.3 GPM mark there are many pumps within about a 2dbA (not perceptible) grouping.  The Koolance PMP-450 with COV-RP450 top having a very slight (and perhaps testing error) edge in the charts.  The Koolance PMP-400 + COV-RP400, Swiftech MCP-35X, and Koolance PMP-450S are all similarly good here as well.  The PMP-450 sample 2 for some reason (suspect sample variance/impeller balance), was slightly higher.  The DDC-1 was also a bit more noisy.

All of the pumps were of good noise level though, and generally when decoupled were producing under the GT-15 noise level at around 1500 RPM.  If you had 10 each 40 dbA fans running in the background that total is 50 dbA, so it doesn’t take a whole bunch of fan noise to quickly mask pump noise “WHEN” the pump is properly decoupled.

So…what happens when you have a worst case mount, direct metal to pump contact….

All bets are off….There is really no consistency other than the general lack of consistency and general rise in noise level.  There are some things to learn here though, the bumps and dips are scattered throughout which means the vibration frequency and speed can be potentially “Tuned” to hit a low point.  If you have a solid mounted or less than desirable pump mount that is causing noise problems, you should seriously consider turning it down/up to see if you can find a low point in the noise curve.  Each case and each installation will likely have a unique harmonic noise/rpm profile/pattern, you just need to find the right pump speed to fall on the dips or low points.


  • Pump decoupling has HUGE benefits, up to 15 dbA lower noise levels than pumps without decoupling.
  • Pumps without decoupling are erratic in noise with massive peaks and valleys in noise level throughout the RPM range.
  • Thick Acetal pump tops may provide some benefit to reduction in noise levels over thin factory pump tops.
  • Pump sample variance does also affect noise levels, this may be due to how balanced the impeller is. Luck of the draw.
  • PWM pumps such as the Swiftech MCP-35X provide much more control and RPM range than voltage control.  They also provide the ability to dynamically increase decrease pump speed on thermal needs.
  • In general, all of these pumps are extremely silent pumps when decoupled.  Most general users with fans over 1000 RPM would typically have a hard time hearing these pumps at all in a normal fan noise masking environment.  Critical noise folks using ultra slow speed fans should put extra emphasis into pump decoupling methods and undervolting or reducing pump speeds.

Bottom line, if you want an extremely quiet pump, work on completely decoupling it from your case and consider tuning speed to seek the low points along the noise profile.  I would also highly recommend using pumps with PWM or fan controllers with thermal throttling capabilities to dial these pumps up and down with load.  Dynamic pump speed reduction setups allow for both ultra silence AND peak power when needed.



Welcome to a pump decoupling noise comparison test.  This test will focus on consistency using just one pump, the Swiftech MCP-35X and compare a direct metal contact (no decoupling), the factory neoprene pad, and a chunk of egg-crate.  I was also experimenting with microphone and sound level meter setup because I wasn’t very happy with my previous video results.  It seems having the microphone on the test bench was artificially introducing some vibration type noise into the audio recording and possibly into the sound level meter as well.  This time around I docked my Zoom H1 on top of my Canon T2i which is sitting on a tripod a couple of feet away.  I also place the sound level meter on some cushion to also decouple the sound meter from vibration.  I’m starting to notice that while fans generally have very little vibration, pumps obviously do to the point where the instruments can be affected by those vibrations if instrumental decoupling isn’t done as well.

Also doing a little work in YMEC software to take a more detailed look at frequency response.  Here are the three scenarios with the egg-crate decoupler as the baseline in the middle overlayed each of the other two so you can see the frequency spike differences.  While the neoprene pad helps, it’s not nearly as good as the thicker softer egg-crate foam.  The downside is that any sort of foam like this will trap heat, but this is just comparing some decoupling scenarios.  Decoupling AND cooling the pump base at the same time is a challenge.  I have heard of some people suspending pumps by tubing alone.

Here is that frequency response comparison at 100% PWM.  Zoom H1 microphone is approximately 2′ away mounted to camera on separate tripod.  This does seem to avoid any vibration induced noise on the microphone itself.  Of coarse this is tested in extreme silence to try and sort out any fine details.  Even with the microphone place a couple feet away, using software A-weighting I’m seeing upwards of 6dbA improvement using the neoprene pad over direct metal contact, and around a 12dbA improvement using the egg-crate as a decoupler.  This is fairly substantial and easily perceived difference in this silent testing environment.  No doubt that decoupling makes a noteworthy improvement to pump noise in silent environments.

A quick A-weighted frequency response comparison/overlay

And the video recording, zoom to the very end for just the 100% PWM sound clip comparison.

The pump used in this experiment was sponsored by Gabe from, thanks!