Flint Acoustics Distortion Measurements

[Flint]

I thought it would be useful to create a thread where you could look at the distortion measurements I make of various speaker systems while doing my thing. Note that in all cases, the measurements were made from the listening position at the owner's preferred listening levels. So, this is about what the owners hear, not some lab measurement. It also means the conditions are never exactly the same - other than the test gear utilized to capture the data.

I am using the Dayton Audio OmniMic measurement platform which includes a calibrated USB measurement mic and software. I play the test signals through my Sony HiRez Walkman.

Follow along as I'll be posting the results of every system I measure going forward for comparison. And, remember, the measurements are being made at the listening position at the levels the user prefers to use when enjoying the system.

The charts show the primary output response of the speaker being measured (the top black line in the chart) as well as the 2nd and 3rd harmonic (red and purple line, respectively). It also has a line for the combined harmonics, or THD (blue line). By calculating the difference between the main output (black line) and the THD line (blue line), I can get the THD as a percentage for any frequency. So, on the charts I added a table on the bottom left which shows the THD as a percentage as 5 frequencies, starting with 40Hz, or the lowest reasonable frequency for the speaker, and then 100Hz, 400Hz, 1kHz, and 4kHz. A true THD measurement cannot be made above 5kHz with this hardware.

I the SPL axis is shifted to reflect the measurement levels, and each horizontal division line represents 10dB change.

Also, since I am measuring the system in a room at listening distances, not just the speakers in an anechoic space, I am showing what you would actually hear. If an amp adds lots of distortion, like a single-ended tube amp, it will be included in these measurements.

I hope you guys find this valuable.

 

[Flint]

Below are charts for some original SVS speakers I am currently using in my home.



I use the MBS01 with a SB12 NSD in my family room driven by a set of great AudioSource mono-block amps. I placed the mic where I usually sit when watching TV in this room which puts my ears about 8 feet from the tweeters.

These exhibit typical THD for their class and are very good, though the sealed sub's THD is higher than I recall measuring from the larger vented version of the same unit several years ago. Also, chances are very good the sub was rattling some things in the room and increasing the THD measurement. I am showing what I hear, so rattling counts as part of the measurement.

The overall THD is below 0.5% from 100Hz to the top end of the measuring range. This isn't anything to scoff at.


______________________________________________________________________



The SBS01 is a small set of speakers I've used in my tiny little office for a long time. They are driven by a swell Topping USB DAC / AMP which is connected to my desktop PC. The mic was placed where my ears would be when working at my desk, which is about 20 inches from the tweeters.

The SBS01 clearly has higher THD in the bass, as would be expected. Even at these much lower driving levels, they are higher THD than their bigger siblings above. If I recall, these smaller speakers from SVS cost less than half the MBS01.

 

[Flint]

Next up, my sets of AudioEngine self-powered speakers:




I have these mounded on wall brackets in my main bedroom above the headboard. They sound amazing to me and the bass tends to be stronger than I could ever want in a bedroom. I measured with the mic at the foot of the bed, since the curves where I lay my head were pretty bad (as you'd expect).

The THD is pretty low above 100Hz given their size and cost. Below 100Hz the THD isn't terrible at all, and at the tuning frequency of about 50Hz, where I listed the percentage calculation, the THD is very low for such a small speaker. I am impressed.


______________________________________________________________________


The AudioEngine HD6 speakers are in my nice guest room and are connected to the TV in there. They also have built in Bluetooth, so a guest could enjoy music off their phone. I measured at the middle of the bed, which is likely where they will be heard when watching TV.

The port tuning on these is even cleaner than the A5+, above, but the overall THD is considerably worse than the A5+. I am not in love with the way these speakers sound, but they certainly get the job done.

 

[Flint]

Now for a couple of Mackie professional speakers:




The legendary Mackie HR824 mk1 powered near-field studio monitor is shown above, measured in the setting it was designed for, 30 inches away from the listener who should be sitting at a mixing console.

Clearly you can see how flat the response is above 500Hz, which is a common characteristic of this particular speaker. The THD is pretty good as well. Of note is that between 400Hz and 2kHz the odd 3rd harmonic is as much as 15dB louder than the more pleasing sounding even 2nd harmonic. This could be why some people feel these sound a bit harsh in HT environments.

Still the bass is very clean for a simple two-way speaker and the overall THD is well below 1% from 100Hz up.


_______________________________________________________________________________________


Just for fun I measured one of my self-powered Mackie PA speakers. I bought four of these primarily to use as stage monitors for singers to hear themselves while jamming at my home. Currently I have two of these hooked up to an Amazon Echo in my garage for when I am out there working on speakers. Being very rugged and capable of easily playing loud, they are perfect for the task. In this case, I measured from about 9.5 feet away, as they might be used in a club or outdoors.

The THD is clearly very high at these listening levels (about 95dB SPL average). Like the studio monitors, the 3rd Harmonic is much louder than the more pleasant 2nd harmonic from about 130Hz to nearly 2kHz. I could hear the harmonics clearly as the test tone swept through the operating range. But, these are PA speakers and not intended for high fidelity use.

It is worth noting that PA speakers tend to have higher THD than good high fidelity speakers as they tend to focus engineering efforts on loudness, efficiency, controlled coverage area, and reliability over absolute fidelity. This is one of the many reasons I never recommend true PA speakers for home use.

 

[Flint]

Here are two commercial speakers owned by friends of mine which I measured in the past few weeks;



These speakers were gorgeous! I measured them from the listening position where the owner has loved them for a couple of decades. The Apogee has two planar drivers, one huge ribbon operating down to about 500Hz and one larger magnetic-planar driver (think Maggie) that operates from 500Hz down to 80Hz. Below 80Hz a matching dual 8" woofer cabinet handles the bass. The owner also had a Bag End subwoofer hooked up which was adjusted to play about 25dB louder than the Apogee speakers. It was a strange experience.

I was VERY shocked at how awful the THD performance was on those speakers. At first I thought there was some sort of flaw in the system. However, the data makes sense. The ribbon's THD increases near the crossover at 500Hz, as you'd expect. Also, the high THD spot at just above 2kHz aligns with the reflected sound off the wall behind the speaker. When I turned the speaker to almost 90 degrees to the side, that peak in the THD dropped to match the rest of the spectrum. It is still very high, though. I mean, the THD is over 1% almost throughout the entire operating range. And the high THD in the bass is also common for that Bag End sub which uses a massive EQ for force the cone to move at subsonic frequencies. That poor driver is killing itself to make those levels. I also believe that if the owner turned down the sub 25dB to where it was balanced with the rest of the system the THD would go way down merely because the woofer wouldn't be working so hard. I mean, 25dB is over 100x the power demand. So, if it takes 1 watt to make 78dB SPL at 20Hz (as I'd expect from the driver in that rather small enclosure), in the chart above the sub is getting a solid 100 watts.

Anyway.... while I enjoyed the speakers, I could tell they were lacking detail and added a false sense of shimmer to the recordings I was listening to.


__________________________________________________________________________________


Our friend Dentman allowed me to measure his new-ish Canton DC 509-2 tower speakers mated to his classic SVS tube-style subwoofer with an aftermarket plate amp. This was in his HT, after applying the foam acoustic panels, with the mic placed about 20 inches forward from where he had placed the listening position. I just felt it was a better place for the listening position, so I made lots of my measurements from there rather than the current location of the seating.

Overall, the THD is well behaved, but the metal cones demonstrate the typical odd order distortions, but not as badly as the Mackie PA speaker or the Apogee flat panels. Still, the THD at decent listening levels in his room remained well below 1%, That pretty good.

 

[Flint]

Now for my own speaker designs. I'll start with the low end and work my way up to my flagship products.



You guys should have seen my thread on recycling a pair of 2.5" full-range drivers from a Sony table-style clock radio. I used PVC pipe fittings to make an enclosure and port, and used a simple baffle of MDF to mount the drivers. I am now using these speakers on my little office desk in my family room where I work from time to time on my notebook PC. I have a very inexpensive Dayton Audio 25 W digital amplifier to drive them, and they sound pretty good for the task. I put the mic where my head is when I am working at the desk and played at the levels I tend to use, which isn't all that loud.

The THD in the bass is pretty high, over 1% until about 120Hz, but at higher frequencies the THD isn't terribly high at all. Of course, if I drove these loud enough to fill the room with sound, the THD would be incredibly high. But that isn't how I use them. After all, these are in the same room as the SVS MBS01 / SB12 NSD system. If I need louder music, I use the larger system.


______________________________________________________________________________


This is my master bath system. I also wrote a thread about this system which is a 3.5" full range driver and a pretty good 10" sealed subwoofer. They are all driven by a nice Dayton Audio 2.1 digital amplifier. I put the mic at my standing ear level directly between the speakers in the middle of the bathroom. I tend to play it loud as I like to hear music clearly over the sound of the shower or when brushing my teeth - both of which are pretty loud activities.

The THD in the bass is not representative of the subwoofer itself - there are just tons of rattling noises in the room. But, that's still what I hear, so I cannot remove it from the test. The full-range, however, is surprisingly clean given its size. It operates from about 150Hz up to the highest frequencies, and the THD is surprisingly low at these higher than common levels. I recommend that driver to anyone looking to make a decent fullrange speaker.

 

[Flint]

Some more of my custom speaker builds below...



The Lil Joker is a coaxial outdoor speaker and the Arthur subwoofer is a sealed 12" woofer also for outdoor use. They are driven by the same model of Dayton Audio 2.1 digital amplifier as my bathroom system. These are mounted under the roof on my patio outside. The sub sits between the two metal chair on the porch. I put the mic where my head would be if sitting on one of the porch chairs and set the level at about the loudest I'd ever dare listen to music out there.

The THD is pretty high in the subwoofer's range, which isn't a surprise given I used the cheapest 12" subwoofer driver I could find. But the coaxials also exhibit pretty high THD. They are a pleasing sounding speaker, so I am a little surprised by the measurements. I am going to look into this one and perhaps update the chart if I find some sort of anomaly in the measurement process.


______________________________________________________________________________________


I measured my huge line array from a pretty far distance of over 12 ft because that's where all the drivers are most aligned. I did not turn on the subwoofers at all. So, this chart is only the line array which is 16 full-range drivers and 6 planar tweeters.

The THD in the 16 drivers in the huge array is incredibly low considering those are $2 drivers. Imagine getting over 95dB SPL from 13 feet away using $32 worth of drivers with a THD well below 0.5%!!! That's simply insane!!! The tweeters, however, are not blessed with the cleanest output. I just have to accept that. They, too, are very cheap drivers, but they are not exhibiting the insanely low THD those woofers are showing.

Crazy!

 

[Flint]

Finally, my flagship speaker designs...



The Rocketman speakers utilize some of the finest drivers available. I measured them as they are setup for demo in my front room with the seating about 8 feet from the speaker (that's a typo in the chart, it should read "2.5M"). As with all my ultra-high-fidelity speakers, I measure things at higher listening levels which is closer to my actual "critical listening" levels.

The THD is pretty darn good at these levels, maintaining a THD of less than 0.5% from 60Hz to the top end of the measurement gear's range. At lower SPLs it is even better. The bass distortion is higher, but not bad at all. I am very happy about these results and it shows when listening to great recordings on these speakers.


___________________________________________________________________________


My state of the art speakers, the Statement 1, utilized an amazing compliment of drivers with elliptical voice coils in the midrange and tweeter which reduce distortion and drive 3rd order distortion completely out of the way. I measured these from my listening position in my primary listening room at nearly 100dB SPL.

As you can see, even at this extremely high playback level, the THD is below 0.2% from about 80Hz through midrange and treble. There are tube amps which cannot perform at these distortion levels. The bass, too, is very clean with THD remaining below 1% to nearly 30Hz. At these SPLs, that is damn near unheard of. As a result these speakers reveal detail and resolution in recordings that is on par with the finest headphones. It also important to point out that the 3rd harmonic is well below the 2rd harmonic over the majority of the operating range other than the one anomaly centered at the crossover frequency range centered at 310Hz. I intend to experiment with the crossover settings to see if I can reduce that artifact while maintaining the amazing sound I already get from these.

 

[Flint]

That's it for now. I'll post more data once I make more measurements.

 

[PaulyT]

Cool, very interesting to see so many parallel measurements on a wide variety of speakers. Wow that THD on the Statement speakers is insane (ly low).

 

[Dentman]

Some great info here. It's nice seeing in real world conditions, with such variety.

 

[heeman]

Real World data is so much more valuable than "spec data".............Thanks @Flint !!

Did you perform any Harmonic Distortion measurements when you were out in the Rolling Farmland of WI??

 

[Randy]

Impressive stuff. Thank you again for all of your time and effort putting all of this stuff together and sharing it with us.

 

[Flint]

A large focus of this exercise is to show performance for speakers as they are being used - even enjoyed.

It would be insane to put my tiny 2.5" Sony Full-Range speakers in my listening room and run them at 100dB SPL. They'd likely blow if I attempted to drive them that hard. Likewise, it is physically impossible to conveniently place my Statement 1 super-speakers on top of my little desk to use as PC monitors.

The right speaker for the job, right? But, when used for the job at hand, how do they perform?

 

[Flint]

I got a great opportunity today to measure a classic set of Sound Lab A3 speakers in a good large room driven by gear which was too fancy for my understanding. Below are the THD measurements for both the left and the right speaker because there was significant variation between them.





As you can see, these huge speakers have a very impressive bass output, especially considering they are Electrostatic panels.

The THD was relatively low in the primary operating range above about 70Hz, but there were significant differences between the two. The owner had sent the right speaker back to the factory for repair when it was about 14 years old, so that could be the cause of the difference. But, the speakers have a controls for the Bias voltage, brilliance, and bass compensation. Here's a photo of the panel on the rear with these controls:



It is entirely possible that these controls are performing identically on each speaker.

Overall these are very good sounding speakers, but I have to point out that above 200Hz on both speakers the 3rd harmonic is the most dominant source for distortion. As we all know, odd order harmonics are more harsh, brittle, and sharp than even order harmonics which are considered to be soft, mellow, and warm. The prevalence of odd order harmonics over even order could very easily be why these (and all ESL speakers) are perceived as being more detailed, resolved, and have higher clarity. Very often, enhancing certain distortions can make one think they are hearing more detail than with other speaker - but they are actually hearing distortion artifacts.

Overall, these are great speakers. I listened to them for about two hours after the measurements were taken and I really enjoyed them.

 

[Flint]

Here's a measurement from the second generation of the Lil Joker & The Arthur subwoofer setup in my living room.



I am very surprised at how well it measured in terms of THD. It could be better with a more robust subwoofer. Also, you can see the 3rd Harmonic is the primary contribution the THD above about 600Hz all the way to the top end of the measurement range. This is not ideal, but it sounds pleasing as a "fill the room with nice sound" speaker.