Saturday, 2 May 2020

MUSINGS / MEASUREMENTS: Multiple subwoofers to reduce nulls. The USB/UFO faithful. And thanks for the blind test submissions!

A few weeks back, I ran into this interesting article - "Is the room the most important component?".

In summary, it seems like the article is basically saying that we can rearrange our gear or perhaps treat our rooms in ways that sound good, thus making the room less important than a general consensus might suggest. There seems to be an undertone of trying to downplay the role of the sound room and suggesting that one can spend more money on high quality gear and still benefit. OK, sure, to some extent that's true; but there are obviously limits. After all, if the room is way too small, cubical, highly reflective and impractical to treat, speakers inappropriately shoved deeply against walls, or if there is no space behind the seating position, there's obviously no point spending $$$$ on gear that one can barely appreciate! In my opinion, the quality and size of the room and quality of the gear (especially speakers) should be reasonably balanced.

IMO, without doubt, the room does play a major role in the sound quality; I think it would be silly to suggest otherwise even though I have heard some completely deny this over the years! For example, objectively we can easily show the nodes (nulls) and antinodes (peaks) resulting from reflections and standing waves in our small domestic listening rooms. Subjectively, these effects/limitations are easily audible as well. The way we arrange the speakers will interact with the inherent properties of our listening room in ways much more significant than much of the concerns "hardware audiophiles" often speak of or obsess over (like which CD player/DAC/streamer/server we use, cable differences, or if jitter even is audible :-).

The above should be obvious to readers already. Over the last month, with "social isolation" in place, there was time after work to try out something I've wanted to play with for awhile. Let's see if I can smooth out the low-frequency response in my room by experimenting with the use of an additional small subwoofer...

I. The issue with a single sub...

For reference, consider the previous work by Earl Geddes (nice summary here) and Welti & Devantier (2006). The idea of having multiple subs to handle low frequencies below 100Hz is well-discussed by now in 2020 and many home theater buffs and audiophiles already appreciate this. In summary, the hope is that by using multiple subs in a room, we will excite multiple room modes in a more "balanced" fashion so that in aggregate, the resulting frequency response will hopefully avoid deep nulls and very extended peaks.

For the discussion today, let's use my room as an example and see what could be done to improve things... Here's approximately what my room looks like as a floor plan:

For years, I've been running a single subwoofer - the excellent Paradigm Signature Reference SUB1 in the left front corner of the room. This sub IMO sounds excellent. Capable of clean, deep, unbloated sounds, power to literally shake objects off tables if pushed and the experience of the "compression" in the room can be to the point of discomfort. I almost never run it to such levels of course since my family would complain 2 floors up in the house if I turned this bad boy up at night in the basement :-).

At >100lbs and packing 1700W continuous power, I've always left the SUB1 in that location as a convenient spot given the other pieces of furniture and where my built-in cabinets are located in this room (mostly on the right wall). There's a problem with this location however which I haven't been happy with over the years. From the listening sweet spot on my sofa, there are sadly some rather deep nulls within the 40-70Hz region especially with signals in the left channel regardless of what I do to optimize the sub's internal DSP setting, adjust volume levels or twiddle with the variable phase control. The "best" I could achieve looks like this. (Note: No global DSP room correction applied, 1/12 octave smoothing for each side with 1/6 smoothing for average frequency response.)

Looking at the graph, we can easily see that the two speakers are reasonably congruent above 250Hz, but below that, the room plays a much bigger role in the sound. This transition starts around the "Schroeder frequency", usually for small rooms like this, somewhere from 200-300Hz. (As usual, I encourage you to measure your own room and see for yourself!)

With digital room correction applied (such as using Acourate as discussed over the years), I can smooth the peaks without too much effort, but those relatively deep nulls are another matter! Generally, it is not recommended to use strong EQ to boost these (typically) bass frequencies for various reasons - including the fact that adding unreasonable amounts of gain will cause strain to your amp and speakers, and potentially introducing distortions.

Let's consider then the idea of adding another sub to improve the bass response. I suspect that if one were to ask audiophiles about this, most might question the wisdom of doing so and suggest if one were to do such a thing, insist on getting another identical sub. While an identical sub might be ideal (not necessarily true unless proven so for the specific room!), it would both be rather expensive given the cost of the SUB1 but more importantly, this would be impractical as well! Where am I supposed to put another one of these in my room that would not get in the way of cabinets, doorways, or just for convenience?!

Thankfully, remember that the ears are not particularly sensitive to bass frequencies or directionality below around 100Hz (THX and home theaters typically set their crossovers at 80Hz). As such, "timbre matching" isn't really that important, and when crossed over low enough, we have good freedom of speaker placement.

So, let's try doing this with a much less expensive and smaller (slightly larger than 1' cubed!) option - the Polk Audio PSW111 which I already have at home being used for a small bookshelf system upstairs. Listed as US$300, you should be able to find these on sale for less. This is a small sub with only an 8" driver and reasonably powerful 150W continuous Class-D amplifier in the box. For its size, it digs quite deep with usable frequencies down to ~30Hz and I like that the sound is "fast" and not boomy when pushed up to moderate levels. It's a bottom-ported design and I believe the -3dB point is something like 42Hz. Remember, I'm not looking for another sub to enhance the lowest frequencies down to 20Hz since the Paradigm SUB1 can already do this, I just wanted a device that can interact primarily in the 40-70Hz range to reinforce the sound and hopefully in the process neutralize the deeper nulls there...

For completeness, as you can see in the pictures above, this little device can be fed with line-level RCA input as well as speaker level inputs (wire clips). I'll be using the RCA input (inexpensive shielded Amazon Basics subwoofer cable good enough so long as no audible noise pickup) fed from my Emotiva XSP-1 preamp while the main subwoofer (SUB1) is fed from the preamp's XLR output. Controls on the Polk include volume, variable low-pass filter adjustment between 60-120Hz, 0/180° phase switch, and the power switch can go into an "Auto" mode to save on electricity.

II. Hypothetically... Let's simulate the room for placement options first...

Okay, suppose that little sub might help, the question then is obviously, "Where should I put it to do the most good?". And for that, let's fire up Room EQ Wizard (I used version 5.20 beta 47/48 while working on this) and let's have a look at some "modeling" of the room.

Using "Room Sim", I can plug in the approximate size of my room, the characteristics of the speakers, and explore where I can put "Sub2" so that at least theoretically, the nulls will not be as deep.

There were a few locations I could find including the front right by the main speaker, and the rear left wall which looked like they would work based on the simulation. I ultimately settled on this placement based on the modeling results, listening with sub at the various locations, and for convenience:

Remember that Room Sim models a rectangular room whereas my space has a tapered front along with some irregularity of the right wall. As such, the simulation won't be exact, but we can see from the dotted "Ref" frequency curve that there are various deep nulls around 45Hz and 62Hz which correlates to some extent with the "Archimago's Room Response" left channel measurement above. If we were to add a second subwoofer with approximately the parameters of the Polk with LF -3dB around 40Hz located to the rear right of the room as circled, the predicted frequency response curve will change to the continuous black line. This looks beneficial in reigning in that ~30Hz peak while limiting the depths of the 45/62Hz nulls.

III. Placing the Polk PSW111 and measurements

Let's do it! Here's the little Polk sub ("Sub2") situated as per the simulation above beside the rear right surround Paradigm Studio 80 speaker; you can see the miniDSP UMIK-1 measurement microphone in the foreground. I've updated the room layout plan.

For listening and measurements, the electronic audio chain looks like this:
Roon running on Windows 2016 Server machine in another room --> ethernet --> Oppo UDP-205 --> XLR out --> Emotiva XSP-1 preamp --> Hypex NC252MP amplifier --> Paradigm Signature S8 v.3 front speakers 
Emotiva XSP-1 sub out* --> XLR --> Paradigm SUB1 
Emotiva XSP-1 sub out* --> RCA --> Polk PSW111 
* signals to SUB1 and PSW111 contain summed bass content
So how does it measure once I adjusted the subwoofers for relative volume, phase (Polk phase -180°SUB1 0°), and crossover point (70Hz for Polk while SUB1 has internal DSP setting also around 70Hz)?

If we focus just in the frequency range where the little Polk sub would have most impact, we see that indeed between 35-90Hz, the major dips are "filled in". The left channel nulls at 47 & 68Hz have been neutralize. Likewise, the right channel peak at 78Hz has been removed (with only a small change in the 30Hz peak). Of course, it's not perfect but on the whole, the extremes have improved to a degree that will assist further optimization. These changes are already audible on tracks with smooth bass lines.

IV. Room correction DSP optimization

The next step is to create the Acourate room correction DSP filters. These are processed through Roon at playback (procedure as discussed here and here). In the last while, I've been playing with 4 filter "curve" settings as targets at my listening sweet spot which I can adjust on-the-fly depending on mood and the kind of music I'm listening to. Here they are:

I've got both "FLAT" targets as well as the psychoacoustically preferable "HARMAN"-like targets (see Toole, 2015). Note that for the "HARMAN" family, I do subjectively prefer a little more bass so what I did was introduce the taper from around 500Hz to 20kHz (I used a -7dB taper down to 24kHz), then added a boost from +1-3dB from 250Hz down.

The "DIP" room curves include a notch centered around 3.5kHz. As per this discussion with the late Siegfried Linkwitz, note how he discussed dropping the 3-4kHz region by 4dB to create a more "diffuse-field sound". This could help with many close-mic'ed recordings that could sound harsh in that "upper midrange" frequency region where our hearing is the most sensitive. For me, -3dB with some of my pop and 80's music sounded good especially with the overall "HARMAN"-like shape where the high frequencies are already gradually deemphasized. As I've discussed before, as a "more objective" audiophile, I think it's important to appreciate the stuff that can make a real difference through objective analysis, but also balance that by "knowing thyself" subjectively and optimizing the system to one's perceptions and preferences; nothing wrong with "euphonic" adjustments which is how I see the role of these "target curves".

DSP curves assigned as presets in Roon for easy selection/switching.
I won't bore you with the details around tuning Acourate settings since this will vary for everyone. I followed Mitch Barnett's recommendation when we chatted a little while back about using a smaller window for correction of the high frequencies to be beneficial. I also didn't want the correction filters to attenuate the signal too much so designed the room curves as above based on my measured response and allowed the filter generator to add up to +4dB gain where needed.

Here are the final pre- and post- room frequency response curves using the "HARMAN+DIP" curve as the target with dual subs as calculated by Acourate. For comparison, I also had a look at the effect of a similar filter using just the single Paradigm SUB1 without the little "helper" Polk sub:

Notice that having dual subs boosted the dips from 30-70Hz. This made it easier for the DSP to smooth out the frequencies <100Hz as can be seen if we compare the pink highlighted section. Note though that adding the little Polk sub did have side effects, such as a slightly bigger dip around 120Hz and the 25Hz dip is about 1dB deeper - nothing's perfect. ;-)

Another interesting observation we can appreciate here is that the Paradigm Signature S8 speakers appear to have incorporated a little "dip" around 3kHz already as highlighted in yellow similar to the -3dB 3.5kHz "DIP" purposely introduced in the target curve.

Remember that the above graphs are calculated "test" results created in the Acourate software. Let's finally remeasure the room again with REW and make sure that actual "real life" Roon playback with those filters applied resulted in the expected improvements. These measurements were made with the room as it would be when I listen to music - a small padded coffee table in front of the sofa, guitar in the corner and various other things like a stacked tower CD rack by my right front speaker.

1/6-octave smoothed average frequency response in green.
Looks good with reasonable correlation to the test convolution plotted above in the Acourate software.

To have a look at how sitting off-center changes the frequency response, here are measurements with and without DSP activated at the central sweet spot compared to 1.5' left and 1.5' right - did DSP treatment result in any more seat-to-seat variation?

1/6 octave smoothing for all graphs to make it not look "too busy".
As one expects, moving away from the sweet spot (in this case 1.5' to the right and left) will change the frequency response the person hears depending on the presence of those nulls and peaks at the location in the room. Whether DSP is engaged or not, notice that there are some strong peaks at 42 and 36Hz at 1.5' right and left of the central "sweet spot". On the whole, with DSP turned on, the graphs looked a bit less dramatic than without but I would say seat-to-seat consistency sounds about the same with or without DSP.

Let's finish off with a couple other measurements to check that there are no worrisome issues with the Polk sub in the system - let's start with the step response captured at the listening sweet spot (standard REW 500ms window):

Looking at -20ms before and +75ms after the initiation of the step, the time domain has been cleaned up significantly with the DSP active. Notice that the peak amplitude arrives by <5ms and the sound is "concentrated" within <15ms. In comparison, we can see that without the DSP, the energy is "smeared" with peaks approaching the strength of the initial deflection out to about 50ms. Remember again that this measurement is taken from the listening sweet spot about 11' from the main speakers with all the furniture in place; thus I'm not expecting the ideal "right triangle" step response, but rather evidence of improved time alignment (which appears to indeed be the case).

BTW, I think this is what actual time-domain "deblurring" looks like folks... Not whatever Bob Stuart and MQA were trying to sell us over the last number of years. ;-)

Regarding room reverberation, here's the RT60 with both right & left channels playing and feeding both subs, measured at the central "sweet spot" at the sofa again. The T60M (highlighted) is calculated from the detailed decay graph (not shown):

I would have liked the cyan EDT (Early Decay Time) to have been better below 200Hz. Along one of the walls in the room, I have a cabinet where I store some CDs, headphones, and other gear. The glass panel and cabinet door will rattle with deep bass and I suspect it's contributing to much of the low-frequency measured anomalies. Otherwise, the T60M is staying between 300-500ms from 100Hz up. Not bad I think for a domestic listening space although not ideal for music production control rooms (want to keep RT60 between 200-400ms for that purpose as per EBU3276 standard).

V. Listening...

Contrary to certain "subjectivists" who seem to think objective-leaning folks don't listen (!!!), I did of course make sure to listen to the differences adding the little Polk sub made. In fact, this project took a number of evenings to fine tune and the write-up above is simply a summary sparing the reader the trial-and-error details. Using data from the room simulations, not only did I listen but also made quick measurements at 3 different sub placement positions before settling on the final placement above. It was only once I settled on the final placement, did I fine tune the phase and adjust relative volume levels between the Paradigm SUB1 and Polk PSW111. From there, I did the Acourate room sweep recordings and constructed the various DSP filters based on personal listening preferences developed over the years... Finally, confirmatory REW measurements including the time-domain step response and off-center measurements to complete the investigations.

As I've expressed before, it's not hard for a pure "subjectivist" to write and review products, or claim that they "hear" differences and details. Admittedly, it's a lot more effort to drag out the measurement microphone and perform the objective "work" but IMO it's worth it both intellectually and learning to appreciate that the objective and subjective elements of this hobby go hand-in-hand. There's certainly a "joy" in performing this exercise as a "hardware audiophile". Ultimately, to optimize fidelity, one will need to do one's own homework since nobody else will have your room, your gear, and your subjective preferences.

As I finish writing this on my laptop while listening to the final result, I like what I'm hearing. The beautiful percussion work on a classic audiophile track like "Drum Improvisation 1" off The Sheffield Lab: Drum & Track Disc is presented with a nice wide sound stage across the front with instruments of the drum kit nicely laid out and projecting a subjective sense of depth. With so much of our music synthetic or heavily processed these days, it's a joy to listen once awhile to naturally recorded material such as this to remember the experience of high dynamic range and the feeling of the visceral "attack" of a bass drum played at reference volumes. Another naturally recorded album with tons of bass would be Reference Recording's Organ Sensation Felix Hell. Of course, almost any large organ recording will likely have prodigious bass when reproduced well.

One of my favorite tracks from UB40 is "Kingston Town (Extended Mix)" which I got as a single back when Labour Of Love II was first released. Awesome sounding bass line which is easily missed if one's system has limited low-end reproduction. If one is more interested in electronic music, Melleefresh vs. Deadmau5's "Whispers" (Cocktail Queen) sounds great with a nice system... Oh yeah, of course Yello's stuff like "Planet Dada (Flamboyant)" (The Eye) is a nice demo track as well.

Finally, thanks to Mitch Barnett for this article that dissects the bass fundamentals in Rebecca Pidgeon's "Spanish Harlem" (The Raven) which we can use to listen for unevenness below 100Hz.

VI. Conclusions

I like what I hear with the dual sub set-up so far and probably will listen to this for the next while before trying anything else to further optimize the system ;-).

Based on this experiment, I do believe excellent results can be obtained with relatively inexpensive tweaks like the addition of this little sub. I don't hear or see anything wrong with mixing and matching different sized subs or brands so long as we can appreciate the limitations of the device in achieving what we want and carefully tuning the effect - ideally guided with objective measurements. For example, with the little Polk PSW111, I'm not going to be pushing its volume to the max (nor do I need to even at reference levels). I know this sub will not reach below 30Hz which is why it's being paired with the much more power Paradigm SUB1 for those deep deep rumbles. I'm also keeping the low-pass crossover set around 70Hz to target the effect within 30-70Hz and reduce the chance of speaker localization.

Ideally, it would be nice to have better control of the subwoofer crossovers and even digital correction filters for the subs rather than a global filter like this. Obviously that would take extra work and complexity which to be honest might or might not be worth the time and effort given the improvement I'm hearing.

Speaking of localization effects, although I cannot prove it, I did find it preferable to place the little Polk to the rear right while the larger SUB1 stayed on the left front. One of my experiments was to place the Polk at the far left rear corner of the room. While frequency response measurements looked fine, subjectively there just seemed to be an excessive left-sided "heaviness" to the sound in my listening tests. Like I said, I can't prove this since it could all be psychological knowing that both subs were located by the left wall.

Have fun experimenting!

For those who have never taken a measurement mic to your room (miniDSP UMIK-1 highly recommended BTW), I consider it a bit of an "audiophile rite of passage" to do this as only then can one truly, and personally appreciate the effect of your room. Once we appreciate the dB variations in the frequency response, the time domain irregularities, and perhaps how reverberation time might deviate from the ideal in our rooms, then I think we can also truly contextualize just how little difference some of our components (like cables perhaps!?) actually contribute to the final sound!


OMG - this is ridiculous. I see that about a month ago, John Darko took another stab at claiming significant audible differences between digital cables with this video. As I mentioned a few weeks back, I do think there is a big difference between the "experts" in the audiophile niche he's polling and those engineers who might have worked on developing/implementing the USB standard (from the likes of Microsoft, Intel, AMD, Apple, XMOS, TI...). In court for example, experts disagree on all manners of things all the time! The fact that he's only advancing the opinion of one set of partisan "experts" isn't really all that helpful in the absence of any kind of evidence! It's rather telling that he turned off the comments section on that YouTube video... Gee, I wonder why?

Seriously folk, unless we see some evidence for things like USB cables making a difference, an appeal based on the opinion of "experts" without reference to any documented science is simply worthless. There is no "period pain" (apart from our current "pandemic period pain" I suppose). There is no change in paradigm coming. "Flat Earth" and "Bits Are Bits" are not analogous whatsoever. Proprioception and the idea of a spatial body schema are also not new concepts BTW that popped up since he left school.

Based on my private conversations with a few respected audio industry engineers over the years, I do not think many actually believe boutique USB cables are at all necessary even if they don't say this publicly. Nobody has presented any evidence that USB cables significantly change sound quality from a DAC. If one needs an analogy, rather than using the idea of a "Flat Earth", I would submit that those like Darko who vehemently support USB cables making a significant difference are more like "UFO Believers". Yes, they provide all kinds of testimonials. Sometimes they even provide "footage" (like the blurry Pentagon UFO videos lately) of demos where something sounds different, but they don't examine the "evidence" deeper to look for shenanigans like changes in volume. Like the belief in UFOs, it's "fun" and for the most part "harmless" of course so long as one doesn't go overboard and get shot trespassing into Area 51 or in the case of audiophile cables, one doesn't mind paying the "snake oil premium" over otherwise good generic products.

Darko's testimonial video is simply an example of wishful thinking, psychological susceptibility, and a desire to promote products consistent with the wishes of his advertisers and the Industry IMO. By all means, try boutique USB/digital cables for yourself and do it blindly if you can within a return period if the product is expensive. I think very quickly you'll realize that all this stuff he's talking about can be (and should be) safely ignored like UFO or other paranormal testimonials you might have encountered over the years.

[BTW, as a sci-fi fan, I would love to witness humanity making "first contact" with extra-terrestrial life! While obviously much less dramatic, I would likewise love to see evidence that this US$800 1.5m AudioQuest Diamond performs better than this US$6 1.8m AmazonBasics USB "printer" cable connected to a high quality DAC...]

In closing, I want to thank everyone who took part in the latest "Is high harmonic distortion in music audible?" Internet Blind Test. The number of responses has reached >60 participants thus far and while I said I was going to close it off at the end of April, just in case there are some stragglers, I'll close off the survey after this weekend so get any last minute submissions in!

Have a happy and safe May, everyone. I need to get some server hardware upgrades and backups done this coming week - updating to Windows Server 2019 as part of the change and installing a very good (so far) yet inexpensive TP-Link AX3000/AX5 WiFi 6 router. With society slowly opening up post-first-wave COVID-19 around here, there will also be some planning and adjustments at work I need to address so there might not be as many blog posts this month although I will of course analyze and summarize the results on that Internet Blind Test :-).

Hope you're all enjoying the music!


  1. Hello Archimago! Very interesting story. I'm curious whether the phase inversion of Polk sub was the only time domain adjustment you've done manually and whether for the rest you've just thrown Acourate on. Also, what were the crossover types and slopes you used for subs?

    1. Hi Mikhail,
      Pretty well, the Polk was inverted. The Paradigm SUB1's response was controlled by its internal DSP setting with about a 4th order low pass.

      As for the Polk PSW111, I'm not sure although it would be interesting to measure. I know that other Polk units tend to use a 4th order 60-120Hz crossover as well.

      For sure I threw Acourate at the problem and listened to make sure I didn't hear a problem and then measured to see if there were major issues.

  2. Hi Arch,

    I agree with your assessment of the Darko video.

    "There's certainly a "joy" in performing this exercise as a "hardware audiophile".

    I think that must put me out of the "hardware audiophile" circle.

    I have some nice floor standing speakers (one pair of Thiel 2.7, another pair of Joseph Audio Perspectives) both of which go down to about 35Hz or so. (I've owned floor standers that go lower, to almost 20Hz).

    I find the bass quality and depth very satisfying, but just "being an audiophile" and seeing the endless hype on subwoofers I figured I'd give it a whirl. I've been one of those allergic-to-subwoofers audiophiles because I never encounter subwoofer set ups that sound to me fully integrated. They always sound "subwoofery." And I always hear from subwoofer enthusiasts "that's only because you haven't heard a well set up subwoofer." And then I hear that person's system and...I hear the subwoofer.

    Anyway, I bought some nice JL Audio 110E subs, even bought the JL CR-1 crossover (and have some other subwoofer DSP stuff in a box), and frankly, after doing some tests, not being happy, and reading all the advice from subwoofer enthusiasts "You HAVE to use measuring software and tweak, tweak..." (it's astounding how much time and energy some people have put in to their subwoofer tweaking!)....I think I've about thrown in the towel.

    I think I'm just not cut out for all the effort a subwoofer takes to get it as integrated as I would like. Not to mention I truly hate the aesthetics of subwoofers, the extra cables, the extra gear.

    I've kept this stuff on the "maybe I'll finally get motivated to put the effort in" but, so far...nope. Your article reminds me to..maybe...give another try. But if I can't find the time to do it while in lockdown I don't know when I'll ever do it.

    That isn't a missive against subwoofers. I admire those who take the time to learn the technical side and really get it right, and everyone has their thing.

    1. :-) Vaal,
      Yeah, the subwoofer integration bit IMO does require getting the motivation to measure and confirm. For year, I've had subs in the movie/sound room and either got lazy and did nothing other than "adjust by ear" or had the receiver apply Audyssey and other similar algorithms which was fine for movies but did nothing for the 2-channel side. I only started really bothering with the measurements once I got the Emotiva XSP-1 preamp with HT bypass so I could switch what was being fed to the subs depending on whether I was watching a movie (LFE signal) or signals from the 2-channel feed.

      Sub placement and tweaking simply requires keeping an eye on too many variables if one is just using ears. Without instrumentation, it definitely is a long suffering process getting the low-pass frequency right, volume (especially relative volume if 2+ subs!), appreciating the subtle phase effect, and placement. Each of these variables interact and improvement at certain frequencies easily mess up issues elsewhere.

      Well, I hope you get a chance at some point to drag up the gear and try your hand at integrating your sub :-). Then again, depends a lot on the music you like since there's not that much music where we would think strong frequencies below 35Hz need be considered "essential" for enjoyment of the music!

  3. Wow, yet another post pertinent to my setup. I just purchased another sub, the very reasonably-priced Hsu Research VTF-2 MK5. It will play along with an SVS PB-2000. They're both very similar in size, weight, power output and freq. response measurements.

    Where I veer off is that this is all in a tiny room. Yes, it's idiocy but that's never stopped me before. Playing with a pair of L910's, the SVS was very overworked for little profit, and the second sub will not be a panacea. But, we are moving next year, so the purchase is for that more than present listening, though it'll be fun trying to get some actual gain out of the two subs in a room that presents almost complete nulls due to lack of room for bass freq. lengths.

    1. I forgot to mention, the Hsu sub arrives Monday.

    2. Alright trog69,
      Have fun! Hmmm, "tiny room" you say? Curious how tiny are we looking at for the Hsu and SVS!?

    3. 12x14! I should add that so far I've not opened the Hsu sub boxes and might just leave it unopened until our move sometime after the new year. It seems a ridiculous amount of bass output for such a tiny room, and I worry I'd only find that even with two of them the room is too small to allow reproduction of such long bass freq. I do not have any bass correction other than that on the plate amps of the subs, as I'm presently using the Emotiva pt-100 preamp, with dual summed sub outputs.

  4. Hi Archimago. Good article, where you can go even much further when adding more little subs in the room. There are also some "older" AES papers about that, for example some from G√ľnther Theile, also some published for IRT. Juergen

    1. Hi Juergen,
      Thanks I'll have to have a search through the AES archives on work! Hope all is well in Germany!

  5. Love all your hard work. Science is good to verify what our ears can often mistake as improvement. I have often done what you have in my cars and in my room to determine what is happening. Whether it is right or not I have often played white and pink noise in my room and recorded it with a measurement mic and them put those 2496 files into my computer and looked at the FFT to see what is going on. At 73 I don't trust my ears all the time. Like you I am looking for drastic increases or minuses in the EQ.

    I once had a tube mic pre and listened to all the hype about "tube coloration" and found out using my FFT display that by overdriving the 12ax7 tube all it did was give a huge suck-out at 12khz. Probably some added distortion as well, but what most struck me was the problem at 12khz. No more overdriving a tube for me.

    As for cables I think I fall into the "can you hear it" or "can you measure it" camps. I have ordered a AQ Forest USB cable ($89) , but honestly do not expect a difference from the decent, no name cable I have, but I also have some very thin ones that I am not using, although they might work for short runs and not for audio purposes. I don't buy $500 cables or speaker wire, that kind of money should be added to the purchase of better gear or speakers I would think.

    I am expecting an improvement in the Ifi usb Filter 3, but I will know this week. I will do one or the other first and try and hear improvements and then both together, changing only one thing at a time to see if either is a game changer.

    It is fun when you can fix an audio problem without spending money, like you did. Kudos.

    1. So my IFi Purifier 3 came today and it is a model A and not the B that I ordered. Now we understand how important "standardization" is and who decided we needed so many types of USB connectors? Maybe by the time I kick we will have used all the letters in the alphabet. Oh well.

    2. Hi Jim,
      Good that over the years you've been able to check out the measurements and figure out what various equipment is doing to the sound (like that 12kHz suck out you found in the tube gear).

      I think it's important to get into the science stuff because this is "good for the soul" as it were as audiophiles obviously interested in our hardware. Now that so much of our gear is "high fidelity" already, much of the differences we can hear I believe will logically be subtle... And I think this subtlety will more and more be evident in the objective demonstrations (like the frequency response curves) rather than subjective descriptions with meaningless claims we see written all the time in the likes of magazines and online articles.

      Alas, IMO John Darko's video is an example of abdication of one's own responsibility to learn the science, try to understand it for oneself, and in the process be able to achieve a level of critical thinking which will be more essential in a techologically based society where "news" comes at us from all sides and ultimately we're left to figure it out for ourselves...

      Have fun with that iFi filter! Lemme know if you hear a difference, in what way, and would be awesome if you could measure any difference.

    3. BTW with regards to USB-A, -B, etc... I do hope that the current USB-C iteration will be the last major version.

      Hope you get the right model soon!

  6. Thanks much for this post and the link to your earlier post "How Much Difference Does It Make? - On Balance and Adequacy for audiophiles". Based on this, I started thinking about how to reduce the 63Hz peak in my set-up. Considering absorption measurments I wondered about involving the two built-in cupboards in my room. I was completely dumbfounded - when opening 2 of the 4 cupboard doors I can reduce the 63 Hz peak to an acceptable SPL and extend the bass response down to well below 50 Hz. When opening all 4 doors I introduce a new peak at 50 Hz, well above the average SPL. Lot's to play with - and certainly the single most efficient sound improvement at no costs! Thanks much again!

    1. Great that you're experimenting Unknown!

      Yeah, as I mentioned in the text, I likewise have some cupboards and in-wall storage in the room that I know can misbehave, the most obvious is when I play louder bass material (typically >80dB SPL around 50-100Hz) with audible rattling. BTW, I can reduce this somewhat with some Blu-tack applied on the doors I rarely open to absorb the vibrations.

      It's also because of this that I have the 2 absorption panels placed at the 1st reflection points relative to the sweet spot I discussed a few years back:

      Lots to play with and these small changes can certainly result in significant effects :-).

  7. I watched Darko’s “I Trust in Experts (Don’t You?)” video also. Not because I thought I would learn something, but I was curious on how he was going to use expert findings to back his very subjective views on audio equipment. He also delves into the subject of how experts have shown that the “very real” reason why one digital transport can sound significantly better than another, is jitter and electrical noise, and eventually we will believe the experts. Besides, he says, it happened in the case of cables where people originally did not think there was an audible difference, but now they do. What? Maybe his subscribers, but there are plenty of people who disagree with that assertion. He ties this all into his analogy of the "flat Earth" and how we are simply in the resistance phase of believing the experts, just like in the past. He doesn't however get into why people came to accept that the Earth is indeed round; because it was irrefutably proven, by objective scientific measurements, that were checked by other scientific experts in the field. Like you said, it's easy to find "experts" to back up a claim ( I see it all the time, especially now, on my social media platforms). What makes an expert's claims legitimate in my eyes are published studies that have been peer reviewed for accuracy.

    1. Well said Joe,

      I think it's important to appreciate that the "flat Earth" example he uses is totally inappropriate as an analogy of "digital cables make a difference".

      The problem with people not accepting the correct "spherical Earth" model for generations was that "common sense" told them that the Earth seems flat. It is in fact the subjective perception/experience which grounded people into this and in order to resist the limited human perception of what they saw, as you mentioned, objective ways were employed to explain how the curvature would be subtle to see based on estimates of the actual size of this globe we walk on. And in time, with acceptance of this fact, things simply "made sense" once we appreciated that the spherical model explained things like day and night cycles, the seasons due to the earth's axis, and the unified consistency of a heliocentric solar system with all planets we observe also being spherical in nature.

      In arguing that "digital cables make a difference", he is using the same principles as the "flat Earthers"! It's arguing that his "perception" (that which made people believe the Earth is flat) is now the arbiter of "truth" when as far as I can tell, all objective measurements, controlled listening trials, physical principles, and engineering efforts point to the ideal that digital transmission will not sound different and that cables are simply conduits that will not impart their own sound signature unless literally "broken"! Like "flat Earthers" he rejects scientific principles and objective results and takes faith in his idiosyncratic beliefs and perceptions.

      To speak about "experts" as he presented IMO is painting a bad picture of those people he referred to. I bet that if we took the experts he listed one by one and sat them down, and had a good detailed conversation with them, discussed specific examples of this cable, that DAC, this other computer/streamer, requested evidence, I think we'd be able to get to the nuances of what these "experts" actually believe. I doubt the opinions will be as simple as what he's presenting in such broad strokes!

      Alas, the crew of so-called audiophile "journalists" these days do no such thing when it comes to careful interviews and thoughtful reality testing. Questions are presented as "yes" or "no". "Truths" are conflated with their own personal preferences. Subtleties are described as if they're obviously perceivable "veils" lifted and other nonsense that somehow substantially improves enjoyment of music.

      As a "reporter", a "journalist", one also has to be a kind of "expert" as well. An expert in reading the biases of the people they interview. An expert in language and communication both in how questions are presented and how they communicate to their audience. Perhaps most important of all, expertise in managing their own biases and being able to think critically.

      Alas, I see none of these things in what Darko presented. And not just him but the majority of the audiophile writers these days. These are not journalists... They're salesmen (and the token saleswomen).

  8. Thanks once again. I have one question: did the addition of the second subwoofer enlarge the usable listening area? I ask because I have often read that multiple subs not only smoothen response, but unlike dsp eq also do so over a wider area. You did post a before/after graph at 1.5 feet left and right, but that was only with/without dsp, and not single vs dual subs.

  9. As usual a superb job, I love how you shed such great truth to subjectivity vrs objectivity. My 1943 old house has so many rattles that I have removed all the slats from the front closest, taped all the front windows, and have placed a 2x6 wall of isolated SoundGaurd Insulation behind my Klipshorns. My Neighbor on that side calls the cops too often. I bought 6 of Neoprene Foam Strip Roll by Dualplex, 4" Wide x10' Long 1/8" Thick, Weather Seal High Density Stripping with Adhesive Backing everywhere there was vibration. My fav listening room from my Bud Louis, with B&W 804's, and a pair of DB-1's, and a small center sub, also points out that 2 subs are usually better than one. He has his listening room dialed in with a sound stage that is second to none I have heard. After reading this, or while I was reading, I had to put on my fav bass riff, Chicago, I'm a Man on their remastered original Transit Authority.

  10. Unfortunately, you will continue to get sub-optimal sound by following the popular fashion of believers who neither understand the science nor accept blind listening tests.

  11. The deleted comments were on spam messages advertising commercial dissertation writing services.

    1. Hey Willem,

      Every few days I try my best to pick out comments that are ads or spam like that... The price to pay for not moderating comments!

      I hate it when blogs moderate all comments and one is never sure whether time spent posting will ever get seen by the author or others.

  12. This comment has been removed by the author.

  13. Seeing this I wonder if the quality of the second subwoofer matters much, given that this was indeed a very modest sub. I understand that it does not extend as low as your main sub, but does e.g. a 40 Hz tone sound worse?
    I am pondering the recently tested Elac sub1010 as an infill for my B&W PV1d main sub, but only for the stuff below about 50 Hz.

  14. In the end the little sub that I bought was a Kef Kube8b. It is pretty affordable here in the Netherlands, and it looks very good in a modern interior. However, just when I decided to use at as a second sub in combination with the B&W PV1d main sub, the PV1d failed. So while I am waiting to see if the PV1d can be repaired economically the little Kube8b has to do main sub duty. It clearly does not go down as low as the PV1d with its dual 8 inch drivers, and output does not seem as well defined, but it is not bad and a lot better than nothing. However, all this also made me think about adding a third sub in Earl Geddes style. And following his example (and yours) I wondered if I should go for a really large Ueber sub like the Arendal 2s, or something a lot smaller like a Kub12b. The room is large at 7000 cubic feet.
    Did you ever ad a third or even fourth small sub, now that you got the multisub bug?

  15. Archimago, I experimented with DallasJustice's and Wayne Parnham's flanking sub technique and although subjectively it wasn't bad as I am a proponent of adding more speakers or subs as it does help fill a room and add warmth but in this case it introduced some SBIR issues from the flanked sub. The quality of the sub could have also had something to do with playing slightly higher frequency range 50hz to 170hz but thats just cojecture. So, I stuck with my 2 powerful sealed subwoofers in the front corners and my 15inch mains that also roll off slowly like a closed box and technically play also as subwoofers. 4 powerful sealed bass drivers coming from infront provide a superb tactile experience with a nice dry punchy slam. Then I experimented with another two 12inch suboofers in the back corners and now I finally understand what the experts mean by localise, even with a low crossover point it was annoying to have too much bass coming from all around and particularly from the rear although the measurements weren't that bad. So then I made two small 8 inch subs 200 watts, rock solid powered by 800 watt chinese class D amp and placed one in the opposite polarity of the height mode which fit perfectly up on my ceiling absorber panel and the other on the opposite polarity of a lenght axial mode against my orignal two front subwoofers. Definitely can't localize anything, there isn't this wow difference but I can't do without it, as it feels up the room and just adds a spice to the bass. Regarding measurements, on REW SPL I have very flatish downward rolling off bass with no nulls or massive peaks under 120hz but there are still some long decay times at 70hz and 120hz which I guess are just an offshoot of the room but I can't figure out. Maybe I am not understaning the difference of how a room mode can be attenuated but not decay. Anyway point being is that from my amatuer experience more subs are definitely better but you want the power coming from the front and the othr subs to add flavour rather than being the same or just as powerful as the ones at the front.