Wiim Amp Ultra for Quad ESL-63s and SVS 3000 Micro sub

A while back I bought a Wiim Amp Pro (WAP) to replace the electronics in my bedroom stereo system. After I realized the bass management can be used as a crossover, I decided to try it in my living room system, driving the Quad ESL-63s that I recently rebuilt, and an SVS 3000 Micro subwoofer. I was impressed with the Wiim amp's performance and decided to put the WAP back in the bedroom and I bought a Wiim Amp Ultra (WAU) for the Quads/sub (20% off on Black Friday!). The WAU is similar to the WAP, but uses a different DAC and has a higher power output- 100W/ch at 8 Ohms and 200W/ch at 4 Ohms. It also has a touch screen I don't really have a use for.

Wiim Amp Ultra sitting on top of SVS 3000 Micro subwoofer.

The WAU has been reviewed ad nauseum:

WAU at Audio Science Review

WAU at Soundstageaccess

WAU at Darko Audio

But why?

The Quads, as wonderful as they are, are not perfect. The upper end of the audio spectrum (beyond my ability to hear it) is rolled off a little (easily corrected with an equalizer in the WAP or WAU), and they are incapable of producing low bass. Some people also complain of limited "dynamics" and maximum SPL - to me those are the same thing- if maximum SPL is limited, of course, "dynamics" will be limited.

The Quad's poor bass performance can be blamed on two things. First, they are bipolar radiators which means they emit sound from both the front and back sides. The front side and back side radiation are 180 degrees out of phase, so when the sound wavelength they produce is long compared to the size of the speaker, the front and back radiation tend to cancel and the result is weak bass. Second, the spacing between the diaphragms and stators in the drivers limits the maximum diaphragm excursion, and thus maximum sound pressure level (volume). The greatest excursion is demanded when reproducing low frequency sounds, so if you can prevent those low frequencies from going to the Quads, they can play everything else louder. This also addresses the "limited dynamics" some people complain of. 

The bass management in the WAP/WAU can be configured to keep the lows out of the speakers and send them directly to the subwoofer. The crossover is a Linkwitz-Riley 4th order type which means the low frequency roll-off in the Wiim amp will be 24 dB per octave below the crossover frequency. One octave is a doubling (or halving) of frequency, so one octave below 90 Hz is 45 Hz. So at 45 Hz, the signal going to the Quads from the amp will be 24 dB below what it would have been without the crossover being turned on. That means the Quads will be able to play much louder than they would if the full range signal were being sent to them. 

Linkwitz-Riley crossover response curves for 2nd (12 dB/oct), 3rd (18 dB/oct), and 4th order (24 dB/oct) implementations. The WAU/WAP use the 4th order curves. This image comes from the Rane site linked above. No, there won't be a suck-out at the crossover frequency. When the outputs of the drivers are summed acoustically, in your room, the response at the crossover frequency will be flat.

The SVS 3000 Micro sub has an 800 W amplifier built in and can produce lower bass at much higher output than the Quads ever could, so configuring the amp and speakers this way is a win-win situation. I get the lows that the Quads can't produce well, and the whole system can play louder. This is going to be true of any speakers you use that have poor low frequency output/response, including about 99% of all bookshelf speakers.

System Setup: The Subwoofer

The Wiim amp's bass management and the subwoofer can both be configured via my phone or tablet. It's a little bit of messing around, but once the configuration is done, it doesn't need to be done again. 

Connect the sub output on the Wiim Amp Pro to the LFE input on the subwoofer. Open the SVS app on your phone and switch to LFE mode - that tells the sub's DSP that it will only receive low frequencies at its input so it doesn't need to run a low pass filter of its own. In my system I set the subwoofer output to -20 dB, but your system may need a different setting. This can be changed later, as needed.

Much more detail here.

System Setup: The WAP or WAU

Connect the speakers to the jacks on the back of the amp and the sub output to the subwoofer's LFE input. Open the Wiim Home app on your phone. Select the amplifier and open its settings menu. Select the "Sub Out" item. Turn Sub Output on, set the level (start at 0dB and increase later if needed), set the crossover frequency (the default is 80 Hz which is pretty good for most speakers, including the Quads), you'll set the phase later, so don't worry about it for now, switch "Subwoofer Bypass Mode" off, and "Main Speakers Output Bass" off.

Play some music that has some low bass. As you listen, flip the phase switch back and forth between 0 and 180 degrees. At one setting, the bass response will experience a dip and at the other setting, a peak. You can usually hear the difference pretty distinctly. 

The final setting to make is to use the Wiim Amp's bass sync feature. The subwoofer and Wiim amp both have some delay resulting from the signal processing that goes on in their DSPs. There may also be a different "time of flight" between the main speakers and the sub and your listening position. Ideally, you want the subwoofer to be time aligned with the main speakers. The Wiim amps have the ability to perform the synchronization built in, but it's less than ideal. It uses a mic built into the amp to pick up test signals generated in the amp. It will then report the delay and adjust the signal(s?) to the main speakers and sub to be properly time-aligned. It would be better to use a mic at the listening position (as RoomFit uses), so right now, to do it right you have to put the amp at the listening position when you run the bass sync. Fortunately, using a mic at the listening position is possible in the latest beta release of the firmware for the amps, so in the near future you'll be able to use the same mic you use when you run RoomFit at the listening position.

More details here.

I set up Roomfit in non-boost mode to adjust response from 20-200 Hz using a Harmon target curve with ERB smoothing and plugged a UMIK-1 calibrated mic into my tablet and here is the result:

Then I turned on the PEQ and boosted the response above 10 kHz by a few dB. Finally I ran the subwoofer and main speaker sync and it set an 8ms delay on the sub and it all sounds great.

Listening

When I want to play music, I select it via Tidal Connect or LMS and touch the play button on the screen. The Wiim Amp Pro wakes up and starts playing which triggers the sub to start playing within a few seconds. I can start, stop, select new music, skip ahead, skip back, and control volume, all from my phone, so there are no remote controls to hunt for or juggle and I don't have to go to the amp and sub to turn them on. They just start when I want to hear music, and when the music finishes, they both drop back into standby mode. 

The amp can be placed out of sight, under furniture or in a cabinet, because there's no need to touch it. Do give it a little ventilation though because as efficient as class D amps are, they do generate a little heat:

WAU top side thermal image after playing for an hour at moderate volume, with low frequencies routed to the SVS 3000 Micro sub.

WAU bottom side thermal image after playing for about an hour at moderate volume.

This sort of operation won't satisfy you if you prefer to handle records or CDs and/or you like to twiddle knobs and flip switches, but for me it's ideal.

And in case you are wondering, yes, it sounds great! If you want more flowery superlatives, see some of the video reviews linked above. I don't have the vocabulary that those guys do. 

A Stand for the SVS 3000 Micro Subwoofer

I recently got an SVS 3000 Micro subwoofer to add some low bass to my stereo system. It's amazing what 265 mm cube box can do. It's available in shiny "piano" white or black finish. I went with white so it wouldn't show cat hair.

Ms. Kitty's fur gets everywhere, so I have a robot vacuum cleaner that scoots around and cleans most of it up between vacuuming jobs with a real vacuum cleaner. I didn't like the idea of the robot vacuum cleaner bumping into the subwoofer over and over (or even once), so I decided to make a small stand for it. I measured the vacuum cleaner and found that 100 mm of lift was all the sub needed.

I made a CAD model of the sub for this project and maybe others in the future, then designed the stand. The sub's feet are set at the corners of a 196 mm square.

This is a CAD rendering of the sub sitting on the stand. This is how I often make CAD drawings- just enough detail so see what I need and to design 3D printed parts like the end caps for the verticals. Eight 1/4-20 button head cap screws hold the whole thing together.

I dug out some left over 1" t-slot aluminum and took it to the makerspace and cut and milled it to size (4x 170.6mm and 4x 100 mm), then drilled some tool access holes and threaded the center holes with a 1/4-20 tap. Finally, adding some 3D printed TPU end caps for the vertical t-slot pieces prevent the sharp edges of the t-slot from damaging the sub's feet or the floor.

Printing end caps on UMMD using white TPU to match the sub. With the 1 mm nozzle printing in 0.5mm layers, prints are a little sloppy but finish in about 20 minutes. A diagonal cutter quickly cleans off the blebs and hairs.

I assembled the pieces on a granite counter top that is pretty flat and everything came out square and very solid. The TPU end caps fit tightly and stay put without any screws or glue.

The sub on the stand. Vertical t-slot pieces are 100 mm long and horizontal pieces are 170.6 mm long. I used white TPU to print jam-fit end caps for the verticals.

Now it's safe from the robot vacuum cleaner!

Update 8/3/24: I forgot that I had ordered some screw-in rubber feet for this project and they were delivered today. I installed them and now the sub sits just a little higher off the floor. The screw -in feet are nice because the floors in the old building I live in are neither flat nor level, so now I can make adjustments as needed.

It's hard to see them, but they are there- black rubber screw-in feet. They have 1/4-20 threads and I tapped the frame parts before I assembled them, so they were ready for the feet.