HSU D15-Chimera SC Dual 15” Extreme Subwoofer First Listen

HSU D15-Chimera Introduction

HSU Research has always pushed the envelope in some regard for every one of their releases. As a business, they were the first to release fully cylindrical subwoofers back in the 90s. They were the first to offer variable port tuning in the mid-2000s (check out our review of the original VTF-1 for a blast from the past). They were the first to have an electronic Q control. The VTF-15h was the first to use flared triangular ports. The list goes on. The proprietor and chief engineer, Dr. Poh Ser Hsu, seemingly has no interest in doing something that has already been done, even if only to have a presence in some market segment. He seems compelled to offer products that are unique in some way. This must be why he is the one starting trends, as with cylinder subs and variable tuning, rather than following them

One innovation that Dr. Hsu brought to market but is mostly forgotten now is a port extension module. The VTF-3 MK3 subwoofers could be had with an optional port extension accessory that HSU Research called the ‘Turbocharger.’ It was a set of curved tubes that extended out from the rear-mounted dual ports of the VTF-3 MK3 and led to a box that rested on top of the sub that had massively flared port ends. By essentially making the ports larger, the Turbocharger enabled the VTF-3 MK3 to produce a lot more deep bass. As with all variable-tuned subwoofers, the VTF-3 MK3 could adjust its port tuning frequency so users could trade deep bass output for deeper extension. Sealing one of the ports increases the depth-to-width ratio of the port system as a whole, and that lowers the resonant frequency of the system. However, sealing one of the ports halved the port volume area that could be used to produce sound, and that halved the output that the port system was capable of. The Turbocharger elongated the ports and increased port volume so that the VTF-3 MK3 could maintain the same output it had with both ports open down to the tuning frequency of its single-port operating mode. In other words, it did away with the compromise that variable-tuned systems usually have to make; you can have your cake and eat it, too. 

It never really caught on, and I believe the reason for that is that it looked rather strange. Nonetheless, it was an interesting idea: a module that increases port output. If the core idea had caught on, that could have led to some interesting places for those bassheads who craved big output at seriously deep bass frequencies.

I discussed the Turbocharger because it portends HSU Research’s announcement of a new subwoofer as well as a port accessory that is much more ambitious: the D15-Chimera and the Supercharger. The D15-Chimera is a dual 15” sealed subwoofer, and the Supercharger is a module that turns that sealed subwoofer into a ported one. I can’t recall any subwoofer system like it; it is totally unique, although its lineage extends back to the Turbocharger. Let’s discuss the base subwoofer, the D15-Chimera, before we get into the truly unusual Supercharger module.

The D15-Chimera uses the same 15” driver that HSU Research uses on all of their other 15” woofer subwoofers. It’s a very capable and versatile driver, as can be seen in our reviews of the ULS-15 MK2 and VTF-TN1. The Chimera uses two of them in a dual-opposed mounting so that they are firing on opposite sides of the cabinet. This is advantageous since they will cancel out their individual momentum, so the cabinet will not have any rocking motion vibrations from the drivers. The drivers are powered by a 1,200-watt RMS amplifier. The Chimera is basically like two ULS-15 MK2 subs in one enclosure. A single ULS-15 MK2 was a phenomenal sub, so doubling that performance will make the Chimera an absolute beast (no pun intended). The Chimera has all the features that the ULS-15 MK2 does, including a Q control, different operating modes, XLR inputs, and speaker-level inputs. 

A nifty feature of the Chimera is that it can be used in either an upright or horizontal orientation. If the user wanted to save some floorspace, it could have an 18” x 18” footprint, albeit with a 30” height. However, if the user would prefer a lower-profile subwoofer, it could also be stood on its long end for an 18” height. An extra advantage of the dual-opposed vibration cancellation is that it allows the Chimera to be used as an end table; in its horizontal orientation, its dimensions make it very suitable for an end table. Users can set things on it without having to worry that they will be rattled off by vibrations, although they will want to use an end table mat to avoid scuffing the satin black finish. The lack of vibrations also allows the Chimera to be used as a speaker stand if the user wants to convert their standmount speakers to a full-range system. The Chimera can accommodate this while always having the plate amp on the rear panel of the subwoofer, since there are two sides of the subwoofer where the amp can be mounted. That sounds strange - why would a subwoofer have an optional location where the plate amp can be mounted? That brings us to the ‘Supercharger’ module..

HSU D15-Chimera Sealed to Ported Beast Mode

The D15-Chimera is a cool subwoofer, but it in itself is not all that groundbreaking, since there are other dual-opposed sealed 15”s on the market. However, the Supercharger, an accessory for the Chimera, totally transforms it. It can be attached to the Chimera, which turns it from a sealed subwoofer into a ported subwoofer. Some readers may be thinking that's not a big deal since they can just plug the ports on their ported subs and do the same thing, but what the Chimera and Supercharger are doing is much more sophisticated than that. Yes, you can simply plug the ports on your ported subwoofer, thereby sealing it, but the internal volume for the driver is not at all optimal for that configuration. In other words, it is a very compromised sealed subwoofer; internal volume makes a big difference in how a loudspeaker or subwoofer will operate. Besides, you are now using an enclosure for the sub that is twice as large as it needs to be by simply plugging some ports to create a sealed subwoofer. By contrast, the D15-Chimera is the appropriate enclosure size for a sealed system using those drivers, and the Chimera plus Supercharger is the appropriate size for a ported system. 

The amp mounting cutout on the backside of the long end of the panels can be removed, and the Supercharger attaches to that, thereby doubling the interior volume of the subwoofer. What this does is make room for four huge flared ports within the Supercharger, each with a 4” diameter and a 25” length. That much port volume promises a huge amount of port-generated output, so the low-end bass of the Chimera plus Supercharger is going to be massive. What is more, the Chimera plus Supercharger supports variable tuning, so some of the ports can be plugged for a lower port tuning frequency and thus deeper bass extension. 

Of course, as we mentioned before, that does come at the cost of some output, but at least the user is given that choice. With all ports open, the Chimera has a -3dB point of 17Hz, with three ports open, its -3dB point drops to 15Hz, and with two ports open, its -3dB point is an astonishingly low 14Hz. This sub should have no problem diving into infrasonic realms where sound is felt more than heard. 

Another advantage of the Supercharger system, aside from allowing an optimal enclosure for a sealed subwoofer, is that the modular approach makes dealing with a monster subwoofer much easier. The Chimera plus Supercharger system as a whole weighs over 150 lbs. and is an extremely large system, but users do not have to deal with all of that at the same time. The Supercharger rests on the ground, and the user has to set the Chimera on top of it and attach the unit. Since the Supercharger is the same size as the Chimera, users only have to physically deal with modules half the size of the Chimera plus the Supercharger. It will be a two-man job to pick up and set the Chimera on top of the Supercharger, but it shouldn’t be that physically demanding with a friend to lend a helping hand. And then you get to show off the beast’s capabilities to your assistant! Since the attachments points of the Supercharger are symmetrical, you can chose to have the ports firing in front for a more aggressive look or have them firing in the back for a cleaner look. 

If HSU Research merely released the Chimera alone, that would have been pretty cool, but the Chimera plus Supercharger shows that they are not out to make a ‘me too’ product. As with so much of their products in the past, HSU Research wants to push design forward by doing something original and unique. The Chimera alone is not so huge that it may be able to find a place in family room systems or other shared living spaces, but the Chimera plus Supercharger isn’t likely to see many spaces outside of dedicated home theaters on account of its size. That makes the Supercharger a relatively niche product, but, like the Turbocharger before it, a very cool one nonetheless. 

HSU D15-Chimera SC Subwoofer Listening Impressions

By Jacob Green

I had the opportunity to audition the D15-Chimera SC at T.H.E. Show SoCal. The simple 5.1-channel demo system used an Onkyo receiver to power 5 of Hsu’s new MFL-6 speakers, which are slated for release on June 23rd, 2025. The speakers utilize a constant directivity horn for “superior clarity and smooth response, even when off axis,” according to Hsu Research. The speaker’s angled front baffle allows for flat wall-mounting while still providing toe-in toward the listening position for optimal imaging. The angled front panel also ensures that the front and back walls are not parallel, thus reducing standing waves. Exact pricing was not yet available, but Dr. Hsu told me that he expects the MFL-6 speakers to cost around $300 each, making them the least expensive speakers I heard at the show by a significant margin. The D15-Chimera SC subwoofer was positioned in the front right corner of the room. There was a second sub in the rear left corner, but it was not in use during the demo I heard. We were listening to the D15-Chimera SC with three ports open.

Then the presentation changed gears to focus on the D15-Chimera SC’s abilities as a home theater sub. The opening scene of Blade Runner 2049 sounded very immersive for just a 5.1-channel system, and the bass was not at all localized to the sub’s front-corner position. Using 5 identical speakers probably helped create the even-sounding soundstage. In a scene from Dune, the repeating “thump” sounds coming from a mechanical pump included both higher-frequency transients and low-frequency resonant information. The system managed to produce a surprisingly smooth transition from the speakers to the sub, so the pump sounds came across as realistic and not noticeably divided into distinct frequency bands. The speakers also had impressive dynamics for their size, but the obvious star of the show was the D15-Chimera SC subwoofer. The volume level of the sub was set higher than it should have been for an ideal balance, but this was a subwoofer demo, after all. When some characters were swallowed into the dessert sand, their demise was accompanied by truly seismic bass that seemed to come from the center of the Earth. Not just impressive bass, but borderline scary bass. I look forward to learning more about this sub’s capabilities from James’s formal review, and I just hope that he takes pity on his neighbors.

HSU Research D15-Chimera Subwoofer Conclusion

As with all HSU subwoofers, these are very high-value products in terms of price-to-performance. The D15-Chimera is priced at $1,799 (not including shipping), and the Supercharger is an additional $499 (again, not including shipping). At $2.3k for a Chimera plus Supercharger stack, it’s not cheap, but considering its performance potential, it's nearly unrivaled in terms of value. The only other comparable subwoofer in that price range is the Monoprice Monolith M-215, but it is much heavier and more physically difficult to deal with, and Monoprice does not have many of the same customer service benefits as HSU Research. For those who are excited by the Chimera plus Supercharger, HSU Research is offering a $150 pre-order discount for any order placed before July 11th, 2025. Audioholics is planning on running a full review of this wild new system from HSU Research, so stay tuned to see exactly how much bang for your buck can be had from the D15-Chimera and its Supercharger. 

Unless otherwise indicated, this is a preview article for the featured product. A formal review may or may not follow in the future.