Hsu Research ULS-15 mk2 Subwoofer Review

S

shadyJ

Speaker of the House
Thanks very much for the help, guys. I don't know if there are special challenges in placement of this particular sub (the Hsu),or for that matter just a sub of this size; but even if placement wisdom can be generalized, I'd appreciate a pointer to a reliable tutorial on integration. I mean, they are all over the place, but it sounds like I just shared a link to one with bad info. I am too new at this...I don't know the difference!

Hsu's own suggestions in the quick-guide/manual seem pretty casual and worry-free. Maybe I am making too much of it.
If you want precise integration between the subs and the main speakers, you need a way to measure the response. That means getting a measurement mic and measurement software. If you don't need that level or precision, just run some tones and listen for any cancellation that might be occurring. Use something like this tone generator, and listen to frequencies around the crossover point for reduced output. If you sense a reduced amount of output around the crossover frequencies, there might be some phase cancellation occurring. in that case, switching to opposite phase might fix the problem- but more likely, the problem will be a matter of room acoustics rather than phase mismatch, in which case no phase setting can correct that problem.

If I were you, I would just follow Hsu's placement and setup recommendation. That should get you to a reasonably good sound. After you get on that footing, there are more tweaks you can do, if you care to, but I think it would be getting way ahead of you and potentially confusing to dig into that stuff before you even have your first sub.
 
John Parks

John Parks

Full Audioholic
If you want precise integration between the subs and the main speakers, you need a way to measure the response. That means getting a measurement mic and measurement software. If you don't need that level or precision, just run some tones and listen for any cancellation that might be occurring. Use something like this tone generator, and listen to frequencies around the crossover point for reduced output. If you sense a reduced amount of output around the crossover frequencies, there might be some phase cancellation occurring. in that case, switching to opposite phase might fix the problem- but more likely, the problem will be a matter of room acoustics rather than phase mismatch, in which case no phase setting can correct that problem.

If I were you, I would just follow Hsu's placement and setup recommendation. That should get you to a reasonably good sound. After you get on that footing, there are more tweaks you can do, if you care to, but I think it would be getting way ahead of you and potentially confusing to dig into that stuff before you even have your first sub.
Also, HSU provides a lovely CD with some excellent recordings and test tones for evaluation and setup! :)
 
KEW

KEW

Audioholic Warlord
Good choice on the ULS-15. I think it is among the best values in a sub and not one you are likely to outgrow, ever (unless you hang out with some of the severely deranged bass-aholics here:D). Certainly a pair of them will want for nothing for music in any normal sized room!

Here is a great 5 minute video Marshall did so you can be ready to do the sub crawl when it arrives:
 
Last edited:
Langston

Langston

Audiophyte
Like several other reviews I've read on this site, the ULS-15 MK2 review was probably the best I've seen on the topic. Tons of work with excellent and sometimes unusual measurements. Partially based on this review I purchased a pair of these subs to go with the MartinLogan CLS loudspeakers I just rebuilt and modified. The support at HSU Research is as good as their products, when I sent an email asking how to increase the maximum low pass frequency from 90Hz to 150Hz, I got an immediate reply with instructions including the obligatory "your warranty will be toast" warning. This simply included changing (4) 10kΩ resistors to 6kΩ, which I did with parallel 15kΩ resistors to make it easy to clip them off and return the subs to OEM operation if I changed my mind someday. HSU treats their customers like adults. Amazing.

I've attached pictures of before and after near field measurements while keeping the high pass alignment constant (EQ1, Q=0.3).

Before (OEM).png

After (MOD).png

Resistors (MOD).JPG
 
S

shadyJ

Speaker of the House
Like several other reviews I've read on this site, the ULS-15 MK2 review was probably the best I've seen on the topic. Tons of work with excellent and sometimes unusual measurements. Partially based on this review I purchased a pair of these subs to go with the MartinLogan CLS loudspeakers I just rebuilt and modified. The support at HSU Research is as good as their products, when I sent an email asking how to increase the maximum low pass frequency from 90Hz to 150Hz, I got an immediate reply with instructions including the obligatory "your warranty will be toast" warning. This simply included changing (4) 10kΩ resistors to 6kΩ, which I did with parallel 15kΩ resistors to make it easy to clip them off and return the subs to OEM operation if I changed my mind someday. HSU treats their customers like adults. Amazing.

I've attached pictures of before and after near field measurements while keeping the high pass alignment constant (EQ1, Q=0.3).
Wow, very cool of Hsu to give you those instructions! To be honest, very few other manufacturers would even be knowledgeable enough to know what to do; they just buy the amps and assemble the products.

May I ask why you wanted to modify the low pass filter instead of just getting an external crossover? I suppose it's less expensive, but it does void the warranty.
 
Langston

Langston

Audiophyte
I love simplicity and I'm sure the long term cost will be less than adding a high quality active crossover in front of the subs. I also didn't want the potential degradation of an active high pass in front of the CLS amp, thus I'm using a simple passive high pass around 100Hz to yield a net acoustic high pass at 150Hz to integrate with the subs. I'm about to make outdoor ground plane measurements of the subs at the same distance as the CLS loudspeakers to phase align the passbands through the crossover region. Should be finished this week. :)
 
Langston

Langston

Audiophyte
Sorry to make another post for such a small bit of information. The input impedances of the (3) connector types should be included in the documentation, but aren't. This is helpful to know when paralleling multiple units. The DUT was a HSU ULS-15 MK2, but the results are likely consistent across their self-powered product line.

Impedances were consistent from test frequencies of 100Hz to 100kHz independent of gain control. Rounding is used below, measured impedances were ± 1% of these figures. The test instrument used was a Keysight U1733C LCR meter.

Balanced XLR inputs: 20kΩ
Unbalanced RCA inputs: 10kΩ
Speaker level Banana Jacks: 1kΩ
 
Last edited:
T

Touchez au grisbi

Enthusiast
I've run into an issue that Hsu HQ has already given me some assistance with, though it looks like I might have to ship the amp back to them for inspection and possibly repair. Curious if anyone here has had comparable problem:
After using and enjoying my ULS-15mk2 for over a year, it suddenly wouldn't power up. The red 'standby' light on the back would light up faintly (not bright red as before); and when switched to 'on', the green light wouldn't come on at all. The rubber ring around cone was not vibrating at all as it had been just a day before. No changes in set-up, no power surges AFAIK, haven't moved the sub much at all since finding preferred position a year ago. Hsu tech support was very attentive and patient via email, had me unscrew amp plate and check connections inside; I sent them a bunch of sloppy photos of inside and it wasn't clear if there was loose connector etc. Only asking about this in this thread on the off-chance someone has dealt with this and found simple solution, and it's my fault for not communicating properly with Hsu support...I would like to avoid having to mail the amp back!

Also: I thought I'd posted a thanks to all of you for offering info when I was first considering getting my ULS-15mk2, but apparently I completely spaced out or dropped the ball when posting. I did get the ULS, and I've been very happy with it until this little snag.
Never having had a sub, I have no point of comparison, but I'm completely sold on it. It's frequently a night-and-day difference from my previous 2.0 situation, which itself was not shabby because I was using Philharmonic BMRs with a decent amount of low-end.
Anyway, very late thanks for the help. You guys were a ton of help, and the sub experience way exceeded expectations...I hope to always have at least a small one from now on.
 

newsletter
  • RBHsound.com
  • BlueJeansCable.com
  • SVS Sound Subwoofers
  • Experience the Martin Logan Montis
Top