HSU STF-2 vs. VTF-2??

NewPolkie

Hey guys,

I finally decided to go with HSU sub instead of Velodyne CHT-12. My decision was based on the this forum's posts - most people here seem to prefer HSU or SVS over any other brand. I hope I am making a right choice.

Now my question - since I am not a techie in HT area - can someone explain the difference between the STF and VTF line of HSU subs. Are VTF worth the extra $$. Again, I am not a techie so please be gentle on me and keep your responses in lay man terms. Thanks!

I am planning to buy the sub directly from HSU website. I guess I'll need the sub cable too. They have 20 ft. cable for $20.00. It seems like a good deal to me. Those Monster cables for same length are over $50. Are they any better? What should I be looking for when buying these cables? Please advise.

Dr. Spec

The STF-2 is essentially a VTF-2 in the Maximum Extension mode.

The VTF-2 can be operated in the Maximum Output mode with both ports open for more output in the 30 Hz region.

I'm currently reviewing the STF-2 and it has a flat, deep, and accurate FR. It gets to about 22 Hz in a moderate size room before trailing off.

For a 10" woofer with a single 3" port, it can play pretty loud. The SPL limit at the seats before the onset of dynamic compression is about 110 dB in the 23-26 Hz region. That would equate to about 107 dB peaks on a C-weighted SPL meter set to Fast.

The sub is more comfortable in the 105 dB region (as read on the meter) for bass peaks, as distortion is lower as you move away from its compression limits.

If you stay within its clean output limits, the STF-2 will reward you with accurate and deep bass.

kingtut

Ed, how big is the moderate size room? Are you close to completing the review? Can't wait for the SVS 10" sub to come out to see how it will fair in comparision to the Hsu 10 incher.

Dr. Spec

Ed, how big is the moderate size room? Are you close to completing the review? Can't wait for the SVS 10" sub to come out to see how it will fair in comparision to the Hsu 10 incher.

My room is about 2000 ft3. I've done most of the objective measurements, but still need to write the report. Time will tell if the new SVS product will stand up against the STF-2; I imagine SVS has already tested the PB10-ISD against all expected competition.

I am curious - do you feel the STf-2 is as "accurate" as the STf-3 you previously reviewed, let alone any svs you own?

Sean, from a FR standpoint, the STF-2 digs about as deeply at the STF-3 (maybe 2 Hz less). The 2M ground plane FR of the STF-2 was commendably flat (one of the most important aspects of accuracy). In that respect it about equaled the STF-3. The STF-3 has higher dynamic limits and is capable of more output at the same THD limits, so in that respect it is a superior sub. But within the clean limits of the STF-2, the two sound almost identical.

The strength of the SVS has always been four fold: flat, clean, deep, and loud. The STF-3 and the PB1-ISD were virtually in a dead heat down to 24 Hz for FR, and down to 30 Hz for THD limited output. In fact the STF-3 is actually a bit louder at some of the higher mid bass frequencies due to its lighter suspension design.

But below about 25 Hz, the SVS started to walk away, and the deeper I tested, the more the advantage grew. The clean output advantage of the SVS in the 18-20 Hz region was really large.

Regardless, I have found the STF-2 to be a very good sounding sub with a deep and accurate FR and decent output and distortion figures for a single 10" driver and a single 3" port. The sealed design you recently built might exhibit a better impulse response and lower group delay (assuming you nailed the design), and if you are keen to those parameters, you might find it more to your preference over the STF-2 you also owned. The audibility of IR and GD are the subject of much debate, though.

Of course much of the audible "advantage" (if you want to call it that) of the sealed design has more to do with the fact that it can't play as deeply, and this is almost always perceived as more "musical" than the vented design that digs deeper. If you impose a 35 Hz 2nd order high pass on the STF-2, you might find it sounds nearly identical to the sealed unit you built.

Dr. Spec

If memory serves me correctly (as everyone knows at times it fails), you commented on how the STF-3 boasted a superior driver than the STF-2 (cone size aside). Apparently according to your current words, the STF-3 while the better product, is only minimally so.

How much better really depends on the application. In a small room where you might never see the limits of the STF-2, there would be no reason to step up to the STF-3. In a larger room, it will make a huge difference, as the STF-3 is capable of 2-3X the clean output of the STF-2 at the lowest frequencies. Where the STF-2 would be soft bottoming and farting, the STF-3 would still be clean and strong.

In reference to my DIY design - SPL aside, it did everything the STF-2 could only better. dig deeper, accuracy, you name it..

I'm glad you like how your sub turned out; it's a nice design. :cool:

Dr. Spec

It is hard to imagine an FR much more accurate than that of the STF-2. It is +/- 2 dB from 100-25 Hz ground plane at 2 meters.

It may simply be that Lil' Thunder reacts differently in the room and displays an FR more to your liking.

Until you assess the in-room FR of both subs in the 25-80 Hz region, drawing conclusions about the accuracy of either is a shot in the dark.

It may very well be - all other things equal - that you prefer the sound of a sealed subwoofer. But until you eliminate other variables and then conduct DB testing between the two, that remains speculation.

The important thing is Lil' Thunder sounds great to your ears, and in the end, that's all that matters.

Dr. Spec

Go here for the test tones and here for the RS meter correction factors. Burn the CD, get the spreadsheet for pdjami, and go to town.

http://beyond_gomer.tripod.com/

http://members.tripod.com/~terryctheater/shivaphotoalbum/page11.html

Dr. Spec

My burner is kaput. Paul should be able to burn you a copy; he's been great about passing on the knowledge we shared when I helped him set up his PB1+. That's what it's all about - helping Polk brothers.

kingtut

Ed, thanks for the update on the Hsu testing. As always your info is so thorough and informative.

Dr. Spec

Ed, thanks for the update on the Hsu testing. As always your info is so thorough and informative.

No problemo. The review is now mostly written, and I'm doing a few DVD SPL peak checks.

I'm going to run the draft by Dr. Hsu before publishing, to make sure every looks OK re: the specs on the unit, etc.

pjdami

Doc,

Nice to see you reviewing the Hsu subs now. That's great. Perhaps one of these days you will get your hands on one of those RELs or a new Velodyne.

I thoroughly enjoy the STF-2 in my dedicated 2 channel rig in my home office. It really sounds nice in there. Actually, I can't even tell that it is on unless I turn it off. Placement was key here.

Sean,

I can email the test tone files to you and you can burn a disk if you have a cd burner. I will have to split the files up on several emails though. Doc is absolutely correct, until you run a sweep you are only guessing at what the sub is doing. The sealed design may exhibit less "boundary" effects than a ported sub (like the STF2 that you had) and hence have less room gain and why it sounds better to your ears. Just a hunch here; perhaps Doc may elaborate a little more here if sealed designs are less prone to huge room gain effects.

Paul

Dr. Spec

perhaps Doc may elaborate a little more here if sealed designs are less prone to huge room gain effects.

It would be highly unusual for a sealed design to exhibit a flat ground plane response to 25 Hz; the enclosure would have to be quite large.

At my place the STF-2 does indeed exhibit considerable room gain below 35 Hz.

The typical higher corner frequency of the sealed unit (30-35 Hz), combined with its shallower 2nd order roll-off, combined with room gain (typically a 2nd order transfer function), can actually result in a more accurate FR in the deepest octave as compared to a vented unit with a deep tune point (which will exhibit a lot of room gain).

The reason companies like SVS and Hsu design for a flat anechoic response is that they can't predict what size room the sub will be placed in. The largest rooms exhibit almost no room gain, so you can't always rely on it to boost the bottom octave.

Dr. Spec

The port for lil'thunder will be arriving shortly. When I have time, I will install it and then mess around with the sub some more.

Why mess with success?