$600 Subwoofer Shoot-Out: SVS PB1-ISD vs. Hsu STF-3 – Test & Review (1 Viewer)

[Craig Chase]

Sasha - As a Hsu and SVS owner, and a hobbyist, I read Ed's review with interest... and I have to say it was the most thorough test I have ever seen.

He used a lot of criteria, the most important being a panel of listeners with great ears.... and not just deep bass, though that IS the job of a subwoofer... the best sounding, deepest bass for the $$$$ spent...true ?

I recommend reading the review in its entirety... then posting your thoughts on the whole review...

I know I learned a lot from it...

Plus... you should be proud, the STF-3 DID make the finals...

 

[steve nn]

I recommend reading the review in its entirety... then posting your thoughts on the whole review...

That would be great. Many of us would really appreciate your response and opinion in regards Sasha. If you can find the time?

 

[Edward J M]

Actually guys, I made a lot of changes to this report in direct response to constructive criticism from Hsu-philes.

1) I revised and clarified the amplifier feature descriptions, including adding the range of the low pass filter control, and better explaining the whole concept of EQ and infrasonic high pass filtering.

2) I changed the description of the SVS' near-field and in-room FR extension advantage, and removed the specific reference to 18 Hz from the FR and IR screen shots.

3)I gave the STF-3 additional points for the in-room FR score, because they were even closer when I re-ran the data set with a new audiophile grade sound card installed.

4) I (meticulously) re-ran THD at 18, 20, 22, 25, 30, 35, 40, 50, and 60 Hz because Hsu spporters felt the original 18-30 Hz data biased the SVS. I agreed, and ran the whole spectrum. I even went to the trouble of calculating average (THD limited) SPL over several different bandwidths using two different methods. And I gave the STF-3 additional points in this category too, because it scored very well in the 30-60 Hz region.

In short, I responded to every (constructive) criticism leveled at this review, even when (some of) my critics sniped at me from other forums, despite my sincere request for direct comments in ths thread. And I will also say Curtis Chang has both publicly and privately been a voice of fairness and common sense both during the shoot-out, and after it was published. He made several valuable suggestions (not the least of which was going with the Nousaine method for THD calculations), and his input has been greatly appreciated.

Regards,

Ed

 

[Sasha_G]

Are you sure you want me to be honest?

 

[Poh Ser]

Note that frequency response is one thing, but max output at each frequency is another. For those who considers below 25 Hz to be the most important, they can get that with the STF-3 by plugging up one port. Just like some people who prefers an overdamped sealed box speakers with a systme Q of 0.5 versus a maximally flat system Q of 0.7, you get some of that effect by plugging up one port on the STF-3. Maximum output at 20 Hz should increase somewhat - the port output is contibuting instead of cancelling at 20 Hz compared to the two port open situation.

 

[Craig Chase]

Sasha - Absolutely I would want to hear (ok...read) your impressions of the entire review...

Dr. Hsu, as with Sasha, finding out what you think of everything, including any improvements you deem need improving in a review process would be fascinating and educational.

 

[Edward J M]

No question about it. Assuming the new tune point is approximately 20 Hz with a port plugged, THD limited output has to increase at 20 Hz as opposed to two ports open. Cone excursion will be considerably damped since the resonator is functioning optimally at that frequency.

Yes, frequency response is one thing. And THD limited output is another. Taken individually, neither tells the entire story.

The increase in THD-limited output at 20 Hz created by plugging a port will never be fully exploited unless EQ is applied to the FR curve to re-obtain a maximally flat response in the 40-20 Hz region.

Bottom line, plugging a port on the STF-3 will not result in an optimal FR, and will not fully take advantage of the increase in THD-limited output, unless EQ is applied to the system. Which, not coincidentally, is exactly what you have accomplished with the VTF-3.

And Sasha - I expect no less than constructive comments aimed at improving future reports. As a preemptory comment, had the STF-3 won the shoot-out, I imagine you would have had a different opinion of my report.

Regards,

Ed

 

[Craig Chase]

In the interest of fair play, Ed extended an invitation for me to let him test one of my VTF-3's, and posting the results... Is anyone interested in what the VTF-3 can do when really worked over ?

 

[Dave Simpson]

Hey Craig,

I'm currently using an STF-3 on a trial basis, awaiting the arrival of the VTF-3 here in Canada. I'd be quite interested in Ed's findings, and I'm sure I'm not alone.
Cheers!

DS.

 

[Craig Chase]

Dave - I sent Dr. Hsu an e-mail over the weekend asking permission to test the subwoofer. As long as he is willing to give his OK on having Ed test one of my subwoofers, I will see to it Ed gets one. I will keep you posted.

 

[Edward J M]

The idea is to have both Craig and I involved in setting up and generating the test data.

In addition to testing the VTF-3 under exactly the same near field and in-room conditions as the STF-3, if the weather cooperates we'll break out the ground plane stuff and have some fun outside, too.

Just to be clear, the VTF-3 data will not be part of this review; it will be posted under a different thread. This shoot-out report stands alone as a fixed tune $600 subwoofer comparo.

But since the subject of variable tuning has generated SO much interest, Craig and I figured what the heck - if he's coming upstate for business, I told him to throw a VTF-3 in his (admittedly small) 'Vette hatch and swing by for a visit.

The logical comparison for the vari-tune VTF-3 is one of the variable tune SVS models, like a 20-39 PC+. This would be the next step up for both companies in terms of tuning, performance, and price. And while the form factor is different, we all know the woofer doesn't care/know what the enclosure geometry is, just how much air and vent is inside.

Ed

 

[Craig Chase]

Ed - The vette is a 2004 convertible, so the subwoofer won't fit in the trunk. However, in the interest of science, I would drive it up in my Aviator.

And since Ed is the brains, HE gets to do the work - I will be running the bar.

We ARE allowed to have SOME fun... aren't we ? ...

 

[Dave Simpson]

Sounds great, fellas! I look forward to your results. Thanks, and cheers.

DS.

 

[Stephen Hopkins]

Great info and results, but I'd love to compare my $300 EBS AV12 & PE 272 Watt amp combo.

 

[Sasha_G]

Port-plugged STF-3 excels at 20 Hz.

Dr. Hsu sent a private message to Edward about our exciting discovery.

With one port plugged, the STF-3 performed 14 dB higher at 20 Hz in the 10% distortion test! That’s right, not 1.4 dB, but 14 dB. That would make it the deep bass winner in this comparison.

Outdoor distortion measurements

Dr. Hsu also brought up some problems with measuring distortion indoors, and encouraged outdoor measurement for future shootouts. With indoor measurement, room acoustics can skew the results so that 2nd or 3rd order distortion measurements are very non-representative and misleading.

Variable distance instead of variable phase

It is probably better not to use a variable phase dial in many cases. The same thing can be achieved with any “subwoofer distance” setting found in Dolby Digital receivers. Variable phase dials add delay to the bass signal, just like the “subwoofer distance” does. The advantage of the “subwoofer distance” on a Dolby Digital receiver is that all the speakers can be times so they all arrive to the listener at the same time. This would be very difficult to do with just the variable phase dial on a subwoofer.

 

[qualen]

What do you do when using two subs that are not co-located? Most recievers do not have dual LFE outputs.

 

[Edward J M]

Spin Doctor: A person responsible for assuring that others interpret an event from a particular point of view.

(sigh) I suppose it's time I responded to this post.


Perhaps Hsu Research should then simply omit the 0/180 phase switch on all of its subwoofers and ask users to rely solely on the "subwoofer distance" in the pre/pro set-up menu? What about stereo applications where the user doesn't have a "subwoofer distance" in the set-up menu? What about dual subwoofer applications where they are not co-located?

The goal for the end user is to optimize the FR curve of the system (including the L/R mains) at the listening position. This can be accomplished with the "subwoofer distance" in the set-up menu, the phase control on the subwoofer, or even a PEQ. A variable phase control simply offers a wider range of adjustment than a 0/180 phase switch. Many SVS users have reported optimal FR curves with the variable phase control adjusted in the 90-120 degrees region; something not possible with a 0/180 switch.

 

[Poh Ser]

Our company tries to respond quickly to customer needs. This issue of getting high output below 25 Hz is a good example. Previously, we felt that the majority of customers who buy the STF-3 do not need response below 25 Hz. Posts like yours make us reconsider that. We came out with a very simple and cost effective solution to make the STF-3 more appealing to consumers like yourself – plug up one port. The fact that our manual did not mention the option does not mean that one cannot do it or that it is not recommended. It is a different story if we said specifically in the manual that we do not recommend operating the subwoofer in that fashion.

The loss in output with 10% harmonic distortion when switching to one port is not as bad as you think. Thanks to the soft power supply of the BASH amp, with one port open, the impedance at 25 Hz is much higher than when both ports are open. With both ports open, the impedance at 25 Hz is very low. The maximum voltage swing the amplifier can deliver is much lower than when one port is open, where the low impedance is shifted down to around 18 Hz. The result is no loss of output at 25 Hz for 10% harmonic distortion. The woofer has a much higher excursion at that SPL compared to the two port open case (roughly 10 times higher), but harmonic distortion is still below 10% up to the same SPL. The only 1/3 octave spaced frequency measured that showed significant reduction in output with the 10% harmonic distortion criteria is 31.5 Hz where we measured a 2 dB reduction.

Regarding frequency response, using one port versus two ports and not adjusting the EQ is roughly equivalent to comparing a sealed box system with a system Q of 0.7 to one with a system Q of 0.5. The frequency response starts to roll off earlier. In this case, the roll off begins at around 40 Hz, being down about 2 dB by 25 Hz compared to both ports open. However, Edward’s expectation of the frequency response being down 7 dB at 20 Hz compared to the two ports open situation is erroneous. Edwards forgot that with both ports open, below 25 Hz, the output of the port gets out of phase with respect to the woofer output. This result in a 24 dB/Oct acoustic roll off below 25 Hz. This is absent in the one port open condition, down to the single port resonance of around 18 Hz. This means that the roll off rate between 25 and 18 Hz is far gentler with one port open. The result is the frequency response at 20 Hz is down less with one port open than with both ports open, even without changing the EQ.

Now, some customers do prefer an overdamped frequency response. Some feel that it gives a ‘tighter’ bass. Hence I would not dismiss this option entirely. In fact, I will make it official that customers who prefer an overdamped characteristic can set their VTF-3 or VTF-2 to two ports open EQ, and plug up one port. It posts no danger to the subwoofer (on the other hand, we do NOT recommend opening both ports and setting the EQ to one port open).

Regarding indoor distortion measurements, I must say that I did not realize the potential effect of room modes on measured distortion until a week ago. I have always assumed that while the actual SPL at 10% harmonic distortion one can get at a specific frequency in ones room compared to what Tom measured in his room would be different, I would expect the difference between two subs as measured in Tom’s room would translate to the same difference in any room. So, if sub A played 10 dB louder (10% harmonic distortion criteria) at 25 Hz compared to sub B in Tom’s room, it would also play 10 dB louder when I have both subs in my room. Unfortunately, this is not necessarily true. Let me illustrate.

Let us say we are measuring harmonic distortion of subwoofers at 20 Hz in room 1 which has a 20 dB peak at 40 Hz and a 20 dB dip at 60 Hz (deliberately made large to bring the point across). Lets us assume two subs that put out equal SPL at 6% harmonic distortion, sub A has 5% second harmonic, and 1% third, the other (sub B) has 1% second, 5% third. When measured in the above mentioned room, second harmonic is increased 10 fold (sub A to 50%, sub B to 10%), while the third harmonic is reduced 10 fold (sub A to 0.1%, sub B to 0.5%). At that same SPL, sub A will measure about 50% while sub B will measure about 10% in that room. When you bring the same two subs into room 2 that has a 20 dB dip at 40 Hz and a 20 dB peak at 60 Hz, the reverse is true – sub A will measure 10% while sub B will measure 50%. Based on the measured results in room 1, I would have expected sub A to be far superior to sub B in room 2 as well, but it is not.

Obviously the above is an extreme case to illustrate the point. If you can find two spots in your room where you can place the mike and the subwoofer such that the frequency response of the room is flat from the lowest measured frequency (e.g. 16 Hz) to the highest significant harmonic (e.g. 3rd harmonic) of the highest frequency you will measure (e.g. 100 Hz), the results of your indoor distortion measurements will be accurate. This example requires a flat room curve between 16 and 300 Hz. I have not been able to find this in any of my rooms.

Note that it is irrelevant that two subs have identical frequency response in the same room. Sub A and B in the above illustration can have identical frequency response. What matters is whether the two subs have identical harmonic distribution. If all subs have identical harmonic distribution (same ratio of 2nd to 3rd harmonic, 2nd to 4th, etc.), then the room effects will not have any influence on the measured results. The same measured difference will be transferable from room to room.

Even reviewers make mistakes. I know that I have made lots of mistakes. What is important is to learn to challenge what is taken as the norm, and not assume that the norm is the truth. After all, people originally thought the earth was flat, and if no one challenged that, we would not be where we are today. We need to learn from our mistakes.

As a last note, Don Keele and Keith Yates measures distortion outdoors.

 

[Edward J M]

Hi Poh Ser:

When I compared these two products, the weather in upstate New York was not conducive to outdoor measurements.

I found an indoor near-field test location that provided a very flat, quasi-anechoic FR for both subwoofers. I measured frequency response and THD in that test location, and reported the results. I did not make any "mistakes" per se; that is simply how the subwoofers performed at my test location.

Considering our test rigs and test locations are totally different, the chances of us generating identical data are slim to none. Even if we both measured the same subwoofer outside ground plane, we still wouldn't obtain the same test results, because we use different mics, hardware, and software. That doesn't mean either data set is necessarily invalid. It is far more important to generate repeatable test data with your own test rig, than attempt to duplicate another reviewer's test data.

In your PM, you indicated you wanted to send me another STF-2 because you felt the one I bought might have been defective. To date, I have not received that subwoofer. If you would also like to send me an STF-3 (with a port plug), I will retest it outdoors ground plane for FR and THD with both ports open and with one port plugged, and report the test results in a different thread. I will even test the STF-3 in both tunes against a VTF-3 MKII if you would like. Maybe I can even get Craig Chase to help me. I will ship the subwoofers back to you at my expense.

Regards,

Ed

 

[Lew Crippen]

I just want to know if that testing outdoors would be on a carpet? After all, according to some views, testing without the required carpet is invalid.