OK- It's Been 4 Weeks- PSB Subsonic 6i vs SVS 25-31 PC Plus (1 Viewer)

[Craig Chase]

Thanks Tom, I actually understood the effect of the input signal in 1977, when I hooked up my first system.

Again, TN did NOT specify at what level of output the subwoofers were run, just that they were run at maximum output level.

 

[Edward J M]

Good ol' power compression. Heck, look at the abuse Yates dished out in the WDD shoot-out. He drove some of those subs into severe compression - 10-15 dB at the lowest frequencies. A few of them had (laughing) an F3 around 50 Hz at the highest sweep levels!

That's why I suspected a few pages back that TN couldn't possibly be maxing out the sub, despite setting the plate amp to full; he knows better than that. 85 dB will be within the uncompressed limits of virtually any sub he measures.

If he is guilty of anything (and it's probably his editors trying to save space), it's a bit of ambiguity and brevity in the test description, which in turn lead Craig to an erroneous assumption about the sweep volume.

 

[KenWA]

Hello all,

I hope everyone here had a good Christmas! I added some posts to this thread on Christmas Eve, and I'm impressed at the number of posts that have been added since!

Since this thread has already digressed a couple of times, I'll add yet another digression here! Over at diyaudio.com there is a current thread having to do with the issue of "fast bass", which has been mentioned here a number of times. The discussion is somewhat technical and there have even been a few posts talking about measurement methods, as there have been here! Here is the URL:

w w w. diyaudio. com/forums/showthread.php?threadid=47580

I hope some find it interesting! (Sorry about the odd formatting of the URL.)

 

[Jack Gilvey]

Actually, what he specified was this:

I measured the direct-field frequency
response of each subwoofer in the
optimal corner of my 7,500-cubic-foot
room with its level control turned fully
up and its crossover set for maximum
bandwidth.

The difference may seem semantic, and that's understandable, but there's an important (and, apparently, not obvious) distinction between turning the level control fully up and running at "maximum output level". At least as I see it.

 

[Craig Chase]

Jack, It is clear from your questions you have never done a proper Frequency Response measurement. As Mark Seaton has suggested to several people, the best way to perform one is with pink noise. Doing pink noise is FAR more telling than is the quick sweep function on the TrueRTA ... Quick sweep is a fraction of a second, and does not tell much about the subwoofer's performance in the real world. It DOES make for pretty curves, though. Pink noise makes the subwoofer WORK.

Pink Noise means you do not single out one particular frequency, either. It means a broadband response will be played, in this instance, by the subwoofer in question.

SO... Your question as to which frequency one maxes out is not an answerable question. ALL frequencies are played.

You may start the sweep at, for example, 80 dB ... and chart the response there. As a general rule, when one charts such a response curve, one also states the SPL's at which the response was done. For example, when I posted the response curve for the Maestro, I left all the pertinant information on the screen for all to see. TN did NOT do so in this review.

In the case of the Maestro, The total SPL being generated was slightly over 90 dB, with the average at any given frequency being about 83 dB...

If you actually LOOK at the FR curves posted by TN, and compare them to the Max output per frequency, a VERY unusual phenomenom is evident... the FR curves (typically done at a MUCH lower level than the max output for 10% THD) are CLOSE to or INFERIOR to the MAX OUTPUT Curves...

What struck me as REALLY odd was how POOR several already measured subwoofers were, the LFM-1 REALLY stood out. Edward had already measured the STF-3 as flat to 22 Hz... PLUS I have read the Audioholics review on the LFM-1, and THEY showed the LFM-1 at flat to 18 Hz at 90 dB ...

Audioholics ALSO showed excellent results for the SVS-PB12-ISD/2 ...

I started to wonder WHY did TN get such poor response curves... and his statement about having the subwoofer's volume control set at maximum AND the fact his FR curves were no better than a curve based on Max output bar graphs was VERY evident.

If you take EVERY one of Edward's reviews, and charted a Max output chart, vs. his FR curves, the FR curves are ALWAYS FAR "FLATTER" THAN HIS MAX OUTPUT CURVES... yet Nousaine posted the opposite. Look at the Max output Bar graphs of the LFM-1 and the PSB Subsonic 6i, and compare those to the FR curves posted by TN.

Also ... If you ever DID take a FR curve at the max output of ANY subwoofer (you do this by running pink noise and increasing volume until he subwoofer starts to overload) , it typically WOULD look similar to the individual Max Output curve, were you to chart THAT. It is not a difficult thing to prove. Take Edward's PB12-Ultra/2 ... and run a response curve with pink noise at 90 dB ... it will be pretty flat to below 20 Hz.

Try it, especially in a LARGE room like Nousaine's, at 120 dB, and you will see ... well... results like TN got for his Frequency Response Curves.

You would see a pretty sharp rolloff below 30 Hz.

REMEMBER, when you think about this discussion, the absolute nonsense that was posted about James and his findings on the PSB subwoofer... it was said he might be hearing a rolloff below 35 Hz. There are numerous other MORONIC statements as to why the PSB just could NOT be as good a subwoofer as the SVS. He was told to use a BFD an eliminate the below 30 Hz bass from the SVS. This list goes on...

YET ... When he posted solid results to below 25 Hz... THAT was then proof that the PSB was lacking...

Even the fact that the PSB was stronger vs. the LFM-1 than the SVS was against the STF-3 at 20 Hz was irrelevant to you, and Ilkka ...

We also, as of this point, have a quote from an almost six year old review from TN stating he used an 85 dB output level for the FR curves. That is NOT confirmed for this review.

So Jack ... go for it... find me in either Yates OR Edward's reviews where the FR curves are WORSE than the curves from the Max output graphs.

And if you want, bring ANY subwoofer you want to my home. We will chart FR curves at 85, 100, 115, and 120 dB ... and you will see the 120 dB curve will be pretty close to a chart made by individual max outputs at each given frequency.

And yes, as it turns out, we DO know that the MLSSA method for measuring deep bass WILL show an earlier roll off than will Ed's RTA style measurements.

And yes, I accepted that it may well NOT be that TN was using max output levels for his FR measurements (and I said so freely, BTW). At least the end result WAS proven ... That it was TN's measurement method that gave the PSB a relatively poor showing Vs. the SVS, NOT the subwoofer's performance.

So tell me people, Ed, Ilkka, Jack... Where is YOUR admission that telling James he had an inferior, deep bass lacking subwoofer was erroneous ?

 

[Edward J M]

I already made this admission above regarding the fact I didn't know TN used MLSSA to measure FR. And I still contend that an abrupt roll-off at 25 Hz - be it 6 dB or 12 dB will not be perceived by the listener as a strong infrasonic bass response.

I never said the PSB was inferior; quite the contrary. My only goal was to determine why he might prefer the sound of one sub over another. I offered the reason could simply be the in-room roll-off below 25 Hz, and/or a peak higher in the curve (allowing bass instruments to be more easily followed). Maybe if he swept both subs in the same location, we could learn something from his subjective impressions, but he has been silent on the issue.

I could care less he prefers the PSB over the SVS. I care a LOT about WHY, because it should be our collective goal to correlate subjective impressions with objective data. And if we can't show a good correlation, then we are measuring the wrong things.

 

[Jack Gilvey]

I don't recall addressing James. I'm sure it's a nice sub,though. Why would anyone care what you or I say about it? I forgot what sub it is.

Ed...excellent post.

 

[Craig Chase]

Gentlemen, If you two are honestly going to try to say that there was not an attempt to put James down, fine. TN's data WAS used to "put the PSB in its place" ... NOW you want to say things like "I don't remember which subwoofer it was" ... Righto (to use your term).

A LOT of other people see it differently.

Ed, as for your assertions, I know you are a talented engineer, and like to spend time talking with people about the numbers that are possible with subwoofers, I don't agree with a lot of what you posted.

You said Yates was getting compression at higher SPL's which were causing, in some cases, F3 points of 50 Hz. Now it won't occur. You said The LFM-1 and the STF-3 are nearly identical. Well, now they may not be. I could go on, but I have several businesses which need year end analysis/forecasts done.

Just remember this, a reviewer is supposed to be independent of any one brand. A reviewer should not care about the product he is testing.

 

[paul clipsel]

Reviewers are always going to be subject to biases, even if they don't set out to be biased. I have read enough reviews to know even the tone of a review regardless of the objectivity can have a big negative or positive influence. That's why manufacturers forge strong friendship's with reviewers and why some brands product seems to get reviewed by the same group of reviewers consistently. I take them all with a grain of salt, even more so the new breed of quick electronic ones which are now done for internet only consumption.

Mind you there are reviewers and then there are "Reviewer's", and guys like Nousaine have obviously earned enormous respect through years of research, they are not just overnight sensations who are open to ruining years of hard fought reputation.

PC

 

[Nigel Hooper]

I don't think we can consider forum "reviewers" to be above average users. Now Yates, writers at Stereophile etc. ARE reviewers. The rest are hobbyists like the rest of us.

 

[Edward J M]

I never put James down for liking the PSB. In the course of using TN's (and later James') data to help explain WHY he preferred the PSB, all sorts of other interesting things were uncovered about TN's measurement methodology that ultimately will prove very useful down the road. In this respect, I think the thread was a smashing success.

Regards,

Ed

 

[Craig Chase]

Edward and I are communicating via PM, and I have also sent him my toll free number to my office... so we can discuss things "off line" ...

For the record, though... I have not said Edward has used TN's review to discredit the PSB ... I DID say TN's review has been used here, in this thread, to that end, and THAT is not debatable.

For all those who have waded through this mine field, accept either my thanks or apologies, as you see fit.

 

[Jack Gilvey]

I see that my humor, like TN's test setup, was not obvious enough. Cool (to use your term). Anyway, didn't "put James down" (not that he would care), and I'm sure it's a neat sub. My friend absolutely adores the Sony SA-WM40 I gave him as a gift, and I certainly don't "put him down" for it.
It's always fun when I venture out of the DIY forum. Enjoy your subs.

 

[Ilkka R]

My words exactly.

ps. Sorry for answering so late, I've been on holiday...