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Another PB10-ISD review (1 Viewer)

Ilkka R

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Ilkka


I already knew that... ;)

Hey guys, I think this has gone offtopic. If the conditions in Day After Tomorrow would come to NY, the results wouldn't change as much as they did on COFs review. We aren't talking about any 1dB or 2ms change...
I would think twice before letting that guy review another SVS product, who knows what kind of results he gets. :)

I believe this link shows his true capabilties as a reviewer.
 

ChrisBee

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Mar 4, 2004
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Thanks for posting these results Ilkka.

There does seem to be some variation across reviewer's results dependant on methodology, equipment etc.

Isn't it time that a standard test set-up and method was agreed?

There is often considerable sales potential (and potential loss) resting on these results. Take the case of the review that resulted in this thread. There were people making purchasing decisions willing to post their their choices on the fora based on this single review.

The make-or-break rumour mill in the hobby is hardly a basis for real progress in making true comparisons between competing products. Given a variety of results to chew on the rumours could be true or false. Or both!

As an example my own floorstanders roll off at 40Hz on my simple downloaded tone testing with a Radioshack SPL meter in my 30 foot room. Yet I had a discussion on another forum where the same speakers rolled off at 50Hz using the same testing techniques. (Though in a smaller room)

This suggests that even offering personal recommendations of a product on an NG could be frought with difficulty. Unless we actually know how well most examples of a particular maker's product perform. Which might be very difficult to prove. Since the manufacturers aren't going to volunteer this information freely.

If we all knew that a particular sub or speaker maker had a variation of 10Hz between their product's roll off points. Wouldn't we be more careful about making purchasing decisions? How would we even go about it?

Out of interest could these outdoor subwoofer tests be carried out in very large indoor spaces? Like dance or sports halls or school gymnasiums or assembly halls? This might at least bring some of the variables within a tighter range. Such spaces are probably lying empty for some of the time and available for limited use by private appointment.

ChrisBeee
 

Ilkka R

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I wouldn't concentrate too much on that frequency response COF measured. What I'm trying to prove that the "panel decay" test he did doesn't prove anything. Nothing about SVS's lack of bracing or anything else. The sound differencies he "heard" was caused by some other "things".
And also that Sunfire sub he used as a reference is NOT a good sub. I'm hoping that few of those who already had second thoughts will think once more...
 

Edward J M

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Actually, I posted Mark Seaton's description of the methods used by the different testers. Apologies if this wasn't sufficient.

Rather than paraphrase, here is the "In The Lab" link to Nousaine's latest round of sub reviews. Nousaine uses a 6.5 cycle tone burst at 1/3 octave intervals, and limits THD to 10%.

Whereas I was limited to 97 dB @ 22 Hz @ 2.7% THD using sines, I could measure right up to 10% THD at 22 Hz using a 6.5 cycle tone burst (since the amp wouldn't limit the output). I wouldn't be surprised if the actual 10% THD limit at 22 Hz for the PB10-ISD is around 100-101 dB (2M GP).

Ditto for 20 Hz, although THD was already 8% using sines, so there won't be much disparity between the two methods at that frequency; you might be able to squeak out another 0.5 dB at 20 Hz before THD hit 10%.

Note that Nousaine tests indoors in a 7500 ft3 room at 2 meters. His data cannot be extrapolated to other rooms, nor can it be directly compared to ground plane data; there are far too many variables involved.

Regards

Ed

http://www.soundandvisionmag.com/ass...micsubslab.pdf
 

Edward J M

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I'm not doubting COF/IG measured a difference in decay between the two configs (braced vs. unbraced). Since the change occured at an extremely low dB level, I'm questioning its audibility under controlled blind testing. The psychoacoustics of listener bias are very well documented and anyone can fall prey to it. Believe it or no, even an apparently unbiased tester has been proven to influence the listener if he knows which product/version is being played, hence my recommendation for the double blind vice single blind.

At this point, reception for the idea has been zilch, so unfortunately it will be hard to prove anything, Ilkka. Rather than pick apart COF/IG's test methods, we should focus on the audibility of the modification - that's what everyone really should care the most about.
 

Ilkka R

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As I said earlier, if we look at the decay time at -25dB level, it is the same, braced or unbraced. So I think it's rather clear that happened just as you said.
I also believe that if Hifilehti (or any other respected reviewer/magazine) could measure PB10's 3D spectral decay plot, it would be better than Sunfire True Subwoofer MK II's, braced or unbraced.

It is no wonder that he disliked PB10's sound because he is used (and likes) Sunfires, as Ed says
>>>"full bodied" and "complex" sound of the Sunfire - lots of audible distortion harmonics being created at low frequencies>>>

PB10's distortion- and boom-free bass will sound bad to his ear.
 

Mark Seaton

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Careful when making guesses about measurement differences on subs like the Sunfire or Velodyne DD series (Bag End would also have similar problems). The limiting makes for a response which changes as you change the level above some point. When the level changes, the response changes, and many matters of decay change as well.
 

EdwinK

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I included a link in the original topic where the review by COF was published, getting some nice and informative responses by COF and others there. You can check it out here:

www .soundandvisionmag.com/idealbb/view.asp?mode=viewtopic&topicID=35490&num=20&pageNo=5#290436 (remove space)

ps: a pitty that newbies cannot post links here..
 

paul clipsel

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I see in sub reviews the THD results get worse as frequency gets lower, and I imagine the PB10 is no different?

PC
 

ChrisBee

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"I see in sub reviews the THD results get worse as frequency gets lower, and I imagine the PB10 is no different?"

PC

This seems to be true of all domestic subwoofers for which I've seen figures. Regardless of design or driver size.

Even large pipe organs are incapable of producing very low frequencies without harmonics unless the pipe bore is very wide in relation to length.

What is the answer to lowering distortion at these very low frequencies in a normal domestic setting? Perhaps Frank's 8-pack is the way to go? An 8-pack of PB10's? :)

Is the distortion problem tied up with the velocity of the air movement necessary to reproduce these very low frequencies artificially?

ChrisBee
 

Edward J M

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They don't call Tom Nousaine "The Ace Of Bass" for nothing. He has vast experience actually measuring (not simulating or modeling) low frequency acoustics and subwoofer behavior. I use his reviews as a benchmark, and give him credit whenever possible. Keith Yates' work on the Ultimate AV Subwoofer shoot-out has likewise been brilliant and to me sets a new benchmark in outdoor testing.

I hope Tom tests a PB10-ISD too; it would be the only way to truly compare against other products he has tested. The only caveat is that he used to test in a smaller room (like 2500 ft3), and the results from those subwoofers would have to be extrapolated to his current and far larger (7500 ft3) room.

Some of the "Nousaine subwoofer summary spreadsheets" floating around the internet attempt to do this, but I would caution you that this would merely be an educated guess (in the larger room you lose a few dB and a few Hz of extension type of thing). As Poh Ser Hsu recently pointed out, the harmonic spectra distribution (and hence the THD limit) will certainly vary from room to room. That's why I will continue to ground plane on any future reviews - it removes one of the largest variables (the room) from the consistency equation.

Regards,

Ed
 

Mark Seaton

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While in general I agree this is a good conceptual goal, it could be hugely misleading to some. The post which Ed quoted earlier, and where I made the above comment can be found here: Comparative Testing & Such

As I also pointed out in that post, the only way you can have perfect bandwidth uniformity is through amplifier limiting. Take any subwoofer with a poor bandwidth uniformity and use a smaller amplifier. You just improved its bandwidth uniformity! This would imply that a subwoofer with greater headroom where it is not limited mechanically is a lesser performer than the same design with 1/2 or less the power. A much better measure may be how loud a given subwoofer can deliver consistent response down to some frequency. Looking at ranges down to say 35Hz, 25Hz, and 16-20Hz individually would be more telling. The other problem is compression. Burst or short term output will almost ALWAYS be greater than average output over some longer time interval. With any sort of program content, there is need for both average and peak capability, and both have merit.

While direct comparison of numbers is very useful, they hold the most merit when all things are equal, which is rarely the case with current product offerings.
 

Edward J M

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One would hope that a manufacturer wouldn't limit amplifier output at higher frequencies simply for the sake of improving bandwidth uniformity. But certainly that would be one way of accomplishing that. I think such a tactic would be obvious though, in terms of overall output. If a sub can only manage 75 dB @ 20 Hz @ 10% THD @ 2M GP, it would be pretty bizarre to artifically limit that subwoofer's output to 75 dB at all higher frequencies simply for the sake of achieving a 100% bandwidth uniformity rating. You'd need about 10 of them for any decent overall output. :b

I'd like to think improved bandwidth uniformity would result from louder/cleaner output at the deeper frequencies achieved through better design (woofer/enclosure/vent etc.), and this is clearly what SVS has accomplished with the PB10-ISD.



No doubt my next addition to testing methodology should be a slower sweep to look at true compression. This would be an interesting compliment to the dynamic output result that the QuickSweep provides.

What would you suggest for software to accomplish this Mark? And how long of a sweep do you think is required to assess true compression and average output? I noted a recent WinMLS user stated that sweep is about 5 seconds. And I think LMS and TEF are 30 seconds. TIA.

Regards,

Ed
 

Mark Seaton

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Hi Ed,

One of the important factors to understand is that inherent to improving the low frequency output of a design, you will generally see an according increase in dynamic headroom and linearity at higher frequencies as well. In a more simplistic case of a sealed box, if there was sufficient power, the bandwidth uniformity would not really change, but the overall level would increase.

The point to be made here is that I feel looking at dynamic capabilties and long term compression should be more telling. The incrementally increased frequency responses directly display this uniformity as it applies to increasing levels. One key here is to increase the levels electronically a known level (say 5, 6 or 10dB) and observe the increase in output. Some software will allow you to set a reference curve where you can display the differnce which makes this easier to see.

Here is an example I did with our Radical. A pink noise input or log-swept sine would have been a better test, but the point is clear.

I would suggest using pink noise sent through a reciever where you could start at -20dB or -30dB and increase to 0dB in steps. The TEF software allows precise, numerical output settings, so I generally use that, other programs may offer similar. I would test with a 100Hz low pass somewhere in the system, and then increase the level while testing at each level for at least 30 seconds. One caveat in this testing will be very low frequency energy, where high pass filtering and mechanical limits will come into play. I would think that two tests, one using pink noise input low passed at 100Hz, followed by band limited pink noise of 25Hz to 100Hz would be very telling of real world performance. Do note that this sort of testing could indeed permanently damage some subwoofers, and power ratings and suggestions of a manufacturer should be observed. Combine these with the fast sweeps or the Linkwitz tone bursts along with some distortion measurements as you have been providing, and you have a good picture of what any subwoofer will do.

This sort of testing brings up another issue, in that I would make an argument that while a nice thing to have, when optomizing a package size and total value, it is fully justified to have more output at say 25Hz than below 20Hz if the subwoofer offers any extension down that low. How much a difference between these levels is still useful or justifiable is up for debate and dependent on the room, system, and listener desires.

Keep up the good work!

Cheers,
 

Edward J M

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Thanks for the feedback, Mark. Your input and guidance at several forums is invaluable and always highly informative & cutting edge.

TrueRTA does have a pink noise generator, and the output level for both the QuickSweep and the pink noise generator can be altered in 0.1 dB increments.

I'm not sure if the TrueRTA pink noise generator is bandwidth limited; I'll have to ask designer John Murphy. It might have a lower limit of 10 Hz (which is also the lower limit of the QuickSweep). I don't believe the bandwidth can be altered, regardless.

I'll have to experiment with the pink noise as a complimentary test to the QuickSweep. Since pink noise has equal amounts of energy per fractional octave, it should appear as a flat response on the RTA display (provided the subwoofer itself has a flat FR). And since the pink noise is continuous, it would be a good indicator of continuous output capability and/or power/thermal compression as the signal strength increases.



Indeed. 30 seconds might roach the VC or blow a fuse in the amp. I'll experiment with different time intervals, starting conservatively at say 5 second intervals, and then try longer intervals and see if power/thermal compression becomes more of an issue as the duration increases.

I can also grab screen shots at each input level and compare the graphs, so we can see the effects of compression setting in at each level.

Great suggestion, Mark; I hope it can be integrated into my test methodology without much hassle. I'll keep you updated on my progress. Thanks.

Regards,

Ed
 

adan

Auditioning
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Nov 8, 2004
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Tom/Ron (of SVS),

Do you have any suggestion of how can I add internal braces to my PSB1-ISD?I got mine two months ago,they sound really great,great that my neighbors complained of their rooms being shaken,despite the fact that the apartment walls are made of concrete!But some of my friends shake their heads when they knocked the panels of the SUB and hear a hollow cabinet, no internal braces.Help!
Thanks.

Adan888:b
 

MikeCocc

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Sep 29, 2003
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Do you have any suggestion of how can I add internal braces to my PSB1-ISD?I got mine two months ago,they sound really great,great that my neighbors complained of their rooms being shaken,despite the fact that the apartment walls are made of concrete!But some of my friends shake their heads when they knocked the panels of the SUB and hear a hollow cabinet, no internal braces.Help!


Adan,

Why would you want to mess with a sub that, in your own words, is working great?

Just tell your friends not to touch the sub anymore... :D
 

SVS-Ron

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Jun 2, 2001
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1,074
Adan,

Tell your friends your $600, 1" walled sub will probably eat theirs for breakfast (at least on a price/performance ratio). Invite them to bring theirs over sometime and see who's what.

You don't need to add any internal bracing with a box built this well and a cube design; simple as that.

Your friends determine the sound quality of an amp by picking it up (to see how much it weighs) I suppose ;^)?

As noted above, find new friends if all else fails. 8^0

Ron
 

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