Preliminary IMD measurements for subwoofers (2 Viewers)

[Tom Vodhanel]

>>>I fail to see the vague point. I think it's painfully obvious that Peter means this: Given the same basket, motor and cone, a design with more Xmax will have less Sd due to the surround (generally speaking), and therefore more excursion for the same output as a design with less Xmax...all else equal

 

[Ilkka R]

Now we are talking.

 

[Jack Gilvey]

My point in that thread, which I restated a few times before it sunk in, was that specific performance characteristics of the amp are important only insofar as they're manifest in the performance of the complete system. I've not noticed a consistent theme of high THD, or limited dynamic range, in the BASH-powered products I've read reviews of.

 

[Mark Seaton]

I, you, TV and many others know there are a multitude of factors that have to be ballanced. What I fail to see is any case where Peter has qualified or further specified any such statements. More importantly, it has been repeatedly insinuated that this is a point of differentiation in their products, yet all the explaining has been done by everyone but Peter.

I can think if many ways in which such an argument could be made, but we have no idea what Peter or Hsu is referring to. If this philosophy was what they felt, why didn't they go with a pair of 12-14mm Xmax 12" drivers rather than the single 12" with 23-24mm of Xmax? Why didn't they instead go to a 15" driver which would have only needed 14-15mm to equal the volume displacement? Again we can make guesses, but why don't we let Hsu explain what they mean themselves? Peter jumped in here in a technical and measurement oriented thread, I don't see it a stretch to expect related discussion continue on those terms.

 

[steve nn]

This is what has me stumped.. along with the explanation itself. It seems as though Peter has been making a argument for SVS from the angle I'm looking at it.

 

[SteveCallas]

Ok, case closed then. When comparing two subs that both utilize a single 12" driver, all else being equal, the one with the driver that has more excursion will be more capable.

 

[dave alan]

Maybe you misunderstood my comment, so I'll be perfectly clear:

First, I made no comments about any plate amplifier metting it's rating or not.

I simply mean that ID companies use cheap plate amplifiers with cheap circuitry and they purchase them because they are low cost. Dirt cheapest implying the lowest price for a given configuration of plate amp

How about if I reword it to read low 'enough' cost?

Honestly, you make it sound as though not only is price no object, but SVS actually seeks out the most expensive amplifiers on Earth.

BTW, Tom...care to post what you pay for a 500 watt Bash amp so that we may put it into perspective vs any number of high quality monoblock amplifiers coupled with a seperate subwoofer preamp/processor?

Maybe you could post test results of the LP filter, analog PEQ and all pass filter sections, as well as the control pot specifics, etc., etc.?

In any case, you may get away with labeling Indigo plate amps as 'very high quality' amplifiers in your usual haunts, or maybe you mean vs other plate amps 'made in China', or maybe you mean vs anything HSU uses, or whatever, but in this case, you're simply headed nowhere with the argument.

I am always amazed at how you label someone who has a different view than you do as a person who 'feels the need to post such misleading information about SVS...' and get away with it.

Surely, if I felt a need to do such a thing, you could mount more evidence than a single sentence taken out of context. Please tell me that the results of your search turned up more information than this plate amp comment on which you could justify saying publicly that I 'feel the need to post misleading information about SVS'.

So you know, I've never felt a need to publish misleading information about anyone or anything.

As far as the '...or how we evaluate components used in our products' comment, I have no idea how you evaluate anything, nor do I have much interest in the subject.

Dave

 

[Mark Seaton]

Hi Steve,

Since all else is often not equal, I would better qualify the statement above in stating:

When comparing two subwoofers utilizing a single 12" driver, the system with the more linear driver within the excursion required for a given level, the better we would expect it to perform in terms of HD and IMD.

 

[dave alan]

Sorry, Mark. As I said above, I now see that this is something that has been previously discussed between SVS and HSU fans and reps, so it goes much deeper than appeared by Peter's first post in this thread.:b

So, help me out here. What exactly is this thread about?

Dave

 

[Tom Vodhanel]

>>>Maybe you misunderstood my comment, so I'll be perfectly clear

 

[Edward J M]

I’d just like to clarify the use of the term “Doppler Effect” or “Doppler distortion” as referred to in this context. It is not the same as intermodulation distortion, and the two should not be confused.

Frequency modulation in a loudspeaker playing two tones simultaneously does exist. If this FM were caused by the Doppler Effect, then it would occur where the cone velocity is the highest – at the zero point crossing. Conversely, if this FM is caused by a phase shift, it would occur at the point of the peak phase shift, which occurs at the point of maximum excursion where cone velocity is essentially zero.

Therefore, if the FM was caused by the Doppler Effect, the pure (electrical) waveform and the modulated (speaker) waveform overlaid on an o-scope would show perfect matching at the peak cone excursion (i.e, zero velocity) point, and would show the largest discrepancy at the zero-crossing (i.e., highest velocity) point.

Conversely, if the FM was caused by a phase change, the pure waveform and the modulated waveform overlaid on an o-scope would show perfect matching at the zero-crossing point (i.e, no phase change), and would show the largest discrepancy at the peak cone excursion point (i.e., highest phase change).

Fortunately, this exact experiment has already been conducted, and sure enough the overlay is perfectly aligned at the zero-crossing points and shows the largest disparity at the peak cone excursion points, thus indicating the FM is caused by phase modulation and not the Doppler Effect.

Furthermore, an analysis of the higher frequency waveform (as it rides the lower frequency waveform) shows the higher frequency arriving slightly before the electrical signal on the positive peaks of the low frequency waveform, and slightly after the electrical signal on the negative peaks of the low frequency waveform. This is the very definition of frequency modulation.

Thus, FM is caused by a phase shift created by the change in cone position relative to the listener and not by the Doppler Effect, which would require the entire loudspeaker to be physically moving through space toward or away from the listener. Furthermore, this phase shift is completely independent of the low frequency modulation frequency, and is strictly a function of the peak-peak excursion of the woofer.

Due to the extremely narrow operating bandwidth of a subwoofer and the requisite close spacing of the two tones, this FM effect is exceedingly small. Fortunately, the magnitude (i.e., frequency deviation) created by this phase modulation is identical to that predicted by conventional Doppler Effect, despite not actually being caused by it. This makes it easy to calculate using Ilkka’s experiment as an example.

The maximum velocity of the woofer cone occurs at the zero crossing point and is calculated by:

Vp = 2 * pi * fL * Xp

where Vp is the peak cone velocity in meters per second, fL is the low frequency in Hz, and Xp is cone displacement in meters.

Using a 10 mm stroke (20 mm P-P) and a 30 Hz tone, peak cone velocity is 3.77 meters/second.

Using 70 Hz as the modulated frequency, the change in frequency caused by the change in cone motion is given by:

Delta fH = 2 * pi * fL * fH * Xp / c

where fH is the high frequency (modulated) tone in Hz, and c is the velocity of sound (typically 345m/s).

So delta fH = 0.765 Hz for 20mm P-P with a 30 Hz/70 Hz tones. Therefore you will see 70.765 Hz and 69.235 Hz at the positive and negative waveform peaks, respectively.

Now doing the same thing for a 20 mm stroke (40mm P-P): peak cone velocity is 7.54 meters/sec and the frequency differential is 1.53 Hz. So you will see 71.53 Hz and 68.47 Hz, at the positive and negative waveform peaks, respectively.

The upshot is that phase-induced frequency modulation distortion (which is a direct function of cone excursion) is not only completely insignificant within the confines of the narrow operating bandwidth of a subwoofer, but will obviously be totally masked by the conventional intermodulation (i.e., sideband) distortion components shown in the spreadsheet and in Ilkka’s S/T SpectraPro screen shots.

For more information on the o-scope experiments conducted, go to the following hotlink. The author gets full credit for the above analysis; I just condensed his work for the purposes of this discussion thread. http://sound.westhost.com/doppler.htm

Regards,

Ed

 

[dave alan]

Tom,

Post the price. Put up or shut up. Let's match my BS posts to yours. Shall I begin the search?

If price is the LAST consideration for you, how is it you ended up with the Samson amp?

Every worst case about your Company?? Are you insane? What are you basing this paranoia on? The plate amp post? Tom, seriously...get a grip.

Dave

 

[Ilkka R]

Dave and Tom,

Please take your discussion of the cost of BASH amps somewhere else. This thread has nothing to do with it.

 

[Tom Vodhanel]

Dave,

Your request for SVS to post our pricing is ludicrous and has nothing to do with your claims. No OEM is going to post a list of their component pricing...that would be a legal violation with the vendor. You probably know that of course(since you are close friends with the owner of a direct competitor to SVS)...so you put me/SVS in another one of your unreasonable "lose/lose" scenarios. Go get me a list of OEM/vendor pricing for hsu/av123/aixom/seaton sound ect...and then come back and ask the same question. Using your "logic" here...anyone could say that

"""XYZ.com uses the cheapest parts possible in their product. The "proof" of that is they refuse to disclose their confidential vendor pricing agreements with the public."""



The Samson amplifiers were more expensive than the original amps we used(fidek). We changed because we liked the performance better. (and the fans were not as noisy).

I've posted the truth, and corrected your mistakes. At this post...you can ignore that and continue to post inaccurate criticisms about SVS. That would not be very ethical(imo)...but that is your choice.

Tom V.
SVS

 

[Tom Vodhanel]

Deal Ilkka,

Sorry about the hijack.

Tom V.
SVS

 

[SteveCallas]

I agree with that 100%, I was merely getting back to Peter's original comments about the downfalls associated with high excursion drivers and why his company chooses to avoid them. He was making it seem - early on and not in this thread - as though the drawbacks outweigh the benefits of using high excursion drivers, even with "all else being equal", which I realize won't ever be the case.

 

[Charlie Campisi]

Well, I was hoping to learn something since I am in the market to upgrade my sub. I was looking at offerings from both of the manufacturers posting in here. I'll still shop for whatever sub seems to sound the best, but this thread has done nothing for me to enhance the "best customer service" labels that are often attributed to both of these companies.

 

[steve nn]

Hang in there Charlie, this happens every once-in-a-while. Many of us post with our own filters influenced by past Threads and posts.

 

[dave alan]

Ilkka,

You mean the amp can't contribute to these distortions?

Exactly what IS this thread about? Is it about you and Jakeman or Tom and Peter?

I believe I'm the only person to ask you a pertinent question in this entire thread.

Tom has chosen to pull his usual crapola and he's chosen me for the receiving end. If he apologizes, I'll honor your request.

Otherwise...no deal.

Dave

 

[Ilkka R]

I'm still puzzled why Tom brought those certain issues up in this thread, especially when some of those quotes were taken from another forum. If he needs to clear/explain some things, I think he should open a new thread for them. This is only my humble request.