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Tymphany / Peerless STW-350 Testing

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Driver notes and measured impedance and parameters for this 15" are now uploaded.

Sealed cabinet testing is imminent in the next few weeks. 

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Post that data!

This is the platform for the new SVS ultra no? Is this a 15 or 16"? We need to get that new SVS sub. I'm dying to see how it does against the old one.

 

 

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Svs is based on the same platform but is a different frame, cone, surround , etc...

The ground plane tests on this one should be popular. 

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You mention that the suspension compliance is not likely very linear because the former is so large compared to the spider.  Whether or not that's the case, it's interesting to note that compliance linearity is not very important if the driver is mounted in a tiny sealed box.  In that case, the stiffness of the air spring dominates and effectively helps linearize the restoring force.  I'm not certain, but I think this would be the case for most vented alignments too, at least at or above tune.

One "flaw" with Klippel measurements is that it's only testing in free air.  The Kms adds to whatever force is provided by the back pressure in the box, so "real world Xmax" with regard to overall compliance is likely higher than Klippel reports, depending on usage.  Similar considerations arise with regard to BL.  For example in a high Qtc sealed alignment operating at Fs, motor force is quite weak compared to the innate mechanical resonance,  isn't very strong  which in a high Qtc sealed alignment has much less influence on frequencies at Fs than at frequencies far from Fs.

Klippel also fails to account for how distortion products are reproduced by the acoustic characteristics of a system.  In a sealed box, BL non-linearity is imparted to the cone motion in form of a distorted motor force, but acoustic output vs. motor force drops dramatically below Fs in the sealed box system, which results in the sudden rise in distortion below Fs in sweeps.  For large room / outdoor applications where room gain may be weak, a driver may produce very offensive distortion at frequencies below Fs at Xmax well below the "70% BL threshold".  OTOH, the same driver in I.B. or a much larger cabinet may not roll-off nearly as rapidly at its bottom and may have much less distortion for the same Xmax.

My point with Klippel is that Xmax derived from arbitrary cut-offs (e.g. 70% BL) can't really be used as a simple "yard stick" to compare drivers to one another.  The plotted data of parameter variation vs. excursion is very useful but should be interpreted in the context of the overall system and intended use.  I haven't seen the Klippel data for this driver, so I'm only guessing here.  But if the testing suggests a low Xmax based on Cms (at 50% or whatever), that may not be all that important for the systems that use this driver.

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Good post SME.

Rather than linearizing the suspension stiffness small air volumes may tend towards making the overall compliance worse in certain cases. The air inside an enclosure is a little harder to compress than expand. It gets worse as the enclosure volume gets smaller and the cone displacement gets higher. IOW higher compression and expansion and a larger differential. This asymmetry causes additional even order distortion. It may be enough to wipe out any gain in symmetry over the free air suspension stiffness. In some cases it may worsen it.

In smaller sealed cabs the BL and current induced distortion often seems to be the much bigger issue and would appear to outweigh any possible improvements in restoring force symmetry. Larger air volumes provide greater low end efficiency and with less power applied for the same output the distortion usually lowers substantially. In an IB vs very small sealed scenario like mentioned this would be most apparent. The lowering of distortion in larger air volumes would also partly be the reduction in air spring asymmetry. In general high Q alignments exhibit worse deep bass distortion than low Q ones.

Your last paragraph is spot on. Klippel is very useful but it has limitations.

As far as this STW-350 driver goes it'll be tested in a sealed cab of about 3cu ft (85L). It may be a bit less after driver displacement. I'm most curious to see what its distortion profile looks like and how well the massive diameter coil prevents thermal compression.

 

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9 hours ago, Ricci said:

Rather than linearizing the suspension stiffness small air volumes may tend towards making the overall compliance worse in certain cases. The air inside an enclosure is a little harder to compress than expand. It gets worse as the enclosure volume gets smaller and the cone displacement gets higher. IOW higher compression and expansion and a larger differential. This asymmetry causes additional even order distortion. It may be enough to wipe out any gain in symmetry over the free air suspension stiffness. In some cases it may worsen it.

Thanks for this clarification, and I agree that a small box can make overall compliance linearity better or worse.  It depends.

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Klippel is good at driver in isolation but I do agree, max output and distortion tests with 20,000 watts outside does tell us a different picture with respect to the entire designed system 

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