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Old 14th May 2009, 07:56 PM   #5591
Elias is offline Elias  Finland
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Hello,

Quote:
Originally posted by Jmmlc
About the distortion of the envelop due to reflections, I disagree, 1) for the "speed" perception in the bass register, only an, initial part of the envelop has to be taken in account
2) for those low frequency (wavelength more than 2meters) the difference of phase between the reflected wave and the direct wave will be small.

Take 2 louspeakers having same Mms and diameter, the firts one loaded in a bass enclosure and the other one in bass-reflex, having the same low frequency cut-off. Listen them in the very same conditions, despite the room influence, the "speed" perception of the one loaded in close enclosure will be better than the one loaded in BR and this has to be related to the very different group delay curve at ferquency lesser than 150-200Hz.

This is an easy demonstration than phase is important in the perception of "speed" and that phase "mixing" due to reflection have not the importance that you said (even if has some influence for sure) .
Well, to be accurate the envelope does not exist in real world since it's not a physical quantity, rather it's a mathematical measure only. The thing is at low freqs the ear does not detect the envelope but what is perceived is the phase difference of the ear signals, or possibly the phase relations of harmonic components. It is the fundamental component below the envelope where the phase is detected, not the phase of the envelope, and reflections alter the phase of the fundamental. Actually in a mathematical sense the envelope can remain the same altough the phase of the fundamental is varied since the envelope is a result from amplitude modulation and not related to the phase of the carrier.

Of course then comes the question what is the detection threshold.

The case of the closed box and reflex box comparison is an exellent showcase to demonstrate that any resonance should not be part of a high quality reproduction system.

Make another comparison in a room between a closed box bass and a dipole bass. There is a diference in accuracy, speed or whatever one likes to call it, and it's because of less reflections of the directional source altering the amplitude and phase of the original waveform.

- Elias
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Old 14th May 2009, 08:14 PM   #5592
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Quote:
Originally posted by MBK
Actually the issue of timing / phase of harmonics vs. fundamentals should not be dismissed out of hand. Years ago I have been told by a violin maker friend, ...
Hi,

isn't it about loudspeakers instead of violins? I had some tens of 15"er bass chassis at hand to test those against each other. I repeated that procedure with tens of 12"ers. I did it for fun only. If You are talking about subjectivity, how far is it with You? Did You ever experience personally what the everlasting talk is about? Me was not able to distinguish speed or the like with that drivers mentioned (600$$ .. 60$$). They all sounded literally the same if equalized correctly and used within a living room of about 50 square meters UP to ANY level. After that casual tantalizing subjective experience I really wonder what people mean when seperating speed versus non speed. Am I deaf? Or - less severe - just lacking fantasy?

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Old 14th May 2009, 10:55 PM   #5593
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I am sympathetic to ScottG's subjectivist position. I hear things that have poor correlation with nearly any measurement I can dream up. Yet they are repeatable on blind A/B switchovers, so in a subjective sense, they are real enough, although difficult to track down.

An example: audiophiles wrangle about which CD player and/or transport & DAC has the most bass "speed" and impact. On the face of it, this is absurd. Red Book players may have a variety of different oversampling schemes and digital and analog lowpass filters, but that's at the top of the band, not the bottom. The behavior at the low end is exemplary by nearly any objective measure - the opamps are running at close to full gain, dithering is most effective at low frequencies, and highpass filtering, if done at all, is nothing more than a single-pole 5 Hz filter to chase out DC offsets from the opamps.

So a pair of audiophiles might gang up on me and do a CD player comparison, and yes, they sound different in bass range. Kinda-sorta, but not in a way that makes a lot of difference to me. But some people really obsess about bass, so I'm sympathetic, and listen some more. Yes, if I focus on it, the differences are there, and are repeatable in a blind setup. I don't much care, but it's a big deal to others. There's nothing much to grab onto in the measurement world, but there are some experiments that can be tried.

Open up the case and twiddle with the power supplies. In the amplifier world, this usually produces results. Split up the L and R supplies, go with shunt regulation and low-overshoot rectifier diodes, and rig an A/B switch so stock and modified supplies can be compared on an A/B/A basis.

Yes, the bass sounds different now, but not in a way I could describe usefully. Invite said audiophiles over again - the bass-freak guys. Repeat blind tests over again - yes, they are hearing differences in the power supplies, all right, despite the very high PSRR figures of the op-amps. Maybe the sonics of the power supply is sneaking into some other part of the player - who knows? - but these things do respond to different power supplies, which has no effect on frequency response, transient response, or THD or IM distortion at all.

My take is that some indirect parameter has changed, which in turns affects the dynamic - not steady-state - performance of the opamps or another analog portion of the player. Maybe the DAC converter is sensitive to the source impedance of the power supply (many are), and lower-quality supplies have instantaneous changes in source impedance. Gary Pimm has devised instrumentation that shows instantaneous changes in source impedance as the current demand is modulated, and real supplies deviate from the perfect voltage source with an arbitrary output resistance that is the usual model. In other words, power supplies exhibit current-modulated nonlinearities, just like amplifiers, and these can be frequency-dependent.

When audiophiles use words like "speed" or "impact", what they hear may - or may not - be real, but it is most likely to be an indirect parameter with no direct relationship to frequency response, impulse response, or distortion at all. This is typically the case for CD players and amplifiers, where what they're describing are subtle power-supply faults, not anything to do with the usual measured parameters.

When audiophiles describe bass drivers as having differing qualities of "speed", "impact", or "slam", I'm pretty sure it has nothing to do with frequency and impulse response, and I'm not sure if 2nd vs 3rd-harmonic distortion profiles are the cause either. Delta-inductance effects are probably getting closer to the truth, along with anomalous flux fields in the gap - but that's pretty much sheer speculation on my part. Driver manufacturers with experience in magnetic field geometry are better qualified to answer those questions.

I invite readers to scroll down to the bottom part of my Newell and Holland book review, where Paul Frindle describes the quite extraordinary lengths he went to in order to chase out persistent colorations in two different studio consoles. Customers complained about the fault, and rather than blowing them off, he went to a lot of work to discover the rather subtle cause. Who would expect that each channel would need its own statistically independent dither source? That kind of thing isn't in the literature, but that's what he found. My guess is the whole bass "speed" and "impact" thing will be equally elusive.
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Old 14th May 2009, 11:24 PM   #5594
Salas is offline Salas  Greece
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Purpose is listening. So if we are unhappy when listening, something is not done as good as it could, me simplistic says.
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Old 14th May 2009, 11:36 PM   #5595
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Instead of twiddling with CD player to "chase the bass", why not do something with the speakers. Let's say equalize using linkwitz transform.
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Old 14th May 2009, 11:42 PM   #5596
Salas is offline Salas  Greece
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A competent component appears good, best, indifferent, depending of how it slots in the big picture. If all else is well done then we know more of its true character or lack thereof.
There are efficient and inefficient ways to tweak. Depends on the system and its manipulator's wits, means, and strategy.
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Old 15th May 2009, 12:19 AM   #5597
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Quote:
Originally posted by gainphile
Instead of twiddling with CD player to "chase the bass", why not do something with the speakers. Let's say equalize using linkwitz transform.
But that is cheating ! You HAVE to find the most obscure way to affect the frequency response of the complete system. Instead of having - shudder - tone controls on your preamp to add more bass/treble, you have to start with power cables, then move onto speaker cables, interconnects, mains filtering devices, springy/rigid supports, cones under CD player, half tennis balls under CD player, Mpingo blocks, harmonix devices, freeze your picture, cryogenically treat cord of your corner lamp, replace red LEDs with blue ones in your power amp indicator, demagnetize CDs, demagnetize LPs, paint everything you can with C41 lacquer, then remove the said lacquer from inside your CD player (with great difficulty, but hey, that is progress), replace the stuck drivers because C41 went into the magnet gap and solidly glued your mids (from which you carefully, but with an extraodinary success, removed dustcaps just a week before), then proceed to sell all of your HiFi components an replace them with something that is much more flavour of the month while rubbishing the gear that you have praised into the stardom just a week before.
Don't laugh, this is more or less a true story (maybe more than one person involved)

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Old 15th May 2009, 12:52 AM   #5598
Salas is offline Salas  Greece
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Old 15th May 2009, 03:28 AM   #5599
xpert is offline xpert  Afghanistan
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Quote:
Originally posted by Lynn Olson

I invite readers to scroll down to the bottom part of my Newell and Holland book review, where Paul Frindle describes the quite extraordinary lengths he went to in order to chase out persistent colorations in two different studio consoles. Customers complained about the fault, and rather than blowing them off, he went to a lot of work to discover the rather subtle cause. Who would expect that each channel would need its own statistically independent dither source? That kind of thing isn't in the literature, but that's what he found. My guess is the whole bass "speed" and "impact" thing will be equally elusive.
.. and so did I. The console had a problem with a faulty implementation of something. The difference to a correct implementation was measurable. The issue could be resolved. It was hidden in the sheer complexity of that console. To listen to the customers complaint was worth the effort.

With audiophiles we have a messed up situation ever since. People are complaining about a shortcoming in personal pleasure. The very stereo doesn't do as good as has been promised. There is no switch somewhere tagged: "heaven on/off". Marketing invented cures for that. The pleasure is not the music anymore but fiddling with the stereo for itself.

A honest engineer has to decide which customer is worth an ear and which - alas is not. A crucial need taken into cosideration might be repeatability. If that very customer ain't able to identify a good versus a bad systems again in a (double) blind test, then any invest into alterations is not worth it.

An other one is wether the customer is willing to have his complaints resolved. Regarding that bass speed issue a simple amplitude vs. frequency optimization will do 99,99% of the trick. But that probably is not allowed since (a) it has to be one subwoofer only and (b) equalizing is not "high end", e/g because there are evil minded capacitors inside. Maybe it's (c): whilst having speed it has reduced boom.

Let them pay.
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Old 15th May 2009, 04:04 AM   #5600
Salas is offline Salas  Greece
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Somebody asked me once if his tube amp will be as good as before after I will use the scope on it!!!!!!!!!
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