Topic: Different Stuff (Read 8063 times)

maverickronin · « **Reply #50 on:** September 08, 2012, 10:51:50 PM »

Quote from: arnaud on September 08, 2012, 10:30:58 PM

I see... So, you mean that the Edition 8 does not apply to the club?

Hehe. I think the bouncers should probably turn it away at the door.

ihasmario · « **Reply #51 on:** December 20, 2012, 05:22:21 AM »

I'd like to resurrect this thread, this time with a discussion on the merits of Impulse Responses, CSD and other such measurements that seem to give an impression of "clean-ness" (whether or not this is the case). How valid can an impulse response/csd be as a measurement of headphone technical fluency in a piece of music? While the measurement has scientific and mathematical merit, looking at things like damping, I can't recall more than a sngle piece of music that had a full spike to immediate silence, without the presence of reverb or echo. Essentially, what I understand therefore, is that the measurement doesn't actually provide real world application for musicians or indeed people listening to music. It is my contention, further, that Planar technologies with even force distribution (and true and even push/pull for a moment across the whole surface) will perform better in a test that shows continued motion than a dynamic headphone. In my experience, a lot of stats and planars don't have a lot of mechanical damping.

Just for my own curiosity; is anyone able to measure the relative performance of three different technologies (dynamic, electrostatic, and planar) with two impulses played with inverse polarity with respect to eachother? That is to say, a force followed by a normalising force, and then treating the measurement in the same manner an impulse response is typically considered after the second force. If possible, can we experiment also with distances (time) between the two, and the relative intensity of the normalising (inverted) force?

ultrabike · « **Reply #52 on:** December 20, 2012, 06:14:16 AM »

Impulse response measurements fully characterize linear systems that do not change over time. Linear systems are those that do not add frequencies on their output that where not there in the first place in their input. Real world systems are not fully linear or fully static over time, but many are very close. The more linear a system the better. For those non-linear issues there are other types of measurements that deal with noise, harmonic distortion, among other things.

Things like damping are linear properties which are captured by the impulse response. Frequency response and CSD plots display information gathered by the impulse response in a much more readable and convenient way.

Seldom is an actual spike used to obtain the impulse response. Instead, a pseudo-random noise signal is generated whose auto-correlation function is an impulse (spike). That signal sounds like white noise, because it is white noise. There are other methods, but those don't use a spike either for practical reasons.

It is my understanding that if if two headphones exhibit similar impulse response, then they will perform similarly in test with continued motion regardless of driver technology. There are however differences in non-linear behavior. AFAIK, some stats and orthos exhibit very low non-linear behavior relative to dynamic and BA technologies. If there are perceived differences not shown by the impulse response, probably best to look at non-linear issues.

Note also that when characterizing systems, the pseudo-random signal is usually repeated back to back. This results in an impulse train after auto-correlation. So in most cases the equivalent of multiple impulses already go through the system. Furthermore, the pseudo-random signal itself already changes polarity rapidly before auto-correlation post-processing.

Cristello · « **Reply #53 on:** December 20, 2012, 09:46:07 PM »

Maybe to satisfy those in a similar boat as IHasMario, Tyll (and other measure-ers) could consider whether or not a double impulse chart might be more telling? I.E.-- looks the same, except two spikes ~.001 seconds apart.

(great description of linear vs. non-linear systems, though

)

ultrabike · « **Reply #54 on:** December 20, 2012, 10:17:04 PM »

If one sees the raw results from a pseudo-random noise generator, IME it is hard to tell what's going on. I've done it when I developed one of these things for a DSL modem in order to detect bridge taps, load-coils, opens, and shorts. It's all there, but it's like having time shifted, random-polarity mini-impulse responses riding on top of each other.

When you apply the auto-correlation, then you get a nice clear impulse response that is far more telling of what is going on. If we were to apply two (or more) impulses with all kinds of crazy polarity shifts we would get closer to the raw results from the pseudo-random generator signal. Hard to tell, specially if the system exhibits some type of reverberation funkyness a la ultrasone ED 10.

ihasmario · « **Reply #55 on:** December 21, 2012, 05:18:27 PM »

Thanks for the great reply ultrabike.

Quote from: ultrabike on December 20, 2012, 06:14:16 AM

It is my understanding that if if two headphones exhibit similar impulse response, then they will perform similarly in test with continued motion regardless of driver technology.

Is this truly the case? It is my understanding that the force for dynamic headphones is applied at the voice coil, which is for most speakers is behind and at the centre of the cone (hence moving cone), whereas a planar devices forces can be considered as occurring at all points along the system.

If we consider reconstructions of the system, taking for example a wobble board for planar designs, and a circular piece of paper with a string (knotted at either ends) pushing back and forth at the centre, it seems to me that the restoration force is more effective. Or, to put it another way, there is less of the original force present at the moment of impulse in planar designs, because the force is evenly distributed, whereas the circular piece of paper would still be moving forward at it's outer most points provided they aren't restrained or damped in some fashion, which would infer an artifact during playback, in my opinion (but not during a single impulse test).

Could be wrong though, just curious

How relevant do you consider an impulse test in demonstrating the musical qualities of headphone systems (where frequency response would be rated highly, in most cases).

ultrabike · « **Reply #56 on:** December 21, 2012, 05:34:00 PM »

I'm not an acoustic engineer, but this post was very helpful to me and it addresses the effect of the shape of the driver on the pressure wave: http://www.head-fi.org/t/223263/the-stax-thread-new/20355#post_8967417

When we talk about the impulse response of a headphone, we are really talking about the impulse response of the pressure wave that results from it's driver. It is therefore IMO very relevant.

I'm also of the opinion that you don't have to understand or believe in impulse and frequency responses to enjoy music, or to evaluate if certain audio equipment is performing to expectations. I believe your ears come first.

ihasmario · « **Reply #57 on:** December 21, 2012, 05:42:03 PM »

Hm, looks like I need to do more research.

I'm not an acoustic engineer either (obviously....), just a curious musician who engineers acoustics (poorly). and a primary school teacher

Edit: Hot damn, head-fi finally has a following of people who don't like the LCD-2? Well, damn. The LCD-2 was bad enough for me to start wondering about square waves, which started my research!

ultrabike · « **Reply #58 on:** December 21, 2012, 05:55:13 PM »

No worries mang. I'm just posting what I think I know, ... and there is definitively loads of stuff I don't know. Relatively speaking, I recently started to become very curious about audio. I love music, but I'm not a musician. I'm a fan of the bass guitar and the accordion. Maybe one day I'll get formal about it

ihasmario · « **Reply #59 on:** December 21, 2012, 05:59:40 PM »

Are there any audio books you've read you'd like to recommend, particularly in terms of headphone design and measurement types? I'd like to read more than what I have already, which have mostly dealt with design and equalisation, most of the measurement stuff has been speculation and my own understandings from simple phyisics/maths

Author Topic: Different Stuff (Read 8063 times)

maverickronin

Re: Different Stuff

ihasmario

Re: Different Stuff

ultrabike

Re: Different Stuff

Cristello

Re: Different Stuff

ultrabike

Re: Different Stuff

ihasmario

Re: Different Stuff

ultrabike

Re: Different Stuff

ihasmario

Re: Different Stuff

ultrabike

Re: Different Stuff

ihasmario

Re: Different Stuff

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Author Topic: Different Stuff (Read 8063 times)

Cristello