AKG K701 vs. Sony SA5000 - first impressions - Page 7

Quote:
extremely susceptible to cavity resonances


Resonances are not the same as phase distortion induced by reflective surfaces that delay some of the sound relative to the on-axis sound.

The SA5000 is an open design and not a closed cup design, so reflected sound from the rear of the cone does not bounce back into the ear to cause phase distortion - thus open designs are superior to closed.

The SA5000 does have offset cones, angled outward at the cone part closet to the rear of the ear, to make the cone more forward firing as opposed to the side firing of the K701. I m not sure this helps that much. However, there is a plastic bridge extending from the cone edge to the rear of the earcover mount. This allows for of-axis reflections from the cone to hit the plastic bridge, then reflect into the ear as delayed sound relative to the on-axis and more direct sound. This delay of perhaps .03 milliseconds should not be enough of a delay to be perceived as phase distortion and should cause no problem. The operative word is 'should' as no one knows, but delays of .5 milliseconds (nearly 17 times longer) have been shown to be a problem.

Resonance is another. The plastic bridge described above may have some resonant frequencies from vibrations of the material itself and not from reflected sound. Grado has made some great products with his care in reducing resonances.

Coating the plastic bridge in the SA5000 ear cup, with a sound absorbing material might help, as JaZZ has advocated.

I made two pieces of crescent (curved to the driver curve) wedge-shaped (the sharp edge goes into the cup recess while the flat edge is the exterior part that is visible on the outside) inserts out of memory foam. These slip inside the part of the cone to the rear of the earpiece to cover the plastic bridge.

I listened to the SA5000 with and without these inserts, on a harsh passage of a CD that is well recorded for the most part.

What a fantastic difference! Made the SA5000 free of any problems. They must be sized to an exact shape that I have discovered. I will sell them for $100 per pair and will even include shipping.

Seriously, I thought some improvement might have been detected but I couldn't be sure.

Maybe JaZZ can advise on the best sound absorbing material for such inserts. Worth a try.

Would you believe my dog just ate them!

One of a kind prototype of perfect size.

However, the foam material is indigestible and I can recover them in a day or so - just have to watch my dog carefully.

I'll clean them up and they wil be as good as new.

Meanwhile, I sell my Galatic Ultra IC cable for $100 per foot. Now this is a cryoradiated treated copper cable that is out of this world.

Can't take paypal as they froze my account.

Art: The SA5000 does have offset cones, angled outward at the cone part closet to the rear of the ear ... This allows for of-axis reflections from the cone to hit the plastic bridge, then reflect into the ear as delayed sound relative to the on-axis and more direct sound.


AsuAmo76: I believe for the most people this cone is screened behind their ears. In this case only small part of signal would be reflected.

Art: The on-axis sound coming out of the SA5000 driver does not hit the plastic bridge near the rear of the earpiece. It goes straight to the ear, toward the rear of the ear canal, and is collected there in the ear to enter the ear canal.

The off-axis sound from the driver, off axis on the side near the plastic bridge, can hit the plastic bridge and reflect from there into the ear. This sound will travel up to about 10 mm longer than the more direct on-axis sound. This is the same sound in both instances, just delayed-reflected relative to the direct sound. My rough estimate is that the delayed sound will arrive at the ear about .03 milliseconds later than the direct sound. This is a very small delay. There is much other reflected sound bouncing all around the outer ear before it enters the ear canal, and this is true whether listening to headphones, speakers, or live sounds in the environment. I do not think these minor delays, relative to direct sound that goes straight into the ear canal, are important. Delays of reflected sound on the order of .5 millisecond (about a six inch longer path of reflected compared to the direct sound), or longer, do create phase distortion and muddy, or even distort/shatter, tones. Reflected sound traveling 12 feet or longer than direct sound can provide ambience sound good.

Art: This delay of perhaps .03 milliseconds should not be enough of a delay to be perceived as phase distortion and should cause no problem. The operative word is 'should' as no one knows, but delays of .5 milliseconds (nearly 17 times longer) have been shown to be a problem.


AsuAmo76: My physics is rusty, please correct if I am wrong. 0.03ms corresponds to 1cm and this is 1/4 of 8kHz wavelength. For the high frequencies signal delay is more important than the phase. Probably that's why we have this threshold.

Art: Signal delay creates phase distortion when a non-delayed signal arrives less than about 8 milliseconds to .5 milliseconds later than the same signal that is not delayed. This can smear the tone image (shorter delays) or even lend a shattering effect (longer delays) to the sound. If long enough, the delay will create a mild echo effect and add depth and space and ambience tot he tones.

Resonance is another. The plastic bridge described above may have some resonant frequencies from vibrations of the material itself and not from reflected sound. Grado has made some great products with his care in reducing resonances. Coating the plastic bridge in the SA5000 ear cup, with a sound absorbing material might help, as JaZZ has advocated.


AsuAmo76: I can't understand your focus on the bridge. For me it's the whole construction is problematic. The plastic itself looks and feels cheap, compare to hd600, with less holes and edges. I will try to reinforce the peripheral surfices.

Art: Looks don't count. The plastic could have a very low resonnance and be fine. All materials in or near the ear piece of a headphone should have low resonnace. Grado used porous aluminium filled with a dampening material, in the HP-1,2, and 3 headphones to reduce resonances.

I have no basis to think the SA5000 has a resonance problem. I do not believe sounds reflected off of the plastic bridge in the ear cup of the SA5000 will cause any problem anymore than sounds bouncing around the folds of the outer ear cause problems in any kind of listening anywhere. That will not stop me from trying to sell my foam inserts for $100, as a solution to no really existing problem, since they only cost me a quarter to make.

Art:...There is much other reflected sound bouncing all around the outer ear before it enters the ear canal, and this is true whether listening to headphones, speakers, or live sounds in the environment. I do not think these minor delays, relative to direct sound that goes straight into the ear canal, are important. Delays of reflected sound on the order of .5 millisecond (about a six inch longer path of reflected compared to the direct sound), or longer, do create phase distortion and muddy, or even distort/shatter, tones. Reflected sound traveling 12 feet or longer than direct sound can provide ambience sound good.

Resonance is another. The plastic bridge described above may have some resonant frequencies from vibrations of the material itself and not from reflected sound. Grado has made some great products with his care in reducing resonances. Coating the plastic bridge in the SA5000 ear cup, with a sound absorbing material might help, as JaZZ has advocated.

JaZZ: I don't believe it's a resonance issue, but in fact reflections with their smearing effect as well as hollow-space resonances.

Art: Don't understand. Can't have resonance in hollow space. A particle can resonate but space can not. The ear cup materials can resonate but the ear cup space can not. Right or wrong?

JaZZ: Even the concerned wavelengths -- isolatedly considered -- would be enough to justify the postulation of audible effects if you measure the distance from the center of the driver to the reflective surfaces.

Art: The audible effect here would be a reflected wave reaching the ear canal at a time delay relative to the exact same non-reflected (direct) wave. I wonder whether delays of less than .1 of millisecond have any audible effect at all. Delays from ear cup reflections are .03 milliseconds or less, close to those from reflections in the folds of the outer ear. I used to think that the larger soundstage of headphones compared to canal phones was due to ear cup reflections but now I think it could be simply due to larger cone surfaces where ear cup reflections are inconsequential. You think that ear cup reflections of delayed sound are important. That gives me pause for reflection, and you may well be correct.

JaZZ: Moreover the baffle/driver-earcup-earpad-ear/headskin system represents a hollow space where multiple reflections are created, so it makes no sense to rely on isolated parameters such as the dimension of a reflective surface within this system.

Art: OK. The hollow space is not a source of reflections in and of itself, but its material enclosure materials are the source of reflections. Since the SA5000 has more hollow earcup space than the K701, there are longer delays (on the order of .03 milliseconds or less) in the SA5000. I am understanding you now.

JaZZ: The SA5000 may be an «open» design, but the openness is only valid for the rear, not the front of the driver, since the baffle is closed (to separate front and rear sound waves), in constrast to e.g. HD 650 and K 701
.

Art: What baffle? Are you saying the K701 and HD650 rear driver sound can come around to the front and mix with the front driver sound? That would cause phase distortion more than internal ear cup reflections from front sound alone.

JaZZ: So it makes sense to coat the bare surfaces within the earpieces (in front of the driver) with sound-absorbing material. I've made best experiences with black velvet, both with speakers and headphones (particularly my electrostats). -- I chose black velvet since the light-absorbing property may be a hint for slightly higher acoustic absorption, too. -- Anyway, I wasn't really happy with the result after lining the one obvious surface within the SA5000, because it took some of the brilliance and freshness away, although the sound had become more organic, which is a positive effect. The problem with sound absorption to minimize parasitic reflections around the front of a sound source is that it creates sort of an imbalance between higher and lower frequencies when it comes to direct and reflected sound, since higher frequencies are easier to absorb. This may be the cause for the perceived dryness as result of the provisional and incomplete lining measure, which I suppose would become even more pronounced with full lining. The sonic result will also highly depend on the resulting frequency response, since the latter will definitely be influenced.

Art: Excellent! Great analysis. You have convinced me that even reflected sound delays of .03 milliseconds and smaller can influence the original direct sound to some audible extent and cause a phase (IM type) distortion of immediate and delayed sound in the sound stream.
However, the parasitic effect only applies to reflected and not direct sound, and does not apply if the reflected sound is sufficiently absorbed, and most importantly, phase distortion is mainly a problem with treble rather than bass frequencies (bass phase distortion is more tolerable).