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On Group Delay and Spatial Effects

Joined
Jul 30, 2019
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Location
Montreal, Quebec, Canada
#1
Er, actually, this thread should probably be in the psychoacoustics area. Can a mod move it?

Introduction and observation:
Following the fairly well received post on the relationship between group delay and spatial effects in headphones, I thought I'd start a new thread on the matter, gathering further evidence, eliciting further thoughts and opinions, and acting eventually as a repository for the results of armchair research, that I hope to conduct in an effort to prove or disprove the hypothesis, that

Hypothesis:
Group delay (as well as frequency response; particularly around 8 kHz and possibly around 2 kHz - aka, the Blauert bands) is responsible for much of the out-of-head soundstage and instrument separation phenomena.

Definition:
Let's define soundstage to be sound emanating over the sum of the two angles formed between the nose and the ears; depth, the apparent distance from the centre of the head to the location of the sound; and imaging, the location of various sounds in the soundstage.

Examples:
  1. two sounds coming only from a single point in the middle of the head indicates a soundstage, depth and image of zero
  2. sounds going from ear to ear with each source of sound a pinpoint in the space close to the head indicates a soundstage of 180 degrees (I refuse to use radians), a small depth and high imaging.
  3. Sounds surrounding the head coming from afar and seemingly diffusely indicates a soundstage of 180 degrees, large depth and low imaging

Data:
Let's begin with some data and comments gathered by our host, Amir. Note, that the list is as yet incomplete: I'll be updating it more tomorrow and in the days to come. For now, there's no especially clear image - except this: headphones with good soundstage seem to have clean group delay graphs, with some messiness around the 2 kHz region, and a spike around 9 kHz. One pattern that is emerging is, that too messy a graph indicates too many confused reflections, lessening the spatial effect - whilst too clean a graph indicates too few reflections and a non-existent spatial effect. I hope to further refine these findings as I gather data and am able to form better analyses on them.

Maker - Model - Group Delay Graph - Amir's related comments
Beyerdynamic DT990 Beyerdynamic DT 990 Pro Measurement 250 ohm headphone Group Delay.png rather good spatial qualities
Beyerdynamic T1 v2 Beyerdynamic T1 V2 Measurements Headphone group delay.png [No comment given.]
Bower & Wilkins P5 Bowers & Wilkins P5 Measurement Group Delay Portable Headphone.png [No comment given.]
Focal Celestee Focal Celestee Group Delay Measurements.png soundstage is mostly whacked in the middle of your head
Focal Clear Focal Clear Measurements Group Delay.png [No comment given.]
Focal (Drop) Elex Drop X Focal Elex Group Delay Measurement.png [No comment given.]
Focal Utopia Focal Utopia Group Delay Measurements.png a halo of sound about 25 to 30% outside of your head with very nice instrument separation
HEDD Headdphone HEDD Headphone Measurements Group Delay.png maybe a bit better than a typical headphone with its center of your head response
Hifiman Ananda Hifiman Ananda Group Delay Measurements Open-back Planar headphone.png speakers away from your ear [...] It nicely pushes the sound out some and leaves room for instruments to image between it and the ear.
Hifiman HE-6 Hifiman HE-6 Group Delay Measurements.png Spatial effects were reasonable
Philips Fidelio X2HR Philips Fidelio X2HR Measurement Group Delay.png Shaving off those resonances also collapses the soundstage by some 20 to 30%. [...] increasing the strength of the [high] shelving filter [...] cost even more in soundstage. [... It has] good spatial effects
PSB M4U 1 PSB M4U 1 Measurements headphone group delay.png massive spikes in high frequencies indicates reflections inside the cup [...] The [eq] boost between 1 and 5 kHz opened the soundstage and detail/instrument layering.
Sennheiser HD650 Sennheiser HD650 Measurements Group Delay.png Where is not so good is the spatial qualities. There is a nice open circle that the sound sources emanate from. It starts from your ears and circles forward. There is no sensation of space beyond that. Nor that nice layering [...] I always get a feeling of the sound closing
Sennheiser HD800S 1608853778796.png What was remarkable and uncanny was separation of instruments. It was as if this headphone would take every element in the music, pull it apart, and then position it in different spatial locations in a 6 inch space around each ear. I wouldn't call it "soundstage" as much was it was this fun and captivating effect.
Sony MDR-7506 Sony MDR-7506 Group Delay Measurements.png little soundstage [...] dull, middle of the head image [...] boring spatial effect.
Superlux HD668B Superlux HD668B Measurements Group Delay Semi-open Headphones.png The large drivers provide good bit of spatial information (separation of instruments), creating a soundstage that dangles from your ears down and to the back with the mono content behind your forehead.
 

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