Similarity between voiced glottal fricative and schwa sound?

Question

I remember trying to whisper a schwa sound (mid central vowel). I thought that it sounded like an H sound. So, I tried to voice the h. It sounded a lot like the schwa. I wonder why. Is there a link between the schwa (ə) and voiced glottal fricative (ɦ) that is special/unique?

Voiced glottal fricative: https://vocaroo.com/bTQvTicS54b Schwa: https://vocaroo.com/2aT7C1d5u8n

Note: I saw someone asked about if voiced h is an approximant for schwa. That is not the right term, but I see where that person was going.

Answer 1

As a native speaker of Ukrainian which has [ɦ], I should say it is really very much like schwa except for the fact that [ə] is a real vowel and [ɦ] is a real consonant, the glottis muscles are noticeably more strained when pronouncing [ɦ] as compared to pronouncing [ə] with which the muscles are not strained at all. There is also a noticeable amount of noise in the sound of [ɦ] which is absent in [ə].

Answer 2

In your examples, the production labeled "voiced glottal fricative" is 2/3 voiceless glottal fricative with the right 1/3 being voiced, followed by a very long schwa. The percept of schwa can be explained because most of what you hear is schwa.

There is a similarity between schwa and h, that they are often characterized as "neutral state" segments, because they don't have characteristic oral cavity articulatory gestures that other consonants and vowels have. Schwa is neither front nor back, high nor low, and h has no oral cavity constriction, instead it takes on whatever tongue position the surrounding vowels have and only contributes a breathy laryngeal source.

In any sustained consonant, the tongue has to be somewhere. That position is usually where schwa is, unless the consonant demands a different position (e.g. [s]). It is possible to produce [φ] with the tongue in the position of [i, æ, ɑ], but it is not normal to do so – also, because of the constriction formed by [φ], you have a hard time hearing the difference. With [h], there is no supraglottal constriction because of the consonant, so you can clearly hear the neutral schwa-like tongue position that you assume when you try to produce just [h].

Answer 3

As I wrote in answer to Voiced H as an approximant for schwa?:

[h], customarily referred to as a voiceless glottal fricative, in reality denotes any voiceless articulation with no interruption of the airflow in the oral cavity, with no defined configuration of the tongue or the lips. [ɦ] is the same except the vocal folds oscillate to some extent. So some argue they are best regarded as placeless consonants.

So if you try to produce [h] in isolation with the normal articulatory setting, the position of the tongue and lips probably resembles that when producing [ə], so that if you voice it you will be producing [ə].