Odd Phonograph...

[gramophoneshane]

but are they re-entrant?

That is debatable.
The 157 certainly isn't considered a re-entrant model by UK or Aussie collectors. That honour only goes to those with 4 sectioned horns.
However, I have come across original advertising here, which lists the 157 as a re-entrant, including one by The Gramophone Co., Sydney, from xmas 1928.
I've been lead to believe it was never listed as a re-entrant in UK advertising though.
So, did TGC in Sydney just get it wrong, or is it modern day collectors that dont have their facts straight?
It is a little puzzling that "company" advertising in 2 different countries would list the 157 differently.

[Steve]

I've been lead to believe it was never listed as a re-entrant in UK advertising though.

I have ALL the late 20's HMV Instrument catalogues and in none of them is the 157 described as having a 're-entrant tone chamber'. Instead they simply used waffle like "....all new scientifically folded horn with matched impedance..." blah blah blah.

From a TECHNICAL point of view, the 157 is a re-entrant machine though because the same principle of sound amplification is followed as in the larger models BUT the horn is only a tiny chamber split into TWO pathways instead of FOUR in the bigger models. All the bigger machines with the latter design were classified as 're-entrant' ie Models 163,193,194,202 and 203. Also the Automatic 1A etc.

So even though the sound re-enters or reunites the single horn at its mouth, in the same way as in the designated 're-entrant' models', the fact that it was effectively half a re-entrant horn, stopped HMV from giving it the honor of the new fangled term.