Quite a stir about these at the moment.. Apparently tuned for Celestion FTR18 4080 HDX.
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The overall depth of the Celestion is 205mm, for PD1850 it's 187mm, so talk of 1850 not fitting in there is rubbish.
Someone please confirm chamber measurement (from rear baffle to inside of front baffle), or contact Ligwa for the info, as I'm sick of asking.