The Fisher F75, like almost all metal detectors made today DOES have a built-in speaker. Note that I said: BUIILT-IN.
Having an INTERANL speaker with ports in the housing to allow the user to hear the audio response is something I make use of quite often. Generally I prefer to use headphones, but there are times when I am away from people and noise and just kind of enjoy listening to the audio report from a detector's speaker.
I flash back to 1971/'72 when I used a Fisher Orion, and a couple of other early-era detectors, that came with a set of headphones. They did NOT have a built-in [size=small](internal)[/size] speaker, just a ¼" headphone jack. If you didn't want to use headphones, and most of those that were supplied with the detector, you could purchase an EXTERNAL speaker. It is simply that, a Speaker that is attached EXTERNALLY that you plugged into the ¼" jack and ... shazam! ... you had a speaker to listen to.
Many of the earlier Metal / Mineral Locators came w/o a speaker, and some up-line models had a built IN speaker but no headphone jack, while others started to feature BOTH a Built-In speaker as well as a Headphone Jack. I know the first three home-built Metal / Mineral Locators I built from March of '65 to early '68 didn't have a Built-In speaker, just a jack for headphones.
So, YES the F75 has a speaker and you can listen to and adjust the Volume, but it is an Internally located speaker and NOT an External speaker.
Monte