[deegles]

For voices you need passive sound isolation, not active noise cancelling. Try these: Howard Leight by Honeywell Sync Stereo MP3 Earmuff (1030110), Black https://www.amazon.com/dp/B004U4A5RU/

They also give off a very strong “I’m busy” vibe

If that’s still somehow not enough, wear these concurrently (this is great for planes too): Etymotic High-Fidelity Earplugs, ER20XS Standard Fit, 1 pair, Polybag Packaging https://www.amazon.com/dp/B00RM6Q9XW/

Also recommend the above with these foam tips for longer wear, I’ve done up to 16 hours with only a little discomfort: Shure EABKF1-10M Medium Foam Sleeves (10 Included/5 Pair) for E3c, E4c, E5c, E500PTH, i3c, i4c & SE Earphones (Black) https://www.amazon.com/dp/B0015PN3W6/

[porker]

How about for lower frequencies: motorways, busy roads (no individual car noises; a solid background roar)? They make having the window open here a nightmare.

[jfries]

Isn't this exactly when active noise cancelling works the best?

[QuantumGood]

I've had these for a year and like them: Professional Safety Ear Muffs by Decibel Defense: amazon.com/gp/product/B01BEENYCQ/