Soundproofing Between Offices

[Paul Allen]

I 'office hack' (if there is such a thing). I lease an office suite, use one of the offices for my business, and sub-lease the other three. My current tenants are all personal coaches/counselors; solo practitioners with businesses unrelated to one another. They all pay the rent on time and take a turn vacuuming the common areas, so I am happy with them.  I hope they all renew their leases when it is time. 

The walls between the offices within the suite only go to the top of the suspended ceiling. Above that is about 30 inches of space for pipes, wires, ducting, etc. When the counselor in the office next to mine is with a client I can hear them talking. I usually can't make out what is said, but it's a problem. The tenant has told me when I am on the phone or with a client it can be disruptive when she is with a client.

I am sure the sound is going through the suspended ceiling space. How can I (cheaply) soundproof between offices? I am handy, but it isn't practical to extend the walls to the hard ceiling (my first thought). There's just too much 'stuff' up there in the way. A local contractor wants $3,500 to just do my office. I'd prefer something that costs less and makes things better for everyone.

Ideas?