If you were asking this question 15 or 20 years ago,
there would be some good products to recommend,
but now there are no really good blank cassette tapes available in stores.
In the last several years, I have seen only Sony HF (so-so),
TDK D (also so-so, probably not quite as good as HF)
and Maxell UR (better than the other two, but not better enough).
I use UR C-90's to record Amateur Radio Newsline once a week,
and the results are OK, but then there is no music on that program.
The length does make a difference, but not because of the length:
Longer tapes require a thinner backing, which is a cause of trouble.
If you use any of the tapes I listed above for real music, use only C-60's.
For spoken or rap, use up to C-90's.
Don't use tapes longer than C-90's for anything,
and especially not in a boombox.
Some boombox makers used to include warnings in their
instruction books that said to avoid any tape longer than a C-60.
The reason (that they never mentioned) is that the take-up tension
of the transports they put in those big old boxes was somewhat weak,
and longer tapes would not always be properly wound on the takeup hub
in the record or play modes. The result was called a "tape spill",
which occurred as the capstan and pinch roller continued to pull tape
from the supply hub. Without the takeup doing its job, tape would go
all over the place inside the machine until it was hopelessly tangled.
You may be able to get something passable from Deltamedia (tape.com).
They have some 'house brand' (custom-loaded) cassettes that
should be at least OK, and they are available in any length
from 1 minute to whatever they can cram into the shell.
The one problem with this is that you must order 100 (or multiples of 100)
of whatever length - no mixing of lengths within any hundred is allowed.
I would recommend that you use only Type I ("ferric") tapes, because
many boomboxes won't record properly on Type II (CrO2) blanks,
and you probably wouldn't detect any audible benefits from Type II
anyway -- it usually requires a good home deck
and decent speakers to be worthwhile.
If you want to get some tape that will sound really good,
try to find some of these as new old stock in 'record stores',
or unused ones from garage and estate sales or thrift stores:
TDK OD, AD, AD-X, AD-S
MAXELL UD, UDS-I, UDXLI, UDXLI-S
Whatever you do, never use a Memorex tape. Period.
A friend of mine could tell you more than enough about why.
Good luck, and have fun, but don't expect today's tapes to
produce anything like the sound quality of the "good old stuff"
that is no longer available. It simply will not happen.
Answered By: spacemissing - 4/6/2011