There are two points where equalization matters - record and playback. A recording made with NAB record eq must be played back with NAB playback eq, and a recording done with IEC record eq must be played back with IEC playback eq. Though NAB is the standard eq used in the States, Tape Project tapes are done with IEC record eq and need IEC playback eq. We chose IEC because it takes much better advantage of the performance of modern tape formulations, whereas NAB eq was established back in the late 40's. If you are making your own tapes, the record eq and playback eq will depend upon what eq settings that particular tape recorder has available. Most all made for US machines have NAB and a few have IEC. The machines that don't have IEC playback eq need to be modified for IEC playback, either by changing the internal electronics or by modding the machine so it can connect the heads directly to outboard playback electronics like the Bottlehead Repro amp.
If your machine just has NAB record and play eq but no IEC eq, use NAB to make your own tapes. If you upgrade to a Bottlehead tape head preamp in the future, the preamp can play back either IEC or NAB eq'd tapes.
Now on top of all this, you really should have the record bias adjusted for the brand of tape you choose to get the very best performance. Record bias is a separate adjustment issue from the eq issue, and you will need a competent tech to do that job for you.
