i saw that the Gemara says its asur to make songs from pesukim in shir hashirim (& some say any pasuk in tanach), so what is the heter for all these songs on tapes & that are sung in concerts & listened to in cars for entertainment?
It is true that according to the strict halacha, it appears that making songs of Pesukim can be a problem (in particular, but not only, with respect to Shir Hashirim), aside from mitzvah settings.
However, the common custom is to be lenient, and though one can be stringent for oneself, there is not need (and it would not be proper) to prevent others from this.
This idea of not listening to songs with Pesukim is based on the Gemara (Sanhedrin 101a), where we find that “One who reads a Pasuk from Shir HaShirim and transforms it into a sort of song … brings evil to the world, since the Torah wears sackcloth and complains before Hashem, ‘Your children have made me into a musical instrument that is played by scoffers’.”
This Gemara is not noted by the Rambam or the Shulchan Aruch, but it is mentioned by the Magen Avraham (560:10, citing from Maharil), and by the Taz (560:5). The Mishnah Berurah (560:14) and the Aruch HaShulchan (560:7) also mention the Magen Avraham’s ruling.
Rav Moshe Feinstein (Iggros Moshe, Yoreh Deah 1:173) thus writes that “In my humble opinion it is forbidden lechatchila to make records of Pesukim, which are made purely for listening enjoyment.” However, Rav Moshe himself writes (Yoreh De’ah 2:142) that the common custom is to listen to such songs, and this is prevalent even among pious Jews, and there are a number of possible justifications for the practice.
One is that the prohibition applies specifically to singing Pesukim in a “degrading” setting, such as at a wine banquet (see here). This idea emerges from Rashi, from the Yad Rama, and from Rav Yaakov Emden’s glosses on the Gemara, and the Aruch HaShulchan writes that it is permitted to sing songs of praise to Hashem even in a non-mitzvah setting.
Beyond this, it can be suggested that in today’s world, where music is all around us, it is surely better to sing Pesukim that to join the empty music culture surrounding us.
See also here (an article by Rabbi Chaim Jachter) for further ideas on the subject.