SMA HAS NMAC WITH SECOND SMA WHEN IN TWR CONTACT FOR APCH.

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MY ACFT; C-R172K WITH 210 HP FULL IFR EQUIP AND LORAN MAINTAINED TO 135 SPECS. OTHER ACFT; PROBABLY C-150/152. I WAS MAKING A QUICK DSCNT FROM VNY 140 DEG RTE. I FLEW MOST OF IT AT 8500 FT MSL AND WAS CLRED DOWN TO 6500 FT MSL AT APPROX COMPTON. FURTHER CLRNC DOWN TO 4500 FT MSL WAS RECEIVED AT A FEW MI AFTER MOBIL. I WAS GIVEN THE N TWR FREQ APPROX ABEAM LGB; THEN SWITCHED TO THE S WHEN THEY REALIZED I WAS GIVEN THE WRONG FREQ BY APCH CTL. I WAS ASKED WHERE I WAS AND I REPLIED ON THE VNY 140 DEG HOLLYWOOD PARK RTE SBOUND PAST LGB. I WAS THEN TOLD TO ENTER L DOWNWIND FOR RWY 25L AND RPT REACHING. ON THE WAY DOWN AT APPROX 3500 FT MSL; I SAW A C-150/152 TO MY L SINCE WE WERE AT ABOUT THE SAME ALT. I HASTENED MY DSCNT AND TURNED STRAIGHT UNTIL THE TFC WAS NO FACTOR. I WAS LOOKING FOR TFC BUT I WAS ALSO CONCERNED ABOUT STRAYING TOO FAR OVER THE WATER. 2 MAJOR THINGS WOULD BE HELPFUL HERE. HAVE SOME TYPE OF STAR WRITTEN OUT FOR BOTH RTES AND THE ARPTS AROUND THEM. THERE IS BLANK SPACE ON THE BACK OF THE LOS ANGELES TCA CHART. THE SECOND IS THAT THE CTLR SHOULD PAY MORE ATTN TO WHERE HE IS CLRING PEOPLE TO GO; ALTHOUGH TECHNICALLY; NEITHER ACFT WAS IN ANYBODY'S AIRSPACE. I FELL IT IS INEXCUSABLE TO IGNORE ACFT BECAUSE THEY LEGALLY CAN. P.S.; I AM FINDING THAT MORE AND MORE CTLRS ARE REQUESTING RAPID DSCNTS RECENTLY THROUGHOUT CA. THIS ISN'T GOOD FOR 3 REASONS: SHOCK COOLING OF ENG; SAFETY; PAX NERVES.