Welcome to SquashGalaxy. Whether you're an aspiring or accomplished doubles player, here are some thoughts on racquets for your next purchase.
Racquet Design: In general, teardrop frames offer a longer but narrower sweet spot, while bridge frames offer a shorter but wider one. In singles a longer sweet spot is useful for reaching the ball - like when you're desperately trying to lob out of the front of the court! In doubles, players more often have to deal with the ball flying through the middle of the court, and a bridge frame offers a more forgiving sweet spot for this. Bridge frames also generate less torque when striking the ball, meaning the racquet is less likely to twist in your hand.
Weight and Stiffness: Many players prefer a slightly heavier frame (140g+) for doubles. While you might find 120g frames on the singles court, these are rare on the doubles court. And you probably won't find many flexible, "whippy" racquets either. The greater resistance from the heavier doubles ball can be countered by a stiffer and heavier racquet, strung tighter than in singles. Imagine trying to play tennis with a squash racquet - the ball would overpower the frame! While a doubles ball is not THAT different from a singles ball, a slightly heavier and/or stiffer racquet will benefit most players.
Balance: Generally, a head-light racquet offers great control and is easier to volley with than a head-heavy racquet. Since the balance rests closer to the player's hand, the player can more easily control the racquet, especially with a short swing - it takes less to get the racquet moving. Great control and easier volleys are essential for doubles, given how fast the ball moves across the middle.
Obviously, personal preference plays a big role in what racquet a player will like! But for doubles, the vast majority of players will be well served by a head-light bridge frame that's slightly heavier and stiffer than their singles racquet.