I have a question that really bothers me.When I put a new set of strings on my acoustic guitar, the sound's so crispy, then after 2 days, the sounds turned into dead or dull, but when I loosen them for a few days and tighten them again, when I start to play, they sound like new again...so do we really need to loosen the strings after we play to retain the crispiness of the strings or is there any other way ? I've already tried boiling them and although it helps...but we can't do that every week since it can affect the strings.
Well - I am not sure exactly what is going on but I will offer some ideas that might help.
First of all, you need to be sure you are using good quality strings from a reputable manufacturer. Poor quality strings tend to go dead quicker than better quality strings. You might try reading some on line reviews to see what others are saying about the various brands. I've always had good luck with D'Addario - but there are other good ones as well.
The next thing you need to be sure you are doing is "stretching" your new strings in after you install them. I never loosen my guitar strings unless I am flying with my guitar or placing it on long term storage. You should not have to do that on a guitar that is played regularly.
One thing that always happens with newly installed strings is they start slipping on the tuning posts as tension is applied during tuning and playing.
Some folks call this slippage "stretching" but there is little actual stretching that occurs on steel guitar strings but "stretching" is a descriptive analogy because the effect is the same as if the string actually stretched.
So to stabilize your tuning, after all six strings have been brought to proper pitch, go back to the fattest (sixth string) and gently tug on it near the center of its length to "stretch" it. This will tighten up some of the slack where your string is wrapped around the tuning post and firmly seat the ball end in the bridge. You will notice after you do this that it is now out of tune (flat). Turn your tuning key to bring it back into tune. You can even go a tad sharp. Then repeat this process of gently tugging ("stretching" the string til it plays flat) and re-tuning until you can no longer make it play flat by tugging on it. Now the sixth string is nice and tight on the tuning post and will not be as inclined to go out of tune when you start playing.
Do the same thing for each subsequent string. Be especially careful on the skinnier strings not to tug too much or you could actually break the string. Tug just enough to make the string play flat.
Finally, after you have "stretched" in all the strings, go back through each string one final time to make the minor adjustments that may have been necessitated by the added tension to the neck.
There is one other thing I should mention just in case. I have heard that some folks have a very acidic body chemistry that tends to corrode steel strings more quickly than normal - or their hands sweat when they play and the salt causes oxidation of the strings at a rapid rate. If this is the case - the best solution is to use a coated string such as Elixir Polyweb or Elixir Nanoweb or D'Addario EXP. The protective coating will keep the corrosive elements away from the strings and allow them to survive longer while maintaining their crispness.
Hopefully one of the foregoing ideas will provide the solution you are looking for. Good luck!