Great strings do not react equally well on all instruments. While it is good to follow advice for choosing the strings that you think will suit your playing needs, style, and instrument, don't be afraid to experiment based on what you learn. Your instrument may need to be adjusted to reach it's maximum capability. The bridge, sound-post and strings play a huge role in sound production. Many instruments need high tension to play out while others will open up with less tension. It is a good idea to have a well-recommended and trusted luthier look at your instrument.
Sound posts require adjustment, even replacement, from time to time; the top of the violin near the f-holes begin to rise with age. Strings need changing after a particular amount of usage or age because of drying, wear, and metal fatigue. Old strings lose their tone quality, power, and overtones; some say as quickly as after 300 hours of playing. Cold, heat, and humidity also impact your instrument. It's a good idea to see a luthier for regular check-ups on your stringed instrument. While some violins, violas, cellos and basses are stable, maintaining great sound throughout the seasons, others are sensitive to the slightest weather changes.
Before testing strings, make sure your instrument has the optimal set up. Check the sound-post; is it in the right location? Is it straight and vertical, not leaning in any other direction? The ideal location for the sound-post is from almost against to approximately 3/16 of an inch, or one bridge thickness behind the center right bridge foot (towards the tailpiece). Too close can increase power but loose response. Search for the right spot.
A good bridge is a straight -- not warped. A properly set bridge will fit the belly of the instrument as perfectly as possible.
Besides reading this article, selecting the best strings for you and your instrument also means seeking other violinists' opinions, discussing string selection on forums such as The Fiddlerman Forum, and comparing the different string brands.
What kind of sound do you want to get out of your instrument? Loud, bright, strong, brilliant, metallic, rich or soft, warm, sweet, dark, thin, dull, etc...?
Depending on what characteristics your instrument already exhibits, you'll need to either enhance, adhere to, or counteract its natural qualities.
Steel core strings tend to sound brighter, stronger -- more brilliant and metallic. They fit the dull toned instrument. Used mostyl in genres such as country and folk, even jazz. However, They sometimes are difficult to play in tune because of their non-flexible character. When applying pressure with the bow, the pitch often sharpens a bit.
Synthetic core strings (Fiddlerman's favorite) are in between steel and gut strings; often the best all around choice for a strong, yet, warm sound. In some cases, they produce more volume than steel strings. Generally, the synthetic core strings have a perlon -- fancy name for plastic core. There are, however, variations of materials that are called composite, Zyex, nylon strands, etc.... These are well-worth trying.
Gut Core Strings are the oldest and least popular choices, today. They are considered the warmest sounding. Although, many synthetic core strings equal their warmth, and surpass the gut core in volume and power as well. Use gut core strings with bright and brilliant sounding instruments or when tuning down. Baroque musicians commonyly use gut core strings.
Strings Tensions, which one do you choose? If you don't already know, start with the medium tension. They are designed to suit most instruments. The thicker strings are called Stark, Forte, and Heavy tension. The thicker strings require more tension to reach the correct pitch, and therefore, produce more tension, pressure resulting in more power. By the same token, the extra tension reduces action time and responsiveness. The thinner strings are called weich, soft, light, or dolce tension. Because they are thinner they need less tension to reach their pitch, producing less tension, pressure and resulting often in less power. However, they usually will have quicker action and reponse, and sound more bright.
If just one or two of your strings are too bright or weak sounding, you may want to try a thicker string. If one or two of your strings are too dark sounding or non-responsive and slow, you may want to try a thinner string. Usually, you'll want to get a set of strings with the same tension, but at times, it may be necessary to mix the strings to get a well-balanced dynamic from bottom to top.