First of all, I have never created or enforced any kind of requirements regarding what instruments students use to practice at home (unlike some private teachers), and never will. However, I do have recommendations for both piano/keyboard students and trumpet students as to what instruments to purchase or rent. First, I will address those folks looking into pianos and keyboards, followed by those looking into trumpets.
I strongly recommend that students use an instrument that has at least 61 full-size touch sensitive keys. Such an instrument would be in the category of “keyboards” (see definitions below). I also highly recommend that students use an acoustic or digital piano for practice.
For prospective students that are looking to purchase an instrument, my recommendations are in the following order:
1) New acoustic grand piano
2) Used grand piano (in good condition)
3) New acoustic upright piano
4) Used upright piano (in good condition)
5) Digital piano with internal speakers, preferably enhanced with high-quality powered monitor/speakers
6) Digital piano without internal speakers (“stage piano”) connected to high-quality powered monitors or speakers
7) Keyboard with 88 fully-weighted keys
8) Keyboard with 88 semi-weighted keys
9) Keyboard with at least 76 keys
10) Keyboard with at least 61 full-size, touch sensitive keys
*NOT recommended: any keyboard with less than 61 keys or mini-size keys
An acoustic piano is the traditional type most people associate with the term piano. The label of “acoustic” refers to the fact that the sound is produced mechanically without electronics – crudely described: felt-covered wooden hammers strike metal strings when keys are pressed down, with the resulting sound amplified by a soundboard contained in a large wooden chamber. There are two types of pianos: uprights (sometimes called “verticals” because the strings are vertical to the ground) and grands (horizontally positioned strings). Uprights are measured by their height, while grands are measured by their length. Uprights can be spinets (36-39”), consoles (40-44”), studios (45-49”) or upright grands (50-60”). Grand pianos can be petite (less than 4'11”), baby (5'0”-5'1”), medium (5'2”-5'8”), full (5'9”-6'2”), recital (6'3”-6'9”), semi-concert (6'10”-8'10”), or concert (over 8'10”).
A digital piano is designed to mimic the feel and sound of an acoustic piano, with the sound being produced electronically. Most digital pianos utilize a “hammer action” mechanism which imitates, on a much smaller scale, the process of a hammer striking a string in an acoustic piano. However, instead of a string (or multiple strings) being struck, an electronic trigger generates the sound. Digital pianos also imitate the feel of acoustic pianos by means of “weighted” keys, which provide the kind of resistance that is naturally felt when the keys of an acoustic are pressed down, setting the mechanical parts into motion. “Graded” keys, another feature on most modern digital pianos, generate the feel of greater resistance toward the lower end of the keyboard and less resistance toward the upper end, which also copies the feel of playing an acoustic piano. Digital pianos have varying amounts of features that include at least a few additional sounds (such as organ, strings, guitar and bass) and can be found in both portable and console models (those that have a built-in stand).
Keyboard is a catch-all term used for entry-level instruments (beginner models) with internal speak systems, as well as professional synthesizers and workstations, both of which do not normally have internal speakers. Keyboards usually have 61 or 76 keys (although there are models have as many as 88 and as few as 44) that are not weighted like those on digital pianos, but rather make use of a simple spring mechanism, giving them a much lighter feel. Some models have a “semi-weighted” action, which provides the feel of slightly greater resistance, more similar to weighted keys. Although most keyboards have a feature called “touch sensitivity” (meaning there is a response in volume level based on the force with which the keys are pressed), the cheapest often do not, and should be avoided at all costs. Unlike most digital pianos, which focus on high quality piano sounds, keyboards have a large number of onboard sounds and other features. Synthesizers and “workstations” both fall into the category of keyboards, but are designed more for professional use, as they are very expensive in comparison to beginner models and contain advanced sound editing functions that the average piano student will not find useful.
Again, I have never created or enforced any requirements for students regarding what instruments they use. In my opinion, any trumpet is fine for a beginning student, although I do recommend that students avoid purchasing the very cheap Chinese instruments that are available online (sold under various brand names), as well as plastic trumpets. Used trumpets are generally fine as long as the valves are in good working condition and there aren't large dents on the tuning slides. Also, I recommend that young students (particularly in grades 4-6) use trumpets with a medium bore (usually designated as “student models”) because they will be easier for them to play until their lung capacity and overall size/strength becomes more fully developed. Any mouthpiece with a relatively small diameter and shallow cup size will also be helpful for most beginning students. For advancing students, particularly those that make it past grade 6 of trumpet study, assessments should be made on an individual basis as to what instrument and mouthpiece will best suit their needs and budget.