Владислав, представьте себе, что П. меня доставал и после нашего форума. Еще вылазил на разных форумах, писал мне в соцсети, буквально, пару лет назад последний раз. Я допустил тогда ошибку, слишком долго все нагнеталось. И после того случая я принимаю решение намного быстрее.
Картинок нет, только текст. From what I can tell through most of the range of the guitar the back is a 'loser', in the sense that any energy it picks up from the strings is likely to reduce the output of the instrument. This is not a bad thing when you understand it properly, and can't be avoided in any case. The back can contribute to output in one important way; it can boost the low-range power.
The only part of the guitar that can produce useful sound and is directly connected to the strings is the top. It makes sound in the low range mostly by pumping air through the soundhole. As you get up around the open G string pitch it makes more sound directly, like a loudspeaker. These two motions are focused, if you will, at the 'main air' and 'main top' pitches; around G on the low E string and near the open G string pitches, respectively. At the 'air' pitch the top and back are moving more or less like a bellows in most cases: they both move 'in' or 'out', reducing or enlarging the volume of the box, at the same time. At the 'top' pitch they usually move the other way: when one is pulling air in at the hole the other is trying to push it out. This can get complicated, as a lot depends on the frequency relationships between the two parts. This is one of the things you can use to modify the tone of the instrument. There are also lots of other 'top' resonances that color the sound, but the main air and main top modes produce most of the power.
The back moves in response to air pressure changes inside the box, or else from forces transmitted by the sides from the top to the back. Either way it's taking energy out of the top that might produce sound more effectively, since the top is lighter than the back, and faces in the right direction for the audience to hear. One path to making a louder guitar is to make the back or sides as heavy as possible, to reduce or eliminate the motion of the back. At least some Smallman's use a very thick rosewood back that is bent to an arch resembling that of a violin, and then carved. Another tactic, used by Trevor Gore, is to bolt heavy weights to the sides below the waist, which more or less eliminates the transmission of sound through the sides at the 'main top' frequency. This makes the top 'loudspeaker' both larger and probably more active, so it can produce more sound. Other folks have moved in that direction with weights in the neck and tail blocks, heavy laminated liners, and so on. Laminated sides are supposed to reduce such sound transmission by making the sides stiffer: I have no data on that, and can't say how well it accomplishes it's task, but I suspect that mass counts for more than stiffness here.
At the low frequency end of the guitar's spectrum, where the back and top are both tending to pump air through the hole together, they can cooperate to produce a stronger sound. If you imagine a guitar with a perfectly rigid back at the 'air' resonant pitch, the air will be moving 'out' of the sound hole at the time when the top is pushing 'in'. Some of the air coming out of the hole will tend to flow over the the top and fill in the space the top is vacating, so that bit of flow is lost in terms of sound production. If the back is working like a bellows at that pitch it can help to pump air through the hole, and make up some of that potential loss.
This can possibly be made more effective if the back is both heavy, and has low damping. Such a back can act as an effective 'flywheel', storing the energy it gets from the top with relatively low loss. The energy it takes from the top is actually reducing the 'phase cancellation' relative to the sound hole because the top moves less, so that, in the end, more sound can be produced. This sort of action is most effective if the fundamental resonant pitch of the back is fairly close to the 'main top' resonant pitch, but you do have to be careful. If it's too close you can get a 'wolf' note: the guitar extracts all the energy from the string fairly quickly, and turns it into sound. You get a string that has a fundamental that is twice as powerful for half as long. Since you're not very sensitive to even fairly large changes in power, you are not so likely to notice that the note is loud, but the lack of sustain stands out.
I plots I've made of the top motion wen it's driven by a frequency sweep at more or less constant power, the back resonances above the 'main back' mode tend to show up as 'dips', showing that they're stealing energy from the top. Most of these dips also show up in spectrum charts of the sound of the guitar measured from out in front. At first blush you might think that you'd want to eliminate those dips, but I think that would be a mistake. It's easy to see why if you think of the extreme case of a guitar that only had a 'main top' and 'main air' resonance. Basically, such an instrument would have an output spectrum with two peaks: a lower one at the 'air' frequency (lower due to the phase cancellation I spoke of earlier) and a taller peak at the 'top' pitch, where the air flow and top motion tend to add up rather than cancelling out. Above that 'top' peak the sound would die off simply, probably at more or less 6dB/ocatve. The spectrum of every note above that 'top' pitch would be exactly the same, with no variation at all in the tone color beyond what you could introduce by using a different stroke or changing the location of the pluck. Even that variation would be less than you'd like.
Thus it seems to me that the 'dips' in the spectrum caused by the higher order back resonances (above the pitch of the 'main back' mode) serve to introduce some tone color into the sound. Again, if the back material is dense, so that it doesn't move a lot, it won't take much energy out, and if the damping is low it can 'store' it for a little while and return it at some other frequency. This provides a rational for using high density low damping wood such as a rosewood for the back. IMO, the density is probably more important than the damping. At any rate, guitars with truly 'dead' backs, like Ovations, do seem to me to lack tone color.
As always, there are lots of opinions as to the best balance of 'activity' and 'reflection' in the back, and a lot depends on just what you're trying to do with the guitar.
Касаемо дек гитар и куполов к ним. Не секрет ни для кого, сезонное колебания влажность+температура - означает изменение площади дек, надо это дело компенсировать и все-таки вид немного выпуклого приятней впуклого. Теперь про дно. Вот наш форум он таки подразумевает уважительное отношение населения друг к другу, посему экзекуции по отношению к не особо адекватным "я считатаю .., а вы тут нубы" должно только приветствоваться иначе оно и будет дно. Есть же такое наблюдение: - Американский форум: задали вопрос - получили ответ. - Израильский форум: задали вопрос - получили кучу вопросов в ответ. - Российский форум: задали вопрос - узнали "какой же вы му.ак." Оно нам надо в такое превращаться. Увы некоторые изначально культурные форумы, стараниями полу интеллигентов, к сожалению превращаются в дно, в точности как в этом наблюдении.