<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; = charset=utf-8"> <META content="MSHTML 6.00.2800.1106" name=GENERATOR></HEAD> <BODY dir=ltr style="FONT-SIZE: 10pt; FONT-FAMILY: Arial; BACKGROUND-COLOR: = #ffffff"> <DIV> <DIV> <DIV> <DIV><SPAN class=000513816-02022004>Dale,</SPAN></DIV> <DIV><SPAN class=000513816-02022004></SPAN> </DIV> <DIV><SPAN class=000513816-02022004>You wrote:  </SPAN></DIV> <DIV><SPAN class=000513816-02022004></SPAN> </DIV> <DIV><SPAN class=000513816-02022004><FONT = color=#000040>"...interesting to note that when...booming the board with the fist to hear its innate resonance = & if your face or hand is near any of the nose bolt holes just = how powerful a blast of air comes thru there!"</FONT></SPAN></DIV> <DIV> </DIV> <DIV>That is an interesting observation.  I think a rush of air = that comes from striking the board doesn't come from the periodic vibration of the = board (which makes up the boom sound it makes when you strike it), but rather = from the one-time relatively slow and high amplitude displacement caused by = the initial strike itself.  Sort of like the way a ride-cymbal or = a gong swings when you hit it, but the swinging is only incidental to the = sound you hear, which come from much faster vibrations within the material.  <SPAN class=000513816-02022004>I = think </SPAN>the frequencies from the strings that we want to transmit would be more in = the range of the board's self-vibration than in the relatively very slow movement = of the initial displacement when you strike it.<SPAN = class=000513816-02022004>  </SPAN><SPAN class=000513816-02022004>That isn't to say there aren't = similar losses at relevant frequencies, I just don't know if you could = tell a whole lot about them by feel.  What you've witnessed would = definitely be a loss as far as it goes.  Part friction, part acoustic short circuit.  </SPAN></DIV> <DIV><SPAN class=000513816-02022004></SPAN> </DIV> <DIV><SPAN class=000513816-02022004></SPAN>An analogy to the d<SPAN class=000513816-02022004>i</SPAN>stinction as to whether the air = coming through says anything about the acoustic effects of the hole at relevant = frequencies could be made by making an experiment with a ported loudspeakers.  If <SPAN class=000513816-02022004>you</SPAN> = push the cone in with your hand, air will come out the port, and it comes = out for all practical purposes perfectly in time to fill up the extra space in = the room made by the cone going in, so there will be no pressure change, any = any potential acoustic product that might occur by repeating this in = and out movement is cancelled out.  <SPAN = class=000513816-02022004>That's one kind of acoustic loss.</SPAN></DIV> <DIV><SPAN class=000513816-02022004></SPAN> </DIV> <DIV><SPAN class=000513816-02022004> <DIV><SPAN class=000513816-02022004>The other kind is friction = loss.  </SPAN>In loudspeakers, a factor is considered "purely" lossy, or = Q-reducing, when the output <SPAN class=000513816-02022004>at any reasonable = playing level </SPAN>is so disorganized or attenuated as to have negligible acoustical effect, destructive or constructive, compared = to the energy dissipated as heat.  <SPAN class=000513816-02022004>C</SPAN>ompressions and = rarefactions going through tiny pin-holes in an enclosure are such an example.  Their = waveforms coming out the other side are very distorted in the amplitude = domain <SPAN class=000513816-02022004>and </SPAN>maybe in the = time-domain<SPAN class=000513816-02022004> also</SPAN>.  <SPAN class=000513816-02022004>Basically these pin-holes have a current = limiting function as well as an energy dissipating function, so the higher the = amplitude, the more distorted the exiting waveform.  Somebody with a better scientific or engineering background can correct me if my terms are not correct. </SPAN></DIV> <DIV> </DIV> <DIV>In the case of soun<SPAN class=000513816-02022004>d</SPAN>board holes, <SPAN class=000513816-02022004>I think </SPAN>conduction = of coherent soundwaves <SPAN class=000513816-02022004>at most frequencies and = realistic amplitudes </SPAN>will probably almost always turn out to be = substantial, or at least significant, compared to the friction = losses.  <SPAN class=000513816-02022004>(</SPAN><SPAN class=000513816-02022004>But = that doesn't necessarily mean it will be s</SPAN>ubstantial or = significant <SPAN class=000513816-02022004>at important frequencies </SPAN>compared to = overall output of the instrument<SPAN class=000513816-02022004>.)  = </SPAN></DIV> <DIV><SPAN class=000513816-02022004></SPAN> </DIV> <DIV><SPAN class=000513816-02022004>But then there's also the other, = third component, which is the reactive one.  Reactive paths involve = energy storage and time-delays.  </SPAN></DIV> <DIV> </DIV></SPAN></DIV></DIV></DIV></DIV> <DIV><SPAN class=000513816-02022004>Going back to the loudspeaker, if we n</SPAN>ow whack it (or sharply tap it), instead of just = pushing it, <SPAN class=000513816-02022004>we</SPAN>'ll get a similar = puff of air, but if the speaker is relatively undamped (it might be hard to find one = undamped enough, but it helps if one of the wires is disconnected) there will = also somewhat of a drum sound that sometimes even has a recognizable pitch.  Imagine hitting the big gong that's suspended -- the = gong swings an inch or a few, but the sound comes from the faster vibrations<SPAN class=000513816-02022004> -- i</SPAN>t's the quivering = of the gong, not its slow swing back into plumb, that makes the sound.  = The reason for referring to the ported loudspeaker is that at the = <EM>quivering</EM> frequency, the air going in and out of the port will be delayed so that = it is in almost perfect timing to <EM>add</EM> to the effect of the = cone's movement<SPAN class=000513816-02022004>.  </SPAN>When the cone = goes out, the air goes out, so the acoustic output is reinforced by the "hole" at = this point, even though the first puff of air that came out of the port -- corresponding to the swinging of the gong -- represented acoustic canceling.  <SPAN class=000513816-02022004>This reversal, = phase reversal, i</SPAN><SPAN class=000513816-02022004>s because there = is now a <EM>reactive</EM> path</SPAN>.  </DIV> <DIV> </DIV> <DIV><SPAN class=000513816-02022004>Now if <SPAN class=000513816-02022004>we</SPAN> excite the cone with a periodic = source, say by coupling it to a string, there will be acoustic reinforcement from = the hole/port until the frequency of the string used is so low = that <SPAN class=000513816-02022004>the port output simply follows the backwave = of the cone in phase (non-reactively).  </SPAN>Now we don't know yet if at = the relevant frequencies the holes act more like the port does at or = above its tuning, or more like the way it does below its tuning, as from from = a slow push.  We hope either more like the latter or like neither.  </SPAN>The <SPAN = class=000513816-02022004>reactive </SPAN>reinforcing behavior of the port in a speaker happens when the = spring of air inside the cabinet aligns through the cross-sectional area of the = opening with the mass of the air inside the tube, and <SPAN class=000513816-02022004>we</SPAN> can get a pretty good idea how all = this works by just taking a weight and suspending it from a rubber = band.  </DIV> <DIV> </DIV> <DIV>Use a weight that's heavy enough or a rubber band that's thin enough so the natural periodic bouncing motion is slow, so = that it's easy to observe the timing of it relative to motions of your hand.  Hold the end of the rubber band and bob the weight up = and down.  If <SPAN class=000513816-02022004>you</SPAN> do = it very slowly, the weight will go up and down with your hand.  = As <SPAN class=000513816-02022004>you </SPAN>increase the = speed, <SPAN class=000513816-02022004>you'll </SPAN>reach a frequency where = the weight will be moving up and down opposite to the motion of your hand.  At = this frequency, the resonant frequency of the band/weight system, it will = take only very small motions of your hand to keep the weight bobbing quite a = bit.  This corresponds to the tuning of a ported speaker, and represents the = lower limit of substantial bass response (and just like your hand, the = excursions of the cone are controlled by the opposing forces of reactance of the = system, reducing distortion or preventing the speaker from mechanically = bottoming out.)  <SPAN class=000513816-02022004>Connecting to some = other current discussions about soundboard stiffness and mass etc., there is now also = a very high impedance relationship of the weight/spring to your hand, and = energy is reflected back to your hand and thus dissipated very slowly.  If = your hand was a string it would have long sustain at this frequency.  = </SPAN>Now continue to move your hand up and down faster, and the motion of the = weight will diminish, and will continue to diminish as you increase the = frequency.  So at higher frequencies there is neither constructive nor destructive = interference coming out of the port; the higher frequencies "see" the port as a = sealed hole, and speaker behaves as it would in a sealed box in these = frequencies.</DIV> <DIV> </DIV> <DIV><SPAN class=000513816-02022004>And if we r</SPAN>e-did this whole = experiment with the weight in thick oil to add substantial = resistance to the system<SPAN class=000513816-02022004> (or by </SPAN>add<SPAN class=000513816-02022004>ing</SPAN> big air-brakes made out of = cardboard to the weight<SPAN class=000513816-02022004>), we'd have some idea of the resistive or friction-loss component.  You'd see that = resonant motion is attenuated -- but also that losses from destructive = interference below resonance would be substantially reduced.  </SPAN></DIV> <DIV><SPAN class=000513816-02022004></SPAN> </DIV> <DIV><SPAN class=000513816-02022004>So now we have a couple of = common-sense analogies to all three components of the soundboard hole's = behavior -- 1) acoustic short circuit; 2) friction losses; and 3) reactive = (mass and/or spring).  </SPAN></DIV> <DIV><SPAN class=000513816-02022004></SPAN> </DIV> <DIV><SPAN class=000513816-02022004>What I don't know how to do is to = quantify these effects relative to overall acoustic output, because I don't know = what physical context to put it in.  Even in the case of simple = resistance, I think we still have to compare the amount of resistance to the = pressure differential at the opening (analogous to voltage), or compare that = path to the other available paths.  In the case of certain kinds of = reactance, we'd </SPAN><SPAN class=000513816-02022004>have to know even more.</SPAN></DIV> <DIV> </DIV> <DIV>I said in my earlier post that since there is no enclosed body = of air between the vibrating membrane and the hole, there isn't any = mass/spring system involved in soundboard holes.  Now I'm not so sure that the elasticity of air <SPAN class=000513816-02022004>in </SPAN><SPAN class=000513816-02022004>propagating soundwaves might </SPAN>itself not make such an equation possible for analyzing the = effect of the holes.  Intuitively, it seems like there would be a = frequency where the mass of the air in the hole would substantially inhibit conducting air-vibrations through the hole<SPAN class=000513816-02022004>.  = (O</SPAN>n the other hand, if, owing to the thinness of the board that frequency = were so high that its wavelength was comparable to the hole size, you might as = well forget <SPAN class=000513816-02022004>about the reactive = component and just look at the current capability, location and resistance of the hole -- </SPAN>both because the air won't act as "a" mass when the = hole and wavelength sizes are similar, and also because we're talking = about frequencies up around the second partial of C8, or higher<SPAN class=000513816-02022004> depending on the actual hole</SPAN>.<SPAN class=000513816-02022004>)</SPAN>  That might be modelable as an = inductor, but to get any quantitative results from that you have to put it in = context of system capacitance <SPAN class=000513816-02022004>and/</SPAN>or resistance.  It's that system component -- in the soundwaves themselves or in the atmosphere <SPAN = class=000513816-02022004>(or in the pressure differentials, or the impedances of other available paths) = or </SPAN>whatever, that I'm not grasping<SPAN = class=000513816-02022004>.  I don't think I ever dealt with anything like that.  (Well, = of course I did, by living at all, but I'm saying consciously or = explicitly, you know what I mean.)</SPAN>  <SPAN = class=000513816-02022004>So (Terry) my confidence that I could figure this out in my = earlier reply to your post may have been premature.</SPAN></DIV> <DIV> </DIV> <DIV>If it turns out these holes aren't so good, it seems like an = acoustically sound answer to the problem could come quite cheaply and conveniently in = the form of the usual suspension systems used for loudspeakers -- either a = sealed version of the little accordion-like "spiders" attached to the = voice-coil behind the cone (outer-edge attaches to the SB, inner edge to the nose-bolt), = or something like a foam or rubber half-roll surround.  <SPAN class=000513816-02022004>Maybe t</SPAN>he stiffness could even be = chosen to support desired impedance characteristics in the = soundboard.</DIV> <DIV> </DIV> <DIV><SPAN class=000513816-02022004>I'll be interested to hear = anything you notice from the experiment you proposed with your Steinway = D.</SPAN></DIV> <DIV><SPAN class=000513816-02022004></SPAN> </DIV> <DIV><SPAN class=000513816-02022004>Trent Lesher</SPAN></DIV> <BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px"> <DIV>-----Original Message----- <BR><B>From:</B> Erwinspiano@aol.com [mailto:Erwinspiano@aol.com] <BR><B>Sent:</B> Sat 1/31/2004 10:28 PM <BR><B>To:</B> pianotech@ptg.org <BR><B>Cc:</B> <BR><B>Subject:</B> = Re: Dipole Effects and Leaks in Soundboard; was Isolated = Air-Movement<BR><BR></DIV> <DIV> <DIV>In a message dated 1/31/2004 4:35:49 PM Pacific Standard Time, tlesher@sachnoff.com writes:</DIV> <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px = solid">As for the holes, although there's no substitute for somebody taking = frequency spectrum measurements from a variety of positions and then plugging = the holes up and doing it again, I think I can handle that question a = little more satisfactorily than the other one.  I wish I still had the = equipment to take some measurements myself, but various upheavals = took their toll some years ago.  But give me some data if you want and = I'll see what I come up with. <BR><BR>Best r egards,<BR><BR>Trent Lesher<BR><BR>(tuning student, amateur pianist)</BLOCKQUOTE></DIV> <DIV><FONT face="Times New Roman" color=#000040>     <FONT size=4> Trent</FONT></FONT></DIV> <DIV><FONT face="Times New Roman" color=#000040><FONT size=4>     Interesting post. This may be trivia = but it is interesting to note than many times when I'm working on an unstrung = piano & booming the board with the fist  to hear its innate = resonace & I</FONT><FONT size=4>f your face or hand is near any of = the nose bolt holes just how powerful a blast of air comes thru there! It would = seem that a great deal of air is continually leaking thru these holes. = Might this be a friction loss as you describe? WOuld the effeincy of the whole = mechanism indeed increase if the hole were sealed or eliminated or are they = benificial? I think I'll get someone to play vigorously on My Stwy D and then I'll = see if I can feel any significant exchange from underneath the piano around = the bolt holes.</FONT></FONT></DIV> <DIV><FONT face="Times New Roman" color=#000040 size=4>  = Dale Erwin</FONT></DIV> <DIV><FONT face="Times New Roman" color=#000040 = size=4></FONT> </DIV> <DIV><FONT size=2> <P> </P> <P> </P> <P> </P> <P>EVEN MORE IMPORTANT NOTICE: Never mind the message below. It's = intended for law-client-related communications, and the computer people at the law = firm where I work seem to have made it impossible to keep it from being = added to one's e-mails, otherwise I would turn it off and it would not appear = below. For purposes of this message it may be considered as meaningless, = random clutter. Piano tuners, technicians, rebuilders, makers, designers, = scientists, craftsmen, artisans, musicians, engineers, enthusiasts and friends = need not trouble themselves. Despite what the notice says, you are hereby = notified of nothing (except that you are hereby notified of nothing).</P></FONT></DIV></BLOCKQUOTE></BODY><P align=center><FONT face=Tahoma size=2><FONT = color=#0000ff>****** IMPORTANT NOTICE ******<BR>This e-mail, and any = attachments hereto, is intended only for use by the addressee(s) named = herein and may contain legally privileged and/or confidential = information. If you are not the intended recipient of this e-mail, = you are hereby notified that any dissemination, distribution or copying = of this e-mail, and any attachments hereto, is strictly prohibited. If = you have received this e-mail in error, please immediately notify me at = (312) 207-1000 and permanently delete the original and any copy of any = e-mail and any printout thereof.</FONT></FONT></P></HTML>