Re: USB sound cards (Zlatan Ribic )

Subject: Re: USB sound cards From: Zlatan Ribic <zlatan@xxxxxxxx> Date: Thu, 18 Dec 2014 10:40:53 +0100 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY> Dies ist eine mehrteilige Nachricht im MIME-Format. ------=_NextPart_000_0012_01D01AAF.18F87740 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable I think no one in this discussion (except Bob) is "electrical engineer" Zlatan From: Oberfeld-Twistel, Daniel=20 Sent: Thursday, December 18, 2014 9:43 AM To: AUDITORY@xxxxxxxx=20 Subject: Re: USB sound cards Series resistors are often put in for reasons of stability, for example = when driving capacitive loads. An example is shown in figure 2 of the = attached PDF. =20 I also always believed that a low output impedance is optimal for = precisely controlling a "reactive" load like a loudspeaker, although = this is of course not the most power-efficient design (-> see impendance = -matched transmission lines). At least that is what most texts on = amplifier design suggest - but anyway, that might be wrong and hey, I'm = only a psychologist, not an electrical engineer ;-)=20 =20 [Although I actually had to build a low-noise headphone amplifier for my = PhD experiments, because back then my lab wanted to save the money for = something like a TDT device=E2=80=A6 Interesting experience.] =20 Best =20 Daniel =20 =20 PD Dr. Daniel Oberfeld-Twistel Johannes Gutenberg - Universitaet Mainz Department of Psychology Experimental Psychology Wallstrasse 3 55122 Mainz Germany =20 Phone ++49 (0) 6131 39 39274=20 Fax ++49 (0) 6131 39 39268 http://www.staff.uni-mainz.de/oberfeld/ https://www.facebook.com/WahrnehmungUndPsychophysikUniMainz =20 From: AUDITORY - Research in Auditory Perception = [mailto:AUDITORY@xxxxxxxx On Behalf Of James Johnston Sent: Thursday, December 18, 2014 6:16 AM To: AUDITORY@xxxxxxxx Subject: Re: USB sound cards =20 Not sure of your point, Jont. Of course it is the current through the = voice coil that actually moves the diaphragm and thus makes the = pressure. None the less, the back EMF is key, especially for low-frequency system = designs, and the back EMF is converted to current by both the internal = and external resistance. This is a key part of the filter design = problem that makes the system something approximating flat at low = frequencies. I'm not sure who you think is putting resistors in series, one generally = avoids that, except for the obligatory resistance of a crossover if one = is using a passive crossover system. =20 On Wed, Dec 17, 2014 at 3:51 AM, Jont Allen <jontalle@xxxxxxxx> = wrote: Jim + Auditory-list While it is true that speakers are "designed" to be driven by the = voltage, our detailed research has shown that it is the current that controls the pressure (i.e., force on the cone). If you = want the details I already sent the links, but I'll send them once more, just in case you missed it. The theory of how the current drives the force is given by our ASA = presentation from last month, at the special session on historic = transducers: http://hear.ai.uiuc.edu/public/Allen/NK_ASA_Indianapolis.pdf * Kim and Allen (2014) Historic transducers: Balanced Armature Receiver = (BAR), ASA meeting INDY, IN, Oct 30, 2014 pdf The full theory is in a Hearing Research article: http://hear.ai.uiuc.edu/public/KimAllenMar20.13.pdf * Kim, Noori and Allen, J.B. (2013). "Two-port network Analysis and = Modeling of a Balanced Armature Receiver, "Hearing Research, special = MEMRO 2013 issue (pdf)=20 Ms Kim's (i.e., Noori's) PhD thesis has the most complete story, and is = available directly from her (noorimail@xxxxxxxx). Because it is the current that determines the pressure, via the = electrical input impedance, and because this impedance can be (i.e., is) = reactive (have inductance), it can be tricky to figure out what is going = on. One must know (i.e., measure) the load impedance, or at least the = current. Also the distortion is mostly determined by the nonlinear flux = vs current (i.e., B-H curve), as described by Hunt, for example. Hunt mostly quotes Mott and Minor's BSTJ Jan 1951 article, adding little = new material to their story. In the interesting case of the Etymotic ER-3 (insert headphone), they = place a 10 ohm resistor across the input terminals.=20 So if you try to beat this with a series resistor, you will not be = successful in changing anything, because all the current is going into = that 10 ohm resistor. I opened up one of my ER-3 and cut out the resistor, and then I could = see what was really going on. It worked better too. When that ER-3 went back for repairs once, they were shocked to see the = resistor was missing. I had to admit I cut it out, and wanted it left = that way. In general, adding a series resistor to your circuit, is working blind. = You will likely get a random result, and random is never better. Thus I dont advise it unless you are willing to measure the input = impedance and the resulting frequency response of the headphone. While = there are some interesting things you can do with a series impedance, a series = resistor is not one of them. Jont Allen On 12/16/2014 06:12 PM, James W. Beauchamp wrote: I agree with Bob. Most loudspeakers are designed to be driven byan ideal = voltage source. Under this criterion they attempt to get the flattest = possible response overall. This is not necessarily the most efficient = response. In fact, some loudspeaker designs, like the Small-Thiele = closed-box non-vented design, are very inefficient. Jim Bob Masta = wrote:From: Bob Masta <audio@xxxxxxxx>Date: Sun, 14 Dec 2014 09:15:19 = -0500To: AUDITORY@xxxxxxxx: Re: USB sound cards On 13 Dec = 2014 at 21:59, Richard F. Lyon wrote:On Sat, Dec 13, 2014 at 5:52 AM, = Bob Masta <audio@xxxxxxxx> wrote: It's the other way around: Adding = resistance in thedriving circuit gives poorer damping. "Damping Factor" = fora power amplifier is the reciprocal of output impedance. Bob, I = wasn't aware of that definition.I was thinking of = http://en.wikipedia.org/wiki/Damping_ratiorather than = http://en.wikipedia.org/wiki/Damping_factorOops, you are correct... I = should have said it is *proportional* to the reciprocal. Is there an = understanding of why high "damping factor" would be good?Jont's findings = suggest otherwise (I believe he's saying the current istypically more = relevant than the volage).The second reference you cited covers it under = "Explanation". Basically, a conventional electrodynamic speaker is both = a motor and a generator. Imagine that the speaker receives a momentary = voltage pulse, after which is is instantly disconnected from the source. = The speaker would ring at its resonant frequency, damped only by = friction. The generator would be creating a voltage, but no current, so = no load to add damping. However, if instead of disconnection the leads = were *shorted* after the pulse, the generator would be driving all its = current into the zero-ohm load, giving a maximum damping effect. = Conventional loudspeakers are designed to be driven by voltage sources, = not current sources. The current may be more "relevant" (in the sense of = force generation), but not for getting a flat frequency response from a = conventional speaker design. (Although there have been occasional = attempts at current drive, the ones I recall required special dedicated = amplifiers.) Best regards, Bob Masta D A Q A R T AData = AcQuisition And Real-Time Analysis www.daqarta.comScope, = Spectrum, Spectrogram, Signal Generator Science with your sound card!=20 --=20 James D. (jj) Johnston Independent Audio and Electroacoustics Consultant ------=_NextPart_000_0012_01D01AAF.18F87740 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML xmlns:v =3D "urn:schemas-microsoft-com:vml" xmlns:o =3D=20 "urn:schemas-microsoft-com:office:office" xmlns:w =3D=20 "urn:schemas-microsoft-com:office:word" xmlns:m =3D=20 "http://schemas.microsoft.com/office/2004/12/omml"><HEAD> <META content=3Dtext/html;charset=3Dutf-8 http-equiv=3DContent-Type> <META name=3DGENERATOR content=3D"MSHTML 11.00.9600.17496"> <STYLE></STYLE> </HEAD> <BODY lang=3DDE id=3DMailContainerBody=20 style=3D"PADDING-TOP: 15px; PADDING-LEFT: 10px; PADDING-RIGHT: 10px" = leftMargin=3D0=20 link=3Dblue topMargin=3D0 vLink=3Dpurple CanvasTabStop=3D"true"=20 name=3D"Compose message area"> <DIV>I think no one in this discussion (except Bob) = is=20 "electrical engineer"</DIV> <DIV>Zlatan</DIV> <DIV> </DIV> <DIV style=3D"FONT: 10pt Tahoma"> <DIV> </DIV> <DIV style=3D"BACKGROUND: #f5f5f5"> <DIV style=3D"font-color: black">From: <A=20 title=3D"mailto:oberfeld@xxxxxxxx
STRG + Klicken, um = Verkn=C3=BCpfung zu folgen"=20 href=3D"mailto:oberfeld@xxxxxxxx">Oberfeld-Twistel, Daniel</A> = </DIV> <DIV>Sent: Thursday, December 18, 2014 9:43 AM</DIV> <DIV>To: <A=20 title=3D"mailto:AUDITORY@xxxxxxxx
STRG + Klicken, um = Verkn=C3=BCpfung zu folgen"=20 href=3D"mailto:AUDITORY@xxxxxxxx">AUDITORY@xxxxxxxx</A> = </DIV> <DIV>Subject: Re: USB sound cards</DIV></DIV></DIV> <DIV> </DIV> <DIV class=3DWordSection1> Series=20 resistors are often put in for reasons of stability, for example when = driving=20 capacitive loads. An example is shown in figure 2 of the attached=20 PDF.<o:p></o:p> <o:p> </o:p> I=20 also always believed that a low output impedance is optimal for = precisely=20 controlling a "reactive" load like a loudspeaker, although this is of = course not=20 the most power-efficient design (-> see impendance -matched = transmission=20 lines). At least that is what most texts on amplifier design suggest - = but=20 anyway, that might be wrong and hey, I'm only a psychologist, not an = electrical=20 engineer ;-) <o:p></o:p> <o:p> </o:p> [Although=20 I actually had to build a low-noise headphone amplifier for my PhD = experiments,=20 because back then my lab wanted to save the money for something like a = TDT=20 device=E2=80=A6 Interesting experience.]<o:p></o:p> <o:p> </o:p> Best<o:p></o:p> <o:p> </o:p> Daniel<o:p></o:p> <o:p> </o:p> <DIV=20 style=3D"BORDER-TOP: medium none; BORDER-RIGHT: medium none; = BORDER-BOTTOM: windowtext 1pt solid; PADDING-BOTTOM: 1pt; PADDING-TOP: = 0cm; PADDING-LEFT: 0cm; BORDER-LEFT: medium none; PADDING-RIGHT: 0cm; = mso-element: para-border-div"> <P class=3DMsoNormal=20 style=3D"BORDER-TOP: medium none; BORDER-RIGHT: medium none; = BORDER-BOTTOM: medium none; PADDING-BOTTOM: 0cm; PADDING-TOP: 0cm; = PADDING-LEFT: 0cm; BORDER-LEFT: medium none; PADDING-RIGHT: 0cm"><FONT=20 color=3D#1f497d size=3D2 face=3DCalibri><o:p> </o:p></DIV> PD=20 Dr. Daniel Oberfeld-Twistel<o:p></o:p> Johannes=20 Gutenberg - Universitaet Mainz<o:p></o:p> Department=20 of Psychology<o:p></o:p> Experimental=20 Psychology<o:p></o:p> Wallstrasse=20 3<o:p></o:p> 55122=20 Mainz<o:p></o:p> Germany<o:p></o:p> <o:p> </o:p> Phone=20 ++49 (0) 6131 39 39274 <o:p></o:p> Fax  =20 ++49 (0) 6131 39 39268<o:p></o:p> http://www.staff.uni-mainz.de/oberfeld/<o:p></o:p>= https://www.facebook.com/WahrnehmungUndPsychophysikUniMainz<o:p>= </o:p> <o:p> </o:p> <DIV=20 style=3D"BORDER-TOP: medium none; BORDER-RIGHT: medium none; = BORDER-BOTTOM: medium none; PADDING-BOTTOM: 0cm; PADDING-TOP: 0cm; = PADDING-LEFT: 4pt; BORDER-LEFT: blue 1.5pt solid; PADDING-RIGHT: 0cm"> <DIV> <DIV=20 style=3D"BORDER-TOP: #b5c4df 1pt solid; BORDER-RIGHT: medium none; = BORDER-BOTTOM: medium none; PADDING-BOTTOM: 0cm; PADDING-TOP: 3pt; = PADDING-LEFT: 0cm; BORDER-LEFT: medium none; PADDING-RIGHT: 0cm"> <SPAN=20 style=3D'FONT-SIZE: 10pt; FONT-FAMILY: "Tahoma","sans-serif"; = FONT-WEIGHT: bold'>From:<FONT=20 size=3D2 face=3DTahoma><SPAN=20 style=3D'FONT-SIZE: 10pt; FONT-FAMILY: "Tahoma","sans-serif"'> AUDITORY = - Research=20 in Auditory Perception [mailto:AUDITORY@xxxxxxxx <SPAN=20 style=3D"FONT-WEIGHT: bold">On Behalf Of James = Johnston <SPAN=20 style=3D"FONT-WEIGHT: bold">Sent: Thursday, December 18, 2014 = 6:16=20 AM To:=20 AUDITORY@xxxxxxxx <SPAN=20 style=3D"FONT-WEIGHT: bold">Subject: Re: USB sound=20 cards<o:p></o:p></DIV></DIV> <SPAN=20 style=3D"FONT-SIZE: 12pt"><o:p> </o:p> <DIV> <DIV> <DIV> Not sure of = your point,=20 Jont. Of course it is the current through the voice coil that actually = moves the=20 diaphragm and thus makes the = pressure.<o:p></o:p></DIV> None the less, = the back EMF=20 is key, especially for low-frequency system designs, and the back EMF is = converted to current by both the internal and external resistance.  = This is=20 a key part of the filter design problem that makes the system something=20 approximating flat at low = frequencies.<o:p></o:p></DIV> <SPAN=20 style=3D"FONT-SIZE: 12pt">I'm not sure who you think is putting = resistors in=20 series, one generally avoids that, except for the obligatory resistance = of a=20 crossover if one is using a passive crossover=20 system.<o:p></o:p></DIV> <DIV> <SPAN=20 style=3D"FONT-SIZE: 12pt"><o:p> </o:p> <DIV> <SPAN=20 style=3D"FONT-SIZE: 12pt">On Wed, Dec 17, 2014 at 3:51 AM, Jont Allen = <<A=20 href=3D"mailto:jontalle@xxxxxxxx" = target=3D_blank>jontalle@xxxxxxxx</A>>=20 wrote:<o:p></o:p> <DIV> <SPAN=20 style=3D"FONT-SIZE: 12pt">Jim + Auditory-list While it is true = that=20 speakers are "designed" to be driven by the voltage, our detailed = research has=20 shown that it is the current that controls the pressure (i.e., force = on the=20 cone). If you want the details I already sent the links, but I'll send = them=20 once more, just in case you missed it. The theory of how the = current=20 drives the force is given by our ASA presentation from last month, at = the=20 special session on historic transducers: <A=20 href=3D"http://hear.ai.uiuc.edu/public/Allen/NK_ASA_Indianapolis.pdf"=20 target=3D_blank>http://hear.ai.uiuc.edu/public/Allen/NK_ASA_Indianapolis.= pdf</A> *=20 Kim and Allen (2014) Historic = transducers:=20 Balanced Armature Receiver (BAR), ASA meeting INDY, IN, = Oct 30,=20 2014 <A = href=3D"http://hear.ai.uiuc.edu/public/Allen/NK_ASA_Indianapolis.pdf"=20 target=3D_blank>pdf</A><o:p></o:p> <DIV> <SPAN=20 style=3D"FONT-SIZE: 12pt"> The full theory is in a Hearing Research=20 article: <A = href=3D"http://hear.ai.uiuc.edu/public/KimAllenMar20.13.pdf"=20 target=3D_blank>http://hear.ai.uiuc.edu/public/KimAllenMar20.13.pdf</A><B= R>* Kim,=20 Noori and Allen, J.B. (2013). "Two-port network Analysis and Modeling of = a=20 Balanced Armature Receiver, "Hearing Research, special MEMRO 2013 issue = (<A=20 href=3D"http://hear.ai.uiuc.edu/public/KimAllenMar20.13.pdf"=20 target=3D_blank>pdf</A>) Ms Kim's (i.e., Noori's) PhD thesis has = the most=20 complete story, and is available directly from her (<A=20 href=3D"mailto:noorimail@xxxxxxxx"=20 target=3D_blank>noorimail@xxxxxxxx</A>). Because it is the = current that=20 determines the pressure, via the electrical input impedance, and because = this=20 impedance can be (i.e., is) reactive (have inductance), it can be tricky = to=20 figure out what is going on. One must know (i.e., measure) the load = impedance,=20 or at least the current. Also the distortion is mostly determined by the = nonlinear flux vs current (i.e., B-H curve), as described by Hunt, for=20 example. Hunt mostly quotes Mott and Minor's BSTJ Jan 1951 article, = adding=20 little new material to their story. In the interesting case of = the=20 Etymotic ER-3 (insert headphone), they place a 10 ohm resistor across = the input=20 terminals. So if you try to beat this with a series resistor, you = will not=20 be successful in changing anything, because all the current is going = into that=20 10 ohm resistor. I opened up one of my ER-3 and cut out the resistor, = and=20 then I could see what was really going on. It worked better = too. When=20 that ER-3 went back for repairs once, they were shocked to see the = resistor was=20 missing. I had to admit I cut it out, and wanted it left that = way. In=20 general, adding a series resistor to your circuit, is working blind. You = will=20 likely get a random result, and random is never better. Thus I dont = advise it=20 unless you are willing to measure the input impedance and the resulting=20 frequency response of the headphone. While there are some interesting = things=20 you can do with a series impedance, a series resistor is not one of=20 them. Jont Allen<o:p></o:p> <DIV> <DIV> <SPAN=20 style=3D"FONT-SIZE: 12pt"> On 12/16/2014 06:12 PM, James W. = Beauchamp=20 wrote:<o:p></o:p></DIV></DIV></DIV> <BLOCKQUOTE style=3D"MARGIN-BOTTOM: 5pt; MARGIN-TOP: 5pt"> <DIV> <DIV><PRE>I agree with Bob. Most loudspeakers are = designed to be driven by<o:p></o:p></PRE><PRE>an ideal = voltage source. Under this criterion they attempt to get = <o:p></o:p></PRE><PRE>the flattest possible response = overall. This is not necessarily = <o:p></o:p></PRE><PRE>the most efficient response. In = fact, some loudspeaker designs, = <o:p></o:p></PRE><PRE>like the Small-Thiele closed-box = non-vented design, are very <o:p></o:p></PRE><PRE>inefficient.<o:p></o:p></PRE><PRE><o:p> </o:p></PRE><PRE>Jim<o:p></o:p></PRE><PRE><o:p> </o:p></PRE><PRE>Bob Masta = wrote:<o:p></o:p></PRE></DIV></DIV> <BLOCKQUOTE style=3D"MARGIN-BOTTOM: 5pt; MARGIN-TOP: 5pt"> <DIV> <DIV><PRE>From: Bob Masta <A = href=3D"mailto:audio@xxxxxxxx" = target=3D_blank><audio@xxxxxxxx></A><o:p></o:p></P= RE><PRE>Date: Sun, 14 Dec 2014 09:15:19 = -0500<o:p></o:p></PRE><PRE>To: <A = href=3D"mailto:AUDITORY@xxxxxxxx" = target=3D_blank>AUDITORY@xxxxxxxx</A><o:p></o:p></PR= E><PRE>Subject: Re: USB sound = cards<o:p></o:p></PRE><PRE><o:p> </o:p></PRE><PRE>On 13 Dec 2014 at = 21:59, Richard F. Lyon wrote:<o:p></o:p></PRE> <BLOCKQUOTE style=3D"MARGIN-BOTTOM: 5pt; MARGIN-TOP: 5pt"><PRE>On Sat, = Dec 13, 2014 at 5:52 AM, Bob Masta <A href=3D"mailto:audio@xxxxxxxx" = target=3D_blank><audio@xxxxxxxx></A> = wrote:<o:p></o:p></PRE><PRE><o:p> </o:p></PRE> <BLOCKQUOTE style=3D"MARGIN-BOTTOM: 5pt; MARGIN-TOP: = 5pt"><PRE>It's the other way around:  Adding resistance in = the<o:p></o:p></PRE><PRE>driving circuit gives poorer = damping.  "Damping Factor" = for<o:p></o:p></PRE><PRE>a power amplifier is the reciprocal = of output impedance.<o:p></o:p></PRE><PRE><o:p> </o:p></PRE></BLOCKQUOTE><PRE>Bob, I = wasn't aware of that = definition.<o:p></o:p></PRE><PRE>I was thinking of = <A href=3D"http://en.wikipedia.org/wiki/Damping_ratio" = target=3D_blank>http://en.wikipedia.org/wiki/Damping_ratio</A><o:p></o:p>= </PRE><PRE>rather than <A = href=3D"http://en.wikipedia.org/wiki/Damping_factor" = target=3D_blank>http://en.wikipedia.org/wiki/Damping_factor</A><o:p></o:p= ></PRE></BLOCKQUOTE><PRE>Oops, you are correct... I should = have said it is <o:p></o:p></PRE><PRE>*proportional* to = the reciprocal.<o:p></o:p></PRE><PRE><o:p> </o:p></PRE> <BLOCKQUOTE style=3D"MARGIN-BOTTOM: 5pt; MARGIN-TOP: 5pt"><PRE>Is there = an understanding of why high "damping factor" would be = good?<o:p></o:p></PRE><PRE>Jont's findings suggest otherwise = (I believe he's saying the current = is<o:p></o:p></PRE><PRE>typically more relevant than the = volage).<o:p></o:p></PRE></BLOCKQUOTE></DIV></DIV><PRE><FON= T size=3D2 face=3D"Courier New">The = second reference you cited covers it under = <o:p></o:p></PRE><PRE>"Explanation".  Basically, a = conventional electrodynamic <o:p></o:p></PRE><PRE>speaker is = both a motor and a generator.  Imagine that the = <o:p></o:p></PRE><PRE>speaker receives a momentary = voltage pulse, after which is <o:p></o:p></PRE><PRE>is = instantly disconnected from the source.  The speaker = <o:p></o:p></PRE><PRE>would ring at its resonant = frequency, damped only by <o:p></o:p></PRE><PRE>friction.  The generator would be creating a voltage, but = <o:p></o:p></PRE><PRE>no current, so no load to add = damping.<o:p></o:p></PRE><PRE><o:p> </o:p></PRE><PRE>However, if instead = of disconnection the leads were = <o:p></o:p></PRE><PRE>*shorted* after the pulse, the = generator would be driving <o:p></o:p></PRE><PRE>all its = current into the zero-ohm load, giving a maximum = <o:p></o:p></PRE><PRE>damping effect.  = <o:p></o:p></PRE><PRE><o:p> </o:p></PRE><PRE>Conventional = loudspeakers are designed to be driven by = <o:p></o:p></PRE><PRE>voltage sources, not current = sources. The current may be <o:p></o:p></PRE><PRE>more = "relevant" (in the sense of force generation), but not = <o:p></o:p></PRE><PRE>for getting a flat frequency = response from a conventional <o:p></o:p></PRE><PRE>speaker = design.  (Although there have been occasional = <o:p></o:p></PRE><PRE>attempts at current drive, the ones = I recall required <o:p></o:p></PRE><PRE>special dedicated = amplifiers.)<o:p></o:p></PRE><PRE><o:p> </o:p></PRE><PRE>Best = regards,<o:p></o:p></PRE><PRE><o:p> </o:p></PRE><PRE>Bob = Masta<o:p></o:p></PRE><PRE><o:p> </o:p></PRE><PRE>           D A Q = A R T A<o:p></o:p></PRE><PRE>Data AcQuisition = And Real-Time Analysis<o:p></o:p></PRE><PRE>          <A = href=3D"http://www.daqarta.com" = target=3D_blank>www.daqarta.com</A><o:p></o:p></PRE><PRE><F= ONT size=3D2 face=3D"Courier New">Scope, = Spectrum, Spectrogram, Signal = Generator<o:p></o:p></PRE><PRE>   = Science with your sound = card!<o:p></o:p></PRE></BLOCKQUOTE></BLOCKQUOTE> <SPAN=20 style=3D"FONT-SIZE: = 12pt"><o:p> </o:p></DIV></DIV> <SPAN=20 style=3D"FONT-SIZE: 12pt"> -- = <o:p></o:p> <DIV> <DIV> <SPAN=20 style=3D"FONT-SIZE: 12pt">James D. (jj)=20 Johnston<o:p></o:p></DIV> <DIV> <SPAN=20 style=3D"FONT-SIZE: 12pt">Independent Audio and Electroacoustics=20 Consultant<o:p></o:p></DIV></DIV></DIV></DIV></DIV></BO= DY></HTML> ------=_NextPart_000_0012_01D01AAF.18F87740--

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