I have one test instruments to test with, a VOM. I have several old speakers that I want to hook up to a amp I am trying to build. How do I determine the impedance of the speakers with only a VOM ? What value of resistance would I measure across the speaker coil for different speaker impedance of say 4 or 8 or ? and other ohm speaker impedance ? Is there a table someplace ? TIA
Speaker Impedance
Started by ●December 15, 2017
Reply by ●December 15, 20172017-12-15
OGee wrote: ---------------> > I have one test instruments to test with, a VOM. > > I have several old speakers that I want to hook up to a amp I am trying > to build. > > How do I determine the impedance of the speakers with only a VOM ? > > What value of resistance would I measure across the speaker coil for > different speaker impedance of say 4 or 8 or ? and other ohm speaker > impedance ? >** The "nominal impedance" of a moving coil speaker is 20% higher than the coils's DC resistance.> Is there a table someplace ?** No need for one. .... Phil
Reply by ●December 20, 20172017-12-20
OGee wrote:> I have one test instruments to test with, a VOM. > > I have several old speakers that I want to hook up to a amp I am trying > to build. > > How do I determine the impedance of the speakers with only a VOM ? > > What value of resistance would I measure across the speaker coil for > different speaker impedance of say 4 or 8 or ? and other ohm speaker > impedance ? > > Is there a table someplace ? > > TIAResistance will always be a few ohms or less, WAY below "impedance" which is literally a complex function of frequency , amplitude, loading, and speaker environment. One "preferred" measurement method was to use a 1KC signal; one point of thousands; totally misleading and almost useless. Just connect each one in its own preferred environment (box, baffle, boffle, horn, etc) and listen to it where you would like to place it (living room, bedroom, car, concert all, etc.). The ear is one of the better test instruments.
Reply by ●December 20, 20172017-12-20
Robert Baer wrote: ---------------------> OGee wrote: > > > I have one test instruments to test with, a VOM. > > > > I have several old speakers that I want to hook up to a amp I am trying > > to build. > > > > How do I determine the impedance of the speakers with only a VOM ? > > > > What value of resistance would I measure across the speaker coil for > > different speaker impedance of say 4 or 8 or ? and other ohm speaker > > impedance ? > > > > Is there a table someplace ? > > > > TIA > > > Resistance will always be a few ohms or less, >** Ignorant bullshit.> WAY below "impedance"** FYI fuckhead - the OP was after the "nominal impedance". What you see quoted in data sheets and printed on drivers.> which is literally a complex function of frequency , amplitude, loading, > and speaker environment.** Not at 400Hz it fucking isn't. Your ignorance is only exceed by your stupidity.> > Just connect each one in its own preferred environment (box, baffle, > boffle, horn, etc) and listen to it where you would like to place it > (living room, bedroom, car, concert all, etc.). > > The ear is one of the better test instruments. >** Time for you to go home Bob, the nice men in white coats are calling you to dinner. .... Phil
Reply by ●December 20, 20172017-12-20
On 20/12/2017 08:21, Robert Baer wrote:> OGee wrote: >> I have one test instruments to test with, a VOM. >> >> I have several old speakers that I want to hook up to a amp I am >> trying to build. >> >> How do I determine the impedance of the speakers with only a VOM ? >> >> What value of resistance would I measure across the speaker coil >> for different speaker impedance of say 4 or 8 or ? and other ohm >> speaker impedance ? >> >> Is there a table someplace ? >> >> TIA> Resistance will always be a few ohms or less, WAY below "impedance" > which is literally a complex function of frequency , amplitude, > loading, and speaker environment.It isn't always way below the complex impedance. The resistive component at DC is usually as low as it ever gets and the frequency dependent reactive components add to it. It shouldn't depend on amplitude unless you are saturating the magnetic components or about to blow the fuse. If you measure it on DC and round up to the next power of two in ohms you won't be that far off the nominal impedance. It does vary a lot with frequency depending on the crossover network and drivers used. The OP might find the Wiki entry on loudspeakers nominal impedance helpful: https://en.wikipedia.org/wiki/Electrical_characteristics_of_dynamic_loudspeakers When you look and the |Z| and phase response of some hifi speakers it is surprising that they work at all. B&W 802D a case in point - nominally a 8 ohm speaker with excursions <4 ohm and >20ohm around 2-3kHz crossover. https://www.stereophile.com/content/bw-802d-loudspeaker-measurements> One "preferred" measurement method was to use a 1KC signal; one point > of thousands; totally misleading and almost useless.Using a continuous tone sine wave at real power into a loudspeaker is a good way to kill it if you hit a resonance. Real speaker tests are done by sweeping sufficiently quickly not to allow a resonance to build up or more usually with narrow bandpass pink noise.> Just connect each one in its own preferred environment (box, baffle, > boffle, horn, etc) and listen to it where you would like to place it > (living room, bedroom, car, concert all, etc.). > > The ear is one of the better test instruments.The ear is surprisingly easily tricked. An oscilloscope or spectrum analyser is much less easily fooled. -- Regards, Martin Brown
Reply by ●December 20, 20172017-12-20
Martin Brown wrote: ---------------------- ( snip some metal patient's garbage)> > > It isn't always way below the complex impedance. The resistive component > at DC is usually as low as it ever gets and the frequency dependent > reactive components add to it. It shouldn't depend on amplitude unless > you are saturating the magnetic components or about to blow the fuse. > > If you measure it on DC and round up to the next power of two in ohms > you won't be that far off the nominal impedance.** You need to explain the "next power of two" bit - cos it reads like pure gibberish. The correct procedures are to find the lowest, resistive impedance with a sine wave test in the mid frequency band OR just add 20% to the DC reading. This for a cone loudspeaker driver tested *on its own* - NOT a system or some other contraption like a horn driver.> Using a continuous tone sine wave at real power into a loudspeaker is a > good way to kill it if you hit a resonance.** You have posted this drivel before, it is still wrong and always will be. .... Phil
Reply by ●December 20, 20172017-12-20
On Wednesday, 20 December 2017 09:53:52 UTC, Phil Allison wrote:> Martin Brown wrote: > > ---------------------- > > ( snip some metal patient's garbage) > > > > > > > It isn't always way below the complex impedance. The resistive component > > at DC is usually as low as it ever gets and the frequency dependent > > reactive components add to it. It shouldn't depend on amplitude unless > > you are saturating the magnetic components or about to blow the fuse. > > > > If you measure it on DC and round up to the next power of two in ohms > > you won't be that far off the nominal impedance. > > > ** You need to explain the "next power of two" bit - cos it reads like pure gibberish. > > The correct procedures are to find the lowest, resistive impedance with a sine wave test in the mid frequency band OR just add 20% to the DC reading. > > This for a cone loudspeaker driver tested *on its own* - NOT a system or some other contraption like a horn driver. > > > > > Using a continuous tone sine wave at real power into a loudspeaker is a > > good way to kill it if you hit a resonance. > > > ** You have posted this drivel before, it is still wrong and always will be. > > > .... PhilAt resonance, impedance rises quite a lot, much reducing power draw. Speakers don't have enough in-band resonance to destroy themselves, or they'd not be reliable or acceptable sounding in use. Excluding outliers like 1920s moving iron speakers etc. NT
Reply by ●December 20, 20172017-12-20
On Wednesday, December 20, 2017 at 3:21:29 AM UTC-5, Robert Baer wrote:> OGee wrote: > > I have one test instruments to test with, a VOM. > > > > I have several old speakers that I want to hook up to a amp I am trying > > to build. > > > > How do I determine the impedance of the speakers with only a VOM ? > > > > What value of resistance would I measure across the speaker coil for > > different speaker impedance of say 4 or 8 or ? and other ohm speaker > > impedance ? > > > > Is there a table someplace ? > > > > TIA > Resistance will always be a few ohms or less, WAY below "impedance"I've got two speakers in my lab. small '32 ohm' Resistance = 30 ohms. Car size speaker, '8 ohms', R = 7.3 ohms. I know little of audio stuff, but I'm thinking Phil A's 'rule of thumb' of adding ~20% to the resistance measurement is sound advice. :^) George H.> which is literally a complex function of frequency , amplitude, loading, > and speaker environment. > > One "preferred" measurement method was to use a 1KC signal; one point > of thousands; totally misleading and almost useless. > > Just connect each one in its own preferred environment (box, baffle, > boffle, horn, etc) and listen to it where you would like to place it > (living room, bedroom, car, concert all, etc.). > > The ear is one of the better test instruments.
Reply by ●December 20, 20172017-12-20
On Wed, 20 Dec 2017 06:41:30 -0800 (PST), George Herold <gherold@teachspin.com> wrote:>On Wednesday, December 20, 2017 at 3:21:29 AM UTC-5, Robert Baer wrote: >> OGee wrote: >> > I have one test instruments to test with, a VOM. >> > >> > I have several old speakers that I want to hook up to a amp I am trying >> > to build. >> > >> > How do I determine the impedance of the speakers with only a VOM ? >> > >> > What value of resistance would I measure across the speaker coil for >> > different speaker impedance of say 4 or 8 or ? and other ohm speaker >> > impedance ? >> > >> > Is there a table someplace ? >> > >> > TIA >> Resistance will always be a few ohms or less, WAY below "impedance" > >I've got two speakers in my lab. >small '32 ohm' Resistance = 30 ohms. >Car size speaker, '8 ohms', R = 7.3 ohms.What is "car size"? 4000lbs? ;-) Car speakers aren't 8-ohms, rather 2-ohm (that V^2/R thing), usually.>I know little of audio stuff, but I'm thinking Phil A's >'rule of thumb' of adding ~20% to the resistance measurement >is sound advice. :^) > >George H. > >> which is literally a complex function of frequency , amplitude, loading, >> and speaker environment. >> >> One "preferred" measurement method was to use a 1KC signal; one point >> of thousands; totally misleading and almost useless. >> >> Just connect each one in its own preferred environment (box, baffle, >> boffle, horn, etc) and listen to it where you would like to place it >> (living room, bedroom, car, concert all, etc.). >> >> The ear is one of the better test instruments.
Reply by ●December 20, 20172017-12-20
On Wednesday, 20 December 2017 09:21:09 UTC, Martin Brown wrote:> When you look and the |Z| and phase response of some hifi speakers it is > surprising that they work at all. B&W 802D a case in point - nominally a > 8 ohm speaker with excursions <4 ohm and >20ohm around 2-3kHz crossover. > > https://www.stereophile.com/content/bw-802d-loudspeaker-measurementsLooks fairly tame. It's moving iron speakers your statement does apply to, but even they can produce fairly clear speech. NT
