On Wednesday, December 20, 2017 at 10:34:44 AM UTC-5, k...@notreal.com wrote:> 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? ;-)Grin... It says 5210MWG midrange on it. https://www.ebay.com/itm/4-Generic-5210MWG-Replacement-Midrange-Speakers-PAIR-8-ohms-with-grills-/382219141906>Car speakers aren't 8-ohms, rather > 2-ohm (that V^2/R thing), usually.That makes sense, I said I know little of audio. :^) GH> > >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.
Speaker Impedance
Started by ●December 15, 2017
Reply by ●December 20, 20172017-12-20
Reply by ●December 20, 20172017-12-20
On 12/20/2017 12:21 AM, 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. > > 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. >Why do you care? Stated another way, "What are you gonna do with the information when you get it?" Isn't the impedance going to be critically dependent on the enclosure? And to a lesser degree, the acoustics of the room? 40 years ago, I experimented with trying to get a decent sounding speaker in a pickup truck and ended up using an amplifier with negative output impedance.
Reply by ●December 20, 20172017-12-20
On Wed, 20 Dec 2017 10:34:32 -0500, krw@notreal.com wrote:>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.With a "12 V" car battery voltage you can get about 4 Vrns output voltage from a half bridge, i.e. 0.5 W into 32 ohms or 8 W into 2 ohms. Some full bridge ICs claim 22 W into 4 ohms, requiring 14.4 V battery voltage (alternator maximum output voltage). With a DC/DC inverter power supply, the voltage swing and speaker impedance can be more freely selected.>>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. :^)At least the DIN standard specifies that the actual impedance at any frequency should be at least 80 % of the nominal impedance, agreeing well with Phil's rule of thumb.
Reply by ●December 20, 20172017-12-20
On Wed, 20 Dec 2017 03:40:30 -0800 (PST), tabbypurr@gmail.com wrote:>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.Martin is speaking perfect english. Has to do with powers of 2. Low-ish impedance speakers have typically been rated at an impedance that happens to be a power of 2... Like 2, 4, 8, 16, 32 Ohms. boB>> >> 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 > >At 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
boB wrote: -----------> > > >> > 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. > > > Martin is speaking perfect english. Has to do with powers of 2. > > Low-ish impedance speakers have typically been rated at an impedance > that happens to be a power of 2... Like 2, 4, 8, 16, 32 Ohms.** Wellll blow me down !!! That trick works even for 1 ohm speakers, cos 2exp0 = 1 But is purest sophistry. Nominal 6 and 12 ohm speakers are common too, it don't work for them. The "add 20%" rule is based on loudspeaker physics and always works for cone drivers that have impedance minima in the band from 250 to 400Hz. ..... Phil
Reply by ●December 20, 20172017-12-20
On Thursday, 21 December 2017 00:27:07 UTC, Phil Allison wrote:> boB wrote: > > ----------- > > > > > >> > 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. > > > > > > Martin is speaking perfect english. Has to do with powers of 2. > > > > Low-ish impedance speakers have typically been rated at an impedance > > that happens to be a power of 2... Like 2, 4, 8, 16, 32 Ohms. > > > ** Wellll blow me down !!! > > That trick works even for 1 ohm speakers, cos 2exp0 = 1 > > But is purest sophistry. > > Nominal 6 and 12 ohm speakers are common too, it don't work for them. > > The "add 20%" rule is based on loudspeaker physics and always works for cone drivers that have impedance minima in the band from 250 to 400Hz. > > > > ..... Phil5 ohm used to be very common fwiw. And before that 2k-ish. NT
Reply by ●December 20, 20172017-12-20
tabbypurr@gmail.com wrote:> > 5 ohm used to be very common fwiw. And before that 2k-ish.I used to see 3.2 ohm speakers, as well. That was back when the US still used ninnyfarads.
Reply by ●December 20, 20172017-12-20
>"The "add 20%" rule is based on loudspeaker physics and always works for cone drivers that have impedance minima in the band from 250 to 400Hz. "Sounds like a relatively crude approximation. Also, correct me if I am wrong, that impedance minima is still higher than the DC resistance I assume. I would find it very hard to believe there is enough EMF to make it go lower, but stranger things have happened. Like the tunnel diode that should not work.
Reply by ●December 20, 20172017-12-20
On Wed, 20 Dec 2017 17:40:47 -0800 (PST), jurb6006@gmail.com wrote:>>"The "add 20%" rule is based on loudspeaker physics and always works for cone drivers that have impedance minima in the band from 250 to 400Hz. " > >Sounds like a relatively crude approximation. > >Also, correct me if I am wrong, that impedance minima is still higher than the DC resistance I assume. I would find it very hard to believe there is enough EMF to make it go lower, but stranger things have happened. Like the tunnel diode that should not work.The impedance of any device must be (equal to or) higher than it's DC resistance or it's a battery. Why should a tunnel diode not work? Both the tunnel diode and speaker will have "negative (incremental) resistance region(s)" but there is nothing untoward about that.
Reply by ●December 20, 20172017-12-20
On Wed, 20 Dec 2017 20:51:46 +0200, upsidedown@downunder.com wrote:>On Wed, 20 Dec 2017 10:34:32 -0500, krw@notreal.com wrote: > >>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. > >With a "12 V" car battery voltage you can get about 4 Vrns output >voltage from a half bridge, i.e. 0.5 W into 32 ohms or 8 W into 2 >ohms. Some full bridge ICs claim 22 W into 4 ohms, requiring 14.4 V >battery voltage (alternator maximum output voltage).OK, you got the arithmetic right(ish). The typical car amplifier is more like 50W into a 2-ohm speaker.> >With a DC/DC inverter power supply, the voltage swing and speaker >impedance can be more freely selected.Obviously. What do you think a 400W boost regulator costs? What does it add to the cost of the car. What's the market? ...just to "freely select" speaker impedance. If more power is needed, 1-ohm speakers or dual voice-coil speakers (using two amplifier channels driven from the same source) are a lot cheaper.> >>>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. :^) > >At least the DIN standard specifies that the actual impedance at any >frequency should be at least 80 % of the nominal impedance, agreeing >well with Phil's rule of thumb.
