jurb...@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. >** A comment about "jurb" and not the physics of loudspeakers.> Also, correct me if I am wrong,** Believe me - YOU are wrong. .... Phil
Speaker Impedance
Started by ●December 15, 2017
Reply by ●December 20, 20172017-12-20
Reply by ●December 20, 20172017-12-20
tabb...@gmail.com wrote: -------------------------> > > > ** 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. > > > > > > 5 ohm used to be very common fwiw.** Not much....> And before that 2k-ish. >** For one like this? https://i.pinimg.com/originals/de/d5/7c/ded57c0a7403541ab8412995203a0b7d.jpg .... Phil
Reply by ●December 20, 20172017-12-20
tabb...@gmail.com wrote: -------------------------> > > > ** 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. > > > > > > 5 ohm used to be very common fwiw.** Not much....> And before that 2k-ish. >** For one like this? https://i.pinimg.com/originals/de/d5/7c/ded57c0a7403541ab8412995203a0b7d.jpg .... Phil
Reply by ●December 21, 20172017-12-21
<krw@notreal.com> wrote in message news:ck4m3dl14n550qbo1o60u8gh5hj5ktokja@4ax.com...> The impedance of any device must be (equal to or) higher than it's DC > resistance or it's a battery.Unless there's an impedance in parallel with the DCR, like capacitance. Fortunately, that doesn't happen to voice coils until well into the MHz (and even then, the valley is probably much higher than the DCR, due to other losses). Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: https://www.seventransistorlabs.com/
Reply by ●December 21, 20172017-12-21
On Thursday, 21 December 2017 03:04:06 UTC, Phil Allison wrote:> tabby wrote: > > ------------------------- > > > > > > > ** 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. > > > > > > > > > > 5 ohm used to be very common fwiw. > > ** Not much....it was widespread in the 50s/60 here> > And before that 2k-ish. > > > > ** For one like this? > > https://i.pinimg.com/originals/de/d5/7c/ded57c0a7403541ab8412995203a0b7d.jpgyep :) NT
Reply by ●December 21, 20172017-12-21
On Wed, 20 Dec 2017 21:01:49 -0500, krw@notreal.com wrote:>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.That sounds like some kind of PMPO power :-). 50 W sine into 2 ohms is 10 Vrms, 14,1 Vpk or 28.3 Vpp. Theoretically, this would require 28.3 Vdc half bridge or 14.1 Vdc full bridge power supply. For bipolars in (darlington)emiter follower configuration, add two Vbe drops for a half bridge or four Vbe drops in a full H-brudge configuration. At those currents Vbe might be in the order of 1 V, requiring 30 V resp. 18 V supply voltage. With a common emitter voltage amplifier stage at output, there will be one resp. two Vce(sat) drops. With Vce(sat) of 0.7 V, the power supply needs to be at least 29 V resp. 15.5 Vdc. These voltage levels are clearly out of the safe area for "24 V" resp "12 V" lead batteries.>> >>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.A 400 W DC/DC converter doesn't cost a lot (at least outside car audio outlets). Since that converter needs about 40 A current it should be installed into the engine compartment close to the car battery. This might add some cost due to the environment requirements. BTW, with the increased use of hybrids and full electric cars with high battery voltages for the electric motors, why not use the motor battery for also driving the audio amplifiers :-)
Reply by ●December 21, 20172017-12-21
>"** A comment about "jurb" and not the physics of loudspeakers.> Also, correct me if I am wrong,** Believe me - YOU are wrong. .... Phil " If you mean about the impedance, it certainly is not capacitance causing it. Or was just that you being Phil ?
Reply by ●December 21, 20172017-12-21
>"BTW, with the increased use of hybrids and full electric cars withhigh battery voltages for the electric motors, why not use the motor battery for also driving the audio amplifiers :-) " That would make them incompatible. Also in 24 volt systems there is usually a battery balancer if there is to be any 12 equipment run off it. In a nutshell, a nominal 12 volt supply will yield about 8.9 watts into 8 ohms. Divide and multiply as needed, like 17.9 into 4 ohms, and so forth. Looking at the DC convertor in a standard cat amp, it doesn't add that much cost on a manufacturing level. The transformer is cheap, you need a uPc type chip for the drive/control. The pound of silicon is cheap these days. Just a bunch of MOSFETs in parallel. the heatsinks cost more. heatsinks you got a tradeoff, either alot of aluminum or cheat with a high efficiency design, which is a more expensive solution, or maybe even one of those berylium heat pipes. (which doesn't really lend itself well to this application)
Reply by ●December 21, 20172017-12-21
tabb...@gmail.com wrote: ------------------------> > > > > > > > ** 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. > > > > > > > > > > > > > > 5 ohm used to be very common fwiw. > > > > ** Not much.... > > it was widespread in the 50s/60 here >** I was responding to the "fwiw" bit.> > > And before that 2k-ish. > > > > > > > ** For one like this? > > > > https://i.pinimg.com/originals/de/d5/7c/ded57c0a7403541ab8412995203a0b7d.jpg > > yep :)** Got a pair of those in your home stereo have you ? ..... Phil
Reply by ●December 21, 20172017-12-21
On Thursday, 21 December 2017 12:19:00 UTC, Phil Allison wrote:> tabby wrote: > > ------------------------ > > > > > > > > > > > ** 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. > > > > > > > > > > > > > > > > > > 5 ohm used to be very common fwiw. > > > > > > ** Not much.... > > > > it was widespread in the 50s/60 here > > > > ** I was responding to the "fwiw" bit.ahh :)> > > > And before that 2k-ish. > > > > > > > > > > ** For one like this? > > > > > > https://i.pinimg.com/originals/de/d5/7c/ded57c0a7403541ab8412995203a0b7d.jpg > > > > yep :) > > > ** Got a pair of those in your home stereo have you ?Unfortunately mine are unmatched and not connected to a stereo. Stereo would give twice as many in-band resonant frequencies. NT
