Speaker Impedance

-------------------------

** Not much....

** For one like this?

.... Phil

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/

it was widespread in the 50s/60 here

yep :)

NT

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.

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 :-)

** 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 ?

high 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 o hms. 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 ty pe chip for the drive/control. The pound of silicon is cheap these days. Ju st 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 des ign, which is a more expensive solution, or maybe even one of those beryliu m heat pipes. (which doesn't really lend itself well to this application)

------------------------

** I was responding to the "fwiw" bit.

** Got a pair of those in your home stereo have you ?

..... Phil

ahh :)

Unfortunately mine are unmatched and not connected to a stereo. Stereo would give twice as many in-band resonant frequencies.

NT

Good point.

Yes, I was thinking more in these terms.

Remember, it's the real part of the impedance that makes noise (and heat).

No.

Assuming 0% distortion. Automotive amplifiers are typically rated to

10% distortion (most claim something around 49W). BTW, they're all full bridge. Half-bridge makes no sense.

They have the new fanged transistors called Metal Oxide Semiconductors.

If you didn't have a dick, you'd be a woman. Hmmm.

Clueless.

Because high-voltage semiconductors are expensive, too.

Double that, again, for a full bridge output.

Wrong.

-----------------------

** The "add 20% to the DC value " rule for nominal impedance has a breakdow n.

If you find the exact impedance minimum frequency, then the impedance value is perfectly resistive and it follows that components making up the value are also resistive - the reactive ones have self cancelled.

We all know the biggest component, voice coil resistance which accounts for about 80%.

The next is friction losses in the spider and surround, which accounts for about 10% closely followed by eddy current losses in the magnet structure.

Last and least is actual sound radiation at under 1%. Move the test frequency a little and the impedance rises due to motional ba ck emf OR voice coil inductance. Both these the effect of reducing current flow in the voice coil and so drive force which must de taken into account when designing the enclosure, crossover points etc.

.... Phil

own.

ue is perfectly resistive and it follows that components making up the valu e are also resistive - the reactive ones have self cancelled.

or about 80%.

r about 10% closely followed by eddy current losses in the magnet structure .

Nice, Thanks.

George H.

back emf OR voice coil inductance. Both these the effect of reducing curren t flow in the voice coil and so drive force which must de taken into accoun t when designing the enclosure, crossover points etc.

Do the math. 8.9 W into 8 ohms is 8.5 Vrms, 12 Vpk and 24 Vpp, thus

8.9 W is for a bridged amplifier.

Your figures are _already_ for a bridged amplifier.

For example TDA2005 in bridged configuration produces 20 W into 4 ohms with 14.4 Vdc and 10 % THD and 22 W into 3.2 ohms.

Such high THD allows a quite significant clipping i.e. non-sinus waveform.

A simple inverter would cost much less than a few high quality amplifiers it is feeding.

You assume a sine wave (i.e. 0% distortion).

Of course but that's reality.

Wrong.

8 ohms. Divide and multiply as needed, like 17.9 into 4 ohms, and so forth.

Double that, again, for a full bridge output. "

No, that is for a full bridge. That's right, half bridge only puts out 2.25 watts/8 ohms.

uch 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 y ou 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 bery lium heat pipes. (which doesn't really lend itself well to this application )"

"Wrong."

Which part ?

8.9 W is for a bridged amplifier. "

You beat me to it.

All of it.

If there are plain on conde drivers (woofers, midrange, tweeters) and you are lonly looking to drive a "nominal" impedance with the amp your are building so you roughtly know the load. I agree with Phil 1.2 times the DCR is a good estimate for Nominal. It will only be near the DCR at frequencies below the responate peek (FS) and also about an octave above. Then the inductance takes over and it rises.

For crossover design you need to account for the impedance in the range you are crossover over the drivers. One way is the use a R-C shunt across the coil to cancel the impedance rise with frequency and make the impedance look more flat and resistive. These are commonly called Zobels.

Once you identify the nominal impedance. Normal resistive parallel/series conbination rules apply for speakers operating on the same frequency range. If you put a properly desiged crossover between the woofer, mid and tweeter, then even though you have three "8 ohm" speakers in parallel, the total impedance remains 8 ohms since they do no operate in the same frequency range.