Whats the differance in impedance in ohms of a speaker? - Page 1
Forum section: electronics / beginners

author: yada
author_rank: Frequent Contributor
timestamp: May 01, 2017, 12:26:29 am
content: Are henry's and ohms of a speaker the same thing? I realize that a four ohm speaker has a much difference resistance in ohms (resistance that's turned to heat as opposed to turned into magnetic force), but is this ohms rating at a standard frequency? Can they be converted?

author: retrolefty
author_rank: Super Contributor
timestamp: May 01, 2017, 12:40:29 am
content: Best to go (back?) and study basic AC theory, it really helps to unravel these kinds of questions.The Ohm can be a measurement of resistance as in a DC circuit but an Ohm is also a measurement of reactance in an AC circuit, called it's impedance. Reactance is it's DC resistance + it's either capacitance or inductive reactance. Your speaker will have a DC resistance less then it's rated impedance, the additional amount the results of the inductive value of the voice coil. A 4 ohm rated speaker will not measure as 4 ohms of DC resistance.

author: Paul Price
author_rank: Super Contributor
timestamp: May 01, 2017, 12:41:24 am
content: A voice coil is a cylinder of copper wire wound on an insulating form made of paper or plastic. This voice coil is closely suspended around a magnetic core that the voice coil moves towards or away from. This means the inductance of the voice coil changes with the coils position and is not constant, The voice coil has a copper loss resistance that stays fairly constant but has a fairly large temperature coefficient that causes the resistance to vary with high volume levels, but slightly, but this copper resistance gives you ohms reading of a speaker. Because there is also inductance and resistance present in speaker impedance, an ohm meter would almost always read something less, but close to the speakers ohm spec.The voice coil is relatively few turns of wire, and without being suspended in the magnetic core, would be in the uH range, but the magnet the coil is very closely magnetically coupled with would bring the inductance up into the mH range.

author: yada
author_rank: Frequent Contributor
timestamp: May 01, 2017, 12:52:15 am
content: Its a linear motor. So how does this match up to your amplifier? Does the amp have to compensate differently to match the current to the voltage? I thought house speakers were higher ohms because they are higher voltage, easier to step down from 110 or 220. Where as car amps are higher current because they are sourced at 12v?When you see old speakers that are only 10 watts but are the same db as newer 100 watt speakers why do they make them *less efficient now? Or is it because you would have better mid bass response because more energy can match the cone closer to the sound? Why not use a more efficient speaker and a bigger amp?

author: Paul Price
author_rank: Super Contributor
timestamp: May 01, 2017, 01:20:23 am
content: Car radio speakers are lower impedance because there is only 12V approx for the output amp to work with using an audio power amp chip. Since W=(E*E)/R, the lower the impedance of the speaker, the greater the power that can be delivered with only a 12V supply.Home speakers have power supplies that step down the 120/240 line voltage to 15 to 60V depending on the power of the amplifier so higher impedance speakers can be used.The efficiency of a speaker depends on the quality of the construction materials and also to a great deal on the size of the magnet used. Increasing efficiency means increasing magnet size and increased cost to make.Since is cheaper to create an audio power amp chip that delivers voltages to a speaker much greater than 12V, but at a lower current, higher impedance speakers also help to keep cost down while efficiency may be not be the design goal as much as lowering overall cost.When you talk about matching cones to matching "cone closer to sound" I am totally astonished by this unexpected comparison.And I agree with you, "Why not use a more efficient speaker and a bigger amp". Sounds good to me.

author: ebclr
author_rank: Super Contributor
timestamp: May 01, 2017, 01:24:06 am
content: Impedance, Consider the resistive, Inductive and capacitive components.

author: Paul Price
author_rank: Super Contributor
timestamp: May 01, 2017, 01:35:55 am
content: Although an older 10W speaker could maybe create the same dB loudness as a 100W speaker today, not all specs for speakers are honest and the comparison may not be valid.Pushing 100W of audio power into the 10W speaker would burn out the 10W speaker even if the 10W speaker is a more efficient speaker in delivering the same dB rating.But the 100W speaker would obviously be able to create much more deaf-making dB's than the 10W speaker when driven to its full rated power.

author: Brumby
author_rank: Unknown
timestamp: May 01, 2017, 02:27:09 am
content: Quote from: Paul Price on May 01, 2017, 01:35:55 amYou're talking about sensitivity - which is something quite different.

author: Electro Fan
author_rank: Super Contributor
timestamp: May 01, 2017, 02:46:30 am
content: Quote from: Brumby on May 01, 2017, 02:27:09 amYes, efficiency and sensitivity are sometimes used interchangeably but there are some distinctions. Speaker performance is impacted by not only electrical design but also by acoustical design. The size of a cabinet and the design of the cabinet (for example ported vs acoustic suspension) will impact how many watts are required to achieve a particular sound pressure level. A common measurement is to determine how many dB will be produced at 1 meter from the speaker with 2.83 Volts of input to the speaker.http://www.audioholics.com/loudspeaker-design/loudspeaker-sensitivity

author: edpalmer42
author_rank: Super Contributor
timestamp: May 01, 2017, 03:27:49 am
content: The impedance of a speaker is a very slippery concept. If you plot the impedance of a speaker (particularly a woofer) vs. frequency, it looks like a mountain range. There is no consistency whatsoever. Part of that is due to the enclosure and the effect it has on the speaker. Bass reflex? Acoustic suspension? Horn? Yes, there are a few horn woofers. So you look at the graph, squint, and pull a number out of midair and say that it's an 8 ohm speaker. This has little to do with the DC resistance of the coil.The amplifier doesn't know what the speaker impedance is, it just drives as hard as it can and hopes for the best. It's designed to drive almost any speaker. The limitation is that as the impedance drops, the amp has to put out more current. At some point, it runs out of room and the output clips or does some other ugly thing. Maybe a fuse blows. In the days of tube amplifiers, they often had different output terminals for different speaker impedances. This helped balance the output to the speaker which was more important for tubes. Tube amps can't put out as much power as transistor amps can, so the speakers had to be more efficient.The biggest thing that affects speaker efficiency is the enclosure. A horn is the most efficient, followed by bass reflex, then acoustic suspension. If a horn needs one watt to reach a particular loudness, an acoustic suspension might need 20 or 50 watts for the same loudness. That's why large outdoor venues often use horns. They need lots of sound! In your home, efficiency doesn't matter. The frequency response, dispersion, even the look of the thing, are more important.Ed

author: Keicar
author_rank: Regular Contributor
timestamp: May 01, 2017, 05:14:15 am
content: Quote from: edpalmer42 on May 01, 2017, 03:27:49 amYep, this hits the nail on the head with regard to 'nominal impedance' - I guess at best the nominal impedance suggests that an amplifier that is happy driving a resistive load of the same value should also be able to drive the speaker in question without tears, hopefully...Cheers,Karl.

author: Assafl
author_rank: Frequent Contributor
timestamp: May 01, 2017, 07:35:46 am
content: Quote from: Paul Price on May 01, 2017, 01:35:55 am)Actually it is usually better to drive a 10W multi driver speaker with a 100W amplifier than vice versa.The reason is that given a low sensitivity 100W speaker, you are likely to drive the 10W amp to clipping. Clipping causes a square wave which has lots of power in the tweeter range. Since a well designed speaker accounts for maybe 1% (at most) of total power to the tweeter - so now you'll have more than the maximum of 1W into the tweeter. Sadly for the tweeter, most people would not notice the distortion (way up in frequency) - and the tweeter will eventually fry. If you are lucky, expensive tweeters will have ferrofluid on their coils which may save your tweeter (or cost more to recone...BTW - in the alternate scenario - if you were to abuse the 10W speaker by increasing the volume above 10W using the 100W amplifier - your woofer would exceed Xmax - and that woofer flapping banging distorted sounds awful - making most listeners lower the volume to where distortion stops; however - having someone leave the volume knob at 100% will probably destroy your loudspeaker - hence it is better to have a 25W amplifier drive a 10W speaker.NB - This was the original reason for the difference between RMS and the awful "musical power" ratings (so common in the British audio industry in the 70-80's). The idea was that - by way of example, a 10W RMS amplifier (i.e. rated for 10W continuous power) would not distort - say - until the voltage levels of a 25W amplifier. So the tweeter would be spared. If however, you were to run the amp at 25W over a continuous time - the output devices or fuses would probably fry.Over time these numbers became just marketing numbers for boom-boxes with no real design purpose as part of the disintegration of the audio industry into its current, cynical pseudo-technical marketing stance.

author: Zero999
author_rank: Super Contributor
timestamp: May 01, 2017, 09:01:28 am
content: Quote from: Assafl on May 01, 2017, 07:35:46 amYes, and you know where the worst place on the Internet to learn about electronics is? An audio forum. There may be a few genuinely knowledgable people but unfortunately there are loads more clueless people who regurgitate marketing wank with the best of intentions.

author: Assafl
author_rank: Frequent Contributor
timestamp: May 01, 2017, 03:03:42 pm
content: Quote from: Hero999 on May 01, 2017, 09:01:28 amDIYAudio is pretty good...