Stereo Question: Low power requirements?

[GMac]

Magnificent stuff Wheels and now Cam. I do like Wheels post just above this and are looking forward to stereo shopping. I've mates who have spent moonbeams on 'special wire', suckers

I love this thread.

[MidLandOne]

For those of us who are not deaf old roadies and have to make do with a simple head and a coupla automobile speakers rather than a zillion watts I just checked the current draw of our Alpine head to give an idea for mundane installations .

With 2 channels driven into 2 (yes only 2 ) Alpine 4 ohm speakers around 6-1/2 inch diameter in the saloon, head claimed 25 watt per channel (with all the warnings on that previously given). At turn on and minimum volume with head's tuner as source it draws approx 1 amp straight off. To get it drawing noticably higher current with a CD as the source I would have to evacuate the boat to save my ears .

[Alan Wheeler]

If this helps. The trick about speakers wires is size. The more current capacity the better. Clarity and bass response is a result of control of the speaker cone. When the amplifer says "move forward!" you want the cone to move forward, no delay. When the amplifier says "stop!", you want the cone to stop. But there is a slight problem. It's called inertia. Not only is the weight of the cone a concern, but the fact that you have a vast volume of air to start and stop moving. So the cone wants to resist movment and then wants to overshoot once it has moved. To control this, the output end has to have "grunt". This "grunt" is a result of the amplifiers design and is called dampning factor(DF). DF is measured as a resistance across the output connectors (with the amp turned off of course) and really good output stages will be measured in the range of points of an ohm. There is a formula that then uses this resistance measurement and the result is a value of DF. A DF of greater than 200 is good. Great in fact. However, if we now make that same measurement at the end of the speaker cable, the resistance will now be much lower(higher number) and even a resistance of say 2 ohms will blow the DF out of the water. The resistance in the cable results in a "spring" effect and the cone is not able to be controlled properly. Realise that the effort to move the cone is seen as current. It is easy to understand if you think of the system as water. The amplifier is the pump, the cable the hose. You may have found that when you place your finger over the end of the hose abruptly, you feel a pulse in the pressure. That is the momentum of the water causing the walls of the hose to expand and contract and the hose acts like a spring. The same happens with the current in the speaker wire. So the cone becomes uncontrolled. The only way to solve the problem is to use a wire large enough and short enough to keep the resistance low.

Now one other aspect can be added here. Lets say you have a resistance of 1 ohm measured across the ends of your cable. If you have one 8 ohm speaker on the end of the cable, then 7/8ths of the current is getting to the speaker, 1/8 is lost as heat in the cable. Now if you connect another 8 ohm speaker in Parrallel, you have a 4 ohm load. Now the amount of loss in the cable is quite a concern as 25% of the power is being disapated into the cable. If you then place a 2 ohm load on the cable, then 50% of that audio power is being lost in the cable.

OK, now add one other dimension. As you add more speakers in Parallel, the power output of the amplifier increase. Great you say...well no not totaly. So lets say we have 10W with an 8 ohm speaker. Making the load 4 ohm, the amplifier is still pushing the same voltage out as a signal, but the result (as can be shown in ohms law) is that the power now doubles to 20W. But remember the above about the loss in the cable. So you don't really get the full 20W. Now if we increase the load to 2 ohms, the power output doubles again and we get 40W. But remember the loss in the cable. Plus remember Watts is power, or "work done". this requires current. Current from both the power supply and the output device. The output device now has to work very much harder and is now powering out heat. Some amplifiers simply can not handle these loads. so you have to read the manual and see if it will handle 2 ohms. Oh and let me throw one other spanner into this now. The resistance of a speaker is actually called Impedance. Impendance is the same thing as resistance, but we use the term impedance because this is AC in a coil which creates a magnetic field. That magnetic field in the coil changes the impedance in relation to frequency. Impedance in an 8 ohm speaker could in fact drop to 4 ohms at some frequencies. A 4 ohm load can get closer to a short and a 2 ohm load does go down to points of an ohm loading. It also goes completely the opposite way as well. It can go into very high figures like 30 or 40 ohms. So at some times depending on the frequency, the output can go from low loads to extreme high loads, all placing effort on the output devices.
So to sum up, keep the loads within that of which the amplifier was designed for, or you may cause the output device to fail.
Keep speaker runs as short as you can, and as large a diameter as practicle.

[Zach]

Very interesting stuff!

So do I have this right that two otherwise identical speakers, one with 4 ohms impedance and the other with 8 ohms, the 8 ohm will be louder for the same power consumption?

If so... cool! Save half the power consumption just by speaker choice for the same db output.

Alan, in my quest to have my cake and eat it too... are there any tricks for reducing resistance over the wire run, besides shortening it or giving it a huge cross section?

Also, in my quest to rid all magnetic interference from my compass... does twisting each pair of speaker cables together effect the audio? On sensitive electronics, like car airbags. They twist the positive and negative together electrical interference doesn't trigger one accidentally. I've had some luck getting rid of ignition system hums on cars by twisting the speaker wires... but don't know if stops the speaker cable from radiating, or just from being effected by other sources.

Bummer. I was going to install the speakers beside the companionway... bad place to put two magnets! A few feet away from the compass.

[Alan Wheeler]

4 ohms impedance and the other with 8 ohms, the 8 ohm will be louder for the same power consumption?

No the other way around. Firstly, a rating on an amplifier will be stated as XPower into a load. So it maybe say..10W@8 ohm. Car Audio is always rated at 4 ohm. So if we have 10W@8 ohm, it will be 20W@4 ohm.
If you are using a Car Amp, it will stated as 10W@4 ohm, so when driving a 8 ohm speaker, it will only be 5W.
But then to complicate matters, the 4 ohm speaker may have been very inefficient and the 8 ohm speaker maybe very efficient and the SPL(sound pressure level) or loudness could be the same as the 4 ohm anyway. And the 8 ohm speaker may sound 10 times better than the 4 ohm.
If I made a mistake in the previous post in regards to that explanation, let me know and I will go back and correct it.

[camaraderie]

Zach...impedance in speakers is "nominal" in that the rating is really only an expression of what type amplification will be comfortable with it. The actual impedance in a given speaker varies by frequency. It really has nothing to do with loudness as a 4 ohm and an 8 ohm speaker with the same SPL rating will play equally loud for a given wattage input.
Example:


This plot of impeance vs. frequency is for a nominal 8 ohm rated speaker. As you can see...there is a dip to 6 ohms at 1049 Hz and this dip mght cause some problems for some amps especially if multiple pairs of this speaker were used. Nothing to worry about...just clarifying.

Wheels...loved your examples of smoke and mirrors. On speaker wire I think it is also important to get wire that consists of as many strands as possible in addition to the right gauge since electrons move on the surface area and this stranding enhances conductivity. But I agree in terms of not wasting big bucks on bogus claims. Other interesting "fixes" over the years include cryogenically freezing your CD's to align their atoms...coloring the edges of CD's with magic marker so light couldn't get in from the edges and distort the music! It was more fun in the analog days when some weird stuff actually did work!!

I agree with you on the additional power saving choice of MP3 devices vs. driving a CD in the car stereo. I have a Zune with 80Gigs myself and this is a very convenient way to get ALL my music on the boat or in the car. Perhaps for the benefit of those who have not yet gone this route, it should be noted that MOST car stereos today have some provision for getting MP3 music into them other than via CD.
1. A front or rear auxillary input jack allows you to plug in an Ipod or similar device into the stereo and use the IPOD to control what you hear.
2. IPOD Ready Car Stereos let you use an Ipod kit to plug in your IPOD and then you can read out songs, artists etc. on the radio itself AND control the IPOD from the radio. This is especially convenient if your radio has a remote control. (Note...such interfaces are almost exclusively IPOD based given their current dominance in the market)
3. Some few radios have a USB port on their face which allows you to download your music to a "thumb drive" and just plug and play.
*******

Now I'll rant for a moment if I may about the state of "sound" today. After 80 years of continuous progress in both home gear and studio recording...it seems as though we are going in the wrong direction. We have a massive shift to less fidelity in music as everyone goes over to MP3 files (yes...I know about lossless)...home speaker systems are dominated by crap "sub satellite" systems with awful sound quality that "fit anywhere"...home stereo receivers are dominate by IC based receivers that claim hundreds of watts of power to 7 channels and deliver nothing cleanly...while the recording studios turn out mostly over-produced, non-musical trash that you don't need a good system to listen to anyway!
The big box stores (Wal-Mart/Sams/BestBuy/CircuitCity) no longer even have decent listening environments and in most cases you can't even hear what you are buying!
It is tough to love music and good sound these days! (End rant)

[Alan Wheeler]

of as many strands as possible in addition to the right gauge since electrons move on the surface

No you need to add that to your snake oil list too. Only very high spectrum frequencies, as in RF and Microwave move on the surface of the wire. Called "Skin effect". Audio is way too low and moves through the entire cross section of the wire. Another snake oil remedy in the industry is using two sets of wires to the speaker. One for HF and one for LF. Apart from adding more cross sectional area to the run, it does not mean the two Freq range flow better down the cable.

[Alan Wheeler]

"sub satellite" systems with awful sound quality that "fit anywhere".

You've heard of Bose then huh? ;-) :-)

It is tough to love music and good sound these days!

Yep, we in the Live Audio industry spend Millions of dollars on our systems to achieve the best quality in soyund, so as the young ones can have clean clear distortion :-)

In regards to the Ipod stuff. I need to catch up. I have been retired for about 6 years now. I am waaay behind. But the industry changes dramaticly so fast.

Hey thanks heaps for posting that graph.

[camaraderie]

Alan...to take it to the extreme...are you saying that sonically, standard house solid Romex cable will be as good as stranded wire? (I understand the physical benefits of stranded). That would be an interesting A/B test!

As to my friends from The Mountain... "no highs...no lows...must be Bose" has always been a mantra with me...Though they are certainly not the worst offenders...I do credit them with starting this awful trend in speakers! Bring back the COFFINS to our living rooms!!

[Rick]

Alan is correct. Long has there been a misconception that "special" speaker wire can improve audio quality. As long as the resistance of the wire is ten times (or more) less than the resistance of the speaker no one would be able to tell any difference in audio quality. By the way, no one has been able to define a method to make a valid A-B comparison test in order to prove the assertion. Certainly if the wire resistance is quite high then poor audio quality will be discernable.

Comaraderie's speaker impedance plot is interesting yet in order to make a valid judgement of such data a plot showing reactance plus resistance along with a plot showing phase (both versus frequency) is required. If the phase changes rapidly versus frequency then complex frequency source components cannot be reproduced accurately. This concept is also true for all transmission lines and filters. Speakers that accurately reproduce complex sound components have what is called "linear-phase" characteristics versus the log of frequency.

Good amplifiers will not be affected by impedance changes normally exhibited by even poor quality speakers.

[hellosailor]

"We have a massive shift to less fidelity in music as everyone goes over to MP3 files"
Look at it this way, when all those kids eventually go deaf from cranking the music, they will be pleased at how little hearing they have lost compared to what they started with.[g]

Then again, I remember in the very early 70's procuring a terribly excpensive Philips CarryCorder and listening to mono cassettes in the middle of nowhere. And it sounded damn fine! Considering the alternatives.

Given the background noises in a car, or competing with earbuds, plain MP3 still beats whistling.

[Roy M]

Alright! Just the forum I've been looking for. I want to project a really, menacing sound track on a boat I am overtaking, something that will cause them to have weird shivers of ominous, impending doom. Something like Jaws. This is for club racing where the only rules that apply are physics and the Coast Guard regs. I don't even need exceptional fidelity, just the power to reach out there and let them know they are about to be taken astern. BWA-HA-HA-HA!

[camaraderie]

Rick... "Good amplifiers will not be affected by impedance changes normally exhibited by even poor quality speakers."
Aye...there's the rub!
Actually it has been my experience that some of the very best speakers require much better amplification than some of the worst. But as a practical matter, there is not much on the shelves of mass merchants in speakers and receivers today that will not work decently together from an electrical standpoint. Sound wise...it is another story.

Transmission lines, linear phase response...and a host of other interesting topics used to be "everyday" topics in the POPULAR priced stereo market. Now such discussions are limited to small bands of audio geeks and limited to equipment that forces a choice between sailing and sound! (Just exaggerating a little bit!) Did home theater kill our passion for sonic excellence?

[Zach]

Originally Posted by Roy M

Alright! Just the forum I've been looking for. I want to project a really, menacing sound track on a boat I am overtaking, something that will cause them to have weird shivers of ominous, impending doom. Something like Jaws. This is for club racing where the only rules that apply are physics and the Coast Guard regs. I don't even need exceptional fidelity, just the power to reach out there and let them know they are about to be taken astern. BWA-HA-HA-HA!

How about the cannon ball firing part of the 1812 overture? Da dun dun da da dun da DAA DA BOOOM BOOM BOOOM.

But I'd just give the guy on the pointy end a Megaphone to scream "NOOO INSURANCE!"

[Alan Wheeler]

define a method to make a valid A-B comparison test in order to prove the assertion.

That has been a major issue and a major way of pulling the wool over a customers eyes in a shop. The closest "best test" approach we have is a double blind test. That means no one knows what is tested when and so no influence can be played on the listener.

along with a plot showing phase (both versus frequency) is required.

Wow!!!!! Rick. Your not just a pretty face. Folks, this is the Holy grail. This is the issue. Phase alignment and relationship. 10yrs ago, this was the area we were at in cutting edge understanding of sound. To have a perfect speaker, it would be called a "point source". In other words, all sound would eminate from one point in space. Of course, it can't be done. No one speaker can reproduce the entire audio spectrum perfectly. So multiple speakers are required to cover the range. The more drivers, the more you spread the Audio out over an area. Then the more sound power you want, the more speakers you need and then the audio gets spread out further and further and the most important aspect of sound, goes out the window. It's called Time. Over the last 10years I worked with some truely amasing speakers and on some amasing projects. The result today is we now have arrays of speakers that are closer to point source. These arrays are called Line Arrays. If you go to a concert, you will now see long verticle lines of speakers hanging each side of the stage. There are some amazing tricks going on with processers and boxes to get the sound to do what we want. There are even "stearable" arrays now. You have a colum of speakers and a processer can tune the array in such a way as to stear the sound in the direction you want it. I and one other guy were the first (that we know of) to use time to create a sound stage in space. When I mean "sound stage" I mean the sound to the audiance should mimic position as it is on stage. If a guitar is stage left, it should sound like it is coming from the left. Easy to do if you are a listener standing in the centre of the stage, but if you are standing extreme right of the stage, you will never hear the Guitar. So we have the Guitar equal in SPL from both right and left speakers and shift the guitar by time alignment. This is exactly how you hear in a "stereo" manner. You can locate sound because you hear in one ear a fraction of a second before the other and the sound comes from a position. Well by using time, we can shift that position to the listener.
But anyway, I am way of track here.
so you want to scare the pants off the boat in front. Well it can be done. To what affect is limited by money. But in a nutshell, speakers that can trow sound some distance sound plain horible close up and speakers that sound great close up are terrible far away. Close up speakers like home HiFi stuff are considered "near feild" speakers. The other issue you are going to have is power. Loudness comes at a cost of power and so you need to have battery reserve to power the amplifier/s.