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Why 2 ohms is not a good idea..

#121
I'm in agreement with Bob. 2Ω is just a standard impedance. I don't think twice connecting 2Ω loads to my equipment. The amps are designed to handle loads like that. I have run with 8 gauge cables and speakons for as long as I can remember. Never had a problem, never had an issue of any kind. One of my cables is about forty feet in length. I use it when I want to run one of my 4Ω cabinets on the other side of the stage. The cable has never felt anything but cold to me and any drop in volume is not noticeable.

I too have had my share of SS amps with burned out output stages. Most of them from 4Ω loads. You simply cannot blame a speaker cabinet impedance for the pathetic designs of some "professional" amplifiers.

Back in the seventies I designed my first SS power amp. Those were the days when that old crappy tube technology was on it's way out the door. I wanted 4Ω capability so I conservatively designed it for 2Ω. 200W/channel dual mono design. It will happily drive a 1Ω load at 270W per channel.

A few years down the road we'll be reading posts like "can I run my Little Mark X at 0.5Ω or should I only use the recommended 1Ω like it says in the manual?"

Paul
 
#122
Earwaxsculptor said:
It seems that a few people need to get a better understanding of Ohm's law in general before stating that a cable gobbles up "X" number of watts etc etc....

There are too many variables that would come into play before anybody can say anything about what is going on in a cable between any said amp and it's perceived load.
Click to expand...

Well, you CAN know the proportion. You'd know more if you knew the watts, or better, the current at all times........ if you are interested....... I thought it was about music anyhow.........

The really low impedances do have problems. The losses in non-speaker areas DO go up, in proportion to the current squared..... so halving the impedance causes the current to double, and the "loss per ohm" to go up by 4 times. There are sound reasons for NOT doing that, based on losses, heat, trying for better efficiency, etc.

On the other hand, it does allow getting given power with lower (safer?) voltage... so.....
 
#123
chicago_mike said:
All you guys who want 1200watts into a 2 ohm load...

I hope you know what you're asking.

1. You do know you lose 1/4 of your amps power thru the speaker cable itself right? Roughly 250watts..into nothing. You only lose 1/16th at 8ohms. We are talking speaker cable lengths less than 3 feet. And what happens if you blow a speaker? 2 Ohms is almost a dead short...NOT GOOD.

Dont use anything less than 10guage if your cable is over 1 foot in length. Yes..1 foot.

Think why your speaker cable gets warm..its a resistor.

2. your transformer has to be able to handle SAFELY over 2 amps consumption. 1 amp consumption is 450 watts. 2 Amp consumption is roughly 1200 watts.

I understand wanting more power..but its about clean SAFE power.

There are many more reasons, but I have seen so many posts about the intrest of high wattage low load output and I get concerned for the safety of my fellow lowenders.
Click to expand...

That's so out to lunch that it defies profanity.

And there's a staggering lack of knowledge in some of the replies.

(Apologies if I'm repeating previously-posted info; I didn't have the stomach to read all the posts.)




One principle is that your cable resistance shouldn't exceed 1% of your cab's impedance, that the cable resistance can then be essentially ignored. That's an EXTREMELY paranoid principle for this application, but does give interesting numbers. I've also tabled cable footages for 10% of the 2 ohm cab impedance. Sorry for the poor formatting.


gauge____feet for 0.02 ohms____for 0.2 ohms
6________21.5________________215.1
8________13.5________________135.3
10________8.5_________________84.7
12________5.3_________________53.5
14________3.4_________________33.7
16________2.1_________________21.1
18________1.3_________________13.3
20________0.8__________________8.4
22________0.5__________________5.3
24________0.3__________________3.3
26________0.2__________________2.1
28________0.1__________________1.3

I included foolishly small gauges due to some of the worries I read about fine spider & internal cab wires. And the foolishly large ones for OP's cabling desires.
 
#124
JustDavid, I didn't read 'em all either, but spot-checking your numbers against some of my measurements I think your numbers are if anything on the conservative side; in other words, I think the losses are even less than what you show.

Now one factor that might be of significance in some applications is the inductance that arises from the twisted wire in the cable. If the speaker doesn't have an offsetting inductive rise to its impedance curve, cable inductance can result in some loss of high frequencies. But that's unlikely to be an issue in a bass cab.
 
#125
Jerrold, I don't think lower voltages on your speaker cables is that big a deal. I don't think too many musicians have blowed their asses off playing with speaker leads.

The problem we bassists run into is the manufacturers have drifted away from 16 Ohm speakers in the last 30 years to favoring 8's and 4's. Of course as our needs of power increased, the need for better performance thermally developed compared to the old 32 Ohm SVT speakers for instance.

We are still parallelling up 4 speakers or 8 or multiple cabs of 8... The end result is 2 ohm loads or the need to go lower.

So we either cure this problem with multiple channels of "Smaller" amplifiers or find ways to drive lower impedance loads with larger machines.

Of course 4000 and 8000 watt amplifiers are available, (very spendy) but to get workable speaker load impedance is tougher than ever.

BOB
 
#127
rbonner said:
Jerrold, I don't think lower voltages on your speaker cables is that big a deal. I don't think too many musicians have blowed their asses off playing with speaker leads.

The problem we bassists run into is the manufacturers have drifted away from 16 Ohm speakers in the last 30 years to favoring 8's and 4's. Of course as our needs of power increased, the need for better performance thermally developed compared to the old 32 Ohm SVT speakers for instance.
Click to expand...

I don't either.

But......

Take 1200W, which is very 'normal" to find in an amp these days......

at 2 ohms, the voltage is about 50V rms. The safety agencies would say that is "hazardous", but it's really not so bad.

at 4 ohms, the voltage is 70 volts rms..... starting to get to where it can give you a good jolt.

at 8 ohms, almost 100V, which is mains voltage in some countries. obviously a potential issue.

At 16 ohms, 1200 watts corresponds to 138V rms, which is higher than US mains voltage. Any safety agency would say that needed to be in a plug like a Speakon, or other 'safe" plug with non-accessible contacts.

100V would be viewed the same way, and at 16 ohms, is "only" 600W. lots of 600W amps around.

The whole thing comes about because while a tube amp can have its transformer wound for almost any voltage, an SS amp has limits because the transistors need to be rated for at least 3X the output rms voltage.

So speakers have gotten to be lower and lower impedances to allow high power with reasonable voltage ratings.

The electric company goes the OTHER way...... they distribute power at high voltage because it is more efficient. Ditto for the "70volt" PA systems used for many applications.

You will pretty much always have larger losses when the same power is sent at lower voltage. 8 ohm, and 4 ohm speakers are likely in teh 'sweet spot" for sensible voltage and yet less loss.

Two ohms is pretty much at the inefficient end of the range. But there isn't anything dangerous about it if the amp is rated for it.
 
#128
Duke, I grabbed the resistance per foot off a reputable-looking site on the 'net & Excelled it up. Measuring is good, but this low a resistance can be hard to measure; how clean the meter leads are can even become a factor.

I agree on your 2nd point; cable inductance & capacitance aren't big factors in short-ish runs to single-digit ohm loads.
 
#132
http://www.audioholics.com/education/cables/speaker-cable-gauge

image.jpg


Recommendations in this article pretty much are what I posted on the first page.
 
#136
two fingers said:
Dude! There is NO good reason for you to have a 100' cable between your head and cab. Even if you don't understand (or believe) any of the stuff being talked about here. Get a freakin 6' cable and be done with it. If you are pulling down any serious amount of watts, a coiled up 100' foot cable for your bass head and cab STACKED ON TOP OF EACH OTHER (even from a performace angle) is just....(trying to be friendly) ........... (trying to be really friendly)............ um.........................(don't say it).......................dumb. :scowl:

Sorry....I tried.......I couldn't help it.
Click to expand...

nope i love this 100" cable LOVE IT
 
#138
Ok, But what about the speaker wire inside the cabinet, on an 1985 svt810e would it be a good idea to change this wire to handle more power of the current amps power. and if so, what AWG would be feezibal. with respect to a 4ohm cabinet.
 
#139
arguijot said:
Ok, But what about the speaker wire inside the cabinet, on an 1985 svt810e would it be a good idea to change this wire to handle more power of the current amps power. and if so, what AWG would be feezibal. with respect to a 4ohm cabinet.
Click to expand...
Don't waste your time. You can use 2 ga. and it still won't have an audible effect.
BTW, spell check is your friend. Use the spell check. :)
 

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