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Why 2 ohms is not a good idea..

#144
chicago_mike said:
All you guys who want 1200watts into a 2 ohm load...

I hope you know what you're asking.

.
Click to expand...

I want administer CPR to the second row with a low B

Any BASS player worth his salt will put together a rig that will give them enough power to sound good but not have to worry about blowing up!
That means safely mating the speakers to the power amp paying attention to the ohm ratings. All of the power amps I have used have mentioned speaker gauge in the manual. One even suggested a higher gauge when running bridge mode.

http://www.audioholics.com/education/cables/speaker-cable-gauge

:hiding:
 
#146
billfitzmaurice said:
Bridge mode is only of value with a higher impedance load, a higher impedance load means less current, and therefore a lower gauge cable could be used.
Click to expand...

Nope.... bridge mode takes the SAME current as the minimum load on either channel.

In bridge mode, each channel is driving its minimum load, but the sum of the two loads is larger. Makes no difference if the load is two cabs in series, each at minimum channel load, or one bigger one at the sum.
 
#147
Jerrold Tiers said:
Nope.... bridge mode takes the SAME current as the minimum load on either channel..
Click to expand...
Not what I said. What I said was bridge mode (series bridging, to be concise) is only of value with a higher impedance load. When the load is of a high enough impedance that running stereo won't give adequate voltage to drive the speaker to full output, as is often the case at 16 ohms, series bridging will double the available output voltage. For the same power dissipation a 16 ohm load will run at half the current of an 8 ohm load, so a smaller wire gauge could be used. If the impedance load is low enough that the amp can deliver adequate voltage for full output there's no advantage to series bridging, but the doubled voltage capability would make it easier to toast drivers, so bridging is a no-win option. Parallel bridging is a different matter of course, but very few power amps offer the parallel bridging option.
 
#148
Jerrold Tiers said:
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.
Click to expand...

Just catching up with the posts, totally agree.

A year or two ago one of my old business pals died. A guy by the name of Pete Dahl. Old Minneapolis guy who owned a transformer company in El Paso... It made it really easy to just pick up the phone and get transformers made. He was a pretty good power supply wizard... But he also did a lot of replacement modulation transformers for AM Broadcast Rigs.

Modulators are just huge audio amplifiers with a HIGH IMPEDANCE output transformer instead of speaker load. SO the guy also understood audio.

Well, I was thinking. I almost hate to even mention this here on a public forum as the idea is going to get picked up by one of the manufacturers. When you do - make sure you send me a big check... :D

If a guy was to manufacture a quite large transformer with a 4ohm input and multiple 4 ohm output taps, even up to four of them you could hang a big solid state power amp on the thing and still drive multiple speaker cabinets without running into low impedance issues.

Sure the thing is a big heavy deal, but I'd just mount it in a box with handles and wheels and put several speakon connectors in and out on the thing.

The amplifier doesn't know the difference between a 4 ohm speaker and a 4 ohm transformer winding if the inductive REACTANCE is the same. The issue becomes colorization of the signal. This is something Jensen has been able to design around in their little signal transformers, that could be a lot of work at the 5000 watt level. (4 1200 Watt amps)

The only limitation here is you wouldn't want to PLUG in this transformer without a load on the output as a transformer is not a load, it is a transformation device.

This is why distributed amplification has become popular with PA applications. Its been done a few times in bass rigs, and I think it might once again become the wave of the future once again as it makes sense.

BOB
 
#149
I've read all of this thread and enjoyed discussion, just to make it more interesting, speakers are rated 8,4,2, ohms at one frequency only. they vary all over the place with frequency, remember they are mostly inductive, so your load could be as much as 40 ohms at some frequencies. then your power output would be much lower and the average power dissipation would vary with each song you play!!!
 
#153
billfitzmaurice said:
Not what I said. What I said was bridge mode (series bridging, to be concise) is only of value with a higher impedance load. When the load is of a high enough impedance that running stereo won't give adequate voltage to drive the speaker to full output, as is often the case at 16 ohms, series bridging will double the available output voltage.
Click to expand...

OK. Agree with your expansion of the original statement.
 
#155
I read the article you linked to, Bill. Makes a lot of sense for outdoor venues.

However, I wonder if maybe the situation changes in an indoor venue. Since most of the audience will be far enough away that the reverberant field will be dominant especially at low frequencies, room interaction might play a larger role than comb filtering. And the room-induced peaks-and-dip pattern is theoretically smoothed for any given location within the room as the number of distributed low frequency sources goes up.

That being said, I've never been a soundman... so the theory I'm referring to may be incomplete or inapplicable. The article suggests clustering the subs in a single location. In your experience, has that worked better for indoor venues than having the subs spread apart?

Thanks.
 
#156
DukeLeJeune said:
The article suggests clustering the subs in a single location. In your experience, has that worked better for indoor venues than having the subs spread apart?

Thanks.
Click to expand...
In my experience and that hundreds of users of my subs, who also would have been unaware of how to properly place subs if I didn't include instructions, including boundary loading and room mode information, in the sub plans. Said instructions should be included in the owner's manuals of every pro-sound sub, but...:rollno:
 

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