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bass_ferret

Impedance etc

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[url="http://wiki.basschat.co.uk/info:amps:impedance_and_wattage"]http://wiki.basschat.co.uk/info:amps:impedance_and_wattage[/url]
[url="http://wiki.basschat.co.uk/info:amps:leads"]http://wiki.basschat.co.uk/info:amps:leads[/url]

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[url="http://www.hometoys.com/htinews/feb04/articles/polk/impedence.htm"]http://www.hometoys.com/htinews/feb04/arti...k/impedence.htm[/url]

An excellent explanation - the best I've encountered on the web.

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[quote name='bass_ferret' post='896' date='May 17 2007, 10:14 PM'][attachment=58:Infomation_O_1_.htm][/quote]...Interesting article although I never subscribed to the view that speakers should be able to handle more power than the amp can deliver....If,for example you're using an amp rated at 800 watts but only use 300 watts of that [plenty loud],then your 1000 watt speaker[s],aren't being driven efficiently and your amp has to work harder..Obviously, at the other extreme if you use a 100 watt head driven hard,then it may be advisable to use more than 100 watts of speaker capacity!...Maybe some tech head will tell me I'm wrong,although I've been doing this most of my life and arrived at these conclusions via trial and error...My general rule of thumb is 50% more speaker capacity than my ACTUAL PLAYING LEVEL....

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[quote name='hipbass' post='69624' date='Oct 4 2007, 06:36 PM']...Interesting article although I never subscribed to the view that speakers should be able to handle more power than the amp can deliver....If,for example you're using an amp rated at 800 watts but only use 300 watts of that [plenty loud],then your 1000 watt speaker[s],aren't being driven efficiently and your amp has to work harder..Obviously, at the other extreme if you use a 100 watt head driven hard,then it may be advisable to use more than 100 watts of speaker capacity!...Maybe some tech head will tell me I'm wrong,although I've been doing this most of my life and arrived at these conclusions via trial and error...My general rule of thumb is 50% more speaker capacity than my ACTUAL PLAYING LEVEL....[/quote]**********************p.s. I 'aint blown a speaker since the 70's

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I've naively never paid much attention to impedance, although haven't messed around with different cabs or heads yet. Figured it would be useful now I'm looking to upgrade, and reading through the article Crazykiwi posted it makes sense now; cheers for that.

Just so I'm sure I've got the right end of the stick;
I currently use a Hartke HA3500 heard with a Hartke 410TP cab.
The head is rated 350w @ 4 Ohms / 250w @ 8 Ohms.
The cab is rated 300w @ 8 ohms, so that means at the moment I'm only getting 250w, right?

The next thing I plan to upgrade is my cabs, and I want to try out the Eden XLT series.
If I get a 210XLT and a 115XLT (both rated 350w @ 8 Ohms) and use them in parrallell (one from each output on the head?) that would result in an impendance of 4 Ohms and full use of my current 350w?

*Edit: I now notice the 115XLT is [b]400w @ 8 ohm[/b], which in my understanding would be fine in the above setup?

I really hope I'm at least close to the money on the maths with this, otherwise I fear I'll never understand! Edited by Biggsy

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[quote name='hipbass' post='69624' date='Oct 4 2007, 05:36 PM']...Interesting article although I never subscribed to the view that speakers should be able to handle more power than the amp can deliver....If,for example you're using an amp rated at 800 watts but only use 300 watts of that [plenty loud],then your 1000 watt speaker[s],aren't being driven efficiently and your amp has to work harder..[/quote]

no, that isn't the case. The speaker rating is simply how much power you can put into it before it shakes itself to bits and/or the glue melts in the voice coil. Tha amplifier doesn't care how close the speaker is to death.

On the other hand, a less efficient speaker needs more input power than an efficient one for a given sound pressure level, so that _will_ work the amplifier harder.

[quote]Obviously, at the other extreme if you use a 100 watt head driven hard,then it may be advisable to use more than 100 watts of speaker capacity!...[/quote]

definitely!

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[quote name='Biggsy' post='96672' date='Nov 30 2007, 02:06 PM']I've naively never paid much attention to impedance, although haven't messed around with different cabs or heads yet. Figured it would be useful now I'm looking to upgrade, and reading through the article Crazykiwi posted it makes sense now; cheers for that.

Just so I'm sure I've got the right end of the stick;
I currently use a Hartke HA3500 heard with a Hartke 410TP cab.
The head is rated 350w @ 4 Ohms / 250w @ 8 Ohms.
The cab is rated 300w @ 8 ohms, so that means at the moment I'm only getting 250w, right?

The next thing I plan to upgrade is my cabs, and I want to try out the Eden XLT series.
If I get a 210XLT and a 115XLT (both rated 350w @ 8 Ohms) and use them in parrallell (one from each output on the head?) that would result in an impendance of 4 Ohms and full use of my current 350w?

I really hope I'm at least close to the money on the maths with this, otherwise I fear I'll never understand![/quote]

Spot on.

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thanks guys for posting this ive never thought about impedance at all before! About to change amp as well so its a good job I saw this

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just a small query... I'm getting an amp that's 2ohm/4ohm switchable. both of my cabs are 8ohm so to use my amp I'm only going to be able to do it when I take both cabs out and run them in series to up the resistance to 4ohm. I'd rather sell one of the cabs and get a 4ohm cab so I can use it singularly.. but what about running a 4ohm and 8ohm cab in series? or parrallel?

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[quote name='JayX' post='125433' date='Jan 22 2008, 01:49 PM']just a small query... I'm getting an amp that's 2ohm/4ohm switchable. both of my cabs are 8ohm so to use my amp I'm only going to be able to do it when I take both cabs out and run them in series to up the resistance to 4ohm. I'd rather sell one of the cabs and get a 4ohm cab so I can use it singularly.. but what about running a 4ohm and 8ohm cab in series? or parrallel?[/quote]
First, you'd need to run them in parallel, not series, to get them to 4 ohms.

If you ran a 4 ohm and 8 ohm in parallel, the impedance would be 2.7 ohms, so I imagine you could do that with the amp switched to 2 ohm (not having dealt with switchable amps, I'm not sure how exactly you have to match the impedance, so check the manual).

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[quote name='tauzero' post='125440' date='Jan 22 2008, 01:55 PM']If you ran a 4 ohm and 8 ohm in parallel, the impedance would be 2.7 ohms, so I imagine you could do that with the amp switched to 2 ohm (not having dealt with switchable amps, I'm not sure how exactly you have to match the impedance, so check the manual).[/quote]

It's generally not a good idea to use two cabs of different impedances (e.g. 4 ohm and 8 ohm). The power drawn by each cab is determined by the impedance of the cab, therefore using different impedances will result in different amounts of power going to each cab, which is probably not desirable. If you want to split the available amplifier power equally between two cabs then use cabs of the same impedance.

Two obtain a 2 ohm load from two cabs you would need two 4 ohm cabs in parallel.

Also check that the amplifier really is happy running into a two ohm load in "real-life" (this is still a little unusual, although quite feasible in high end emps) and that the 2 ohm load isn't just a false spec quoted by the manufacturer to make the amp sound more powerful than it is !

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Cheers for the feedback guys, its a Trace V6 and I've not heard of any problems running it in 2ohm mode. I was just hoping I'd get to keep my Trace 1x15 cab, but looks like I'm better off selling both my 8ohm cabs (Peavey 4x10 and Trace 1x15) and buying a single 4ohm cab like an Ampeg 4x10 out of it?

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Indeed it does, hence my question! Think I'll probably play it safe and get rid of both cabs at the same time then replace with a single as noted. Ta

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Here's a handy speaker impedance calculator I found on the web:- [url="http://www.duncanamps.com/technical/impedance.html"]http://www.duncanamps.com/technical/impedance.html[/url]

Hours of fun :)

Hamster

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[quote name='hipbass' post='69624' date='Oct 4 2007, 05:36 PM']...Interesting article although I never subscribed to the view that speakers should be able to handle more power than the amp can deliver....If,for example you're using an amp rated at 800 watts but only use 300 watts of that [plenty loud],then your 1000 watt speaker[s],aren't being driven efficiently and your amp has to work harder..Obviously, at the other extreme if you use a 100 watt head driven hard,then it may be advisable to use more than 100 watts of speaker capacity!...Maybe some tech head will tell me I'm wrong,although I've been doing this most of my life and arrived at these conclusions via trial and error...My general rule of thumb is 50% more speaker capacity than my ACTUAL PLAYING LEVEL....[/quote]

One industry extreme tech head suggests up to x 10 when using very distorted guitar tones... again this is to avoid distortion of voice coil...

none of us like to be pushed to our limits right? or not for extended periods night after night... ?

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[quote name='bremen' post='96679' date='Nov 30 2007, 03:17 PM']no, that isn't the case. The speaker rating is simply how much power you can put into it before it shakes itself to bits and/or the glue melts in the voice coil. Tha amplifier doesn't care how close the speaker is to death.

On the other hand, a less efficient speaker needs more input power than an efficient one for a given sound pressure level, so that _will_ work the amplifier harder.



definitely![/quote]
True, but surely if you max out the amp, although the speaker can take it, the clipping thats going to occur from pushing an amp to its limit can damage the speaker. Certainly in Live sound PA terms ive always been recommended to run an amp way more powerful than the speaker - the amp can be run at a quarter or half capacity, so its not getting strained or anywhere near clipping, and the speaker, well you arent running that to the limit either so nothing breaks. Correct me if im wrong!

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For years I ran a 300w head into a 350w max cab, the volume of the amp was never over c.60%, which I find is a good rule of tumb to avoid overdriving the amp. Now I know this doesn't equate to only 60% of the wattage going into the cab it has always seemed plenty of headroom.

I can't think I've ever turned the volume past 3'oclock on any amp (about 7, Nige)

Does anyone know how wattage output increases with turning up the volume, is it an exponential type increase?

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[quote name='Mr Cougar' post='219191' date='Jun 15 2008, 01:00 PM']Does anyone know how wattage output increases with turning up the volume, is it an exponential type increase?[/quote]
The numbers, markings etc on the volume control are totally meaningless - see [url="http://wiki.basschat.co.uk/info:amps:gain_power_and_volume_-_a_confusing_menage_a_trois"]here[/url] Edited by bass_ferret

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[quote name='bass_ferret' post='219206' date='Jun 15 2008, 01:35 PM']The numbers, markings etc on the volume control are totally meaningless - see [url="http://wiki.basschat.co.uk/info:amps:gain_power_and_volume_-_a_confusing_menage_a_trois"]here[/url][/quote]

Question then: does the variable resistor that is the volume effect the amount of wattage which goes into the speakers? I read the article, it doesn't say anything about the numbers being meaningless, the volume is like a valve increasing or decreasing the amount it lets through to the power amp in terms of signal, so does it also change the watts that the actual amp sends into the cab or is the wattage being fed into the cab uniform regardless of the volume. 14 years playing and I've never thought about this in detail!

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[quote name='Mr Cougar' post='220258' date='Jun 16 2008, 10:18 PM']Question then: does the variable resistor that is the volume effect the amount of wattage which goes into the speakers? I read the article, it doesn't say anything about the numbers being meaningless, the volume is like a valve increasing or decreasing the amount it lets through to the power amp in terms of signal, so does it also change the watts that the actual amp sends into the cab or is the wattage being fed into the cab uniform regardless of the volume. 14 years playing and I've never thought about this in detail![/quote]

Yes.

If there is no signal coming into the amp there will be no power being sent to the speakers (apart from a small amount of background noise which will consume some power).

If the "volume control" is passive and simply bleeds off some of the signal, then the remainder is sent to the amplifier sections and uses power to amplify it. The more signal sent the amplifier the more power it will use to amplify this signal.

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[quote name='Mr Cougar' post='220258' date='Jun 16 2008, 10:18 PM']is the wattage being fed into the cab uniform regardless of the volume.[/quote]

When you play a loud note the wattage is high, when you play a quiet note the wattage is low, when you 'play' a rest the wattage is zero.

The gain and volume knobs simply act as a multiplier of the power your bass is putting into the amp. Therefore a heavy-handed player with a bass with hot pickups will put out much more power at the same volume knob settings as a lighter-touch player with a bass with quieter pickups.

And obviously even at full power the only time your amp is putting out full power is shortly after you strike the string, thereafter the note is decaying and the power is diminishing.

Alex

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An amplifier will only output its maximum wattage (measured in volts in the wiki article) irrespective of where the master volume is set. So if the signal is hotter in the preamp cos of input and tone settings then the maximum output is reached lower on the master volume than if the input and tone settings are lower. Once an amplifier is pushing out its maximum rated power (or hitting the limiter if there is one on the output stage - there often is) turning the volume up makes no difference.

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