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Trouser flapping cab /s required

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48 minutes ago, Al Krow said:

+3 dB is a doubling of sound intensity, which I accept isn't the same as a perceived doubling of volume, but still worth having if the choice of 4ohm doesn't cost you a penny extra. 

I've had a number of respected sound engineers say that a single 4ohm cab will let the amp 'breathe' in a way a single 8ohm won't. 

No question that two 1x12s or two 2x10s will be louder than a single 2x10, other things being equal, as you have a greater volume of air being pushed. But if you're looking for a single lightweight cab solution, you'll be hard pressed to beat the VK 210 MNT 4ohm for a 500W amp head. 

Trouser flapping per se is just a load of hot air :)

I'm not sure what they mean by "Breathe", Alex, Steve or Bill might be better suited to shed light there?

The other thing that you need to consider when using a 4Ω cab, is that it will put extra wear & strain on the amp's components, as there is an increase in current going through the circuit.  This could mean that you need to get your amp serviced more frequently, which could also lead to it's life expectancy being reduced.

I would always choose an 8Ω over a 4Ω cab of the same, as 1, it allows me to add a 2nd cab if the one cab isn't enough for the bigger gigs & 2, it means that I'm not always running the amp at it's min load.

 

Saying all this, I have a 4Ω EBS 4x10 that I bought from the OP a couple of years ago plugged into a 60 year old Radiovox valve amp.  😂

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Posted (edited)

So if I've got you down right, you would always choose an 8ohm except when you choose 4ohms? 😁

But more seriously, if you are recommending 2 x 8ohm cabs = presenting a 4 ohm load that's going to be exactly the same 'wear and tear' on your amp's parts as a single 4ohm cab.

In any case, I don't accept that today's quality built D class amps, which are often capable of handling 2.67ohms or even 2ohms, are the wilting snowdrops you suggest they are. 

And for smaller gigs you can just turn the volume dial down. 

Edited by Al Krow

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8 minutes ago, Al Krow said:

So if I've got you down right, you would always choose an 8ohm except when you choose 4ohms? 😁

But more seriously, if you are recommending 2 x 8ohm cabs = presenting a 4 ohm load that's going to be exactly the same 'wear and tear' on your amp's parts as a single 4ohm cab.

In any case, I don't accept that today's quality built D class amps, which are often capable of handling 2.67ohms or even 2ohms, are the wilting snowdrops you suggest they are. 

And for smaller gigs you can just turn the volume dial down. 

I only chose the 4Ω as I needed something large for the amp & couldn't find a decent 8Ω in my budget at the time.  It does sound rather good though, but rarely gets used.

The reason I would choose 2 8Ω cabs is because most of the time I would be running just the 1 8Ω cab.  Ohms don't work the same as watts, as in the amp will be running at the same load regardless of volume.

I wasn't suggesting that todays Class D amps are wilting snowdrops, but like all good electronic equipment, they age & require servicing.  I like vintage synths (unfortunately, I don't have any) & they need regular servicing too.

Car analogy time.  😀

You're building a car & now have the gearbox options.  Are you going to put a 4 speed box in & have the engine running close to the redline, or are you going for the 8 speed box & keep things well below the redline?

It's fine to go up to the redline, but the more you do it, the more the engine will need a regular service.

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I guess I've dealt with the same issue by never needing to go anywhere close to the 'red line', by having plenty of headroom. A nice to have that is available if you happen to own an amp that can put out 800W or (in my case) 900W at 4ohms. 

But I think you're saying that a 4 ohm load will more quickly knacker the parts of an amp than an 8 ohm cab regardless of what volume it's putting out? Be interested in engineering basis for this, as it's not something that is immediately obvious to me. 

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1 hour ago, Al Krow said:

+3 dB is a doubling of sound intensity, which I accept isn't the same as a perceived doubling of volume, but still worth having if the choice of 4ohm doesn't cost you a penny extra. 

I've had a number of respected sound engineers say that a single 4ohm cab will let the amp 'breathe' in a way a single 8ohm won't.

6dB is a doubling of sound intensity. 10dB is a doubling of volume. The 3dB voltage sensitivity increase you get from halved impedance has no effect on maximum output, as that's determined by cone displacement, which is unaffected by impedance. Amps don't breathe, and while some sound engineers may think there's an inherent advantage to 4 ohms versus 8 you'd be hard pressed to find speaker designers who share that notion. IMO one's better off to go with an 8 ohm cab, even if you are quite sure that a single cab is all you'll ever need, because things change. The time may come when a 4 ohm cab no longer works for you. Unless you make a change to a valve head that lacks an 8 ohm tap that won't happen with an 8 ohm cab.

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Hey, just buy back your MB NY151s from me. They have Roqsolid covers now too. Cut and bottom by the spade full, light and solid. 

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45 minutes ago, Al Krow said:

I guess I've dealt with the same issue by never needing to go anywhere close to the 'red line', by having plenty of headroom. A nice to have that is available if you happen to own an amp that can put out 800W or (in my case) 900W at 4ohms. 

But I think you're saying that a 4 ohm load will more quickly knacker the parts of an amp than an 8 ohm cab regardless of what volume it's putting out? Be interested in engineering basis for this, as it's not something that is immediately obvious to me. 

I think you're looking at my analogy wrong.  😂

I wasn't relating it to volume, decibels or watts.  Just ohms.  Watts are not a measure of volume, decibels are.  I used to use a 50w amp for PA through 4 15'" full range cabs & another 50w amp to run 2 subs.  That was a loud rig.

Your 2nd sentence is correct.  Ohms is in relation to how much current is being drawn through the circuitry.

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Posted (edited)
45 minutes ago, Bill Fitzmaurice said:

6dB is a doubling of sound intensity. 10dB is a doubling of volume. The 3dB voltage sensitivity increase you get from halved impedance has no effect on maximum output, as that's determined by cone displacement, which is unaffected by impedance. Amps don't breathe, and while some sound engineers may think there's an inherent advantage to 4 ohms versus 8 you'd be hard pressed to find speaker designers who share that notion. IMO one's better off to go with an 8 ohm cab, even if you are quite sure that a single cab is all you'll ever need, because things change. The time may come when a 4 ohm cab no longer works for you. Unless you make a change to a valve head that lacks an 8 ohm tap that won't happen with an 8 ohm cab.

Thanks - a lot of common sense. Although if you have an amp that can handle 2 ohms (which, for example, the DG M900 does) then getting a single 4 ohm cab is not going to limit you if you decide you need to add a second (4ohm cab) and you have the benefit of getting the full output from your amp whenever you want (providing your cab can handle it).

Just on the sound intensity point Bill, are you saying these guys have got it wrong when they say that +3dB is a doubling of sound intensity?

http://www.sounddeadsteel.com/what-is-a-decibel.html

Edited by Al Krow

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Doubling the excursion of a driver results in a doubling of SPL. That requires doubling the voltage to the driver, which equals a four fold increase in power, which gives a 6dB level increase. One can realize that same 6dB by doubling the driver count driven with the same voltage. One may also realize a 6dB increase in SPL in an open space by halving the distance from the source to the listener. You also realize 6dB when you halve the space that the speaker radiates into, for instance when a speaker is mounted in a wall as opposed to being in an open field. The need for at least a 6dB difference to be meaningful is why going from, say, a 50 watt amp to a 100 watt amp is underwhelming. Sheer disappointment was my reaction when I went from s 50 watt Fender Bassman to a 100 watt Fender Dual Showman. That was when I was still in secondary school, it would be another two years before I learned the reason why I should have gone straight to the SVT.

 

 

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1 hour ago, xgsjx said:

I think you're looking at my analogy wrong.  😂

I wasn't relating it to volume, decibels or watts.  Just ohms.  Watts are not a measure of volume, decibels are.  I used to use a 50w amp for PA through 4 15'" full range cabs & another 50w amp to run 2 subs.  That was a loud rig.

Your 2nd sentence is correct.  Ohms is in relation to how much current is being drawn through the circuitry.

I'm missing something here given that V = IxR

The volume knob is effectively a potentiometer (if that's the right term) and increases volume by increasing voltage. Ohms (R) is a fixed. It seems to me therefore that turning volume down has the same effect on reducing current draw and the therefore wear and tear on amp parts as would increasing ohms. 

So me running my bass amp at "half volume" (in very approx terms and assuming a linear response) through a 4ohm cab is going to be the same as running it at full volume through an 8ohm cab. 

I simply don't see your argument about a greater ohm cab extending the shelf life of an amp where the volume is the same for both. 

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1 hour ago, Al Krow said:

I'm missing something here given that V = IxR

The volume knob is effectively a potentiometer (if that's the right term) and increases volume by increasing voltage. Ohms (R) is a fixed. It seems to me therefore that turning volume down has the same effect on reducing current draw and the therefore wear and tear on amp parts as would increasing ohms. 

So me running my bass amp at "half volume" (in very approx terms and assuming a linear response) through a 4ohm cab is going to be the same as running it at full volume through an 8ohm cab. 

I simply don't see your argument about a greater ohm cab extending the shelf life of an amp where the volume is the same for both. 

From what I know (& I could be wrong), a 4Ω load is always going to be a 4Ω load (or there about).  Even at lower volumes, it's still not going to be an 8Ω load (I think you got that bit).

At home volumes, I can see where you're coming from.  But at rehearsal & gigging volumes, the current supplied to get the same volume is going to be greater through the 4Ω cab.  Yes the dials on the amp will be lower, but the lower load means that the current travels greater.  The difference in volume is only a small amount (as you know).  It's not the difference between the amp being at 1/2 volume Vs full volume.  More like on a scale of 1-10, the amp volume being at 8 Vs 9 (taking an approximate guess here, as it really depends on the amp & cabs as well as the bass).

So this is why I would normally choose an 8Ω cab.  Though I do know that most 2x12 cabs are 4Ω & if it were the cab for me, then I'd happily use it & get the extra amp services if it was required.

 

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1 hour ago, Al Krow said:

I simply don't see your argument about a greater ohm cab extending the shelf life of an amp where the volume is the same for both. 

Heat. 100 watts into 8 ohms is 28.3 volts at 3.5 amperes, 100 watts into 4 ohms is 20 volts at 5 amperes. Where creation of heat in the amp components is concerned the primary source of heat isn't voltage, it's current. The same is true of driver voice coils. The lower the current the less heat generated. That's why power lines transmit at very high voltage, typically well over 100 kilo volts. Doing so minimizes current, which minimizes heat in the transmission lines, which minimizes the wire gauge required. It's also why you can run a 500 watt amp with a 16 gauge power cord. At 220 volts and 50% efficiency the amp will never draw more than 5 amperes. Put an amp with the same specs into a car with a 12v power supply and you need a massive mains cable, because you're now maxing out at 80 amperes.

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So 8 ohms might generate less heat but if an amp is designed to give its maximum power at 4 ohms then I would expect 4 ohms to be easily doable.

If the heat generated by 4 ohms is with in the design spec then why should there be a problem with running an amp within its stated range?

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There's a difference between within spec and optimal. Besides, amps aren't intentionally designed to give maximum power at their minimum rated impedance load, it just works out that way.

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17 minutes ago, chris_b said:

So 8 ohms might generate less heat but if an amp is designed to give its maximum power at 4 ohms then I would expect 4 ohms to be easily doable.

If the heat generated by 4 ohms is with in the design spec then why should there be a problem with running an amp within its stated range?

Even more so if the amp is able to handle 2.67 or 2 ohm loads? 4 ohms should be a walk in the park!

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34 minutes ago, Bill Fitzmaurice said:

That's a safe bet...unless it's a Behringer.

How so? 

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1 hour ago, chris_b said:

So 8 ohms might generate less heat but if an amp is designed to give its maximum power at 4 ohms then I would expect 4 ohms to be easily doable.

If the heat generated by 4 ohms is with in the design spec then why should there be a problem with running an amp within its stated range?

Once more: 

If you compare the power between 8 and 4 ohm load, there is difference, yes. Some amp may give 200 W to 8 ohms and even 400 W to 4 ohms but maybe only 500 W to 2 ohms. As the load becomes harder to the amp, the ability (or the lack of it) to drive that load may affect the amp's maximum output. Bigger number equals easier load to the amp. Naturally it is not wise to exceed specifications to any direction.

If you compare sound level between 8 and 4 ohm loads, there is practically no difference. You probably can not hear that.

Amp's wattage has very little to do with loudness. Max SPL talks another language and that is directly related to the cab.

 

It is not intelligent to compare loudness and wattage within a system when parts are separated. You need to take all parts to that equation. If you do not know the max SPL of the cab and its other specs, it is no reason to try to approximate the maximum loudness of the system through a simple number from the amp.

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1 hour ago, Bill Fitzmaurice said:

They're well known for playing fast and loose with specs.

That’s half the fun...

its like motoring of yesteryear... you get in the car and you don’t know if you are going to reach your destination...

likewise... you don’t know if it’ll make it through to end of the gig without smoke coming out from under the hood.

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2 hours ago, EBS_freak said:

That’s half the fun...

its like motoring of yesteryear... you get in the car and you don’t know if you are going to reach your destination...

likewise... you don’t know if it’ll make it through to end of the gig without smoke coming out from under the hood.

You'll next be saying that the Morris Marina was the most fun car ever... 😄 

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IME British cars of the 60s were paragons of reliability compared to Italian cars. Still, having owned an MG Midget it's a damn good thing you did a better job with Hurricanes and Spitfires.

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13 hours ago, Bill Fitzmaurice said:

They're well known for playing fast and loose with specs.

I'd be surprised if they lie about ohms. 

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Posted (edited)
8 hours ago, Bill Fitzmaurice said:

IME British cars of the 60s were paragons of reliability compared to Italian cars. Still, having owned an MG Midget it's a damn good thing you did a better job with Hurricanes and Spitfires.

On the plus side, Midgets and associated Leyland cars were very basic and easy to fix with pliers and a hammer by the side of the road.

Edited by Dan Dare

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