The Steel Guitar Forum

I've read that Fender amps supposedly were designed to handle up to a 50% impedance mismatch, but in the interest of avoiding that -
Want to run a 212 ex cab w a BF Vibrolux (2x10, 4 ohms). I have two nice 8 ohm 12s I want to load the cab with. If I wire the 2 12s in parallel, that should be 4 ohms correct? And then I could bypass the speakers in the amp, run straight into the cab and be matched, yes?
What if I wired the 12s in series for 16 ohms? Would that create 16 divided by 4 for a total 4 ohm load if I run the cab and the amp speakers together? Or am
I commiting amp suicide?
Thanks!

Two 8-Ohm (nominal impedance) speakers in parallel gives 4 Ohms. That's what a Vibrolux Reverb wants, as long as it's the original output transformer. Doesn't matter if they're in the amp's cabinet or an external cabinet.

Two 8-Ohm speakers in series gives 16 Ohms. If you then ran that 16-Ohm load in parallel with the cabinet's 2x10" speakers' 4-Ohm load, the overall impedance would be 1/((1/4)+(1/16)) = 16/5 or about 3.2 Ohms. Not a big mismatch at all, but remember that most (around 80%) of the power will be dropped over the 4-Ohm load. The voltage drop across each will be the same, but the current through the 4-Ohm load will be 4 times higher than that through the 16-Ohm load.

Thx Dave. Forgive my ignorance, but do you mean the amp will lose 80% of its power and the components will be seeing four times the normal current? I'm not experienced with electronics, so I'm pretty sure I'm misunderstanding what you are trying to explain to me.
What would the practical impact of tha be on the output/performance of the amp?

By "dropped" Dave means that's where the current gets turned into moving air. The 4 ohm array will get 80% of the output of the amp and the 16 ohm array will only see 20% of the output. Electricity, like water or people, will follow the path of least resistance, so most will go to the 4. Aim the 4Ohm array at the audience, and use the 16 as a monitor.

Depending on which speaker has a higher sensitivity, that speaker(s) will appear louder. You could also experience frequency jumps during playing where the different resonances of each speaker will "blink" from speaker to speaker. Your treble might sound different through one of the speakers and then the bass will appear or disappear at random.

And if your 2x12 cabinet has certain resonances, (is a closed back especially) then you will also get that frequency "hopping" of certain frequencies ping-ponging between the Vibrolux and the 2x12 cab.

But if you're going to use just the 2x12 cab and the Vibrolux as a head, you will have more control over the sound.


Welcome to multiple speaker anomalies 101.

Great thanks guys. No point in trying to drive a 212 with 20% of 35w, or opening myself up to weird sonic dropouts. I'm sure just running the VR as a head into a big ol Bandmaster 212 cab will give me all the extra girth I could wish for, when needed.

Marc, it's not as linear as you're thinking. The overall sound will be more because you're pushing more air. But not a lot more. You'll also find that it'll probably sound better with more cones moving the air around.

The amp must have enough power to drive your speakers. Use an amp that has 2 to 4 times the continuous power rating of your speakers, is a norm depending on the type of music you'll play and how large a venue.

The louder the music the higher wattage the amp must be.

A 35 watt amp driving more speakers will only clip the amp if the total number of speakers needs more than 35 watts especially if there are high peaks in the music.

I also have a BF Vibrolux Reverb, original trannies so a 4 ohm load from the original Jensons. I have a Peavy 410e cab, 4x10 wired down to a 4 ohm load (the stereo/mono switch has been disabled. If I want to use both the internal speakers and hook up the 4x10 Peavy, what ohm rating will the amp see? Will it hurt the amp?

Dave St-Pierre wrote:I also have a BF Vibrolux Reverb, original trannies so a 4 ohm load from the original Jensons. I have a Peavy 410e cab, 4x10 wired down to a 4 ohm load (the stereo/mono switch has been disabled. If I want to use both the internal speakers and hook up the 4x10 Peavy, what ohm rating will the amp see? Will it hurt the amp?

Fender mysteriously added external speaker jacks on their early amps but in reality if the tranny is set to provide a 4 ohm load (assuming you have the 2x10 version of two 8 ohm speakers wired in parallel) adding an external speaker will provide a mismatch in impedance. The VR will see 2 ohms with both VR and Peavey speakers connected to the VR! Weird I know but many of their, Fender, older amps are this way yet they are still running without issue vs an impedance mismatch on a Marshall. (Danger Will Robinson)

Perhaps you might experiment and use you ears as to whether you like the result of two cabinets (your VR and the Peavey) running at the same time.

Personally I tried this eons ago but with a BF Vibroverb (35 watts into a 15) connecting a Bandmaster cab. The result is audio confusion. As I explained above in my previous post, one set of speakers will want to act like the boss with neither set actually getting the job if you get the drift.

One Fender amp that will do the 2 ohm trick would be a Super Reverb. You could connect two 4 ohm loads to that. But that would be disconnecting two of the SR's speakers or reconfiguring the wiring to make 4 ohms in the SR's cab.

The more things change, the more they remain the same.

The only other way if you insist on using your VR as a head is to change ALL THE SPEAKERS and wire them to achieve a 4 ohm load in total.

You could get two 16 ohm 10 inchers in your VR, wire them in parallel to 8 ohms and then your Peavey cab, if that is a 4x10 those speakers must be 4 x 16 ohm speakers wired in parallel sets to get a 4 ohm load, you would need to swap those out to 4 x 8 ohm speakers, wired in series/parallel to get an 8 ohm load so both the VR's speakers and the Peavey cab's will make 4 ohms TOTAL for your VR to remain impedance happy.

You still there?

And if you don't research which speakers you will use to replace all your speakers as far as frequency response, sensitivity, free air resonance and match them so that everything is balanced, with more of the bass coming out of the Peavey since the VR is open back and rolls off bass just because of its design, even if you satisfy the VR's impedance demand, you are still not out of the woods with the sonic free-for-all that will occur.

Having said all that, you may just want to plug in your 4x10 cab and call it a day.

In the end it's not how many speakers you can connect, it's what sounds the best given your equipment.

If you really want to get down and dirty. Get a Hartke 7000 bass head, it's a Bi-amp system, 350 watts (PER SIDE) with a built-in tube/solid state selectable preamp feature, you can connect 4 ohm 2x10's on one side and then a 4 ohm bass cab (your choice of cab/speaker) on the other and balance the two as far as which cab is louder than the other. There is also a built-in active variable crossover so you can decide which cab gets what frequencies. You will get clear highs and low lows, your bass player might up and quit.



http://www.samsontech.com/hartke/produc ... rs/ha7000/

The amp must have enough power to drive your speakers. Use an amp that has 2 to 4 times the continuous power rating of your speakers, is a norm depending on the type of music you'll play and how large a venue.

The louder the music the higher wattage the amp must be.

A 35 watt amp driving more speakers will only clip the amp if the total number of speakers needs more than 35 watts especially if there are high peaks in the music.

Sorry, but no. Also, no, and lastly, no.

Sensitivity of speakers of all power ratings are determined using a one-watt signal, a higher power rating for a given speaker DOES NOT not require a more powerful amp, in fact often just the opposite is true: Most of the highest power-rated speakers deliver much higher volume and better clarity at such low power levels than most low-power speakers will.

If using a 200-watt speaker it is quite unwise to drive it with 400 to 800 watts of continuous music power. Entirely a bad idea. I have worked a lot of stages in my time but never met this guy Norm so can't speak for his habits and practices, but I imagine his speaker repair bills are ongoing and substantial.

It is true that a 30-watt amp in major distortion mode can take out a 75-watt speaker faster than a 100-watt amp at full clean power will, and sound companies sometimes do over-spec power amps to avoid amp clipping, but for our musical instrument amps - and especially steel guitars - it is always best to go to work with a speaker that can handle everything your amp can put out, plus a bit.

Loudness equates with Sound Pressure Level. Because delivering SPL is dependent on the area of the radiating surface, four 15" speaker sharing 35 watts WILL deliver considerably more usable SPL than one comparable 10" or 12" speaker with the same signal and nominal impedance.

A 35 watt amp with a 2000Hz sine wave wide open can pierce eardrums at a considerable distance with nearly any speaker, using a more powerful amp with the same speaker will not make much difference to a listener.

The load an amplifier faces has nothing whatsoever to do with the power rating of a speaker or speakers. Whether or not additional speakers draw more power from an amplifier depends entirely upon the design of the amplifier, whether transformer-coupled tubes or direct-coupled solid-state, as well as the wiring of the speaker complex. In any case, if the nominal impedances are reasonably matched the achieved SPL before clipping will not be affected by adding speakers.

Lastly, it is important to remember that the various impedance numbers that are tossed around - 4, 8, 16 ohms - represent NOMINAL impedances for a given speaker design, when in fact the actual impedance of every coil-based transducer varies widely with signal frequency. A speaker marked 8 ohms may show a DC (0Hz) resistance of 5 or 6 ohms, may present the rated impedance of 8 ohms at 60Hz only, and an impedance of several times that at higher frequencies.

Virtually any commercial instrument amplifier can easily manage loads of 4 ohms or more, the few that can safely handle 2 ohms are clearly marked as such. Tube amps with transformers are happier at lower-than rated load impedances than higher, but power stays constant, solid-state amps are more powerful when facing lower impedances, but perform better delivering less power into higher impedances.

I am in no way trying to start a flame-up with my respected friend in the Philllpines, but these are the true facts of the matter and if one is going to muck about with this stuff one had best know how it really works.

Sorry, but no. Also, no, and lastly, no.

Read the post again. You didn't understand it. You took things out of context.



Ever hear of a fallacy of argument called the strawman?

Virtually any commercial instrument amplifier can easily manage loads of 4 ohms or more, the few that can safely handle 2 ohms are clearly marked as such.

Mr. St. Pierre's amp does not state the 2 ohm load policy. If he connects his Peavey to his Vibrolux his amp will see 2 ohms when it's designed for 4 ohms..

More straw on the man...

I am in no way trying to start a flame-up with my friend in the Philllpines, but these are the true facts of the matter and if one is going to muck about with this stuff one had best know how it really works.

Ok start mucking Dave...

http://www.crownaudio.com/how-much-amplifier-power

Some additional muck:

http://www.premierguitar.com/articles/A ... nder_Combo

What did I not understand? Please explain the context I missed, I included every word you said, is there more? Here's the deal: You made several statements that are not factual or scientifically supported, and in the interest of communal best knowledge I have endeavored to set facts straight for those present who have no way of knowing any better. It is in no way personal but in these statements you were simply mistaken.

As regards your link, Crown sells power amps to audiophiles and PA users, to entities focused on the absence of all signal clipping, and their marketing department is on their toes in that regard. However, we are talking musical instrument applications here, specifically Fender amps and their extension speaker jacks, in a world where clipping is an essential element of art itself, and where putting a 35 watt speaker into your 100 watt amp is counter-indicated.

I don't know about your straw man, and I have no need of mucking anywhere. So very sorry you feel compelled to go there

Dave Grafe wrote:What did I not understand? Please explain the context I missed, I included every word you said, is there more? Here's the deal: You made several statements that are not factual or scientifically supported, and in the interest of communal best knowledge I have endeavored to set facts straight for those present who have no way of knowing any better. It is in no way personal but in these statements you were simply mistaken.

As regards your link, Crown sells power amps to audiophiles and PA users, to entities focused on the absence of all signal clipping, and their marketing department is on their toes in that regard. However, we are talking musical instrument applications here, specifically Fender amps and their extension speaker jacks, in a world where clipping is an essential element of art itself, and where putting a 35 watt speaker into your 100 watt amp is counter-indicated.

I don't know about your straw man, and I have no need of mucking anywhere. So very sorry you feel compelled to go there

Then I suggest you study fallacies of argument. Your posts reek of them.

If you really read what I said, and got the context then where did you miss my stating this to Mr. St. Pierre?

Perhaps you might experiment and use you ears as to whether you like the result of two cabinets (your VR and the Peavey) running at the same time.

To have preempted your late post of:

in a world where clipping is an essential element of art itself

You assume that everyone wants his rig to sound like Hendrix.

And I did say this didn't I?

depending on the type of music you'll play and how large a venue.

When it comes to steel, many play an 80 to 200 watt amp or more to get real clean tone.

And as far as Crown goes, they are not just for PA systems and audiophiles, many instrumentalists have used Crown amps for decades as the power section of their rigs to get clean sound from a preamp.


And where did I state or suggest this?

and where putting a 35 watt speaker into your 100 watt amp is counter-indicated.

You didn't explain anything to anyone who has "no way of knowing any better" all you did was run around in circles in a mitre.

Look up STRAWMAN DAVE!


Performed by HAL and the 9000
Daisy
Daisy
Give me your answer do...

I realize speaker amp relationship questions can get confusing. And why not, it's a combination of complex systems.

There are many views and opinions on what is a rule and what is an opinion. Huh?

One thing I've learned is since you have an amp system and a speaker system, mating these two is a balancing act.

You need to use your ears and your brain to survive.

Having said that there is always an exception.**

According to the "experts" using speakers that are rated for way more than the amp capacity will not likely hurt the speakers.

And then, if using speakers that are 3 to 4 times the capacity of the amp, the speakers will not be damaged no matter how hard the amp is clipped.**

Will it hurt the amp? In reality this is never a cut and dried answer. There are always the exceptions to the rule.

Will stressing the amp cause it to fail by using speakers that don't flinch because they are rated at a higher wattage than the amp? Maybe.

But here is where it gets interesting.

A speaker has a voice coil and because of the amp signal (voltage), generates heat in the voice coil. Now in order for the speaker to cool itself, the amp must push the speaker cone enough for the air to rush around the coil to cool it. The speaker is a motor.

This cooling function can happen if a "clean" sine wave signal (amp not too overdriven) is being fed the speaker. The excursion of the cone will be enough to allow air to cool the coil.

If a "clipped" square wave (amp pushed way too hard) is being fed the speaker, (and is double the voltage at this point) the speaker's excursion will not be enough to cool the coil. The coil is not moving enough which then causes voice coil overheating. Has to do with power dissipation. Funny how that happens. The speaker is still moving in most cases but under a square wave clipped signal from a not dialed-in too thoroughly rig, not enough to cool the coil.

Depending on the frequency of the signal, a 200 watt amp can push a speaker a large percentage more to a safe cooling operation than a 100 watt amp that is clipping. The extra cone excursion will allow air around the voice coil.

If the speakers are rated the same capacity as the amp can cleanly dish out, if you run the amp for extended periods with a clipped signal, damage MAY result to your speakers.



White line is the dreaded clipped square wave; amp pushed way too hard. The yellow line is the sine wave "clean" signal the amp can safely deliver.


If the speakers are rated for the same capacity as the amp can cleanly produce, running the speakers with a square wave signal will cause damage to the speakers.




At A, B, D, E, F, H, the voltage is changing allowing the voice coil to move to pull in fresh cool air. At points C, G, the coil may be moving a little but not enough to cool properly. During the clipped portion of the waveform, current is still flowing through the voice coil. But more heat is being generated than is proportionally dissipated.

Failure to quote Breaking Benjamin


Now if we're not provided with enough information, we can't arrive at a good enough answer.

So we hop around with vague generalities.

How many watts is the external speaker/cab in question?

Do you like to play distorted or are you Mr. Clean Tone with maximum headroom?

This will figure much in configuring the type rig you would need.

Without proper info the answer is not complete.

Now the exception** is always there.

SRV playing with a 40 watt Super Reverb always managed to blow his Electro-Voice 10"s that had massive wattage capacity... so his tech had spare speakers on hand.

So it comes down to this, unless you can afford a roadie or an amp guru at your beck and call to carry your gear loaded with extra heavy high wattage speakers or get you an extra fresh amp while he fixes your blown amp, you need to kick your ear/brain factor into high gear.





Jack Black?

Brad Pitt??

DiCaprio???

No!

Angus Young's amp guru on the road with AC/DC.


Note:

All the above did not address the tone, the grail of amp/speaker combinations.

Only amp and speaker implosion. And not even speakers failing from the adhesive coming unglued under stress.

How your external speaker/cab will sound with your rig and your playing, is another ball of wax that needs addressing.

in practicality, very few of us, if any at all, have ever fried a Fender Output Transformer. The theory says we can and maybe will should we mismatch the speaker load, the practicality says different.

Fender circuit designs want us to use the primary speaker out for ONE speaker and the ext out for the 2nd. Of course you don't have to do that , you can run multiple speakers off the primary jack, especially if it's a "head" driving a couple of cabs daisy chained.

I have personally connected and witnessed all sorts of speaker conglomerations over the years with Fender amps, 4 ohm OT's 8 Ohm Ot's, it didn't matter, we just plugged em' in.

Is the theory above correct,? of course it is.

When I was in electronics school (late 60's) I ran a 12VDC to AC converter in my car and hooked up my Sony Reel to Reel tape deck in my car. My Professor spent half an hour in class telling everyone why it would not work. He was adamant. So we took a field trip ( to the parking lot) where I turned it all on and we listened to CHICAGO on my tape deck. Our Professor just shook his head and said ' "it's not supposed to work " .

To clarify my original reply for Marc - I said that with a nominal 4-Ohm and 16-Ohm load in parallel, the 4-Ohm load would get (nominally) 80% of the power and the 16-Ohm load would get 20% of the power. I said nothing about loudness. That will, of course, depend on many factors, including the frequency spectrum of the signal being amplified, and the frequency response and sensitivity of the speakers. Dave G. is absolutely correct that the complex impedance curve of the speakers varies with frequency and the matchup between the musical signal frequencies and that speaker frequency response is a big factor.

I also intimated that I don't think using a 3.2-Ohm nominal impedance is a big issue in an amp expecting a 4-Ohm nominal impedance. In general, it is better with a tube amp (which has an output transformer) to use a slightly-lower-than-rated-impedance load than a slightly-higher-than-rated-impedance load. This is discussed a lot of places, including on this forum. The issue is that a higher-impedance load tends to create a higher "flyback" voltage from the speaker back to the output transformer. If this gets high enough, it can cause arcing and subsequent melting of the insulation in the transformer windings.

I think most later Fender output transformers are over-designed and can handle a certain amount of this, but I wouldn't push it. The higher the mismatch and harder one pushes an amp, the more likely something like this is. I have had output transformers go on old Fenders - these were being run with the correct load impedance, I just played them hard for years and years and they finally went. And IMHO, output transformers from certain makes are more sensitive than those hardy old Fenders.

The other thing is that, technically, maximum power transfer occurs when the complex impedance of the amp and the complex conjugate of the load impedance are the same. It is essentially impossible to exactly match these complex impedances in practice. But the closer to matched, the better power transfer. Some people prefer to run unmatched. There are sometimes valid reasons to do this. Myself, I generally prefer to run amp and load as closely matched as possible. But again - I don't think running a 16-Ohm cab in parallel with a Vibrolux's 4-Ohm internal speaker combo is a big issue.

I don't really want to wade into the argument that ensued. But I basically see it from Dave's point of view - I would generally prefer a higher-efficiency speaker in a lower-powered amp. Using a good high-efficiency speaker can bring a lower-powered amp alive, to my tastes. Of course, measuring speaker "efficiency" or "sensitivity" is not necessarily straightforward. Some manufacturers measure sensitivity at one frequency (1 KHz), which doesn't really tell the full story. I like Eminence's approach: http://www.eminence.com/support/underst ... aker-data/

Sensitivity

This data represents one of the most useful specifications published for any transducer. It is a representation of the efficiency and volume you can expect from a device relative to the input power. Loudspeaker manufacturers follow different rules when obtaining this information — there is not an exact standard accepted by the industry. As a result, it is often the case that loudspeaker buyers are unable to compare ‘apples to apples’ when looking at the sensitivities of different manufacturers’ products. Eminence sensitivities are expressed as the average output across the usable frequency when applying 1W/1M into the nominal impedance. ie: 2.83V/8 ohms, 4V/16 ohms.

All I can tell you is that back in the sixties we plugged different speakers and amps together in every combination you can imagine and never blew anything up. Deluxe Reverb's into Bassman cabs, Bassman's running two 2 x 12" cabs. Twin's with a single 15" cab along with the 12's. You name it, we probably did it.

And some of the combinations actually sounded good!