Tin
Club Member
Hoffmans Iron Law only applies to speakers, not amps. Bob Carver builds some killer stuff, you should see the tube amps he puts on eBay. If only I could drop the 10 grand on a pair of Carver monoblocks
The ask Tin about audio thread
- Thread starter Tin
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Hoffmans Iron Law only applies to speakers, not amps. Bob Carver builds some killer stuff, you should see the tube amps he puts on eBay. If only I could drop the 10 grand on a pair of Carver monoblocks
suggtt48116
Banned
Tin
Club Member
A good tube amp doesnt have a warm sound, per se. Many are actually very crystal clear, Ive never owned a solid state amp as clear as my tubes. Also, no digital to analog conversion takes place in an amplifier. The conversion process is done by a digital to analog converter, which will be either a standalone unit or integrated into a source component, such as a CD player. Nearly all of my more recent solid state experience involves NAD, Adcom, and Arcam, which off the shelf would’ve cost me more than what I have into my lowly tube system. You cant compare a solid state amp to a single-ended class A tube amp, not because one is better than the other, but because theyre 2 totally different topologies. As I was saying about even order harmonics above, theyre naturally occurring, everything we hear naturally is even order harmonics, aside from man made odd order harmonics which are present in audio devices. This is what gives single-ended class A its sound. Its by far the best amp topology for live acoustic music and even electronic music. Your class AB push-pull amp, be it tube or solid state, throws the sound at you. With single-ended class A, the sound has a “hanging in the air” quality to it, a flesh and blood tone that cant be replicated in other topologies. It sounds like live music, full of life with an remarkable quality that you wont find anywhere else. Going tubes isn’t a painful experience. In hifi amplifiers, tubes seldom go bad. Guitar players overdrive their tubes to get the desired sound effect, but in the hifi setting, tubes arent run hard. Ive purchased 60 year old tubes that have been used heavily, and still test as new on a tube tester. Ive only had one tube go bad on me, and it was an error on my part because I had wired something wrong. All audio amplifiers sound better with a little warm up period…be it tube or solid state. I usually let mine warm up for 5 to 10 minutes before I get cranking, but its no thing for me to start playing music right after I power it up
Exactly. Its much easier to match an amp to speakers than it is speakers to an amp. If youre going single-ended class A tube, your off the shelf speaker choices will be severely limited, but if you have some DIY skills, itll open up a whole new world of speakers thatll work well with both types of amps. Im a big fan of large vintage coaxial drivers; Electro Voice, Altec Lansing, Tannoy, Goodmans, Knight, Jensen, Lafayette, etc. Nearly all work great with single-ended class A, and cabinet plans abound for all of them. They all have the perfect characteristics of a tube-friendly speaker, higher impedance, high efficiency, and a simple crossover. Most of these drivers are in the 12” to 15” range, and may need very large cabinets, but theyre the perfect tool for the flea amp job.
Tin
Club Member
Wait till something better comes up
Not that theres anything wrong with those, but theyre not the KLH speakers designed by Henry Kloss...the "K" in KLH. Those are the more modern KLHs that were sold in best buy in the 90s and early 2000s.
Tin
Club Member
suggtt48116
Banned
I've read that and many other articles on Hoffmans Iron Law since the early 90's when I was getting into external subwoofers because I couldn't afford speakers that produced bass. Then I can upon the Sunfire stuff and have been convinced that Hoffmans Iron law was no longer relevant.
This is the part of Sunfires (Bob Carver) white paper that claims Hoffmans Law is a myth. I have a actual copy with the hand drawings and all stored away that I got with my Sunfire True Sub Sig. back in '98
a loudspeaker designer can choose two of three variables arbitrarily and at will, but will be stuck with the third.
We can choose: 1) Low frequency limit 2) Efficiency ...... and we're stuck with: 3) Box size
Or we may choose: 1) Box size 2) Efficiency
...... stuck with: 3) Low frequency limit
Or choose: 1) Low frequency limit 2) Box size
...... and we,re stuck with: 3) Efficiency
In short, Hoffman's Iron Law tells us it's not possible to have all three at once.
With the new methods and technology developed for the Sunfire True Subwoofer, We can choose all three at will! And guess what? I chose small size, lots of low bass, and high efficiency. And in the end, Hoffman's Iron Law falls (actually it doesn't fall, but it must be interpreted in a way different from the classical interpretation). A simple thought experiment clearly illustrates that it's theoretically possible to build a much more efficient woofer. The thought experiment is this: Imagine the voice coil being made of a super conductive wire that has zero resistance. Since we know that most of the input power is lost in the voice coil as joule heat, such a voice coil would not generate heat because heat, in this case, is current squared times resistance. If the resistance is zero the heat is zero. If the heat is zero that means instead of one, two or three percent of the input power becoming useful, the speaker suddenly becomes majestically efficient. A super conductive voice coil is clearly not practical, but the thought experiment itself tells us and teaches us it is possible, at least in theory, that fundamental, intrinsic laws of the universe do not prevent us from making a very small, very efficient woofer.
The secret to making this woofer efficient in spite of its small size and high output is to operate its electric motor, that is, its voice coil and magnetic system, far away from stall. Electric motors, when operated away from stall become very, very efficient. An electric motor operating far from stall generates a very large back electromotive force (emf). That is, most of the voltage that's delivered to the motor is subtracted away by a voltage generated inside the motor by virtue of its own motion; that voltage is called the back emf.
Getting back to woofers, all woofers (except the Sunfire) on the face of this planet, operate very close to stall. A scientist would say close to the stall mode. The stall mode is characterized by very little output power and lots of current running through the coils of the motor making the motor very hot. If the motor is turning fast the back emf is large, and the motor runs cool; the remaining voltage that pushes current through the windings is very small because it's counteracted by the back emf, and the motor becomes extremely efficient. As an example, diesel electric locomotives have a minimum operating speed below which the motors come too close to the stall mode and burn up. For passenger trains it's about 12 mph, for freight trains about 9 mph.
A TRAIN AND A MOUNTAIN
Imagine a train going up a mountain, pulling hard. As it goes up the mountain fast, the train is putting out lots of power because the energy of going up the mountain is delivered in a short time. Since power is work per time, a scientist would say Power = mgh/t short, where m is the mass of the train, g is gravity, h is the height of the mountain, and t short is the short time it takes to get up the mountain. The power output is large, and the electric motors run cool. If the train goes very slow it will not be putting out very much power because Power = mgh/t long, where t long is the long time it takes to go up the mountain. When t is small, power output is high, when t is large, power output is low. What's worse is the motors get very hot and overheat. Its motors are operating in stall mode. Now back to the woofer. Because this woofer moves back and forth a lot, the voice coil is cutting many, many lines of magnetic flux in the magnet structure. It's the rate of flux change that generates back emf. The large back and forth stroke of this woofer is good for making lots of air move but it's even better for generating a large back emf. If the voice coil didn't move very far, it wouldn't generate very much back emf. Without a big back emf too much current would flow through the windings and the woofer would overheat. That's the case with all other woofers on the face of the earth. To have a large back emf, lots of voice coil motion is required. Another requirement for lots of back emf is a very high magnetic flux. To have that requires a huge magnet. The magnet in this woofer is 225 ounces and that compares to around 20-28 ounces for a regular woofer. It's about an order of magnitude larger. Now the problem with all this is that because the woofer is moving so far, it makes a large back emf (due to the large stroke cutting many of lines of force). Consequently, if the woofer were driven by an ordinary amplifier, most of the driving force would go away and the woofer would have very little output. Because the back emf is so large, the applied electromotive force to the woofer must be even greater than the back emf in order to overcome it.
That requires an incredibly powerful amplifier. An amplifier that can swing over 100 volts rms.
Since the DC resistance of the voice coil is 3.3 ohms - that means it's a nominal 4 ohm woofer, 100 volts rms into 4 ohms is well over 2,000 watts. The woofer will not burn up because when it's moving, the back emf prevents the damaging stall mode current that would normally flow if it were a resistance load. Only a small fraction of that current flows in the voice coil, but since the magnet is so huge and because the driving force is equal to the magnetic field strength times the current, the force on the voice coil to drive the woofer and move the air is immense even though not much current is flowing. An alternate way to get drive force on the woofer cone is to increase the current, the normal way of doing it, but that makes the voice coil overheat because of the high current. Or we can make the magnet huge. Problem is if we make the magnet huge, the back emf causes us to run out of volts and therefore we need a very special amplifier to overcome the loss of volts. That requires a tracking down converter amplifier. The tracking down converter amplifier is also unique. Without the tracking down converter amplifier, no matter what, this woofer wouldn't be practical. When all is said and done, the effective input power is not 2,700 watts, even though the amplifier has to be capable of delivering 2,700 watts into a 4 ohm load. When it's actually operating into the loudspeaker, the effective power is far, far less than that. And Hoffman's Iron Law suddenly tumbles. To put numbers to this, as any good scientist would, even though this woofer is one tenth the box volume of a normal woofer, when driven to full output at the same volume level and same low frequency as a giant woofer in a big cabinet, by all the laws of the universe and all the rules that woofer engineers and designers have been taught, the input power should be at least 10 times greater than the input power for the big woofer. But that's not the case. The input power is more, but only slightly more.
A THOUGHT EXPERIMENT Suppose we wanted to build a woofer, and we had a 200 watt amp to do it with, an amp that could deliver 28 volts rms to our 4 ohm speaker.
Now imagine we mount our driver into a nice box. Imagine also that our driver has a "variable magnet", so we have a dial outside of the nice box that we can turn to change the strength of the magnet. The dial is calibrated continuously from zero magnetic strength to super magnetic strength. We drive the system with some bass. Of course, with the dial set at zero, there is no output from the woofer. We begin advancing the dial and the bass comes up. As we advance the dial further, the bass gets louder and louder. However, as we advance the dial beyond a certain magnetic field strength, the woofer output begins to drop. The point of maximum output defines the optimum magnet size for our woofer. Consider Figure 1.
[Image]
DISCUSSION OF THOUGHT EXPERIMENT
We know that as we advance our magnet from zero, the product of the current and magnetic field strength (B) produces a force on the voice coil. As B increases, the force increases and the bass increases. However, no sooner than the woofer starts to move, it produces a back emf that begins to reduce the current through its voice coil. As the magnet becomes ever larger, the current becomes ever smaller, until by and by the ever increasing magnetic force cannot overcome the loss of current due to the increasing back emf. Consider Figure 1.
In this illustration, the back emf is 13 volts, leaving only (28-13) = 15 volts to run the woofer.
If we wish to have more bass output we must have a larger amplifier, one that can deliver more volts in order to overcome the dreaded back emf. Now if we had in our possession an amplifier that had virtually unlimited output voltage, say one that could deliver 104 volts rms into 4 ohms with ease, then we could increase the magnet strength and let the dreaded back emf rise because we would know that we have almost unlimited drive to overcome it. See Figure 2.
[Image]
THE PROOF IS IN THE PUDDING
The definitive demonstration.
I have several large and well designed subwoofers here in my laboratory. Klipsch, Bose, Velodyne, M & K, and several others. One of my favorites is a big one.
I hooked up the Big one (cabinet volume 4.3 cubic feet) and drove it to maximum output (its limiter activated) with a warble tone centered at 28 Hz. I measured the power input from the wall socket with a watt meter and measured the output Sound Pressure Level (SPL) with a simple SPL meter. Input power was 240 watts, output SPL was 112 dB. It was awesome!
I then removed the Big one and replaced it with my Sunfire True Subwoofer and drove it with the same signal until my SPL meter again read 112 dB. Input power was actually 40 watts less at 200 watts! Since my limiter had not yet activated, I turned it up until I activated the limiter with maximum output at 115 dB. Double the output of the Big one. Wow! Input power was then 360 watts.
SUMMARY AND CONCLUSIONS
Big one woofer operating in stall mode. True Subwoofer operating far from stall mode.
240 watts input, standard amplifier approximately 200 watts input, tracking down converter 60% efficient at maximum output means (240) X amplifier approximately 88% efficient (.6) = 144 watts into voice coil. means (200) X (.88) = 176 watts into voice coil.
Big one has 4.3 ft3 box volume. Sunfire has 0.38 ft3 box volume.
However, input power for Sunfire should be (by Thiel-Small and Hoffman's Iron Law): (4.3/0.38) x 144 = 1,629 watts
But it's not! It's only 176 watts. An order of magnitude less! Magic, uh? Indeed, at full output, the True Subwoofer requires 360 watts (115 dB) but it should need 2 (twice the output)X 1,629 = 3,258 watts, but it doesn't!!
So that's the secret. The conceptual secret of how this woofer can be so small, put out so much bass and yet not burn itself up and also not draw tons of power from the wall. As a matter of fact, in spite of all the bass it can put out, it uses only a six amp slow-blo fuse. Putting it all together, this woofer is flat to 18 Hz, can move 251 cubic inches of air (again, the same as four 15 inch woofers operating linearly in a box the size of a small refrigerator), the distortion is extremely low, it has a built in power amplifier, a built in crossover system, input volume controls, crossover control, a phase control to allow it to be blended with any other speaker system and it has a two position switch that allows the woofer to be optimized for stereo (flat to 18 Hz) or to have a contour that rolls off very low frequencies if they bother you.
Tin
Club Member
Dont get me wrong, Im not in any way trying to discredit Bob Carver. The guy is an EE, and doesnt use off the shelf parts like your typical DIYers such as me would use. He designs and builds his own stuff. Even the tube amplifiers he sells on eBay, he winds all of his own transformers and chokes to his exact specs. Something most DIYers cant do, either because they lack the knowledge, tools, or both. The Sunfire design uses huge power because it has a tiny enclosure and applies massive amounts of EQ against the natural roll-off to obtain a flat FR down low. The truth of the matter, go to any speaker supply place, such as Parts Express, Madisound, Creative Sound Solutions, etc, and Hoffmans Iron Law quickly becomes fact. Believe me, Ive modeled tons of drivers in boxes, and modeled all sorts of notch filters, baffle step circuits, and Zobel networks...Hoffmans Iron Law cant be beat. Also realize that cabinet design has as much or more influence on the final sound than the chosen drivers themselves. The cabinet is an acoustic instrument, its design plays heavily on the final sound. This is how things like the Bose Wave Radio sound good for what they are. The actual cabinet portion of the integrated speakers is a complex resonator, which makes them sound much bigger than they really are.
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suggtt48116
Banned
Thanks Tin 
do you do HiFi repair? if not who would you recommend to fix something in S.E. Michigan. The last thing I had a problem with was my Denon AVR2307ci receiver and it was only a few months old and the dealer I bought it from sent it to United Radio in New York.
do you do HiFi repair? if not who would you recommend to fix something in S.E. Michigan. The last thing I had a problem with was my Denon AVR2307ci receiver and it was only a few months old and the dealer I bought it from sent it to United Radio in New York.
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Funny you mention SETs, because when I say I'm putting together a 2 channel system, I mean I'm planning to DIY a 2 channel system, at least in the amp and speaker department. I don't have a specific set of speakers I'm trying to build because I want to assemble and experiment with different designs, and initially I'll start with some inexpensive Tube amp designs. I just want to put together a starting point as far as speakers without breaking the bank, so right now I'm looking at full ranger driver type designs for practicality and a starting point.
My goal is to put together a few initial components that actually work together or don't end up being a waste of time -- I'd rather be listening and adjusting than trying to figure out why I'm getting no sound, which is the basis for my question.
I'm familiar with electronics and have a small workshop, and I repair vintage synthesizers for myself and others from time to time, and I'm on and off working on my own modular synthesizer modules for common formats, but all my work has been before the amp and speaker, so this is new to me.
My goal is to put together a few initial components that actually work together or don't end up being a waste of time -- I'd rather be listening and adjusting than trying to figure out why I'm getting no sound, which is the basis for my question.
I'm familiar with electronics and have a small workshop, and I repair vintage synthesizers for myself and others from time to time, and I'm on and off working on my own modular synthesizer modules for common formats, but all my work has been before the amp and speaker, so this is new to me.
Tin
Club Member
Depending on the type of music you listen to, you might not take a liking to single full range drivers. They can sound spectacular, but theyre best suited to less complex music, that was my experience anyway. There is a way around this though, you can always do MJK Open Baffles and go with an active crossover, that way the driver wont beam its upper mids/highs because the cone isnt trying to make bass at the same time. The open baffles can be done rather cheap, should run you less than $500 in parts. The best part of an open baffle is the di-pole radiation, the room has less of an influence on the final sound than a box design. Another good high efficiency candidate is the Econowave, there are many variations, and the crossover boards and and other parts are readily available. The Econowave is modeled after the Altec Model 19...or A7 Voice Of The Theater, going by their retail name. As far as amps, there are many great designs out there. By far, the most popular ones would be the JE Labs Simple 2A3, or the JE Labs 300B Deluxe. Lots of options out there. The 2A3 is probably the easiest triode to work with...as many have said, there arent many bad sounding 2A3 amps out there.
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Tin
Club Member
As you can see, SET amps are pretty simple circuits...generally not much in the signalpath other than maybe a resistor or capacitor, sometimes an interstage transformer depending on the design. Some are even directly coupled.
JE Labs 2A3 (3WPC)
JE Labs 300B (8WPC)
Another very popular one is the Loftin White 2A3, its directly coupled....just a resistor in the signalpath. Thats about as pure of a signal as you can get.
In some solid state equipment, the signal will travel through countless resistors and capacitors before it finally reaches the speakers.
JE Labs 2A3 (3WPC)
JE Labs 300B (8WPC)
Another very popular one is the Loftin White 2A3, its directly coupled....just a resistor in the signalpath. Thats about as pure of a signal as you can get.
In some solid state equipment, the signal will travel through countless resistors and capacitors before it finally reaches the speakers.
suggtt48116
Banned
nothing wrong with the AVR. The Sunfire Subwoofer volume knob from time to time acts up. The volume gets picky when set at a certain level not wanting to turn on all the time (fixing it takes just moving volume up/down) and it's good. I have thought of sending it straight to Sunfire they said a flat rate of ??? can't remember to fix it. Thanks
Tin
Club Member
Tin
Club Member
Absolutely. That would be better than the usual way of having stand mount speakers for the rears. Having floor standers all around means you get more bass and a better sense of realism
If you can, try and run 2 subwoofers...since bass is omni-directional, Id put them at opposite corners of the room. Im looking at houses in your neighborhood...Ill know where to send the cops in the event of loud noise :lol:
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ReiKo
New member
I conned my brother into buying abunch of the AV stuff for his house... Mine won't be done till I get the basement done... Then it's open season....Absolutely. That would be better than the usual way of having stand mount speakers for the rears. Having floor standers all around means you get more bass and a better sense of realism
Tin
Club Member
Let me know when youre ready. How big is the basement? If you have the room, I can track down some good Klipsch Heritage stuff.
3 Klipsch Heresys...for the center and rears
A pair of Klipsch Cornwalls for the fronts mains
You might not even need a sub with all of that...the Cornies will dig down into the high 20Hz range when room gain is taken into consideration
ccbchevy
Club Member
Ok tin got a problem got a 01 f350 diesel after market radio with 3 amps. I have the plug that u hook into the rca ins to run my ipod and satellite radio well when i plug either those in and the are hooked into cig lighter i get engine noise bad unhook from cig no engine noise what is causing this and how can i fix it?