Why do more expensive speakers tend to be less efficient?

[TLS Guy]

Ive tried finding this online and cant seem to find it. Why are my old Cerwin Vega DX3's so efficient at 94db, yet my mid range Infinity Beta 50's are 91db and my girlfriends B&W 804 Nautilus' are only 87 or 89db. Whats the point of having a speaker that takes a beast of an amp to drive vs a speaker thats easy to drive? One would think the Cerwin Vegas would be the least efficent speakers while the B&W's the most efficient. But thats not the case.

Part of your problem is that you are using sensitivity as a measure of efficiency and total sound energy delivered to the room. Sensitivity is measured on axis. If a speaker has poor dispersion more of its energy will be on axis, and it will have a higher sensitivity number. However a less sensitive speaker may actually deliver more acoustic energy into the room and have higher average spl in the room, than the apparently more sensitive speaker.

In general poor speakers beam more than better designs.

As has already been explained, baffle step compensation is important for a properly balanced sound but is a passive design this will lower sensitivity.

That is the next issue, that passive crossovers have line resistance, and the higher the order, the greater the loss. In general a passive crossover consumes half and very often more than half the amp power.

Unfortunately since the waning of the Golden Days of audio, manufacture and design has shifted to the Far East, and there innovative drive has really declined. So endless receivers are churned out year after year, when we could make a switch to fully active speakers. This would garner a huge increase in performance, and avoid the horrid phase angles so prevalent in costly three way passive speakers, that do genuinely call for beast of amps you complain about. This is something that really needs to change.

Added to which you have the trade off of high flux density and loss of bass extension. Also high flux designs tend to have T/S parameters favoring larger cabinets, and then decreased acceptance. All speakers are a difficult compromise with no perfect solutions. In general which ever way you cut it most speakers cluster in the average sensitivity range 87 to 89 db 2.83 volts 1 meter. And then don't forget a four ohm speaker will draw twice the amp power of an 8 ohm speaker for the same sensitivity.

In many ways this is unfortunate, as in this range for speakers in the more easily affordable range there will certainly be issues of audible thermal compression at high spl. with poor performance.

A speaker with good performance at high spl. is still a formidable piece of engineering and can not be done on the cheap.

 

[slipperybidness]

=

That is the next issue, that passive crossovers have line resistance, and the higher the order, the greater the loss. In general a passive crossover consumes half and very often more than half the amp power.

This would garner a huge increase in performance, and avoid the horrid phase angles so prevalent in costly three way passive speakers, that do genuinely call for beast of amps you complain about. This is something that really needs to change.

.

Can you please elaborate on these points a little?

You say that a passive crossover consumes half of the available power. Is this purely resistive losses? Or does this have more to do with the introduction of the phase angle and the power factor associated with the phase shift? Obviously, if you have a low power factor, then you are fighting a losing battle from the start.

Can you comment on a typical phase angle from an average 3 way design? What kind of angle is the norm for today's speakers and + or - ?

 

[Swerd]

Can you please elaborate on these points a little?

You say that a passive crossover consumes half of the available power. Is this purely resistive losses? Or does this have more to do with the introduction of the phase angle and the power factor associated with the phase shift? Obviously, if you have a low power factor, then you are fighting a losing battle from the start.

Can you comment on a typical phase angle from an average 3 way design? What kind of angle is the norm for today's speakers and + or - ?

I'll try an answer. As an example of a passive crossover, think of the woofer circuit in the MB27 DIY design. Note that this speaker's crossover is a 2nd order acoustic design. It may not look like a 2nd order electrical filter, but the acoustically measured roll-off of the circuit combined with the woofer, most resembles 2nd order.

There are 3 inductor coils: 2 large coils in series with the woofer, and 1 in parallel. The larger inductance, the more wire windings there are. So the 2 large coils will produce to most DC resistance and the greatest insertion loss. One way to help minimize this is to use larger gauge wire to wind the coil. Notice that the 2 large coils are made with 16 g wire, and the smaller coil has 19 g.

1.5 mH, 16 g, 0.43 Ω DC resistance
1.0 mH, 16 g, 0.34 Ω DC resistance
0.3 mH, 19 g, 0.3 Ω DC resistance

The 1.5 mH coil, and the 50 Ω resistor in parallel to it, are for baffle step compensation. The 1.0 mH coil generates the low pass frequency. It, along with the parallel circuit containing a resistor, coil and cap (an LCR filter) shaped the woofer's roll-off curve to better blend with the tweeter used in that design.

As you can see, this circuit generates a lot of DC resistance just from those 3 inductor coils. The M-130 woofer is rated by itself (not in a cabinet and without crossover) with a sensitivity of about 90 dB. But the MB27 design has a sensitivity of about 86 dB.

The insertion loss due to the DC resistance of the inductor coils may be the easiest to explain cause of sensitivity loss. I believe it's also the largest cause, but I can't say how it compares to other causes such as a crossover's introduction of phase angle.

 

[AcuDefTechGuy]

You say that a passive crossover consumes half of the available power.

I wonder how that can be proven on measurements?

To prove that a passive XO wastes 1/2 the power. So a 300WPC amp essentially becomes only 150WPC?

Why the heck didn't my Physics or Calculus professors give us that for a cool assignment when I was in college.

But then again, considering the fact that most speakers require less than 50wpc in most consumer cases (one AVS member said he has not seen his McIntosh amp power meter go above 45watts with his B&W 802D2), it's probably no big deal to begin with.

 

[MrAcoustat]

Acoustat 1+1s electrostatic speakers ( 1984 ) 81DB efficiency

 

[slipperybidness]

I wonder how that can be proven on measurements?

To prove that a passive XO wastes 1/2 the power. So a 300WPC amp essentially becomes only 150WPC?

Why the heck didn't my Physics or Calculus professors give us that for a cool assignment when I was in college.

But then again, considering the fact that most speakers require less than 50wpc in most consumer cases (one AVS member said he has not seen his McIntosh amp power meter go above 45watts with his B&W 802D2), it's probably no big deal to begin with.

Probably just as easy (easier) to calculate than measure, should be able to get results within 5-10% of measured values.

 

[slipperybidness]

I'll try an answer. As an example of a passive crossover, think of the woofer circuit in the MB27 DIY design. Note that this speaker's crossover is a 2nd order acoustic design. It may not look like a 2nd order electrical filter, but the acoustically measured roll-off of the circuit combined with the woofer, most resembles 2nd order.

There are 3 inductor coils: 2 large coils in series with the woofer, and 1 in parallel. The larger inductance, the more wire windings there are. So the 2 large coils will produce to most DC resistance and the greatest insertion loss. One way to help minimize this is to use larger gauge wire to wind the coil. Notice that the 2 large coils are made with 16 g wire, and the smaller coil has 19 g.

1.5 mH, 16 g, 0.43 Ω DC resistance
1.0 mH, 16 g, 0.34 Ω DC resistance
0.3 mH, 19 g, 0.3 Ω DC resistance

The 1.5 mH coil, and the 50 Ω resistor in parallel to it, are for baffle step compensation. The 1.0 mH coil generates the low pass frequency. It, along with the parallel circuit containing a resistor, coil and cap (an LCR filter) shaped the woofer's roll-off curve to better blend with the tweeter used in that design.

As you can see, this circuit generates a lot of DC resistance just from those 3 inductor coils. The M-130 woofer is rated by itself (not in a cabinet and without crossover) with a sensitivity of about 90 dB. But the MB27 design has a sensitivity of about 86 dB.

The insertion loss due to the DC resistance of the inductor coils may be the easiest to explain cause of sensitivity loss. I believe it's also the largest cause, but I can't say how it compares to other causes such as a crossover's introduction of phase angle.

Let's see what TLS has to say on the matter. I suspect that the phase angle is at least as big of a robber of power as the inline resistance.

But while we are the topic of inductors, I want to throw out a question that has been bugging me for a while. Why are the typical crossover inductors all air-core inductors? And that is advertised as a selling point. However, from my electronics studies (so far), it seems to me that iron core or some other core inductor actually would be better due to the increased inductance.

Obviously (I think), I have overlooked something or am making a bad assumption somewhere in my reasoning. Can you point me in the right direction as to why crossovers would be better built with air core inductors?

 

[ski2xblack]

Let's see what TLS has to say on the matter. I suspect that the phase angle is at least as big of a robber of power as the inline resistance.

But while we are the topic of inductors, I want to throw out a question that has been bugging me for a while. Why are the typical crossover inductors all air-core inductors? And that is advertised as a selling point. However, from my electronics studies (so far), it seems to me that iron core or some other core inductor actually would be better due to the increased inductance.

Obviously (I think), I have overlooked something or am making a bad assumption somewhere in my reasoning. Can you point me in the right direction as to why crossovers would be better built with air core inductors?

I would like TLS's comment too, but I can answer some basics on inductors. Compare an air core and iron core of the same inductance and the air core will use more copper, making it more expensive. The iron core inductor is less susceptible to electromagnetic fields, where air cores are more so, thus necessitating care in layout so they don't interact with the rest of the crossover bits. Air cores don't saturate, while iron cores do (this should only matter if you feed an iron core enough power to saturate in the first place, although that point will probably generate some argument from the air-core purists). It's a matter of choosing the appropriate compromise to achieve the performance goals.

 

[slipperybidness]

Let's see what TLS has to say on the matter. I suspect that the phase angle is at least as big of a robber of power as the inline resistance.

But while we are the topic of inductors, I want to throw out a question that has been bugging me for a while. Why are the typical crossover inductors all air-core inductors? And that is advertised as a selling point. However, from my electronics studies (so far), it seems to me that iron core or some other core inductor actually would be better due to the increased inductance.

Obviously (I think), I have overlooked something or am making a bad assumption somewhere in my reasoning. Can you point me in the right direction as to why crossovers would be better built with air core inductors?

Just wanted to add some more info, and why I suspect that the power factor (phase angle) is the biggest problem with passive crossovers.

Power factor = cos (phase angle b/w I and V). When angle is 0, the power factor is 1. When angle is 90, the PF is 0. So regardless of the peak value of I or V, the equation is dominated by the cos(angle).

So, true power is V*I*cos(angle)

 

[lsiberian]

I wonder how that can be proven on measurements?

To prove that a passive XO wastes 1/2 the power. So a 300WPC amp essentially becomes only 150WPC?

Why the heck didn't my Physics or Calculus professors give us that for a cool assignment when I was in college.

But then again, considering the fact that most speakers require less than 50wpc in most consumer cases (one AVS member said he has not seen his McIntosh amp power meter go above 45watts with his B&W 802D2), it's probably no big deal to begin with.

If you know the resistances you can mathematically determine insertion loss. It gets fairly complex when you start adding the phase angles and other stuff, but you can mathematically determine insertion loss.

 

[Swerd]

Let's see what TLS has to say on the matter. I suspect that the phase angle is at least as big of a robber of power as the inline resistance.

The trouble I have thinking about phase angle variations is that it depends heavily on frequency. If a musical signal doesn't have the frequencies at which large variations of phase angle occur, the potential problems that come with wide swings in phase angle are slim to none.

I find DC resistance from long lengths of copper wire intuitively easy to understand. As soon as you introduce AC signal with varying frequencies, my intuition goes to pieces. Its much easier to rely graphs of frequency vs. impedance or impedance angle.

But while we are the topic of inductors, I want to throw out a question that has been bugging me for a while. Why are the typical crossover inductors all air-core inductors? And that is advertised as a selling point. However, from my electronics studies (so far), it seems to me that iron core or some other core inductor actually would be better due to the increased inductance.

Obviously (I think), I have overlooked something or am making a bad assumption somewhere in my reasoning. Can you point me in the right direction as to why crossovers would be better built with air core inductors?

Typically air core inductors are favored for reasons that involve the words "saturation" and "hysteresis". I no longer remember what I may have learned in school about that, so I rely on what Wikipedia says.

Inductor - Wikipedia, the free encyclopedia

An "ideal inductor" has inductance, but no resistance or capacitance, and does not dissipate or radiate energy. However real inductors have resistance (due to the resistance of the wire and losses in core material), and parasitic capacitance (due to the electric field between the turns of wire which are at slightly different potentials). At high frequencies the capacitance begins to affect the inductor's behavior; at some frequency, real inductors behave as resonant circuits, becoming self-resonant. Above the resonant frequency the capacitive reactance becomes the dominant part of the impedance. Energy is dissipated by the resistance of the wire, and by any losses in the magnetic core due to hysteresis. At high currents, iron core inductors also show gradual departure from ideal behavior due to nonlinearity caused by magnetic saturation. At higher frequencies, resistance and resistive losses in inductors grow due to skin effect in the inductor's winding wires (Note: skin effect at audio frequencies is insignificant - Swerd). Core losses also contribute to inductor losses at higher frequencies. Practical inductors work as antennas, radiating a part of energy processed into surrounding space and circuits, and accepting electromagnetic emissions from other circuits, taking part in electromagnetic interference. Circuits and materials close to the inductor will have near-field coupling to the inductor's magnetic field, which may cause additional energy loss. Real-world inductor applications may consider the parasitic parameters as important as the inductance.

When people say that air core coils are always better than steel or iron core coils, I wonder if they're concluding that steel or iron core inductors are inferior to air coil inductors because they're cheaper.

Solid core inductors do use much less copper wire, but that can be an advantage both in cost and in lower DC resistance. In my example above, a 1 mH air core inductor made with 16 g wire had 0.35 Ω DC resistance. A 1 mH steel laminate core inductor made with 15 g wire has 0.1 Ω.

In a 3-way speaker with a large woofer, a low-pass crossover for it will require a very large inductor coil. An air core inductor will be expensive, will have a large DC resistance, and will be physically large. A steel or iron core inductor will have much less DC resistance, will cost less, and will be smaller. DIY speaker designers I know think a steel or iron core inductor is an acceptable compromise in that situation.

Which is worse, losses due to DC resistance or magnetic saturation? As the price of copper goes up, this thinking becomes more relevant.

 

[slipperybidness]

If you know the resistances you can mathematically determine insertion loss. It gets fairly complex when you start adding the phase angles and other stuff, but you can mathematically determine insertion loss.

I have my first test on Monday in my AC circuit analysis class, concerning just such topics. The math is more complex, but the same formulas for DC work just the same for AC.

 

[slipperybidness]

The trouble I have thinking about phase angle variations is that it depends heavily on frequency. If a musical signal doesn't have the frequencies at which large variations of phase angle occur, the potential problems that come with wide swings in phase angle are slim to none.

I find DC resistance from long lengths of copper wire intuitively easy to understand. As soon as you introduce AC signal with varying frequencies, my intuition goes to pieces. Its much easier to rely graphs of frequency vs. impedance or impedance angle.

Typically air core inductors are favored for reasons that involve the words "saturation" and "hysteresis". I no longer remember what I may have learned in school about that, so I rely on what Wikipedia says.

Inductor - Wikipedia, the free encyclopedia
When people say that air core coils are always better than steel or iron core coils, I wonder if they're concluding that because steel or iron core inductors are inferior to air coil inductors because they're cheaper.

Solid core inductors do use much less copper wire, but that can be an advantage both in cost and in lower DC resistance. In my example above, a 1 mH air core inductor made with 16 g wire had 0.35 Ω DC resistance. A 1 mH steel laminate core inductor made with 15 g wire has 0.1 Ω.

In a 3-way speaker with a large woofer, a low-pass crossover for it will require a very large inductor coil. An air core inductor will be expensive, will have a large DC resistance, and will be physically large. A steel or iron core inductor will have much less DC resistance, will cost less, and will be smaller. DIY speaker designers I know think a steel or iron core inductor is an acceptable compromise in that situation.

Which is worse, losses due to DC resistance or magnetic saturation? As the price of copper goes up, this thinking becomes more relevant.

Aha, I wasn't considering hysteresis!

Yes, you are correct that the phase angle is very much frequency dependent.

 

[Swerd]

I have my first test on Monday in my AC circuit analysis class, concerning just such topics. The math is more complex, but the same formulas for DC work just the same for AC.

Except for those pesky direction vectors.

Good luck with the test .

 

[lsiberian]

I have my first test on Monday in my AC circuit analysis class, concerning just such topics. The math is more complex, but the same formulas for DC work just the same for AC.

I knew there was something not quite right about you. Playing with electricity is a dangerous game. You should try to get an internship with Harman.

 

[slipperybidness]

Except for those pesky direction vectors.

Good luck with the test .

Thanks for the well wishes. I think I'm pretty much ready, gonna study a few more hours over the weekend. It makes all the difference when you are studying something that you want to be studying. Of course, I'm out to make an A, not just pass.

Direction vectors, I learned the math in high school ~15 years ago. Used it several times in college, so I'm comfortable with all the concepts.

Isiberian: I'm more interested in the electronics building than the speaker building, but I might dabble with speakers a bit too. I already work at a semiconductor factory in a completely different field, running the analytical chemistry labs.

 

[3db]

The trouble I have thinking about phase angle variations is that it depends heavily on frequency. If a musical signal doesn't have the frequencies at which large variations of phase angle occur, the potential problems that come with wide swings in phase angle are slim to none.

I find DC resistance from long lengths of copper wire intuitively easy to understand. As soon as you introduce AC signal with varying frequencies, my intuition goes to pieces. Its much easier to rely graphs of frequency vs. impedance or impedance angle.

Typically air core inductors are favored for reasons that involve the words "saturation" and "hysteresis". I no longer remember what I may have learned in school about that, so I rely on what Wikipedia says.

Inductor - Wikipedia, the free encyclopedia
When people say that air core coils are always better than steel or iron core coils, I wonder if they're concluding that steel or iron core inductors are inferior to air coil inductors because they're cheaper.

Solid core inductors do use much less copper wire, but that can be an advantage both in cost and in lower DC resistance. In my example above, a 1 mH air core inductor made with 16 g wire had 0.35 Ω DC resistance. A 1 mH steel laminate core inductor made with 15 g wire has 0.1 Ω.

In a 3-way speaker with a large woofer, a low-pass crossover for it will require a very large inductor coil. An air core inductor will be expensive, will have a large DC resistance, and will be physically large. A steel or iron core inductor will have much less DC resistance, will cost less, and will be smaller. DIY speaker designers I know think a steel or iron core inductor is an acceptable compromise in that situation.

Which is worse, losses due to DC resistance or magnetic saturation? As the price of copper goes up, this thinking becomes more relevant.

Its been a long time for me too but if I remember correctly, hysteresis is a measure of a transformer's ability to follow the input signal measured from the output. The larger the hysteresis value, the larger the lag of the wavefrom being produced at the output. What I'm not sure of if hysteresis is greater with air core than iron core transformers. Saturation is when you can't pull more current out of the secondary even if you apply more voltage to the primary.

 

[3db]

I have my first test on Monday in my AC circuit analysis class, concerning just such topics. The math is more complex, but the same formulas for DC work just the same for AC.

Good luck.

 

[Swerd]

Its been a long time for me too but if I remember correctly, hysteresis is a measure of a transformer's ability to follow the input signal measured from the output. The larger the hysteresis value, the larger the lag of the wavefrom being produced at the output. What I'm not sure of if hysteresis is greater with air core than iron core transformers. Saturation is when you can't pull more current out of the secondary even if you apply more voltage to the primary.

Thanks for that . Saturation applies here, but probably not hysteresis.

I know it all had something to do with iron magnets with wire windings, but that was about all I could remember. At least I did remember how to spell hysteresis .

A long time ago I learned that saying more can often only reveal my own ignorance. Sometimes its better to say less and keep people guessing .

 

[TLS Guy]

Can you please elaborate on these points a little?

You say that a passive crossover consumes half of the available power. Is this purely resistive losses? Or does this have more to do with the introduction of the phase angle and the power factor associated with the phase shift? Obviously, if you have a low power factor, then you are fighting a losing battle from the start.

Can you comment on a typical phase angle from an average 3 way design? What kind of angle is the norm for today's speakers and + or - ?

Yes, the in line resistances really start to add up, especially in fourth order three ways. In three ways there is usually an L-pad, and always a resistor in series to tame the band pass gain. These losses are particularly significant. Tweeter L-pads operate in an area where there is not much power.

In the budget speaker category, the in line woofer inductors are usually wound with pretty puny gauge wire. Inductors wound with 14 G wire are not very prevalent in commercial products. Then of course except in first order filters, the T-sections shunt quite a lot of power to ground. If they did not you would not get the roll offs required. So there are multifactorial losses. Even with very good components I generally measure 2.5 to 3 db insertion loss for three ways, more for fourth order.

Phase angles do not consume power, as the power is given back. The problem is that there is a gap between apparent and true power, and the amp has to provide the current for the apparent power. This is concealed in the impedance curve. For some designs with low impedance to start with adverse phase angles can present close to a short circuit at certain frequencies. When these angles occur below the 500 Hz range, I can assure they really stress an amp. The B & W 800 D is one of the worst offenders in this regard. Mac have told me they use this speaker as their reference amp stress tester.