Does someone have an exact answer to this question about power amp output?

[Verdinut]

This is a question that puzzles me and to which I have never have never been able to find an answer to:

Most of us know that, when an amplifier drives a speaker, if the frequency is halved, the cone excursion is increased by a factor of four.
What about the amplifier output power? Is it then also increased by a factor of four ?

 

[everettT]

What source are you citing that this is correct?

 

[Verdinut]

That the cone excursion is increased by a factor of four? It's a fact.

One source is a vintage Howard W. Sams book jointly written by Alexis Badmaieff and Don Davis entitled "How to Build Speaker Enclosures".
The late Alexis Badmaieff was the holder of 27 patents in the fields of electronics, acoustics, optics and mechanics.
Don Davis is also an engineer who had been acting in various capacities in the audio field, as a consultant and in extensive work in auditorium acoustics throughout the U.S.
Both of them worked for Altec Lansing.

 

[everettT]

Thanks I'll google it and read up. I would have thought that with different drivers and enclosure types there would variance.

That the cone excursion is increased by a factor of four? It's a fact.

One source is a vintage Howard W. Sams book jointly written by Alexis Badmaieff and Don Davis entitled "How to Build Speaker Enclosures".
The late Alexis Badmaieff was the holder of 27 patents in the fields of electronics, acoustics, optics and mechanics.
Don Davis is also an engineer who had been acting in various capacities in the audio field, as a consultant and in extensive work in auditorium acoustics throughout the U.S.
Both of them worked for Altec Lansing.

 

[HTfreak2004]

No. Amplifier output power is a fixed potential based on available input voltage from the wall times amperage x .80% efficiency before the plug wiring risks over heating and triggering the breaker. Also an amp is built to operate a specific ohm load. That ohm load multiplied by the voltage draw produces the wattage.


(120 volts x 15 amps)x 80% load
=1800 watts x .8
=1500 watts continuous.
Protects the in plug wires from over heating which would burn a house down. Also reduces breakers tripping.
Volts times ohms = watts
My amp is 180 watts per channel.

22.5 volts x 8 ohms is 180 watts or 900 total watts of draw one zone driven. If I used all 3 zones at the same time theoretically I could produce an 1800 watt draw but that would require a massive alignment of the stars to get all zones to place the simultaneous demand on the amp and consequently the plug power limit.

My main point is the speakers excursion is the result of the input power vs its resistance to be moved through space. The speaker has no say on the power be sent to it as it is not a power source but a receiver for power. The amp only receives an instruction from the processor. This frequency at this voltage level to produce (x) wattage for this amount of time.

At a lower listening level the speaker hardly moves even though the amp is sent a 25 hz frequency and passes it along to the speaker. When the volume gain is increased the same frequency is amplified at a higher current and the speaker excursion is increased. A 100 hz frequency can move the speaker excursion further than a 50 hz if there is sufficient current at 100 hz and a lack of it at 50 hz.

It also seems you are trying to quantify the wattage power required to drive a frequency say 50 hz vs 25 hz. Both can be driven with the same wattage but obviously not to the same sound pressure or sound volume. The sound pressure favours lower frequencies and sound volume level is most perceivable between 2500 hz and 5000 hz.

Something way of topic I'd like to add. Notice that 85 db isn't really all that loud. But with 20-25 db peaks it can sound very loud. Why is that? Say your listening to the tv at 65 db then all of the sudden a big crash happens and the db spikes to 85 db. No different than listening at 85 db right. Not exactly. We are sensitive to rapid changes in sound levels and pressure. When the tv show jumps to 85 db from 65 it catches ones attention. The same happens if the sound level was set at 85 db reference level and all of the sudden peaks to 105. We are born afraid of loud noises that happen suddenly not that are a constant.

Speaker excursion is relative to input power and speaker sensitivity period.
Hz have no say in the matter.

Kick back crank it up loud get those ears bleeding and blow down some walls!









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[Verdinut]

Yes! Herz have to do with cone excursion. When frequency is halved, the cone excursion is quadrupled. It was confirmed by engineers.

 

[HTfreak2004]

At watt voltage level.


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[vsound5150]

Yes! Herz have to do with cone excursion. When frequency is halved, the cone excursion is quadrupled. It was confirmed by engineers.

So if 100Hz produces 1mm cone excursion that means 50Hz produces 4mm? Without changing amplitude? That puzzles me too, there must be a change in amplitude to affect excursion, cutting timing in half can be done without changing amplitude. Maybe those engineers were smoking some funny stuff.

 

[TLS Guy]

This is a question that puzzles me and to which I have never have never been able to find an answer to:

Most of us know that, when an amplifier drives a speaker, if the frequency is halved, the cone excursion is increased by a factor of four.
What about the amplifier output power? Is it then also increased by a factor of four ?

Your premise is totally false. However I told you that is just wrong, when I explained it to you before.

The cone excursion versus drive (power) at a frequency is a function of the T/S parameters of the driver and the loading (tuning).

Here is the cone displacement of a 15" driver under constant load. The red line is under optimal vented loading and the orange line in an optimal sealed box.

Vented the cone excursion is the same at 18 Hz as fifty.

Now to get the power draw at a frequency you need the impedance curve.

Here they are vented and sealed.

Since amps keep constant voltage, the power draw will be less at the peaks of impedance and higher in the dips.

So your premise on cone excursion and power is totally wrong and has NO basis in fact.

If you click on the images they will enlarge and you can see what actually happens in detail.

I don't know what engineers you listened to before that, but if they said that they were bottom of the class and then some.

 

[Verdinut]

Your premise is totally false. However I told you that is just wrong, when I explained it to you before.

The cone excursion versus drive (power) at a frequency is a function of the T/S parameters of the driver and the loading (tuning).

Here is the cone displacement of a 15" driver under constant load. The red line is under optimal vented loading and the orange line in an optimal sealed box.

Vented the cone excursion is the same at 18 Hz as fifty.

Now to get the power draw at a frequency you need the impedance curve.

Here they are vented and sealed.

Since amps keep constant voltage, the power draw will be less at the peaks of impedance and higher in the dips.

So your premise on cone excursion and power is totally wrong and has NO basis in fact.

If you click on the images they will enlarge and you can see what actually happens in detail.

I don't know what engineers you listened to before that, but if they said that they were bottom of the class and then some.

 

[Verdinut]

Your premise is totally false. However I told you that is just wrong, when I explained it to you before.

The cone excursion versus drive (power) at a frequency is a function of the T/S parameters of the driver and the loading (tuning).

Here is the cone displacement of a 15" driver under constant load. The red line is under optimal vented loading and the orange line in an optimal sealed box.

Vented the cone excursion is the same at 18 Hz as fifty.

Now to get the power draw at a frequency you need the impedance curve.

Here they are vented and sealed.

Since amps keep constant voltage, the power draw will be less at the peaks of impedance and higher in the dips.

So your premise on cone excursion and power is totally wrong and has NO basis in fact.

If you click on the images they will enlarge and you can see what actually happens in detail.

I don't know what engineers you listened to before that, but if they said that they were bottom of the class and then some.

 

[TLS Guy]

Somehow your replies are not showing up, just my post repeated twice in Quote.

 

[Verdinut]

I agree with you with the fact that the cone excursion is a function of the loading. I use BassBox too for my designs so I am informed when I see the cone excursion displays.

Probably Badmaieff and Davis of Altec Lansing wanted to imply that there was a direct relation of cone excursion and frequency but only when the speaker is in free air.

Of course, when it's installed in a box, we have a completely different system with interaction of T/S parameters and the box loading.

 

[TLS Guy]

I agree with you with the fact that the cone excursion is a function of the loading.

Probably Badmaieff and Davis of Altec Lansing wanted to imply that there was a relation of cone excursion and frequency but only when the speaker is free air.

Of course, when it's installed in a box, we have a completely different system with interaction of T/S parameters and the box loading.

I don't think it would be true in free air. However it is true to an extent for a sealed driver. As the cone tries to move further it is constrained by the air in the box, as the pressure changes rise with cone movement. This is why a sealed alignment has such a high F3. To overcome this amp power has to go up enormously as the speaker has to be Eq at 12 db per octave below the turnover frequency. Remember a 3db boost doubles the amp power. 10 db requires a ten fold increase.

In a sealed speaker the driver is the sole source of output, and a driver cone is a lousy coupler to the air. There is no acoustic transformer at work, like a reflex enclosure, pipe or horn. Pipes and horns are the most efficient. Also pipes encircle. This has been demonstrated to me by organ builders with an spl meter. Speakers have their spl fall by the square of the distance, pipes for some reason do not. The spl/distance fall off is totally different for an electronic organ versus a pipe organ. This why congregations sing more lustily with a pipe organ in a church versus an organ with speakers. The whole congregation feels supported by a pipe organ, which they are.

I think this is a reason TLs sound so different to other speaker systems.

This issue of encircling, which is what organ builders call it, receives little if any attention in the audio literature. On the other hand this is well known to pipe organ builders.

 

[HTfreak2004]

You can prove that frequency isn't the prime factor for speaker excursion yourself. Although YouTube isn't uncompressed audio, choose a bass frequency of 50 hz. Adjust the volume level to 40 db on your receiver or processor measured by an spl meter set to slow c. Feel the woofer excursion with your hand at this volume.
Do the same with 100 hz frequency.
Now amplify the 100 hz frequency to 85 db. Notice the excursion is greater than the 50 hz frequency at 40 db. The result is due to input current driving the woofer not the frequency input. Yes the lower frequency tone requires more power input to produce at 85 db than 100 hz requires however your question isn't useful for home audio because you will never listen to 50 hz all day.

You have zero control over the frequency duration in a recording. Amps are usually built with reserve capacitors to provide instant voltage burst for the dynamic range of an audio recording.

Trying to quantify this is pointless because your not able to dictate how the recording studio intended the audio to sound on your home audio gear.

Just remember the variable frequencies are presented to your speakers regardless of the volume you listen at as the volume gain isn't a filter for frequency delivery. It's a gauge between the receiver and amp designed to increase or decrease the voltage gain produced by an amp up to its limit. This voltage can then be converted to available wattage necessary for controlling the position of a woofer during is space/time travel. A 50 hz frequency signal can produce all kinds of excursions based on available current which we perceive as sound volume.

Listen to audio at whatever db you choose and the frequency affects the speaker excursion different at any change in db listening level. That is voltage related and voltage x ohms governs wattage.





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[Verdinut]

I don't think it would be true in free air. However it is true to an extent for a sealed driver. As the cone tries to move further it is constrained by the air in the box, as the pressure changes rise with cone movement. This is why a sealed alignment has such a high F3. To overcome this amp power has to go up enormously as the speaker has to be Eq at 12 db per octave below the turnover frequency. Remember a 3db boost doubles the amp power. 10 db requires a ten fold increase.

In a sealed speaker the driver is the sole source of output, and a driver cone is a lousy coupler to the air. There is no acoustic transformer at work, like a reflex enclosure, pipe or horn. Pipes and horns are the most efficient. Also pipes encircle. This has been demonstrated to me by organ builders with an spl meter. Speakers have their spl fall by the square of the distance, pipes for some reason do not. The spl/distance fall off is totally different for an electronic organ versus a pipe organ. This why congregations sing more lustily with a pipe organ in a church versus an organ with speakers. The whole congregation feels supported by a pipe organ, which they are.

I think this is a reason TLs sound so different to other speaker systems.

This issue of encircling, which is what organ builders call it, receives little if any attention in the audio literature. On the other hand this is well known to pipe organ builders.

Thanks for your informative reply.

I don't remember if I ever had the opportunity to hear speakers in a transmission line. I heard many loudspeaker systems over the years at audio shows. In the late 1950's, it was not exactly as today. Manufacturer representative were actually presenting their products and you had access to technical papers.
Now, we see mostly retail sales people and most of them don't know much about the manufacturing process etc.

If I have the opportunity to hear some TLs, I will definitely lend a serious ear to get acquainted with those enclosures. They are probably the best for listening to pipe organs, the closest to being in the church or concert hall.

The issue of encircling which you mention is entirely new to me.

I know that I'm stubborn at times. Thanks again for your patience and time.

Cheers,

 

[TLS Guy]

Unfortunately I don't think you will find what I regard as a true TL to listen to.

I'm really purist about this an don't regard it a true TL unless there is useful port output and the system rolls off second order.

The late John Wright of TDL who died in 1999 was the last person to market the type of speakers I design.

Lots of people design TLs, but they come in different flavors. What I design is the reverse tapered line with just enough damping to give one peak of impedance.

What has become popular of late has been the mass loaded TL popularized by Martin King.

I regard this design as basically an improved reflex design.

This is what William Fitzamaurice, a noted designer has to say about mass loaded TLs: - "True TLs are second order, and that's one reason for their appeal. They have rear wave reinforcement at fp, similar to that of a bass reflex, but with second order roll-off below fp. So-called mass loaded TLs are fourth order because they are reflex cabs which incorporate a 1/4 wavelength resonance at some frequency well above system fb."

The UK firm PMC make a large number of TL speakers. Unfortunately what third party measurements exist are not encouraging. They are not mass loaded, but their impedance curves have two peaks and not one. Their frequency responses are not optimal.

So regretfully if you want to audition the genuine article it means a trip to Benedict Lake MN.

As far as I know, John Wright and myself are the only individuals to have designed speakers with dual TL lines. The last flagship speaker he designed and marketed just before his death was a dual line TL. Reviews and third party measurements were impressive. The speaker was very expensive, I think the most expensive on the market at the time, and I doubt many were sold before the company folded after his death.

The reason for the dual line is to have driver support over two and a half octaves. I can tell you it produces the most life like piano, organ and drum reproduction. In fact the whole bass decade really is like the real thing.

Designing and building these speakers is not for the faint of heart. I can tell you that.

 

[mtrycrafts]

...

Probably Badmaieff and Davis of Altec Lansing wanted to imply that there was a direct relation of cone excursion and frequency but only when the speaker is in free air.

...

I wonder if there was a reference to SPL levels being the same for that excursion?

 

[HTfreak2004]

What difference does it really make? Think about it. 50 hz frequency at 40 db isn't very audible. 100 hz sounds twice as loud at 40 db even though it technically shouldn't even though the db level reads the same on an spl meter. Why get wrapped up in cone excursion? Unless you are trying to get a small speaker to produce a frequency it's not capable of at a meaningful listening level. A larger diameter speaker does not need as long excursion as a small speaker to produce meaningful sound volume at low frequencies. It's also possible to use less wattage and a more sensitive larger driver and produce louder listening volumes.

I think the question about excursion between frequencies is pointless. Compare a smaller speakers diameter to larger speakers diameter at the same frequency input and volume output and the smaller driver must move perhaps 4x as far which usually is way past impossible.


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[Verdinut]

I wonder if there was a reference to SPL levels being the same for that excursion?

Greetings!
No, There was no reference to the SPL in either situation in their book entitled "How to Build Speaker Enclosures".