Is SPL less at bass frequencies when the driver is having to cover a full range input

[RayDunzl]

I put more and more "frequencies" in, in case, what would I expect as a sound, how would that sound?

It would eventually become white noise, if all the frequencies are the same amplitude.

The sound becomes a rumbling hiss.

 

[Hayabusa]

This property is known as "superposition", which basically means that, when the loudspeaker is in its linear operating range, the total output of any combinations of inputs will be the sum of the individual output for each of the input. Therefore, the SPL of the each of the frequency component in the output should be the same as if it is reproducing only one single frequency component.

The superpostion will give you a higher peak excursion, so it will limit the maximum SPL of two tones to less than the SPL of each tone.

 

[terryforsythe]

Thanks for the replies so far. Perhaps I need to take this a step at the time, if you could comment as we go. Below is a low frequency sweep of each speaker (Focal Kanta No1 by the way). To my novice mind, the left channel is getting bass boost through the corner of the room and the right channel bass loss due to the distance from the corner and openings. Until about 60Hz that is, when the effects seem to swap. How is this explained? (Mic is at listening position btw, with no EQ, for both channels distortion is significant until 42Hz).

View attachment 440502

I suspect the left speaker near the corner and the right speaker near the opening to other room are the cause of the difference in the frequency resonses. To verify, I would move one of the speakers to the other speaker's location and run a sweep. Then compare the frequency responses of the two speakers in the same location. If they match, that confirms it. If they don't match within a couple of dB when they both are measured from the same location, there is another issue.

 

[gnarly]

At a specific frequency, maybe.

I should think not when comparing octaves.

If so then across 10 octaves the difference in power would be huge.

4x4x4x4x4x4x4x4x4 = 262144 times the power from high to low frequency, same SPL. It doesn't happen.

YES !!!
comparing octaves is just the way of comparing frequencies, to show how excursion vs frequency for equal SPL works ..
utterly mind boggling isn't it ...!!!

To me it explains how little bitty birds, or cicadas rubbing their legs, can be so load.. It takes so little excursion at very high frequencies.
And how whales can make sounds so low...my guess is they can make lot's of excursion

 

[Heinrich]

It would eventually become white noise, if all the frequencies are the same amplitude.

The sound becomes a rumbling hiss.

I see that my attempt to stimulate a little thought is probably always pointing in the wrong direction.

If it were the case that an additional tone influences the strength of another tone, what would that sound like? In real life on the one hand, with loudspeaker reproduction on the other?

Psysiologically that is the case, right? Somehow! But technically, too? If something like this happens on the technical side, does such an effect somehow depend on the absolute volume level, if quiet less, if loud more of the effect? And so on.

Well - basically we have no experience in this respect. So it seems that there is no such effect. Everything you would expect does not occur. So the effect in question is completely implausible. Problem solved, simply by thinking.

I don't want to annoy anyone, but insisting on “measurements” is one thing, scientific thinking is another. Science leads to measurements, not the other way around. On the contrary, science should and must question measurements, question their meaning, attack the models and ideas behind them. Again, not trying to bother. There is no frequency in nature ;-)

 

[RayDunzl]

Frequencies present in a single gently strummed Bass Guitar Note:

 

[gnarly]

Frequencies present in a single gently strummed Bass Guitar Note:

No idea what you're saying. ?? Pls explain.

Because spectral content of music has nothing to do with what was being discussed.
Which was the amount of displacement necessary for a radiator (piston), to produce equal SPL as frequency decreases...

 

[M240i]

A fundamental concept is that for equal SPL across the frequency spectrum, displacement of a driver need to increase 4X per octave lowering.
Since a driver's area is fixed, it means for whatever frequency span it is covering, it needs to increase excursion 4X for each octave reduction....to maintain equal SPL across the range.
4X excursion requires 4X the power (wattage).

Be careful.

 

[alankila]

A fundamental concept is that for equal SPL across the frequency spectrum, displacement of a driver need to increase 4X per octave lowering.
Since a driver's area is fixed, it means for whatever frequency span it is covering, it needs to increase excursion 4X for each octave reduction....to maintain equal SPL across the range.
4X excursion requires 4X the power (wattage).

Not sure about this 4x the power thing. As far as I understand it, the driver cone is being accelerated by the magnetic field in the voice coil. That is, the voltage puts electrons to move, which creates a force in the groove's magnetic field, and that force accelerates the cone, and the acceleration is what creates a pressure wavefront that we can sense as sound.

Now, let's enter proper spherical cow land. In ideal conditions, the voice coil would never leave the magnetic groove, and the cone surround material would not limit excursion in any way, maybe we are even in an infinite baffle situation so that there's no pressure change of a closed cabinet pushing back, either. In such a case, a voltage applied to voice coil should result in an infinite acceleration velocity (and thus position) of the cone without using more power. So, do we really need more power to achieve higher excursion? Or is there really so much restoring force that we actually have to fight back the surround and cabinet's restoring pressure and that's why more power is needed? Or am I completely lost...

Edit: I wrote acceleration there for some stupid reason. I mean constant acceleration and its implications. Many apologies.

 

[sigbergaudio]

No idea what you're saying. ?? Pls explain.

Because spectral content of music has nothing to do with what was being discussed.
Which was the amount of displacement necessary for a radiator (piston), to produce equal SPL as frequency decreases...

I think there are more than one discussion going on at once in this thread.

 

[gnarly]

I think there are more than one discussion going on at once in this thread.

Yep, thx. I see Ray has a couple of discussions going...

Not sure about this 4x the power thing.

For sure, don't just take my word. Research it.
It's much simpler than folks want to make it...which is why it's so seldom raised, i guess.

 

[Hayabusa]

Yep, thx. I see Ray has a couple of discussions going...




For sure, don't just take my word. Research it.
It's much simpler than folks want to make it...which is why it's so seldom raised, i guess.

excursion goes 4 times with one octave change... not the power...

 

[gnarly]

excursion goes 4 times with one octave change... not the power...

And What do you think provides the extra excursion?

 

[Hayabusa]

And What do you think provides the extra excursion?

extra excursion:

Piston Excursion calculator

www.baudline.com

A speaker at 50Hz at 100dB moves 4 times more than that speaker at 100Hz.
The power remains the same to make that 100dB at both frequencies.

 

[RayDunzl]

And What do you think provides the extra excursion?

Longer time of a cycle of the power wave.

 

[M240i]

And What do you think provides the extra excursion?

Looking at it from the other way, if you wanted to maintain the same driver P-P excursion as you go higher in frequency, that would require 4x more power/octave. (SPL would increase.)

Don't worry about it. This is a simple one that trips up many people.

 

[Heinrich]

Perhaps I need to take this a step at the time, if you could comment as we go.

So the real question wasn't about the methodology of the measurement, or what a sweep is, if there was a steady sine hidden in there etc.

Below is a low frequency sweep of each speaker (Focal Kanta No1 by the way). To my novice mind, the left channel is getting bass boost through the corner of the room and the right channel bass loss due to the distance from the corner and openings. Until about 60Hz that is, when the effects seem to swap. How is this explained?
View attachment 440502

One crucial measurement is not provided. The distance of the listening position from the wall behind, and from the left wall.
Anyway, the right speaker gets a fairly big boost at 75Hz, the left at 55Hz. Both show a dip at 130Hz. I don't see a swap of effects. The right shows elevated level around 180Hz also, which is a bit unexpected.

The room and its reflections, resonances included, is a very complicated topic. There are online calculators, but at least in my case the calculatory simulations never fitted my measurement results. Literally never. So, who am I to tell by which movement the speakers could be equalized ;-)

But don't worry. Below 150Hz or so you are in subwoofer territory anyway. The two speakers are going to suplement each other without any ill effect. Still you would have a bit too much bass. The dip at 130Hz, who cares? Too narrow to be of further concern. The discrepancy around 180Hz may trouble you more. To resolve an issue with that is left to you, because the individual settings especially in that relatively high frequency band cannot be addressed remotely.

 

[gnarly]

Hey guys, don't know what I'm smoking today. Pls ignore the 4X power assertion.
4X displacement yes, but not power.
Just screwed up some panels on a DIY sub I'm working on too. Time to take a break....

edit: just measured a small driver with 300 and 600Hz sines, so an octave apart. Free air impedance was the same for those frequencies, hence why chosen.
Same drive voltage gave same SPL and ....same current...so same power.