Cab designing, Xmax + port velocity wrt harmonics

[bodgiebass]

Today, I was playing around with winisd for a new cab for me. I was doing my typical attempt at best compromise of SPL/size/weight for a given driver. As usual, I spent way too long juggling bass extension vs box size vs practical port dimensions (size & velocity). I got to wondering about the real world usefulness of some of these limits.

Cone excursion;
I expect that Winisd (and similar programs I've used) show cone excursion in a beautiful graph at the power level you have entered as if the speaker was tested with a sine sweep gen. It would be very unusual for me to ever produce such a pure tone.

Port Velocity;
Similarly port velocity calculations also seem to be related to a swept sine wave type of affair. Trying to maintain reasonable air speed and reasonable port size is a frustrating battle if you are attempting a low weight system.

My question that I'm hoping someone has some input on, is about those two aspects of the design and how electric bass has a much more frequency distributed loading on the cab than a sine wave produces.
An example: winisd says a driver will reach it's Xmax at 41Hz at 100W. If we were to play an open E on a jazz bass we would have the fundamental 41Hz and some equally large 2nd and 3rd harmonics etc. As these frequencies are simultaneous, wouldn't the spectral distribution of power work in our favour to limit the excursion? Port velocity vs frequency is possibly similarly distributed?

 

[Jaco who?]

My question that I'm hoping someone has some input on, is about those two aspects of the design and how electric bass has a much more frequency distributed loading on the cab than a sine wave produces.
An example: winisd says a driver will reach it's Xmax at 41Hz at 100W. If we were to play an open E on a jazz bass we would have the fundamental 41Hz and some equally large 2nd and 3rd harmonics etc. As these frequencies are simultaneous, wouldn't the spectral distribution of power work in our favour to limit the excursion? Port velocity vs frequency is possibly similarly distributed?

They don't cancel each other out, if that's what you're asking - the 41Hz is still there, and in most cases, it isn't really necessary. If you shoot for the next harmonic, your ear will still hear the E string just fine. A good compromise might be to shoot for around 60 hz, that way with a 5 string, the harmonic of 31.5hz will still be perfectly audible. The way the human ear hears bass guitar is what works in your favor - you can also build a smaller box that can handle more power, and it won't weigh as much.

 

[AlexanderB]

They don't cancel each other out, if that's what you're asking - the 41Hz is still there, and in most cases, it isn't really necessary. If you shoot for the next harmonic, your ear will still hear the E string just fine. A good compromise might be to shoot for around 60 hz, that way with a 5 string, the harmonic of 31.5hz will still be perfectly audible. The way the human ear hears bass guitar is what works in your favor - you can also build a smaller box that can handle more power, and it won't weigh as much.

I see this repeated over and over, as being "a truth". If there were any scientific truth to this, please present any peer reviewed paper, scientific investigation, correctly executed blind a/b test or similar...

In reality, especially at higher volumes, there is a dramatic change in how the 30-60 Hz range adds to the listeners' (and performers') experience! Or why do you think clubs, cinemas, amusement parks, recording studios etc spend REALLY big money in getting the bottom octave, loud, clean and aligned with the rest of the program material.

You could argue if YOU value the result in YOUR cost/benefit analysis, but saying there is no difference is beyond ignorant, it is actually stating that is wrong.

And that is not really an opinion, so I do not feel the "IMHO" is applicable.

However, I am very respectful to the fact that many bass players find a -3dB point in the 50 Hz region (or higher!) to give them good results!

 

[bodgiebass]

My question is about cab design software modeling and whether it has any correlation with real world distributed loading (multi frequency loading) or is it purely sine wave models. Are we using the single frequency situation as our design goal and therefore underestimating a drivers capabilities in the cab model?

Jaco- I can't see where I asked about things cancelling each other out?

 

[BadExample]

Bogey, read fdeck's papers. It's math, not a sine wave simulation.

 

[Rick James]

winisd says a driver will reach it's Xmax at 41Hz at 100W. If we were to play an open E on a jazz bass we would have the fundamental 41Hz and some equally large 2nd and 3rd harmonics etc. As these frequencies are simultaneous, wouldn't the spectral distribution of power work in our favour to limit the excursion?

No. The plot assumes equal voltage at every frequency, and spectral power distribution isn't considered. This does raise a valid point. The signal from the amp isn't going to have equal voltage at all frequencies, and it's quite likely that the voltage swing at the second harmonic will be higher than that at the tonic, especially with lower tunings. Good speaker designers are aware of this, so they don't tune cabs for the lowest excursion and port velocities in the 30-50 Hz region, they tune them for the lowest excursion and port velocities in the 50-70 Hz region.

why do you think clubs, cinemas, amusement parks, recording studios etc spend REALLY big money in getting the bottom octave, loud, clean and aligned with the rest of the program material

They don't. They tend to limit the low end to 30 Hz, because it's too expensive and the speakers too large to go any lower. That includes IMax and THX theaters. Real theaters pale in comparison to good home theaters, where the room sizes are small enough to easily allow 20 Hz extension, while no holds barred HT installations go down to the single digits.

 

[Arjank]

No. The plot assumes equal voltage at every frequency, and spectral power distribution isn't considered. This does raise a valid point. The signal from the amp isn't going to have equal voltage at all frequencies, and it's quite likely that the voltage swing at the second harmonic will be higher than that at the tonic, especially with lower tunings. Good speaker designers are aware of this, so they don't tune cabs for the lowest excursion and port velocities in the 30-50 Hz region, they tune them for the lowest excursion and port velocities in the 50-70 Hz region.
They don't. They tend to limit the low end to 30 Hz, because it's too expensive and the speakers too large to go any lower. That includes IMax and THX theaters. Real theaters pale in comparison to good home theaters, where the room sizes are small enough to easily allow 20 Hz extension, while no holds barred HT installations go down to the single digits.

I have experienced this.
Years ago I build two HT loudspeakers with integrated active subwoofers for someone (port tuned to 28hz). A month or so before I finished these loudspeakers we both went to see one of these Batman movies in a big theater. Then, when I installed the loudspeakers in his living room we watched that same movie and we both looked at each other and asked the same question: "did you hear that rumble in the theater?...uhm...No"

 

[AlexanderB]

No. The plot assumes equal voltage at every frequency, and spectral power distribution isn't considered. This does raise a valid point. The signal from the amp isn't going to have equal voltage at all frequencies, and it's quite likely that the voltage swing at the second harmonic will be higher than that at the tonic, especially with lower tunings. Good speaker designers are aware of this, so they don't tune cabs for the lowest excursion and port velocities in the 30-50 Hz region, they tune them for the lowest excursion and port velocities in the 50-70 Hz region.
They don't. They tend to limit the low end to 30 Hz, because it's too expensive and the speakers too large to go any lower. That includes IMax and THX theaters. Real theaters pale in comparison to good home theaters, where the room sizes are small enough to easily allow 20 Hz extension, while no holds barred HT installations go down to the single digits.

I specifically mentioned the 30-60 Hz octave. With the extended bass response due to room loading, the acoustic SYSTEM response will extend below the enclosure's tuning, and it is not very hard to get into single digit in-room-response for HT application. Costly, yes, and time cosuming to set up, but commercially available components will do the job.

And your definition of "Good speaker designers" are clearly not shared by many, as there are no shortage of commercial bass reflex subwoofers with tunings in the low 30 Hz area. Again, facts vs "opinions", so no "IMHO".

 

[AlexanderB]

My question is about cab design software modeling and whether it has any correlation with real world distributed loading (multi frequency loading) or is it purely sine wave models. Are we using the single frequency situation as our design goal and therefore underestimating a drivers capabilities in the cab model?

Jaco- I can't see where I asked about things cancelling each other out?

Even a modest boost (+ 3dB) on the bass knob on some amps will double the power in the 30-40 Hz region. More dramatic boosts will make the fundamental very pronounced in the spectrum, especially in high Q tone stacks.

One can debate the use of "rule of thumb" substituting actual data, but in my experience, exceeding the winISD 5-10 % port velocity mark will manifest as audible chuffing.

 

[Rick James]

I it is not very hard to get into single digit in-room-response for HT application. Costly, yes, and time cosuming to set up, but commercially available components will do the job.

Not those intended for clubs, cinemas, or amusement parks.

there are no shortage of commercial bass reflex subwoofers with tunings in the low 30 Hz area.

Who said anything about commercial bass reflex subwoofers? Not the OP, not me.

 

[AlexanderB]

Not those intended for clubs, cinemas, or amusement parks.

Who said anything about commercial bass reflex subwoofers? Not the OP, not me.

Again, for proper reproduction of the electric bass (even a four string one), there is a very audible difference between a "regular" cab, vs ACME, Ampeg SVT-410HLF, various "super twelves", Warwick's Hellborg series etc, with good response to mid fourties or lower, especially the ACME.

If it is something useful has to be evaluated and judged by each player, as preferences and needs vary dramatically.

 

[jsa0100]

"winisd says a driver will reach it's Xmax at 41Hz at 100W"

Bodgiebass, if you are choosing to tune the speaker cabinet below the speaker Fs or choose a volume on a ported speaker that is larger than Vas, you will usually get low handling capability (Xmax at low watt).

 

[agedhorse]

My question that I'm hoping someone has some input on, is about those two aspects of the design and how electric bass has a much more frequency distributed loading on the cab than a sine wave produces.
An example: winisd says a driver will reach it's Xmax at 41Hz at 100W. If we were to play an open E on a jazz bass we would have the fundamental 41Hz and some equally large 2nd and 3rd harmonics etc. As these frequencies are simultaneous, wouldn't the spectral distribution of power work in our favour to limit the excursion? Port velocity vs frequency is possibly similarly distributed?

Frequency weighting and distribution absolutely has an effect on system power handling for a given SYSTEM SPL when the input signal is composed of distributed harmonics.

In your example, taking the 41Hz fundamental plus 2nd and third harmonics, assuming that they are distributed 1/3-1/3-1/3, you would look at the SUMMED response waveform which will show a waveform very different than the 3 separate components. There will be a series of sum and different peaks-nulls, the resulting peaks would still be limiting but less demanding than simply the fundamental itself.

In practice, this is why some cabinets (with drivers designed to be forgiving around Xmax) can sound quite acceptable even though theory predicts exceeding Xmax. The same applies towards port velocity, the amount of time slice that the velocity is unacceptable is lower than the fundamental theory numbers might predict.

The math is still right, but you have to use more involved math to accurately model the more advanced concepts. This is similar to the duty cycle approach to power amp design, and the power-bandwidth approach to both amplifier and speaker design... all are based on basic concepts but the basic math becomes more complex as the model becomes more complex (and more accurate).

 

[gmarcus]

Okay so we are off on a big tangent. I think the question is: If I have a 500 watt amp and my cabinet can only handle 400 watts at 40 hz, am I in trouble if I crank it up and play my bass through it. If I play an open E then probably about 1/2 of the power is in the first harmonic at 82 hz so probably not a problem, but you should always listen to your cabinet, if it starts to rattle or fart out then you went too far. If you crank up the bass eq and blast away at full volume you might have a problem. If you are going for a motown sound...you are probably okay.

 

[gmarcus]

Ha I was typing when Aged horse replied.....He's not off on a tangent....he's dropping some real wisdom!!

 

[agedhorse]

Ha I was typing when Aged horse replied.....He's not off on a tangent....he's dropping some real wisdom!!

Actually, most of the important information appears to be tangential but in fact is squarely on topic.

 

[basscooker]

I tend to take the plots for x-max and frequency response as a package...

If I'm looking at -6dB or more around the frequencies that are peaking above xmax, or showing large velocity numbers, I consider it a fair tradeoff if the power I'm modeling at is over 60ish % of the driver's rated power.

 

[Coolhandjjl]

I see this repeated over and over, as being "a truth". If there were any scientific truth to this, please present any peer reviewed paper, scientific investigation, correctly executed blind a/b test or similar...

Google 'The Missing Fundamental'

Bose has capitalized on it and has made millions decade after decade exploiting this phenomena.

 

[JimChjones]

data, but in my experience, exceeding the winISD 5-10 % port velocity mark will manifest as audible chuffing.

This is a combination of empirical observations and the science though. As I have understood it the science predicts an air velocity in the port, but it is empirically observed that values of theoretical velocity in excess of a given value result in chuffing. It doesn't matter if the real values of air velocity in the port are way larger or smaller than the theoretical ones, just so long as they are related so the empirical determination works.

Actually the thing that surprises me most about chuffing is the crude aerodynamics of most ports I've seen. If worried about the phenomenon surely both ends of the ports should have well considered surfaces. I presume it's different in high end kit. Haven't examined any in detail.

 

[okcrum]

I see this repeated over and over, as being "a truth". If there were any scientific truth to this, please present any peer reviewed paper, scientific investigation, correctly executed blind a/b test or similar...

In reality, especially at higher volumes, there is a dramatic change in how the 30-60 Hz range adds to the listeners' (and performers') experience! Or why do you think clubs, cinemas, amusement parks, recording studios etc spend REALLY big money in getting the bottom octave, loud, clean and aligned with the rest of the program material.

You could argue if YOU value the result in YOUR cost/benefit analysis, but saying there is no difference is beyond ignorant, it is actually stating that is wrong.

And that is not really an opinion, so I do not feel the "IMHO" is applicable.

However, I am very respectful to the fact that many bass players find a -3dB point in the 50 Hz region (or higher!) to give them good results!

Actually all you need to do is look at the Fourier Transform of the output signal from an EB. It is predominantly 2nd harmonic.

How is it that you think we hear the fundamental when it's 10 dB or more down due to the superposition of pickup and cabinet response?