Thank you again for your thoughts @b_force Yes I do mean distortion in general. I think the easiest way ask my question, and once again I asked here, because I just it seemed BL would be a major factor. The higher the BL the less it is affected by the loading is my guess, and here it is;
In the case the midrange doubles as the subwoofer....and during playback as a sealed woofer has no issue of high excursion....everything is kept near 2mm...would the introduction of a vent tuned to system cutoff, affect midrange quality in anyway. Essentially would the loading that takes place while playing near Fb affect midrange quality in anyway?
In the case the midrange doubles as the subwoofer....and during playback as a sealed woofer has no issue of high excursion....everything is kept near 2mm...would the introduction of a vent tuned to system cutoff, affect midrange quality in anyway. Essentially would the loading that takes place while playing near Fb affect midrange quality in anyway?
I think this is the answer I was looking for.... Don't you think a stronger motor would also affect the out come of this situation?
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Of course it will for a given Fs, Cms since it will lower Qes, Qts = a higher upper mass corner (Fhm = 2*Fs/Qts), which is similar to the bass 'shy' woman likely hearing it up in the mids.
The easy way to get around it is do like the pioneers did and use a high effective Qt driver (low Qt driver + high output/matching impedance amp), i.e. the lower Fhm, the quicker any resonances decay away.
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Well, yes and no. lol
It kinda depends how you look at this problem.
A stronger motor will raise the sensitivity, which could lead to less excursion actually.
The problem in this case is that the same woofer has to do the lower end as well.
But by increasing the BL, basically the -3dB point shifts up in frequency.
(see that wonderful Eargle book, somewhere in the beginning, described very well).
Which effectively means, lowering the output of the lower frequencies.
But yeah, compression always produces more distortion in general, since you're quite literally squeezing those since waves.
Luckily this is mostly 2nd order, so meh, who cares?
I had the thought that possibly while dealing with the pressure near Fb, the midrange itself, might distort itself. 2nd order distortion with the midrange as the fundamental, then it would be audible yes?
It is an interesting balance...throws me off...High Bl, lowering sensitivity on the bass side....I understand the more you can get the system to what you want it to do without additional filtering the better. Yet a higher BL motor with the FR adjusted by EQ is not the better option vs lowering the BL in order to increase low end Sensitivity?
The system ís a bunch of ‘filters’. You only need to optimize them.
But still, why throw up this small signal TSP wisdom in a topic that actually is about serious cone excursions and the (non)linearity of those, including varying Bl? Or did I miss something?
like I said, I was interested in how BL(x) might be affected by pressure. We've talked about reasons to stay away from F in regards to increased excursion.... but we haven't talked about Fb where excursion has an dip before response falls off....where excursion is no longer the consequence, but pressure is....Until now lol...
BL(x) is affected by cone excursion, hence the name BL (x), or in other words, the BL as function of x (x = excursion).
So as long as something else affects the cone excursion, the answer is yes.
Drastically simplified obviously, given that those other parameters don't cause other issues (which is very unlikely in practice)
One note about Sd modulation.
I found it a little far fetched to be perfectly honest.
In the worst case scenario the difference would be the entire size of the surround.
So lets assume that the surround is 10mm wide for a 6 inch woofer. (which is very substantial)
So if we take a 6 inch woofer with an Sd of 133 cm²
10mm extra on this will give us a Sd of 154 cm²
Which results in a difference of 20*log(154/133) = 1.27dB
This is really worst case, because even a very poor surround would not be that extreme.
In practice this means a very thick and wide surround, which is a extremely bad choice for a mid-woofer to begin with.
Again for situation with no or very limited excursion, this whole Sd story is non-existing.
Another very important point, we haven't ANY objective data and measurements that backup this theory to begin with.
If they want to make a convincing point, please just show us the same driver with just different surrounds.
And I am more than happy to change my skepticism in less than a heart-beat.
Because at this point the whole Sd modulation story, is nothing more than just a little theoretical thought.
Which is fine, but it doesn't hold any conclusions, nor any scientific value.
I found it a little far fetched to be perfectly honest.
In the worst case scenario the difference would be the entire size of the surround.
So lets assume that the surround is 10mm wide for a 6 inch woofer. (which is very substantial)
So if we take a 6 inch woofer with an Sd of 133 cm²
10mm extra on this will give us a Sd of 154 cm²
Which results in a difference of 20*log(154/133) = 1.27dB
This is really worst case, because even a very poor surround would not be that extreme.
In practice this means a very thick and wide surround, which is a extremely bad choice for a mid-woofer to begin with.
Again for situation with no or very limited excursion, this whole Sd story is non-existing.
Another very important point, we haven't ANY objective data and measurements that backup this theory to begin with.
If they want to make a convincing point, please just show us the same driver with just different surrounds.
And I am more than happy to change my skepticism in less than a heart-beat.
Because at this point the whole Sd modulation story, is nothing more than just a little theoretical thought.
Which is fine, but it doesn't hold any conclusions, nor any scientific value.
It is always wise to match a driver's parameters to suitable applications (horn loading, BR, closed, OB, etc.), even though there are ways to make mismatches work.
The resonance frequency fs for a driver is related to Mmt and Cms. It's inversely proportional to the square root of both quantities: total moving mass and suspension compliance:
fs = 1/ ( 2π√(Mmt*Cms) )
When the driver is mounted on a closed box a new resonance frequency fo is created for the oscillating loudspeaker diaphragm (Cmt instead of Cms):
fo= 1/ ( 2π√(Mmt*Cmt) ).
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note that whilst 1.27dB may sound innocuous it represents a gain modulation of around 15%, similar to Bl(x) and Bl(i) modulation - both directly controlling the gain. In other words, 15% wide band IMD.
Sd modulation has been confirmed experimentally by changing only the surround and by a general measurement setup. Near field measurements close to a normal half roll is higher than close to the cone. Moreover, Sd modulation is confirmed by finite element simulation. It was first analysed in AES papers from 1994 and 1995. Technics invented a surround that reduces Sd modulation back in 1992.