You can most certainly do that if you want to, though it can take a lot of time and money to make a proper passive filter that is able to compete with a more flexible 8" or 10" or 12" fullranger + 15" bass reflex solution using DSP.
If you want to make a 15" + CD (Compression driver) combo, that is well and good, if you want to go this route I would recommend getting a CD + Horn combination that work to maybe 8-900Hz, and to get into this range it starts getting more expensive, and for a CD you NEED to use a passive filter to properly protect the driver.
You are free to do whatever you want, I am merely trying to suggest a solution that will be the most efficient in terms of cost and complexity, the Fane 12" FR does not need a passive filter, you do not need a horn for it, it can handle a bit of abuse, the frequency response can be corrected using DSP which I would strongly recommend no matter what kind of design you decide to build.
If you want to make a 15" + CD (Compression driver) combo, that is well and good, if you want to go this route I would recommend getting a CD + Horn combination that work to maybe 8-900Hz, and to get into this range it starts getting more expensive, and for a CD you NEED to use a passive filter to properly protect the driver.
You are free to do whatever you want, I am merely trying to suggest a solution that will be the most efficient in terms of cost and complexity, the Fane 12" FR does not need a passive filter, you do not need a horn for it, it can handle a bit of abuse, the frequency response can be corrected using DSP which I would strongly recommend no matter what kind of design you decide to build.
@KaffiMann hmm them that do to you think of skiping to make a top box and use somting like this Link I khow that they are 10 inch but they look well build.
Yes I modeled these along with JBL 2269 and the BMS 18N862 with similar response in a 170ltr 30hz box. F3 about 35hz 93db.
@Mica_antrnica yes, very hard to compete with ready built speakers for cheap PA, subs is a different question.
@scholl with "these" being the NERO-18SW1900D?
At any rate, I really like value for the money, so I have 4 x SB Audience BIANCO-18SW450
@scholl with "these" being the NERO-18SW1900D?
At any rate, I really like value for the money, so I have 4 x SB Audience BIANCO-18SW450
@KaffiMann
Yes the 18SW1900D in a 170ltr box tuned to 30hz for an F3 at 31hz to be more exact. a 32hz tune will give a little better group delay. BMS has the best group delay and for some reason I tend toward drivers with larger Vas for lower power listening but they're hard to get in the US. I chose this box size and tuning because I already have the boxes.
Yes the 18SW1900D in a 170ltr box tuned to 30hz for an F3 at 31hz to be more exact. a 32hz tune will give a little better group delay. BMS has the best group delay and for some reason I tend toward drivers with larger Vas for lower power listening but they're hard to get in the US. I chose this box size and tuning because I already have the boxes.
Nice!
I bought the 4 x SW450, and then the 1900D launched shortly afterwards, otherwise I might have gotten those because of the space savings.
The 4 x SW450 might have better fidelity, and they should be more efficient per amount of power, so I am happy either way.
Breaking in the drivers running dipole with small baffles is fun, the boxes are going to be around 230 liters each, going for relaxed roll off with around 20Hz tuning to reduce the need for high pass filters.
I bought the 4 x SW450, and then the 1900D launched shortly afterwards, otherwise I might have gotten those because of the space savings.
The 4 x SW450 might have better fidelity, and they should be more efficient per amount of power, so I am happy either way.
Breaking in the drivers running dipole with small baffles is fun, the boxes are going to be around 230 liters each, going for relaxed roll off with around 20Hz tuning to reduce the need for high pass filters.
That's not correct.
The linear Xmax (Xlin)n is calculated using the formula:
(Hvc - Hg) / 2 = Xmax [+/-mm]
Hvc = Voice Coil Winding Depth
Hg = Magnetic Gap Depth
Xlin means that the voice coil remains completely within the magnetic field or air gap and moves proportionally to the current flow.
This value could be called the "theoretical excursion," and it is only a geometrically determined excursion limit that does not necessarily provide information about the actual performance of the loudspeaker.
The value (winding height - pole plate thickness) / 2), which is used to calculate Xlin, is therefore no longer sufficient today.
In reality, at least with PA drivers, it is often the case that the drive can go significantly further beyond Xlin, even if the drive is already partially weakening.
To obtain a meaningful indication of a loudspeaker's maximum power, distortion and IMD measurements should be performed.
Wolfgang Klippel (IEC PAS 62458) has provided templates for a standardization, and he has conducted useful research and proposed a practical standard. This standard states that the linear excursion of a driver ends where the driver (at natural resonance) causes distortion values of 10% (THD). For a realistic assessment of Xmax, the minimum of XBl, XC, and XL (and XD) should always be used.
The actual, real Xmax therefore describes the excursion with still low distortion, which, according to Klippel, should be limited to 10% THD.
Unfortunately, not all driver manufacturers adhere to this standard, as it is not a binding standard but merely a recommendation.
When calculating the actual Xmax, it's also important to note that the voice coil heats up more when it leaves the magnetic gap than when it's in the linear range within the magnetic gap. This can lead to distortion and overheating. Therefore, adequate cooling of the speaker is essential to ensure reliable and stable performance.
And here we come to an important quality feature that many well-known manufacturers rely on: the pole plate!
The voice coil still has almost its full driving force when it's only 50% in the air gap (some say 75%... different sources). And since a thick pole plate increases the power handling almost proportionally to the thickness, this is also a direction many manufacturers of high-performance drivers are taking. This means that with a very thick pole plate, the actual Xmax is much higher. However, the distortion then increases significantly.
In simple terms, this means: the thicker the pole plate, the more powerful the system can be. Cooling for the beaten coil only really exists where the heat can be dissipated, and that's what the large amount of metal is for.
Thick pole plates can help ensure that the system remains stable even under high loads and that the voice coil is cooled more effectively.
And this is one of the most important explanations for why some speakers sound better at higher volumes than others.
So there is definitely a correlation between the ratio of pole plate thickness to voice coil length.
The bottom line is that, for the same Xlin (theoretical Xmax), a driver with a thicker pole plate—i.e., a deeper air gap—is capable of longer excursions than one with a thinner pole plate.
Not to be underestimated in terms of operational reliability.
Despite the proposed standard by Klippel, there are still different methods for determining a speaker's Xmax value, and the values can vary depending on the manufacturer.
For example, FaitalPRO and Fane add an additional 1/3 of the pole plate thickness.
18Sound does it differently again and adds 1/4 of the pole plate thickness. B&C, RCF, Oberton, and Lavoce do the same.
Beyma adds 1/3.5.
Therefore, the formula for the actual Xmax of a powerful PA driver is as follows:
Here are some examples of some well-known PA drivers:
18Sound: (Hvc - Hg)/2 + Hg/4 = Xmax
B & C: (Hvc - Hg)/2 + Hg/4 = Xmax
Beyma: (Hvc - Hg)/2 + Hg/3.5 = Xmax
Faital: (Hvc - Hg)/2 + Hg/3 = Xmax
Lavoce: (Hvc - Hg)/2 + Hg/4 = Xmax
Oberton: (Hvc - Hg)/2 + Hg/4 = Xmax
RCF: (Hvc - Hg)/2 + Hg/4 = Xmax
Regards
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Well, I will agree that I did not write it according to all the manufacturers definitions, my formula is about halfway between your ideal formula that noone is taking into account anymore, and the limit of loss of control that most manufacturers seem to use these days.
I mixed it up, will still stand by my formula as a more sensible value than what is in most datasheets.
Your reply seems very comparable to what most AI would write... Not a compliment.
Good for you, that you noticed the discrepancy and wanted to address it, we have had a lot of discussions revolving this topic. It is very important that we look at the quality of information, and do not take anything for granted in this day and age of influential marketing.
Again, I am not disagreeing with the information in your post, but your view seems to closely correspond with the purely idealistic viewpoint, and while it (the content) is completely correct, it does not take into account that you still have some very useable performance a little bit outside of the (coil height-gap depth)/2.
Forgive me if I came across a bit harshly, not my intention.
It has been some years now where I have spent a lot of time with my studies and other voluntary positions in addittion to fulltime work, so I am finally starting to have more time to get back to my beloved hobby a bit more.
At the risk of repeating myself, we have had similar discussions here before, because of the nature of this forum this information is very fragmented and scattered across forum segments and threads, where people have been looking at the influence of the magnetic gap flux density on the coil windings during various amounts of cone excursion, in most cases you still have a fair bit of strength and therefore control of the cone movement a little bit outside of the ideal, ofcourse the best part is the (coil height-gap depth)/2 where you get the very best efficiency and low distortion, if you can settle with "very good" instead of "best" then you are still within a tolerable level of distortion, but you get a bit more SPL at not much cost of conscience.
So, let us dive back into this:
Thinking about it, I am no longer 100% certain where I picked up the (coil height-gap depth)/3*2 = Xmax
I most definitely started out with the same idealistic view as the one you are presenting now, it is through the influence of others that I decided to review my strict look on reality.
Completely aware that the manufacturers are using different means, I blame marketing at least in part.
Still, after much debate I think @chris661 was one of the people that wrote on this topic in a way that I revised my outlook, not entirely certain where I picked up the formula or if it was deduced through my own logical conclusion, but it was intended as a way of getting an indication of where one can get "reasonably good quality" instead of the more traditional "the best quality".
Trying to look at it now it may have been the case that after a chain of deduction I decided on this formula myself and accepted it as truth for achieving "reasonably good and still realistic" rather than "perfect ideal" results.
Like you very accurately write here about the various manufacturers basis of calculation:
18Sound/B&C/LaVoce/Oberton/RCF:
(Hvc - Hg)/2 + Hg/4 = Xmax
(25.2-10)/2 + 10/4 = 10.1mm
Beyma: (Hvc - Hg)/2 + Hg/3.5 = Xmax
(25.2-10)/2 + 10/3.5 = 10.45mm
Faital/SB Audience:
(Hvc - Hg)/2 + Hg/3 = Xmax
(25.2-10)/2 + 10/3 = 10.93mm
I remember looking extensively at these different standards, much the same as you are doing, and looking for a way to make a more uniform result that could correspond with a certain level of quality.
If memory serves I remember that I ended up with my formula because I realized that something like:
(Hvc - (Hg*0,75)) / 2 = X
or
(Hvc - (Hg*0,66)) / 2 = X
Does not take into account the travel of the coil through the magnet gap from both sides equally.
If you want to ensure a certain percentage of the voice coil is within the magnet gap I figured it is a more effective formula to do like the manufacturers and add the "+ Hg/4 " segment after the "(Hvc - Hg)/2" part ensures that you have voice coil windings in 75% of the magnetic gap which seemed like a reasonable level of quality seeing as the magnetic force dives quickly after this (my conclusion after looking at endless amounts of magnet structure performance analysis).
After spending an inordinate amount of time looking at all these things it dawns on me that it is much simpler and faster to do:
(Hvc - Hg)/3*2 =X than doing (Hvc - Hg)/2 + Hg/4 which I deemed the most reasonable form of calculating "reasonably good control and distortion" from comparing the different manufacturers perspectives.
So using my simpler formula to ensure 75% of the magnetic gap is filled with voice coil we get:
(25.2-10)/3*2 = 10.13mm
Versus:
(25.2-10)/2 + 10/4 = 10.1mm
Summary:
You are entirely correct in your reply, we have had the exact same origin of frustration and annoyance.
The difference is that I decided on a relatively simple formula that I could accept and trust as giving me reasonably realistic results while allowing for a small amount (in most cases within 3-5% distortion, and with less potential for thermal effects provided you allow for a few other factors, different discussion), and I have apparently used this formula for years without telling anyone about my basis of calculation.
So I apologize, though I am still perfectly happy to continue using my (Hvc - Hg)/3*2
Hope you understand.
Meanwhile, our FANTASTIC forum continue to trundle onwards:
Again, I am not disagreeing with the information in your post, but your view seems to closely correspond with the purely idealistic viewpoint, and while it (the content) is completely correct, it does not take into account that you still have some very useable performance a little bit outside of the (coil height-gap depth)/2.
Forgive me if I came across a bit harshly, not my intention.
It has been some years now where I have spent a lot of time with my studies and other voluntary positions in addittion to fulltime work, so I am finally starting to have more time to get back to my beloved hobby a bit more.
At the risk of repeating myself, we have had similar discussions here before, because of the nature of this forum this information is very fragmented and scattered across forum segments and threads, where people have been looking at the influence of the magnetic gap flux density on the coil windings during various amounts of cone excursion, in most cases you still have a fair bit of strength and therefore control of the cone movement a little bit outside of the ideal, ofcourse the best part is the (coil height-gap depth)/2 where you get the very best efficiency and low distortion, if you can settle with "very good" instead of "best" then you are still within a tolerable level of distortion, but you get a bit more SPL at not much cost of conscience.
So, let us dive back into this:
Thinking about it, I am no longer 100% certain where I picked up the (coil height-gap depth)/3*2 = Xmax
I most definitely started out with the same idealistic view as the one you are presenting now, it is through the influence of others that I decided to review my strict look on reality.
Completely aware that the manufacturers are using different means, I blame marketing at least in part.
Still, after much debate I think @chris661 was one of the people that wrote on this topic in a way that I revised my outlook, not entirely certain where I picked up the formula or if it was deduced through my own logical conclusion, but it was intended as a way of getting an indication of where one can get "reasonably good quality" instead of the more traditional "the best quality".
Trying to look at it now it may have been the case that after a chain of deduction I decided on this formula myself and accepted it as truth for achieving "reasonably good and still realistic" rather than "perfect ideal" results.
Like you very accurately write here about the various manufacturers basis of calculation:
I will now take these different formulas and use my SB Audience 18SW450 as basis of calculation:
18Sound/B&C/LaVoce/Oberton/RCF:
(Hvc - Hg)/2 + Hg/4 = Xmax
(25.2-10)/2 + 10/4 = 10.1mm
Beyma: (Hvc - Hg)/2 + Hg/3.5 = Xmax
(25.2-10)/2 + 10/3.5 = 10.45mm
Faital/SB Audience:
(Hvc - Hg)/2 + Hg/3 = Xmax
(25.2-10)/2 + 10/3 = 10.93mm
I remember looking extensively at these different standards, much the same as you are doing, and looking for a way to make a more uniform result that could correspond with a certain level of quality.
If memory serves I remember that I ended up with my formula because I realized that something like:
(Hvc - (Hg*0,75)) / 2 = X
or
(Hvc - (Hg*0,66)) / 2 = X
Does not take into account the travel of the coil through the magnet gap from both sides equally.
If you want to ensure a certain percentage of the voice coil is within the magnet gap I figured it is a more effective formula to do like the manufacturers and add the "+ Hg/4 " segment after the "(Hvc - Hg)/2" part ensures that you have voice coil windings in 75% of the magnetic gap which seemed like a reasonable level of quality seeing as the magnetic force dives quickly after this (my conclusion after looking at endless amounts of magnet structure performance analysis).
After spending an inordinate amount of time looking at all these things it dawns on me that it is much simpler and faster to do:
(Hvc - Hg)/3*2 =X than doing (Hvc - Hg)/2 + Hg/4 which I deemed the most reasonable form of calculating "reasonably good control and distortion" from comparing the different manufacturers perspectives.
So using my simpler formula to ensure 75% of the magnetic gap is filled with voice coil we get:
(25.2-10)/3*2 = 10.13mm
Versus:
(25.2-10)/2 + 10/4 = 10.1mm
Summary:
You are entirely correct in your reply, we have had the exact same origin of frustration and annoyance.
The difference is that I decided on a relatively simple formula that I could accept and trust as giving me reasonably realistic results while allowing for a small amount (in most cases within 3-5% distortion, and with less potential for thermal effects provided you allow for a few other factors, different discussion), and I have apparently used this formula for years without telling anyone about my basis of calculation.
So I apologize, though I am still perfectly happy to continue using my (Hvc - Hg)/3*2
Hope you understand.
Meanwhile, our FANTASTIC forum continue to trundle onwards: