Or maybe - woofer from a dream!
I like to beat something in this dream field with my drivers. I will make one, or better two drivers 4" - 5", 150w - 300w each, with all known and unknown (mine) advanced technologies like for cone stiffness, with NEO radial magnetized motor etc, than put them in small box to reach the best result what is possible from such small application.
For example, when I looked on B&W PV1 few times, I became more and more attracted because I saw like always - they used in all important details, best logical technical solutions to get on the end just deserved the best results for honest effort in research. I like to use such, or maybe some Isobaric Bandpass box solution, but I am not sure. For the beginning maybe I don't need to reach 21Hz, +- 3db like PV1, but I like to move something forward in small applications.
I have experience mostly in ported and sealed systems normal sizes with matrix and other good damping solutions, just to get first of all clear sound. But to get good efficiency and quality from small box, here I would like to have cooperation and advices from enthusiastic, but serious and honest audio fanatics.
Peter
I like to beat something in this dream field with my drivers. I will make one, or better two drivers 4" - 5", 150w - 300w each, with all known and unknown (mine) advanced technologies like for cone stiffness, with NEO radial magnetized motor etc, than put them in small box to reach the best result what is possible from such small application.
For example, when I looked on B&W PV1 few times, I became more and more attracted because I saw like always - they used in all important details, best logical technical solutions to get on the end just deserved the best results for honest effort in research. I like to use such, or maybe some Isobaric Bandpass box solution, but I am not sure. For the beginning maybe I don't need to reach 21Hz, +- 3db like PV1, but I like to move something forward in small applications.
I have experience mostly in ported and sealed systems normal sizes with matrix and other good damping solutions, just to get first of all clear sound. But to get good efficiency and quality from small box, here I would like to have cooperation and advices from enthusiastic, but serious and honest audio fanatics.
Peter
You face at least two problems. First, to produce bass you must move a lot of air. The smaller the diameter of the cones, the longer the stroke and/or the more of them you need. For ultra long throw drivers with a high Xmax, you will need a long magnetic gap that has a uniform magnetic field over an extended length or the restoring force will not be linear as the excursion becomes greater.
The other problem you face is FR. While Thiel and Small turned woofer/enclosure design into a cookbook recipe, I still prefer to think about the entire phenomenon using Newton's second law of motion. It's an ordinary second order differential equation whose approximate solution is very well know. Once you understand it, it's easy to see why a sealed acoustic suspension design works best, especially if you also know the ideal gas laws (Charles' law, Boyle's law etc.) To design for linear response down to a very low frequency from a small box, the cone mass will have to be very high. This will reduce the effective F3 of the driver in the enclosure, the system resonance frequency. The driver free air resonance will have to be well below 20 hz. Damping material should be selected to achieve a damping factor of .707 which gives the lowest bass without a peak. Response can be extended below the system F3 for at least an octave by using a 12db bass boost calibrated to be hinged at the system F3. Original Bose 901 did something like this but the supplied equalizer's boost was only 6 db per octave. Bose used nine 4" drivers in an enclosure less than one cubic foot. Each drier was rated at 30 watts. With an additional 6db per octave boost and a cut where the system is underdamped resulting in a 7db peak at around 250 to 500 hz, the system can be made flat to below 30 hz but the power requirements are enormous. Several pairs with about 600 to 1000 wpc will result in very high output to below 30 hz with 10% THD. After series II, the design was altered to a ported version which was much more efficient but I don't think it had nearly the low frequency capabilities.
The other problem you face is FR. While Thiel and Small turned woofer/enclosure design into a cookbook recipe, I still prefer to think about the entire phenomenon using Newton's second law of motion. It's an ordinary second order differential equation whose approximate solution is very well know. Once you understand it, it's easy to see why a sealed acoustic suspension design works best, especially if you also know the ideal gas laws (Charles' law, Boyle's law etc.) To design for linear response down to a very low frequency from a small box, the cone mass will have to be very high. This will reduce the effective F3 of the driver in the enclosure, the system resonance frequency. The driver free air resonance will have to be well below 20 hz. Damping material should be selected to achieve a damping factor of .707 which gives the lowest bass without a peak. Response can be extended below the system F3 for at least an octave by using a 12db bass boost calibrated to be hinged at the system F3. Original Bose 901 did something like this but the supplied equalizer's boost was only 6 db per octave. Bose used nine 4" drivers in an enclosure less than one cubic foot. Each drier was rated at 30 watts. With an additional 6db per octave boost and a cut where the system is underdamped resulting in a 7db peak at around 250 to 500 hz, the system can be made flat to below 30 hz but the power requirements are enormous. Several pairs with about 600 to 1000 wpc will result in very high output to below 30 hz with 10% THD. After series II, the design was altered to a ported version which was much more efficient but I don't think it had nearly the low frequency capabilities.
Thanks very much for your replies!
My approach is first of all to build small drivers, because anyway I like more smaller drivers because of their smaller distortions of cones. Now, for the game I want to be so small 4" -5". I know that they should have very long cones excursion, and I would like to use because of that o.e. - NEO radial magnetized motor which can to have very long, and strong magnetic gap if I will find I hope, appropriate NEO magnets.
For cones, my idea is to be first of all very stiff, but I don't like to be too heavy, although I know that is favorable for lower Fr, because more heavy cones - give also more distortions due to inertia in motion. Rather I would care more about quality and power of magnet motor to beat with him air and other suspensions, than with higher mass of cones. I know that for smaller woofer applications is also favorable to have some equalizations for low frequencies like bass booster or some DSP, but at least for the beginning, also I would like to care more about quality of drivers and much more about casing them.
So, here I am more worried about box solution, because I like to care about acoustical problems properly. For good example I mentioned PV1 which have two 8" drivers placed in opposite to each other in very strong, sealed Al case, but for my design I need just to be smaller. Box should be so strong what is not so big problem in small designs, but drivers should be very precise cased like in any small woofer design to get optimum results, with care about relations between driver characteristics and volume and shape of box. I mentioned also some Isobaric 4th order Bandpass solution, but in general I am not sure about box solution, so I needed some appropriate recommendations.
All of my ideas and yours opinions here, is for this beginning - just directions which should be narrowed, but of course, not to completely rejected. So please, feel to be welcome here with all yours good experiences and opinions.
My approach is first of all to build small drivers, because anyway I like more smaller drivers because of their smaller distortions of cones. Now, for the game I want to be so small 4" -5". I know that they should have very long cones excursion, and I would like to use because of that o.e. - NEO radial magnetized motor which can to have very long, and strong magnetic gap if I will find I hope, appropriate NEO magnets.
For cones, my idea is to be first of all very stiff, but I don't like to be too heavy, although I know that is favorable for lower Fr, because more heavy cones - give also more distortions due to inertia in motion. Rather I would care more about quality and power of magnet motor to beat with him air and other suspensions, than with higher mass of cones. I know that for smaller woofer applications is also favorable to have some equalizations for low frequencies like bass booster or some DSP, but at least for the beginning, also I would like to care more about quality of drivers and much more about casing them.
So, here I am more worried about box solution, because I like to care about acoustical problems properly. For good example I mentioned PV1 which have two 8" drivers placed in opposite to each other in very strong, sealed Al case, but for my design I need just to be smaller. Box should be so strong what is not so big problem in small designs, but drivers should be very precise cased like in any small woofer design to get optimum results, with care about relations between driver characteristics and volume and shape of box. I mentioned also some Isobaric 4th order Bandpass solution, but in general I am not sure about box solution, so I needed some appropriate recommendations.
All of my ideas and yours opinions here, is for this beginning - just directions which should be narrowed, but of course, not to completely rejected. So please, feel to be welcome here with all yours good experiences and opinions.
NEO magnet for such requirement should be cylindrical with S pole inside, N pole outside, around 2" outside diameter, 1,5" inside and 2" long. For every kind of magnet is possible to make such shape, but for this purpose only Neo is enough strong.
For NEO, it is big piece, and strong like crazy. I don't believe I will find easy such, but I can make such motor construction with few smaller. I don't know whether is possible, even in magnet company to magnetize such closed construction, but B&W even said, it is hard for production in similar magnet motors to put NEO magnets inside.
Once I had bad experience, when I found my thumb in sandwich between two NEO pieces 5*5*1 cm :-(. I don't even tried to extract my thumb from them to not destroy top of my thumb when they will approach nearer to each other. I could only with big screwdriver to separate them. So, now I have knowledge, I must be careful.
For NEO, it is big piece, and strong like crazy. I don't believe I will find easy such, but I can make such motor construction with few smaller. I don't know whether is possible, even in magnet company to magnetize such closed construction, but B&W even said, it is hard for production in similar magnet motors to put NEO magnets inside.
Once I had bad experience, when I found my thumb in sandwich between two NEO pieces 5*5*1 cm :-(. I don't even tried to extract my thumb from them to not destroy top of my thumb when they will approach nearer to each other. I could only with big screwdriver to separate them. So, now I have knowledge, I must be careful.
You have not anticipated the real problem. You can make it go low, you can't make it go LOUD!
As you lower the Fs of the speaker, the mass goes up, and there is a finite limit to the flux in the gap and the number of turns in the gap, this limits the maximum force/mechanical power that can be created and used. In practical terms this means a very low 1w/1m SPL rating.
You also have severe issues in keeping the coil in the gap, and maintaining the suspension linearity at the same time...
This is why all dynamic speakers are a compromise in action... a balancing act of sorts...
"...you know it don't come easy..." - Ringo Starr
_-_-bear
NEO Dan, the magnets are cheap or such a speaker is cheap??
As you lower the Fs of the speaker, the mass goes up, and there is a finite limit to the flux in the gap and the number of turns in the gap, this limits the maximum force/mechanical power that can be created and used. In practical terms this means a very low 1w/1m SPL rating.
You also have severe issues in keeping the coil in the gap, and maintaining the suspension linearity at the same time...
This is why all dynamic speakers are a compromise in action... a balancing act of sorts...
"...you know it don't come easy..." - Ringo Starr
_-_-bear
NEO Dan, the magnets are cheap or such a speaker is cheap??
If a small cone area and extremely long travel (excursion) is the target, you might want to think about not driving the cone directly. Using a connecting rod and mechanical advantage will overcome 2 of the bigger problems - gap length and maintaining linear travel. The motor would have to be VERY strong.
That is how I'd try to do it.
That is how I'd try to do it.
Usually it's "Efficiency - Small Enclosure - Low Frequency --- Choose two!"
It's physically impossible to build the woofer you want to design. Even if you use a underhung voicecoil and thus reduce Le and Mmd, you still have to face other problems. If you want a low fs, you need to have a soft compliance, resulting in high Vas and a large enclosure. If you make the diaphragm heavier, efficiency is lower.
The large xmax will cause further problems in midrange, such as Doppler and IMD distortion, problems with the large and heavy surround and so on...
If you want to design a small subwoofer, then do it, but effiency and midrange performance will be bad.
In Germany we call such an allrounder a "eierlegende Wollmilchsau", which can be translated as "egg producing pig that gives milk and wool". There is no such thing, otherwise someone would have done that before.
To be serious and honest, as you requested, I don't think you have enough knowledge to design your own driver. This topic is far more difficult than one would think, as I learned when I attended a Klippel course...
How do you intend to produce these drivers? Do you have a manufacturer at hand?
Sorry to crush you dreams,
Spatz
It's physically impossible to build the woofer you want to design. Even if you use a underhung voicecoil and thus reduce Le and Mmd, you still have to face other problems. If you want a low fs, you need to have a soft compliance, resulting in high Vas and a large enclosure. If you make the diaphragm heavier, efficiency is lower.
The large xmax will cause further problems in midrange, such as Doppler and IMD distortion, problems with the large and heavy surround and so on...
If you want to design a small subwoofer, then do it, but effiency and midrange performance will be bad.
In Germany we call such an allrounder a "eierlegende Wollmilchsau", which can be translated as "egg producing pig that gives milk and wool". There is no such thing, otherwise someone would have done that before.
To be serious and honest, as you requested, I don't think you have enough knowledge to design your own driver. This topic is far more difficult than one would think, as I learned when I attended a Klippel course...
How do you intend to produce these drivers? Do you have a manufacturer at hand?
Sorry to crush you dreams,
Spatz
Both:
cPath_1_15 | products_id_2 | Neodymium NdFeB Magnets 1 Pair 2" OD x 1.75" ID x 1" 45 Deg N42SH - Applied Magnets & WindMax Wind Turbines
An externally hosted image should be here but it was not working when we last tested it.
DIYCable.com : Intro » Home » Exodus Subwoofers »
An externally hosted image should be here but it was not working when we last tested it.
Both:
cPath_1_15 | products_id_2 | Neodymium NdFeB Magnets 1 Pair 2" OD x 1.75" ID x 1" 45 Deg N42SH - Applied Magnets & WindMax Wind Turbines
An externally hosted image should be here but it was not working when we last tested it.
QUOTE]
Thanks a lot to all of you, specially to NEO Dan for magnets information!
This magnets looking almost exactly what was needed, but they sell this magnets in pairs which is opposite magnetized. Maybe if this company will give all to be same. With 4 pairs is possible to get full cylinder, but for 2" long gap, it need 8 pairs. With 16 magnets, it's looking to be something heavy for handling in assembling full motor, but anyway.
It's possible to assemble magnet motor for this purpose with also few rectangular magnets which can be easier to assembling. Here in Serbia I found one magnet company which promised to help me, but they looking like to play with me when I made my final order to them. They like to sell me rather 1000 pieces I think.
I like that gap can be even something longer than 2" in order that moving coil almost never go outside of gap, but for REAL good magnet utilization, iron pole extensions must be VERY heavy. "B-Hive Motor" is appropriate example. You can see there how is fat iron extension on the bottom of motor, but I think maybe is not enough.
remove a few, and you can narrow it down a bit
cPath_1_15 | products_id_457 | Rare Earth Magnets 8 in OD x 4 in ID x 1/2 in Neodymium Wind Generator - Applied Magnets & WindMax Wind Turbines
beats me how you will manage to get the poleplates placed
cPath_1_15 | products_id_457 | Rare Earth Magnets 8 in OD x 4 in ID x 1/2 in Neodymium Wind Generator - Applied Magnets & WindMax Wind Turbines
beats me how you will manage to get the poleplates placed
Peca,
Unfortunately neo radial is not as strong as you might think. You are correct about needing more steel in the return structure, the field strength is not enough to saturate the gap for this configuration.
To truly saturate the air gap you must use the steel to concentrate the magnet surface area down to a smaller air gap.
IMO you are trying to squeeze too much into a small package. You will not find a 130mm cone + surround assembly that is suitable for 20mm +/- excursion, and a spider may exist but not for a 130mm chassis.
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