I notice most of the DIY machines I see use midrange driver motors. They have a lot of heft.
As I understand, groove depth is 0.030".
A tweeter motor should have an X-max of 0.050" and a large tweeter 1.25" dome will probably be closer to 0.080". Double that, for X-diff of a full cycle and a tweeter easily has the range.
Further, a tweeter with lower X-max will be more efficient than a midrange with higher X-max, within the band the tweeter operates.
I've come to believe 10W, run through a 1.25" tweeter VC, ought to have enough control authority over the cutting tool.
Further, an Fs of 800Hz might be an OK place for that problem. A 3" mid will tend to have an Fs in the 300~400Hz range which is a bit less desirable location for problems.
Can someone help me understand how driver resonance changes while cutting? I would assume it would go down to a far lower frequency but real data would be great.
What is wrong with my thought process? I'm obviously an outlier. Everyone else is going with larger drivers but I don't see any vented pole drivers so I'm not sure the larger drivers are intended to dissipate heat.
Thanks for the great site.
Driver size
Moderators: piaptk, tragwag, Steve E., Aussie0zborn
Re: Driver size
Hi,
You don't care at all about the acoustical performance of the driver. The main parameters you need to investigate are:
1. moving mass
2. BL factor
3. Power handling.
4. Main resonance due to mass and suspension stiffness.
They all interact. For example, you can find drivers that have high power handling and large BL factors, but you typically find that the moving mass is very high. So you end up trowing away large amounts of power to accelerate the mass. Once you couple the driver to the stylus, you will be adding more moving mass and perhaps stiffness. That will likely move the main system resonance down as you suggest. The location of the resonance is of concern. Below resonance, you are in a stiffness controlled region of control. Above resonance, you are mass controlled. In the mass controlled region, its all about force and acceleration. In the driver, force is produced by current in the voice coil. So I2R losses mount quickly when you try to accelerate the mass. Getting moving mass low and resonance high is a good thing, but if you carry that too far, you find that the response of the cutter is easily modified by the cutting load of the stylus on the cutting medium (think of a voltage source with high internal impedance driving a low impedance load). In closed loop design, this is mitigated somewhat. In an open loop head it can become a problem. So I guess what I'm saying is, that you have to run all of the numbers to see if a candidate for a driver is a good choice as compared to another.
Hope that helps.
Mark
You don't care at all about the acoustical performance of the driver. The main parameters you need to investigate are:
1. moving mass
2. BL factor
3. Power handling.
4. Main resonance due to mass and suspension stiffness.
They all interact. For example, you can find drivers that have high power handling and large BL factors, but you typically find that the moving mass is very high. So you end up trowing away large amounts of power to accelerate the mass. Once you couple the driver to the stylus, you will be adding more moving mass and perhaps stiffness. That will likely move the main system resonance down as you suggest. The location of the resonance is of concern. Below resonance, you are in a stiffness controlled region of control. Above resonance, you are mass controlled. In the mass controlled region, its all about force and acceleration. In the driver, force is produced by current in the voice coil. So I2R losses mount quickly when you try to accelerate the mass. Getting moving mass low and resonance high is a good thing, but if you carry that too far, you find that the response of the cutter is easily modified by the cutting load of the stylus on the cutting medium (think of a voltage source with high internal impedance driving a low impedance load). In closed loop design, this is mitigated somewhat. In an open loop head it can become a problem. So I guess what I'm saying is, that you have to run all of the numbers to see if a candidate for a driver is a good choice as compared to another.
Hope that helps.
Mark
Re: Driver size
Thanks, Mark. I appreciate your response. 