One of the last additions to the OS-SE formula was the 'k' parameter. Basically, by increasing this value above 1.0 it's possible to use an OS profile that would otherwise correspond to a bigger throat (and vice versa).
The attached images show the results for k = 1, 2 and 5.
The overall waveguide diameter was about 10.5", a bigger k also makes the waveguide a little longer.
The attached images show the results for k = 1, 2 and 5.
The overall waveguide diameter was about 10.5", a bigger k also makes the waveguide a little longer.
Attachments
I think that you misunderstood my comment. I analyzed a generic CD with a model with the intent of developing a new one. I have not analyzed any specific devices so I don't know any specific device parameters. I can show the effect of any parameter, but not what those parameters actually are in a real device.
Yes, increasing the gap reduces the HFs but increases the excursion capability. This is the point that I made earlier.
I would guess "typical" Mmd to be 6-10 grams and BL of about 20 Nt/amp, but I don't know for sure. The "gap is usually about 1 mm (I would guess) and sets the limit for excursion. Compression ratios are what Mabat suggests.
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Someone tried to model DE250 in this thread (2009): Modelling compression drivers
Featuring Dr. Geddes as well: Modelling compression drivers
There's also a mention of TAD TD-2001: Modelling compression drivers
Code:
Ree=6.3; |Voice coil resistance [ohm] ......(Re)
Le=0.11e-3; |Voice coil inductance [H] ......(Le)
Bl=9.3; |Motor conversion factor F=Bl*i [Tm]......(BL)
Mms=1.4e-3; |Mechanical mass [kg] ......(Mms)
Rms=.5; |Mechanical resistance [Ns/m] ......(Rms)
Cms=30e-6; |Mechanical compliance [m/N] ......(Cms)Featuring Dr. Geddes as well: Modelling compression drivers
There's also a mention of TAD TD-2001: Modelling compression drivers
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The catch, imo, is that some 1" drivers are better suited to low crossover points - say between 800 and 1000 Hz - than others.
If you want to cross a 1" driver really low, < 800 Hz, you'll need a specific driver and often also a deep horn. I've seen examples of TADs TD-2001 that were used from around 500 Hz.
The DE250 for instance, does take 900 Hz, but definitely not 500 Hz.
One might argue, why not use a bigger driver?
That was my argument before, but lately I've been taking a more balanced view.
In this context, Legis experiments with the TAD TD4001, FaitalPro HF1440 and the HF108 coupled to his Yuichi horns, are interesting.
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Of course, excursion is important, as it is related to the magnet structure and diaphragm characteristics.
Bigger (more powerful, lighter, stiffer, or better (diaphram) damping) translates to less excursion and also higher efficiency, implying lower voltage.
Pet007's measurements show the DE250 generates more output below 1000Hz, compared to the Celestion and Sica.
Bigger (more powerful, lighter, stiffer, or better (diaphram) damping) translates to less excursion and also higher efficiency, implying lower voltage.
Pet007's measurements show the DE250 generates more output below 1000Hz, compared to the Celestion and Sica.
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1.4 gram moving mass seems unlikely to me as it has to include the voice coil. That's a very small mass.
I tried to calculate it based on rough estimates of the volumes and it was about 1:1, titanium diaphragm : copper voice coil, around 1.5 g total. So I don't have a problem with that number.
JBL states 3.5 g for 4" titanium diaphragm in JBL 2445: https://jblpro.com/en/site_elements/tech-note-characteristics-of-high-frequency-compression-drivers
JBL states 3.5 g for 4" titanium diaphragm in JBL 2445: https://jblpro.com/en/site_elements/tech-note-characteristics-of-high-frequency-compression-drivers
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Understood. I thought you might have measured the parameters for the DE250 and/or DE500 since you've used them a lot. Thanks for the reply anyway.
I actually found that document recently and was going to link it, but I guess you beat me to it
. Most HF drivers I've seen use aluminum voice coils (or CCA), including the JBL 2445. FWIW, [URL="http://www.seas.no/index.php?option=com_content&view=article&id=364:e0055-06-t35c002&catid=50&Itemid=360]SEAS has a 35mm dome tweeter[/URL] with a Mmd of 0.47g. So 1g or so for a 44mm CD diaphragm (especially a plastic one) seems possible.
I did, a long time ago, but I just don't know where they might be now. Back some time here at DIY, I described how I measured them, I thought that I posted some values.