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NSW6021 Inductance Model Comparison

3K views 21 replies 6 participants last post by  classicality 
#1 · (Edited)
John ( @Red Five ) asked me to compare Normal vs Lossy inductance models in hornresp to measured frequency response of the Alpha Devastator with the Eminence NSW6021-6.
I decided to be a bit more thorough and also compare vs the Alpha with a plugged port and the submax v3.

Since Josh ( @Ricci ) has measured this driver, I also included models with his measured specs including semi-inductance parameters. I know the driver he measured was on a different basket than these production models, not sure how specs would be altered.
EDIT: Per Josh’s advice later in this thread, models updated to factory specs, only modified with the data-bass semi-inductance model. /EDIT

John, ( @LTD02 ), this may be helpful to you.
A huge thanks to you for the submax v3 design and many others.

Close mic measurements were taken with mic three inches from front of mouth. Submax centered, Alpha centered on port/qw divider. Cabinets were side by side, out into the room

I did forget to take close mic measurements without the HPF’s engaged. I added equivalent filters to the HR models to compensate. The cabs are in their final locations now, and submax is not moving again until I do. [emoji16]
Highpass Filters:
Submax v3: Second Order Butterworth at 17hz
Alpha: Second Order Butterworth at 18hz
Alpha Plugged: Second Order Butterworth at 16hz

Alpha Devastator:



Alpha Devastator with one port plugged:



Submaximus v3:



It appears to me that the normal inductance model is closest on Alpha and Alpha plugged. It is hard to determine which fits best on v3.

John, Josh, or anyone else, pm me your email address if you would like me to send you these sweeps to look at.

EDIT2:
I performed sweeps on my other two readily-available enclosures for more data.

First is my Mini Devastator v1, loaded with a B&C 18DS115-4.

This enclosure stays much closer to the normal-le model.

Second is my Stereo Integrity HST18d2 mkIII in 10.5 cu ported at 11hz. I wasn’t exactly sure how to close-mic a ported direct-radiator, so I tried two methods. “Cone” is taken from center of cone, “cone/port os taken halfway between the edge of the come and the port mouth.

Not a great match on this one, but I believe the lossy le model fits best by a safe margin.


What I expected to show out of this outlandishly-longwinded post: Use normal le models for pro drivers, use lossy le models for long-throw theater drivers.

What I believe I actually demonstrated:
Use normal le modeling for devastators with pro drivers.
Maybe Use lossy le for the HST, it fits slightly better.
I have no idea what is going on with my submax.

Chris
 
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#3 ·
The max models are strange. All of the previous tests (maybe only 2), indicated that the model matched the real world repsonse pretty close. Yours is pretty far off.

Is it possible that your driver isn't broken in enough to get the FS lowererd down to where Josh measured his?
 
#4 ·
The max models are strange. All of the previous tests (maybe only 2), indicated that the model matched the real world repsonse pretty close. Yous is pretty far off.

Is it possible that your driver isn't broken in enough to get the FS lowererd down to where Josh measured his?

Its been used an equivalent amount to the driver in Alpha. I would expect a loosening of the suspension to increase the low-end, not decrease it.
As for accuracy, no idea. I know my dimensions aren’t perfect, but shouldn’t be far enough off to greatly affect the model. I did make sure the throat was to exact dimensions by using full length bracing.

Chris
 
#6 ·
I could be wrong, but the FS has a big impact on the shape of the response in the FLH. If the FS of the NSW is high, you get that peak then dip on the bottom. That flattens out as the FS drops. Try taking your max model with the NSW and raising the FS of the driver and see if it matches closer to your results.
 
#10 ·
Here's a couple of things to consider when comparing measured response vs sim.

Close mic sub response is not the same as half-space measurements from a few meters. It's close enough for most uses but close mic response tends show greater low end and less top end compared with outdoor GP. It's not uncommon to see 100Hz be -3dB relative to 15Hz in the close mic vs half-space measurement. The simulations are usually for a half-space environment.

Drivers specs can vary quite a bit. Like a lot even from the best MFG's. It can make a difference. Hopefully most units would be within close enough tolerance that they all "work" in the same cab design. I'm confident in the spec I pulled from the Eminence driver that is posted at DB, but that unit was well broken in. Factory fresh ones probably will be somewhat different. It shouldn't make a huge difference but it will make some. This is why I always try to use the same driver that I've pulled specs from for the in cabinet tests. Then I know what the driver specs are so if the sim is way off, it's because the sim inputs are wrong for representing the cab. This is how I end up confident that the inputs for the cab in HR are correct.

Were the "DB" specs used exactly those from the website? If so your particular NSW6021-6 driver might be somewhat different and those may not match that well. What I would recommend is use the factory specs but add in only the semi inductance parameters from the particular driver I measured. Usually the specs from the MFG's like B&C, Eminence, Faital, 18Sound, etc, are averaged over tests of many units and should be close enough. The semi inductance specs won't be exact for your driver but should give a closer match. Obviously the best thing to do is measure the exact driver being used. Driver measurement is prone to error and variation even then. Impedance measurements are very handy for comparing real result to sim. In some ways more useful / easier than the FR. No worries about mic placement for example.

The inputs in HR may not be as optimized as they should be for representing the cab. This can easily account for big differences. For example the Alpha measurements posted above show notable differences between any of the sims and the measured result in the 75-150Hz octave. It looks like the vent resonance is not at the frequency it is being sim'd to be and there is possibly some sort of internal resonance or chamber effect going on as well in that area. The V3 response is even more different. Not very close to the sim.

In a nutshell you have a bunch of variables that can all stack up and create large discrepancies between what was measured and what was sim'd.
If you have the capability an impedance sweep of the driver in free air and then in the cab would probably be the quickest easiest way to see how close the driver specs used in the sim and the cab sim itself are.
 
#11 ·
Thanks for the guidance Josh!

I will redo the graphs with factory specs plus your semi-inductance parameters.

I’ve been meaning to learn how to do impedance measurements for the quad dev. I can do them here as well once I am able.

I’m not pulling the driver out of the submax, but can on the alpha.

I actually thought the alpha response was close to sim. I guess you have a tighter tolerance on close. [emoji16]. I do suspect rear chamber resonance in the upper end of the response. The rear chamber is over 50” tall. I have two pillows fastened to the cabinet walls that help greatly, but probably don’t completely fix it.


I also thought the vent resonance was close. I was interested that it showed closer on the plugged alpha models vs the normal. Those two are the exact same model with port area reduced by 1/3.

I didn’t account for the volume of the plugged port, haven’t seen a straight answer on whether it should be or not.

Again, thanks for the help.

Chris
 
#12 ·
@Ricci
I replaced the graphs in the original post with the data-bass spec models. They are now showing factory specs with data-bass semi-inductance parameters. The eminence specs are close enough to your measurements that this change made an almost imperceptible difference in the model.

I should add that the original point of this post was to demonstrate my observations on inductance modeling with pro drivers. That is, that pro drivers model much closer to measured with the normal inductance model than the lossy inductance model. Even massive-coil, long-throw versions like the NSW6021. I only included the data-bass parameters because they exist, and I like analyzing data.

The submax ended up being a useless data point, as I can’t see any model correlating closer than the other.

On that note, I should also add models for my ported HST’s and Mini Devastators. I will work on that now. They will only be normal vs lossy inductance, as data-bass doesn’t have measurements on those drivers.

Chris
 
#14 · (Edited)
HST 18 specs are at DB. 2 versions.

Agreed for the most part. It breaks down like this IMHO.
Use semi inductance specs if available. This a more accurate way to describe the driver behavior. For any driver including mids and tweeters. If it doesn't match well then the sim inputs aren't describing the speaker well or the measurement isn't under the conditions the sim is setup for.

If you don't have semi inductance available. Lossy LE sort of works for big coil, high stroke drivers. Especially those without shorting rings. Its a ballpark guess though so won't be that accurate but better than nothing.

Pro woofers it depends...if they have shorting rings just use normal 1kHz generic inductance. If they don't have shorting rings Lossy LE in HR might be better...Or not.

There are a bunch of old threads here and at DIY Audio on this with comparisons.

I'll send you an email about measuring impedance later. There are some good old threads on that too. All you need is a precision resistor, 2 channel sound card, bunch of cables or wire, REW or LIMP and maybe an amplifier ( preferred). For driver testing add in some ferrite hobby magnets, a digital scale and a few clamps and heavy objects.

Edit: I guess my definition of a close match is probably different than most. Good point. I see 3 or 4 dB differences though.

Also how close to a wall is your Submax? Is it in a corner? If the sub is real close to walls it will still affect the close Mic.
 
#20 ·
off topic..but what is everyone using to power these with? im running my pair off an NX-6000..just curious how much i am missing out on by not having more power..
 
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