I win first naysayer
behind the scenes pics from SI is awesome. If I ever get something worthy of spending some $$ on sound inside, you've probably pushed me to give those guys a little $$.
i didn't know you tuned the GODDAM MAGNET on speakers and shit. Those things are magic. so I guess that makes you guys Wizards?
Yup, small company. Two guys building subs (aside from the Chinese-built SQLs and HT18s) and James was building crates for the 24s.
Nick does all of the designing of component speakers and subs. Since it's such a small company when someone disparages the company or products, he takes it personally because he gives a shit about what he's producing.
I had no idea you could change the QTS on a speaker. Cool!
Me either
And I worked in a high end home audio manuf. Guess they were to cheap or that shit didn't exist 30 years ago.
As far as "tuning the magnet"/changing Qts...
Any subwoofer is going to want a volume of air behind it. A sub is an electromechanical device and needs an air spring to help control it. That air spring comes from the enclosure.
A sub with a Qts of .4 will want/need less of a volume of air behind it than a sub with a Qts of .7 which which needs no enclosure. Just mount that fucker on a baffle to separate front wave from back wave and send it. You can also do this with a sub with a Qts of .4, but I'd reduce applied power. The SQLs I do trunk baffles with have a Qts of .43. Since there's nothing to control them, you have to regulate the applied power so you don't over-drive them. They sound killer.
If you take a sub with a Q of .7 and put it in an enclosure your system Q will be above .7 - over-damped. A lot of cheap, "get loud" subs have a high Qts, need large(ish) enclosures, and don't like to be tuned low. Most shops that sell these send them out in prefab enclosures that are tuned in the 35-40Hz range. Which is great, because those subs typically don't want to play low.
When we design enclosures we'll typically shoot for an enclosure that will put the Q of the sub/enclosure system at .7 for an "ideal" alignment. Ideal meaning the most musical sub/enclosure.
Now...this is where I'll make sense in my head, not type it clearly, and confuse/lose people.
I'll try not to be confusing...
The mechanical Q (Qms) and electrical Q (Qes) give you the total Q of the subwoofer, or Qts.
Qts is calculated by multiplying Qes by Qms, then dividing that result by the sum. Qts = Qes x Qms / Qes + Qms
Mechanical Q (Qms) comes from the mechanical bits that control cone travel. The spider pack and surround. You can change Qms by changing the spider pack and surround material. That means different materials or more layers in the spider pack or different materials for the surround, or a change in the thickness of the surround material. A durometer change of a rubber surround can change Qms at the same material thickness.
Electrical Q (Qes) comes from the magnet and coil.
To change Qes with the sub you can change its motor force (Bl). Bl is actually the relationship between the gauss/magnetic strength of the magnet and the coil/inductor. The L in Bl represents the inductor. It's a lower case L, not a capital I.
You can also change Qes by changing the coil. A sub that's using a 4-layer flat-wound aluminum coil will have a lower Bl than the SAME SUB that's using an 8-layer bi-filar copper coil.
So...to change the total Q of the subwoofer (Qts) either the Qms or Qes has to change. The things that change Qms and Qes also change a slew of other things. I'm not getting into them and adding to the confusion, but that 8-layer bi-filar copper coil is heavier than a 4-layer flat-wound aluminum coil. So that means an increase in moving mass (mms). Then there's what happens with an increase in mms and the mechanical suspension (Qms) and how that heavier coil lowers Fs...
Now, back on topic...
So when a HS-24 leaves the the shop the magnet is fully charged. Basically zapped on the magnetizer to the point that the gauss strength of the magnet doesn't increase with additional hits on the magnetizer.
So the HS-24s are sent out to customers with a motor/coil/spider/surround combo that gives the sub a Qts of .4.
With a sub thats already built with a fully magged/charged magnet, the ONLY way to change Qts is to reduce motor force (Bl) by de-gaussing the magnet slightly on the magnetizer. This is done by flipping the polarity on the magnetizer leads, setting voltage, and zapping the motor.
Since a speaker is an electromechanical device, and changing the gauss strength of the magnet changes Bl, the force applied to the moving components with a given amount of input energy will also change with that change in Bl. A reduction in gauss strength means a reduction in Bl. Makes sense. Less magnetic energy, less electromagnetic force.
When we reduce Bl, with the same mechanical suspension components (spider pack and surround) the ratio between those components and motor force changes. When going from Qts of .4 to .7 the mechanical suspension (Qms) increases in strength relative to Qes.
How flat is the response across that passband?
How fast does it fall off outside the passband?
How much does the impedance of the woofer vary within the passband?
Inquiring PA guys have questions.
Below is where I modeled this SQL-15 in the current sealed enclosure vs the parallel 6th. Horizontal lines are 5dB.
There's a peak at 60Hz, but that's because of my decision to push high-side tuning to 83Hz. While the peak is on screen there, it's a non-issue since I'm running a 70Hz LR4 low-pass in the processor.
So the below image is the modeled anechoic response with it tuned to 19Hz on the low side and 83Hz on the high side compared to the same sub in the sealed enclosure I had been using.
Since the parallel 6th is two ported chambers, they both have a rolloff of 12dB per octave. That means without an electrical crossover both the high at low sides would roll off at 12dB per octave as shown on screen.
In the xB I'm only running a low pass filter on the sub in the processor. So the low tuned side of the enclosure (19Hz) has a rolloff of 12dB per octave below 19Hz and, since the low-pass crossover in the processor is a 4th order Linkwitz-Riley at 70Hz, the roll-off on the top end of the passband is 24dB per octave due to the crossover set in the processor.
So now you're probably wondering why the fuck I tuned the high side to 83Hz instead of 70Hz.
In modeling I found that the higher I tuned the high side, the more output I gained across the entire passband. The enclosure became more efficient across the entire passband. So I tuned higher to get the overall acoustic gain in efficiency and set an electrical crossover where I wanted it.
The trick is that that graph only shows anechoic response. You know that the response changes if you move the enclosure from one room to another or even change placement in a room due to transfer function and room modes.
Maybe tomorrow (later today, fuck...) I'll heave that fucker back in the xB and take in-car RTA measurements and do some SPL tests before I take it out for good.
Here's impedance (blue) measured with DATS. Impedance peaks at 13.46, 28.2, and 75.3. Not sure what's with the weird dip at 19Hz.
Would be interesting to see what the measurement looks like on Smith & Larsen vs DATS.
Now you'll probably know the following already, but I'm going to type it out for others that are wondering...
Just as in a room, you have sounds that are reflected and reverberant. This is due to the wavelength of the frequencies.
The frequency at which sounds in the car (or room) go from reflective to reverberant is called the Schroeder Frequency. The Schroeder Frequency is the point at which the sound waves are longer than the length of the listening environment (your vehicle's interior cabin).
When those sound waves reverberate, the pressure waves build up in the car and you get what's called "cabin gain".
This cabin gain is usually 12dB per octave below the Schroeder frequency.
If you jump back up to the graph on the computer screen you can see I've got a 12dB per octave rolloff down low at a little over 23Hz.
BUT I have a 12dB per octave boost starting higher thanks to cabin gain.
To calculate wavelength you divide the speed of sound by frequency. Just raw numbers. Don't let units confuse you.
1,127 ft/sec / 40Hz = 28.175 ft
1127 / 40 = 28.175
Another:
1127ft/sec / 70Hz = 16.1ft
1127 / 70 = 16.1
Later I'll post about the whole horn-loaded thing if someone reminds me and wants to know WTF I'm planning there and how it works.
