How to Build a Sub1500

[Don McRitchie]

1

[Don McRitchie]

2

[David Dryden]

All I gotta say is "COOL!"

[Don McRitchie]

1. Cast Aluminum Frame. The high structural rigidity of the cast aluminum frame eliminates the possibility of flexing under the stress of the incredible 32lb motor structure attached to the Sub-15. This frame enables the use of a very tight voice coil gap to increase magnetic and thermal efficiency.

2. Nitrile Rubber Surround. A nitrile rubber surround material is utilized for proper centering of the cone through out the large excursion range of the Sub-15. Through the use of FEA, the surround’s material, geometry and thickness were optimized to lower asymmetrical suspension motion under heavy excursion, lowering 2nd harmonic distortion.

3. Kevlar Cellulose Composite Cone. The Kevlar cellulose composite cone is incredibly stiff and well damped. This results in very low distortion of the cone’s shape from the high acceleration forces and the reactive forces of the small acoustic suspension enclosure it is used in.

4. Polyester Cotton Composite Spider. A polyester cotton composite material is used for the spider. This material offers greater reliability and long term stability than standard cotton spiders. The careful optimization of the geometry and damping of the spider eliminates DC offset problems at high excursion, reducing 2nd harmonic distortion. The careful design of the force vs. deflection of the spider yields symmetrical limiting that works in conjunction with the electromechanical system to eliminate non-linearity. This results in very low 3rd harmonic distortion.

5. Four-inch Edge-wound Copper Voice Coil. The 4in edge-wound copper voice coil with a 45mm winding length is used for increased thermal capabilities and superior excursion. Both of these features result in very low power compression and high output at low frequencies. The edge winding of the voice coil is used to attain greater coil area in the gap for increased force and control of the transducer’s moving assembly. A composite former material is used to for greater thermal stability, strength and lower distortion.

6. Vented Cavity Below Spider. The cavity below the spider is vented to reduce the dynamic compression effects of air being trapped under the spider during heavy excursion. This significantly lowers 3rd harmonic distortion.

7. Inductance Modulation Reduction. A copper ring is placed in the magnetic gap to reduce the effects of inductance modulation caused by the voice coil moving through the gap. It also lowers hysteresis losses due to the non-linearity in the steel and places a more symmetrical magnetic fringe field around the coil. These features lower the symmetrical non-linearity in the coil motion reducing harmonic distortion.

8. Aluminum Shorting Ring. An aluminum shorting ring is placed in the motor to reduce the effects of flux modulation caused by eddy currents generated when the coil moves through the magnetic gap. This ring acts as a Faraday loop swamping out the eddy currents and its effect on the voice coil motion. Reducing this effect results in lower non-linearity in the coil motion lowering the 2nd harmonic distortion in the Sub-15.

9. Uncoventionally-vented Pole Piece. The unconventional venting in the pole piece effectively vents the cavity under the dust cap to minimize dynamic compression effects on the cone motion. It also acts a cooling mechanism for the voice coil and magnet structure lowering power compression.

10. Finite Element Analysis-designed Motor Structure. The 30lb motor structure on the Sub-15 has undergone extensive FEA optimization to increase efficiency and eliminate the gross non-linearity common in off-the-shelf low frequency transducers. The geometry of its low carbon steel and 112 oz ferrite magnet have been optimized for very high magnetic flux in the gap. A T-shaped pole piece has been utilized to keep the magnetic flux above and below the gap symmetrical. These components all work together to increase the force and transient characteristics of the motor, and minimizes the non-linearity in the cone motion at high excursions. This results in greatly reduced harmonic distortion in the Sub-15.

[boputnam]

Don, I just knew you had a cool shop in the back of your place.

I just never figured you for a goatee...

[JuniorJBL]

That is Awesome!!

[sebackman]

Brilliant !!!

My batch should be here in Europe by Monday.

Thank you

//RoB

[mikebake]

Cool thread. Gets me even more pumped up to get these things utilized. I have thought of even perhaps using them in a 3 or 4 way design. Giskard is investigating them, and thinks the 95db sensitivity stated in PE looks high; it appears more like an 89db driver, sez he.
And a nice one, at that!

[johnaec]

I have thought of even perhaps using them in a 3 or 4 way design. Giskard is investigating them, and thinks the 95db sensitivity stated in PE looks high; it appears more like an 89db driver, sez he.

PartsExpress actually says it's 92 dB 2.83V/1m - I believe that translates to about 87 dB at 1 watt/1m.

I will say that in a 2.4 cu.ft. cabinet, it puts out substantially more at 40hz than either a K140 or E140 - I've compared them.

I'm also planning on a 3/4 way design for the future. I've figured on 2012H for mid-bass, but am really unsure about above that. I've been considering 3 way with 2404H HF, but that puts the crossover kinda high for the 2012H. Or possibly the 2426H with ?? horn. I've also considered 4 way, with 2405 HF and either 8" 2118H or 5" 2105H mid-highs. 'Any suggestions?

John

[johnaec]

Don - how do you manage to track down such incredible info, pics included, for such a limited edition speaker like the 1500 SUB? Amazing!!

John

[4313B]

Originally posted by johnaec
PartsExpress actually says it's 92 dB 2.83V/1m - I believe that translates to about 87 dB at 1 watt/1m.

I was referencing their CLIO output.

dBSpl 94.29 [dB]

Whatever...

[johnaec]

I was referencing their CLIO output.

Oops - my bad. I was just reading off their description page...

John

[Don McRitchie]

Originally posted by johnaec
Don - how do you manage to track down such incredible info, pics included, for such a limited edition speaker like the 1500 SUB? Amazing!!

John

Wayback Machine:

http://www.archive.org/

Do a search for:

http://www.revelspeakers.com/

and then

"Sub-15"

[jbl]

Thanks Don,
What type of "glue" is used for the cone and dust cover?

jbl

[4313B]

I don't know what JBL calls it but it tastes like grape flavored Bubble Yum...