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Jaycar 15 inch Venom subwoofer

Jaycar Part no: 2345 - Cost $99.95aus (18th December 2006)

Estimated value for cone area highlighted in red
Z - Nominal Impedance4 ohm
Pe - Power Handling250W
SPL - Sensitivity88.48 dB/watt@1m
Re - Voice coil resistance3.5 ohm
Fs - Resonant frequency25.65 hz
Qms - Mechanical Q3.552
Qes - Electrical Q0,578
Qts - Total Q0.497
Vas - Equivalent volume150.7 litres
Xmax - Maximum excursion15 mm
Sd - Cone Area750 sq cm
EBP - Efficiency Bandwidth Product44 - Best in sealed

Here is my parameter file for this driver for WinISD Pro ver 0.50a7

 

Note: As of 8th August 2007, the Venom range of drivers has been discontinued

 

This driver performs best in a sealed or Infinite Baffle enclosure. For comparison purposes, I've relaxed the 130litre limit on box size - the higher Vas of a 15inch driver makes this mandatory for a ported design.

According to William Cowan at cowanaudio the suspension becomes noisy above about 12.5mm excursion and Xlim seems to be 20mm one-way. The following designs stick to the 12.5mm limit. When working out maximum power for the IB designs, the 20mm limit is used.

Firstly I'll present some conventional sealed and ported designs.

Further down in a separate section are some Infinite Baffle designs for those with deeper tastes and deeper pockets....

Conventional designs

Box size Tuning frequency Port details
Ported 400 litre - 180w-4ohm - Altronics 150w amp 18hz Four 102mm ports @ 680mm
Sealed Jaycar design 49 litre - 250w-4ohm - Behringer A500 amp
Sealed 150 litre - 180w-4ohm - Altronics 150w amp

Project files for WinISD Pro ver 0.50a7
400 litre ported 18 hz tune
49 litre sealed (Jaycar design)
150 litre sealed

SPL

SPL graph
Ported design scores well but at the expense of a huge 400litre box and high group delay.
Jaycar 49litre design needs 250w. This is from an unboosted amp. If using the Jaycar amps which have boost @ 35hz, the response will be worse.
150 litre sealed design is easiest to live with - not huge, no filter required and only the 150w Altronics amp required. 10dB down on the ported design at 20hz though, so will only be half as loud for serious HT use.
 

Cone excursion

Excursion graph
The ported design requires an 11hz high pass filter
 

Port air velocity

Velocity graph
 

Port Flares

Calculated with Flare-it
I would recommend 25mm heat molded flares for the four 102mm ports
The intakes should be flange mounted with a 13mm routed flare or you could fit a donut ring . If you are using a heat molded flare, you could do a one-piece design with a 20mm flare on the inlet

See the Porting section for more detail on the design, construction and purchase of flared ports.

 

Infinite Baffle designs

An Infinite Baffle (IB) design is a sealed design where the box is infinitely large. In reality, the box needs to be at least 10 times the combined Vas of the drivers. The box is usually the roofspace, a space under the house, or an adjacent room such as a garage.

Since the drivers are not compressing air in a box or charging up a port, the transient response is excellent. The unrestrained movement also means that it takes less power to reach excursion limits.

Since we're using less power and doing without any contribution from a port, more drivers will be needed.

If you're interesting in exploring IB further, check out the experts at the Cult of the Infinitely Baffled. To use their forums you need to register, but it's free and worth it.

All designs are modeled with a space of 10,000 litres. This is a bit larger than the minimum size for 4 drivers ( 150 * 4 * 10 = 6k ) and a bit smaller than the minimum size for 8 drivers ( 12k litres). It's around half the 18k litres that a twelve driver design would like - increasing the modeled volume just results in slightly less power being required than shown here.

 

Sealed - IB4 Four driver Infinite Baffle - 190w - Behringer EP1500 amp max 480w ....( 8 ohms / channel )
Sealed - IB8 Eight driver Infinite Baffle - 410w - Behringer EP2500 amp max 1050w ....( 4 ohms / channel )
Sealed - IB12 Twelve driver Infinite Baffle - 670w - Behringer EP2500 amp max 1700w ....( 2.7 ohms / channel )

Project files for WinISD Pro ver 0.50a7 Four driver Infinite Baffle
Eight driver Infinite Baffle
Twelve driver Infinite Baffle
See the driver wiring options page for how to wire up these systems

SPL

SPL graph
The solid lines are for when excursion is kept to 12.5mm to keep distortion at bay.
The shaded areas are for when excursion is allowed out to 20mm, which is the suggested Xlim. This will involve some distortion, but the drivers will be OK.
 

Cone excursion

Excursion graph
The excursion graph is the same for all three designs.
The black line is the resulting excursion for:
The grey line is the resulting excursion for:
 

Displacement

When comparing IB systems, a common measurement is the amount of air displaced, which is worked out by the formula:
Displacement = Sd * Xmax * 2 * Number of drivers ...... where Xmax is the one-way value. The result is expressed in litres

Displacement in litres
at 25mm p-p
Displacement in litres
at 40mm p-p
Four drivers7.512
Eight drivers1524
Twelve drivers22.536

 

Suitability for horizontal mounting

When a driver is mounted horizontally, the cone will sag due to gravity. If the sag exceeds 5% of Xmax, then it is unsuitable.
According to the formula at Parts Express ......
Percentage of Sag = 24,849 / ( Xmax * Fsē) ...... where Xmax is the one-way value
This driver comes in at around 3% of our limit of 12.5mm, so it should be OK

 

Behringer Feedback destroyer

You may wish to buy a Behringer Feedback destroyer which allows you to even out the in-room response. Peaks due to room nodes can be cut with up to 12 parametric equalisers. You can also factor in a house curve for a tailored bass response.
The DSP1124P has been supeceded by the FBQ2496. Here's a comparison:

DSP1124PFBQ2496
12 parametric equalisers per channel 20 parametric equalisers per channel
Can store 10 different sets of filters Can store only one set of filters
Most likely will be v1.3 which has a MIDI port
which won't talk to REW (see below).
A small stock of units are v1.4 which has no problem
No problem talking to REW
Better dynamic range
Discontinued - may be hard to find Available now
List price around $200 aud List price around $300 aud

 

Rumor has it that you can pick up the older model for about $170 so shop around... If you go for the FBQ2496, don't confuse it with the DEQ2496, which is a crossover management device.

You can analyse your room using the free Room EQ Wizard software written by John Mulcahy.

The software will even upload the new settings into the BFD via the MIDI port on your computer. If your BFD is ver1.3, you'll need to enter the settings manually. If you have a BFD, you can check it's version by holding in the Filter Select button during power up. Mine turned out to be v1.3, so it was manual entry for me! Reading the values from REW meant that this was no big deal.

See here for a guide on using REW.

I've used the software to explore a couple of potential locations for an IB. See my writeup here.

I've now built the twelve driver design. Report here.

 

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