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 Impedance||4 ohm|
|Pe - Power Handling||250W|
|SPL - Sensitivity||88.48 dB/watt@1m|
|Re - Voice coil resistance||3.5 ohm|
|Fs - Resonant frequency||25.65 hz|
|Qms - Mechanical Q||3.552|
|Qes - Electrical Q||0,578|
|Qts - Total Q||0.497|
|Vas - Equivalent volume||150.7 litres|
|Xmax - Maximum excursion||15 mm|
|Sd - Cone Area||750 sq cm|
|EBP - Efficiency Bandwidth Product||44 - Best in sealed|
Here is my parameter file for this driver for WinISD Pro ver 0.50a7
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....
|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|
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.
Port air velocity
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
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 )|
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.
The black line is the resulting excursion for:
- a four driver design with 190w applied or
- an eight driver design with 410w applied or
- a twelve driver design with 670w applied
- a four driver design with 480w applied or
- an eight driver design with 1050w applied or
- a twelve driver design with 1700w applied
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
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:
|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.