JBL 2245H as an IB ??

[djgaloot]

I am wondering if the JBL 2245 would work well in an IB installation?
What size amp would be required for this application?
Below are the specs from JBL
Thanks,
Dave

SPECIFICATIONS
Nominal Diameter: 460 mm ( 18 in)
Rated Impedance: 8 ohms
Power Capacity: 600 W continuous program
Sensitivity: 95dB SPL, 1W@1m
Frequency Range: 20 Hz to 2 kHz
Highest Recommended Crossover Frequency: 800 Hz
Recommended Enclosure Volume: 225 - 450 L (8 - 16 ft3)
Effective Piston Diameter: 406 mm (16 in)
Maximum Excursion Before Damage: 25 mm ( 1 in peak to peak)
Minimum Impedance: 7.1 ohms ± 10% @ 25°C
Voice Coil Diameter: 100 mm (4 in)
Voice Coil Material: Edgewound Copper Ribbon
Voice Coil Winding Depth: 24 mm (0.96 in)
Magnetic Gap Depth: 9 mm (0.35 in)
Magnetic Assembly Weight: 9.1 kg (20 lb)
Flux Density: 1.22 T ( 12,200 gauss)
Bl Factor: 21 N/A
Effective Moving Mass: 0.185 kg Positive voltage on BLACK terminal gives forward diaphragm motion
THIELE - SMALL PARAMETERS:
fs: 20 Hz
Re: 5.8 ohms
Qts: 0.27
Qms: 2.2
Qes: 0.31
Vas: 820 L (29 ft3)
Sd: 0.130 m2 (200 in2)
Xmax: 9.5 mm (3/8 in)
Vd: 1,230 cm3 (75 in3)
Le: 1.4 mH
no (Half space): 2.1%
Pe (Max): 300 W Continuous Sine Wave
Volume Displaced by Driver when Mounted in Enclosure: 8.5 L (0.3 ft3)

[ThomasW]

Generally speaking pro-sound woofers aren't a good choice for IB subs unless you plan on buying them by the dozen.

Why?

The usable swept volume is low. Having only an Xmax of 9.5mm is a problem for IB use since drivers in IB subs are excursion limited, not thermal limited like subs in other alignments.

In addition accordion surrounds tend to be noisy when pushed to extremes.

[djgaloot]

Jul 4, 2008 11:35:17 GMT -7 ThomasW said:

The usable swept volume is low. Having only an Xmax of 9.5mm is a problem for IB use since drivers in IB subs are excursion limited, not thermal limited like subs in other alignments.

Okay, I think I understand; you want an Xmax much greater to move more air and there is not as much resistance (=energy=heat) due to the IB configuration.
How much swept volume is normally required for a listening "area" about 12' by 12' with 7-1/2 foot ceilings? It is not a totally closed room as one side continues into another area.

Thanks for your quick input!
Dave

[ThomasW]

It's difficult to provide a formula given the personal differences in what people consider "adequate" output. As a result the usual recommendation is to construct a manifold that will hold 4 drivers but start with a pair. The 2 extra openings are blocked off for evaluation purposes. If/when more output is needed the openings are ready for those drivers.

If you're wanting unlimited amounts of bass start with a pair of Fi-IB18"s, add more later. If your needs are more modest the new Exodus Audio DPL-15"s are a nice option. There are threads about both these drivers in this loudspeaker forum.

12'X12' is of course a nightmare from an acoustical standpoint....

[marcuswilson]

Thomas, your comments on pro subwoofer drivers are generally correct, but the JBL 2445 has a foam surround, so does not suffer from the noise and the suspension is likely to be more linear.

I certainly agree about the excursion limitation in IB. But I note that most of the ported designs I have looked at are excursion limited at the lowest octave of their response.
In PA systems, if these boxes are driven to over excursion, the voice coils overheat and will burn up if this goes on too long. They overheat because the coils spend too long out of the gap, away from the cooling of the magnet assembly. People think these damaged drivers have been just overpowered, but it is often over-excursion.

I am planning to try JBL 2245s for IB subs, but will probably be using 4 per side. 4 X 18" at 9mm each should produce a reasonable SPL.

At the present, I have one 2245 in a box with a tube coming out the front (I'm not sure if this should be admitted on this forum) and it's reasonable, butI think it can be done better with IB.