Acoustic Elegance kindly sent me some new drivers to replace my originals which had the wrong specs. John, the very knowledgeable owner of AE had suffered some personal tragedies over the last couple of years. This had affected his control over the company's products. He has now restarted his business on a more secure financial footing with far better quality control and redesigned products
These new AE IB15 drivers are currently available in sets of four for $400US plus freight. Four is probably a safe minimum with these 15" drivers in an IB. I found that muting any two of my four drivers makes a serious difference in output. That means more excursion is required to handle peaks. More excursion may be beyond the limits of only two driver's in an IB.
Warning! Click this image at your peril! The enlarged image is 400kB so don't attempt it on a slow modem! I posted this large image to show the sheer quality of these AE drivers. Smaller images just don't seem to do them justice. The new drivers have a lower Fs of 16Hz which means they should produce more deep bass straight out of the box. I had been using maximum boost of +16dB on the BFD at 20Hz on my old drivers which had a measured Fs of 32Hz.
The graph below clearly confirms the massive improvement. The blue trace represents just two new drivers in the manifold. The other curves show the old drivers without bass boost in pairs and all four. Levels have been matched to make comparison easier. The 11-12Hz peak is a room boundary effect common to both old a new drivers. As it is free bass and not requiring extra power from the amplifier, or extra cone excursion, I think I can safely ignore it. Or even consider it a bonus. There aren't many subwoofers which can claim 11Hz at well over 100dB(C-weighting).
I had no problem getting 100dB(C) at 10Hz [uncorrected] on my Galaxy 140 SPL meter except for the physical discomfort. Though completely inaudible the feeling of pressure in the room is intense. The Galaxy cal. file adds nearly 11dBs of correction to the REW response at 10Hz. This suggests that my IB is producing a true 110dB(C) (and over) at 10Hz without reaching the driver excursion limits. The room gain factor at 11Hz is probably helping here though I have no idea where this gain is coming from. There seems to be no linear dimension between boundaries which would have this free and beneficial effect unless the sound waves are folding at the stairwell. It is also possible that the room below is acting as a Helmholtz resonator with the open stairwell as its port. The IB manifold opening is quite close to the stairwell and may be driving the room below like a giant reflex loudspeaker enclosure.
The new drivers show obvious signs of much greater care in manufacturing and have had a complete facelift. The cones are now made of reinforced paper instead of the original poly material. The cones are now heavily flared compared with the straight-sided cones of the earlier models. The basket has been given a black finish with bright edges to the legs of the basket. The spider is also black instead of yellow. The earlier screw terminals have now become a sprung push-release type. Much easier to use, perhaps, but I would have liked much more room in the cross-hole for thicker cables. I'm using original 79 strand to connect the EP2500 amps to the drivers. The push terminals will not quite accept doubled wires no matter how tightly they are twisted together. The magnet backplates now have rounded shoulders and a smoothly flared pole vent. The quality of the machining is very much higher than on my old drivers.
At first I was running the new drivers in series pairs per channel because that was how the old drivers were wired. The new drivers have an 8 Ohms impedance which meant the amplifier was seeing 16 Ohms per channel. Despite hitting over 112dB on WOTW "machine rising" I felt the new drivers sounded a little quieter than the old ones. The old drivers were 4 Ohms each in series pairs for 8 Ohms and 450 Watts per channel. I have now rewired the new drivers in parallel pairs for 4 Ohms and 650Watts per channel or 325 watts per driver. This has increased output nicely over the former series pairs arrangement. Output now matches the older driver with plenty of weight on my favourite classical organ CDs and the bass-heavy pop and rock numbers I use to confirm bass quality and quantity.
This is an REW frequency response trace measured at the listening position using the Galaxy 140 SPL meter as test microphone with its matching calibration correction file loaded.
Here my BFD has been reprogrammed to match the new driver's output in the very deep bass. The trough between 12Hz and 25Hz has been filled with a small but wide boost filter at 20Hz. Further small filters at higher frequencies have smoothed the response nicely. The constantly rising slope to 12Hz could hardly be called a house curve. More of a ramp. This final curve seems to suit my ageing ears and my room. The image above is a subwoofer only response graph from REW. [Room Eq Wizard] This test software is available as a free download to members of Home Theatre Shack forums. John Mulcahy, the brilliant and generous software author, is usually able to answer specific questions about the software itself. General questions about its use are usually fielded by the very knowledgeable moderators of the specialist REW forum at the HT Shack.
Below are the manufacturer's T/S Parameters for the new AE IB15. Based on my own experience with these new IB drivers I heartily recommend them in sets of four for IB use. The sheer quality and quantity of bass they provide in a manifold IB is staggering using an EP2500 amplifier and 80Hz crossover. Your main speakers are much more likely to be the limiting factor in any sound reproduction system involving an IB. Given the amount of crossover overlap at high listening levels, even with a 24dB/octave crossover, requires a good quality floor stander with 110dB capability and at least 40Hz extension.
Thiele-Small parameters of the all new Acoustic Elegance IB15.
Fs: 16Hz
Qms: 6.8
Vas: 439L
Cms: .45mm/N
Mms: 220g
Rms: 3.239
Xmax: 18.5mm
Xmech: 25mm
Sd: 830sqcm
Vd: 3.07L (p-p)
Qes: .78
Re: 5.5ohm
Le: .33mH
Bl: 12.49
Pe: 500W
Qts: .7
1WSPL: 86dB
2.83V: 87.3dB
Here is one of the best online lists of Thiele-Small parameters and their meanings.
Car Audio: Thiele-Small Parameters
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