Hi, I am looking for some opinions as to whether or not I am on the right track and what you would recommend for drivers.
My room is approx 2200 ft3. 20L x 14.6W x 7.6H. The ceiling and front wall are effectively bass traps. Acoustically transparent screen and fabric covered wall treated with Roxul safe and sound 1.5 ft from foundation wall for front wall. Ceiling joists treated with safe and sound with a 10" air space to floor above. The rear of the room is about 1/3 open to the rest of the basement.
Subs to be mounted on front side wall vertical array.
I came here today with the same question. However I am not really interested in the IB318. I know it is promoted heavily on this board, but it just does not appeal to me - I think because I just do not like drivers where the suspension eats so much into the cone area. I feel like the UM18 is a viable competitor.
I am however, looking at either 8x IB385 vs 4x UM18-22. When comparing, is it appropriate to combine the cone area and xmax differences for volume of air moved? The UM18-22 has approx. 50% more cone area AND 50% more xmax, so that gives it 2.25x air displacement for 2.16x cost.
So comparing cost and displacement, they are about equal - slight advantage UM18. Sensitivities are about equal as well. Power handling is higher on the UM18-22 vs 2x IB385, so maybe that gives it an output advantage.
IB385 is 8-ohm, UM18-22 is dual 2-ohm, but since I'd be using twice as many IB385, that's sort of moot. I did read somewhere that it's possible to adjust resistance with DVC drivers by wiring in a resistor or something. I don't know if I want to mess with that though. I don't think it's necessary if I choose an amplifier that matches up.
I'm not sure what else to compare. Maybe the deciding factor is that IB385 is being discontinued, or that UM18-22's beastliness makes it more impressive.
But regarding accuracy and sound quality - or frequency response and output, is there a property that makes 1 better than the other?
Last Edit: May 16, 2016 9:07:31 GMT -7 by grandpixel
Post by grandpixel on May 29, 2016 23:09:14 GMT -7
I've been playing with WinISD and an excursion calculator.
Give the UM18 its RMS 1000 Watts in infinite baffle, and it will be putting out 116.3 dB at 32 Hz, which requires 21.75 mm excursion for an 18" driver - UM18 xmax is 22 mm.
Give the IB385 its RMS 350 Watts in infinite baffle, and it will be putting out 112.2 dB at 37.5 Hz, which requires 14.23 mm excursion for a 15" driver - IB385 xmax is 14.3 mm.
As far as I know, that means below those frequencies, the drivers become excursion limited, rather than power limited.
At 20 Hz: SPL for an 18" driver at 22 mm excursion is 108.2 dB (310 W for UM18) SPL for a 15" driver at 14.3 mm excursion is 101.3 dB @ (70 W for IB385)
At 15 Hz: SPL for an 18" driver at 22 mm excursion is 103.2 dB @ (190 W for UM18) SPL for a 15" driver at 14.3 mm excursion is 96.3 dB @ (45 W for IB385)
At 10 Hz: SPL for an 18" driver at 22 mm excursion is 96.2 dB @ (125 W for UM18) SPL for a 15" driver at 14.3 mm excursion is 89.3 dB @ (35 W for IB385)
So 4x UM18 should give you about 120 dB at 20 Hz, 115 dB at 15 Hz, and 108 dB at 10 Hz.
Given that IB385 are less expensive and require less power than UM18, you could double the drivers with half the power for about equal performance. But considering the IB385 is being discontinued, I would rather go with the UM18.
Another factor is that these numbers are based on 18" and 15" diameters. I don't have the actual diameters. I suppose I could use the baffle cutout diameter, which is about 1 1/4" less for each driver? This would require more excursion to achieve these numbers.
Regarding the IB318, I know excursion is its advantage, but I don't see Thiele Small parameters on the Fi website. Where can I get this information so I can model?
Also I think the practical diameter would be a good bit less for IB318 than UM18. Because the surround suspension is so huge, it might model more like a 15" driver, regarding xmax required to reach a certain output at given frequency. I just don't think it's moving as much air as UM18 at same excursion level.
Post by grandpixel on May 30, 2016 23:46:06 GMT -7
So I did some more searching on the IB318, and I think my issue has been that the photos on the Fi website are of the wrong speaker. Look at that photo and imagine it's an 18" - you can understand my reluctance.
For drivers my recommendation is a pair of the single 4ohm Fi IB3 18"s
I realize the Pyle amp has an attractive price. Unfortunately Pyle products are notoriously unreliable, perhaps you'll luck out with a good one.
I just went down to the States to pick up my IB318's. They are monsters!
Anyways, when you recommended the pair of single 4ohm's, I assume it was so I could wire them in parallel and bridge the amp in order to get the most power from the amp. But you know what they say about assuming.