mlah384 Posted October 30, 2015 Report Share Posted October 30, 2015 What are the thoughts on the FTW-21 from IST? I'm on the 2nd round of a group buy for them on AVS, BUT i'm not sure if they will do the 2nd round. If they don't, I'll need to have a plan B. Currently I have a media room with two Dayton UM18-22's. They are each in a 9cu ft ported enclosure tuned to 18hz (AVS mini marty) and are on the front wall under my LCD. I power them with an inuke 6000dsp. It's not enough for me. My room is an open concept that opens into kitchen, dining, foyer, breakfast, and two hallways all with 12ft ceilings ;( - not bass friendly at all. The rest of my system are 1099's (which set on top of the subs) for LCR and Volt 10's for surrounds (5.2 set up) all powered by Denon 4520 AVR. I also have a concrete foundation ;( My plan was to add four FTW-21's. I wanted to build two end tables to place on each side of my couch, each containing two FTW-21's in dual opposed at about 13-14'ish cu ft. and power them with a Clone bridged mono at 4ohms for max power. I wanted to go sealed for ULF. I watch 99.9% movies so I want to feel the 3-18hz that I'm currently missing. For Plan B my thoughts were to buy 6 more UM18-22's and build four dual opposed sealed enclosures for all 8 and get rid of the big ported boxes. But not sure about that route... Then my testosterone starts talking and wants to sell the UM18's and get 8 HST-18's instead, but that's a very pricey route. Any input or wisdom is greatly appreciated! Thanks! Link to comment Share on other sites More sharing options...
lukeamdman Posted October 30, 2015 Report Share Posted October 30, 2015 For the group buy price I don't think the FTW-21 can be beat. The HST-18/UXL-18/FTW-21 all have nearly identical xmax only the FTW has ~50% more diaphragm surface area. My plan for them is similar to yours with large dual-opposed boxes (mine are ~13.3cu.ft before drivers/bracing). Link to comment Share on other sites More sharing options...
mlah384 Posted October 31, 2015 Author Report Share Posted October 31, 2015 Yeah, I hope the GB goes through the second round... I just resurrected an old thread on AVS that said the HST-18 models well in a 2 cu ft sealed enclosure?! Wow... And the Sundown Zv4 18 models even better in the same small sealed cab? That's like a dream come true for small footprint! Link to comment Share on other sites More sharing options...
Ricci Posted November 2, 2015 Report Share Posted November 2, 2015 The FTW-21 is the same motor and coil as the UXL I believe. It should have similar performance characteristics as the UXL except be capable of about 3dB more output. However the box will need to be a little bigger than the 18 obviously. I wouldn't say that the HST or Zv4 model well in 2 cubes. Really peaky and almost impossible to get enough power on them to use the extra excursion they offer over other drivers. Not sure you can even fit one in 2 cubes. They are deep drivers. Link to comment Share on other sites More sharing options...
Bossobass Dave Posted November 2, 2015 Report Share Posted November 2, 2015 Correct, you add approximately 3dB going from 15"==>18"==>21"==24", respectively. That's just raw displacement math and it assumes a correct increase in air spring as displacement capability increases. Math also disregards power handling, mechanical noise, non-linearity, etc. You can get away with 2 cubes per 15" but, as Josh notes, no way you gain anything by cramming bigger drivers in that space. We put a pair of HST-15s in approximately 4.5 cubes net, obviously 2.25 cubes per 15. They do exceptionally well in that space, assuming proper signal shaping, low signal chain roll off, matched amplifier power and gain matched signal chain. The 18" version needs double the air space. Approximately doubling the air space per 3dB increase in ULF output works fairly well, within the same platform of driver. Link to comment Share on other sites More sharing options...
mlah384 Posted November 2, 2015 Author Report Share Posted November 2, 2015 The FTW-21 is the same motor and coil as the UXL I believe. It should have similar performance characteristics as the UXL except be capable of about 3dB more output. However the box will need to be a little bigger than the 18 obviously. I wouldn't say that the HST or Zv4 model well in 2 cubes. Really peaky and almost impossible to get enough power on them to use the extra excursion they offer over other drivers. Not sure you can even fit one in 2 cubes. They are deep drivers. Correct, you add approximately 3dB going from 15"==>18"==>21"==24", respectively. That's just raw displacement math and it assumes a correct increase in air spring as displacement capability increases. Math also disregards power handling, mechanical noise, non-linearity, etc. You can get away with 2 cubes per 15" but, as Josh notes, no way you gain anything by cramming bigger drivers in that space. We put a pair of HST-15s in approximately 4.5 cubes net, obviously 2.25 cubes per 15. They do exceptionally well in that space, assuming proper signal shaping, low signal chain roll off, matched amplifier power and gain matched signal chain. The 18" version needs double the air space. Approximately doubling the air space per 3dB increase in ULF output works fairly well, within the same platform of driver. Thanks Ricci and Boss! What's the ideal enclosure size for sealed vertical dual opposed FTW-21's? Does the distance from the woofer to the floor matter? as well as the space from the woofer to the top (since it will be an end table)? I was thinking 12-14 cuft range? Ricci, If I end up getting the FTW's, I might consider shipping one to you so you can test it, and then pay for it to be shipped back. Boss, Do you sell a modified/enhanced version of the FP14k? I was planning on buying a clone, but if you have one that has a better power supply, I'm all ears! Thanks! Link to comment Share on other sites More sharing options...
Ricci Posted November 3, 2015 Report Share Posted November 3, 2015 Ideal size depends on what size enclosure or shape you can live with and also what the amplification will be IMO. Even if you went with a sonotube type cylindrical enclosure it will need to be a minimum of about 23 to 24" diameter. I'm not sure of the exact depth of the FTW-21 driver but I'd figure you need a bare minimum of 15" of depth behind the driver. After driver displacement the driver would probably see about 3cu ft in that size tube. A good middle of the road volume for each FTW-21 would be around 6cu ft. With 2 in one tube you are probably looking at a bare minimum of about 40" in height and that'll be a bit undersized for the drivers. Link to comment Share on other sites More sharing options...
lukeamdman Posted November 3, 2015 Report Share Posted November 3, 2015 Ideal size depends on what size enclosure or shape you can live with and also what the amplification will be IMO. Even if you went with a sonotube type cylindrical enclosure it will need to be a minimum of about 23 to 24" diameter. I'm not sure of the exact depth of the FTW-21 driver but I'd figure you need a bare minimum of 15" of depth behind the driver. After driver displacement the driver would probably see about 3cu ft in that size tube. A good middle of the road volume for each FTW-21 would be around 6cu ft. With 2 in one tube you are probably looking at a bare minimum of about 40" in height and that'll be a bit undersized for the drivers. I just grabbed these from Mark's website: Mounting diameter: 20.03" Outside diameter: 21.37" Mounting depth: 10.39" Link to comment Share on other sites More sharing options...
Bossobass Dave Posted November 3, 2015 Report Share Posted November 3, 2015 Actually, IMO, ideal size depends on the Vas of the driver. The stiffer the suspension (the lower the Vas), the smaller the air spring (enclosure size). A general formula I use is Vas * 40-50%. Final size should be determined by the amount of power you want to feed the system with. For example, the HST-15s have a Vas of 5 ft^3. Times 40% = 2 cubes of box and .5 = 2.5 cubes. We put them in 2.25 cubes and according to my decade long preferences, they worked very well in that space. The HST-18s have a Vas that's exactly double that of the 15s, so doubling the box volume to 4-5 cubes would be my ideal. The Vas of the FTW-21 is listed as 18 ft^3. I would put them in 7.2-9 cubes, averaged to 8 cubes, as a start, then experiment with signal shaping and power plant to arrive at the ideal symbiosis. So, the general rule of +3dB per 3" nominal diameter increase and double box size per 3" nominal diameter increase has held pretty true over 100 or so sealed box system builds over the years. Use less power for larger box and more power for smaller, within the driver's power handling capability and intended source and in-room response. Add multiples to arrive at desired playback levels. Link to comment Share on other sites More sharing options...
Ricci Posted November 3, 2015 Report Share Posted November 3, 2015 Interesting... I pretty much ignore Vas due to the variability. I usually do a bit of testing and look at the excursion profile, the drivers thermal handling ability and the amplifier requirements or capabilities and use that to size the enclosure volume. Link to comment Share on other sites More sharing options...
mlah384 Posted November 29, 2015 Author Report Share Posted November 29, 2015 Actually, IMO, ideal size depends on the Vas of the driver. The stiffer the suspension (the lower the Vas), the smaller the air spring (enclosure size). A general formula I use is Vas * 40-50%. Final size should be determined by the amount of power you want to feed the system with. For example, the HST-15s have a Vas of 5 ft^3. Times 40% = 2 cubes of box and .5 = 2.5 cubes. We put them in 2.25 cubes and according to my decade long preferences, they worked very well in that space. The HST-18s have a Vas that's exactly double that of the 15s, so doubling the box volume to 4-5 cubes would be my ideal. The Vas of the FTW-21 is listed as 18 ft^3. I would put them in 7.2-9 cubes, averaged to 8 cubes, as a start, then experiment with signal shaping and power plant to arrive at the ideal symbiosis. So, the general rule of +3dB per 3" nominal diameter increase and double box size per 3" nominal diameter increase has held pretty true over 100 or so sealed box system builds over the years. Use less power for larger box and more power for smaller, within the driver's power handling capability and intended source and in-room response. Add multiples to arrive at desired playback levels. Thanks Boss! How would you power these if they were in four separate enclosures, two up front close to each other, and two as end tables? It would be great if all four were together and I could run a fp14k bridged mono, but I don't think that would work since they will be split up? Link to comment Share on other sites More sharing options...
Ricci Posted November 29, 2015 Report Share Posted November 29, 2015 Bridge the amp. It will perform better. You may have to get creative with the wiring but it can be done. Link to comment Share on other sites More sharing options...
mlah384 Posted November 29, 2015 Author Report Share Posted November 29, 2015 Bridge the amp. It will perform better. You may have to get creative with the wiring but it can be done. Thanks Ricci... I worry about the timing being off, etc ... If it's bridged then I won't be able to tune them separately? Link to comment Share on other sites More sharing options...
Ricci Posted November 30, 2015 Report Share Posted November 30, 2015 Correct you will not be able to delay them separately. However I do not find that this is a big concern in most cases. If you delay the sounds to arrive at the same time at one LP in the room it will necessarily degrade the arrivals at another point in the room. Link to comment Share on other sites More sharing options...
lukeamdman Posted December 1, 2015 Report Share Posted December 1, 2015 My boxes for the FTW-21 drivers were finished last week: I also had to buy 24 pillows to stuff the boxes with!! Link to comment Share on other sites More sharing options...
Rowan611 Posted December 1, 2015 Report Share Posted December 1, 2015 Those look great Luke. 24 pillows.....wow!!! Link to comment Share on other sites More sharing options...
lukeamdman Posted December 1, 2015 Report Share Posted December 1, 2015 Those look great Luke. 24 pillows.....wow!!! Yeah, that's about $60 worth of pillows lol! Link to comment Share on other sites More sharing options...
mlah384 Posted December 1, 2015 Author Report Share Posted December 1, 2015 Nice job Luke! I can't wait to hear your impressions! Link to comment Share on other sites More sharing options...
lukeamdman Posted December 8, 2015 Report Share Posted December 8, 2015 I never noticed how high the impedance of the UXL was for Josh's testing: Since the FTW uses the same coil/motor, I'm looking forward to measuring the impedance in my large dual-opposed boxes with two of these drivers wired in parallel. If the lowest point really is ~5.1ohm for a single driver like Josh measured, I think I could get by with powering all 8 of these off a single sp2-12k amp. Link to comment Share on other sites More sharing options...
lukeamdman Posted December 17, 2015 Report Share Posted December 17, 2015 Oh snap...there's a chance I'll get the drivers by Friday! Link to comment Share on other sites More sharing options...
mlah384 Posted December 18, 2015 Author Report Share Posted December 18, 2015 I roughly calculated the cu ft of air space in my open concept room and it's anywhere from 8000 cu ft to 9000 cu ft depending on if you include hallways or not. And if doors are open to other rooms, it will be a lot more. I'm wondering if four FTW21s on a clone will be enough? Especially for single digits? Two will be up front facing MLP and the other two will be end tables about 12-14ft away from front two. If I need to time align, then I'll need to get the four channel 20000q over the fp14k. But the 20000q may be too much amp for the ftw21s? Link to comment Share on other sites More sharing options...
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