Hello Everyone,
I occasionally monitor the stats from our website and in this case saw a lot of traffic coming from here. I figure it would be good to come on and comment on some of the questions. The lead times were very long with the group buy. I expected things to be very busy having three group buys happen at once. What I did not expect was the long two month delay receiving parts due to the west coast dock labor dispute. Ships sat in harbor for up to a month at the worst time. Ships were also not returning to China so our steel and frames had to wait a long time to be loaded on a ship. Chinese New Year fell in that time as well further delaying things. I am now current on all TD/Dipole/SBP/IB woofers. Lead times are about 2 weeks right now on those woofers. Lead time for the TD18H+ and Dipole18 is a little longer yet. Freight cost has become more reasonable as UPS has been very good to us with new rates as well, up to 72% discount on UPS Expedited service.
Regarding the original question, there are very few woofers that can play up to 600Hz and also play the lowest frequencies without a subwoofer. In most cases you choose which is the most priority and then accept that the other will not be so good. To play high requires very good inductance control and reduction of flux modulation. Very few woofers at all address this. To play low requires high power handling and also high Xmax. Parameters also need to allow for a moderate enclosure size. The TD15H has the best combination of those anywhere. The 14mm Xmax, 500W power handling, and incredibly low inductance is not available in any other driver. The Vapor Audio Nimbus was mentioned. In this review, Ryan Scott mentions why the Nimbus wouldn't be possible without the TD15H. There were no other options.
Vapor Audio Nimbus White Speaker Review | A Unique Audiophile Experience
None of the other drivers listed have nearly the 14mm Xmax. It would take two or more of most of these drivers to equal the output of a single TD15H at low frequencies. Enclosure size would also need to be much larger with any of the more efficient woofers. If looking to play low and be used without a subwoofer, the efficiency cannot be so high. Hoffman's Iron Law dictates that the response will begin to roll off much higher as efficiency is higher. The only option then is to use EQ to boost the low end. This again requires higher power handling and enough Xmax. Most drivers listed including TAD, Volt, and Focal do not use any shorting rings to address the flux modulation and keep inductance linear with respect to excursion. Also realize that all other woofers listed have dustcaps. This is not an issue when used in bass only applications. However, this creates a resonance lower in frequency than the cone breakup. In most cases you can see this in the impedance curve between 600-900hz. Even if crossed over steeply at 600hz, this resonance is problematic. Some of the Altec drivers attempted to address this by using a dustcap with a soft screen in the middle. It creates other issues though. The TD15H is the only one that uses a phase plug instead to completely eliminate this issue of dustcap resonance.
ATC, TAD, and Flex Units are the drivers most often compared to AE. The best comparison to the TD15H of all drivers on the market is the Audiotechnology FlexUnits 15E10225. We actually reference them in our paper on designing for low distortion. They did address flux modulation and Le(x) distortion to a higher degree than most.
Designing for Low Distortion: Lambda 001 Motor - AE Speakers The Flex Units still have inductance that is more than twice as high as the TD15H as they do not have a Full Copper Faraday Sleeve covering the entire pole. They also have only 8.6mm Xmax vs 14mm Xmax. They are not quite as efficient. Here in the US they are much more expensive than a TD15H, but it may be about the same end cost there. If they are available more affordably there, the Flex Units is probably the next best option to the TD15H if you willing to sacrifice some low end output and extension, and a little detail on the upper end. I have yet to see any woofer that can compare to all the TD15H can offer though.
Best Regards,
John