There appear to be 2 questions looming herein. The first is a quetion concerning an infinte baffle setup. The second is a question about a sealed floorstanding version.
I will first comment on the sealed iteration. I think that I addressed this previously, but couldn't find my previous comments. The short summary is that a sealed 1801 in 16.5 liters simply didn't sound equivalent to the 22 liter ported 1801 in the bass region. The ported speaker really sounds better. The negative effect might invade the midrange too, but only slightly.
There are a few possible reasons for my/our generally inferior impression of the sealed 1801.
1. The sealed 1801 places higher demands on cone excursion at lower frequencies. While the W18 does have 5mm of X-max, it's not a real woofer. The port does indeed unload the driver below about 30hz, but this is minor. Above the 34hz tuning frequency the ported cabinet actually restrains cone travel. Given practical music input the ported cabinet is preferred. There really isn't any musical bass below 30hz, but there are huge quantities of mucial bass above 41.5 hz. This is the lowest fundamental for a bass guitar.
2. The result of the restrained cone travel from the ported cabinet seemed favorable in the midrange, but this was very very slight. This is simply due to the decreased doppler distortion (IMD) present. Consider the woofer is coincidentally producing a bass note, and a midrange female vocal. The cone is making large swings for the bass note and ALSO making small ripples for the female vocal - at the same time. The result is doppler smear of the female vocal.
3. The sealed cabinet produced less bass in the 40-50hz zone. This is theoretically true, and it was audible. Having the proper balance of bass in the 40-50hz is very pleasing.
Please understand that a sealed cabinet woofer can sound absolutely phenomenal when all is correct. Unfortunately the W18E001 midwoofer is not the correct starting point. The results for the W18E001 will be the same in a sealed cabinet regardless of cabinet shape.
Now... the infinite baffle. Presumably you wish to build the 1801 with an open-back. To this my answer is unfortunately "no". There are cancellations at the sides of the response pattern that must be accounted for when place in-room. When executed correctly the result can be pleasing, but the crossover MUST be designed for this. There are also several other demands placed on the drivers without cabinet suspension. This is extremely complicated, but the simple way (my version) to understand this is that cancellations will happen between the front and back wave. These happen at the sides of the cabinets. Because of these cancellations the driver must push significantly air to obtain equivalent SPL into the room. Sigfried Linkwitz has some excellent material on this subject published on his web page. Applying this material to the proper set of drivers with a specifically designed crossover is very viable. With the 1801 it is not.
Unloading the bass from the 1801s is a good thing, but you will have to use a high pass unit. Using a smaller sealed cabinet of 16.5 liters would be just dandy in this application because there is no signal in the bass region. You should probably run the high pass crossover around 60-80hz. Emilio Provenzano (Eproven) did something like this with very positive results. If you are interested, please search this forum for his posts about subwoofers and integration with the 1801s. If the search comes up "empty", query him directly.
I hope Dave gets around to the 3-way idea soon.........
Yeah, me too. I have 3 more long-term customers waiting for 1801s, and a deck (honey-do) that will happen before I resume work on these things. I have been much more focused lately, and am finishing 1801pr's about every 2 weeks!
Please let me know if I missed any of your concerns.
Dave
