Well, I'm a little behind here on the thread, so let me try to catch up. First, I'll go back to Mitchell's questions. Optimum volume for the HE15 in a ported or PR system is about 4 cubic feet. As you increase the size over 4 cubic feet, you can get some gain in the output below Fb, however, you also begin to limit your output at the excursion peak. So by increasing the enclosure size, you gain output that is below the audible frequency range, at the expense of some output between 20-30Hz. IMO, this is not a worthwhile tradeoff.
Next the sealed vs PR issue. Here are a few graphs showing the comparison between the two. First of all is the frequency response. As you an see, the sealed enclosure begins to roll off much higher in frequency. The F3 point in this system is around 75Hz. At 20Hz, the sealed system is down 9dB compared to the PR system. It would take a large amount of EQ, and also a large amount of power to equalize the response of the sealed system to be flat:http://www.stryke.com/pics/HESvsP-response.gif
Now, in the case that you were to build this enclosure, and equalize the system to be flat, the max acoustic power is still severely limited in the sealed system. This is based on hoffman's law, taking into account the enclosure size, and overall displacement. From about 45Hz down, the sealed system will be limited to much less output than the PR system. At 20Hz, the PR system is capable of 15dB more output than the sealed system. The woofer and pair of 18" PR's just have much more volume displacement capability than the woofer alone in the sealed box:http://www.stryke.com/pics/HESvsP-max.gif
The other thing we need to look at between the two systems is the excursion. In the following graph you can see that in the range of abut 18-30Hz, the PR system has a much lower excusrion. Over this range the PR system has much better power handling. If you were to EQ the sealed system to be flat to 20Hz, you would need approximately 8 times the power to make up 9dB, and would more than tripple the excusion of the orange line in this range. This would push the woofer past it's excursion limits. What this means is that not only does the PR system have more output over this range, but that it can do it with much less power, and with lower distortion:http://www.stryke.com/pics/HESvsP-excursion.gif
As far as the aluminum goes, it doesn't sound like the greatest idea to me, but it is possible. For $1000 you could get a cabinet shop to build a very nice enclosure from wood. If you do want to go with the aluminum though, and you are putting in a pair of woofers in 8 cubic foot, you will need something for support. A brace in the middle, or some ribs welded in on the sides to help keep the enclosure from flexing would be good. You may want to look at the plans for either the Power15.6 or Power15.4 enclosures on the website and have them do something similar to the brace for your enclosure. Also, with regards to the metal grills, keep in mind that you will have to build those out about 1 1/2" to allow clearance so the woofer does not hit it.
Placing woofers on opposite ends of the enclosure helps to cancel vibrations in the enclosure. This is not nearly as critical with the woofers as it is with the PR's though because you have much less mass moving. A woofer with 250gram Mms moving will not shake a 200lb enclosure, but a PR with 2500grams will if there is not equal and opposing force to cancel it's motion.
The difference between single and dual woofer systems, if you keep the same volume per woofer(around 4cf) is just the output capability. The dual woofer system in 8 cf is capable of 6dB more across the board, compared to a single woofer in 4cf. If you were to put 2 woofers in 4 cf, the F3 point would be higher, and the system would have even a sharper rolloff, needing more eq to flatten the response.
As far as the template goes, this is available in the enclosure CAD drawings. The hole cutout size is 14". If you plan to countersink the woofer into the enclousre, you will need 15 3/4" to allow for the basket and the rubber gasket to fit into the recess.
Yes, if you order now, expect delivery by mid August. This is a preorder deal where I take orders and receive the money when I place the order with the manufacturer. This allows me to offer the woofers at $395 instead of the typical $1000 retail on them. On June14 I will be placing the order with the manufacturer and I am expecting 4-6 weeks for the woofers to get here. The PR's may take slightly longer as I have a 30day lead time to get parts, and then have to build all of them. To give myself enough time, I am stating delivery will be by mid August, but I should begin shipping by august 1.
Yes, there was another preorder back in November last year. This is when Bob, as well as others, purchased his woofers.
For terminal cups, cabinet feet, etc, check with Madisound. They have a good selection and have very good service.
When I referred to the 18" PR's being better than the 15" PR's, I was not talking about the 15" PR's like Bob has. I was referring to the HEPR15's that were offered during the last preorder period in November. These HEPR15's had a much stiffer suspension than either the 18" Pr's, or the current 15" PR's. This caused a loss of several dB in the low end range.
The 6 15" PR's like Bob has will perform almost identically to the 4 18" PR's. The only reason I offered both systems is because the 4 18" PR's require a cabinet 45" tall, and the 6 15" PR's fit in a 36" tall cabinet. Some people find the shorter cabinet to be more practical for their rooms. For a single woofer enclosure, the 2 18" PR's work better than the 3 15" PR's. The third PR on the back of the enclosure tends to rock it around quite a bit, where the 2 18" PR's directly cancel each other.
As far as the quantity issue goes, if over 100 are sold, the price drops $20 for everyone. Thilo is expecting a 100 driver order, but I am still able to order only 50 drivers if necessary. The deal will go through, whether enough are sold for me to drop the price or not is the only issue. So far, I have not spent any money on advertizing. I have lived just on word of mouth from my customers. As a result, if people get the word out about the drivers to help me sell more, I can reward everyone by dropping the price.
I would not suggest using the HE15 over 100Hz. Actually, 80Hz would be my suggested crossover point. Due to the large VC, the woofers have a high inductance. They are a true subwoofer. If you are looking for something to go with the Unitys, the TD woofers, or Lambda PL woofers are really the way to go.
The MDF enclosure for the 15.2 weighs about 85lbs. The woofer is 48lbs, and the 18" PR's are about 20lbs each. So about 173lbs for the entire subwoofer, plus any veneer, laminate, wood top, etc that you would put on there. Prices do not include shipping. Any orders of over 100lbs will be shipped out BAXglobal. Shipping for the 173lb system should be less than $80 to anywhere in the USA and is guaranteed in 3 days or less.
Well, think that answers everything for now. I'm going to try to catch up on emails now as I know some of you have asked questions to me there. I should be caught up by the end of the night.