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-   -   6th Order Bandpass HT Sub, would like some feedback (http://www.diyaudio.com/forums/subwoofers/129048-6th-order-bandpass-ht-sub-would-like-some-feedback.html)

pjpoes 1st September 2008 01:14 AM

6th Order Bandpass HT Sub, would like some feedback
 
Hey Guys, ok so I was originally going for 4th order, but I'm now thinking 6th order. Ok so I have a few models running around, and my proof of concept experiment worked out well enough that I want to move forward with a larger HT sub. I ran some measurements on my TC3000 driver (which as I have mentioned, is not an off the shelf version), and with the coils measured on their own, I get an Le of 2.05mh, and roughly a 4 ohm resistance (2.68 dcr). In series, as its wired right now, I get a DCR of 5.3 ohms, and an Le of 4.08mh. Unfortunately my laptop is temporarily dead, so the rest of the measurements are "locked away" until its repaired. Based on what I had saved in my desktop computer from some earlier measurements, I came up with a box that is roughly 6 cubic feet internally for the first chamber, and tuned to 10hz, and a second chamber of roughly .75 cubic feet and tuned to 50hz. The lower tuned chamber will have a passive radiator, and the higher tuned chamber will use a slot port. The design is somewhat similar to what I believe Mark Seaton is doing, in case he happens to see this, but I don't know that to be true. None the less, he did inspire me to try this.

Ok idea number two would be an almost identical box, but with a Dayton Reference RS315HF-4 instead of the TC3000. Both seem to work pretty interchangeably. The big difference is a tuning of 40hz for the smaller chamber. Also, while the driver can handle more power, it seems that just 100 watts is needed to reach xmax with this driver in this enclosure, which would be roughly 105db's from 20hz to 60hz. The TC3000 would handle its full 2000 watts before hitting xmax down to 10hz, and would be near 120 db's by comparison. However, I don't have a 2000 watt amp for that driver, but instead would feed it with a 1300 watt amp. If I did the Dayton, I would probably just use a more models 2 or 300 watt amp, maybe the Dayton Bash model.

I had mentioned this idea to Dr. Geddes in an email once before, and I believe he referred to it as a leaky box which is very hard on the driver excursion wise. I didn't realize quite what he meant until I began playing with it, now I see. The TC driver I think is the better choice, but really, either will work well, the Dayton generally can't do more than 100db's at 20hz regardless of box design, so the added efficiency and lower distortion isn't such a bad thing. Both of these designs show a -10db of 10hz and a -3db of 16hz.

pjpoes 1st September 2008 01:23 AM

I wish I had taken pics, its kind of funny to think back on it, but my Proof of concept involved building a 1 cubic foot box with one side missing, and an adjustable set of ports on the front. I then put gasket tape all around its edge, and clamped it to my 4.5 cubic foot ported box, tuned to 21hz. While the design didn't match what I want to built, I made a model for this so I could compare, and things turned on pretty good. The model predicted a big peak around 85hz with the front tuned to 75hz, and while I saw around a 3db rise there, it wasn't as big as predicted. Once the crossover was added to the equation it was flat down to 20hz, had a minus 3db at 16hz and a -10 at 14hz in my room, but at 1 meter.

Patrick Bateman 3rd September 2008 01:55 AM

personally I've never had good results with dual-reflex bandpass enclosures. They always sounded odd. In addition, you can get very close to the same efficiency using a single reflex bandpass if you juggle the chamber volumes a bit.

So the single reflex gives you 80% of the bandwidth, almost identical efficiency, it's simpler to build AND it's less error prone.

Hard to argue with that.

Also, I wouldn't dream of building a single OR a dual reflex bandpass unless you have a method of measuring the woofer's T/S parameters and the impedance curve of the box. In my most recent design I had a leak that ruined the entire resonator, due to a leak. It was a piece of cake to see it in the impedance curve.


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