Dayton RSS390HF-4 15"?

[bottomfeeder]

Originally posted by DougSmith



Why cancellation? The port is the only way out for the sound. I want to build a trio of bandpass subs according to Earl Geddes' design philosophy to go with the Abbey's I currently have on order: two broadband for the ~50-150 Hz range (with B&C drivers) and one ULF (so far the Dayton HF 15" is looking attractive). It's a bit ambitious, but I enjoy the challenge of doing the research, learning and building things myself. I'm not sure how to model square ports, but that might be interesting. I have been using WinISD, Unibox and Speak to do the modeling (WinISD for initlal approximation and the others to verify and refine things). Here are some mockups of the designs I am thinking of (rectangular box link and sonotube link). I don't see any problem with the port length, only the fact that they come fairly close to the box and baffle walls in these designs (I would welcome any comments from folks who have tried something like this). I am planning to use an outboard 3-channel amp capable of putting out ~200W into 8ohms or ~300W into 4ohms and Behringer DCX2496 for filters and bass management in conjunction with my existing Yamaha AVR.

-Doug

On your 50" 7.36 cubic that should sound good !
I still would go sealed (check it winisd) let room gain bring up the low end where it hugely improve group deley , improve transient response (reduce boominess) avoid tuning issues, etc

[DougSmith]

Bottonfeeder... Yes, group delay is pretty high for that bandpass design (peak of ~39 ms at ~20 Hz), but it is still less than 1 cycle across the design bandwidth and most likely wouldn't be a problem. A sealed design (190 l box) does indeed have much lower group delay, but that goes up to ~15 ms when a low pass filter is added to create the desired roll-off at 50 Hz. Overall it has ~2db less response at 20Hz (probably not a big deal, as you say, especially since my room is very long and has a mode at ~20 Hz). One potential issue, though, is that the cone excursion goes way past xmax with 300W driving it.

Looking at a number of different designs, I see that those which produce a curve such as the one I linked previously (flat top with fairly steep rolloff on either side) also have fairly high group delay. On the other hand, those that produce a more rounded curve with smoother rolloff have lower group delay. I am now thinking that this may be more desirable. Another driver I modeled is the Acoustic Elegance AV15-H, which has similar output at 20Hz to the Dayton bandpass (in a similar sized enclosure) and produces a more rounded curve with lower group delay (peak of ~21 ms at ~20 Hz, which is less than half a cycle). Overall, that looks like it will mate better with the B&C broadband subs I am already committed to (drivers on order), curves are linked here: SPL, Group Delay.

-Doug

[bottomfeeder]

Wow looks like you will be down 4 db 20-100 HZ !
Thats awesome !
Have you choosen a amp ?
I recomend something with R&L gain adjustments , the graph looks close but the amp adjustment will work like a 2 ch eq allowing for variances in your room to blend.
Are you using a externall xover ?
This setup reminds me of a schametic I have been looking at for 15 years , its a externall electronic xover that splits the sub signal
with the idea you get a good sub for the 20 hz area and another to fill the 50hz up .
Please post some pix of your cabinet building !!