[hddummy]

so you didn't have a real reason behind the values you chose other than it was one notch lower in the boost tables.

 

[Mike P.]

The cone excursion of the default values dictated that a lower HPF could be used. The next lower HPF was 24.3 hz.

 

[hddummy]

Gotcha. Anything lower and you driver it past Xmax at these power levels. By the way, what subwoofer design software is that?

 

[Mike P.]

WinISD Pro (version 0.50a7)

 

[hddummy]

Small problem. If I extend the port the additional length to get 27Hz tune, the end gets too close to the center brace. I would have to keep 29, which isn't bad or extend the port to about 39 inches total length so that it ends at the brace. That is getting too long and port resonance could come into play. I could also reduce the port cross section, which would reduce the length requirement for a given tune. The question is, what are the dimensional limits on a slotted port. It is currently 8.5 x 1.5, if I go down to 1.25, my port length goes down to 31.25" and my port air speed is about 13m/s. I think I'd be good and I get the added benefit of some extra effective volume. I just don't know if that is too thin for the slot. Any help?

 

[Mike P.]

With a 29 hz tuning a 8.5 x 1.5 slot port is 32.5 inches long. With a HPF at 24.3 hz and the boost that goes with it and 500 watts input power the port air speed is 32 m/s at 29 hz, definitely at the limits. I'm not sure how you're coming up with 13m/s.

 

[hddummy]

I'm using Unibox right now, but I'll download WinISD and double check. I'm modeling with two drivers at 250W total input power. This is what I get. Of course this doesn't account for frequency response of the amp itself.

 

[Mike P.]

I modeled peak air speed with 500 watts input power.

 

[hddummy]

yeah...the amp is 500....until you wire two 4ohm drivers in series, which of course drops it to 250, giving 125 to each driver.

 

[Mike P.]

Forgot about that ohm thing. :whistling:

 

[hddummy]

so, what do you show for port air speed at 250w? I guess that means the excursions you were showing was based on 500W as well...i can probably boost the low end a little more.

 

[Mike P.]

Green is with 250 watts input, HPF at 21.6 hz and 2 db of boost from 25 - 30 hz. Maximum air speed is 25 m/s at 28 hz. Pink is the wrong modeling of 500 watts.

 

[hddummy]

I've been messing around with WinISD and several different combinations of Port Tune and Amp Boost/HPF settings. I think I have settled on a good solution. Thanks for your help and encouragement.

 

[hddummy]

I guess nothing is settled until it's built....right? In an effort to reduce port air speed, I've tweaked it more. Box volume 31l, tune to 28Hz, port dims: 1.375 x 8.5. Response changes marginally, port is a few inches longer, air speed drops to 20.5m/s.

 

[Mike P.]

Sounds good. Don't forget your camera when you start building. :yes:

 

[hddummy]

You bet! I hope to start making dust next week.

 

[hddummy]

OK..... I've made some progress, so here are some pics.

All the parts cut out:

The eventual home:

Dry fit check:

Port up close:

 

[Mark Holmes]

Really nice round over cuts on the corners. You must have a really nice bit. :bigsmile:

 

[DragonArt]

Very professional-looking work so far! :clap: I also like the design although I would have built a [email protected] rear loaded horn with those drivers hsd: :dumbcrazy, but I guess that would be kind of a overkill.

 

[hddummy]

Thanks! Yeah, it is a 1 1/4 round over bit, but I only cut it to 1 1/8 depth. I wanted to keep that slight edge on the face instead of driving the radius down flush with the front face. I was out of town this past weekend, so I hadn't made much progress. Also, I only glue and clamp one piece on at a time. A lot of guys will just throw it all together and tack it with nails or screws to hold it while it dries. I should get finished pictures up this weekend.