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Big Mac Boy's Boombox
I want to build my BIL a boombox. My plan is to make an active 2-way with DSA115-8 woofers and Dayton Audio KADB-430 board. I haven't decided on tweeters yet.
This is the sim for the woofer.
I'd like to try to use a passive radiators but the PE DSA passives seem to be tuned way too low. I need to tune to 63Hz but the passive radiator is already tuned to 28Hz. I've never worked with passive radiators before so, am I missing something or do the marketing folks think they will sell better if they all have a really low but unusable Fs?
Ron
Comments
That is just it's natural Fs and doesn't really play into how it will work in your enclosure. Similar to the way any given diameter and length port will tune different in different size enclosures. I just plonk the info in winISD and it will give you an idea what will/won't work. If the PR gives too low of an enclosure tune with no added weight it will have a rolled off response not unlike a sealed enclosure. If it has a humped response then you can add weight to drop the enclosure tune down to flatten it out.
However keep an eye on the PR excursion. As you add weight and power it will boost excursion.
Looks like that amp actually is listed to do the rated 30watts into 8ohms.
So, at max crank with the DSA115-8, a .1cf enclosure with the DSA135-PR (no added weight) will have an F3 ~75hz, and keep that first vented driver excursion hump just within xmax, until shooting past xmax at ~55hz. PR excursion goes up to near 9mm which is past the 8mm xmech. Though it doesn't pass 8mm until 52hz. By that point the driver is already past xmax, and you'd likely be dropping off applied power via DSP to keep the driver safe. I think you're golden with that combo.
I checked the DSA175-PR too just to see (same driver, power input, and enclosure size): With 25grams added weight will get a hair lower (71hz F3) while keeping PR excursion to about 6mm.
ND140-PR with ~15grams added would work too. I know it doesn't carry the same family look. Just mentioned since it was cheaper.
Thanks. I've never used winISD but will give it a go. I've yet to see a chip amp that doesn't clip at half it's rated output. I guess I better order some passive radiators to play with.
Ron
I would tune my port or PR for maximum useful power handling, and then use Sigma Studio to jazz it back up. Enable the loudness-based EQ curve capabilities like the big boys at JBL and Google. Those filters are VERY easy to enable by just dragging a few things around.
Sorry to be the bearer of bad news, but I don't think you're gonna have this project done in time for Christmas.
Unfortunately winISD isn't the most awesome to work with regarding PRs. It requires you enter the PR specs each time for different PRs. So no creating a PR database to pick from. And it doesn't have a calculation to start with a rough "ideal" tune so it always starts with 1.766cf enclosure and no added weight on the PR. But hey it is free and reasonably quick to get a tune once you understand what is needed.
This project isn't at the top of the things to do list and there's a lot of tech to get a handle on so I expect it's going to take a while.
One complication with an amp with DSP is you’re stuck with the vendor’s DSP program or you roll your own. If you were planning a passive crossover look at the KAB boards (w/o DSP) instead of the KABD (with DSP) boards. I took a quick look at the KABD-430 user manual and the default SigmaStudio DSP program it ships with. It uses 4 pots to control different functions, depending if the amp is in 4.0 or 2.1 mode (see attachment from user manual). I can tell you more about the DSP program’s innards if you want to go active.
Here's what I do when using WinISD and PRs:
Create a vented project and modify box volume and tuning to meet your needs.
Now create a PR project, enter PR values with no weighting and set box volume to match the vented project. Add weighting to adjust PR. With some PR's you'll see that they won't work, even with no weighting.
I like Unibox for PR designs.
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Ed, my original post said I'd be going active. I intend to use the DSP for the crossovers, baffle step and any EQ that might be helpful. I've done a number of projects with MiniDSP's so I think I can manage this. If I can't I'll holler because I get the impression you know a lot more about DSP than I do.
I've downloaded Unibox and I'll give it a try after I break in the woofers. FS is supposed to be 63 and they measure 70 and 74.
I bought myself a PE strobe for Christmas and I used it on a speaker for the first time tonight. You can freeze a woofer cone in motion if you sync the strobe with the cone. If you un sync the strobe by a Hz you can watch the cones move in slow motion. I break in woofer by setting them side by side and wiring them out of faze and feed them a sin wave at Fs. In this short video you can see what I mean. The phone camera video doesn't work well with a strobe.
https://drive.google.com/file/d/1WB0PJQ7shkqBCjlI4PbIi0dBpYaQYi0V/view?usp=sharing
Ron
When I heard of that thing I immediately wanted to use it to watch a driver hit breakup and see how the cone distorts. Or even watch what the surround is doing lower down where you get those response dips.
I'm sure you'll do fine Ron! Just be aware that SigmaStudio is whole different animal than the MiniDSP interface. I figure anyone who can master SoundEasy can master anything.
I have barely scratched the surface of SE but I had looked at SigmaStudio and it looked manageable to me. Time will tell.
Fret not. You'll be fine. Save early, save often, use descriptive filenames.
I measured the drivers and I came up with a PR design using UniBox that was very close to the design DrewsBrews came up with. With a little DSP magic I might be able to put a small amount of boost on the low end with the right high pass and go sealed. It takes a rather long port to go ported. I think it's time to build a test box.