small passive radiator boombox: how to model?

pao

Member
2013-04-17 3:06 am
I'm inspired by the Jambox and am trying to build a small, portable boombox. I know (as everybody knows) that their trick is to use a passive radiator. Before diving in, I want to know what kind of sound I can expect. I picked out a 2" tweeter (for simplicity, I'm just using one, at least for the first cut): 2" Paper Cone Midrange Tweeter 4 Ohm 289-127. And the smallest PR I could find (3"): Tang Band W3-1335A Passive Radiator 900-W3-1335A. The boxes I'm working with are cigar boxes, around 0.05 cu. ft. (much larger than the volume inside Jambox).

Modeling this thing in WinISDPro, it looks terrible! graph. f3 is about 230Hz (eyeballing from the graph). The PR contributes no more than a bump on the side of the slope. Depending on added weight, the bump moves to the new Fs, but it's way too small to hear (like 1dB).

I wouldn't be surprised that such a small tweeter can't produce bass, but the Jambox works so well. Response curves for Jambox (there aren't many) show a flat response all the way down to ~60Hz.

What am I doing wrong?
 
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dumptruck

Member
2010-05-04 5:02 pm
MN
The driver choice is wrong. There is no getting around a 333Hz Fs. Look at something more like TB-W3-1876S. Models quite well with the 0.05 ft³ and 3" passive radiator you mentioned, so long as you can figure out how to add some mass. A pair of the passives per driver would be better. Of course, then you'd need to cross to something else for mid-tweet duties. Aura NSW1-205-8A?
 

pao

Member
2013-04-17 3:06 am
I gave up on modeling and just build something that someone else said sounded nice. Same enclosure. A pair of Dayton ND65-4 2-1/2" drivers, and the aforementioned PR. I haven't sealed it or tuned the PR, so it sounds like what you'd expect: surprisingly good low end from this little box, but even I can hear it needs some work. I should model this and see how it looks. Guessing that this 84Hz Fs will make it look a little better.
 
Something that someone knowledgeable said sounds good is good enough for me. Got any pics? Im going to go ahead with my BMR12s and 2x W3-1335A. Using 1/4" MDF, I am thinking 0.8L per driver. I am not sure how to calculate volume for use with a PR, but that is the volume someone recommended at PE for a ported (1"D, 2"L port) box with the BMR12. Does anyone have input on this driver/PR match and volume? Thanks.
 
Available passive radiators will never fit your needs as the Fs of these are much too low to be of any use for a portable build. Instead use a low cost normal speaker with very high Xlim (Xmax doesn't really matter). It makes it much easier to model correctly, Fs is in the right range for a portable build, and last but not least you can experiment with putting different filters on the (passive) speaker to improve performance and limit midrange output (a 100µF series cap is a good starting point).

For example, this http://www.madisoundspeakerstore.co...urasound-ns3-193-8a1-3-black-cone-wide-range/ will fit most very small builds as a passive radiator as the Xlim is a staggering 20mm p-p.
 
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Thanks Saturnus, i noticed that was the driver/PR you suggested for the Micro Boominator. I wanted to build that, but the Faital drivers are like $45 each x4! I ended up just going with a port since I already have the HiWaves.

I will probably end up doing another build though. What might be an acceptable Xlim range (when I look for drivers, I dont see an Xlim, only Xmax)? Also, you suggest putting a cap on the PR. I was under the impression that the passive speaker is not actually wired to anything. I apologize in advance if these are newb questions that have been answered before.
 
I was under the impression that the passive speaker is not actually wired to anything.

That's the 2nd and major advantage of not using a passive radiator but an actual speaker. You can actively filter it. Please keep in mind that everything is opposite. Higher resistance means less resistance to cone movement, lower resistance means more resistance to cone movement. So a series capacitor is a LP filter, a series inductor is HP filter, and BP filter is achieved by a cap and inductor in parallel with each other. These are connected to the speaker acting as passive raditor's terminals obviously, and not to anything else.

Xlim just have to be large enough. Model the build at absolute peak wattage it can receive and that should be it. In the µBoominator it's 19mm p-p absolute max, which gives a headroom of a whopping 1mm. Same for the active drivers, btw. (Though I should mention that the actual absolute maximum p-p cone movement of the "passive radiator" is 23mm p-p without the active filtering capacitor).

Yeah. The µBoominator isn't supposed to be cheap, it's supposed to be the best ultra-portable boombox ever made, and ever will be made. Just like the original Boominator is on a much larger scale.
 
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dumptruck

Member
2010-05-04 5:02 pm
MN
I'm having trouble finding this micro boominator. Do you have a link? I'm currently doing a boombox type of build that is meant to fill a hole in the designs available for those types of designs, so of course I've been keeping the boominators in mind, but I may have missed that one.
 
I'm having trouble finding this micro boominator. Do you have a link? I'm currently doing a boombox type of build that is meant to fill a hole in the designs available for those types of designs, so of course I've been keeping the boominators in mind, but I may have missed that one.

Boominator MINI (development thread) - Speakerplans.com Forums - Page 19

This is the "Mini" discussion, but the "Micro" discussion starts about halfway down pg 19. Sorry if Im not supposed to post links to other speaker building sites.
 

bpmoose

Member
2014-01-06 8:04 pm
I gave up on modeling and just build something that someone else said sounded nice. Same enclosure. A pair of Dayton ND65-4 2-1/2" drivers, and the aforementioned PR. I haven't sealed it or tuned the PR, so it sounds like what you'd expect: surprisingly good low end from this little box, but even I can hear it needs some work. I should model this and see how it looks. Guessing that this 84Hz Fs will make it look a little better.
hey Pao,

I'm also trying to build a small enclosure for a pair of nd65-4s. How did your project turn out? Do you have any pics or specs of the enclosure?