NSB portable boom box help

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Posted this over at PE's forum and forgot to post it here. I'll put both of my posts into this one:


Looking to get a little input on a fun project I’m about to begin. I’m designing a portable “boom box” that will house 9-18 NSBs with a line of 3/8” buyout Onkyo tweeters. For the source I will have a built-in CD player of some sort, probably a cheap portable unit. Where the CD player will plug into the box (1/8”) I will also allow for it to be unplugged and a different source, say an MP3 player, can plug in. For amplification I would like to use a Sonic Impact T-Amp, taken out of the plastic case, mounted inside and wired to run off a sealed lead acid battery that will be housed in the bottom of the boom box. I will probably use a 10-15 amp hour battery which should allow me to run the CD player and T-Amp for 20+ hours between charges. The battery will have exposed + and – terminals on the outside bottom of the boom box to allow a charger to be hooked up to it. I might also incorporate a very small 12v power supply inside the box to allow it to run off a wall outlet if it will be used near one. Ok, now that you have a basic idea of what I’d like to accomplish…

The part I’m not so sure about is how many NSBs to run and how to mount them. At first I was thinking a single line of 9-12 NSBs (36-48” line) with a line of 16-24 Onkyo tweeters. Then I got thinking, why not do a line of NSBs, with a line of Onkyos in the middle and another line of NSBs? I know this would cause problems and was thinking I would run the one side of NSBs full range (until they cross to the onkyos) and run the other side of NSBs as a 0.5 woofer instead of using a BSC circuit. Or I could mount the other line of NSBs on the back of the boom box tower creating a bipole with natural baffle step correction. I would like high sensitivity, given that I’ll only have about 5w of power for these, and running them all on the front would give me another 3db of sensitivity, but would I encounter any kinds of lobing problems with this, or does that not matter since this will be a single speaker? With 9 NSBs I’ll be at 96db/1w. 103db/5w at 1 meter. These will be used outside, probably 5-10 meters away, so there I’m looking at 89db/5m and 83db/10m. This is if doubling of distance equals a -6db loss. I doubt I’ll get the -3db/doubling distance that line arrays get indoors, due to the floor and ceiling acting like the line. Another thing I could do is run the 2nd channel of the T-Amp on the other 9 NSBs, effectively doubling my power. My initial idea was to run one channel each on the woofers and tweeter.

Lastly, I was going to go with a ported version to extend the low end but the more I look at the graphs I think I’m going to go with a sealed. The sealed allows for a much smaller box and the low end extension only suffers a little bit. With a 1 cubic foot sealed enclosure for 9 NSBs I get a flat response down to 137hz, -3db at 108hz, -6db at 91hz, and -10db at 73hz. The T-Amp has major bass drop off after 60hz so getting decent extension after that won’t really even matter. With dual 1 cubic foot enclosures the boom box will have dimensions that are roughly 11w x 9d x 48h. It will also have two wheels for easy moving, 2 feet so it’s level with the wheels, and 2 carrying handles.

Well, sorry for the long post but I just felt I needed to throw it all out there for you guys to digest! Let me know what you guys think. I already have the NSBs and Onkyos, and am looking to make this a cheap project. I will probably go with half inch ply to make it lighter and use decent bracing, covering it in box carpet. I’m hoping to keep the whole project under $100! I also have a few of the Madisound 100-150w plate amps for $25 that can be modded for full-range. With one of those puppies I would have no problem with the volume, but then it wouldn't be entirely portable. WHAT TO DO?!?!


*************POST #2***************

Thanks for the reply and the link, Jim. Very informative.

Using that info I think I will make the 2nd line of woofers a 0.5. I used The Edge baffle compensation program and made the speaker and it looks like the response will be -3db at 150hz. With this I was thinking of using a 1st order butterworth low pass at 150hz, so the 0.5 and the other line of woofers will both be -3db at 150, summing as a 0db at that point. This will take care of the BSC and not cause any lobing effects that would have been there if I had run the second line full range. The only downside is the need for a fairly large inductor for a project that's going to be so cheap. I took a screenshot of The Edge showing the baffle step information:


Let me know what you guys think! Thanks!
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.