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Boom Box in a Suitcase . . .
My brother needs a better speaker but has a house full of kids (Qty 5) so it will be a few years before I can pass down some of my electronics to him for use in a dedicated listening room.
He suggested that a boom box w/ Bluetooth would be his best use [portable] so I have been cogitating and looking for low cost high value solutions.
I was given a milspec Pelican Case [Lowell - good friend donation] which is O-Ring sealed around its perimeter with an internal volume of approx 1 cu ft to stuff everything into.
Any flexing of the case-back-wall enclosure will act as a passive radiator I suppose, so I want to go sealed . . .
Looking at PE's stuff I think the best solution right now is:
Single Dual Coil Woofer (on hand) --> https://planetaudio.com/product/ac8d/
MT's - either this coaxial --> https://sbacoustics.com/wp-content/uploads/2020/11/4in-SB12PFC25-4-COAX-OEM-only.pdf
. . . or this Full Range --> https://www.aliexpress.us/item/2255799957255651.html?spm=a2g0o.order_detail.order_detail_item.4.1647f19cE7IyW7&gatewayAdapt=glo2usa
Trying to keep it simple for now [He has 31 band EQ in his app] and use what parts/drivers I have available as much as possible.
Anything I build is going to be better than that little Bluetooth single speaker they are listening too right now and my brother is very aware of the SQ coming from my systems - he just needs his wife to understand it . . .
Any suggestions would be welcomed and I will add details to this thread as they become known to me.
TIA.
Comments
That little bluetooth amp will take 24v. The key to getting the most out of these little class D amp boards is to get them as much power as they can take. Even if the boards in theory can deliver 50wx2 +100w (likely into 2 ohms on the sub channel), they can't come close with a 12v or 15v power supply. I have a some 19v Asus monitor supplies I use, but going to 22v or 24v is even better.
The Dayton KAB boards are nice if you get the accessories kits, which have nice LEDs and volume pot.
I don't think I'd bother with an 8" sub in the pelican case and with what is likely going to be less than 50 watts. If I did use the sub channel, I'd use the Tang Band W5-1138SMF.
If it were me, I'd build an existing design of a pair of TM speakers into the case - like Dayton 4 Deluxe, Heliums, PWRRYD's latest with the MAC-04, etc.
The woofer has pretty low sensitivity (85db) and every chip amp board I've measured clips at half the power they spec. The power supply is only 60 watts so there's no way to get the rated power from the amps. So it won't play real loud.
I'm planning a boombox with one of PE's 4 channel DSP Bluetooth boards. That way I don't have to spend money on crossover parts.
https://diy.midwestaudio.club/discussion/2455/big-mac-boys-boombox
I look forward to seeing what you come up with.
Ron
@ David - I had in fact selected the 24VDC PS originally but the power plug is 2.5mm while the amp takes a 2.1mm yet, I can cut the cord and wire direct to the screw terminals on the amp. I have updated my cart accordingly.
I'll look into those other speaker designs you mentioned although I am trying to keep this simple and mostly to parts/drivers on hand.
@Ron - I figured that the amps' built-in Sub XO (adjustable) could handle the cross-over from the woofer to the coaxial or full-range-driver and I do have the passive XO parts for the coaxial - using the 31 band EQ on top should smooth out the remaining bumps in the frequency response - in an effort to keep this simple.
The woofer is to roll-off around 50Hz with a Qtc of less than 1.0 peaking from 65 ~ 110 Hz and doesn't need to be loud - just fill in the low end - the focus is upon the midrange from 200 Hz and up for intelligibility.
They will be listening at low volume [85db?] and in near-field seating arrangement.
Having a lot SPL/power on hand will only encourage the kids to see if they can blow it up when left unsupervised.
If nothing else it gives me a chance to test out some idea's for little cost . . . I'll keep you posted.
IMO it is most likely to cancel out the woofer some and reduce volume, or peak at a higher frequency becoming more of an anoying buzz. I'd try gluing some bracing to the back wall that extends up behind to the woofer flange so it is screwed directly to the woofer. That way it can be unscrewed and the case can still be opened to work on it.
And I assume you are doing something to partition off the other drivers inside?
Yes, the idea is speaker boxes inside a case with the drivers protruding out the front case-wall with protective grill covers. But now brother is reconsidering size and looking into small box unit and I think he aught to just listen to his iPhone w/ earbuds - I doubt he is going to get the big/well defined sound he is looking for in a tiny package.
I'll wait and see what size footprint he decides upon as a design constraint - he can boost with his EQ.
I'm off in a different direction now like a dog chasing a squirrel while on drug sniffing duties at the airport . . .
Gonna take these two [detachable] Dayton MK442's [as mains] stood on end in a D'Appolito config to flank a central column with the sealed 7" subwoofer, amp, cord and PS storage therein.
https://www.parts-express.com/Dayton-Audio-MK442-Dual-4-2-Way-MTM-Speaker-Pair-300-4560?quantity=1
The whole thing will fit in a 22" x 8" footprint ~17" tall with wide horizontal dispersion and good low end plus, the detachable mains can be spread apart when the venue allows for better imaging and sound stage.
Just awaiting approval of the footprint from the bro . . .
Got this contraption mocked-up/bread-boarded & sounding great with parts on hand tonight - clean, crisp and tight sounding - I might have to keep it for myself . . .
It gets loud with no discernable distortion now that the MK442's are crossed around 150 Hz [guess] high pass with an external passive XO. (The little DTA 2.1 BT amp runs the mains [4 Ohm nominal] full range and it's adjustable XO only applies itself to the sub-out and it sounded muddy without the external XO [250 uF series capacitor allows me to push them to full volume without the amp overloading/clipping] - keeps the MK422 speakers from playing lower than can cleanly reproduce).
Once that little sub goes in a sealed 0.40 cu ft central box it will all come together - needs only a tad touch of EQ around 2 ~ 3Khz and that's it.
This setup has completely changed my perspective concerning D'Appolito alignments - they rock!
@Brad (HiFiSide) . . .
What is the external offset dimension of your speaker hanger brackets please? --> https://www.jfcomponents.com/product-page/60-x-90mm-terminal-cup
I need your ^ [brackets] to attach/detach the MTM cabinets from the Sub enclosure . . .
Thanks!
Well, I thought I had the amp overload/clipping taken care-of with that 250 uF capacitor but I ran into this tune and it made me go back to a 200 uF Cap as it is very demanding of the system - try it and see how your system behaves, please --> on TIDAL --> "Train Song", Vinnie Colaiuta - Jing Chi album.
You Tube -->
(it kicks ass).
Vinnie is a beast🤘🏼
No sh*t! Phenomenal drummer - everything he touches is gold.
I really HATE to admit it but this little boom box project is smoking my black tower build in the same space with a lot less cost. I don't even have that little 7" sub inside a box yet - just sitting on the table between the mains.
Plugging the ports on the MK442's allows me to get rid of the series capacitor without clipping the amp!
Thanks for the info, Brad!
Next - I figured out what was causing all the amp drop-outs - the sub was shaking the bench and the alligator clips holding 3 capacitor leads together while testing high-pass XO were opening and closing the connection and the amp didn't like it. Put the caps in a breadboard and now the settled upon XO for the mains remains at 250 uF.
Sub cabinet base design:
Turns out that these MK422 MTMs are no longer available from PE - they have been discontinued but the component parts are available.
I still have one single MK442 left but need another to make a pair - If you know anyone with a functional unit - please let them know I am interested in acquiring one for a future build as they sound great in the right configuration/environment/room.
Woof Box ready for brother to examine construction method and glue up himself tomorrow evening . . .
Nice rabbets or rebates. Dado stack ?
Router Bench using 3/4" straight flute bit (dull).
Sharpening stones arrived today - time to tune up the carbide table saw blade and router bits ahead of attacking oak lumber . . .