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How to get good bass response from a Boombox??
How to get good bass response from a Boombox??
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Old 15th December 2011, 09:11 PM   #1
ThunderMonkey is offline ThunderMonkey  United Kingdom
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Question How to get good bass response from a Boombox??

I am planning on building a small portable boombox with two 4" drivers and two tweeters. The genres of music I listen to demand a pretty prominent bass response and I'd like the boombox to keep up. For the woofers I was thinking a pair of monacor sp60's since they're pretty cheap and have quite a low resonant frequency. However, I am unsure what tweeter's would be suitable to use alongside these drivers. The high frequencies aren't that important to me, so some cheap ones should do fine. Any recommdations??
Also the other day I was testing out TDK's line of boomboxes, and I was pretty impressed by the bass those things can pump out considering their fairly compact design. I was wondering what tricks the manurfacturers use to get good low end performance from such an undersized box?
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Old 16th December 2011, 10:49 AM   #2
BHTX is offline BHTX  United States
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No bites yet, eh? I'm guessing you've already searched the boombox threads on this forum? IIRC, there's some pretty cool stuff people have done. Read though those, if you haven't already.

I'm also guessing that this boombox's amplifier would also be powered with a battery of some sort? If so, you might want to take into consideration the sensitivity of the loudspeakers.

If you'd like to get decent bass at reasonable levels, you might want to consider a separate woofer or two, with it's own amplifier, similar to those TDK boomboxes you mentioned. Also, if you choose your drivers carefully, you don't necessarily HAVE to use tweeters (just a thought, since you posted in the full-range section of this forum).

TDK boombox: Beastie Boys Make Some Noise MSG - YouTube
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Old 19th December 2011, 06:09 AM   #3
18Hurts is offline 18Hurts  United States
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I had a JVC boombox that used a 4" "subwoofer" that looked to be a bandpass type alignment.

My JVC Kaboom box uses two 6.5" "subwoofers" that run in ported chambers and it's own amp. It is not small by any means....

Now for the weird

You want two 4 inch speakers that produce bass...and you want it loud and small at the same time. Don't we all! Always pondered something like that, there is a way that would look cool, extends the bass downward and is not too large or expensive.

Peerless 5.25 inch passive radiator will operate in 2.5 liters of air space which is very small.

Peerless 830880 Peerless 5.25" Mini Passive Radiator: Madisound Speaker Store

Use two very efficient 4 inch full range speakers--these will work well.

Tang Band W4-930SF 4" Paper Cone Full Range: Madisound Speaker Store

Now the trick, the 4 inch full ranges have 2mm of Xmax and the 5.25 inch passive radiator has 6mm of Xmax--you won't overdrive it with two 4 inch full ranges. The Tangbands are rated ported in a .2 cubic foot box to hit 80Hz. Maybe a .6 cubic foot box with two Tangbands and tune the passive radiator to around 60Hz should give you the kick bass you desire.

It will have that TDK "look" with the larger passive jumping around in the center as it is motivated by the two 4" full range speakers movement. It looks like a sub, it has the stroke (12mm peak to peak) of a sub and produces low tones like a sub--but it's not. No amplifier or crossover required--but it looks like one so you'll gain cool points.

The Tang 4 inch full ranges have a 70Hz resonant frequency so in theory, if you make the box large enough....the passive can be tuned low--down to 50Hz but it will kill the power handling of the 4 inchers and require an even larger box. The TB speakers are 6 ohms--not sure if that is an issue with you or might work if you run bridged amps with batteries or not. The TB is very efficient for a 4 inch full range with 2mm of Xmax--89dB at one watt so a good place to start. Power handling is 25 watts RMS so if you drive them with a 5 to 10 watt amp, they should be able to handle tuning at 50Hz. A decent deal at $23 each.
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Old 19th December 2011, 08:23 PM   #4
ThunderMonkey is offline ThunderMonkey  United Kingdom
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Thanks for the replies. I have spent hours trawling through countless other boombox threads and have been really impressed with what some poeple have managed to come up with. What I really wanted to know about was the ways manufacturers try to cheat the laws of physics and get away with such small box sizes.

The design with the passive radiator seems like a really good compromise to get rid of the weight issue. If made using lightweight matierials it shouldn't weigh more than 3 or 4 kilos. That 4" tangband driver looks good, the spec is fairly similat to the sp60 but it uses a neodymium magnet. Although by making things more complicated there must be a way to get it even more efficient.

How about if I used 4 of those tangband drivers and split them between two seperate bandpass boxes wih an isobaric configuration. That seems to work out quite efficient although it might need a bit more space and weight. Each bandpass box can work on different frequency ranges then I can use tweeters to make up the high end. Honestly I don't have much idea what I'm talking about, would there be a more efficient box design to get the loudest bassiest sound out of a relatively small space??
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Old 19th December 2011, 09:07 PM   #5
18Hurts is offline 18Hurts  United States
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Bass tricks are band pass boxes, front loaded horns and tapped horns. Forget the horns for a boom box! That would leave you a bandpass box which is also quite large--not sure of the gain VS size/weight over ported or passive radiator type venting though. The smaller the box, the less efficient the output will be although you can get low tuning.

How big is this boom box going to be? What is "small" and what is "big"?
Another option is the Silver Flute wool cone woofers which can be had at 4 ohms. About as much SPL available as the Tangbands but 5.5 inch woofers have a resonant frequency of 42.5 Hz which is very low for such a small woofer. They are 4 ohms to get the most power out of the T-amps or around 15 watt each. Two of them with 3.5mm of Xmax would work well with one 6.5 inch passive radiator if it has at least 8mm of Xmax.

Silver Flute W14RC25-04 ohm 5-1/2" Wool Cone: Madisound Speaker Store

Figure around a cubic foot for the two 5.5 inch woofers and a passive radiator should get you close. The passive can be tuned until you get the response you want in the real world. The Silver Flutes are very flat out to 4KHz so a simple tweeter crossed at around 3KHz would work well.

Vifa BC25SC06-04 1" Textile Dome Tweeter: Madisound Speaker Store

Those tweeters are very loud at 4 ohms but it gives you the option to pad them down to taste to mesh with the Silver Flutes.

I'm assuming you are going to make a boom box out of a simple 12V T-amp so the above drivers are 4 ohms to take advantage of that. The passive allows you to easily tune the bass response to whatever size box you bend up with and will give that strong cone excursion people like to watch as a cool factor. It also keeps the box sealed so sand, beer, insects etc. can't get inside the box.

The downside of the design is the 6.5 inch passive radiator--PE does not have their inexpensive line go that small--the 8 inch model would work but I'm not sure if you'd want something that big to fit in the box.
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Old 20th December 2011, 02:29 AM   #6
ThunderMonkey is offline ThunderMonkey  United Kingdom
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Hi, thanks for all this info, its really helpful and I've learned quite a bit.

Ideally I would like it to be small enough to be carried around easily. So probably around the same size as the TDK boombox or maybe slightly bigger. I'm planning to use an amp32 from 41hz. I have about 4 of them I built a while back just sitting on a shelf so I might as well make use of them.

Those Silver Flute drivers seem quite impressive, especially for the price. Perhaps I could use four of the 8oohm versions in a boominator style arrangement. This seems to give quite a high SPL, although I don't if this will be as portable as I would want it.

The two Silver flutes and a passive radiator sound much more practical. One cubic is about the size I was hoping for and it should be enough to rivil most commercial small boomboxes. If I need a passive radiator it shouldn't be a problem since I have lots of old speakers which sould easily be converted into one.

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Old 20th December 2011, 03:37 AM   #7
18Hurts is offline 18Hurts  United States
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The Silver Flutes should do it for you,

I found a good calculation for passives, if it is the same size, make sure the passive has 220% higher Xmax than the active woofer. Two 5.5's is around the same surface area as a single 6.5" so go for 10mm of Xmax just to be safe.
If you go with an 8", it's Xmax would be around 5mm which might work better for your goal.

If you want to cut costs--there are the Aurasound 6" woofers on closeout.
The Aurasound 6" close out woofers come in 4 ohm, are 3dB more efficient than the Flutes and are rated down to 65Hz in a .45 cubic foot (12.7 liter) box. $11.50 each or $8 each if you buy 4 or more.

Aurasound NS6-255-4A 6" Paper Cone Woofer 4 ohm: Madisound Speaker Store

Since you can deal with a 1 cubic foot or 30 liter box, and cost is a major concern.... the Aurasounds would be the lowest cost and highest output option considering they don't need a low pass filter ($$) and the Vifa tweeters will handle a crossover filter at around 7KHz with a simple capacitor that costs about $2.

Cost Aurasound woofers $23
Vifa tweeters $40
Single cap for tweet $2
8" passive radiator Build your own

You are out around $65 + shipping and wood. Other options for tweeters to cut costs would be the Sinar Baja 1" dome tweeters on close out for $5.85 each. Can't get much cheaper than under $40 in parts--just make sure to cross the Sinars at least 7KHz to protect them. They are 92dB at 8 ohms so should mesh smoothly with the Aurasounds...
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