Boombox on the Cheap

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LaStrange

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Joined 2014
#1
I'm a high school student getting into speaker design and I thought I might start with a boombox. I was inspired by Saturnus's boombox thread, but I don't need anything that powerful or BIG. I am limited to a budget of ~$100, not including a battery or case. Astounding sound quality is not really a goal; I just want something to listen to at a party or while I'm working. I usually listen to Jimmy Buffet, Zac Brown, Big Band, Jazz, but no electronic, dubstep, etc. So my targets appear to be clear vocal range and a little bass. Does that sound right?

Because I'm new*, I thought I would try to avoid any type of crossover to start with and just use a pretty good full range driver. Currently, I'm considering either 4x Dayton Audio PA130-8 in a stereo bipole configuration like the boominator, or 2x FaitalPRO 4FE35 with one driver each for left and right channels. Using 2x PA130-8 in parallel (4ohms to amp) should yield 93 dB SPL, whereas the faitalpros are rated at 91 dB SPL. Feel free to think about largish enclosures 😀. I need to be able to carry it by myself, but am not planning on transporting it long distances by hand.

*I did actually try to configure a basic 2nd order L-R crossover with online calculators, the PA130 and a cheap GRS tweeter, but after spec'ing parts on PE, I realized that each channel of crossover + tweeter would probably cost ~$25, with just the simple LC circuit, bringing me up to ~$100 even before the amplifier.

The TPA3116D2 class D is getting pretty good reviews across the board, is relatively cheap, and has a convenient voltage requirement (~12-24v) which is easy to fit with either SLA or Lithium-derivative batteries. It also provides plenty of power in case I want this thing to get loud.

What I'd like to know: is this a reasonable choice for drivers and an amplifier (keeping in mind my budget), what kind of enclosure would be best, and what kind of performance could I expect? I would love any advice or criticism you all have to offer (especially the criticism 🙄).

Thanks
 
#2
You sound well informed for a youth 🙂 Your choice of music helps your design: instead of bass (hard with your platform), instead pick drivers capable of good mids and highs. Since you are young and can hear bat whistles and butterfly farts 🙂 you may need a tweeter after all. I vote for no h/w x-over but consider EQ or DSP in your sources. Nearly anything has an EQ in it nowadays, and you can do DSP or convolutions with Foobar2000 or similar on the windoze platform. I think you are off to a good start. Please share your build when you have it.

Sent from my NV570P using Tapatalk
 
#3
You are on the right track. Those are excellent driver choices. The 4FE35 will have better treble up to 18kHz. The Daytons will have higher sensitivity as you can add 6dB when running drivers in parallel (for same voltage). The Daytons are 89dB and in parallel become 95dB. Bipolar is great idea. For a boombox - use the trick of reaching the harmonic of the fundamental you want rather than go real low as it is tough to do with small drivers in 4pi space. Tune the PA130-8's to about 80Hz with a bass reflex. They will trick you into thinking you have 40Hz which will sound pretty good. The PA130 cannot go to 40Hz as the fs is rather high and xmax is limited.

However, one of the best sounding speakers I have is the 0.53x Karlsonator with a single PA130-8. You could make four of those side by side and back to back for very wide dispersion and rich full bass down to 70Hz.

http://www.diyaudio.com/forums/full-range/239338-mini-karlsonator-0-53x-dual-tc9fds.html

You can always augment with piezo tweeters if needed with simple bypass cap.

Choice of amps is excellent - another is the TDA7498 they cost about $11 and are rated 100w if you want the extra power.
 
#4
Soldermizer,
With it being a boombox, I can't guarantee that the source will have EQ (ex. cheap MP3 player). However, I'll consider tweeters.

xrk971,
I'll probably go with the 4FE35, single driver per channel, and save a bipole build for later. Just out of curiosity, which piezo might be applicable here? Also, would the full range need to low passed? Inductors are $5-10 / channel.

Can someone chip in with a reasonably simple to construct enclosure? I personally am not good at woodworking, but my family knows how.

Thanks
 
#5
LaStrange said:
Soldermizer,
With it being a boombox, I can't guarantee that the source will have EQ (ex. cheap MP3 player). However, I'll consider tweeters.

xrk971,
I'll probably go with the 4FE35, single driver per channel, and save a bipole build for later. Just out of curiosity, which piezo might be applicable here? Also, would the full range need to low passed? Inductors are $5-10 / channel.

Can someone chip in with a reasonably simple to construct enclosure? I personally am not good at woodworking, but my family knows how.

Thanks
Click to expand...

No inductor needed for full range just a small cap to run tweeter as super tweeter above 12k or so. Simple box is 0.4x Karlsonator. Easy to build and best bass for the effort.
 
#7
xrk971,
I'll probably just use a ported enclosure for this build, but I'm going to assemble your .4x Karsolnator with a single Vifa TC9FD per channel, TDA7297 amp, bookshelf speaker style. I'll post to that thread when I get around to it.

sreten,
The podzuma actually influenced my initial choice of drivers, but after the dual PA130's, pro tweeters, and crossover, it ended up being too expensive. Once I removed a single PA130, I then had to find new tweeters, and I still had to deal with the crossover. The sprite however, is an interesting base to work from.

What's the difference in rear vs front porting (or do I mean venting)?
Is there any benefit in letting the piezo tweeter handle parts of the high-mid range, like 6-7k and up? Also, how would I attenuate the piezo by a few dB?
Could the tweeter be mounted toed slightly outward to increase off axis dispersion (did I say that right?)?

On another note, without reading the few hundred pages of TPA3116 thread, is the blue-black Yuan Jing TPA3116 (from PE) reasonably good without mods?

Thanks
 
#8
xrk971,
I'll probably just use a ported enclosure for this build, but I'm going to assemble your .4x Karsolnator with a single Vifa TC9FD per channel, TDA7297 amp, bookshelf speaker style. I'll post to that thread when I get around to it.
Click to expand...

Kool! Looking forward to seeing it. This is the exact setup (amp too) that I have as my kitchen radio or mp3 player. The speakers sit up high above the kitchen cabinets and the K's are upside down so the driver aims down. I have a long 3.5mm jack to plug into a phone.

What's the difference in rear vs front porting (or do I mean venting)?
Is there any benefit in letting the piezo tweeter handle parts of the high-mid range, like 6-7k and up? Also, how would I attenuate the piezo by a few dB?
Could the tweeter be mounted toed slightly outward to increase off axis dispersion (did I say that right?)?
Click to expand...

Outdoors as a boombox, location of port won't matter. If speaker is near a wall, aiming at wall can enhance bass and perhaps make it too boomy. Aiming forward it may leak mids if inside is not well lined. Not a big deal. Aim up even or to the side doesn't matter for a boombox.

Is there any benefit in letting the piezo tweeter handle parts of the high-mid range, like 6-7k and up? Also, how would I attenuate the piezo by a few dB?
Click to expand...

Add a few ohms in series with tweeter to attenuate - get several 5 watt resistors ranging from 1R, 2R, 3R, 5R, 10R and mix and match to taste.

You don't want to let the tweeter do too much of the treble in the "telephone band" where the magic of the full range driver is at its best. This is the 600Hz to 6kHz range where the phase coherency of the full range should be left undisturbed. So you could XO at 6kHz. I would go higher like 10k or more and let natural roll-off of the full range do its thing so you won't need to low pass the full range.

If you want a good sounding 3116 amp with no mods, the black/blue YJ is not the best. Get the Ybdz 3116 here:

Online Shop Free Shipping! 1pc TPA3116 Class D digital amplifier 50W +50 W with Silent Sleep Design|Aliexpress Mobile
 
#9
xrk971,
Could you tell me why the YJ board is worse? (curiosity)
If I wanted shipping within a week or two, the AliExpress seller would charge me ~$25, getting from PE is just easier (ignoring the nearly doubled price).
I plan to use a volume pot, so the turn-on thump should be taken care of (hopefully?).
I'm not terribly worried about SQ; I yield to your expertise though, if it is significantly better, I'll look into it.

When I get back to my house I'll download WinISD and start modeling boxes for the 4FE35.

Thanks.
 
#10
The YJ does not have the optimal PCB layout as some of the components are farther away from the IC pins than needed. Mostly the bypass caps on the input power supply rail. However, it can sound very good indeed with mods as member rhing has demonstrated. So if you are in a time crunch - it can be good - just swap out the two big electrolytics with quality ones. Panasonic SEPF 330uF 25V are my favorite (ultralow ESR).

The SMAKN TPA3116D2 is also good - tighter PCB layout. You can get that in a few days and it comes with volume pot so that saves you. Also has higher gain which is perfect for mp3 or cellphone as a source. I have this and really like it - nice build quality too.

http://www.amazon.com/gp/product/B00KCEHS54

You might want to check out the Dayton RS100-4 - it has optimal Qts for vented and 55Hz box that is smaller and has 4mm xmax.
 
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#11
The SMAKN one looks good, saves money on pot and 3.5mm jack like you said too.

The RS100-4 looks pretty similar to the 4FE35, except slightly (tiny) lower efficiency. You mention Xmax. I know it means "excursion"-> how far the cone can physically move, but how is this related to getting more power out of a vented box?

Also, what does a Q of .707 indicate for normal tunings, and why does Saturnus recommend Q= ~1.2 for boombox builds? (I can change threads if this is in the wrong place)
 
#12
3" drivers by definition have no meaningful bass. Putting them in high Q boxes causes peaking at the bass cutoff. If you are lucky this peaking will occur in the 80-100Hz range. This reinforces the harmonics of the true bass an octave below fooling our ears into thinking that the speakers have "great bass".

Bob
 
#13
Thanks Bob!
Now on the other end of the spectrum:
I read somewhere that to high pass a piezo tweeter, in addition to the capacitor, a dummy load (ex. 4 ohms) should be put in parallel b/c the piezo is primarily capacitive. Would putting this filtered tweeter in parallel with the 4 ohm full range appear as 2 ohms to the amplifier? Is this even necessary?
 
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#14
Because a piezo is a capacitive load you can use a resistor as a highpass filter, it will also help with keeping the amplifier stable. A capacitor in series with a piezo can be used as attenuation, probably needed as most piezo's are way more sensitive than your average 3-4" speaker.
 
#15
lutkeveld,
How would I calculate the cutoff frequency of the resistor-piezo high pass? I was thinking 8-10 khz with this piezo: GRS PZ1016 2" x 5" Piezo Horn Tweeter Similar to KSN1016A

Is this page accurate? http://www.frugal-phile.com/piezo-XO.html

I'm trying to figure out what components I need to test the tweeters before I complete the PE order.
For the full range driver, I'll probably use either the FaitalPro 4FE35 (4ohm) or the Dayton RS100-4. I still need to figure out if the dayton's higher Xmax will significantly improve its response in a vented box.
 
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#16
F3=1/(2pi*R*C)

The manufacturers almost never list the capacitance of their piezos. You could measure it yourself. Or use a pretty high value resistor only for stability reasons. However you'll have some frequency response overlap and most piezo's don't perform that well in the low end, it would be better if you'd use the resistor also for filtering purpose.
 
#18
Thanks lutkeveld!

sreten,
I was testing piezos b/c they really are dirt cheap. Would the tang bands (or other cheap dome tweeter) require anything more than a high pass capacitor? I can't use them specifically b/c they're 8 ohm and my full range (4 ohm) is at least as sensitive.

I'm inclined to design the box without piezos to begin with and see if adding them later helps the high end (for almost no increase in cost).
 
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