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Old 13th March 2012, 07:30 PM   #1
nanonymous is offline nanonymous  Germany
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Hey there!

I discovered the Boominator thread and I was amazed by the idea and theperfection in design. Building a own boombox sounds like a lot of fun and I also need one for chilling at the lake in the summer because I hated when friends played music with their phones. The sound quality hasn't to be extraordinary good but it shouldn't be sloppy either. Building the whole Boominator though is a bit over my budged. Time is also kinda tight as I'm going to write "Abitur" (german A levels or smth) in the next months.
This project is my first regarding sound so I don't have any experience with building speakers yet.

My idea was to build the Boominator just in small with 4 Monacor SP-60s and some tweeters or piezos for the higher frequencies. I gonna use a lepai amp instead of the amp6b becaues I have one spare around. That shouln't be a problem as it uses the same chip, or am I wrong?

After reading the Boominator thread I could filter out the following advantages
of the bipolar configuration:
  • makes the construction solid
  • augmented bass response of "front"-mounted speaker
  • automatic magnetic shielding
  • baffle step is gone
  • 1dB sensitivity increase per speaker pair
Do these points also apply for the small SP-60s?

I already did a rough model in Sketchup, which is I think too small because
each chamber has only around 2 liters.
Click the image to open in full size.
Having read some small things about volume calcultaion for the cabit here and there I still have not much of a clue how to do it properly. All those factors like bipolar design, outdoor don't make it less confusing. I could figure out that a closed design is better if I want to keep it small. Could you please give me some pointers on how to calculate it right or even give me an idea how many liters are recommended.

I'm also very uncertain what the sensivity of the whole box will be.
My simple calculation so far was:
1 Monacor - 90dB for one channel on one side
2 Moncaro - 93dB for stereo on one side
4 bipolar - 94dB because of bipolar gain
This calculation is more than borked but I don't know a better way to do it right now.

Another thing I'm not sure about is what I'm going to use for higher reqencies.
I have to admit that I didn't do much research yet, but maybe someone nice just tells me what is the best way to do it .

Thank you all in advance!


Last edited by nanonymous; 13th March 2012 at 07:43 PM.
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Old 13th March 2012, 07:47 PM   #2
nanonymous is offline nanonymous  Germany
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What the **** is happening? I edited out a line break that I was missing and now the whole post is gone.
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Old 13th March 2012, 08:08 PM   #3
tinitus is offline tinitus  Europe
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Old 13th March 2012, 10:40 PM   #4
Bigun is offline Bigun  Canada
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I have no knowledge on these things - but I'm wondering if the cheapest and fastest route to success might be to buy a used commercial boom-box and re-fit it with your own stuff. You would re-use the speakers and the box - fit your own amp and find a way to mount some solar cells on it.

When you have it up and running the time pressure is off and you can build the one of your dreams at a leisurely pace.

Just a thought.
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
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Old 14th March 2012, 07:57 AM   #5
nanonymous is offline nanonymous  Germany
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Thanks for your suggestion!
To be honest: I'm too proud to buy something premade . I've looked up my calender and I have a month where school is voluntary. So I think I could manage that.
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Old 14th March 2012, 07:48 PM   #6
nanonymous is offline nanonymous  Germany
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I've found a thread at 41hz.com where a very similar design is discussed.
The answer to the most of my questions can be found in that thread. Especially this post by grandmaster Saturnus helped me a lot.

I'm still clueless with the calculation of the system sentivity. How do I calculate it properly?

Like suggested in the 41hz.com thread I'll settle with the Dayton ND16FA tweeters with an cap in series. From what I could gather they are cheap and have a good dispartion. I'm sketching a new model with the size of 15cm*15cm*54cm and I'll provide further update of my progress
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Old 19th March 2012, 11:45 AM   #7
nanonymous is offline nanonymous  Germany
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I'm about to order the drivers but I don't know which version of the Monacors I should get.
Shall I buy the Monacor SP-60/4 or SP-60/8 and how do I wire them so the amp won't just turn of?
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Old 19th March 2012, 11:48 PM   #8
dangus is offline dangus  Canada
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I have a suggestion: visit a few car audio dealers and see if they have any "pulls" from installs in recent model cars. I found a pair of 6x9 OEM speakers at a thrift store recently: they had tiny neodymium magnets and composite frames, which made them incredibly lightweight (made in Mexico, 4 ohms, 20W, no brand name, just various part numbers which don't come in Google searches). (I haven't ~listened~ to them yet, but they seemed ideal for a portable system, possibly mounted in the sides of a thrift-store picnic cooler.)
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Old 20th March 2012, 08:14 AM   #9
Boscoe is offline Boscoe  United Kingdom
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So do you now what enclosure size you need yet? Are you going ported or sealed? Can you get hold of any other drivers? How loud are you expecting it go? Do you want bass or is this just for casual listening? Does your amp use a single or dual supply (as in it has a positive and negative input or just positive?

Personally I would go with ported as you going to get more bass SPL that way which you'll already be lacking with those small drivers unless your box size is too small to tune it low enough which means you might as well go sealed.

As your question to loudspeaker impedance I assume you have a two channel amplifier you'll be connecting two drivers to one output. You need to match your speaker impedance to the supply voltage to get the best efficiency. So if you need 20W into the two speakers which are connected up to give you four ohm then your best off with a Vs of about 14V or a 12V battery might just scrap it if charged well.
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Old 20th March 2012, 12:18 PM   #10
gmarsh is offline gmarsh  Canada
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The /4 and /8 speakers might have different TS parameters, make sure you take that into consideration with your box design.

Whatever one you go with really depends on how loud you want the stereo, and how long you want the batteries to last. Your options basically are:

- Least loudest / most efficient: Use a 2 channel amp, and wire 4 ohm speakers in series for 8 ohms.
- 3dB louder / less efficient: 2 channel amp, 8 ohm speakers wired in parallel for 4 ohms.
- 6dB louder / least efficient: 4 channel amp, 4 ohm speakers.

I'm eager to see how this turns out. I'm building a full-sized Boominator but also want to build a smaller one. I was considering Eminence Beta-8A's but if I can build even smaller with Monacors that'll be excellent.
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