First Boombox project, need advices!

[toxicious]

Okay so I have decided to build something that can play some music for me. It is the first time building anything like this so all help is appreciated :P

Here is a sketch i made of the thing I am going to build:



Those are the speakers I have not yet decided to use but looked into:

http://www.brl.se/sv/artiklar/ljud-o.../alpha626.html

and an AMP6-Basic (Ordered) + MC Battery.

What I've read u shouldn't use car speakers. But the thing is, I go in school, and I am building this on the handicraft lesson for fun (nope not festival using...yet!).
The speakers above were used by another guy whoms boombox is on the picture.
If someone can recommend other speakers that sounds better It would be great, though I don't want to spend a lot of money on this project as it's for fun. So a total cost of 100 dollars (700 swedish kronor) including shipping is the limit. (Shipping from USA is therefore not a good idea if it's not super cheap).

I am also going to isolate the inside of the speakers' sections, but don't know with what material nor how much.

And finally which material should I use for the box? On the sketch I have drawn 12mm something (MDF?), but I want the best wood u can use. As I said I am building this in school so I don't pay for the wood :P

Please comment on the sketch and if there is something I should think about

[V-bro]

Ah there it is!!

[V-bro]

Okay,

even to cut cost this is a bad speaker choice. The 92db efficiency is at 2 watt, so remove 3db from it to see the real spec. With that in the back of your head they aren't that efficient at all and will be slammed deeply into the ground even by a fair hifi speaker. Plus the hifi speaker will show a much much more linear behaviour in a boxed up situation.

There must be thousands of ways to go by, but one I have a lot of experience with and have always exceeded my expectations is the Monacor SP60. I buy these little woofers for less than €10 a piece and they are super efficient, have quite low resonant frequency, are super linear and reach up to very high frequency without nasty behaviour. Added to that the mechanical power handling of them is unequalled by any driver I know, even at ten times the cost....

Take two of them per channel and you get roughly 6db extra efficiency!!!!

Then add a tweeter. If you want to stay at the same level (lack of) quality as the speakers you chose now we can get this sorted out in a matter of seconds. All you then need is a capacitor between the tweeter. Take a nicely efficient tweeter, so they can be nicely matched to the level of the little woofers.

You can upgrade the sound quality later on with a real filter....of which I can hand you out the design.....

Then NO, DON'T take MDF!!!!!

MDF is a super nice material for home audio speakers, but I take your boombox will be taken to all sorts of places? A BIG down side to MDF is that any drop of water or even moisture will make it soft and spongy, even swell up.

My advise is to use plywood!!!

Then something you should think about, MAKE IT ONE BOX!!! Don't make the left and right speaker separate compartments!!! The response graph of the same driver configuration in separate boxes will not reach as deep in the bass as one single large compartment....Surely add bracing panels, but I would make sure the air can breathe nicely through the whole contents of the box!!

[toxicious]

Awesome answer
I looked up the Monacor, and well they are cheap
http://www.amazon.co.uk/Monacor-SP-6.../dp/B002DUNDAO
Do you mean that I should have a total of 4 in the box? If so, in which config would be the best? Should I put them in some sort of "Boominator" setup (back to back)? Or should I just put them all on one side?

Should I still isolate the box with something or is it enough to keep the edges sealed?

And about the tweeter, do you have any recommendations there? I should have 2 right?
What is the best solution to access the inside of the box without breaking the seal? Just a wooden door with some rubber strip, or maybe a metal plate?

Thank you so much for taking the time I will receive the amp in max 2 days so I will start with it, then in about 1 week I will start with the box.

[V-bro]

No problem off course, many friends of mine have built designs with these little drivers and without any exceptions they were more than satisfied.

Their predictable response also makes them fairly firgiving and fairly easy to implement. Only thing they need is a well built well sealed housing with the right amount of liters. I find 3-4 liters per speaker in a sealed enclosure to work very well, so that is 6-8 liters for two in one box, 12-16 liters for four.

I would indeed take four and the placement of them depends on what you want. If you want very wide radiation the Boominator set-up is very good, but then you should also use four tweeters.

If you don't mind one-sided radiation this will give best efficiency. The efficiency and phase response is always best when all speakers are placed as close to each other as possible. This rule always applies, but for better stereo effect it is best to make two groups of drivers with a bit of distance in between.

A very good tweeter is the Monacor DT-28N. These have been used for several boombox projects by persons I know and with very good results. But there are more options. Some persons like to use piezo tweeters, these are also very cheap and you could then apply a few more of them to get more spread in the radiation pattern. You have to understand that bass always has a fine radiation pattern due to the long wave length. It goes all the way around and radiates even from the back, even though the woofer is in the front. For tweeters this is a different story, they have fairly limited spread. Solving this is less easy as it seems though, because two tweeters can horribly interfere and give terrible phase problems when two radiation patterns are mixing. This is called 'comb filtering'.

This works well enough with the boominator because they both radiate in a 180 degrees different direction and don't really get to mix.

So if you want good high freq. spread a good solution could be placing two tweeters in a small pod on the top radiating 180 degrees from each other. Key is to keep them as close to each other as possible, yet don't let their radiation patterns mix....

The metal plate idea is a good solution, like a plate amp... You could also make a small internal box to make sure the speaker boxes are never really opened. This box can then hold the amp, battery and/or power supply. A metal plate door then can form a good heatsink for the amp...

Good luck!

[toxicious]

Hmm okay. I think I will go with just one-side placement of the woofers, the boominator setup can wait until next project :P
My box will be about 35 liters total, but around 25 liters will be for the speakers I think (depending on how big that innerbox will be).
So I guess also 2 tweeters will be enough. Those Monacor were quite expensive compared to a piezo (26 euro each, 2-5 euro each), so it feels like my economy is running away...but then I reminded myself that if I don't spend some money on this I will probably buy a new computer part which will be more expensive and quite useless as I already got a good computer lol :P
Something like this then:

4 x Monacor SP-60/4 = 48£ including Shipping (Amazon)
2 x Monacor DT-28N = 58£ including Shipping (europe-audio, fuck their prices)
1 x AMP6-BASIC = 41£ including Shipping (here :P)

= 147£

Anyway, to the speaker setup. Please rate those setups from worst to best (paint in 2 minutes):



I think the 1. is the coolest, but maybe it is useless to have 2 tweeters to the same "view"?
1 + 3 (moved tweeters) is okay in look too. The 5 and 6 are a little wicked but maybe their killing the others in performance?

Good idea with the heatsink, will sketch a new sketch when I know the setup for the speakers

Thank you again for helping me, I am getting even more excited now!

[V-bro]

Lol, yes, this is becoming a fun project!

Mind you the tweeters determine 99% of the stereo effect, so with two tweeters (being L and R) it is best to keep them spaced as wide apart as possible. What I posted above only counts for two tweeters connected to the same channel (producing identical signal)

Best spot for them would be fairly close to the sides as this will enhance radiation. What also enhances radiation is to round the edges of the box that are next to the tweeters (or the whole box for that matter)

A box shape like this isn't only for the good looks, it's mainly to enhance the radiation pattern:

(look at the rounded edges of the box where the tweeter is)

Then 25 liters is quite large, this would work with a ported box and the SP-60 is suitable to be used like that. Only I wouldn't recommend it, it will destroy the precision of the response in the bass area...

I would make the whole design a bit smaller....or add more SP60 drivers off course...

So design number one looks great, but then with the tweeters moved from the middle to the corners...

[V-bro]

Actually design number 4 is also quite good...



And then make a small internal compartment in the back, and maybe another one for controls and lights in the front as well. These can be inter connected with a PVC tube to be able to put wiring through.... Then both sealed with a metal hatch to be able to open it up again.



Oh and isolating the box works really well with polyester wool or that grey knobby foam...

[MickB]

... one I have a lot of experience with and have always exceeded my expectations is the Monacor SP60. I buy these little woofers for less than €10 a piece and they are super efficient, have quite low resonant frequency, are super linear and reach up to very high frequency without nasty behaviour. Added to that the mechanical power handling of them is unequalled by any driver I know, even at ten times the cost....

V-bro, do you happen to know how much those SP-60s weigh? The specs on the Monacor site don't give a weight for that driver.

Sorry to barge in on your thread, toxicious, but it is relevant (sort of)

BTW, I agree about plywood being a good material for the box. I'm obsessed about keeping the weight to a minimum for the portable systems I build and they have to be able to take some big knocks. I use 9mm exterior (WBP) plywood. It's very light and extremely tough if you construct it carefully. As it's not very thick I use quite a lot of internal bracing (made from 4 mm ply with holes cut in it for lightness) so that the larger panels can't flex in and out from the internal pressure changes. Thicker ply is stiffer and needs less bracing but it's also heavier so it depends what your priorities are.

[Saturnus]

If I may inject a small comment in the discussion here. I'd go with a bipolar design for these driver and this use. It's vastly superior in every way. The normal caveat against bipolars are that they have lower sensitivity from the front side than a system where all drivers are front facing. That is incorrect. If the design of the front facing drivers is to be correctly implemented the resulting baffle step correction needed will take away the sensitivity advantage of the front facing driver design completely. And you're left with a system that has all the drawbacks of a front facing system, and no advantages over a bipolar design.

The reason for this are the small cabinet dimensions and the relative short distance between back and front which makes pretty much makes a bipolar an omnipolar speaker.

EDIT: I'd also not chose the Monacor D28 (or D25) tweeters. They're vastly too expensive compared to their performance. This tiny little tweeter that snap-in on a 9mm front plate only costs $8 each and are widely regarded for excellent performance.

http://www.parts-express.com/pdf/275-025s.pdf