Yet another boombox-type build. Hopefully somewhat different.

[rrudd]

Hi there! I just ordered my first kit (the amp6) to put in something along the lines of a boombox. I want the build to be really small though, and I'm facing some challenges as I'm not that cunning in loudspeaker acoustics (but eager to learn).

The build I'm attempting will be something along the lines of 500x140x160mm (around 11 liters, including room for the amp and SLA battery). Now, I've read up as much as I can on this subject, and the common opinion seems to be that a couple of Monacor SP-60/4s and DT99s would work well in a non-vented box of about 8 liters. I was thinking, however, of adding another couple of SP-60s, either down-firing or in a bipolar setup. Mainly in order to increase bass. This is where my uncertainty begins.

Is there at all any point in adding these speakers to my design without doubling up the enclosure size (which I won't). Is there even a marginal difference in bass reproduction or will I just mess up the acoustics of the box? I tried calculating using Saturnus' boominator idea (venting, heightening the Fres and decreasing the enclosure size), but to be honest, I really can't make any sense of it in this application. I'm not that picky with super linear response and so on, I just want something that sounds relatively good and "impressive for its size".

Thank you all!
/Raoul

[V-bro]

Hi, why not make it just 8 liters? Or make it vented afterall? Vented will produce lower bass tones down to around 60hz (a bit at the cost of power handling though) Then you do need to take two separate compartments....

You can also make an Isobaric enclosure type with two drivers per channel. This will produce very low bass tones, but a little bit at the cost of efficiency.... I use such speakers in my car with SP60/4 drivers and AMP15 and it sounds extremely good!

[rrudd]

Well, I could definitely make it 8 liters, I'll probably build a small 2-3 liter enclosure for the electronics, but would that work with four SP-60s? I thought you had to double the volume of the enclosure for that to work properly.

I just read up on isobaric enclosures, and from my understanding, a setup with two monacor's magnet to magnets in separate 4 liter cabinets and wired out of phase would achieve this? But does this work with full-rangers? And how do the tweeters fit in the equation? Venting is an option too, but I'm not too sure on how to calculate their size, position and impact on enclosure size.

Sorry for the many questions, I'm really enthusiastic right now.

/Raoul

*Edit* It seems with an isobaric setup I'd have to make the enclosures half the size, and that sensitivity really suffers? At least this is what Wikipedia told me. Or is this true only when placing them cone-to-magnet (which would make sense to me)?

[V-bro]

No, that's really too small for four... If you don't want to wake up the whole neighbourhood, but just want some pleasant sound for on the road a single SP60 per channel is fine though.... Not everyone uses a portable box for parties, me for instance...

It would also save space to place the electronics inside the speaker compartment itself, just makes it a little less accessible perhaps and a little bit harder to make it air tight. Especially the connectors, but you can make a little connector box and put the amp in the actual speaker box like a plate amp.

In Isobaric the trick is to have them coupled really well, so best is to minimize the volume between the two 'membranes' and then look upon them as a single driver with much lower Qts and smaller Vas and lowered Fs. Ajdesigner has a simulation program for Isobaric which is freeware... Mind you that the filter of the 'rear' driver is crosses a LOT lower than then front one, all midrange tones produced horribly deteriorates the sound quality. So they are not simply wired in parallel, but first individually filtered. This can be two identially laid out filters, but just with different values. But for low crossover points you need ridiculously large and fairly expensive filter components if you want them to be of good quality. Like 10mH inductors, caps are not a big issue here though, these can be cheap bipolar electrolytic caps of just a few cents....

SP60 drivers are not really fullrangers by the way, only for low-fi applications perhaps. A tweeter is simply added as with any two way system.

[rrudd]

Thanks for the quick reply. I think I'll scratch the isobaric idea, since I'm already on a tight budget and kind of want to keep it relatively simple without real filters, just a cap and resistor for the tweeter. So, to get back to my original thought: As I've already ordered four SP-60s, will it do ANY good to make the box a single, 8 liter compartment and have the four speakers mounted back to back (perhaps separate them and add a couple of small vents), or should I just stay with two?

[V-bro]

I'd then take two. There are ways to decrease cabinet size*, but they aren't really pretty. With a simply too small box it'll just sound pretty horrible....

* By adding a really large series capacitor. This is often done with those tiny subwoofers available in shops, like from brands like REL.

Adding vents will only make a larger box necessary, don't do it....or it can act as 'variovent' but I never really found them to work really well....

[rrudd]

Would adding said capacitors reduce sound quality? Or efficiency of the system? Wouldn't they just act sort of like a primitive high-pass filter? The box doesn't have to be extremely loud. I'd just like to avoid shrill, tinny sound as much as possible and enjoy warm, rich tunes at both low and high volume.

Again, thanks!

[qbone]

Hi there, sorry to barge in on this thread, but the starter asks some questions which I have too, but it never really got answered.
I am a boombox with 4x SP-60. I wanna make 3 compartments, one on each side for 2 speakers and 2 piezos, mounted back to back in a bipolar design, and one in center for electronics and battery.
When I do this, should I then double the volume of the enclosure?

V-Bro mentioned in some thread that a SP-60 need 3 or 4L, but never more than 5L.. In a bipolar design should I double up and make each compartment 8L then? Or is there some fancy calculations that I just havent been able to find?

I really hope you can answer me this, thanks

[V-bro]

So this is what you wanna build?
http://www.41hz.com/forums/showthrea...P-60-or-HP-10T

As you described for tho drivers you just double the internal volume. And then 8 liters should work fine in a sealed box. The latter being the best choice for a compact boombox anyway...

Good calculation software (free) is winisd or ajdesigner, the latter have a sealed, vented and bandpass box calculator. You do need to know how to fill in the parameters though, which is already quite a study, but afaik the help function in ajdesigner guides you through that pretty well...

http://www.ajdesigner.com/speaker/index.php

[qbone]

Thank you very much V-Bro!

Yeah I have tried out a few calculators earlier, just wasnt sure if I had to double to volume in a bipolar build, but you answered that

I have already read a ton of those threads with these speakers, and gotten pretty much all my questions answered, this was the last I needed to know.
I have gone with the 8ohm version though, and my plan is to connect two parallel in each channel with piezos.
The piezos I have chosen is Monacor MPT-001, I saw them recommended in the boominator thread on diyaudio, and figured they might be just as good with these speakers