DIY Self amplified micro speakers (Or the best self power 2L speaker)

[tktran]

It occurred to me that after building bigger and bigger speakers (NaO IIRS, Statement II), eventually I have no space in the house for all of them. So they end up getting de-reployed in friends and relatives's home on "long-term loan" :W

So now I am determined to build a small micro speaker and compact (14L or less) 'sub'woofer

I am aiming to beat something like the Sonos Play:1. For those who don't know, this is a tiny cabinet of 2-3 litres, (external dimensions 6.4" x 4.7" x 4.7" ). From a consumer perspective it doesn't need a separate amp, but from a designer perspective, it's a biamped active 2-way design, which mates a 3.5" woofer to a compact 1" tweeter, with a DSP/amp for crossover/equalisation/dynamic EQ functions. And with the DSP they've managed a massage a reasonably good FR, as far as small speakers are concerned. (see Brent Butterworth's measurements at: http://stereos.about.com/od/Wireless...asurements.htm )

It costs US$400 a pair.

I would like to think it is possible to build something of this size, that one could just connect a smartphone via 3.5mm line-input to use in a home/office or bedroom. Has anyone come across played around with such a design?

[JonMarsh]

I've thought about doing something like that, to build a 2.1 desktop computer system, but more like that on steroids- i.e., use a small 3" "full range" driver such as Vifa TG9FD-10-04, for the satellites, and under the desk with a 7" Wavecor balanced drive SW182BD01, and a Wavecor PR223BD02 passive radiator. would probably use a small desktop stereo amp for the full range units, and a Hypex DS2.0 or DS4.0 for the sub plate amp.

For me, it's about the same amount of work as what you describe, but the results might be a bit nicer. I just don't have much use for a speaker with a -3dB point of 88 Hz; right now I'm using some AudioEngine A5's in the computer room (nice bamboo) but they're not designed tonally for desktop use- wind up being too heavy in the lower midrange and upper bass, and don't really have low bass.

[5th element]

I've built a couple of systems at different sizes that are quite like this.

The first is a bluetooth speaker that you can see documented here.

http://www.htguide.com/forum/showthr...and-wires-time!

It's a battery operated, wireless (bluetooth) device that uses a DSP/DAC/Class D amp combo chip from TI, using the SB65WBAC, from SB Acoustics. These are tiny but sound fantastic given their obvious short comings.

I have also made a variation on these that trade out the bluetooth module for an ADC, to give a stereo analogue input and an S/PDIF input for digital connections. These are also battery operated.

More in line with what you had in mind though is a small two way pair of loudspeakers. These use an AP100Z0 + TM25F1 per side to move air. Internally they use an S/PDIF converter, an ASRC to match sample rates and a pair of TAS5706B chips from TI. The 5706Bs are digital input, stereo, class D amplifier chips that take the digital input, process it though a DSP core, then convert the direct digital signal into a PWM stream for driving the class D output stage, with the amplifier literally performing D/A conversion at the output inductors of the power stage. A true 'digital amplifier' if there were ever to be an appropriate time to use the phrase.

This sounds very good and I use the DSP capabilities to perform the crossover duties so that the loudspeakers are completely active. The TAS5706 also has PWM outputs for driving an additional power stage that would be useful in turning the system into a 2.1 or 2.2 (two sub) system if you were so interested. The sub channels have limited DSP capabilities (not many biquads), but they do use double precision biquads which are useful for bass applications.

[tktran]

Well whilst browsing from my armchair for design ideas that doesn't look like a giant eyeball (Devialet Phantom), I came across this:

http://kiiaudio.com/en/tech-acou.html

Seems fascinating. Looks like it was designed by Engineers, not Marketting, because it seems to be an all out assault on to produce a small speaker that sounds like a big speaker, and not something that fakes it by boosting 100Hz...

[---k---]

I swear I saw a post recently where someone used a PE Kit amplifier board that didn't cost much less than $100 (probably less than $50), but it had a sub-woofer out on it.
I tried to find it, but couldn't remember the thread. And when I looked at the amp kits, I didn't see a big flashing "Subwoofer out" in the description. But, man if you could find an amp board with a sub out, that would make this a much simpler project. I wonder if a call to PE would answer it quickly?

[---k---]

Ahhh, it just floated to the top at PE. Check this out:

http://www.parts-express.com/magalog/v1/pdf/Tom_Zarbo_Full.pdf

There are a couple threads to. Pretty cool stuff.

[5th element]

Seems fascinating. Looks like it was designed by Engineers, not Marketting, because it seems to be an all out assault on to produce a small speaker that sounds like a big speaker, and not something that fakes it by boosting 100Hz...

Well to be fair it is actually a fairly large loudspeaker. That's a SEAS DXT tweeter used at the front with what looks like a 6" driver below it. The speaker itself then has two more bass drivers on the rear with two PRs on the side, the cabinet is very deep. Still it's a lot smaller than a proper full sized, floor standing three way.

Certainly though this is no speaker designed by the marketing department, which is nice to see, but sadly the actual raison d'être for this design may as well have been cooked up by a load of hippies high on some real good wacky-backy.

The first major issue with what they are saying is that bass in small rooms does not reflect off of walls and bounce around like you think it might do, the wave lengths are far too large for that to happen.

The second is that they are showing (apparently) an example of a standard loudspeaker with side mounted woofers crossed over at 250Hz. Well for a start you don't even need the side mounted woofers because any standard width loudspeaker will be radiating omnidirectionally by
by 250Hz anyway and will be throwing as much sound backwards as it is forwards.

What this looks like they are doing however is applying delay to the additional woofer channels to change the radiation pattern of the loudspeaker away from being an omni at low frequencies. We all know that open baffle, dipole bass loudspeakers energise a room in a way that is more effective at smoothing out room modes than standard monopoles and the same is true for loudspeakers with other radiation patterns too, such as cardioids. As far as I can see this is all that they are doing here, using digital delay and bandpass filtering to create bass nulls around the back of the loudspeaker. This wont alter the way the bass reflects off of adjacent walls, but it will alter the way in which the loudspeaker energises the modal region of the room.

Ironically for 'smaller' loudspeakers this is the exact opposite, maybe, of what you'd be wanting to do as altering the radiation pattern causes some of the sound to null via destructive interference, ergo you're going to be throwing away efficiency and bass energy. This is usually something you do not have to spare with small loudspeakers.

It's nice however to see someone actually approaching the issue of improving bass reproduction in small spaces from the right point of view, rather than simply trying to make something that booms the lowest and loudest.

I do hope they include different, selectable, radiation profiles for the bass so that you can pick the one that works best in your room.

[TEK]

Going off topic here, but... Congrats to 5th Element with his 1000'th post :-D

[5th element]

Oh how about that! Thanks for catching

[---k---]

More impressive, it was 1000 quality posts. :T

[dar47]

I'll never have 1000 quality posts, to goofy:lol: Appreciate all your efforts.:T

[5th element]

Thanks guys

I know that some of my posts are more on the goofy side of things though

[fbov]

...I am aiming to beat something like the Sonos Play:1. ...It costs US$400 a pair.?

From what you describe, this might be a better benchmark when cost is considered.

http://emotiva.com/products/powered-monitors/speakers/airmotiv-3b

The trick with something small is getting enough bass. I did a not so mini-speaker based on the Fountek FR-88. Bass reflex model was highly inaccurate; bass extension wasn't there. I ended up with a MT/TL over 2' tall, but the little buggers put out some bass!! They run full range, with a contour network to flatten response.

Best of luck,
Frank

[tktran]

The Emotiva does look interesting. I haven't seen any measurements on it though.

It does get hard for DIYers compete at that price tag though...

[---k---]

Agreed. But, it is possible. And besides we don't do this to save money but to be able to be outside in our garage building stuff.

Did you see the link I posted? http://www.parts-express.com/magalog...Zarbo_Full.pdf

Here is the amp kit:
http://www.parts-express.com/21-hi-f...8-vdc--320-608 15Wx2 + 30W Sub.

Then there are several small designs out there you could shove in there. Jeff Bagby has a couple posted at PE. As does Wolf and Paul Carmondy.