Notices

I would build one myself, if I was you. Parts won't cost much on electronics stores and you can find circuit diagrams from internet.
Without lowpass filter it would be a speaker which might play lower sounds than other speakers, but it would be also playing the higher sounds, which would sound bad.

To run a subwoofer you need to tap into the sound signal - ie, through the headphone out port. But by doing this, it automatically turns off the internal speakers. So, without some sort of script to keep the speakers active, it's one or the other AFAIK.

Hi there.

I've been testing the subwoofer along with the n900.

For now i use an amp from other subwoofer to make the mini-sub to work and use this method to make it work along with the n900 speakers without having to open it up:

http://talk.maemo.org/showpost.php?p=722226&postcount=5

Must say that the result is awesome! Now i have to make the low-pass filter and receive the mini-amp.

Could someone say the exact components to make the low pass filter, so that i can go the electronic store and buy them? I went there today but they didn't know (neither did i ) what are the exact values to my project ( watts and that sort of things...). When i said i didn't know anything about electronics i wasn't joking

Thanks

hehe it works fine the fix with the alsamixer, thanks to qwazix

great stuff!!

didn't expect to find other diy audio guys on here. i'll have to post some details of my diy class D active speakers tomorrow.

They run from mains or self power via 60 Ni-MH cells - and have a smps / dc-dc in progress for car use.

Runs upto about 150 watt peaks before clipping with 55V rails. once i have the dc-dc going well should manage more.

the whole projects been on pause for months now - i generally get time to work on it around christmas, but i will post photos of its current state. the amps are entirely my own design built from op amps, logic ic, comparators, fet drivers and some tiny power fets all on diy pcb (double sided etched).

Nice, i didn't know about this "hack". Thanks for info. Anyway, as laasonen said, without lowpas filter, Your woo will try to play all spectrum. Once, I connected wrongly cables to 5.1 sound system - test voice was going through sub. VERY strange experience

Okay,

as promised .

First I should add that many of the parts used in these are what I happened to have around - I was trying to make these as cheaply as possible.

I built the cabinets years ago allowing space to later add amps in the back - which shortly after I did, some based on the design by Johan Sorensen (http://hem.passagen.se/johanps/).

No overly happy about these i set about designing my own inspired by his design.


From the front - Some fairly rough n ready looking DIY speakers.


From the rear - the one on the right houses the mains PSU ( A toiroid transformer (approx 350VA from memory - thogh not sure) for the 50V rail and a small 15V SMPS for the control voltage and battery charging).

The one on the left houses the batterys, amps and control circuit.

Battery bank

50 Cells (not 60 as earlier stated). They are configured as 5 banks of 12 Volt (2500mAh). 4 banks go in series to provide a nominal 48V (about 55 when fully charged) and the final bank provides the control voltage. When plugged in to charge the bank of relays configure each with a constant current regulator and each set of battery and regulator in parallel so will charge from around about 15 volts.

Control circuit

This has several functions - there is an MCU (atmega48p which controls the startup and shutdown procedure by switching transistors (which in turn switch relays) and monitoring supply and speaker rails for correct operation.
It also has a few LED's to show operating status and any fault conditions - including clipping - excessive clipping leads to automated shutdown in order to protect the connected speakers.
Clipping detection is currently crude - but is effective. It simply monitors each speaker rail (full bridge design so both for each speaker) if they get to close to 0V or the power rail a clip is assumed)

The amps

The amps are a full bridge design allowing for needing only one main power rail. A separate lower voltage (10v regulated) rail drives the logic, op amp, comparators and FET drivers/FET gates.
The power rail level has no effect on the gain of the amp - so is able to run from pretty much any voltage (between 10 and about 80) - this should with some extra effort make it possible to only run the large toroid when lots of power is required.
The design is a self oscillating type which oscillates at around 500kHz (with the help of a resistor/capacitor - it tries to run at about 1.6MHz left to its own devices which dissipates to much energy due to switching).
The power FETS are tiny!! 4mm by 4mm yet can deliver incredible power considering their dimensions. There is nothing more than a area of copper (reinforced by some thick copper conductors) on which they are mounted in way of a heatsink.

It was some time ago so i cant recall exact numbers but I think with a 1kHz sine wave dissipating 40Watts RMS into a test load resistor I measured approximately 95% efficiency.

I am using these for full range - not just to drive the bass units!

Speaker ocnnections
I have allowed for connecting the amps to other speakers. Whilst the speakers themselves are likely to be better than your average cheap home "HiFi" speakers - they are certainly no contender to Propper HiFi speakers.

These connection allow the amps to be connected to decent speaker so the amplifiers can be compared directly with others on a set of decent speakers.

Speakers
As you can see the cabinets are built from MDF. They have been designed according to the Thiele/Small parameters for the drivers - which are them selves some cheap Skytronnics things. Despite their costs (£15 for bass/mid driver - £8 for the tweaters) they are pretty good performers.




This is what i lashed up to make it easier to control - I initially had the pre-amps and volume knob on the rear of the speakers but this quickly proved inconvenient when used in the car. So this litte unit now contains the preamps, volume knob, and a USB DAC IC. There is a switch to select between analog/RCA in and the USB DAC.

Despite its appearance this setup sounds pretty incredible! I have had a number of audio buffs from various backgrounds (Some home HiFi enthusiasts (my dad included!) another electronics engineer who has worked with audio, and a guy who works with professional audio equipment for recording) listen to this and all have been amazed.

Is there any other "fix" with alsamixer that allows me to turn on the internal speakers + the headphone jack at the same time?

That fix that i mentioned earlier was the responsible for one of my internal speakers to blow up (or become silent) one year ago, on my first n900.

If you do that hack, the internal speakers gain much more bass and lose "surround power" ( it appeares to have less stereo widening).

You could try it but don't abuse on the hp dac value and then just unplug the jack and listen to the diference.

Is there any way to activate the speakers without those two "consequences" to happen?

Thanks

If i remember correctly, You mentioned that Your speaker blow up cause You "tweaked" some values to high, from "safe defaults" provided in hack thread. Maybe we just need to put values even lower? If not, I'm absolutely sure that stereo widening effect can be regained by just correctly mixing few different output gauges on alsamixer. Experiment, but don't put any higher than default value - it's better to gain little quieter effect, than blowing speaker

That's what i'm doing now
But is strange because it gains more bass with this hack, when it should provide the same sound . I've tweaked with all that parameters before without reaching the default sound

That is why i'm asking to someone that really knows what he is doing about this, before i do something stupid again

And i'm going to upload some videos, maybe tomorrow, with the n900 and the subwoofer to show you guys something, instead of just anoy you with this questions