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arma61 26th February 2006 03:19 PM

Help for low/bass freq.
Hi all, I'm building for my son a box (like a tools box) that will contains his PSP and related stuff, my idea is to make it also an aplifier box, so I'll have on the cover 2 laudspeakers (took from an old stereo cassette record (a good one!) to which there are already connected two tweeters with a capacitor (I think to cut low freq). I've already made 2 amplifiers with 2 tda7053B and a tone control with a tda1524A (I've made the PCB myself and it's working fine, if anybody's interested in this PCB pls ask), my question is , I have another loudspeaker bigger than the other two that I would like to use as a subwoofer, but there is no space left for another circuit/PCB under the cover. Do you have any suggestion how I can have only bass freq on this single loudspeaker using few passive component (R,C,L)?, please bear in mind my electronical knoledge is limited to 3 years I've studied in the old '70s!!!. thanks for you help.

xstephanx 26th February 2006 06:34 PM

Downfire the subwoofer, and use an inductor of the right value, but try to cut it off on the higher side of things (150-200hz) so that the inductor values dont get rediculously huge.

arma61 26th February 2006 09:50 PM


Originally posted by xstephanx
Downfire the subwoofer, and use an inductor of the right value, but try to cut it off on the higher side of things (150-200hz) so that the inductor values dont get rediculously huge.
Thanks xstephankx for your reply but it's not clear what u mean, or may be my post was not clear enough, I don't know too much frequency, inductor and things like that. What I really need is something ready made, I mean ''1 capacitor of x nF, one restistor of xohm and so on''. What I need is to hear more low freqs. than now, so no HiFi sound, I've already connected this single loudspeaker and I hear more low freq but I hear also all the other freq. Thx again.

baggins 27th February 2006 12:29 AM

If you want to play around and have got some old broken teles or
computer bits try to find the coils in the switch mode supplies unsolder them ,smash the ferrite cores out of them and wire them up in series
with the big speaker till you get the high frequency cut you desire. you can just add them up like resistors.

arma61 27th February 2006 10:51 AM

Help for low/bass freq
thanks Baggins, do I have to connect them in series on one wire ( the + ?) or in parellel across the two wires?, do they have to be connected also to ground?, are the same of what I can find in old transistors radio ? Thx 4 ur help

sreten 27th February 2006 11:24 AM


your in danger of converting stereo to mono.

What you need to do is this :

Set up your amplifiers in bridged configuration but with stereo inputs.

Connect left and right speakers in antiphase which will make the
overall configuration phase consistent.

The bass with a series inductor is then connect betwwen L+ & R+.

Note that a bass unit will need to have a particular sensitivity
that matches the Left and Right speakers for this to work well.

You also need to make sure the amps can drive the bass unit
impedance in bridged configuration.

You can also connect series capacitors to Left and Right
if they overload at low frequencies.


sreten 27th February 2006 11:59 AM

Hi again,

the other option without bridging the amplifiers
is to use a dual voice coil bass unit.

You would need an inductor for each channel
as each voice coil is seperately driven by L + R.


baggins 27th February 2006 02:02 PM

Hi my submission purely related to finding cheap air wound coils to mess about with .Treat the bass unit with the coils as one unit for the purposes of the circuit ,from whats been said it appears like your setting up a difference signal channel ,this used to be used as a pseudo surround sound rear channel in the old days.You would get more bass by fitting 2 smaller units and keeping the channels separate
I think.

richie00boy 27th February 2006 03:03 PM

Have you tried that coil tip baggins? Seems to me that you will need a shedload of inductors chained to get enough inductance...

What sreten is suggesting is how most car amps work. He left out some imprtant info thugh ;) You actually need one amp non-inverting with gain=x and the other amp inverting also with gain=x. Then the inverted channel you connect the speaker the other way round. This maintains phase when the usual inputs are used, but also provides a bridged summed channel should you wish to connect a speaker across the output of each channel.

It's not a difference channel, just a neat way of doing it which also has the benefit of symetrically loading the PSU and making it run nicer when only stereo (2 speakers) are used.

baggins 27th February 2006 03:39 PM

Well my whole point was to help the guy to try and experiment on the cheap, he had said he didnt understand inductors etc. etc. He was hardly likely to go out and start buying MilliHenries worth of them
without Knowing what they did.

About the values he could always leave the cores in at the expense of distortion (vast) to prove that it works and then maybe purchase some decent air cores when hes got enough confidence to apply the formulas and decide on the values .

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