Mini amp speakers: PC speakers?

[Morocotopo]

Anyone used those cheap ass PC speakers as a speaker for a Ruby / LM386 / aroun 1 Watt amp?

Planning to finally box (well, put in a micro combo box that I have to make) my bridged 386 amp, around 1 Watt, to have a thingy to take anywhere. The PC speakers usually don´t do anything below 100 Hz and over, let´s say, a few K. So nice for electric guitar in theory...

Experiences?

Edit: no, I´m not going to buy a 6" Eminence or Weber, tight economic times here in Argentina.

[mth5044]

Play a guitar track from your computer and find out!

In my experience, they will sound just as bad with a guitar amp as they do with normal music. Still, is hearing something better than not hearing at all?

[Ice-9]

I'm not sure if this still applies but last time I checked out those little speakers they were something like 70 Ohms and not the usual 8-16 ohm speakers, so I guess the circuit it is used with would need to take this into account ?

[thomasha]

Hi, I made a small submini combo with two of them that had 4 ohms, and it sounds good enough for a small AMP, but I had to add a capacitor to tame the highs.
I tested them against a television one and they were better and cheaper.

[Mark Hammer]

They can be good, but they can vary widely, as can the cheesy plastic cabs they come in.  But stick them in a wood cabinet and they show their better side.... as good as they can be.

[Morocotopo]

70 ohms? Weird, I supposed they had a 386 or something like that to power them...

Good idea about the cap to tame highs. Like, a cap from positive to ground on the speaker?

Mark, I plan to put it in a wooden little cab, not to use the plastic speaker cab. As a matter of fact the idea is to get some free broken PC speakers at my local computer repair store, I´m sure they have some gathering dust, and recycle the drivers out of them. Maybe even make a micro 4 x 3" cab! That would be something. Would have a "Marsh" logo ´cause the whole word wouldn´t fit, he he.

[thomasha]

Yes,
but I have seen a schematic with two 22uF capacitors with the negative side connected to the positive side of the speaker and the positive side of one cap connected to the other, like here:
http://www.jjs.at/electronic/class_a_subminiature.html

I made two small combo with these speakers, as I said before, the one with the computer speakers is the best one, take a look:
This one with one 3" 8 ohm TV speaker


and this one with two 4 ohm oval computer speakers

It lacks bass, but if you get rid of the annoying highs it's really a nice small amp. It's exactly 4 times smaller than a marshall 18W combo.
cheers

[Morocotopo]

Cute little things Thomasha! That´s kind of what I´m aiming for.

Yes,
but I have seen a schematic with two 22uF capacitors with the negative side connected to the positive side of the speaker and the positive side of one cap connected to the other, like here:
http://www.jjs.at/electronic/class_a_subminiature.html

I see. Those caps back to back are to make a non polarized cap out of two polarized ones, so the idea is the same, a cap from + to ground.

[Mark Hammer]

That mini-Marsh is adorable!  Nicely done.

I started a thread over at MEF, asking about the purpose of a midscoop.  A great many amps are designed to produce a midscoop.  If you use the Duncan Tonestack calculator applet, you'll see that the standard Fender/Marshall tonestack tends to produce a substantial midscoop, and that it takes a lot of turning things down to yield a "flat" response.  I believe the midscoop exists for a few reasons.  One is certainly that such tonestacks are entirely passive, so the only way to allow for treble or bass boost is to turn the mids much further down.  But I think the other motivation for it is that the voicing of many guitar speakers and cabs is such that upper treble and deep bass is simply hard to achieve, such that a pronounced midscoop allows for a somewhat flatter response when you finally hear things.

What made me think about this was recently seeing some pics of a studio with the legendary Auratone cubes sitting on the mixing desk.  Those speakers were, and may well still be, fairly standard in many studios.  They were dinky little things, with a 5" driver (same speaker found in the Bose 901/801) in a rather compact cabinet, and were intended to represent the "everyman" speaker.  If the mix sounded good through the Auratones, and not just on the big Tannoys suspended from the wall, then it would sound good in the car, through the kitchen table-radio, low end stereos, and so on.  What is not immediately apparent is that, although they are single-driver speakers, there is a passive network inside that provides a midscoop to compensate for the resonance of the cab, and small volume, and yield a flatter response.

So, where am I going with this?  Your average cheap computer speakers are not really intended to provide any sort of music fidelity, and the cabs are designed more to provide enough room to look adequate, and fit everything in, while using a small-enough amount of plastic to keep costs low.  Little or no thought is put into any aspect of the amp, drivers, or cab, so as to achieve a relatively flat and realistic frequency response.  But that doesn't mean you can't tweak things to do so yourself.  In other words, a larger wooden cab for those 3" drivers, with a suitable port, and an appropriate midscoop to complement the cab and speakers, might yield a more balanced sound.  The bass won't shake your solar plexus, but you may be able to make it sound more natural, and less boxey.  In other words, more like a guitar amp and less like computer speakers.

That presents two challenges.  One is identifying the actual response of the cab and speakers, and where the unwanted resonances are.  The other is figuring out how to attenuate those resonances such that whatever tone controls you include sound like they are functioning as they might in a standard full-sized guitar amp.  My guess is that a network similar to the midscoop filter found on many late-60's Japanese fuzzes (or similar to the "Contour" control found on many smaller SS practice amps) might be ideal.

Incidentally, I have a bunch of those little 2-1/2" full-range speakers that were found on the luggable Macintosh Classic units.  A computer recycling place near me used to pull them from the palettes of Macs they had coming in, and sell them for a buck apiece.  They have large magnets, and foam surrounds, and actually had a pretty decent sound in the Macs themselves.  They have a 64ohm impedance.  I always wanted to make myself a small scale Marshall stack with them.  I think I probably have at least 8 of them.

[Morocotopo]

Interesting Mark. The passive midscoop would be some R´s, C´s and L´s, right?

By the way, I have a Danelectro Honeytone in the bench, pots busted (they are the worst quality I´ve ever seen, like, the shafts broke and now rotate 360 degrees, horribly scratchy, extra tiny. Took out the knob from one of them and the whole shaft came out...). I´m tracing it for the fun of it. Sounds offensively boxy, 3" 8 ohm speaker. All through hole construction. No attempt made at all to make it sound a bit more natural.

[Mark Hammer]

Interesting Mark. The passive midscoop would be some R´s, C´s and L´s, right?

Could be, and was, in the case of the Auratones, but doesn't have to be.  It could simply be the right sort of RC filtering, and cascaded stages of such.  But I think the harder part is figuring out what the unaltered frequency response of one's speaker/cab combination is, so that a strategy can be devised for tailoring the complementary response of the pre-amp circuit.

[Morocotopo]

You could test the speaker/cab with a flat power amp and, with a parametric EQ, find by ear the best mid scoop and then incorporate that into the tone shaping of the preamp...

[induction]

I see. Those caps back to back are to make a non polarized cap out of two polarized ones, so the idea is the same, a cap from + to ground.

It seems like the non-polarity of the cap would be fairly important in this case.