New enclosures for PC speakers -

This project is about creating better enclosures for the 3.5 inch speaker drivers that came with my PC speaker system that was converted to an amplifer in this thread:

http://www.diyaudio.com/forums/chip-amps/283845-pc-speaker-electronics-amplifier-conversion.html

Removing the 3-inch speaker drivers and testing them externally yielded some interesting and encouraging results. Placing them in cardboard boxes generated a surprising level of clarity and some semblance of bass.

The speakers do sound better when 'liberated' from their enclosures. There are several reasons for this, as far as I am able to ascertain. The speaker grille probably cause a lot of diffraction, and also resonances. The box formed by the front of the speaker enclosure and the speaker box also causes some level of 'boxiness' and resonance.

I hope to design and build speaker enclosures for the speakers.
Specifications:

Impedance: 4 Ohms
Power Handing : 3 Watts
Size : 3 inches

Measurements:

Frequency response : 100Hz to 12,000 Hz (pure tone)
Max output : 75 dB at 1 metre
 
Last edited:
This is the PC speaker it is taken from

Picture of old PC speaker that the drivers are taken from. Pics of drivers next.
 

Attachments

  • pcspeaker1.jpg
    pcspeaker1.jpg
    461.9 KB · Views: 413
Pictures of Drivers and test enclosure

PC_Speakers.jpg
PC_Spkr2.jpg
cardboardenclosure.jpg

Pictures of the speaker drivers. These are small units, about 3 inches across and capable of all of 3 Watts.

I have attached them to a cardboard box and cut a port of equal size underneath the speaker.

First tests were amazing. Clear sound from the drivers now freed of their cage, and the bass port generated audible, if not sufficient bass. A huge improvement over the original.

I am now convinced of the effects of a ported enclosure, so how do I proceed?

This calculator gives a list of resonant frequencies - do I need to make the box larger?

This calculator gives the port length, is this more or less OK?

Next attempt will be with plywood or hardboard since the proof of concept works it will only sound better in a stiffer enclosure?

Any suggestions?
 
Last edited:
Online calculator results

The first site gives a list of freqencies, they are all different for L W and H. This seems OK, however. If I make the box larger I can get the frequencies lower so I get more bass, is this how it work?

For the size of the box, 0.0635 cu ft, I get the result of 1.84 vent lenght for 2 inch diameter port. "Tuning frequency" is the required frequency? Time to experiment.
 

Attachments

  • Enclosuremodes.jpg
    Enclosuremodes.jpg
    82.1 KB · Views: 388
  • Portlenght.jpg
    Portlenght.jpg
    49.5 KB · Views: 373
Last edited:
Without at least knowing its Fs and effective piston dia. or area [Sd], choosing a cab alignment is a crap shoot at best.

Yes, 'BIB' [bigger is better] rules when trying to get the most bass out of a driver. Tuning frequency is F-box [Fb], i.e. the frequency it's tuned to, which normally would be > Fs if Qts is <~0.403 [Fs tuning] and < Fs for > ~0.403 Qts, but if you don't know what it is, then all you can do is experiment with vent length to find the flattest response and if it isn't flat enough with just a hole in the baffle, then you have to use a larger tube and start over; and if the bass is still too lean, then start over with a larger cab.

Odds are though is that the driver has as high as a 250 Hz Fs with a very high Qts, so the only viable vented alignment is a stuffed TL if the latter is true.

GM
 
Couldn't I figure out FS by using a sine wave input and find the frequency at which the highest DB output is measured? The definitions for Fs I have not found very useful.

Don't see why not, but have never tried it, so not sure if there's any specific considerations. Historically, it's measured with a voltmeter, resistor, frequency generator: Measuring Loudspeaker Driver Parameters

GM
 
Hardboard material

Switched my building material to hardboard, costing less than $1 equivalent for a 50 cm by 150 cm piece.

A hole saw attachment made cutting holes for the speakers easy.

Initial testing showed acceptable sound - without completing the back panels yet. I was concerned about unnecessary coloration of the sound, not knowing how the new material would react, but it turned out OK. I can always add more layers to damp the sound.

Seems like a cheap material all over the world.

Easy to cut as well, and layering will be stiffer because of the multiple skins in the layer. Let's say it highlighted the need for improving my woodworking skills.
 
Need more bass

My prototype speakers are up and running, and working well enough. Clarity is as good as I would want, but I am havng problems with getting adequate bass.

Whippining out my Android phone, I did a frequency sweep from about 10,000 Hz to 45 Hz. The high end does not concern me here, but the sound levels dropped off abrubtly at about 135 Hz.

Testing with the car audio system, which has adequate bass, showed that the audible frequency response goes down to 65 Hz or so. A casual glance at speaker specs shows that bookshelf speakers are rated at 40 to 50 Hz upwards in frequency response.

Assuming that the sine wave test will show if a speaker is capable of producing a decent bass and drums in music, how do I increase the bass output? I can feel the little 3 inch driver putting out this frequency but it needs to be captured and mechanically amplified.

My cabinet is approx. 12 cm by 8 cm by 30 cm in size. It is fully sealed as I can manage with initial sloppy construction. The books say 0.29 cubic feet or 7 litres is needed for an enclosure for this driver size. Will a port help without increasing the size? I need to aim for a 50-75 Hz tuning frequency, is that correct?

Is more bass gaurateed with a larger cabinet or does it depend on the ratio of the sides? I prefer the speakers to be less than 10 cm deep.