Tiny ported box

[Cubic25]

Hey all,

This might seem ridiculous, but I have a tiny speaker box that I would like to port.
It is a small project I have been doing in my spare time. I have built a little stereo system using stuff I have lying around the house. The speakers are out of an old stereo that didn't work anymore, the box is made out of some MDF I had lying around. The amp is a y148 I got off ebay for $6.

At the moment, it sounds like it is lacking any sort of midbass. Being 4inch speakers, I understand they will never hit the lows, but I was hoping I could achieve some sort of mids.

The speakers are 4inch, 8ohm, 20watts. No idea of any other specs, except that they have a fair amount of excursion for that they are, so they should be able to push some amount of air.

The enclosure for each speaker is rather small, for portability, (I am using it as a site radio), which leads me to believe is the reason for lack of mids.
The box for each speaker is 1.35 litres.

Without knowing the speaker specs, is it possible to design a port that is tuned to around 80hz?

The box that these speakers came out of was ported, but it is long gone, so I have no idea what the port diameter or length was.

Basically, is there anything I can do to get any meaningful bass out of these speakers? They are by no means tinny sounding. They actually sound warm, but just lack bass.

I suppose I could always play around with different sizes and if it sounds rubbish, I could just seal it up again......

 

[rayma]

is there anything I can do to get any meaningful bass out of these speakers?

First try measuring the impedance to find the driver's resonant frequency.
Use an audio amplifier, with a series 1k resistor feeding the speaker, at a low level.
Vary the input sine wave frequency until the voltage across the speaker peaks.

 

[infinia]

Being 4inch speakers

you can probably guess the free air resonance frequency
for 6.5 inchers they are almost always ~50-60 Hz, so yours maybe IDK 70-80 Hz or so.
DL a freeware box program like 'WinSD' and play around with port tuning to your as-built box internal volume. for extra credit you can easily measure Fr and Q with a freq. source and AC voltmeter.

 

[Sonce]

No need for measurements.
1.35 L volume is way too small for a 4" speaker, but you can tune it to 80 Hz with PVC pipe with 1" internal D, about 6" long. Obviously, PVC tube must be mounted at outside of the enclosure - over top, like a chimney.

 

[Cubic25]

Sorry guys. I didn't think I would get so many replies so quickly, so I decided to tinker with it myself before looking back here.

I drilled some 40mm holes and put a 100mm pipe in there. Seems to have worked like a charm. Plays much deeper now and has more punch. I have no idea what it is tuned at.

The speakers are probably acting like they would in an un-boxed situation.

For what it is, it sounds ok. Definitely better than most of the shitty work site radios you hear everyday.

An audiophile would probably have a heart attack though.

 

[Cubic25]

- over top, like a chimney.

Interesting you say this. I did notice that it was a little deeper with the pipes sticking out a bit. Probably because they are taking up less of the boxes volume.