I think we all have heard one or more boxes that are not that great on the low frequencies. And some may have heard individual boxes of the same model that have deeper bass than others. Why it may be so, well, of course there are lot of things that define the characteristics of the sound of an old boombox.
On this post I'll concentrate only on one thing, and that is woofers that are not yet fully "broken in". It means that a woofers cone assembly still haven't flexed enough to have its spider/suspension to loosen up to the point that it is considered to be at its maximum flexibility. So when a woofer is produced, its suspension is usually rather stiff (not always) and the lowest resonant frequency (Fs) is rather high. This means that the woofer reaches its maximum x-max (cone movement) at a higher frequency and when playing lower tones, the woofer actually struggles to turn the electric current to sound.
A woofer needs to be driven at high volume for a decent amount of time for the suspension components to reach their optimal limits, lowering the Fs and getting a better sensitivity on lower frequencies. As the boomboxes usually have only around 2-8 watts per channel with 10% total harmonic distortion (which is a lot), it may be too little for a woofer to break-in as much as it could with more power. So you will need a higher powered amplifier for this method.
For example I'll use my newest addition, the GF-9494X, where I noticed that the right side woofer had much less cone movement and less bass, but the higher bass notes (around 100-150Hz) seemed to have hard punch. When I tested, I noticed that the left woofer had it's maximum x-max at around 80Hz or so (used volume also seemed to play a role, more on that later) but the right one seemed to have it as high as 130Hz!
So, to the method.
(Note: I take no responsibility if you manage to blow up your woofers! Please be careful!)
What you need:
-Woofer(s)
-Amp clamp meter
-Volt meter
-A decent quality home amplifier with no less than 20-50W RMS power output (1% THD)
-PC or laptop (or a dedicated tone generator)
-Internet access or tone generator software (for example http://onlinetonegenerator.com or WinISD)
Also recommended:
-A good ear
-A good nose
-Common sense
-Heatsink (optional, for a better safe margin)
First off, take your boombox apart and remove the speakers or leave them on the faceplate. I suggest removing them for easier handling and control.
Woofers must be "free-air" or installed on an open baffle and NOT enclosured.
Connect one of them to the amplifier.
Make a sound level test, so you have a baseline of how much volume you may need. You can use music or test tone (sine wave).
Connect a volt meter to the + and - of the woofer and clamp meter over one of the speaker leads.
Power is voltage x current. For example 5,35V and 1,00A equals 5,35W.
Adjust the volume so that you can clearly see the cone moving, but are not going above the power rating (usually 2-5 watts) and not driving the woofer too hard.
Now check for your resonant frequency (where the cone moves the most) using the tone generator (use only sine wave!)
Do this for both woofers and start with the one that has higher Fs.
Make the connections again and this time, start with the frecuency that makes the cone move the most.
(If the frequency is very low, under 50Hz for example, the gains from this method may be indistinguishable. I will test other woofers (Goldstar TSR-800 & Crown CSC-850L) to see what numbers I get from them.)
Start with a low to moderate volume and carefully raise it until the sinewave starts to make unwanted noises from the speakers mechanics, or you reach the power rating. Then back it down a bit and let it play with smooth output.
(Sharp for example seems to have very on point numbers, for example 5W NOM 8W MAX, but most may only have the maximum rating and usually more than 10W may just fry the voice coil or even break the suspension. Some have a given wattage range, so its better to keep to those ratings.)
If for some reason you start noticing burning smell, or odd noises, immediately lower your volume or stop completely to cool down the voice coil. You may also use a heatsink (add a bit of thermal grease in between) on the magnet backplate, as it will reduce the heat load from the voicecoil. A slight burning smell is normal and it may not be critical as it depends on the lacquer used on the voice coil.
Play the sine wave for a couple of minutes. You may try to vary it somewhat to see if the sensitivity changes on the other frequencies. You can also search for a more inaudible frequency that still makes the cone move enough, so the test tone will be more pleasant to your ears.
Stop and test for the maximum x-max again and see if the Fs has lowered.
(For the Sharp woofer, I got it down from around 110-130Hz to around 70-100Hz depending on the volume. It seemed that when playing at around 5-6 watts, the maximum x-max was delivered at considerably higher frequency (90-100Hz). When played at a more realistic 2-3 watts, the frequency was around 65-80Hz. I also noticed that when I had a longer pause at testing, the Fs would rise back slightly.)
Continue testing and breaking in as long as you want, or the woofer can handle without getting too warm. It's normal to have the magnet warm to the touch, but for longer break-in, I suggest using a big heatsink on the magnet backplate with some added thermal grease.
The volumes during testing probably exceed 85dB so I suggest some sort of ear protection or positioning the woofer so that it has the least sound output directed to your ears (on the sides). This is a bit tricky because you still need to monitor the sound from the woofer for any inconveniences or oddities.
For the Sharp GF-9494X, I did this and got noticeable change at least on the right side woofer. I think the overall sound is now a bit deeper and warmer with more "feel" to it.
If you have any suggestions, comments or questions feel free to leave them below.
On this post I'll concentrate only on one thing, and that is woofers that are not yet fully "broken in". It means that a woofers cone assembly still haven't flexed enough to have its spider/suspension to loosen up to the point that it is considered to be at its maximum flexibility. So when a woofer is produced, its suspension is usually rather stiff (not always) and the lowest resonant frequency (Fs) is rather high. This means that the woofer reaches its maximum x-max (cone movement) at a higher frequency and when playing lower tones, the woofer actually struggles to turn the electric current to sound.
A woofer needs to be driven at high volume for a decent amount of time for the suspension components to reach their optimal limits, lowering the Fs and getting a better sensitivity on lower frequencies. As the boomboxes usually have only around 2-8 watts per channel with 10% total harmonic distortion (which is a lot), it may be too little for a woofer to break-in as much as it could with more power. So you will need a higher powered amplifier for this method.
For example I'll use my newest addition, the GF-9494X, where I noticed that the right side woofer had much less cone movement and less bass, but the higher bass notes (around 100-150Hz) seemed to have hard punch. When I tested, I noticed that the left woofer had it's maximum x-max at around 80Hz or so (used volume also seemed to play a role, more on that later) but the right one seemed to have it as high as 130Hz!
So, to the method.
(Note: I take no responsibility if you manage to blow up your woofers! Please be careful!)
What you need:
-Woofer(s)
-Amp clamp meter
-Volt meter
-A decent quality home amplifier with no less than 20-50W RMS power output (1% THD)
-PC or laptop (or a dedicated tone generator)
-Internet access or tone generator software (for example http://onlinetonegenerator.com or WinISD)
Also recommended:
-A good ear
-A good nose
-Common sense
-Heatsink (optional, for a better safe margin)
First off, take your boombox apart and remove the speakers or leave them on the faceplate. I suggest removing them for easier handling and control.
Woofers must be "free-air" or installed on an open baffle and NOT enclosured.
Connect one of them to the amplifier.
Make a sound level test, so you have a baseline of how much volume you may need. You can use music or test tone (sine wave).
Connect a volt meter to the + and - of the woofer and clamp meter over one of the speaker leads.
Power is voltage x current. For example 5,35V and 1,00A equals 5,35W.
Adjust the volume so that you can clearly see the cone moving, but are not going above the power rating (usually 2-5 watts) and not driving the woofer too hard.
Now check for your resonant frequency (where the cone moves the most) using the tone generator (use only sine wave!)
Do this for both woofers and start with the one that has higher Fs.
Make the connections again and this time, start with the frecuency that makes the cone move the most.
(If the frequency is very low, under 50Hz for example, the gains from this method may be indistinguishable. I will test other woofers (Goldstar TSR-800 & Crown CSC-850L) to see what numbers I get from them.)
Start with a low to moderate volume and carefully raise it until the sinewave starts to make unwanted noises from the speakers mechanics, or you reach the power rating. Then back it down a bit and let it play with smooth output.
(Sharp for example seems to have very on point numbers, for example 5W NOM 8W MAX, but most may only have the maximum rating and usually more than 10W may just fry the voice coil or even break the suspension. Some have a given wattage range, so its better to keep to those ratings.)
If for some reason you start noticing burning smell, or odd noises, immediately lower your volume or stop completely to cool down the voice coil. You may also use a heatsink (add a bit of thermal grease in between) on the magnet backplate, as it will reduce the heat load from the voicecoil. A slight burning smell is normal and it may not be critical as it depends on the lacquer used on the voice coil.
Play the sine wave for a couple of minutes. You may try to vary it somewhat to see if the sensitivity changes on the other frequencies. You can also search for a more inaudible frequency that still makes the cone move enough, so the test tone will be more pleasant to your ears.
Stop and test for the maximum x-max again and see if the Fs has lowered.
(For the Sharp woofer, I got it down from around 110-130Hz to around 70-100Hz depending on the volume. It seemed that when playing at around 5-6 watts, the maximum x-max was delivered at considerably higher frequency (90-100Hz). When played at a more realistic 2-3 watts, the frequency was around 65-80Hz. I also noticed that when I had a longer pause at testing, the Fs would rise back slightly.)
Continue testing and breaking in as long as you want, or the woofer can handle without getting too warm. It's normal to have the magnet warm to the touch, but for longer break-in, I suggest using a big heatsink on the magnet backplate with some added thermal grease.
The volumes during testing probably exceed 85dB so I suggest some sort of ear protection or positioning the woofer so that it has the least sound output directed to your ears (on the sides). This is a bit tricky because you still need to monitor the sound from the woofer for any inconveniences or oddities.
For the Sharp GF-9494X, I did this and got noticeable change at least on the right side woofer. I think the overall sound is now a bit deeper and warmer with more "feel" to it.
If you have any suggestions, comments or questions feel free to leave them below.
