From the conclusions from a 1996 PhD Thesis by Gavin Putland https://hal.science/tel-01546159/document . His thesis deals with stuffing in horns and closed boxes. Very deeply theoretical, his conclusions are clear:
"• Viscosity is the dominant mechanism of damping, thermal relaxation being of
secondary importance;
• The neglect of internal elastic forces in the fibers is justified;
• The departure from thermal equilibrium (which occurs at high frequencies)
has very little effect on the frequency response;
• While the addition of fiber increases the output at infrasonic frequencies, it
reduces the output in the bass rolloff region and does not lower the 3 dB rolloff
frequency; this conclusion applies not only to the overall effect of the fiber,
but also to its thermal capacity alone."
In the body of the text, when he isn't involved with impenetrable theory, he demonstrates that with the right density of stuffing, internal reflections inside the box, are suppressed. No real surprise there.
"• Viscosity is the dominant mechanism of damping, thermal relaxation being of
secondary importance;
• The neglect of internal elastic forces in the fibers is justified;
• The departure from thermal equilibrium (which occurs at high frequencies)
has very little effect on the frequency response;
• While the addition of fiber increases the output at infrasonic frequencies, it
reduces the output in the bass rolloff region and does not lower the 3 dB rolloff
frequency; this conclusion applies not only to the overall effect of the fiber,
but also to its thermal capacity alone."
In the body of the text, when he isn't involved with impenetrable theory, he demonstrates that with the right density of stuffing, internal reflections inside the box, are suppressed. No real surprise there.
I think there are two effects at work, one is the transfer between heat and pressure, which runs back and forth at any speed. This effect accounts for the heating and freezing that occurs when air is compressed and de-pressed.If that were the case, then how would the air being alternately squashed and stretched inside a sealed LS enclosure ever get hot?
The wool, interfacing as a giant surface (as opposed to if it were crushed into a ball), acts as a heat store and so it slows down the 'spring', so I guess it adds a little heat to the cooler air on decrompression, and robs from the warmer air on compression (sort of like living near the sea, the water acts as a heat reservoir).
This has the observable effect of the volume of air in the box acting like it was bigger, as the air cannot heat up or cool down as fast as usual, therefore as hot air causes even more pressure, and the heatup is countered by the wool, the backwave is not resisted so tightly by the air in the box.
Then there is the absorption of the sound energy, which has to turn into heat (in a closed system) as there is nowhere else for it to go.
Most of the pressure ends up just like a spring, whizzing in and out and so - on average - at equilibrium. But also a percentage of energy is lost, like if you speak into a well padded speaker box, and that bit will cause heating.
You have to remember that in a sealed box, there is a significant heat source - the loudspeaker drivers. These are around 1% efficient at converting electrical power into acoustic power, with 99% going into heat. So the inside of the box and lagging can heat up significantly. Whether the temperature of the lagging has an effect is an interesting question. Putland's thesis surprisingly does not address this effect.
The 1% efficiency comes from the fact that the moving mass of the cone is very badly matched to the impedance of the air. The only way of overcoming this limitation is to more efficiently couple to the air using an acoustic transformer - in other words a horn.
The low efficiency of a moving coil driver in a regular loudspeaker also leads to slow variation in drive unit efficiency through thermal compression - the copper voice coil changes resistance at 0.4%/C and typically has a maximum coil temperature of 200C. At that temperature the efficiency drops by 5dB. Then you get a quiet passage, and there is still a 5dB compression until the temperature of the voice coil slowly cools. So you get this lagging effect going on.
It is also an interesting observation that almost all those expensive Watts in your high-end power amplifier go to simply heating the voice coils!
The 1% efficiency comes from the fact that the moving mass of the cone is very badly matched to the impedance of the air. The only way of overcoming this limitation is to more efficiently couple to the air using an acoustic transformer - in other words a horn.
The low efficiency of a moving coil driver in a regular loudspeaker also leads to slow variation in drive unit efficiency through thermal compression - the copper voice coil changes resistance at 0.4%/C and typically has a maximum coil temperature of 200C. At that temperature the efficiency drops by 5dB. Then you get a quiet passage, and there is still a 5dB compression until the temperature of the voice coil slowly cools. So you get this lagging effect going on.
It is also an interesting observation that almost all those expensive Watts in your high-end power amplifier go to simply heating the voice coils!
Ok so I swapped over the wires as recommended, this time I'm still not getting any ST sound, the midrange surround is not as it was before the movement is way less. Over all im not missing any high frequency notes to suggest their is a requirement for the ST. Only time will tell as more music will be played and more listening.
Lets go through the possible changes that may of been done.
1-tweeter change from T27 to H086
2-midrange change from B110 to Celestion/Dynamic.
I don't know much about electronics so if any of could look at the crossover for changes then we may have 3 changes in total.
Thay are connected to the cyrus3/PSXR/XPA. I have only had this for a short time so cannot compare to anything else. I can compare them to my, (correct me if I'm wrong) Pro9TL mk1
On the valve amp/receiver I have (Pioneer ER420) from memory any difference.
Correct me if I'm wrong but 99% of the information from amp to speaker is going to waste as heat inside speaker cab? That's crazy!
I'll declare myself out on contributing to a crossover redesign, Bazza.
I'm just happy that we have got your speakers up and running in their current configuration.
I will disconnect the ST's and test them alone away from everything. This I'm thinking I will do by connecting a headphone jack into a phone which has the ends for the speaker disconnected so it's just bare wire. This way I'm thinking not to much power is given to the ST, also I have a 4uf 50v capacitor. Will the capacitor separate the low frequency and help with answering weather the ST works or not?
Yes it will, and will protect the super tweeter from damaging low frequencies.
I use the headphone output from an old portable transistor radio for quick speaker testing purposes - with a 4 uF capacitor in series if its a tweeter.
Please consider that you may not be able to hear the super tweeter unless you are a young dude and that the music you are playing may not contain very high frequencies anyway.
If you have a multimeter, measure the resistance of the super tweeters to check they are not open circuit.
Bottom line: I would consider the super tweeters to be there simply for decorative purposes!
The supertweeter is probably lobing with the tweeter to the end that it could be varying the treble with frequency.
Getting down to the purpose of a supertweeter is more complex than it appears. Some feel it is to address a failing of the tweeter to reach higher frequencies, or that it has a breakup, or that it beams.
A supertweeter is there to adjust higher frequency room power, and in this particular application where it is inadvertently interacting with the tweeter, I'd be inclined to disconnect it and review the equalisation of the system to see where that stands.
Getting down to the purpose of a supertweeter is more complex than it appears. Some feel it is to address a failing of the tweeter to reach higher frequencies, or that it has a breakup, or that it beams.
A supertweeter is there to adjust higher frequency room power, and in this particular application where it is inadvertently interacting with the tweeter, I'd be inclined to disconnect it and review the equalisation of the system to see where that stands.
Yup. That is why loudspeaker driver voice coils are wound with high temperature insulation and varnish. Tweeters and often midrange drivers have ferrofluid in the magnet gap to conduct the heat away to the driver structure. And bass units have vent holes in the back and sides so that the motion of the driver pumps air into and out of the gap to cool it. Some even have heatsinks on the back of the magnet. There have been drivers made with anodized aluminium cones - again to conduct heat away.
So absolutely 99% of the power from the often megabucks Krell or other power amp is simply wasted as heat in the loudspeaker voice coils, with the remaining 1% as acoustic output you hear.
In a sense good job - because 1 acoustic Watt is around 120dB (distance independent in a sealed room), so if all 100W from your amp was converted to acoustic power with 100% efficiency you would go deaf with 140dB in your living room.
Could this have something to do with it. Hear the 2 white cables without the black stripe is positive, and the 2 are soldered together? Also the ST had 2 black wires connected to the negative and 1 from the positive. So their was some kind of connection going on with the 3 drivers.
I'm going to have a long sit down with some music. Maybe the ST kicks in very high?
Attachments
You know that all the negatives are connected together. Trust what you see, since it isn't clear what a previous owner did to manage their polarity scheme. However, this shouldn't prevent you from choosing your own polarity arrangement by swapping connectors at the driver terminals.
I was kinda hinting at that Bazza!
Precisely!
- Measure voice coil resistance
- Remove ST and power it from another source as you suggested
- Use a kitchen roll tube as a stethoscope to magnify the sound
- Stop assuming the original owner had any idea what he was doing with the wiring!
I could guess why, but that wouldn't be productive.
I'd take my multimeter and check continuity this way. See that all negatives are connected to each other. See that none of the positives are connected to negative. See that none of the positives are connected to any other positive (expect the resistance between T and ST).
So only 1 ST works! ! I then just went for it, swapped phase at amplifier=nothing interesting. Then swapt the M phase unit=peacks in mid up and down but I did hear that annoying pathetic bass, only 1 thing to do their. .that was to swap phase at the bass unit. ."HALLELUJAH" Top side was great I mean really nice midrange including tweeter very good indeed. Bass was coming through deep and correct. But 1 question, can too much woolly damping material hinder poor bass at very low levels?
Good job chaps you are" the A team "