Can you show me some pics of your speakers, don't know much about them. And how do they sound?No, my uncle made them from plans, even with a nice veneer, and i recall the stuffing was a wonderful pure wool, sort of grey and smelt nice, laid around the sides and on the bottom, not as much as in a sealed box.
I have some 'half isobariks' now with an isobarik crossover, which look similar and have the same type of drivers - so I retain an interest, albeit in a different (isobarik sized) sealed box
No, my uncle made them from plans, even with a nice veneer, and i recall the stuffing was a wonderful pure wool, sort of grey and smelt nice, laid around the sides and on the bottom, not as much as in a sealed box.
I have some 'half isobariks' now with an isobarik crossover, which look similar and have the same type of drivers - so I retain an interest, albeit in a different (isobarik sized) sealed box
The wool in the photos is identical to the stuff I used in a pair of Wireless World Bailey transmission lines I built in the prehistoric past. May 1972 https://www.worldradiohistory.com/UK/Wireless-World/70s/Wireless-World-1972-05.pdf p215 onwards, although I built them in around 75/6
The source for this no longer exists. But Herdwick wool is available from https://chimneysheep.co.uk/products/a-useful-bit-of-insulation?variant=45982609604914 and they specifically say that one use is loudspeaker stuffing.
I actually have it shoved up an old unused chimney to stop organ pipe resonance in my listening room.
Just call us the speaker doctors!
I'd be interested to know if you can actually hear a contribution from the super tweeters.
Thanks for the link.
It was Dr. Bailey who identified long-fibre wool as the material with the best characteristics for use in a TL enclosure.
The long-fibre wool slows down the speed of sound, allowing a short TL to behave like a longer one and making it possible to build a less bulky enclosure.
The speaker looks like it could be a variation of the Webb design https://www.falconacoustics.co.uk/downloads/Webb R50 Construction.pdf
It has the same drivers, and a more complex crossover for the B110 - but nevertheless it is close.
It has the same drivers, and a more complex crossover for the B110 - but nevertheless it is close.
FALSE.
The damping does not slow down the speed of sound. What allowed the shorter line was the taper from wide to narrow. This shape decreases the length of line. A taper the other way means a longer line. An invalid assumption was made and an erroneous cause was assigned to the shortening of the line.
Both King & Augpurger’s accuarte models revealed the reality in the early 2ks. Bradbury was shown to be wrong.
dave
Sorry, I was quoting Bailey's and Bradbury's opinions and failed to recognise Augspurger's contribution which decisively reduces the role of the variation in the speed of sound in relation to the response of the TL at low frequencies.
The full story is here: https://transmissionlinespeakers.com/en/articles/introduction-and-historical-notes/
Good link!
The wiring diagram of FIG. 4 in your link is salient in the context of Bazza's rewiring problem.
It also states that the connection of the midrange in reverse phase to the other drivers is correct.
I wasn’t aware of this version at the time but assembled the Mk 2’s found on Dave’s site circa 1977. Now replaced with a much smaller speaker I can lift without help. A good performer for the period. A person my age when I built it took it off my hands.
http://p10hifi.net/planet10/TLS/downloads/Pro9TL-Mk2.pdf
I heard an interesting theory some time ago, about just how wool behaves with sound, and it is connected to it's stellar insulation properties: The the high pressure heats it, and it lets the heat back out during the low pressure bits, thus storing 'air-space' as heat - so it made spaces acoustically bigger than they were.
I did hear (hear, LOL) this a long time ago, and may have mistaken it, but it sounded interesting anyway, and it's plausible given the all absorbed sound in wool must end up as heat.
That does sound plausible until you realise that work is being done and converted to heat by the woofer cone during both compression and decompression.
Have you ever sealed the outlet from a bicycle pump with your finger and operated the plunger several times?
If so you will have noticed that the air trapped inside the pump gets hot.
The same thing happens inside an sealed loudspeaker enclosure that is empty of wool. The movement of the woofer cone compresses and decompresses the air and causes its temperature to rise.
Wool is actually a better conductor than air, so filling a sealed enclosure with wool allows heat to transfer from the air to the wool, helping to keep the air at a constant temperature. It is this near isothermal (equal temperature) condition of the air that I believe results in an apparent increase in enclosure volume.
However, I must do more research!
I can't hear them to be honest, at high volume I believe I can hear them but not 100% sure. Also one tweeter seems to be hitting the higher notes more than the other. The mids are hitting s very high frequency too, when I touch the surrounds on them I can feel movement!, so they are going very high and low. I don't get it. Maybe I have to drive them in much more and give them more hours of playing time. The mids look brand new, ST looks old and the tweeter looks old also.Just call us the speaker doctors!
I'd be interested to know if you can actually hear a contribution from the super tweeters.
The last time I checked I couldn't hear a pure tone of 10 kHz, so I'd be highly unlikely to hear a working super tweeter.
A good tip is to use the cardboard tube from the centre of a roll of kitchen towel as a 'stethoscope'.
This helps isolate the output of a tweeter (or super tweeter) from that of the other drivers to give a better idea if it is working properly.
The high frequency end of a midrange's response can fool an old duffer like me into thinking a tweeter is working when it is not!
Temperature increases with added pressure, but decreases with lower pressure - which is how AC and fridges work, but yes, all absorbed energy must end up as heat, so the temperature overall will rise.
I guess the question is 'does the wood have time to cool down and heat up, as the pressure changes at 40Hz or so
The mids of the era were B110 KEFs, which may have been replaced.
B110s can sag (flip then upside down!), but if you get that much movement, perhaps there is a crossover fault and the B110s failed due to it?
I use 'Spectriod' on my android phone as a listener to identify frequency peaks, just with normal music, I find it good for tuning EQ - perhaps that will see something?
If that were the case, then how would the air being alternately squashed and stretched inside a sealed LS enclosure ever get hot?
