modok wrote: ↑Wed Mar 13, 2019 3:52 pm
A strange feature found in some ancient buildings, temples?, ect, cavities in the walls filled with ashes.
The purpose of these seemed a mystery, historians logically assuming whatever was in the cavity had burned.
To people versed in acoustics it looks like a helmholts resonator, and the ashes are sound absorbing material. And...that's probably right!
Although it surely was not understood scientifically like today, many ancient buildings do seem to be designed to have acoustic effects, Sometimes to produce echos, or to prevent them. Going WAY back!
And interestingly, carbon, like activated charcoal, is still used for high end acoustic treatments, some believe it works better than fiberglass or foam as a dampening material, just kind of messy to work with!
Considering they use charcoal for filters I wonder if it had to do with air filtration and mold prevention? It's interesting that the Bible has a lengthy section on dealing with black mold in the walls of a home 4000 years ago and with the exception of praying over the repaired area it's still the same today... cut it out and if it comes back tear the house down.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
The reason that anti reversionary devices work better closer to the port have a reason.
And the reason is that the reversion is the second reflected wave from the refection between the primary pipes and the collector that is a compression wave.
A 4-2-1 or tri Y header works so that the secondary reflection from the primaries gets cancelled by the primary reflection from the secondaries at RPM:s below the headers tuned. The collector adds another low pressure wave.
I have tried a lot of cancellation boxes added after the collector but what worked best was an oral straight though glass pack muffler with a perforated pipe inside.
It still gave a good low pressure reflection back upwards the collector and it cancelled part of the outgoing reflection and a lot of returning reflections from further down the exhaust.
On my 240 hp engine I gained 12 hp below maximum torque and 2 hp at the RPM of max hp.
