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Message: <blockquote data-quote="Josh Ricci" data-source="post: 132749" data-attributes="member: 1594">Re: No compromises front loaded double 18” cabI'm a little late to the party but this has been an excellent discussion. Ports do shift their tuning as the air speeds get higher and the turbulence increases causing a breakdown in laminar air flow. I have a few measurements showing this effect both in the response shape and the impedance curve. A single, large, circular port is technically the best shape to keep the port operating in an uncompressed controlled fashion. However very large round ports often do not cleanly fit into the box in a manner that fits well with the design or proposed form factor. It is also cheaper and less labor to build a slot vent in most cases. Additionally research shows that larger vent areas support higher volumes of air before noise and compression. You will often see hard or fast rules stated such as keep vent velocity below 17m/s or 25m/s or whatever. In reality the vent shape and area needs considered as well. 30m/s of air through a skinny 1"x 10" slot vent is much different (unacceptable) than 30m/s through a 10" diameter flared pipe. If the vents have sufficient area the cross sectional shape becomes less important. The best paper that I have come across that studies the effects of port behavior was researched by JBL a number of years ago. Let me see if I can find that PDF...I often also read comments such as you will "need" a 3 or 4kw amp to make proper use of a certain driver. What the comment means to say is in order to run the driver up to the very edge of its abilities you will need an amp with "X" amount of power rating. In my view this is the wrong way of looking at things. I prefer to use systems that over spec the drivers and perhaps under power a bit. The last 3 to 6dB out of a driver is always the most distorted and compressed. If you can run a bit under the systems limits it sounds so much better. I would much rather listen to a 18sw115 loaf on a 1200w rated amp than run a TBX100 up to its useful limits. Another factor to think about is voltage sensitivity. This is NOT efficiency. Simulations driven by TS parameters at small signals scale perfectly. The driver behavior does not change whether you input 1v or 100v. This is not how things are in the real world. Many drivers change their behavior dramatically and run out of headroom or thermal handling abruptly which throws all of that small signal stuff out the window. Most bass systems often get operated more towards the upper end of their envelope not the bottom so looking at these small signal parameters is fairly useless. The heavier more expensive drivers, with greater xmax, xmech, and larger heavier voice coils and better motor cooling are more linear devices and do not change their behavior as much when driven hard, plus their limits are higher to begin with. So while you may be looking at a simulation based on parameters pulled from tiny input signals and thinking, I've only got a 1200w rated amp and $250 driver X is a little more sensitive and seems to get louder on that much power than $500 driver V, in the real world it is likely that the less sensitive, heavier duty driver may be louder and cleaner off of the same amp due to much better behavior at those drive levels. Definitely look for high power measurements and Klippel testing on drivers as that separates the paper tigers from the real ones. Be wary of driver companies that have specs that seem to good to be true, but do not have detailed information on things like Klippel reports, the gap height and coil wind height, shorting rings, etc...There are many from all fields.</blockquote>

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