I think I see what you mean, that air resonance alone is not a good predictor of a driver's behavior or performance. So just to finish up with this, does that mean if one driver's air resonance is 35hz, for example, and another's is 90hz, it's not possible to make inferences about how those drivers' performance differs in any area? For example, do those values suggest anything directly about frequency coverage?
David, speaking strictly as a newb, try this simplistic little experiment. Take a driver, not in any cab, play various frequencies through it using a little software tool (e.g. the tone generator from Marchand Electronics, or by making tones in Audacity, or via a test tone CD).
Use low volume, obviously! Note what happens when the frequency is around Fs. The cone starts to behave a little strangely. It may flop around wildly. The driver as a total system is now operating at its point of resonance in free air, and it's "resonating" and not making much music.
See if you can play any tones lower than Fs. Then you can probably see why simple cabs don't generally try to play lower than Fs (ignoring for a moment that driver + cab can lower the Fs compared to free air, because the cab can "damp" the cone by putting pressure on the cone's back which can lower Fs).
If yo uhave an impedance / frequency response plot from the manufacturer, or another source, look at what happens to impedance as it approaches, and reaches, Fs.
Now imagine how Fs would change if, for example, the magnet's strength was greater or weaker (Qts), or if the suspension was stiffer (Vas). Imagine if the cone were heavier -- what would happen to Fs? E.g., if you put a penny on the cone? You can try that. You're just trying to get a feel for the driver as a system of multiple interacting parameters.
Use low volume, obviously! Note what happens when the frequency is around Fs. The cone starts to behave a little strangely. It may flop around wildly. The driver as a total system is now operating at its point of resonance in free air, and it's "resonating" and not making much music.
See if you can play any tones lower than Fs. Then you can probably see why simple cabs don't generally try to play lower than Fs (ignoring for a moment that driver + cab can lower the Fs compared to free air, because the cab can "damp" the cone by putting pressure on the cone's back which can lower Fs).
If yo uhave an impedance / frequency response plot from the manufacturer, or another source, look at what happens to impedance as it approaches, and reaches, Fs.
Now imagine how Fs would change if, for example, the magnet's strength was greater or weaker (Qts), or if the suspension was stiffer (Vas). Imagine if the cone were heavier -- what would happen to Fs? E.g., if you put a penny on the cone? You can try that. You're just trying to get a feel for the driver as a system of multiple interacting parameters.
RJBond, that's very helpful and leaves me a bit puzzled: The stated F0 of a Lowther DX4 is 36hz and the stated frequency coverage extends down to 30hz (so far, at least roughly so good), but in any implementation I’ve seen like the Medallion II that Lowther America sells, the rated response extends only down to 65hz (not as low in fact as some RLH speakers based on the 5” Lowther drivers). Can you help me understand this?
There you're talking about combined systems, not just a driver.
a/ Just because a driver's Fs is at x Hz, that does not mean it will produce useable output all by itself down to that frequency. If it did, there woud be no requirement for cabinets.
b/ The published Fs of the Lowthers is generally wildly optimistic (read 'fictional') -double it & you're usually closer to the truth. Not that they're alone in that -they're not.
c/ Horn LF extension depends on the horn -the Medallions are not tuned especially low.
a/ Just because a driver's Fs is at x Hz, that does not mean it will produce useable output all by itself down to that frequency. If it did, there woud be no requirement for cabinets.
b/ The published Fs of the Lowthers is generally wildly optimistic (read 'fictional') -double it & you're usually closer to the truth. Not that they're alone in that -they're not.
c/ Horn LF extension depends on the horn -the Medallions are not tuned especially low.
Hi guys, I was composing this before I saw Scott's reply, but I'll add it anyway!
The Lowthers are fine drivers, but the factory specs must have been determined in a non-standard way because they don't match the measurements made "in the wild." Check out Martin J. King's measurements:
http://www.quarter-wave.com/Project04/DX4_Data.html
Maybe the measured frequency response doesn't extend all the way down to the factory-quoted Fs because the actual Fs is much higher than the factory figure.
Keep in mind that while a typical vented cab only goes down to about Fs, a really well-engineered cab can go lower. If I had the DX4, I'd be searching for those ultra-finessed cabs that go as low as possible. (I'd also maybe get corners!)
If you want to get the maximum from your DX4's, I recommend at least trying a setup like Mr. Bob Brines, using a computer streaming lossless audio with digital EQ into a nice DAC. I have heard it, and it's amazing, and I never heard the Lowthers sound better.
The Lowthers are fine drivers, but the factory specs must have been determined in a non-standard way because they don't match the measurements made "in the wild." Check out Martin J. King's measurements:
http://www.quarter-wave.com/Project04/DX4_Data.html
Maybe the measured frequency response doesn't extend all the way down to the factory-quoted Fs because the actual Fs is much higher than the factory figure.
Keep in mind that while a typical vented cab only goes down to about Fs, a really well-engineered cab can go lower. If I had the DX4, I'd be searching for those ultra-finessed cabs that go as low as possible. (I'd also maybe get corners!)
If you want to get the maximum from your DX4's, I recommend at least trying a setup like Mr. Bob Brines, using a computer streaming lossless audio with digital EQ into a nice DAC. I have heard it, and it's amazing, and I never heard the Lowthers sound better.
Hi David, yes I think everyone who either owns, them, has heard them, or is familiar with the Martin J. King modeling software used to engineer them, would agree that they are exceptionally well-engineered cabs. Like all speakers, it takes some experimentation (e.g. with positioning) to get the results you want.
I have the Brines LT-2000's built from a flat-pak (by forum member Phil Townsend) and originally had the DX-3's, but subsequently swapped them out several times for different drivers (why not?)
If you go with digital EQ, you have a lot of flexibility with positioning because you can compensate for boundaries or the lack thereof (within reason of course -- using digital EQ to turn a Lowther into a woofer would not be wise, I'm sure everyone would agree).
Speaking of Lowthers, Mssr. Phil Townsend had a pair of PM6A's the other day, and the ultra-heavy frames on those drivers are positively industrial-strength.
In the right fine-tuned cab, with the right music, in the right room, they are easy to love in my opinion. But very often, they are used "raw" and that doesn't show off what they can do. They might be the most misunderstood and mis-used of all single drivers.
I have the Brines LT-2000's built from a flat-pak (by forum member Phil Townsend) and originally had the DX-3's, but subsequently swapped them out several times for different drivers (why not?)
If you go with digital EQ, you have a lot of flexibility with positioning because you can compensate for boundaries or the lack thereof (within reason of course -- using digital EQ to turn a Lowther into a woofer would not be wise, I'm sure everyone would agree).
Speaking of Lowthers, Mssr. Phil Townsend had a pair of PM6A's the other day, and the ultra-heavy frames on those drivers are positively industrial-strength.
In the right fine-tuned cab, with the right music, in the right room, they are easy to love in my opinion. But very often, they are used "raw" and that doesn't show off what they can do. They might be the most misunderstood and mis-used of all single drivers.
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