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LE, not MMS determines woofer "speed"!

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RoadRunnersDust View Drop Down
Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoadRunnersDust Quote  Post ReplyReply Direct Link To This Post Posted: 16 September 2016 at 11:07am
Once you start talking about controlling the cone whilst in motion you also need to specify the amplifier.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve20131 Quote  Post ReplyReply Direct Link To This Post Posted: 16 September 2016 at 11:27am
I don't know much but for 12" tapped horns down to 40hz mms has to be in excess of 80g, preferably 100g and a bl factor in excess of 18 (big magnet).  But for the power handling the voice coil must be larger and thicker glass fibre/paper for strenth so also resulting in a bigger mass.  Sims do not work with low mass units despite 25bl or 10mm xmax
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Post Options Post Options   Thanks (0) Thanks(0)   Quote midas Quote  Post ReplyReply Direct Link To This Post Posted: 16 September 2016 at 12:12pm
Originally posted by 70,s hero 70,s hero wrote:

As I understand it, the inductance ie the given amount of magnetic field , is dependant on various factors, if you take a simple large gauge wire and use that for a coil then the inductance will be much lower than if you use a smaller gauge with multiple windings. The windings in terms of length and gauge have to be selected upon the basis of their ability to handle the current and create a magnetic field. Inductance is directly related to force within the coils flux acting against the fixed magnet,the more windings, the more inductance, common sense would say that a lighter cone  would be more responsive given the same coil assembly otherwise any other view would appear to defy the laws of physics.

What I found with electric motors was, thinner windings with more of them yes gave ultimate higher speed. Less windings with a thicker wire gave faster acceleration/ deceleration. So response time was better. 

Obviously mag strength, coil size, cone composition, surround and voltage impact here.
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70,s hero View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 70,s hero Quote  Post ReplyReply Direct Link To This Post Posted: 16 September 2016 at 12:28pm
Going back to the OP, (I have not read the paper) it makes assumptions that transient response and speed are not linked which seems odd too.
The whole thrust of the argument is that an 18 is as linear as a 15 given the same power etc. As we know that the linearity is dependant on many things, one of which is cone size then the argument to me fails regardless of any other test.  In part though I think that the difference in perceived sound between an 18 and 15 is due to the physical cone size and angle of construction and how that relates to the size of the size of the sound pressure waves it is being forced to produce.?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 16 September 2016 at 12:45pm
There's just too many variables, especially when you get into a large signal model and the small signal TH specs no longer apply. BL is not linear, cones start to flex and leak air, voicecoils warm up and shift parameters etc. All we can offer is general ideas without some very expensive measurement kit and a lot of time.

The only thing that can be defined will, is how you measure transient response. Monitoring decay of an impulse test is a good start but you have to be  careful not to measure room or cabinet effects. Ability of a driver to reproduce a square wave is another potential one. FFT the results and you can see the effects on amplitude and phase shift. Generate the square and you know exactly what harmonics and amplitudes should be present when you measure it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoadRunnersDust Quote  Post ReplyReply Direct Link To This Post Posted: 17 September 2016 at 4:25pm
Having re-read the article I am now somewhat confused about a number of points the author makes:

Firstly, Im not convinced that discrediting values that form a constant directly related to the experiment is such a clever idea unless attempting to force the captured data into an outcome you had previously decided on.

Secondly, its a goddamn loud speaker. I would wager that by the laws of statistics 100% of the loudspeakers on the planet are for playing music.
With that in mind, why does it seem like the author is only interested in movement from a driver at rest across a single impulse (not sure I hear much of that going on in music) whilst addressing and completely disregarding the ability for the driver to reproduce a transient whilst already in motion (like kick drum and snare for example).


Or am I missing something here?
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70,s hero View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 70,s hero Quote  Post ReplyReply Direct Link To This Post Posted: 17 September 2016 at 7:16pm
I guess you have to start somewhere, measuiring a single cycle is the easiest measurment to make, (in lower frequencies) a Kick or a snare could have a duration of two seconds with a decay in the signal over time. The idea that this assuption (the papaer) can have any credibillity appears to be fundamentally flawed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote IanD Quote  Post ReplyReply Direct Link To This Post Posted: 18 September 2016 at 11:56pm
Most of the "it's like a motor, higher force is better" similarities are just plain wrong; as far as bandwidth and speed and transient response are concerned, the T-S parameters tell you how the driver behaves and what the frequency response in the cabinet will be. When people say a driver/cabinet is "fast" what they often really mean is that it's bass-light, ones which are flat down to lower frequencies are often said to be "slow" when actually they're more accurate. A driver with a big heavy cone/coil needs a strong motor force (M-force is the extreme example of this), applying this to a lighter driver leads to low Q and bass rolloff unless the cabinet is designed to work with this -- which usually means a big FLH.

Coil inductance just acts as a bandwidth limiting factor (lowpass filter) if it's linear, and for most PA bass drivers the cutoff from this is well above the crossover frequency -- not always true for drivers aimed at home theatres which can have huge heavy high-inductance coils. But the bigger problem is when the inductance varies a lot with cone displacement, which causes distortion because the filter cutoff changes as the cone moves. So keeping the inductance low and more constant by adding demodulation rings does make for a cleaner sound, which is why the more expensive higher-quality bass drivers often do this.
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