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Old 11th September 2008, 05:11 PM   #71
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Quote:
Originally posted by crazyhub
doppler distorsion...or InterModulationDistorsion?



I'm not sure! Are the the same thing? Would they be related?
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Old 11th September 2008, 05:16 PM   #72
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Quote:
Originally posted by AndrewT
i.e. use narrow band signal to each dedicated driver.
Don't ask a driver to do both mid and bass duty. One driver for bass and a separate driver for mid frequencies.
You're right, that is another way to look at it. However, that being said, which is better in terms of accuracy: fewer crossover points, or reduced bandwidth demand per driver?

In the audio spectrum (excluding sub-bass, so from say 60 Hz on up) how many drivers should one use? Some say you need 3 - low medium high. Some say 2, and there are some who even say 1! I feel you need multiple drivers to cover that range, but at some point a single driver has to take some of the bandwidth and run with it.

But getting back to the topic of this thread - midbass drivers and their use in 2 way designs - how does diameter effect the driver's performance through this band? So far it seems to me that using the largest diameter possible whilst still reaching as high as need be, is the ticket.

So to sum up what we've heard so far (correct me please if I get some of this wrong) In the case of a small midwoofer vs a larger one:

Points for smaller
- lower Mms, tendency toward improved transient response
- more uniform movement of cone, less area to flex, tendency toward lower mechanical non-linear distortions
- higher crossover point usually, higher response facilitating an easier crossover point to tweeter.

Points for larger
- lower Fs probably better low end response
- reduced cone movement also reduces non-linear distortion and intermodulation (same as Doppler?)
- often higher sensitivity, which means reduced power compression, more head-room for transients

Please feel free to add (or correct!)

Jim
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Old 11th September 2008, 07:44 PM   #73
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Jim, I´m a bit concerned about your generalizations, they could possibly be discussed for the rest of the year I´m afraid.

I believe the size of the drivers very much being solved when you are more "conscious" about what you want to achieve and have done some experiments, maybe.

There are some "critical" considerations to be made when designing a loudspeaker and the constructor acts like people use to do; they act in the way they believe is in accordance with the truth, and not necessarily according to what is the absolute truth.
Of course, most people do have to take the economical reality into the equation.

Thus, FWIW here is some of my believes (yes it is off topic but says something about the complexity and the risk of focusing too much on one "item");

Using a single driver for a wide spectrum doesn´t solve many problems. Phase shifts are likely to occur in a more severe manner.

Constant dispersion is something to strive for, but is hard to achieve.

Doppler distortion may or may not be of great importance. It´s about frequency modulation and someone says that the Doppler effect (striking the higher note) in a driver is worst when the driver stops e.g. in it´s most forward position introduced by the lower tone. Some types of music may very well be more prone to be affected by Doppler distortion.

Diffraction occur even when using curved enclosures but is dispersed "better" with regard to frequency.

A baffle step may very well occur even if the enclosure is a sphere.

Standing waves can occur in any enclosure no matter the shape of it. A sphere is likely the worst shape in this regard, but a sphere or a curved shape may withstand pressure changes better than a squared conventional enclosure.

Time alignment is hard to achieve in the simple way of physically offsetting the drivers.

You may not agree to all of this, but this is the reason we see so many variants of loudspeakers.

More interesting reading in this tread, for example in the link to djarchow´s "It´s Just a Phase I am Going Through.

http://www.diyaudio.com/forums/showt...08#post1588608
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Old 11th September 2008, 08:28 PM   #74
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Hi Golden Mean,

Thank you for your comments. It is true, I am speaking in the general sense, as it is my hope to compare the parameter of midwoofer diameter on a general level. When considering only midwoofer diameter, what conclusions can be drawn?

If I understand what you are saying, it is that the problem is too complex to be simplified to this point. That could be! I have much to learn, and I appreciate the feedback.

You mentioned something I find interesting about phase - that phase distortions may occur to a greater extent through a single driver? I understand that drivers have a phase response which is non-linear, but does this mean it is often better to say use a mid and a woofer to cover this band than a midwoofer, as far as phase goes?

Along that line of thinking - does a driver's phase distortion increase as it reaches either end of its useful frequency response? For example - a 'large' midwoofer of 8" is reaching to crossover at 2 Khz, at this point will its phase likely be far from 0 degrees?

Thank you for the link, I will check it out later today!

Jim
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