Midbass Diameter - How to Decide?

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Well, moving away from the theoretical and into the practical, take a look at this page from the Madisound Catalog.

Silver Flute WOOL Cone Woofers -

http://www.madisound.com/pdf/printcatalog/silverflute.pdf

WARNING, this is a relatively large PDF file.

These seem like pretty ideal MidBass speakers. They go reasonably low, they go unusually high, and they are relatively cheap. I also know that there are several tested and proved designs for some of these speakers.

Notice the 20cm/8" at the bottom. Low end appears to be in the 30's or 40's depending on which speaker you choose, and they are reasonably flat up to about 3khz, followed by a small peak, which if flattened would bring the high end up to a clean 5khz.

Admittedly, they are not an exceptionally loud speaker, but they are still reasonable.

It must be the wool.

Steve/bluewizard
 
J.R.Freeman said:
I'm not sure if the smiley face is supposed to denote sarcasm, but he's correct - 2 drivers with the same effective radiating area, will have to move the same amount to produce the same SPL, regardless of efficiency. The higher efficiency driver will just require less electrical power input to do it.

True, but taking T-S parameters and enclosure tunings into consideration changes everything in the lower frequencies, which Tinitus is referring to in his last post. In ANY case, a loudspeaker's cone will have very little to no movement above a few hundred Hz anyway. So, which statement holds more weight in the real world?.. The fact that "2 drivers with the same effective radiating area will have to move the same amount to produce the same SPL, regardless of efficiency" ONLY when you're dealing with frequencies high enough to where that particular driver's/system's T-S parameters and enclosure size/tuning have no effect? Or is it more important to realize that a more sensitive loudspeaker in its suitable enclosure will end up moving a lot less to produce the same SPL at lower frequencies above the system's resonant frequency? As previously mentioned, cone movement will always be extremely low at higher frequencies anyway, so it's usually of very little concern in that regard. So, since lower frequencies is where it makes all the difference, and that's where it's of the most concern, that's where it matters. For instance, how else would one single professional bass system used in concerts have the ability to pump out 120-130+ dB all day from just one single vented 18" woofer with 4-10mm Xmax? Think about it. See what I'm saying? Cone movement at higher frequencies is usually of very little concern in the real world.

Here's a quick example in WinISD, just to put things into perspective..

Two 15" woofers.. a Dayton DVC385-88 15 DVC (15.1mm Xmax, 600w power handling), and a Peavey Low Rider 15" (9.6mm Xmax, 800w power handling), each in their own recommended QB3 alignments.. 8.35 cubic feet at 21Hz and 3.3 cubic feet at about 38Hz, respectively. -3dB points are 25Hz for the Dayton and 46Hz for the Peavey. The Dayton has nearly 90dB/watt sensitivity, and the Peavey has over 94dB/watt sensitivity. These two vented systems are both supplied with 2nd order highpass filters, so that maximum cone movement below and above tuning is exactly the same, which will of course turn out to be right around the tuning frequency of the system.. it ends up being 21Hz for the Dayton and 37Hz for the Peavey. With the two systems described above, the Peavey is given power until Xmax (9.6 mm) is reached, which ended up being an overall SPL of 123 dB. The Dayton is given power until it's able to achieve the same SPL (theoretically ;)) as the Peavey system (123 dB) above the lower frequencies.. which ends up being 2100 watts to the Dayton and only 765 watts to the Peavey. With that, this is what we get. The Dayton DVC is red, the Peavey Low Rider is blue. The plot goes from 0-30 mm, at which point the Dayton goes off the chart..
 

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BHTX said:


True, but taking T-S parameters and enclosure tunings into consideration changes everything in the lower frequencies, which Tinitus is referring to in his last post. In ANY case, a loudspeaker's cone will have very little to no movement above a few hundred Hz anyway. So, which statement holds more weight in the real world?.. The fact that "2 drivers with the same effective radiating area will have to move the same amount to produce the same SPL, regardless of efficiency" ONLY when you're dealing with frequencies high enough to where that particular driver's/system's T-S parameters and enclosure size/tuning have no effect? Or is it more important to realize that a more sensitive loudspeaker in its suitable enclosure will end up moving a lot less to produce the same SPL at lower frequencies above the system's resonant frequency? As previously mentioned, cone movement will always be extremely low at higher frequencies anyway, so it's usually of very little concern in that regard. So, since lower frequencies is where it makes all the difference, and that's where it's of the most concern, that's where it matters. For instance, how else would one single professional bass system used in concerts have the ability to pump out 120-130+ dB all day from just one single vented 18" woofer with 4-10mm Xmax? Think about it. See what I'm saying? Cone movement at higher frequencies is usually of very little concern in the real world.

Here's a quick example in WinISD, just to put things into perspective..

Two 15" woofers.. a Dayton DVC385-88 15 DVC (15.1mm Xmax, 600w power handling), and a Peavey Low Rider 15" (9.6mm Xmax, 800w power handling), each in their own recommended QB3 alignments.. 8.35 cubic feet at 21Hz and 3.3 cubic feet at about 38Hz, respectively. -3dB points are 25Hz for the Dayton and 46Hz for the Peavey. The Dayton has nearly 90dB/watt sensitivity, and the Peavey has over 94dB/watt sensitivity. These two vented systems are both supplied with 2nd order highpass filters, so that maximum cone movement below and above tuning is exactly the same, which will of course turn out to be right around the tuning frequency of the system.. it ends up being 21Hz for the Dayton and 37Hz for the Peavey. With the two systems described above, the Peavey is given power until Xmax (9.6 mm) is reached, which ended up being an overall SPL of 123 dB. The Dayton is given power until it's able to achieve the same SPL (theoretically ;)) as the Peavey system (123 dB) above the lower frequencies.. which ends up being 2100 watts to the Dayton and only 765 watts to the Peavey. With that, this is what we get. The Dayton DVC is red, the Peavey Low Rider is blue. The plot goes from 0-30 mm, at which point the Dayton goes off the chart..

You've shown that the higher efficiency driver needs less electrical power to produce the same acoustic power... I think we are on the same page!

With regards to cone movement vs SPL, I feel you are confusing the issue with extraneous issues like enclosure alignment.

Cone movement is not inconsequential - without cone movement, there is no sound. Two drivers of equal radiating area, mounted in an infinite baffle test-rig, must displace the same volume of air to reach the same SPL for a given test tone. Their cones must move the same amount, regardless of how much power that takes. The driver with higher efficiency requires less electrical power to do this, but both drivers must move their cones the same amount.

When you include enclosure alignments, this may get confusing, as different alignments will have different efficiencies again. For example, if you consider 2 identical 12" subwoofer drivers - one in a sealed enclosure, one horn loaded - within the range of the horn system that driver will have to move less to produce the same SPL. But this is because it is coupled to the air more effectively.
 
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Regarding midwoofer diameter, for those of you interested, I have learned something more.

While browsing Mr. Linkwitz' site (link at bottom) I learned of something called Doppler distortion. I have heard of the Doppler effect, but hadn't considered how it would apply to loudspeakers.

The Doppler effect is essentially a shift in phase and frequency resulting from relative motion between a sound source and its audience. For example, a church bell is ringing at the side of the road. As you approach in your car you hear a tone which is higher than actual. As you pass the bell, the sound drops in pitch. As you move away, you hear a tone which is lower than actual.

Doppler distortion in loudspeakers is fairly straight forward. Imagine two tones are played simultaneously on a single driver. The first is low, the second is high. As the cone of the driver has to move in and out to produce the low tone, it also has to move in and out at a higher rate to produce the high tone. Effectively, the high tone can be thought of as being produced by an audio source which is constantly moving farther away and closer to the audience! This modulates (frequency modulation in fact) the 2nd tone.

Though this is something new to me, it is somewhat intuitive. We have all heard this - a small 5" driver in the door of a car is being pushed to its limits playing something with lots of fast low end like dance music, when suddenly a known smooth sound like a piano or a female vocalist starts to play - and this second tone is noticeably distorted with every kick of the bass drum.

Getting back to the problem of deciding upon a diameter for a midwoofer - a larger midwoofer has to move its larger cone less for a given SPL. Which gets back to what we were just talking about above. If the cone is moving less, this type of distortion is lowered.

So there is a point for a larger midwoofer!

http://www.linkwitzlab.com/frontiers.htm
 
J.R.Freeman said:
We have all heard this - a small 5" driver in the door of a car is being pushed to its limits playing something with lots of fast low end like dance music, when suddenly a known smooth sound like a piano or a female vocalist starts to play - and this second tone is noticeably distorted with every kick of the bass drum.

doppler distorsion...or InterModulationDistorsion?


:)
 
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AndrewT said:
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
 
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/showthread.php?s=&postid=1588608#post1588608
 
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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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