# 12s vs 15s

zhalverson
Copper - Posts: 180
Joined: January 21, 2005
Location: United States
Posted: May 12, 2006 at 11:34 PM / IP Logged

I have taken the required physics for my mechanical engineering degree and half understand the physics involved and COULD understand the rest if I wanted to reference to some other material but the point is that info isn't really useful or relavant to a guy asking "12's or 15's?" IMO.    I think there is more useful information for this question than that I guess.  One thing I've learned though, I could be wrong.  I think I should have just emphasized kfr01's first post...

Steven Kephart
Platinum - Posts: 1,737
Joined: November 06, 2003
Location: Oregon, United States
Posted: May 13, 2006 at 4:58 AM / IP Logged

b_sharp wrote:
 12" or 15" ?? A Node is no motion at the circle edge of the speaker. An Anti-Node is motion at the speaker center. The dominant sinewave is between nodes. So the speaker diameter is it's dominant halfwave. 15 inch dia. speaker = half wavelength. 15 x 2 = 30 inch wavelength. Speed of sound = 1130 ft/s. Frequency = 1130 ft/sec (sound speed) x 1/30 inch x 12 inch/ft. = cyc/sec = 452 Hz. 12inch = 565 Hz. Human ear range 20hz to 20khz. 15" diameter = 452 Hz = musical note A4 12" diameter = 565 Hz = musical note C#5 4 notes difference. 15" over 12" gives 4 music tones better which is hardly a minor scale difference. Minimal. You want at least an octave increase which is a doubling of the speaker diameter. 12" to 24" dia speaker is great. 12" to 15" dia speaker is minimal benefit. ... in music fidelity terms. :-)

So you are comparing speakers based on their upper frequency limits due to cone modes?  I don't think that is very helpful considering the inductance and/or moving mass of the driver will more than likely dominate the upper extention of the driver.  Or am I misunderstanding your point?

kfr01
Gold - Posts: 2,121
Joined: April 30, 2003
Posted: May 13, 2006 at 8:57 AM / IP Logged
I share Steven's questions.
Considering the fact that 12 or 15" bass drivers will be almost always be crossed over at 100hz or lower in an auto application, I would love to know whether or not b_sharp's analysis remains at all applicable...?
New Project: 2003 Pathfinder
haemphyst
Platinum - Posts: 5,052
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: May 13, 2006 at 10:14 AM / IP Logged
Nope. The dominant halfwave he referrs to is the "beaming frequency", and as kfr01 pointed out, the drivers are functioning in bands (at a minimum) two octaves below that.
I was confused by his post as well, and I understood it! And while accurate, it had no bearing on this particular thread. ANY diaphragm will produce ANY frequency demanded by the input, just as the diaphragm gets smaller it will have reduced efficiency as the frequency goes down... while this holds true for large radiators as well, the effective lowest frequency goes up, as the radiator gets smaller.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice.﻿ You should write it down."
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