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thechronic 
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That's probably only 5 inches... too small!
8 inches is the minimum, that's around 20 centimeters
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21-04-2005 21:30 |
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dirk
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Registration Date: 14-11-2004
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| They don't have to be fast to transmit high frequencies, but they have to be fast to track the low frequencies accurately. If they are slow the waveforms are distorted, a sine wave will become more like a saw. With smaller speakers in an array they respond quicker to the changes in the waveform, ie they follow the bass frequencies closer, result: better sound and lower distortion. With 12" woofers you can get results of like 0.05% THD distortion at full power, which results in a pretty damn good sound. |
Unfortunately, I think that is complete nonsence .
A sine transforms into a saw because of the high sound preasure levels Pa systems produce . The speed of sound is proportionate to the densety of the material it travels through. More densety more speed. With very high spl's there is a big enough difference in air densety in the soundwaves for sines to transform into saw's. ( you also need enough distance for this to happen )
The slowness of big woofers has nothing to do with it . Infact to reproduce a saw instead of a sine the speakers has to be able to reproduce higher frequencies and big speakers simply can't do that.
I do agree of cause that a speaker should reproduce the input signal as acurate as posible ( until we can't hear its flaw's anymore ) But why then recomend a speaker with resonance ports like the Genelec's, they certainly can't track the input .
A closed speaker system will outpreform a speaker system with resonance port in acuracy of sound reproduction 9 out of 10.You won't see that in the frequency responce or THD figure because that is measured with sinewaves . But if you use e.g. pulsewaves and then look at the distortion, different numbers will apear.
Closed box 5% Distortion Reflex box 0.05% Distortion measured with sinewaves .
Now measure with pulses : Closed box 15% Distortion Reflex box 100% Distortion or more !!!!!
This is why you don't see phase responce figures of loudspeakers.
And lots of sound/mastering engeneers think that the phase responce of a speakercable/interconnectcable is much more important.
Now if I hear you say again that you think a speaker with resonance port is the way to go I will forever doubt your sanity ( just kidding )[/offtopic]
The VT4889 fullrange speaker has 2x15" woofers for lower frequency's, didn't you know that ?
The 15" Jbl speaker has 90dB sencetivety , 126dB max Spl and 22-125Hz range.The 18" Jbl speaker has 98dB sencetivety , 138dB max Spl and 28-75Hz range.
So for the same spl you need two 15"speaker and one 18"speaker .
You don't need the extra octave of the 15" because both these systems are filtered with high order filters at 60-80Hz .
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The Genelec 7073a uses a 4x12: 19-85Hz - 124dBSPL - THD 0.05%.
Yes you read that correctly: down to 19Hz with only 0.05% distortion at a bone crunching 124dB at 1m distance!!!! try that with a 21" |
A 18" closed tractrix horn can do that and will have much better phase responce than the Genelec or any other speaker system with resonance port.
I recomended two 18"closed sub horns per side for a diy P.A. system and I stand by what I said the full 100 %
Greetings Dirk
P.S.
This is how you can make a speakersystem that has a good chance of reproducing the input signal
A closed box behaves like a second order highpass filter and therefore has 180 degree phaseshift at its resonance frequency . To acurately reproduce the input signal you have to compensate for this phaseshift and a second order allpass filter before the amp can do this.
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21-04-2005 22:02 |
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dirk
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The JBL subs mentioned are designed for different types of line array systems.
The 15" is for the big stadion/outdoor events where they use 20 of those per side. There you don't need high sensetivety but low weight.
The 18" are for the smaler line array systems.
Greetings Dirk.
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26-04-2005 09:29 |
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thechronic
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You read too much theory lol 
In theory closed box (='infinite baffle') speakers are better, but they tend to have a big drop in performance. Reaching high sound levels with an infinite baffle design seems pretty much impossible, especially in the low end, or you would need a huge cabinet to get the required amount of air . Ofcourse putting 15" speakers in a 2 cubic meter cabinet would look ridiculous, so just for looks you'd have to go for the really big ones lol.
I am pretty much aware of all good speaker ranges but have never seen any pro manufacturer making non-ported speakers. If they were so much better every brand would have several models imo, instead of none at all.
Hifi brands might have them but hifi sucks 
BTW I'm really serious about the speed of the woofers. You're talking about high frequencies again. I'm talking about subs that get filtered signals below 75-125 Hz. Big woofers are good for slow sustained bass tones, but not for essential stuff like kick drums.
Really good powered subs have very soft rubber suspensions that improve the speed of the woofers but can tear if you drive them too hard. Also the amps involved would have very high damping factors to improve the control of the speaker movement.
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26-04-2005 13:33 |
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thechronic
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| quote: |
Originally posted by dirk
The VT4889 fullrange speaker has 2x15" woofers for lower frequency's, didn't you know that ?
The 15" Jbl speaker has 90dB sencetivety , 126dB max Spl and 22-125Hz range.The 18" Jbl speaker has 98dB sencetivety , 138dB max Spl and 28-75Hz range.
So for the same spl you need two 15"speaker and one 18"speaker .
You don't need the extra octave of the 15" because both these systems are filtered with high order filters at 60-80Hz .
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So you would filter these subs at 60-80 Hz, while they have a frequency response of 28-75Hz
That would leave you with either a narrow band of 60-75 Hz or nothing 
BTW the 18" model has 2 speakers too.
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Originally posted by dirk
The JBL subs mentioned are designed for different types of line array systems.
The 15" is for the big stadion/outdoor events where they use 20 of those per side. There you don't need high sensetivety but low weight.
The 18" are for the smaler line array systems.
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The difference in weight is 4kg
So with 20 of them you would gain a fantastic weight loss of 80 kg
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26-04-2005 13:56 |
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thechronic
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I spend too much time on forums 
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If you find spam on the site, please hit the button and select my name. I'll personally kick it to the murky depths of hell where it belongs!
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27-04-2005 04:24 |
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-KP-
Cool Producer
Registration Date: 01-04-2005
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is there anything on the web about building X-overs?
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17/03 : Somewhere in Borgerhout...
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13-05-2005 23:24 |
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