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Mark_A_W
Joined: 15 Mar 2006
Posts: 3068
Location: Sunny Melbourne Australia
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| Posted: Fri Mar 27, 2009 10:00 pm Post subject: |
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[quote="ecrabb"] | Mark_A_W wrote: |
Arrgghhh.... Here we go again. When people talk about "fast" bass, they're referring to transient response - or impulse response. You seem to think transient response doesn't exist. If so, you're wrong. It actually does - just not for the reason most people think.
Transient response is real. It's a direct function of voice coil inductance, and it absolutely impacts the sound of a sub. So, if "fast" represents good transient response and "slow" represents poor transient response, then subs can indeed be fast or slow. It has nothing to do with enclosure type, of course. If you'd like, I can probably dig up a white paper or two on the subject.
SC |
Please do so.
Yes, the voicecoil inductances affects the frequency response. Lower inductance = higher frequency response.
Higher frequency response = a tweeter.
Please show me that transient response is INDEPENDENT of the frequency response.
Lower system Q (a way of describing both frequency response shape and the associated damping)= more damped = "tighter" bass.
A high Q, with a bump, causes increased group delay, along with the amplitude rise = one note bass, literally delayed in time.
Read the Adire white papers carefully.
http://www.diycable.com/main/pdf/WooferSpeed.pdf
Fast bass = treble.
And I stand by my comment. Suitability for your environment does not change the fact that an IB sub is the best (and the simplest).
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ecrabb
Forum Moderator
Joined: 13 Mar 2006
Posts: 15909
Location: Utah
TV/Projector: JVC RS40, Epson 5010
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| Posted: Fri Mar 27, 2009 10:25 pm Post subject: |
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Thanks for finding that - that's exactly the paper I was thinking of.
| Mark_A_W wrote: | | Yes, the voicecoil inductances affects the frequency response. Lower inductance = higher frequency response. Higher frequency response = a tweeter. Please show me that transient response is INDEPENDENT of the frequency response. |
Who said they were INDEPENDENT? But, that doesn't mean they're inextricably and proportionally linked, either!
Can't a driver oscillate at 20hz, but have faster or slower transient response depending on the inductance of the voice coil? If frequency response, transient response, and voice coil inductance are proportionally linked, why does the Adire paper summarize by specifically saying you should know a bass driver's voice coil inductance? If it was all about frequency response, inductance wouldn't even be important, would it?
Take a 20hz square wave... To faithfully reproduce that signal with the minimum distortion, you need both low frequency response AND transient response. The ability of the driver to accelerate from a neutral position to the end of its excursion in a given amount of time is transient response...
| Mark_A_W wrote: | | And I stand by my comment. Suitability for your environment does not change the fact that an IB sub is the best (and the simplest). |
So, a Ferrari is simply the best car, regardless of whether you need it to race on Sundays or drive it all week doing HVAC installation?
SC
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garyfritz
Joined: 08 Apr 2006
Posts: 12088
Location: Fort Collins, CO
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| Posted: Fri Mar 27, 2009 10:56 pm Post subject: |
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Steve, I think I gotta agree with Mark on this one. Rapid transients are not bass; rapid transients represent high-frequency information. As Mark said, fast bass (rapid transitions) = treble.
In your example of the square wave, it's not a simple 20Hz signal. It's a combination of a 20Hz sine wave (fundamental), and a 60Hz sine wave (3rd harmonic), and a 100Hz sine wave (5th harmonic), and.... The sine waves decrease in intensity as you go up, but those high-freq components are what makes the rapid transient. See e.g. this page for an example of approximating a square wave with the 1st+3rd+5th+7th+9th harmonics. The more odd harmonics you add, the closer you approach an ideal square wave.
If you wanted to play a 20Hz square wave, the subwoofer SHOULD NOT be playing all harmonics of that 20Hz fundamental. It should play the 20Hz sine wave, and maybe some of the 60Hz, and that's about it. And a 20Hz sine wave has *gradual* transitions. If it didn't, it wouldn't be a 20Hz tone. It would be a mixture of a 20Hz tone and some higher-order harmonics, and the non-20Hz-sine components are high-freq components that should be played by the mid/high speakers, not the sub.
I think, anyway.  It seems strange to spread the different harmonics across several speakers, but that's really what you're doing with the audio signal you normally feed through your speakers. I don't think a square wave is fundamentally any different.
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greg_mitch
Joined: 03 May 2006
Posts: 5320
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| Posted: Fri Mar 27, 2009 11:20 pm Post subject: |
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Oh no!!! MATLAB!!! Everyone hide!!!
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Mark_A_W
Joined: 15 Mar 2006
Posts: 3068
Location: Sunny Melbourne Australia
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| Posted: Sat Mar 28, 2009 2:04 am Post subject: |
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| ecrabb wrote: |
Take a 20hz square wave... To faithfully reproduce that signal with the minimum distortion, you need both low frequency response AND transient response. The ability of the driver to accelerate from a neutral position to the end of its excursion in a given amount of time is transient response...
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The ability of the driver to accelerate from a neutral position to the end of its excursion in a given amount of time is AMPLITUDE (SPL) .
Enough Steve, please. We are derailing this thread completely.
I'll concede that an IB is only the best (no box in room (smallest)/deepest/loudest/tightest/ok, FASTEST in the common usage), IF it is suitable for installation.
As for the other argument, it's esoteric and pointless.
If you have to build a box, I'd build:
1. Big sealed bugger with 15" woofers.
2. Ported box with a response mimicing a sealed box, just with a lower response.
And they must be designed with *at least* a room curve added, and paying attention to the group delay. It's been a while, but UNIBOX (free, excel spreadsheet file) can do this. WinISD (unless they improved it a lot) is too simplistic, good only for quick and dirty driver comparisons.
Mark
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David_Web
Joined: 02 May 2007
Posts: 418
Location: Sweden
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| Posted: Sat Mar 28, 2009 10:06 am Post subject: |
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There IS such s thing as fast and slow bass.
For some woofers it takes several cycles to get up to SPL. And usually quite a few to stop again. (many small 'high power' woofers are like this, not to mention that they fail the golden 40ms threshold at LF.)
The rise and fall times are SLOW. Is that so hard to understand?
Most subs out there are like this. They depend on this technique to get any usable SPL at all by any form of resonator. Like a vent or PR.
Sealed box has this as well when approaching box resonance and thus get a SPL boost at resonance as well (with added excursion).
So FAST bass is when is starts and stops without it taking several cycles. Thus more faithfully reproduce the signal.
There are many factors that play in but LE is usually the worst. Then of course the cabinet as well.
(mms can always be compensated by motor strength)
High Q is a problem as well. But that is usually determined by how tight the user wants the sound. Some prefer a fatter bass.
If you want to design a cabinet. Use Hornresp. Yes it's for horns but a sealed box or vented is just a very short horn. You also get to see directivity. And a lot more.
_________________
SNR of people are ridiculously low.
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Spanky Ham
Joined: 22 Mar 2006
Posts: 5643
Location: Comedy Central
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| Posted: Sat Mar 28, 2009 9:31 pm Post subject: |
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Hmmmmmm, semi-off topic! I guess it is CRT related in that they both have magnets. 
I have only glanced at the thread, but I agree that if you have the ability to make it work then IB is probably the best route. I have also heard a DIY LLT and if you can't go IB then this another option that has a good price/performance ratio.
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stgdz
Joined: 07 Dec 2008
Posts: 107
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