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How to Achieve Awesome Mid Bass.


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falconyellow 
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Posted: March 31, 2008 at 9:01 PM / IP Logged  
This is an awesome post, very informative.
Questions:
How far out of phase do the two speakers have to be before a difference becomes audible? I suppose that time arrival and phase differences would depend both on the frequency as well as the actual difference in path length?
I guess what I'm wondering, is how far off in path length can you get before the difference becomes audible (reflections excluded).
Also, can you use something like the phase plot in WinISD to determine where a mid bass/sub combo should be crossed over? Or does the install affect this too much?
Thanks for the great info!
Steven Kephart 
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Posted: March 31, 2008 at 11:10 PM / IP Logged  

falconyellow wrote:
This is an awesome post, very informative.
Questions:
How far out of phase do the two speakers have to be before a difference becomes audible? I suppose that time arrival and phase differences would depend both on the frequency as well as the actual difference in path length?
I guess what I'm wondering, is how far off in path length can you get before the difference becomes audible (reflections excluded).

About 3 miliseconds at around 1kHz and longer as you move up and down the frequency band.

thadrizzle 
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Joined: April 09, 2008
Location: Georgia, United States
Posted: April 09, 2008 at 10:43 PM / IP Logged  
Thank you, that is easily the most unasnwered question in car audio.  This to me is more important than BASS BASS BASS!!!! and I was deafining myselg with my highs.  Thanks again.
I love this stuff. Took me 34 years to find my calling but, I think this is it. I love pulling wires he! he!
jfinks 
Copper - Posts: 76
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Joined: May 31, 2007
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Posted: April 10, 2008 at 11:33 PM / IP Logged  

speakermakers wrote:
With a laptop and a multi meter it’s quick and simple to test Fs and Qts your self. This is what I do. If it looks like the printed specifications are pretty close to my results then I assume that the rest (less critical) are also accurate.
I have entertained the idea of posting a how to on this subject, but I think it might be a little out of range for most viewers of this site. Let me know if any of you are interested. I just would hate to put a lot of my time into something like that and not have anyone read it.

Um Please do! I have always favored the Dynaudio MW160's for mid bass. The Fs is 55 and QTs is .51 I tend to use very step (24 to 48dB) electronic cross-overs and run them higher than you are recomending 65Hz or 80Hz to around 200Hz. I prefer even order here vs odd order. Your information is great! If you are curious this is a link on the slow going processof system building I am currently in.

DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: April 14, 2008 at 10:22 AM / IP Logged  

jfinks wrote:
Um Please do! I have always favored the Dynaudio MW160's for mid bass. The Fs is 55 and QTs is .51 I tend to use very step (24 to 48dB) electronic cross-overs and run them higher than you are recomending 65Hz or 80Hz to around 200Hz. I prefer even order here vs odd order. Your information is great! If you are curious this is a link on the slow going processof system building I am currently in.

HERE's a good tutorial on measuring loudspeakers yourself.

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jfinks 
Copper - Posts: 76
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Posted: April 16, 2008 at 6:51 PM / IP Logged  

DYohn wrote:
HERE's a good tutorial on measuring loudspeakers yourself.

OoO you know how to get my interest....

Thanks DYohn

falconyellow 
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Location: Oregon, United States
Posted: April 17, 2008 at 12:39 AM / IP Logged  
So back to the midbass issue, if you have "rear fill" speakers playing in this same frequency range (or at least in the upper end of it) won't this potentially cause some major arrival time variations? I know some guys who like to delay the rear fill to give spaciousness, I'm guessing this can cause some bad cancellations at some frequencies?
Any takers? Or is this another topic in itself?
jmelton86 
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Joined: February 07, 2007
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Posted: April 17, 2008 at 12:43 AM / IP Logged  
I would think that having the rear fill delayed (exact OPPOSITE of what you want...) would cause some kind of cancellation.
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DYohn 
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Posted: April 17, 2008 at 12:27 PM / IP Logged  
Yes it's a topic unto itself but yes, any time you use multiple speakers to reproduce the same frequency ranges it can cause cancellation effects, but using time delay properly will allow yu to eliminate this effect.  If you'd like to discuss further, please start a new topic.
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speakermakers 
Copper - Posts: 231
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Posted: April 24, 2008 at 1:53 AM / IP Logged  
I am currently working on a manufacturer show system that employs a single 5” driver in the rear deck that plays from 100-2Khz. The driver is delayed by more than 20 ms and is attenuated in such a way that the sound being emitted from it appears to the listener as a reflection from a distant (nonexistent) wall. This gives the effect of a large listening area. More importantly it gives me control over the apparent size of the listening area.
After just a couple milliseconds of delay the human brain is capable of deciding that a sound is being emitted from a disconnected source. This helps both with the illusion of creating a false reflection and avoiding phase issues. If your brain is not attempting to triangulate a single position of a single sound because it assumes that the delayed sound is a second though related entity then frequency becomes the dominant factor rather then phase.
Of coarse phase is still a factor. My approach is to attenuate the rear speaker to a convincing level (reflections are much lower in level then the source). Secondly I align the phase of the rear speaker to match the phase of the midbasses up front at the hi pass crossover frequency. At a given frequency such as the corner of a hi pass crossover at 100hz the phase will cycle from 0-360 degrees as the delay increases and becomes equivalent to the physical size of that frequency wave. Phase will eventually revert back to zero (360x2=720. 0,360,720 and so on are all essentially phase coherent). Once you delay more than a few times the wave length your brain will decide that it is now hearing two different yet related sounds. As frequency rises phase becomes less and less of a factor.
I have also found that eliminating peaks in the lower response of both the front midbass drivers and the rear driver is critical. A sharp knee and rise in the lower end response of any speaker will kill your efforts to fool your brain into thinking that a sound is located elsewhere. So small sealed enclosures are out. A well damped enclosure is key. In a car that usually means an infinite baffle configuration with dynasorb type materials behind the drivers. Alternatively aperiodic vented enclosures can work quite well.
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