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speaker build, should drivers be off center


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DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: February 19, 2006 at 12:45 PM / IP Logged  

:)  The third harmonic is simply 3X the fundamental.  If your baffle is 7" wide, the fundamental is 1937Hz, so 3rd harmonic would be 5811Hz.  You might hear that as a shrillness or sharp sound that is present no matter what is playing.  IMO if you use a round-over on the edges of at least 1/2" you will minimize the effect as much as offsetting would probably do on that narrow a baffle.  Also, with a 4" and 5" OD, you will offset the center about 1/2", which is 1/2 the diameter of your soft dome.  From what I recall from the few cases where I actually read anything definitive, you want the offset to be at least 1X the OD of the dome... but don't quote me on that.  Oh yes, I remember your black and red design.  Looks great, and I like that offset.  I built a CC similar to yours, except I front ported the woofers under the tweeter. 

BTW, a 7" baffle might cause you some grief with baffle step losses.  Your baffle step will occur around 600Hz (meaning you will lose somewhere between 3-6db of all information below 600Hz) unless you push the speakers all the way against a wall, or include a BSC circuit.  I hate the Xover complexity introduced by BSC, actually, so I always try to increase bass output using porting or by attenuating the tweet so it is a little less efficient than the mid/woof so as to compensate.  Or by using EQ on the channel...

I think you might notice the results of flush mounting your tweeters and surface mounting the woofers (which will help with time alignment by pushing the tweet "back" in relation to the other drivers) a lot more than you would ever notice the possible edge diffraction.  Hell, align the centers and use a round over and be done with it!  speaker build, should drivers be off center - Page 2 -- posted image.

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Steven Kephart 
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Posted: February 19, 2006 at 1:18 PM / IP Logged  

Audio is a very complicated thing, being full of small nuances that can be measured and are often discussed in the DIY croud, as well as in books like Mr. Dickason's.  Unfortunately these topics seem to get blown way out of proportion in their importance like what has happened here.  I mean, to say that "A really well designed crossover is of no use if........[it] has drivers mounted equidistant from two or more edges."  is like saying that a bug smear at the bottom left of your windshield makes driving impossible.  If you are lucky enough to see it, is it really going to effect your driving that much?  That's one of my pet peeves about the Loudspeaker Design Cookbook is that it discusses quite a few of these ideas, but doesn't measure their importance or audibility.  I've been trying to talk Dan Wiggins into writing a similar book as he's so good at explaining the technical stuff so even the beginner can understand (something the LDC could use some help with). 

DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: February 19, 2006 at 1:35 PM / IP Logged  
I agree with you Steven, Rod goes too far.  The crossover is the heart of any loudspeaker system and can be as important if not more important than the drivers used.  Rod Elliot is a genius and I love him but like all geniuses, he can get lost in his own esoterica.  In my opinion things like driver alignment are secondary to system electrical design, but once the electrical design is complete, why not deal with the more esoteric and exotic minor issues?  speaker build, should drivers be off center - Page 2 -- posted image.  Tell Dan I'll edit his book for him.
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Steven Kephart 
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Posted: February 19, 2006 at 2:49 PM / IP Logged  

Oh, I totally agree.  Just as long as they know whether it is worth the cost (being time, money, or cosmetic in nature).  That's why I like to see an accurate description of how important these phenomenon are, to prevent people from taking it too far and getting into stuff like the speaker wire tripods, or jars of acoustic rocks.

Also, it will provide people with a better foundation to make better compromises in their design.  For instance, one popular topic in the DIY world is to use shallower crossover slopes to reduce phase changes (something else from the Cookbook).  But as Dan has argued in the past, this produces other much more audible problems that must be dealt with.  Especially since the phase issue the shallower slope is correcting for probably couldn't be heard unless you listen to sine waves on the system.

stevdart 
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Posted: February 20, 2006 at 8:44 AM / IP Logged  

item to scratch from my materials list:  jar of acoustic rocks...

All you gentlemen gave valuable feedback on this topic and now I have a much clearer perspective going forward.  speaker build, should drivers be off center - Page 2 -- posted image.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: February 20, 2006 at 12:03 PM / IP Logged  

Ah, and one last thing stevedart: make sure YOU are not off-center when you start cutting MDF!  speaker build, should drivers be off center - Page 2 -- posted image.

Oh, and those acoustic rocks must be cryo-treated then activated under a crystal pyramid during the spring equinox before they will work.

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kfr01 
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Posted: February 20, 2006 at 9:00 PM / IP Logged  

Looks like this was wrapped up prior to me getting back from home hunting land. 

Seller accepted our offer.  Close date April 28th!  Now we just need to clean + sell our condo. 

A basement room of 24'x13'   It isn't quite the right dimensions for a big HT room.  A little long and narrow.  But with the right treatments might make an O.K. listening room.  Important thing is that the wife likes the rest of the home.

p.s.   I would buy Dan's book in a heartbeat. 

New Project: 2003 Pathfinder
stevdart 
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Location: Pennsylvania, United States
Posted: February 21, 2006 at 11:40 AM / IP Logged  

Congrats on choosing a house!  It sounds like you've worked out the model for negotiations with your wife re: SAF from early on...so you should be good to go. 

My HT room is similar to yours, even a little narrower.  I found that working the sound system into it worked out well, sub is 1/3 across the end wall and under the TV, rear surrounds are 2/3 back and the last back surrounds-to-be will go in the rear corners.  It's the seating in such a narrow room that presents the challenge.  Do you furnish it like a theater, two rows in tiers, which is probably the easiest to do but limits the way you can use the room.....or do you find just the right size, style and mix of comfortable chairs so that they can either all face the screen or work as a social entertainment area?

My house has limited space so I have to use this room for all of the above.  When I moved the viewing toward the end wall, the traditional furniture pieces suddenly were the wrong size for the room.  Eventually, I'll do a furnishings makeover with slimmer individual chairs that can semi-recline, swivel and have headrests.  And maybe a lower futon-type comfy thing in the front for the kids.  A small bar-type arrangement with stools of the right height will probably occupy an area behind the main seating.  It'll take me a while but it'll get there eventually.

I'm in line for that book, too!

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
stevdart 
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Joined: January 24, 2004
Location: Pennsylvania, United States
Posted: February 23, 2006 at 9:47 AM / IP Logged  
kfr01, there is a link to those mid woofers after all.  They can be seen in that pic of the center channel that I linked above, and the parameters and response graphs are HERE.  Modeling this freq response into a crossover was troublesome due to the large dip and peak smack dab in the center of the range, but because I have listened to these speakers for several months already in the center channel (often with a music source), I've found that the actual response sounds smoother than the graph would lead you to believe.  It was just one of those things where you think, for $4 each how much can you lose by giving them a try?  I'm confident they'll work out in the mains as well as they did in the center.
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
DYohn 
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Moderator spaceThis member has made a donation to the12volt.com. Click here for more info.spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: April 22, 2003
Location: Arizona, United States
Posted: February 23, 2006 at 10:10 AM / IP Logged  
Steve, if you like those 4.5's then sure, use them.  But they have a pretty high fs and really small Vas.  Like I think I told you when you bought them, for the $4 buyout price, sure why not give them a try.  But I suggest you start a speaker replacement fund and when you're ready to replace them all with a much better performing speaker at the same frame size, try the WR125 from Creative Sound.  I think you'll be bowled over by the improvement, and yes IMO they are worth the price difference!  speaker build, should drivers be off center - Page 2 -- posted image.
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