Speaker Rebuild - Radio Shack 40-1271 and 40-1024

[davidallancole]

Thanks gmilitano.

I did not realize this. I understood keeping the subs close together so the distance between the centers is less then 1/2 wavelength at the highest frequency to eliminate any notches in the sound, but not close to the fullranger.

Is this to keep the point source as close together as possible?

[GM]

Greets!

Don't believe everything you read. Remember, the ideal is for the entire reproduction to emanate from a single point source, so the closer the better. In our acute hearing BW it's <1/4 WL, with ~1/3 WL being considered the max, but there are exceptions to the rule, such as if you're far enough away for them to sum or outside our acute hearing BW among others. Indeed, super tweeters are typically many WLs away and sound fine if capped off high enough. Then of course there's D'Appolito and other layouts to create a specific polar response at the expense of one or more performance parameters.

In your case though, unless you use a fairly wide baffle and/or XO steep slope, which has its own trade-offs, the XO point has to be high enough that spacing gets a bit cramped and all things considered, I recommend mounting the woofers side by side to get them close enough. This has the added advantage of narrowing up their horizontal response and widening their vertical to overlap the 1271 more uniformly. With a ~8" acoustic center spacing, a lower order XO can be used to boot. The downside is you lose floor loading and increase the floor bounce, but with two woofers combined with your listening distance it seems a more than fair trade-off.

GM

[davidallancole]

Sorry, time for some ASCII art.

Are you referring to a setup like this GM:

______________
|~~~~~~~~~~~~|
|~~~~~ O ~~~~~| <Fullranger
|~~~~ O O~~~~ | <Subs
|~~~~~~~~~~~~|
------------------------
(Meant to represent a baffle with 3 speaker)

Also, apart from what we are talking about, what do you guys think about this with replacing the bottom speaker with the 40-1024 sub instead of the 40-1271?

http://www.diyaudio.com/forums/showt...?postid=199004

[GM]

Greets!

Yes, butt them right up against each other. IOW, mount the woofers at the extreme top of the cab and the FR at the extreme bottom of the baffle. Note that 'gapping' (spacing up) the baffle is a tuning tweak.

Huh?! You mean use 1271s in lieu of the 1024s? In a dipole? It's fine if you want a system that rolls off this high.

GM

[davidallancole]

Sorry to keep going over this, but I am trying to figure out exactly what you are saying. From what you said in the last post, is the attached picture of the baffle with the speaker placement correct?

Thank you for your patience.

edit: Just got to thinking, are you talking about the 40-1024 being in a box with the baffle attached to the top of the box? I am thinking about the fullranger and subs all being on an open baffle, running everything open baffle.

[davidallancole]

Here is a picture showing what I am refering to with the dipole arangment.

[gmilitano]

Originally posted by davidallancole
Sorry to keep going over this, but I am trying to figure out exactly what you are saying. From what you said in the last post, is the attached picture of the baffle with the speaker placement correct?

I think what GM is referring to something like this.

[GM]

Greets!

Correctomundo, except with the two woofers butted right up against each other. If they're all on a common OB though, Then jam the 1271 down against the two 1024s. Thanks for the sketches, maybe one of these days they'll release a free/cheap/intuitive/quick CAD program for us old farts that have neither the time/patience to deal with a computer geek's idea of how one should work.

GM

[davidallancole]

Hi guys,

Thanks for the info. I have attached a drawing of my new proposed ob. Its 2 feet tall to keep all the speakers close to the ground and will have a tilt backwards so the speakers are pointing up at an angle a bit.

Do you think this would work? I like the looks of it, and so does the girlfriend. They would be smaller than my current baffles.

P.S. I heared a gun shot from a movie last night that was supposed to be up close to the actor, and damn did it ever sound real on my ob. Live and totally dynamic.

[gmilitano]

While I realize that is not to scale, it does not look like the woofers will get much of an enclosure. Were you planning to put the woofers in a ported enclosure and run the full range open baffle?