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

[davidallancole]

Radio Shack 40-1024
http://support.radioshack.com/support_audio/doc15/15880.htm

Radio Shack 40-1271
http://diyaudioprojects.com/Drivers/40-1271/40-1271.htm

Hi guys (and gals),

You may have remember me posting things about me building speakers using these drivers previously, but I am hoping to find a setup suitable for them with a little help.

I like the idea of an OB along the lines of what Scottmoose has mentioned in this thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=104729

But I thought my room may be better suited to running the subs in sealed boxes and putting the "fullrangers" into aperiodic boxes.

Anybody with more knowledge have some suggestions?

I plan on using a bi-amp setup. I haven't built the amps or crossover yet, so that is all variable. I planned on using LM3886 for the subs (have two subs per speaker, thus 4 subs and 2 fullrangers for a stereo set) and LM1875 for the fullrangers. Then I can add an active crossover.

I have attached the layout of my livingroom.

 

[gmilitano]

I never tried the 40-1271 in an aperiodic enclosure, but given the ultra high Q, you will not want much vent resistance.

Open baffle they worked pretty good.

The 40-1024 won't go too low in a sealed enclosure. Below is a very quick sim for the 1024 using ISD online. Perhaps someone could comment on how much room gain you could expect.

 

[davidallancole]

I have been using them in Open Baffle for the last little while and I like them. I have the two subs close to the floor and the fullranger around ear level. The main baffle is 12 inches and the wings are 12 inches and 13 inches. They sound all right but are nothing special. That could be because they are cheap speakers. I can only keep them ~1-2 feet away from the wall.

Right now the speakers are all run in parallel. The subs, you can clearly hear voice out of, so maybe it will be cleaner sounding if I use a seperate amp and crossover for the subs.

I should say the kind of music I listen to as well. Its metal, punk, but I also like things like the Slackers which is basically and R&B band I guess, with horns and clean guitars and what not.

 

[GM]

You may have remember me posting things about me building speakers using these drivers previously, but I am hoping to find a setup suitable for them with a little help.

But I thought my room may be better suited to running the subs in sealed boxes and putting the "fullrangers" into aperiodic boxes.

Anybody with more knowledge have some suggestions?

Greets!

Not really , but I don't get to browse as much as I once did . Anyway, to truly aperiodically damp this driver requires a ~141"^2 x 96" long end loaded pipe stuffed with ~1.5 lbs/ft^3 of polyfil. Shorten the pipe and its CSA must rise to maintain the same total amount of stuffing. Considering the diaphragm's construction though, it may sound very smooth, yet dull/lifeless/excessively compressed, so a folded open baffle seems a better choice overall. Only one way to know for sure though.

WRT the 40-1024, I'm in the build for max gain BW and roll it off as required if need be 'camp', so considering it has enough excursion to tune it low, a ~3.75 ft^3/20 Hz MLTL gets my vote and a worst case scenario is you wind up plugging the vent for a ~critically damped sealed alignment.

GM

 

[GM]

Right now the speakers are all run in parallel. The subs, you can clearly hear voice out of, so maybe it will be cleaner sounding if I use a seperate amp and crossover for the subs.

Greets, part deux!

Well, the MLTL cab could be configured to get the sub drivers up near the mains so that they don't sound 'phasey'/disconnected, though bi-amping with steep slopes is still a good plan.

GM

 

[davidallancole]

Thanks for the responses guys. I am getting the opinion that I should leave these in open baffle form. At the bottom is attached the proposed drawing of what I want to build.

I am not sure what I should do exactly for the croosover point with the subs. If I build the main baffle 15 inches wide (using the chart from http://melhuish.org/audio/baffle.html), I should have a roll of at around 200 Hz? Would I then build a crossover to cross at 200 Hz for the sub? Would it be 12, 24, 48 db/octave? or can I cross lower or should the crossover point actually be higher than 200 Hz?

Thanks for your help everyone.

 

[gmilitano]

...
They sound all right but are nothing special. That could be because they are cheap speakers. I can only keep them ~1-2 feet away from the wall. ...

I should say the kind of music I listen to as well. Its metal, punk, but I also like things like the Slackers which is basically and R&B band I guess, with horns and clean guitars and what not.

That is pretty much the conclusion I came to, they are ok. I never got a chance to mod the drivers, but perhaps that could add quite a bit. For hard music like that, you will likely want to keep the bass notes away.

OB with the LF driver, you should be able to get a pretty good system. Like GM said, keep the drivers close. As for the XO, if you have an adjustable active, you could try different values and slopes till you find a combo that works well.

 

[Geoff H]

Hi David, your plan is very similar to something I have just thrown together.

If you have access to a second amp, use that to drive the bass. Bass control to near max. Quick and dirty way to hear results. I discovered the sensitivities at the desired crossover were very similar, so I could try a passive xo.

My preference is to crossover at about 100Hz. I find that provides the sound of a single driver. Using a series type xo, I broke a few rules. The bass (4 ohm 6x9, fs 50Hz) is shunted with a 470 mf bipolar elect. and the wide range (8 ohm 6") is shunted with the 8.5 v tap on a 30VA transformer.

Like I said, quick n dirty, but it works. I was planning a 20w/60w bi-amp. It only needs a few db compensation from 40-70 hz.

Geoff.

 

[davidallancole]

Thanks guys.

When you are saying keep the drivers close, are you reffering to the just the subs, or are you saying keep the subs close to the fullranger, like in the following picture.

 

[gmilitano]

You will want to keep them close to the fullrange unit.

 

[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/showthread.php?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]

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?