Pioneer B20FU20-51FW Project. Help Please. - diyAudio
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Old 9th July 2007, 02:33 AM   #1
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Default Pioneer B20FU20-51FW Project. Help Please.

Hello all.

I am planning to build a simple speaker setup to replace my current setup. It must be inexpensive, it must be 'dog proof', and of course it must sound good. I have settled on Godzilla's B20/Piezo design for several reasons. It is relatively simple, inexpensive, and according to this forum sounds nice.

Currently I have two modified Radio Shack LX-5 bookshelf speakers with the Lineaum tweeters. The crossovers were rebuilt from scratch with plans off of net and they sound pretty good but they have their problems too. They are bookshelf and I need floor standing, I removed the protective tweeter housing and now we have a 70-lb Labrador whose tail is at the right height to whack them atop their cinder block stands (very nice stands heh). They will be used in a safer location after the new ones are built. My sub is a push-pull T-Line with a small wooden box with a cardboard tube out of the top. I made it with what was on hand and that happened to be two 6.5" Klipsch subs from a blown computer speaker setup. It is roughly based on this design.

Everything is powered with a Pioneer VSX-26TX receiver that was given to me because it did not work. I pulled out the bad DSP card and now it functions as a 4x100 watt receiver without any tone or other controls.

Now to the new speakers:

The attached picture (not to scale, it's a sketch but pretty close) shows where they will live, in place of the LX-5's. My biggest question is since they are in a corner and there are curtains behind one of them, should I go with a rear firing or forward firing piezo?

The box will be made with dimensional lumber based on Godzilla's designs. Either a ~3.0^3ft box ported or a ~1.3^3ft sealed box. I really want to try the ported box and was thinking about having the port centered on top of the box (what do you think) with a dimension of 10.75 x 11.25 x 58.0". If that is not suggested I will go with his sealed design which is 42H x 9.75W x 5.5D inner dimensions. Actually I may lean toward that design for space considerations but I would like the ported for lower bass extension... too many choices.

I may build these without a tweeter and add it later on, this project will be on a budget.

I plan to build the boxes by gluing dimensional lumber with those 90-deg clamps then nailing with thin, long brads.

Please help with comments!
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Old 9th July 2007, 07:32 AM   #2
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The 58in tall cabinet is actually an MLTL, not a reflex cabinet, so the vent really does need to be as close to the floor as possible -putting it on the top of the cabinet will mess the response up something chronic. The driver-centre is best positioned ~23.5in down from the internal top BTW for the smoothest response.

Out of interest, what's worrying you about having the slot vent at the bottom of the front or rear panel? They're very unobtrusive & you get the benefit of coupling to the floor efectively.

If you really can't put the vent there, I'd go for the sealed box. Doesn't have as much LF gain, but it does have a nice clean response.
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Old 9th July 2007, 02:33 PM   #3
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You can put the port on the rear too.
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Old 10th July 2007, 04:09 AM   #4
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Scottmoose: Thanks for clarifying that it isn't a bass reflex design. I can put the port on the bottom.

Godzilla: Hey, thanks for that idea too and thanks for all your work with this driver!

What do you think about piezo placement? I know that people have said it sounds better in the rear but what about in a corner such as this?

I am contemplating either MDF or plywood if I go for the 3 cubic foot box because of the cost. I looked at Home Depot today and once you go past 4' lengths of large dimensional lumber the cost goes up rather quickly. I will check at an actual lumber store soon.

Thanks for the info so far!
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Old 10th July 2007, 07:34 AM   #5
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You're welcome! A rearward firing tweeter should be fine in a corner.

I'd use ply for the construction -much stiffer & less energy-storage problems than MDF. However, if you want to use MDF, I'd advise that you either a) laminate 1/2in to 3/4in material, so you have a 1 1/4in thick board, or b) stick with 3/4in material, but laminate 1/4in concrete board to the inside, which will have the same effect. Bob Brines does the latter, to good effect I understand. Doing either of these things should push panel resonance below the cabinet's passband of operation. A third alternative that's sometimes used is to use 3/4in MDF with 1/4in ply laminated to it.

Remember to brace the cabinet well internally. Ladder braces should be OK horizontally across the box, but a very useful trick is to take a piece of ply / whatever, cut in a swiss-cheese fashion (so it's about 50% air), and brace the rear of the driver-magnet against the rear-panel. It has quite a dramatic effect at killing resonances in the driver-frame & on box-noise.
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Old 13th July 2007, 06:33 AM   #6
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Just to be clear on the crossover for the piezo.

To choose the value for the capacitor I have estimated that others are affixing a value for the load by adding a resistor (assuming non-inductive) in parallel across the terminals of the piezo. So if I chose an 8-Ohm resistor, I would calculate the capacitor for an 8-Ohm load. I also assume we want the tweeter to come in over 10-kHz. It looks to me that we are choosing a capacitor at its -12dB point. So if I wanted the -12dB point at say 10kHz then I would simply look up the value for its -6dB @ 8-Ohms at one octave higher than 10kHz (being 20kHz) and have a capacitor value of 0.99uF, or to round off, 1.0uF.

Is this about right?
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Old 13th July 2007, 02:09 PM   #7
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http://www.zillaspeak.com/piezo.asp

http://www.zillaspeak.com/Crossover.asp

Maybe the above might be helpful.

To me, when facing the piezo forwards an 8 ohm resistor and a cap between .33uf and 1uf sounds best. I think i settled on .47uf actually but it's personal taste.

For rear mounting i settled on a 20 ohm resistor and a 1uf cap but i also use an Lpad to dial in to taste when mounted on the rear.
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Old 13th July 2007, 02:23 PM   #8
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Hmmm, looks like I was a little tired last night when I posted.

Nevermind about the -12dB / -6dB part. For some reason I was thinking that the crossover point was -6dB instead of one octave below that.

The crossover point is actually -3dB isn't it, for Butterworth anyways?

I'll try to get some sleep before posting :/
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Old 18th July 2007, 07:58 PM   #9
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Default yup.

I am thinking of trying this design for some "rock and roll" full range speakers. It will be based on a mltl cabinet (from a 1950s radio) basically, I stuck a pair of these drivers into the old radio cabinet, and it is awesome. the tweeters are the old alnico paper cone jobbies that were in there, with a .68 mfd cap. it is floor loaded, does mega bass

I will be basically copying this design, (with several updates, bracings, and solid wood front panel/BB ply for the rest), and using them as rock and roll speakers, as opposed to a fostex based solution, which is rather analytic sounding for dirty butt/bass rock most of the time.

this driver is hard to beat for tone and ease of setup, etc. really, the fostex stuff is fine, but one must properly consider everything, and then wait, before tone arrives. .

Ill keep slowly updating this topic, over the next few weeks.

Clark
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Old 18th July 2007, 08:46 PM   #10
gychang is offline gychang  United States
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Default Re: yup.

Quote:
Originally posted by blumenco
I am thinking of trying this design for some "rock and roll" full range speakers. It will be based on a mltl cabinet (from a 1950s radio) basically, I stuck a pair of these drivers into the old radio cabinet, and it is awesome. the tweeters are the old alnico paper cone jobbies that were in there, with a .68 mfd cap. it is floor loaded, does mega bass

I will be basically copying this design, (with several updates, bracings, and solid wood front panel/BB ply for the rest), and using them as rock and roll speakers, as opposed to a fostex based solution, which is rather analytic sounding for dirty butt/bass rock most of the time.

this driver is hard to beat for tone and ease of setup, etc. really, the fostex stuff is fine, but one must properly consider everything, and then wait, before tone arrives. .

Ill keep slowly updating this topic, over the next few weeks.

Clark

any chance of pics? gychang
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