The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

[BOBinGA]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

Hi Don,
I'm using ARTA with a calibrated EMM-6 microphone. I also have Soundeasy, but I haven't been able to get the mic calibration file to read correctly there. But I have used it as a double check and it gives the same results within the margin of the mic calibration.

To draw the XO schematic, I used Speakerworkshop since I was familiar with its XO section. And of course, the woofer sim was WinISD.

-Bob

[BOBinGA]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

All I've got tonight is the parts list. Like I said - everything but paint and wire:

Item Catalog No. Qty Price Extension

Tang Band W6-1139SIF 6-1/2" Paper Cone Subwoofer Speaker 264-919 1 $48.32 $ 48.32
Dayton Audio DS90-8 3" Designer Series Extended-Range Speaker 295-422 2 $16.37 $ 32.74
Dayton Audio ND16FA-6 5/8" Neodymium Dome Tweeter 275-025 2 $ 9.64 $ 19.28
Dayton Audio MCA2250E 2.1 Channel Class D Plate Amplifier 300-771 1 $98.80 $ 98.80
Jantzen 1.2mH 20 AWG Air Core Inductor 255-050 2 $ 6.61 $ 13.22
Jantzen 0.20mH 20 AWG Air Core Inductor 255-024 2 $ 3.41 $ 6.82
200uF 100V Electrolytic Non-Polarized Crossover Capacitor 027-366 2 $ 3.15 $ 6.30
Dayton Audio DFFC-0.33 0.33uF 400V By-Pass Capacitor 027-456 2 $ 1.26 $ 2.52
Dayton Audio DMPC-1.0 1.0uF 250V Polypropylene Capacitor 027-410 2 $ 1.18 $ 2.36
Dayton Audio DMPC-2.2 2.2uF 250V Polypropylene Capacitor 027-415 2 $ 1.72 $ 3.44
2 Ohm 5W Resistor Wire Wound 5% Tolerance 015-2 2 $ 0.48 $ 0.96
6.2 Ohm 5W Resistor Wire Wound 5% Tolerance 015-6.2 2 $ 0.48 $ 0.96
5 Ohm 5W Resistor Wire Wound 5% Tolerance 015-5 2 $ 0.48 $ 0.96
Knock-Down MDF 0.04 cu.ft. Micro Bookshelf Speaker Cabinet Pair 300-7060 1 $19.00 $ 19.00
Knock-Down MDF 0.23 cu. ft. Mini Bookshelf Speaker Cabinet 300-7062 1 $19.00 $ 19.00
Round Speaker Wire Terminal Cup Spring Type 260-294 2 $ 1.25 $ 2.50
Perforated PC Board 3-3/16" x 2-1/2" For #320-420 320-460 2 $ 1.17 $ 2.34
Penn-Elcom F1691 Rubber Cabinet Foot 1" Dia. x 1" H 260-774 4 $ 0.98 $ 3.92
Acoustic Sound Damping Foam 1-1/2" x 24" x 18" UL 94 260-516 1 $ 7.90 $ 7.90
Acousta-Stuf Polyfill Speaker Cabinet Sound Damping 1 lb. Bag 260-317 1 $10.80 $ 10.80
Total $301.78

Throw a pair of 8 ohm 5 watt resistors in your shopping cart, too. They will give you an alternative voicing to brighten them up a tiny bit by swapping them for the 6.2 ohm resistors.
-Bob

p.s. How do you make a nice table on this forum?

[[email protected]]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

cut and paste

[keith_correa]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

<snip>p.s. How do you make a nice table on this forum?

Click the "Go Advanced" button in the row of buttons below the "Reply" text area. In the 3rd toolbar - click the 1st icon. Allows you to draw up a table

like

this

[marvin]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

sir, I just try to read and learn. this c-g-d-a-e-b-f-c thing, is this some riff I should know.
thanks, dennis.

+1
I've wondered about that for a long time.

[BOBinGA]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

Arlis, I cut and pasted the parts list table above and you lose all your tabs.

Keith, I saw that and couldn't figure it out the first time. I just now tried that again and now I see how it works. Its painfully slow and you only get one column width, but I'll remember that the next time. Thanks.

Marvin, Dennis(Littleme60), huh? "this c-g-d-a-e-b-f-c thing" went right over my head. Care to explain or are you trolling?

-Bob

[dgodd8848]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

Think he is asking about the mnemonic in Paul's signature, which is related to a musical key having to do with the "circle of fifths". C G D A E B F# C#

[thekorvers]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

Think he is asking about the mnemonic in Paul's signature, which is related to a musical key having to do with the "circle of fifths". C G D A E B F# C#

Thanks for the clarification. I have long wondered about that part in his signature.

Nice write up by the way Bob.

[marvin]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

Think he is asking about the mnemonic in Paul's signature, which is related to a musical key having to do with the "circle of fifths". C G D A E B F# C#

Of course! A circle of fifths! I'll drink to that! :D

[BOBinGA]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

OK, sorry. I didn't notice the reference to Paul's signature.

-Bob

[keith_correa]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

Bob, I used a macro to convert the text of your parts list into the format that is needed for a table. Here it is:

Tang Band W6-1139SIF 6-1/2" Paper Cone Subwoofer Speaker	264-919	1	$48.32	$48.32
Dayton Audio DS90-8 3" Designer Series Extended-Range Speaker	295-422	2	$16.37	$32.74
Dayton Audio ND16FA-6 5/8" Neodymium Dome Tweeter	275-025	2	$9.64	$19.28
Dayton Audio MCA2250E 2.1 Channel Class D Plate Amplifier	300-771	1	$98.80	$98.80
Jantzen 1.2mH 20 AWG Air Core Inductor	255-050	2	$6.61	$13.22
Jantzen 0.20mH 20 AWG Air Core Inductor	255-024	2	$3.41	$6.82
200uF 100V Electrolytic Non-Polarized Crossover Capacitor	027-366	2	$3.15	$6.30
Dayton Audio DFFC-0.33 0.33uF 400V By-Pass Capacitor	027-456	2	$1.26	$2.52
Dayton Audio DMPC-1.0 1.0uF 250V Polypropylene Capacitor	027-410	2	$1.18	$2.36
Dayton Audio DMPC-2.2 2.2uF 250V Polypropylene Capacitor	027-415	2	$1.72	$3.44
2 Ohm 5W Resistor Wire Wound 5% Tolerance	015-2	2	$0.48	$0.96
6.2 Ohm 5W Resistor Wire Wound 5% Tolerance	015-6.2	2	$0.48	$0.96
5 Ohm 5W Resistor Wire Wound 5% Tolerance	015-5	2	$0.48	$0.96
Knock-Down MDF 0.04 cu.ft. Micro Bookshelf Speaker Cabinet Pair	00-7060	1	$19.00	$19.00
Knock-Down MDF 0.23 cu. ft. Mini Bookshelf Speaker Cabinet	00-7062	1	$19.00	$19.00
Round Speaker Wire Terminal Cup Spring Type	260-294	2	$1.25	$2.50
Perforated PC Board 3-3/16" x 2-1/2" For #320-420	320-460	2	$1.17	$2.34
Penn-Elcom F1691 Rubber Cabinet Foot 1" Dia. x 1" H	260-774	4	$0.98	$3.92
Acoustic Sound Damping Foam 1-1/2" x 24" x 18" UL 94	260-516	1	$7.90	$7.90
Acousta-Stuf Polyfill Speaker Cabinet Sound Damping 1 lb. Bag	260-317	1	$10.80	$10.80

[BOBinGA]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

Cool. Thanks, Keith. I really appreciate that.

I don't know if I can get much more of the write up done this weekend, but I will add one more tidbit for now. Here is the impedance curve for the satellites. They are a very easy 8 ohm minimum so you could easily use them in other situations.



You can see the effects of the input capacitor at 65hz. Without the cap, the impedance continues to fall back to 8 ohms and the phase returns to close to zero at 20hz.

-Bob

[BOBinGA]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

Alright, time to get this going again. Tonight, I'll show you some of the satellite construction details.

First, here is the front baffle layout using the 300-7060 knock-down cabinets. I did not offset the tweeter to keep it simple. Everything is centered on the baffle. When I cut the circles for the woofer, the recess was a little too tight and I think I ended up adding a 1/16". Measure the actual drivers before you cut the recesses just to make sure they will fit:



I cut the woofer hole using a Jasper jig on my router. That worked pretty well, but the Jasper jig is too large to cut the tweeter hole. For it, I used a 1-1/4" spade bit in my drill press. This was actually too small by about a 1/32", so I used a rat tail file and reamed it out until the tweeter was a very tight but complete fit. You might practice on a scrap MDF board first. To keep the hole circular, go round and round inside the hole with the file - not up and down. It takes some time, but its not hard to keep things round if you use a steady circular motion. You might use a Dremel tool to enlarge the tweeter opening if its easier, but I don't have one. The fit will be even tighter after you paint the cabinets since the paint itself will make the hole ever so slightly smaller.

My woodworking skills are limited at this point, so I simply spray painted the boxes. I'm sure many of you could do much better, but this easy finish fit my needs. I wanted to make the crossover accessible, so I decided not to glue on the back. I added two plywood strips to the top and bottom of the inside of the back so that I would have something to screw the back into. You can see the one on the bottom here. There is a matching one on the top of the opening. I also chamfered the inside of the woofer opening and I added tape markers for the driver wire connections to save confusion:



Next came mounting the back terminal cup and the crossover. The fit is rather tight, so I covered the connections from the XO to the terminals with electrical tape to prevent it from shorting out anything on the XO board.



You will need 1" spacers to raise the XO board high enough above the terminal cup to prevent the board from contacting the terminals. I couldn't find any locally, so I made my own from refrigerator ice maker tubing ($3 at HD for 10 ft.) by cutting 1" lengths with a razor utility knife. To mount it, I used #6 X 1-1/4" stainless steel pan head sheet metal screws. Stainless (or brass) screws are non-magnetic, so they won't change the value of the inductors that they are close to:




Now onto the box assembly. I mounted the woofer using #6 X 3/4" black screws from PE. Then I threaded the tweeter wires through the tweeter hole.



I connected the tweeter wires and pushed it into the tweeter hole. Since it was a tight fit, I placed a scrap piece of lumber over it and tapped it into place. This created an air tight fit and the tweeter is removable should it need to be replaced.



Then I attached the wires:



Next came the foam for interior damping. I used a 5-1/2" X 7-1/2" piece of 1-1/2" convoluted foam for each satellite box with the convoluted side facing the woofer. The boxes are just slightly too large for this woofer, if you just use the WinISD calculator. But with the added 3/4 ohm resistance from the inductor, it raises the Qtc to almost exactly 0.707, so it ends up a perfect fit for this woofer. I measured it afer assembly and mine came out to Qtc=0.703:





Screw in the back and you are almost done. I didn't even use any sealer or foam tape. These boxes are so tight, that the paint provided all the seal you will need. But do let the paint dry for a couple of days before assembly or you will never get them off again as wet paint is as good as glue.

There is one more detail. You have to add the two 1" high rubber feet to the front of the cabinet. These are needed to bring the tweeter and woofer into alignment. Its a minor detail, but it does prevent a broad 3 db dip in response around 9000hz directly on axis, so they are highly recommended:




Well that's all for tonight. I'll finish this up with some individual driver measurements and some placement and amp setting recommendations in a few days.

-Bob

[BOBinGA]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

In a previous post, I mentioned that the high pass filter on the MCA2250E 2.1 Channel Plate Amplifier might not be set at 150hz like the spec say. It looked to me to be much lower than that, but I did not have any measurements to back that up. Well, today I got a private message asking if I had a chance to investigate this further. This prompted me to get out the measuring equipment and see what the high pass filter actual does. Since its not adjustable, I'm sure many of you will find this useful if you want to use this little gem of an amp.

I don't have a way to directly measure the frequency response of the satellite portion of the amp, so I used an indirect, but just as accurate way to measure it. The PEDS satellites themselves don't go low enough to really show the effects of the high pass filter, so I used the ScanSpeak Discovery 8" woofers I already have in boxes. I first measured their close mic'ed woofer response using a regular amplifier that does not have a high pass filter to get a baseline (blue trace). Next, I left the mic in place and switched the input to the 2250 amp and measured again at the same level (red trace). Here are the two measurements:




The difference between the two curves is the effect of the high pass filter. You can see that it has very little effect at 150hz (the gold vertical line) as the specs lead you to believe. To me, it looks like the real F3 point is about 90hz and the F6 is about 75hz.

From a home theater point of view, this is much more practical than the published specs. If I were modeling this in WinISD for example, I would add a second order high pass filter at 75 or 80hz, which is what you would normally use for a small home theater.

From my perspective, this little amp is actually better than the specs say. The bass boost is really 6db at 40hz and the satellite high pass is really pretty close to 80hz. What more could you want for the price? Other than maybe a little more power, this was exactly what I needed.

Good job PE.


-Bob

[fwiler]

Re: The PEDS - a 2.1 speaker system for your desk, den, bedroom or office

Thank you Bob for such a thorough build thread. Your descriptions and pictures are really helpful for those of us that aren't fluent in speaker building.