Home » Sponsored » Pi Speakers » Tim's 4Pi Speaker Build (Description of My 4Pi speaker build)
Re: Tim's 4Pi Speaker Build [message #81033 is a reply to message #81032] Sun, 25 January 2015 19:16 Go to previous messageGo to next message
timkur is currently offline  timkur
Messages: 13
Registered: November 2012
Chancellor
Cutting the rounded corners for the waveform.

I really like the look of the recessed waveform, but I didn't really know how to cut the rounded corners to fit it in.

This is the approach I took.

First, I traced the outline of the waveform onto the baffle. The distance from the edge of my router to the bit is 2 5/16", so I created another large rectangle around the waveform trace. I needed to clamp pieces of scrap around the baffle to get the guide lines to fit, since 2 5/16" went off the piece on 3 of the edges.

index.php?t=getfile&id=1635&private=0


Once I did that, I clamped down straight edges on the outer rectangle to create myself a temporary jig.

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Then I ran my router all around the jig, and cut out a rectangle. This was easy, as the jig prevented me from cutting something I wasn't supposed to cut.

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I thought long and hard about how to cut these corners. That was really the tough part of this cutout. Ultimately I ended up using a dremel. The rounded sanding bit made it pretty simple to cut the rounded corners. I would have preferred a method that didn't require a steady hand, but I was stumped.

index.php?t=getfile&id=1638&private=0


Overall, it was a nice fit. I'm sure a real woodworker would have been able to do it better, but I'm happy with it.

index.php?t=getfile&id=1639&private=0


Tim
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Re: Tim's 4Pi Speaker Build [message #81034 is a reply to message #81033] Sun, 25 January 2015 19:32 Go to previous messageGo to next message
timkur is currently offline  timkur
Messages: 13
Registered: November 2012
Chancellor
First impressions... uh-oh.

Once everything was cut out, I decided to do some quick sanding and put all the pieces in and try it out before painting it.

I plugged it all in, set it up to do an easy A/B testing with my M&Ks, and started playing some music, expecting to hear pure awesomeness. The bass was definitely more full, but something seemed to be missing on the higher end. My wife said something along the lines of "you probably don't want to hear this, but this sounds muffled compared to your existing speakers." And she was right.

I'm in the process of building 3 of these, so I swapped out the tweeter, midwoofer, and crossover one at a time, and there wasn't any effect.

I was wondering if this was just the case of "different types of speakers sound different", but I wanted to do some measurements anyways to make sure things were ok.

I grabbed a copy of HOLMImpulse (folks seemed to like it and it is free), pulled out the calibration mic that came with my receiver, and stacked my M&K on top of the 4pi... I wanted to make sure the speakers were super close to rule out any room effects. The mic was about 9 feet away.

index.php?t=getfile&id=1640&private=0


The results were pretty clear... I did something wrong with the construction of my 4pi. Sad M&K's are blue, 4pis are red.

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Any suggestions what I did wrong?

I purchased the B&C DE250 8ohm driver... was that the correct one?

Also, as a reminder, I purchased used JBL 2226H's from eBay, which were originally 4 ohm versions but according to the seller were reconed to be 8 ohms.

Any suggestions?

Thanks!

Tim
Re: Tim's 4Pi Speaker Build [message #81035 is a reply to message #81034] Sun, 25 January 2015 21:50 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)

I suppose the JBL recones might be bad, but check the obvious first - Did you get the polarity on the woofer and tweeter right? That notch looks like what you'd see with polarity reversed on one of the drivers.

Re: Tim's 4Pi Speaker Build [message #81036 is a reply to message #81035] Mon, 26 January 2015 00:29 Go to previous messageGo to next message
timkur is currently offline  timkur
Messages: 13
Registered: November 2012
Chancellor
Great suggestion Wayne. It ended up being a reversed polarity on the JBL. I guess mine are backwards compared to what the standard is.

It sounds really nice. A very full and warm sound. It didn't make my M&Ks sound like cheap speakers by comparison, but it is definitely an upgrade!

Not a super flat response curve, but I thought it sounded great. Maybe it's because it was on the floor (compared to the M&K which was sitting on top of it). With better placement and some EQ I bet it will measure out well too.

index.php?t=getfile&id=1642&private=0


Thanks for the quick response Wayne!

Tim

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Re: Tim's 4Pi Speaker Build [message #81037 is a reply to message #81036] Mon, 26 January 2015 16:05 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)

From the looks of that response curve, I'd still say there's something wrong. I hate to say it but my guess is the 2226 cones aren't genuine JBL. I see that pretty often in reconed JBL drivers. With good parts, the region between 500Hz and 1kHz is full and doesn't droop. In fact, since directivity increases, the on-axis output at 1kHz is actually slightly higher than it is at 500Hz.

Re: Tim's 4Pi Speaker Build [message #81039 is a reply to message #81037] Tue, 27 January 2015 01:04 Go to previous messageGo to next message
timkur is currently offline  timkur
Messages: 13
Registered: November 2012
Chancellor
Thanks Wayne. You definitely had me worried.

I started by swapping out the one 2226H for the other 2 that I had. The other 2 were phase wired correctly (not reversed like the first one... now I know what to look for).

The speaker/mic was in a slightly different place compared to yesterday, but both of them had similar curves.

index.php?t=getfile&id=1643&private=0



I was pretty frustrated at that, and so I looked at your response charts on the website, and something caught my eye. They were very similar to the vertical off-axis response (down) chart that you have. So I played around a bit, put the original speaker back in (that had the bad curve in the previous reply) and raised my microphone 2 feet up.

index.php?t=getfile&id=1644&private=0


From what I can tell, this was a measuring error and not a speaker issue. Is that how you would interpret this?

Apparently these are pretty finicky when it comes to vertical placement. I'm guessing you've got a post somewhere that describes the best way to align the speakers. When I get a chance, I'll look for it and if I can find it, I'll post a link here.

Thanks!

Tim
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Re: Tim's 4Pi Speaker Build [message #81044 is a reply to message #81039] Tue, 27 January 2015 10:43 Go to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)

Your chart with the green plot is what the response looks like when measured in the forward lobe. The forward lobe is between +/-20° of the center of the speaker, normal to the baffle.

At the edges of the lobe, you'll see nulls like your red measurement charts show. Then as you move the microphone further outside the pattern, you'll move into the secondary lobes. Response in the secondary lobes has no nulls but HF is rolled off.

You can see measurement of these lobes and nulls in the "Vertical Nulls" video at the link below:

You may have had polarity right initially, but measured in one of the nulls that are 20° above or below the forward centerline. Please see the notes in the crossover schematic for wiring. The 2226H should be connected with red to 2- and black to 2+, which seems backwards. The DE250 also is connected like this, with black to 1+ and red to 1-.

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