Mark K's Speaker Pages

NC DIY AUDIO group budget collaboration 1/2010

 

Update 2 - posted 5/02/10

So, what happened to the budget busters at the DIY? Well, Charlie told me that they sounded a little bright with the prebuilt MAD crossovers. So, I decided to test them the morning of the DIY. Below, you see the curve I obtained.

Eek, this doesn't look good. We chose not to demo them.

It certainly doesn't look anywhere near the curve below. There was not time at the DIY to figure out why, although I had an idea. I suspected that they had swapped the resistors in the volage divider, or, put the wrong values in. Sure enough, they had transposed R2 and R3. Reversing these gives the curve below and the corresponding incorrect comparison curve.

Here's a shot of both units compared after the correction.

The hump at 1k is a little more prominent than I would like, although I think it's very acceptable for a budget design. Often a slight downward tilt, especially if you're going to listen at 1-2m is somewhat preferable. Additionally, the power response will dip at 1-2k, so a slight rise here on axis will be somewhat negated. If you really wanted to be compulsive about this, you could play with R2 and R3 a bit and raise the area above 2k. I don't think this will be much of an improvement, just different.

What's the moral? If you've built this yourself, you're fine. Assuming you didn't make the same error...

If you bought a prebuilt crossover, you should verify that it's ok, or, if it's not I'll show you the "poor man's fix."

If you have the ability to measure impedance, then you can tell if the crossover is wrong. The black curve shows the incorrect crossover wiring. The tweeter impedance dips to below 5 ohms at 10k. It should have the dip at 4k, then a gradual rise, to 8 ohms at 10k.

If you can't measure impedance, you'll just have to look at the xover. This is harder than it seems as the label of the resistors are face down. You can only see them through the PC board. See below. The tweeter series resistor is R2 and should be the 8 ohm resistor. How do you know? Flip the board over-see the image below.

 

It just so happens you can read the value of R2 through the translucent epoxy board. OK so my expanded box lines aren't so straight. You get the picture. You can see the value of R3 because that pesky copper is in the way. Anyway, in the middle you see the 3 ohm symbols. This means that your crossover has a 3 ohm series (i.e. R2 is wrong!-R2 and R3 should be reversed.

Well, the fix is not that hard. One, email MAD-I"m sure they will work something out. However, seeing has how we're diy types, we'll just fix it ourselves. It would be really easy except they glued the resistors really, really well. See my fix below. Basically, desolder R2 and R3 at the ends that are not connected to each other, and then run jumpers to the respective correct locations. See my diagram below. It's not all that pretty, but the electrons don't seem to notice.

Well, that should do it. Happy listening. I'm going to actively cross these at 80 HZ and do a bit of extended listening before I have to give this pair back to Charlie.

 

Update 2 - posted 3/12/10

I've done more work on this project. Below you'll see Jeff Bagby's crossover diagram with one modification by me. The resistors on the lpad have been changed from 6/4 to 8/3. This was just done on the fly to smooth out the curve a bit more. You can retain Jeff's version, but it seems to run slightly hot this way.

Overall this looks very good, smoother than I thought. There is some discrepancy between the original tweeter lpad and what I had to adjust on the fly to get a flatter FR. I will recheck this to confirm. Still this looks very, very good, +/-1.5dB not counting the diffraction dip just above 4k which disappears off axis.

The current xover candidate is below.

The measured curves at 1m/2.83v are shown below.

OK, so is there any real discrepancy between the measured and modeled result?

 I remeasured every component that I used and the actual measured values are below. (The Solen cap may say 5.6, but the meter measures 5.9, etc.)

Overall the actual values are not that far off, but there is some modest variance on a couple of components. I would still get a coil with less resistance on the woofer leg (I used what I had.) I probably would order a 6 uF cap and 0,35mH coil, otherwise everything rounds close to the original schematic.

Using these actual values and overlapping the actual result with the modeled result, I get the curve below. Really, this is quite good. At this point, I'm going to give Charlie the boxes and drivers back and let him put together the actual units and we'll bring them to the DIY next month.

 

 

 

Update 1

I've done some basic measurement and come up with a simple, round one crossover. It needs more baffle step compensation, and could be a bit smoother, although you can only go so far given flush mounting, minimal roundovers, and a very small baffle. See what you can come up with.

The raw curves look like--

The xover circuit and modeled response looks like

 

And the initial measured response is below. Note this is a 1 meter, slightly smoothed flex window (gives a more realistic low end) fairly short window measurement.

 

 

Introduction

Charlie Laub, who you can find over at www.ncdiyaudio.com  has been working on a group buy, budget buster. Below you'll find information on the cabinets, drivers and testing. This is currently a work in progress. So stay tuned for updates.

The boxes are very well made, with nice maple veneer. You have to work around the existing cutouts. One nice feature is that the cabinets have built in threads on the back, so you can easily stant or wall mount. (Yes, not uber audiophile, but makes wall mounting, HT use, etc very convenient!

 

You can find more information about this project on the PE board, at the following thread link--

http://techtalk.parts-express.com/showthread.php?t=214873

 

Driver selection

Woofer- Peerless 850443. Left over NHT stock, $10 a piece. It's being sold off by Jack Hidley. See the PE thread for details. Charlie chose these as they are a ridiculously low priced, high quality woofer. Last I checked, there were over 200 left to purchase. When they're gone, they are gone. Buy now if you're interested. Note the $80 minimum order. See the PE thread for other workarounds.

He brought two by and I went ahead and measured the impedance curves, as well as TS parameters

 

Both units match exceedingly well, both measured free air and in my 4.7 liter test box. Some minor impedance wiggles, but not until 2k, and really, the main one at 3k.

Below, you'll see my TS parameters.

 

They match up well with the small signal TS parameters listed by Jack Hidley found below

http://home.comcast.net/~jhidley/Klippel_reports/11-081-1_LSI_Detailed.htm

As well as Zaph's tests, found currently in his blog. Zaph wipes his blog periodically, so this link will likely vanish after a while.

I haven't modeled them yet. As you can see, since they do ~85 Hz F3 in my somewhat undersized test box (Q=0.8), you should be able to get ~80Hz sealed F3 with a Q~0.75. Ported box modeling to come. Or, do it yourself.

The nearfield curves are below. The Peerless is a bit smoother at 1-2k, but I suspect there is a little more irregularity around 1-2k where the cone is developing modes for the paper cone.

 

 Some limited nonlinear distortion numbers are below.

First up, a 5 tone nonlinear distortion graph. Well, the Peerless, in black, is marginally better than the RS150.

 

Next up, at 400 hz. It's a close call. The RS150 may be ahead, although there really isn't a statistical difference.  What you don't see is the RS150 had better 2,3 order. Again, kind of a dead heat.

 

 

Next up, 1k 3 tone. It's a little difficult to tell here as well. In the first graph, the Peerless is in black. Any excess red is RS150 excess distortion.

 

Since that only shows half the story, I've reversed the curves. Now the RS150 is in black. Any excess red is excess Peerless distortion.

 

So, to summarize the woofer performance, It's as good as the RS150, more or less. Maybe better performance below 100 hz, and marginally worse at 1k. Overall and excellent woofer for $10. Remember, this is really a $40 woofer except it's a buyout, so to speak.

 

 

The tweeter is the vifa DQ25SC16-04.  You can find more about this tweeter at Zaph's site, in his tweeter mismash.

This tweeter is a well known budget champ. I made fun of it over at HTguide, but I didn't really mean to. It's a winner from a distortion standpoint.

At 2k,

 

At 3k,

 

These numbers are excellent. They have moderate second order distortion and are excellent with higher order products. They rival tweeters that are 5-10 times the price. Now, they probably don't go much below 2k, and require a steeper filter. And, the FR curve is a little ragged. But they are excellent for the money.

 

For less than $50 in drivers, and hopefully under $150 total, you get a very, very low distortion small 2 way. 5 of these, sealed, would make an excellent modest spl HT system.

Next up, FR measurements.

 

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