Sunday, October 25, 2015

Focal Profile 918 and Dayton DATS V2

I've been using DATS to test a few drivers and inductors I have lying around.  I also tried measuring the Focal Profile 918s and made a startling discovery.  The minimum impedance is around 2.3 Ohms!  Also, the impedance between 75 and 250Hz remains below 3 Ohms.

No wonder these speakers can tell the difference between a mediocre and stout amplifier.  They are just ridiculously difficult to drive for their class.

This low impedance is probably a direct result of the crossover topology, 2.5 way means that the mid/woofer and woofer are both working in the bass.  Since both are about 6 Ohm devices this would imply a minimum impedance of half this.  Ouch. 

Please note the maximum and rising impedance in the treble are probably my fault.  I've made some EQ changes to the treble which means this is probably not what a stock speaker would measure like above 1 kHz.

Sunday, October 18, 2015

First Impressions of the Mundorf AMT25CM1.1-R

I was so excited to get one of these in the mail I wanted to start blogging right away.  I'll cover the response and harmonic distortion measurements in a future posting. 


Based on my handy dandy DATS V2:

 Fs = 1666
Le=9.47 uH

As expected with such low inductance, the phase plot is practically flat.  Highest measured impedance was around 6.4 ohms at resonance.  Compared to dynamic drivers, this is a remarkably simple and resistive load.


The mechanical drawing, while accurate, doesn't really do the size of the body justice.  The body is really big about the size of some laptop chargers and the flange top/bottom are small and difficult to cut for. 

The front of the tweeter.  Sorry about the rotation.  Note blemishes are due to the plastic shipping film still being on. Kind of a boring shot.

Here is a side view of the tweeter where we can see just how monstruous the body really is.  Mundorf provides a rubberized pad on the flange. 

Here are a couple of interesting things.  Unlike my expectations, Mundorf provides full sized banana jacks and a pair of banana spring clips to attach speaker wire to. I  was expecting spade lugs or quick disconnects.  The left edge is the bottom of the tweeter. Notice the big difference in the width of the flange on the sides (top) vs. the top and bottom (left).  As Lee Taylor of Taylor Speakers pointed out, this can be a real bothersome situation for a cabinet maker.  I suspect the choice was to make this tweeter more palatable for line-array speakers.   In fact I'm kind of tempted to start working on one next.

Also, the corner radius are very small and non-standard 4mm.  Just to be nice, I'll throw in the dimensions below.  As you can see there, there is a 5mm spacing on the top and bottom flanges.  That's not a mistake.  One last comment, the housing is rater flimsy.  It feels like a thin version of the poly carbonate material in the uber-expensive suitcases being sold today and there is no visible way to remove it.  Speaker makers using this would probably want to encase the driver in it's own, well damped, sub cabinet.

The Drivers Arrive

For me this is a bit like Christmas and my Birthday present.  Madisound was kind enough to drop ship one set of tweeter and woofers over to Lee Taylor over at Taylor Speakers. While he is busy with the speaker cabinets I can at least play with them and do some basic tests.  That's all fine and dandy, but something else happened I did not expect.  You can see the problem here. 

I did not realize that the speakers were packed in pairs.  Madisound did a fine job of packing and shiping, but if I had known this was the consequence I might have bought all the drivers at once.  Here's the same view of the tweeter box.


I have gone far beyond merely upgrading with this project so I wanted to start a new blog for everything I work on and discover along the way.

In "Random Acts of Upgrades" I discussed modifying my Focal Profile 918's.  So far I've had quite  a bit of success but I decided to take the plunge and purchase real tools, as well as stop spending so much money on a pair of old speakers.

So far for this blog I have lots to talk about.  The Dayton Audio Ominmic and DATS V2 combination, the Focal's and how they measure, as well as a completely new speaker design I'm calling "No Es Nada" for now.  There's a famous kit offered by Madisound called NADA which got me on my way to my very custom speaker design. In Spanish "Nada" means "Nothing."  So, this design is not Nada and not nothing, so "No Es Nada" (NeN for short) means "Not Nothing."

First, for my skill level and experience I am spending way too much money.  I'm sorry.  I know this.  I wanted something compact and great sounding, but wanted to go my own way.  I disliked the idea of building a kit everyone else built.  Also, I didn't like the ragedness in the SS Beryllium's response.  So I went looking for alternatives and ended up at the NeN design, which uses a Mundorf AMT and SS Revelator.

So this blog will absorb my further Focal tweaks as well as the NeN build, and Dayton tools review.

I hope others come join me on my journey.

If this fails, I'm going to work on home brewed cruise missiles.  Maybe I'll offer cruise missile targeting as a web service.  You only get 60% accuracy per missile, but at a great discount.  Hah.  That's a joke, but I wouldn't be surprised if someone offers that within my lifetime.  Some one call me when it happens.