Tuesday, January 19, 2016

Focal Profile 918 The Ultimate Upgrade Guide

Update - April 2016

This article takes each driver and discusses separate upgrades for each.

The information is correct, but there is a much better Beryllium tweeter mod now. The link to the new tweeter upgrade page is here.  It is a much more cost effective and incredible upgrade to replace the tweeter and install a brand new high pass filter than to do the tweeter modes in the article below.

However, the midrange and woofer upgrades discussed here still apply and are in fact pretty incredible. If you take the Be tweeter mod and do the woofer mod in this page you will end up with speakers far better than the Focal 928/938 series. 


 Original Article

 
If you follow up on the felt and crossover modifications below you will end up with a speaker that has a much smoother and open treble as well as stiffer and more enjoyable and realistic bass. The amount of information you'll gain in the decay of notes and sense of acoustic spaces will really surprise you.

The Focal Profile line was the spiritual, if not material predesessor to the Focal Sopra. As such, it's
got a lot of people wondering how to improve it to reach the Sopra.  Truth is you can probably reach if not exceed the performance of the stock Sopra with the Focal 918's and a little careful attention.

The Profile was the first un-boxy, MDF constructed Focal speaker, while the Sopra uses much of the lessons learned in the construction of the profile, with a central tweeter section to separate the upper and lower MDF sections.  I'll tell you a secret. The main reason Focal put the tweeter section is was to make the MDF manufacturing as cheap as possible. This MDF wedge makes it possible to glue the two MDF tubes together at an angle. Sound quality has nothing to do with the open back tweeter and "infinite horn loading."  Yeah, I know, Beryllium, blah blah.  Sorry but looking at the pictures, and measurements I can tell it has a very similar motor structure to the Profile. 

If you have or can lay your hands on a set of 918's here I'll show you how to make your Sopra drooling friends jealous. The SCR caps in the Sopra's just can't do the microdynamic detail the Mudorf caps can give you. It's not so much in the loud parts, but as signals decay that the Mundorf's will really shine. Pay close attention to this before modifying so you can hear what I'm talking about.  The effects are sometimes spooky too.

In the bass the increased impedance will add a new strength to the speakers.  You've probably unconsciously settled on using these speakers with a subwoofer or at least for movies you have them crossed over fairly high.  This will be gone.  You'll be able to run the Focal's full range without fear, and you'll probably forego a subwoofer at all for music. No joke, take a look at the original vs. final impedance measurements.  The green line is the measured impedance from my  Focal Profile 918.  The blue line is the impedance after making the final woofer modifications discussed below. That's really outstandingly better impedance with no downside but cost for the listener.

If you want to use tube amps with these speakers the complete woofer mods are a must-do upgrade! 

For a pair of speakers the total cost of these upgrades will be around $25 for the exterior felt mods alone, plus $160- $290 for the crossover mods depending on how frugal you want to be. One of the biggest improvements this article will show you won't even cost you a penny. You can try it before you commit to the final woofer modifications.

If you are only interested in the woofer modifications, that will only set you back around $70 and is probably going to be the single most dramatic change you can make. You can definitely do those and come back to the tweeter and midrange modifications, but to place the mid-range caps you'll need the woofer resistors out of the way first. That's the only real restriction.

You can do all three sections or just one, but in order of importance and convenience in terms of access to the PCB:
  1. Tweeter
  2. Woofer
  3. Midrange



Donations

Putting together guides like this takes a lot of expertise, time and tools.  If I have helped you please become a supporting member of the DIY community by securely donating $2 to the cause of independent reviews and advice.



Thank you!


External Modifications

Externally there's a number of things you can do, which apply to the Focal 918, 908 and maybe even the CC 908. If you dont' feel comfortable with a soldering iron, or are afraid, you can make some improvements for cheap without ever opening up your speaker.

Feeling, er, Felting Around

The grill is important to the dispersion pattern, but the plastic adds it's own coloration. The edges on the tweeter add coloration thanks to the diffraction when the sound wave hits the edge. This all ads an edge (pun intended) to the treble which can easily be smoothed over by adding craft felt in the right places.


Felt Tools and Supplies

 Most of these supplies can be purchased via Amazon via my store here. 
Make sure you have a large, clear work surface.  If you prop the grills up they will tip over easily while you are working on them. A clean floor works too. I used 2 pieces of felt per speaker. Using the back of the grill as a general guide, fold  the black felt horizontally and cut it to the width and height of  one of the solid grill wings then make a cut out for the 'V' of the tweeter. You'll use the fold to push the felt behind the grill cloth. Carefully and patiently stuff each folded felt sheet it behind the grill cloth using a narrow piece of cardboard, or some other gentle but stiff tool. A little Zen and deep breathing helps here. Once that's in place, use your fingers to pull out any wrinkles from the bottom and smooth it out from the front. Don't obsess over the looks until you sit down.  No one will notice the "bra padding " effect, just the bodacious sound.  Hahaha, I kill myself.

The felt on the tweeter housing is about 20% of the overall effect. If you are worried about it making your speakers look like stand-ins for Monsters, Inc. don't be, no one will notice. You'll need to use pressure sensitive adhesive (PSA) backed felt.  Pick a color, and trim it roughly to the rectangular size of the tweeter.  I used white and covered both the front and the top with mine.  Use the felt punch to punch a 1 1/2" hole in one end to match the tweeter opening.  Remove the backing and place firmly on tweeter, being very careful not to touch the tweeter dome itself.  Just the V shaped housing.  After you've carefully adhered the felt using your finger tips use a sawing motion with a brand new razor blade and carefully trim the excess. I found it easiest to do this with the tweeter in place, but the big grill off. Just be gentle and remember to saw, not push the razor throught he felt. use about a 45 degree angle on the razor blade and try to keep as much of it flat to the tweeter housing as you can.  This will give you very clean results.

Done!! Sit back and enjoy, you've just smoothed out your Focal's treble.


Feet

The normal feet that come with the Focals are a joke.  Impossible to set properly, impossible to lock in place, and what's worse is they put your speakers, pets and children in more danger by making the footprint far too narrow.

I use these speaker stands from Soundocity and they work great! The benefit for me was being able to point my speakers exactly the right place, but I don't think they made the sound any better.  My floors are not flat, and these stands took care of that problem perfectly.



Crossover Modifications

I am serious when I tell you you may end up with a speaker better than the Sopra's.  It's not for the lazy but it's a fun and relatively quick project. You'll need some soldering skills, the right tools, and patience.  That't it.

You'll make improvements to all sections of the crossover to end up with a whole that is going to sound like much more expensive speakers than before, unless expensive means you must have a big amp.  That we don't do here.

My suggestions are based on thoroughly measuring every driver, and every inductor and trying a number of different approaches as well as spending at least a week of time in crossover simulation design. I also spent a ridiculous amount of money on high end parts I eventually changed my mind about, so please keep in mind that there's a lot of forethought that went into what you read below.
 
In order to do it you'll need to pull out the crossover and replace 3 parts with 4 parts.  Once you are done no one will be any wiser though. In fact, it may be a better idea if you plan on reselling than adding felt to the tweeter.


Necessary Tools

All of the tools recommended here are conveniently available through my web store. 

If you attempt to do this with a cheesy $10 soldering iron and the original tip you'll be really frustrated.  Any desoldering/soldering work should take 10 seconds or less to pull a component off. You'll need more than average output because the PCB has so much copper it will sink the heat off the connection.  This is also where the broad tip comes in.  It will transfer 10x more heat to the board per second than the standard pencil tip will.

Strictly speaking, you don't need a drill or cordless screwdriver, but it will greatly shorten your time to make the crossover mods.

Supplies

The part counts are for a pair of loudspeakers.

Please note that all of the tweeter parts are available through Parts Connexion but sadly not through Amazon:

All of the midrange and woofer supplies are available through my on-line store via Amazon.

Mid-range:

    At about half the prices of the Solen's are Axon's, available through Parts Connexion.  As far as I know they are the same cap with a different brand. If the idea of mixing capacitor brands to you is like having steak knives made up of 3 Wufshof and 1 Henkells then you can certainly substitute Mundorf MKP's for all the caps.  You may need to double up on the 10uFs though, not all makers include 20uF in their wares.

    Woofer:
    An alternate, physically smaller but much harder to mount inductor:

    Tweeter Parts

    In a way, the Focal tweeter here forces you to stay away from more expensive boutique caps, most of them will end up sounding worse in the long run in this speaker. I picked the Mundorf MKP caps due to the synergy with the tweeter.  Mundorf MKPs are warm and smooth with tons of air.  This is a good match for a metal tweeter that's a little ragged but has lots of potential for detail, imaging and depth.  Nothing else in the $5/capacitor price range I know of has this combination.  If money is no object then a good alternate is the Clarity ESA line.  Even more clarity and depth, but about as warm but still affordable at $15/capacitor.

    If price is no object the Clarity ESA's should be your only choice.  If price matters, the Mundorf MKP are the best alternative, but both are very well suited to this upgrade. Caps in higher brackcet can be too neutral or bright by comparison which is not what we really want here. Then there is the issue of physical size.  The MKP's are perfect, and the ESA's just a little chubbier for the location, but completely adaptable.

    The Mills are just excellent all around resistors. Unless you are going for a vintage sound I just can't recommend any other brand in a crossover. Terribly natural, and invisible sounding, small for the power ratings, non-inductive, thermally stable, mil-spec and always spot on the rated values.  It is also helpful that in terms of price they are the bottom rung of "high end" power resistors.

    Mid-range Parts

    Lets start with a picture of the midrange filter.  Being a 2.5 way system, there's no high pass filter here. By the way, I used measured values here.  Obviously buy the closest parts you can. Focal probably wanted a 1.0mH inductor.  1.03mH is just what I happened to measure.


    The caps are in parallel to the driver so not as critical as the tweeter caps. Also, they are the largest in terms of Farads, so staying with high value, and relatively small parts is important.  For this reason the Solen / SCR parts are ideal. If you want to stay "high-end" substitute Mundorf MKP's of the same uF.  More expensive parts in these values are going to be too physically large for the spaces.

    I have selected Jantzen air-core inductors here. Spot on spec and great performers. 

    Woofer Parts

    For the woofer, I picked an inductor that is higher-tech and therefore shorter than a lot of alternatives: the ERSE Super Q series.  The DCR of the ERSE is a good match for the circuit as well.  Being  purely in the woofer, we don't need to worry so much about keeping an air core, plus at 15mH, finding a 12 AWG air core inductor gets expensive fast. This replacement will do wonders for you all by itself.

    You should be able to salvage the existing capacitor, but if you are worried of breaking it, or just want new for the sake of having new here get the non-polarized electrolytic.

      Speaker Disassembly 

      We'll need to pull the crossover out so you can work on it.  Take notes as you go to remember which color goes to which connector! 
      1. Unscrew and unplug the woofer and mid-range. Remove any stuffing that's in the way, but no more than that. Should be just two pads.
      2. Unscrew and remove the rear terminal plate.  Careful! The screw looks the same as the others but it's not.  Mark it or keep it separate.
      3. Unplug the tweeter. 
      4. Optionally remove the tweeter. There's a thumbscrew behind it you can undo with your fingers. This will make it easier to connect the crossover when you are done
      5. There's a white nylon ganglia that holds the cables going from the crossover to the mid-range section.  Unscrew with your fingers. 
      6. The crossover has 2 large Phillips head wood screws at the top.  Unscrew them.
      7. Pull all the cables out through the woofer opening. 
      8. The crossover sits in a slot via friction and a rubber boot.  Rock it to lift it up, then pull it out.
      The entire crossover will come out with wiring in tact. There is no need to cut or de-solder anything but you may need small pliers to grip contacts if a connector won't easily come off.


      Crossover Modifications

      Introduction

      There are three important sections in the picture below.  In red on the left you'll see two rectangles. These are the tweeter components we'll want to replace.  To the right, in a circle, is a part you'll remove and possibly save.


      Choices, Choices

      If you are going to do all of the modifications here, do them in the order suggested.  However, if you are only going to do the woofer mods you can do it by itself you can.


      Step By Step

       Tweeter ResistorOn the top in white the tweeter says "7W2.4 (Omega)JF" That stands for 7 Watts, 2.4 Ohms.  Replace the single tweeter resistor with 2 Mills resistors of 4.7 Ohms in parallel.  This will be equivalent to a 10Watt, 2.35 Ohm Resistor.  Sadly Mills makes nothing closer, but it's quality makes up for the 2% difference in resistor values. Having more watts in a resistor is a good thing, so 10 is better than 7.

      When you replace the resistor, make sure to leave about 1/4" to 1/2" of clearance between it and the board as well as the other components.  This will ensure the best air circulation.

      Tweeter Caps

      Below the  resistor are two black cylinders, labeled "6.8J and 7.5J." That's the capacitance.  They're probably made by SCR for Focal.  They're pretty much crap. Pull them off.  The 6.8uF cap is a straight replacement from Mundorf.

      You'll need to parallel a 6.8uF and an 0.68uF capacitor to get the equivalent of the 7.5uF capacitor. In reality we'll get 7.48uF, within 0.3% of the original.  More accurate than the originals, I promise.

      Be aware that the Mundorf MKPs need a little break in time and are subject to a pendulum effect.  At first they sound good but bright. Then after a day of playing they get grainy.  Finally after about 2-3 days they really mellow and relax.

      Bogus Woofer Cap

      There are kind of two ways to approach the woofer. You can remove one part which will have big benefits or you can do the optional coil replacement and part swap which is going to be even better, but also more expensive due to the $35 coil involved.

      So long as you stay within high-value coils I think this is a totally worth-while modification.  If you try to get fancy the value drops off quickly. See below for the frequency and impedance differences.

      In either event, you'll need to do these modifications before you do the mid-range modifications to create more space on the board.

      The only part in the crossover picture that has a circle is the "Bogus Woofer Cap."  Double check that it is labelled "195uF."  Carefully remove the 195uf capacitor just in case if you intend on doing the optional woofer mods, but leave it's sibling a 440uF cap in place.  Let me show you the woofer low pass filter schematic so you can understand what's going on.



      It turns out that the 195uF cap and the four 10W8.8(Ohm) resistors are all sales props with no redeeming value for the buyer.  They drop the impedance of the woofer to around 2.6 Ohms (very low!) at around 100 Hz. I might even argue that the entire woofer crossover is one giant sales prop.

      Dropping the impedance this low makes the speakers seem more demanding and, by implication, more exclusive, or maybe it convinces buyers to buy bigger amps.  Removing this cap add a tiny amount of bass (almost none) but more importantly, raises the minimum impedance up to 3.6 Ohms, a much easier load for most amplifiers, though still low. Any bass control and slam you notice is not due to the frequency response changing but just how much easier you just made it on your amp.

      By removing the 195uF capacitor you are also breaking the circuit to the 4 resistors it's connected to. You can leave the 8.8 Ohm resistors in place UNLESS you want to do the full mid-range cap mods, below, then you'll need the board space. Make sure you only remove the 8.8 Ohm resistors though.  The remaining electrolytic cap and 40 Ohm resistors are an important part of the low pass function of the filter. Don't bother being too neat. Just clip the resistors off, and de-solder the remaining leads.

      While you have the crossover out you should take a moment to check that the big red coils are actually working. Pay close attention to the biggest  two which straddle the capacitor you have just removed. The leads sometimes get installed too tightly and break after soldering, and perhaps during shipping.  If the leads are in fact broken, you'll need to sand off the red laminate and solder on a jumper wire to complete the intended circuit.

      Final Woofer Mods

      This part is a little complicated, so I'll share the final schematic so we can discuss it:

      Optional Woofer Filter Design


      This change involves replacing the 5mH inductor at the top of the board with a 15mH coil and swapping the location of the 195uF capacitor with it's sibling, the 440uF cap so we can re-use the 40 Ohm resistors. The inductor to the right is the 12mH coil. That one we'll leave in place unless you are just adamant about trying something new.

      Erse Super Q 15mH

      The ERSE Super Q inductor has 3x the inductance of the original so it's going to be about an inch longer than the original.  As a result you'll need to mount it to the back of the board, using the same tie locations as the original inductor. Fortunately there's plenty of space. 

      What does all this extra iron buy you? Quite a bit.  Comparing the original to this modification:



      As you can see above, the impedance no longer goes below 4 Ohms until around 180 Hz, and remains noticeably higher between 20 and 300Hz.  That's a huge win!  If you decide to go absolutely nuts and use film caps, I'll tell you a secret.  Anywhere from 120uF to 200uF will work in this circuit, so if you end up buying a bunch of 20uF film caps you can save some money. This solution is technically better in that it cuts the woofer off sooner than merely removing the bogus cap.

      Woofer Resistors - Optional Changes

      There is an optional change you can make here. You can replace the 4 resistors with Mills 12 Watt equivalents. In addition to cutting the impedance, we are also cutting the peak power through these resistors by half, so we have a lot more safety headroom here than with the original design. However, at 150 Watts that I simulate, the resistors are still a little small and if you want to play with large amps and loud volumes the Mills will give you 20% more safety margin, and degrade less quickly.  Is it worth $40?  I wouldn't do it, but my readers might.


      The Proof of the Pudding


      Now you might say to me "Sure, you can improve the impedance, and you have reduced wasted heat in the woofer resistors but come on, Focal designers are experts! This must ruin the frequency response, right?  Well, not so much. Here we can see the difference between the original modification and the advanced mod.  Original is in blue, mod in red.


      There's almost no difference at all, except for getting rid of that hump around 75 Hz.  If anything, this will make the bass sound tighter and less boomy.  Of course, these measurements are in my room, so a lot of this is room response, but the relative differences are real.

      Why didn't Focal design the crossover this way?  It could just have been cost.  A good 15 mH coil is more expensive than a couple of bi-polar caps and some power resistors. For a $4,000 MSRP speaker you would not have thought this was an issue though.  I think at the end of the day it was the realization that the market does not reward efficient and easy to drive speakers plus the $30 in part savings.  Why spend more money if no one will thank you in the end?

      What makes me sad is that the Sopra measurements I've seen indicate they've taken exactly the same approach there.  Oh, well, maybe I can sell entire crossover upgrades for those owners. :) 


      Mid-range Capacitors

      Make sure you've done the woofer mods, above first.

      If you look at the crossover picture around the tweeter caps, you'll see 2 small cans.  One to the right and one below. The one below should be a 20uF cap and to the right is 47uF.


      47uF

      The 47uF capacitor that's left is part of a notch-filter, a type of equalizing circuit to make up for a driver's foibles.  Replacing it is purely optional, but why disassemble your speaker more than once? Make sure you've removed the 8.8 Ohm resistors, as described above.  There's one additional supply you'll need for this:

      •  About 6" of 16-20 gauge insulated wire.  Finely stranded is easiest to work with.

      Solder 1 of the capacitor leads into the location, and the jumper wire to the other.  Add hot glue to the board and set the capacitor down.  Bend the far lead towards the jumper, and solder the two together. 

      20uF

      This it is the second pole of the high pass filter. Replace it after you've done the 47uF cap replacement. You might need to stand it up, or move it so you may need some jumper wires too. I went a little nuts and used a separate PCB for the mid-range modifications, so I'm a little unsure. Again, space matters, so for extra points replacing this with a pair of 10uF Mundorf MKPs is an option but not sure they'll fit.  Worthwhile?  A little.


      Mid-Range Coils

      The part to the left of the tweeter resistor is a 1.0mH coil.  It's at the very top and left of the PCB. This is the first pole of the mid-range low pass filter.  Iron core coils really should be reserved for woofers, so this makes me sad.  At the very least it should be an air coil.

      The coil replacement IS worth doing, but there's just not a lot room on the board.  I cheated and ended up making an entirely new circuit board for the midrange, before I decided it was complete overkill.

      Use plastic wire ties to secure the air-coil in place. Make sure the axis is aligned the same way as the original.  If you turn it around you'll risk magnetic coupling with the first woofer coil.  It's OK if it overhangs the top of the board so long as it's secure and not going to rattle against the board. Be careful not to get near the rubber boot due to the partition that's there.  For this reason you may have an easier time mounting it on the backside of the PCB.

      Wire ties are your best bet here, but hot glue can also help.  You will probably have to adjust the orientation of the wire tie 90 degrees to the original so the tie goes through the center of the coil, and crosses on the top of the board. This will keep everything out of the way of the partition the crossover rests on.

      There is also a 0.6mH coil in the schematic is part of a notch filter. I do not recommend replacing it due to being in parallel and of relatively low value. It's fitted between the two plastic donuts at the bottom of the board. If you must spend money though, this is a good replacement.

      Reassembly Tips

      Reassembly proceeds pretty much like you'd expect it.

      Rear connector

      To make threading the wires from the crossover to the rear connector easiest, I used masking tape and attached the ends to the end of an extensible magnetic holder.  The kind you can use to grab a loose screw in an unreachable place.  A wire hangar or similar would do the trick too.

      Thank You for Reading


      It's been a pleasure having others with similar interest stop by. If you've enjoyed this exercise it and benefited from the recommendations, please drop me a note and say hello or thank you in the comments.
       

      8 comments:

      1. Nice work Nigel. Fascinating. Wish this was published 8 years ago when I got my 918s.

        ReplyDelete
      2. Do Focal 7-6Vs lend themselves to crossover upgrades? Are there schematics available online?

        ReplyDelete
      3. Is it good for profiles 928 ?

        ReplyDelete
      4. Hi Nigel, are you still on this blog here? I would really like to try to upgrade my profile 918s, but am a little scared to just dive in...!

        ReplyDelete
        Replies
        1. I would do the bass mods, some are very simple. :)

          Delete
      5. Do you know which Focal tweeters you can update with if you don't go outside Focal's brand?

        ReplyDelete
        Replies
        1. Not possible anymore, Focal has pulled out of the DIY market, you can't buy their tweeters except in car kits.

          Delete