THE 66% SOLUTION
by Craig Schmidt
"You should go live with Dr. Gizmo" my wife shouted. "See how he
likes running the vacuum cleaner around all of these speakers and space
heaters (my tube amps)". "And now you want to build these monsters
(pointing to my drawings)". "But remember honey, I could be out
drinking (which I do) and chasing women (which I don’t)". She walked
away muttering about the good doctor and farm animals. This meant that
I was free to start my latest project aptly named because it is 2/3
horn and 1/3 wideband. (I feel I should warn you that this speaker
system uses a complex crossover. So people with stomach problems should
stop here or else have a bucket, bag, or something to ease the burden
just in case.)
I wanted to try and build a cabinet with non-parallel sides. The
pictures show what I came up with. The cabinet is three layers. ¾ inch
MDF is first, followed by ¼ inch solid red oak, then American walnut
veneer. I think they look cool especially when they are positioned in
the corners. I also wanted to recess the drivers this time around. What
a pain in the ass that was for me (even with a circle jig) but it came
out fine. I did put in one 2 by 3 brace front to back. A pound and a
half of Acousta Stuff was used on the insides and one strip of my
secret stuff placed on the back wall.
I would like to discuss the driver choices a little as they go
against the normal somewhat. The wide band driver is a 12 inch Beyma
G125. It goes down to about 40 Hz. And up to just over 6 kHz.
For about 60 U.S. dollars each, these are such a bargain I think I
am going to start to cry. The chassis on this baby is massive. Solid
cast aluminum. There is no flexing here. (In my opinion this is a very
important criteria especially when you are dealing with a driver this
size.) It also comes with a huge ferrite magnet, and a real 2inch
copper voice coil. The mass is low compared to other 12 inch units I
checked out. The Beyma is about 98 dB efficient. The cabinet came to
about 3.4 cubic feet. I used two 4inch ports to serve this giant, as
one would have been ridiculously short plus I feel you should use the
biggest total port size you can. Two ports are better than one.
Moving up the ladder is the Morel MHT-36 horn loaded tweeter. This
driver uses a cloth cone (hand doped to optimum whatever) and has a
gigantic magnet assembly for a high efficiency rating (97 dB).
These were very hard to get. I could not find anybody who stocked
them and none of the vendors volunteered to order them except for Parts
Express. The problem with that was I got better pricing from the
distributor than P.E. They cost 75 dollars each.
Now last but not least is the midrange (my favorite part). Sorry, but I have to ramble on here a bit.
There must be special place in Heaven for people who can build wood
horns. They are magical, mystical, and just plain beautiful. When you
hold one it’s like holding a newborn, that is if you get the right ones
which at first I did not! The black horns you see in the picture are
from Raft Craft through EIFL.
They were a little cheaper than the Fostex 400 horns but they were
Japanese so the quality has to be there, right? Wrong! The horns
function fine, in fact they sound great but at $320 each, plus a
hundred each to ship them, the quality of construction that the
Japanese are famous for is just not there period! There are paint runs,
spots that were not painted properly, and areas that were not sanded
properly. Chips in the wood (under the paint), plus poor hole alignment
for the driver was the last straw for me. Oh, they offered to replace
them but at almost a total of $400 more for shipping (neither EIFL or
Raft offered to compensate me in any way for the shipping which really
pissed me off!) it just was not going to happen.
I decided to replace them with what I should have purchased in the
first place, the Fostex H400’s. They list at $500 each but they are
worth it! They are perfectly built with a beautiful finish. (I sit and
stare at them. My wife comes over and feels my forehead a lot when I do
this.) For what it is worth, I found a place that discounts Fostex
products and has, in my opinion, better service than EIFL. HIFIDO
gave me a 17% discount on these horns and I have heard from other
people I have turned on to them, they are getting the same discounts.
(If anyone would like further details on this please email me.)
It was only natural to use the Fostex D1405 driver. In my opinion
all Fostex drivers are works of art. This unit is no exception. (I wish
I could figure out why wood horns sound so natural like this combo
does.) While a lot of horn drivers are designed for p.a. or studio use,
these are designed for hifi use and you can hear it! Now get some
coffee or some other beverage and I will extrapolate on the crossovers.
I am not a fan of these devices but how else was I going to get all
of these units working together. (As it turned out from extensive
listening, I did not need all you see in the pictures). In all honesty,
I had a load of fun working on these and did learn a little too. I did
get help though. North Creek Music sells the best (my opinion) parts
for crossovers. (They have a website. If I remember correctly it is
northcreekmusic.com). Their coils are hand wound under low tension to
exact specs. And they are automatically matched. The wire size you use
is important because resistance builds up. They recommend 10 to 8 gauge
for woofers! The best I could do was 12. Let me tell you that with 12
gauge solid copper wire, a 2.8 mH coil is HUGE and HEAVY! I can only
imagine 8 gauge looks like. North Creek’s capacitors are also something
else. They recommend cascading (paralleling) the capacitors until the
required value is reached. The bottom line is they are very high
quality and very expensive but once again you get what you pay for. The
pots are the now very famous Fostex R80b’s. I will not bore you with
construction details except to say that soldering these coils was a
pain in the ass. The lacquer, or whatever it is that is used an
insulator, is tuff stuff and has to be taken off first. I had to scrape
it off with my Xacto knife down to raw copper and then solder with a
gun. Forget about using an iron unless it’s a high wattage unit!
The basic design for this crossover evolved from a suggestion that
comes with the D1405. The woofer crosses over at around 900 Hz at 12 dB
per octave, the tweeter at around 10 kHz but 6 dB per octave. This is
ok because the Morel can actually go down below 1 kHz although I would
never run it that low. The midrange is a band pass. I took Fostex’s
suggestion here thinking they know what is good for their own driver.
Now when I first started listening to the completed speaker the
sound was quite acceptable but I noticed some harshness from the Beyma
especially when I was close to the driver (meaning having my ear right
up to it). After farting around with it for a while, I bypassed the low
pass crossover totally for the wideband unit. The strange noise
magically disappeared! I cursed for a while over this because I could
not figure out why a coil and a cap could cause what was happening but
figured that I should be happy that I was able to get rid of the
problem by removing rather than adding.
As always , the famous question, how do they sound?
The soundstage that these speakers present is life size and while I
thought they would beam, they do not! Depth is also excellent. I could
go on but what’s the point. You would have to hear them for yourself.
Yet, there really is a point. One is, wood horns sound wonderfully
realistic and second, awfully expensive. This project cost me a lot of
money in more ways than one. (I had to appease the little woman.) So if
you are married and still want to enjoy the sound of wood horns, you
must either be a master craftsmen with angel wings or you must stop at
the bank for funds for the speaker project and jewelry for your spouse
(unless of course she is a hifi nut like you and I). I sent along a
picture of my wife for Dr. Gizmo. My wife says she wants a picture of
him for the dartboard. Isn’t she sweet?