Frugal Horn MK3 Build Log and Testing

[klh2000]

Welcome to the Frugal Horn MK3 build thread!

This will document my build and testing of a pair of Frugal Horn MK3s

 

 

Post index links:

 

  Build process/painting

 

First Post (This One)

 

Second Post

 

Third Post

 

Fourth Post

 

Fifth post

 

Sixth Post

________________________________

 

Measurement/evaluation

 

Seventh Post

 

Eighth  Post (Could be coming soon)

 

Background Information:

(Note: I will refer to the speakers as FH3s from now on)

 

The FH3 is a horn speaker that was designed by certain people over at the diyAudio forum, and most notably, Dave from Planet10 Hifi. They can utilize many different full-range drivers,

 the most common choices are the Fostex Fe126en and the Mark Audio Alpair CHR-70.3. This speaker is different to many speakers because it only has a single, full-range driver. Today, most speakers of this size either have a tweeter and woofer or a woofer-tweeter-woofer (MTM). The reason why these single driver seakers are able to sound as good as they do, is because of the complicated design of the cabinets the drivers are in.

Here is a picture of a finished FH3:

 

 

 

The Build:

The pair of speakers that I am going to build will be in a piano black finish, with Fostex Fe126en drivers.

 

The first thing I did was hop on parts express and order the terminal cup, floor spikes, Acousta-Stuff, acoustic foam, and some 3/4in screws.

 

 

The reason this is called the Frugal Horn is because it is so cheap to build! Everything in the picture cost about $50USD, and this is everything except for the drivers and plywood. The next major expense of the project was the plywood. The plans call for 3/4 inch birch plywood, and that isn't very cheap in my area of the US; The cost for a 4x8 sheet was $70USD.

        The next thing to do was bust out the dial calipers, tape measure, and circular saw to begin marking and cutting out the different pieces of the speakers (forgot to mention: one 4x8 sheet is enough for two speakers).

 

 

 

 

Unfortunately, I forgot to take pictures of all of he pieces that were cut out, but here is a clamped together mock-up of what they will (sort of) look like:

*Notice the hastily done lens blur in photoshop :)*

 

The backs of each speaker will be curved, just like in the example photo when they're done.

 

 

The next thing to do was to glue-up the internal structure and and add some of the damping according to the plans:

Fig. 1

 

I forgot to add the orange "fluffy" damping that goes just below the driver, I figured it out after listening to how shouty they were when I first tried listening to them. The plans called for about 50g of damping (I used Acousta-Stuff):

(Sorry for the blurry photo)

 

That 52g pile of damping was then stuffed into the "v" on the inside of the speaker before I glued the second side on. The hole for the driver is only four inches (104mm), so it is difficult to fit your arm through and around the baffles that are inside afterward:

 

 

I also forgot to mention the acoustic foam that goes around the area that the driver is in. This foam is used to minimize reflections inside the area of the cabinet that surrounds the driver. These reflections can come back through the cone of the driver, and cause unwanted distorion or noise.

 

That is all until the next update!

[KaminKevCrew]

1 hour ago, klh2000 said:

-snip-

Very cool! I will definitely be following this project! Hopefully this summer (hell, maybe even winter break) I can build something like this. That looks like a ton of fun!

 

Do you have a link to the instructions for how to build them? 

[klh2000]

12 minutes ago, KaminKevCrew said:

Very cool! I will definitely be following this project! Hopefully this summer (hell, maybe even winter break) I can build something like this. That looks like a ton of fun!

 

Do you have a link to the instructions for how to build them? 

Here are the plans: http://www.frugal-horn.com/fh3-plans.html

and please don't quote the OP, just -snip- it

 

 

[KaminKevCrew]

2 minutes ago, klh2000 said:

Here are the plans: http://www.frugal-horn.com/fh3-plans.html

and please don't quote the OP, just -snip- it

 

 

Fixed. Sorry! And thanks for the link!

[klh2000]

Just now, KaminKevCrew said:

Fixed. Sorry! And thanks for the link!

You're welcome.

[klh2000]

Forgot to mention: The speakers should be "finished" (They never will be ) in about a month or so.

 

[klh2000]

On 10/28/2016 at 7:02 PM, klh2000 said:

-snip-

 

*I am going to use new posts each time because I am hitting the 20mb limit for the pictures*

 

I have gotten the damping installed into both speakers, and painted the areas that I won't be able to get to once they're fully assembled.

 

(Don't worry about the edges not matching up, we will use a router to fix that )

 

As you can see, the wires pass through the rear baffle, and because these speakers are full-range, there isn't a crossover inside; The driver is connected directly to the amplifier. The only thing I might add is a zobel network, it will help to tame the "spikey" impeadance of the drivers.

 

 

 

As I mentioned previously, the edges were pretty terrible and needed to fixed. you can see the before (left) and after (right), the router made the edges much better, but they will still require some filler. I used a router to match the edges using a flush trim bit, and used a 1/4in round-over to make the edges round.

 

So, the router doesn't leave perfect edges, and some filler was needed. I did apply are rediculous amount here, but it still works out. The part was lots and lots of sanding. I started off at 120 grit, then worked my way up to 400 grit. I never took pictures of the sanding because it was generally boring, it was just hours upon hours of the same thing.

 

That is all until the next update!

Go to Next Post

[KaminKevCrew]

35 minutes ago, klh2000 said:

-snip-

Very cool! I personally think that new posts each update works better, since those that are following this (as I am) then get actual notifications when you post an update, which we don't get when you edit a post. 

 

Honestly, it's better to use more filler rather than less, as you can always sand off excess.

 

Looking good!

[klh2000]

57 minutes ago, KaminKevCrew said:

Very cool! I personally think that new posts each update works better, since those that are following this (as I am) then get actual notifications when you post an update, which we don't get when you edit a post. 

 

Honestly, it's better to use more filler rather than less, as you can always sand off excess.

 

Looking good!

I am still behind on these updates though, I actually just got out of the spray booth. The primer is already done and wet sanded. Maybe I'll write more tomorrow

 

[klh2000]

On 10/28/2016 at 7:02 PM, klh2000 said:

 - snip -

After hours of sanding, the speakers are up to 400 grit, and ready for the primer. I am going to use a 2k primer because of it's high build; this will help to fill in any imperfections in the wood. I went with ColorXtra CXP400Q, the main reason is because it is cheap .

 

 

 

So, it was off to the spray booth: I put about a pint of the primer in my SATAjet 3000, and began to spray the cabinets. I had the gun set up to spry a little bit on the dry side, this allowed me to get about three coats on in about an hour.

 

I waited about 24 hours before I began to sand the primer. I stayed at 800 grit the entire time, it left a fine enough finish for the priming stage. Just like before, this was hours of wet sanding. It left the primer at a sort of dull-mirror finish.

 

 

That is all until the next update!

[spwath]

How did I miss this?
This is really cool. I heard about the frugal horn a few months ago, I would do one if I had more room

[klh2000]

17 minutes ago, spwath said:

How did I miss this?
This is really cool. I heard about the frugal horn a few months ago, I would do one if I had more room

They don't take up too much space, they are about 3ft tall, 6 inches wide, and 1.5 ft long. This thread only shows up about once a week though, I should update it more often.

[spwath]

4 minutes ago, klh2000 said:

They don't take up too much space, they are about 3ft tall, 6 inches wide, and 1.5 ft long. This thread only shows up about once a week though, I should update it more often.

I dont have room....

Picture:

Spoiler

 

[klh2000]

40 minutes ago, spwath said:

I dont have room....

Picture:

  Reveal hidden contents

 

Oh my...

I do have a little bit more space, but I had to cram all of my furnature into one side of the room to have a proper area for the speakers. I had to move my synergy F3s out of the way too, but those speakers are massive.

Spoiler

 

This was before I sanded them (I just couldn't wait to hear them )

 

 

 

Spoiler

 

(Notice the networking disaster on the wall.)

 

 

[klh2000]

Fourth Post

 

 

It's finally time to apply the base coat! I didn't want to spend too much money here (hence the name: frugal), so I went with a pint of Nason PX8 black. The chrysler black that I chose is very common, and it cost about $30 USD.

 

I sprayed the cabinets with a DevillBiss Finish Line with a 1.4 tip. The resulting finish was almost good enough on it's own, but I had to do a little bit of danding with some 1500 grit in order to get the base coat flat enough for the clear.

 

 

 

That is all until the next update!

[klh2000]

Fifth Post

 

Sorry it's been so long, I've been busy around the holidays.

 

We left off on wet sanding the base coat, so I guess it is time for the clear. I will be using a spot clear, which really isn't suited for this type of work, but I already had some on hand, and it's cheap .

 

 

I forgot to take a picture in the paint booth, but here is a picture a few days later after the clear coat was hard enough to touch, you can see the orange-peel (the waviness) This problem will be fixed after I wetsand the clear coat with 1500 grit sandpaper, and then use rubbing compund to buff it.

 

 

Wetsanding the clear coat will take out the orange-peel by flattening out all of the "bumps". Here is a diagram of what orange peel is, and how much to sand:

 

 

The sanding will take out all of the variation in clear coat thickness, this is what it looks like after wetsanding:

 

You can see that the clear is now a frosted/dull finish, this is exactly what you want before the buffing stage. In the lower left you can see some dark spots, these are low points in the clear that still need sanding.

 

That is all until the next update!

 

 

 

[klh2000]

Sixth Post

 

I left off on the wetsanding of the clear coat, and removal of the orange peel. This post will be about the semi-final finishing of the speakers.

 

After the wetsanding comes the buffing, I will be using a heavy cut rubbing compound for the initial buffing, a maybe a polishing compound in the future. I think this should yield good enough results for the time being.

 

 

I will apply the compund to the surface of the clear coat, and a little on the wool pad on the buffer. When buffing, I used a series of back and forth motions. You need to make sure that you don't stop on one area for more than a second or two otherwise you may "burn" a hole in the clear coat from the friction of the dry wool against the clear coat.

 

 

After that, I just used a buffer with a woo wheel at  a medium to high speed to bring the dull, wetsanded finish to a mirror-like shine!

 

 

 

You may be able to see some small scratching, this can be removed with a soft foam wheel and some finishing compound. I don't think I will be performing this step, just for the sake of time.

 

This is the build/painting process pretty much complete, all that is left is some finishing touches and the meausrement/evaluation portion of this log.

 

That is all until the next update!

[spwath]

looking nice

[klh2000]

1 minute ago, spwath said:

looking nice

Thanks.

[klh2000]

Seventh Post

 

Well, now that the build process is over, I can take some measurements with Room EQ Wizard. I don't currently have a calibrated microphone that is 100% suitable for these measurements, but my Yamaha YPAO mic will have to do. So I threw together a stand for the mic from some scrap wood, this stand will place the center of the mic directly in line with the dust cap on each driver

 

Here is the test set up:

The mic is placed 1 meter away from the speaker in a terrible room (for acoustics) and is given 2.83v. This is the equivalent of 1 watt at 8 ohms, doing this allowed me to also test the efficiency of the speakers with a 1 kHz test tone.

This was as close as I could get it to 2.83v.

 

I ran a sine wave sweep from 150Hz to 10kHz, I couldn't do much outside of that range due to the non-ideal microphone and room acoustics, but here are the results:

 

Left

 

Right

 

As you can see, there is a peak at 400Hz for each speaker, this is most likely why people describe the Fostex Fe126En as "shouty". Some songs can be "shouty" if the singer's voice is in the range of the peak. If you look at each graph closely, you may be able to see that each speaker is not identical, this is because the left speaker is not in a corner, and the right speaker is in the corner of the room (that is why the low frequencies are a little bit higher on the right speaker). These speakers are very sensitive to room placement, and should be placed in the corners of the room, the walls almost become part of the horn where the exit is at the back of the unit.

 

I am new at using REW, so any suggestions would be appreciated!

 

That is all until the next update!

[spwath]

you should get a minidsp umik-1, nice easy to use mic for rew.

 

 

[klh2000]

2 minutes ago, spwath said:

you should get a minidsp umik-1, nice easy to use mic for rew.

 

 

I was looking at those, and the dayton umm-6, but I'm too cheap to buy one . This all leads to spending more money though, because after looking at the mics, I was looking at DSPs and such.

[spwath]

2 minutes ago, klh2000 said:

I was looking at those, and the dayton umm-6, but I'm too cheap to buy one . This all leads to spending more money though, because after looking at the mics, I was looking at DSPs and such.

also measure speakers outside to avoid room issues. But right now would be tough if you are not in a warm climate

[klh2000]

27 minutes ago, spwath said:

also measure speakers outside to avoid room issues. But right now would be tough if you are not in a warm climate

I'm in upstate ny, so the weather changes every 5 minutes , but it is not very nice out currently.

[spwath]

26 minutes ago, klh2000 said:

I'm in upstate ny, so the weather changes every 5 minutes , but it is not very nice out currently.

me too. That's why I'm not measuring my new speakers yet