Frugel-Horn Mk3

In late 2006 – ’07 a small group of enthusiasts collaborated to develop a compact, inexpensive 

corner-horn design for the DIY community. This project became the very successful 

Frugel-Horn, which even spawned an extremely expensive commercial adaptation. 

The Frugel-horn Mk3 [FH3] is a ground-up new design, with the objectives of improving upon 

the performance of the original box in a substantially simpler cabinet that would be tolerant 

of a wide range of drive units. Topologically, it is a tapped hypex corner-horn (approximated 

by 2 conical sections) with an internal choke serving as a low pass filter. The curved terminus is 

carried over from Ron Clarke’s contribution to the original cabinet, and helps the wavefront 

exiting the horn mouth to return to its more natural spherical shape. 

The cabinet has to date been successfully tested with Fostex FE126En, FE126e, FE127e, 

FE138eSR*, Mark Audio CHR-70, CHP-70, Alpair7, CSS EL70, and Tangband W5-1611. Suitable 

drivers should fall into, or be near the envelope of parameters defined by this set of drivers. 

Additional drivers will be added to the above list as and when they are tested. Adjustment & 

tuning of the cabinet is accomplished with varying amounts of damping, and proximity to rear 

boundary walls / corners. 

* (this driver does bass really well in FH3, but has other issues which preclude it being recommended) 

FH3 is made freely available for DIY builders to make their own cabinets; we see it as an 

introduction to back-loaded horns, from which people may wish in future to move on to larger 

and / or more complicated designs. 

Use of deflectors & supraBaffles yet to be explored. 

Frugel-Horn Mk3 

25-february-2012 | © 2010, 2012 Frugal-Horn.com 

Note: any commerical entity intent on manufacturing complete speakers or flat-paks for 

resale will need to follow the guidelines on the Frugal-Horn site: 

www.frugal-horn.com/use.html 

This project’s contributors: 

DIYers who went ahead, assisted in beta testing, offered comment and suggestions 

diyAudio: host for interactive discussion threads 

Scott Lindgren design & documentation 

Ron Clarke: the curved mouth 

Chris Bobiak: Original test builds & drawing contribution 

Colin Topps: drawing contribution 

Your name here: you can help with FAQ, assembly diagrams & pictures, photo gallery. 

Probably more. 

Local cottage industry to make & distribute flat-paks encouraged, please contact Dave 

(david@planet10-hifi.com) 

Drawings/Contents (provisional) 

i0/ Intro 

i1/ Pictures 

i2/ Notes 

FH3-0/ Plan 15mm 

FH3-0.1/ Details 15mm 

FH3-1/ Plan 15mm + 18mm baffle 

FH3-2/ Plan 18mm 

FHx/ Plan 5/8” 

FHx/ Plan 3/4” 

FH3-5/ Alternate Choke Point Execution 

FH3-6/ Side pattern creation 

FH3-7/ Side template (metric 15mm) 

FH3-8/ Side template (imperial 15mm) 

FH3-9/ swappable supraBaffle (updated) 

D-0/ Damping 

D-1/ full size side felt template (15mm) 

C-0/ 5x5 15mm cut plan 

C-1/ 4x8 15mm cut plan 

C-2/ 4x8 18mm simple cut plan 

C-3/ 4x8 18mm cut plan (updated) 

C-4/ 4x8 18mm alternate cut plan (updated) 

please email me with 

corrections & suggestions to make this document 

more useful 

Major Sponsors 

& Cheerleaders

Pictures 

25-february-2012 

more pictures at http://www.diyaudio.com/forums/full-range/199849-fh3-build-gallery.html

Notes 

——————————————————————————————— 

'/ quality multi#ply/plywood is recommended& In general" void free" 

the greater number of plies the better 

,/ reference build is ,6mm plywood" to allow rebate for some drivers 

,%mm ba7es recommended 0ie Alpair 81 

+/ if MDF or particle board used a minimum panelthickness of ,%mm" 

good multi#ply minimum ,+mm 

)/ the most di9cult detail in the build is the joint at the bottom of 

back" inside divider& A number of means to achieve this are detailed 

$/ a removable vestigial supraBa7e is shown that allows 

experimentation with di-erent drivers 

6/ a full size supraBa7e can be added as shown in the Frugel#Horn 

Mk, document 

*/ A full height rear de.ector based on that shown in the Frugel#Horn 

Mk, document can be added 

8/ a stealthWoofer based on a full#height de.ector is under 

development& 

Donations 

———————————————————————————— 

Frugel#Horns have always been free for DIY builders to 

construct& We received many inquiries by buiders who wanted 

to send some money& For this iteration we would encourage you 

to pay it forward with a donatation of money or time to some 

charitable organization& Listed below are some choosen by the 

three main contributors to the design & documentation& 

Quite literally" every little helps& 

Royal British Legion: www&britishlegion&org&uk 

Alzheimer!s Research UK: www&alzheimersresearchuk&org 

Cancer Research UK: www&cancerresearchuk&org 

Donor!s Choose: www&donorschoose&org 

Save The Children: www&savethechildren&org 

Big Brothers Big Sisters: www&bbbs&org 

Chris , 

Chris + 

Chris ) 

——————————————————————————————— 

for those without major woodworking kit" a growing number of 

independent .at#pak vendors ar ecoming on#line& Canada 0North 

America1" Netherlands & UK 0Europe1 & Australia as of this document 

revision 

Notes 

)'#september#+',, 

Comments & tips pulled form forum posts 

——————————————————————————————— 

Bob Brines: 

Taking Colin!s diagram !sheet C"#$" here is how I would one#man it 

out of a $x% panel& 

'& Build yourself a T#square cutting guide out of scrap material& You 

can (nd the instructions out there on the Internet& 

''& I have a )!x*! sacri(cial table top on a pair of saw horses& I can still 

manage to get a $x% sheet of plywood on it" but I can no longer get a 

sheet of MDF on it& For MDF" I just drop the sheet on the driveway 

and put $ +x$!s under it& 

,& With a circular saw" cut o- the $ ,$'mm pieces& 

+& Cut between the remaining doubled pieces& 

)& Now you can rip the individual pieces on a table saw as long as you 

can rig some kind of out.ow table& I have a jig that (ts my router 

table so that it can double as an out.ow table for the table saw& Of 

course" if you don!t have a table saw" you can do this with a circular 

saw and the rip fence you made above& 

You can get the two cross cuts done at Lowes!/HD 0speaking to the 

USA now1" but my experience is that their panel saws are not square 

in any axis and I have to re#cut the ends& Also" the utility blade in their 

saw really tears up the cut& I have a *' tooth blade in my circular saw 

that does an acceptable job& Not as good as the %' tooth blade in my 

table saw" but acceptable& 

That!s my technique& YMMV& 

Bob 

——————————————————————————————— 

PDRCanada: 

Another tip for cutting sheet goods on saw horses&&&&&& 

Go to your nearest hardware store buy a +!x$! pc of + or )2 white 

styrofoam and a roll of duct tape& 

Cut the stryo to match the top of your saw horses&&&&&&use the duct 

tape to fasten it around the top of the horse& 

You can now cut your sheets with out hanging them over the saw 

horses& Just cut thru the styro&&&&&make sure your styro is deeper than 

your saw cut& 

When the styro gets beat up&&&remove and replace& 

This method is used on jobsites all over to cut large panels& 

——————————————————————————————— 

Poultrygeist: 

A3er much frustration in searching for ,/+ 4 0 ,+mm 1 cotton or wool 

felt I found an unlimited supply at my local auto junk yard& The carpet 

backing from ,55'!s Fords is ,/+ inch thick" works great and costs 

nothing& Had it not been up for sale I would have scavenged my own 

Mustang but instead I found a F,6' donor which surrendered enough 

felt for a herd of horns&

' 

6$ &"07 

!/#& mm 

radius 1-234 

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Notes: 

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$" optional %&'' mm wide"diameter supra(ba)e not 

shown* Its purpose is to move the ba)e(step drop o+ to 

where the horn action starts ,attening lower midrange FR 

&" intended for Fostex FE!$-En. CHR(/'. Alpair /. EL/' 

0" damping will di+er for each driver 

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$" joint detail at lower end of the internal panels % # degree 

angle cut on the inside of rear panel can be cut on table saw 

with tenoning jig and blade set to #deg or carefully sanded 

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Note: example uses !%mm material 

As originally designed 

A di*cult piece to cut 

Modi+ed for easier build 

Adds an additional piece, not all that tolerent 

of thicker material 

Alternateeasier build 

Overcomes material thickness issues- 

Requires extra material . !'& round with 

radius of build material 

Frugel/Horn Mk( !v0 

sheet FH(/% . alternate choke point 

execution 


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Frugel2Horn Mk$ )v4 

sheet FH$2( 5 curve chord & height 


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To fabricating a side panel template by 

hand+ the curve can easily be drawn 

using a narrow ,exible board -)&./ MDF 

works great0 and the . points as 

dimensioned1 

Mark points A+B -chord ends0+ C -chord 

centre line0 and D -segment height0 

on the work2piece1 Use a square to draw a 

perpendicular line -C2D0 

Clamp or screw a wood block straddling the 

centreline at D+ clamp the 

,exible board to this block and each end of 

the chord - A & B0 then draw 

the curve1 

Cut to the outside with jig or band saw+ and 

carefully sand to line

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$%& %'()*

Frugel-Horn Mk3 1v0 

sheet FH3-9 – removable supraBaffle 

(15mm) 

designed by C Bobiak | drawn by dld 

26-november-2011 

© 2010, 2011 Frugal-Horn.com 

Notes: 

0/ drawn with 18mm panels 

1/ shown on FH3 in 15mm material 

2/ 

these dimensions allow for a small gap 

to accomodate veneer,laminate etc, if 

needed the wings can be made tight to 

the sides and the vertical edges can be 

sanded flush. 

85 

[3 11/32] 

86 

[3 3/8] 

cut out on backside of sB is 

20mm down from the top 

(15mm pnels, would be 

23mm down with 18mm 

panels) 

200 

[7 7/8] 

BaffleCutout 

175 

[6 7/8] 

115 

[4 17/32] 

208 

[8 3/16] 

120 

[4 23/32] 

70 

[2 3/4] 

165 

[6 1/2] 

110 

[4 11/32]

!"#$ %!#mm& cotton or wool felt 

!" FE!#3En blue 4 orange 

#" CHR5, blue 4 orange 4 #,.2,g 

+" EL5, blue 4 orange 4 #,.2,g 

2" A5 blue 4 orange 4 #,.2,g 

starting point 8 +, 

grams of poly(u) - 

average ,'9 lbs'01+ 

%yellow 4 green& 

poly.(u) %BAF/ acoustistu)/ pillow stu6ng .. di)erent 

colours represent di)erent 7zones$ to add stu6ng too& 

increasing density as you approach 

the point' Take the equal density 

(u) on the right and squeeze it into 

the point %*+,g - ! oz & 

Frugel.Horn Mk+ !v, 

sheet D., 8 damping plan 

designed by S Lindgren : drawn by dld 

#5.september.#,!! 

© #,!,/ #,!! Frugal.Horn'com 

walls lined around driver to minimize 

re(ections 

this is the area subject 

to additional poly.(u) 

damping/ depends on 

driver 

see notes page ix for 

driver.by.driver 

%at !"# lb"01+ this 

volume would need 

*2,g %!'2 oz& of (u)

!*& 

+, !.%/&- 

Full Size when printed at !""# 

Remember these need to be mirror image pairs 

Note: 

speci$cally for !%&' felt material as relevant to planet!"(hi$ )atpak kits 

!,* 

+0 !%!0- 

Frugel(Horn Mk/ !v" 

sheet D(! 1 Side felt template 2!,mm3 


&5(september(&"!! 

© &"!"6 &"!! Frugal(Horn7com 

!*" 

+, !%&-

$/% 

-' $()0 

Notes: 

$( 'mm kerf & trim allowance 

)( very tight cut plan 

1$' 

-#) #(#)0 

*/$ 

-)2 '(#)0 

internal 

internal 

back 

back 

bottom top 

ba!e 

Frugel"Horn Mk# $v% 

Sheet C"% & 'x' $'mm cut sheet 

layout by Chris Bobiak 

drawn by dld ( )*"sept")%$$ 

© )%$%+ )%$$ Frugal"Horn,com 

top 

bottom 

ba!e 

$/% 

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$*) 

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internal 

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03 "*&1 

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0#, "*"+1 

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Frugel!Horn Mk" #v$ 

Sheet C!# % &x'( #)mm cut sheet 

layout by David Dlugos 

drawn by dld * +,!sept!+$## 

© +$#$- +$## Frugal!Horn.com 

Notes: 

#* )mm kerf & trim allowance 

+* room to increase kerf for CNC 

"* works for #++$x+&&$mm sheets

!"# 

$% !&'( 

"%4 

$!, !&!5( 

!"# 

$% !&'( 

4## 

$*% .&!5( 

Cut ! 

Cut ' 

Cut * 

Cut " 

Cut % 

Cut 5 

Then cut out the 

rectangles to make the 

sides out of 

Frugel)Horn Mk* !v# 

Sheet C)' + "x,- !,mm simple cut 

layout by Colin Topps 

drawn by dld & '.)sept)'#!! 

© '#!#/ '#!! Frugal)Horn0com 

Notes: 

!& %mm kerf & trim allowance 

'& minimal cuts to break up the sheet 1ie 

at the lumber shop2 Dimensions 

rounded up to the closest higher mm or 

!&,3

869 

[34 3/16] 

baffle 

baffle 

195 

[7 11/16] 

140 

[5 1/2] 

830 

[32 11/16] 

back back 

top 

top 

459 

[18 1/16] 

bottom 

bottom 

internal 

internal 

756 

[29 3/4] 

140 

[5 1/2] 


Sheet C-4 – 4x8’ 18mm alt cut 


drawn by dld / 25-february-2012 

© 2010 – 2012 Frugal-Horn.com 

Notes: 

1/ 5mm kerf & trim allowance 

2/ room to increase kerf for CNC 

3/ works for 1220x2440mm sheets

459 

[18 1/16] 

195 

[7 11/16] 

top 

top 

bottom 

bottom 

baffle 

140 

[5 1/2] 

baffle 

back 

optional parts for a 36mm 

tall stabalization base 

back 

406 

[16] 

internal 

279 

[11] 

internal 

460 

[18 1/8] 

140 

[5 1/2] 

756 

[29 3/4] 

830 

[32 11/16] 

869 

[34 3/16] 


Sheet C-3 – 4x8’ 18mm cut sheet 


drawn by dld / 25-feb-2012 

© 2010, 2011, 2012 Frugal-Horn.com 

Notes: 

1/ 5mm kerf & trim allowance 

2/ room to increase kerf for CNC 

3/ works for 1220x2440mm sheets 

4/ optimized for maximum offcut not 

easiest cutting & maintaining grain 

matching

Frugel-Horn Mk3

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