Angular spiral

The 3D-Spiral Horn Speaker Building

Angular spiral

Added on 25 Sep. 2006

Updated on 14 Dec. 2007

Helix-AG250BS, AG200 & AG140
My audio system

There are complains about difficulties for building a spiral.
I have come up recently with an "angular spiral" for a square cabinet.
It may remind you of an emergency staircase.
It is easy to build and has an equivalent advantage to a circular spiral with a clear sound and an ability for reproducing a deep bass.

The angular spiral is formed with slanted "sonic fins," which are made from rectangular planks glued to a wall of a cabinet.

The concept may be applicable to a TLS, a back-loaded horn and a bass-reflex port.
bassref

Revised on 28 Apr. 2007

My design principles

(1) Constant pitch and narrow opening (AG100, AG200, AG180 and AG140) are better than expanding pitch and wide opening (AG150).
(2) The appropriate rear opening may be 30mm diameter without relation to an effective corn area. The rear opening is critically important for prevention of booming perhaps caused by low back pressure.
(3) The optimum number of fins may be 4 on each side plate.
(4) The desirable air chamber may be small with just enough depth for a driver.

Is this a type of Transmission Line Speaker (TLS)?

I don't know what is a TLS exactly and if the above angular spiral is a type of TLS or not.
Some definition is described as below.

With TLs, the enclosure functions as a low-pass filter 
with a 90degrees phase shift, absorbing all the rear wave energy
 of the woofer except for frequencies below about 75Hz.
TLs can be characterized by:
 
    * Low cabinet resonance
    * Relativley loud deep bass (below 50Hz).
    * Highly damped impedance peak.
    * Decreased cone motion in the 40Hz region.
    * Low degree of mid-bass coloration.
    * Rather low overall efficiency.

My angular spiral designs do not use a damping material at all and a good portion of the rear wave energy is emitted through the rear opening. Also, the impedance peaks of angular spiral seem to be very big compared to those of typical TLS.
I don't know whether these differences with above definition of TLS have essential significance.

Helix-AG140BS

For 8 cm (3") full range : Revised on 19 May. 2007

This is a modified version of AG140. Full range drivers used are, Fostex's 8 cm FF85K.
Fins on each side plate were increased to 4 from 3, and the cabinet depth was increased by 2 cm. A damping material was not required.

The lower limit was extended about 10Hz for 4 fins comparing to 3 fins. Hence, feeling of acoustic field was improved significantly.

(25 May. 2007)
AG140M : The design was modified for 18mm thick MDF.

(1 Apr. 2007)
Recently, I put on SA/F80AMG to AG140BS cabinet instead of FF85K, and have been surprised freshly by the change of sound quality with different drivers.
SA/F80AMG has an affluent bass no less than adjoining AG250BS.
On the contrary, FF85K has a crisp and clear sound with a sense of speed.

Z series

(29 Aug. 2007)
AG140Z : The fin configuration was altered for front opening.

Thickness of the plank is 15 mm for cabinets and fins.
Edges of the fins are rounded for a smooth sound passage.

Helix-AG160BS

For 10 cm (4") full range : Revised on 28 Apr. 2007

Full range drivers used are, Fostex's 10 cm FE103E. The baffle hole diameter is 100mm for allowing the installment of FE108E sigma.
Fins on each side plate were 4. A damping material was not required.

(4 May. 2007)
AG160M : The design was modified for 18mm thick MDF.

(23 Nov. 2007)

AG160Z : The fin configuration was altered for front opening.

Thickness of the plank is 15 mm for cabinets and fins.
Edges of the fins are rounded for a smooth sound passage.

Helix-AG180BS

For 12 cm (4.5") full range : Uploaded on 10 Apr. 2007

Full range drivers used are, Fostex's 12 cm FE126E.
Fins on each side plate were 4. A damping material was not required.

I have confirmed the difference of frequency response between 4 fins and 5 fins are negligible small. Therefore, 4 fins are better for work saving.

(26 Apr. 2007)
AG180M : The design was modified for 18mm thick MDF.

(7 Aug. 2007)
AG180Z : The fin configuration was altered for front opening.

Thickness of the plank is 15 mm for cabinets and fins.
Edges of the fins are rounded for a smooth sound passage.

Helix-AG200BS

For 16 cm (6.5") full range : Uploaded on 14 Feb. 2007

I have built a pair of book shelfs mounted with 16 cm (6 inches) full range, Fostex FE166E.
Each side plate has 5 fins. A damping material was not required.

They have a pleasing sound with plenty of deep bass and with a crisp and clear mid-range as anticipated, almost equal to AG250BS.

(28 Jul. 2007)

AG220Z : The design was modified for 21 mm thick MDF.

Thickness of the plank is 15 mm for cabinets and fins.
Edges of the fins are rounded for a smooth sound passage.

Helix-AG250BS

For 20 cm (8") full range : Uploaded on 26 Jan. 2007

I have built a pair of book shelfs mounted with 20 cm (8 inches) full range, Fostex FE206E.
Each side plate has 4 fins. A damping material was not required.

They have a pleasing sound with plenty of deep bass and with a crisp and clear mid-range as anticipated.
Frequency response is more flat compared to Helix-L150 with the same FE206E.

(13 May. 2007)
The optimum rear opening may be 35mm x 2 holes (equivalent to single 50mm hole).
The influence of rear opening on frequency response.

(14 Dec. 2007)

AG280Z : The fin configuration was altered for front opening.

Thickness of the plank is 15 mm for cabinets and fins.
Edges of the fins are rounded for a smooth sound passage.

Helix-AG100

Uploaded on 25 Sep. 2006

This is the first example of the angular spiral.
Six acoustic fins are fixed on each side-plate. All fins are put in equal angle.
Full range drivers used are Fostex's 8 cm FF85K.

The measurements of frequency responses and impeadance characteristics indicate the lower limit is about 54 Hz and bass reflex behavior still acts an important role.
The sound is clear and crisp with sufficient lower level.

Spiral passage (Unit of length: mm)
•Thickness of plywood is 12mm. •Acoustic absorption material is not used

Helix-AG100M

Uploaded on 17 Feb. 2007

The design was updated by increasing fins and reversing the direction of open mouth for more deep bass.
The performance is not proofed yet.

Helix-AG150

Uploaded on 1 Oct. 2006

This is the second example of the angular spiral.
Similarly to AG100, six acoustic fins are fixed on each side-plate.
But, they are put in different angles for forming an expanding sound passage.
A damping material was not used initially, but it was revealed later that a plenty of Thermo-wool in the throat was effective for obtaining a high quality bass.

Full range drivers used are Fostex's 12 cm FE126E with low Q_ts (0.25) designed for back loaded horn.

The sound is clear and crisp with sufficient and well controlled lower level.

Full-range	FE126E (Fostex)
Height	800 mm (except base)
Width	150 mm (except base)
Depth	180 mm (except base)
Air chamber volume; V	2.9 liters
Rotation number of spiral; n	5
Rotation number of sonic fins	6
Max length of sound passage; L	280 cm
Cross sectional area of throat; S	37 sq. cm

Spiral passage (Unit of length: mm)
•Thickness of plywood is 15mm.

Helix-AG75

Uploaded on 21 Oct. 2006

This is the third example of the angular spiral.
The spiral port of H75 was replaced with an angular spiral port.
ag75-h75

The sound of AG75 is similar to H75.
The frequency response of AG75 is almost the same as H75. Both have a strong and broad peak at 150 Hz, and now clearly the peak is attributed to the microphone MM-TMM-1, which has been used recently insted of broken Primo EMU-4535-2.

Angular Spiral passage
(Unit of length: mm)
ag75-spr

Helix-AG200

Uploaded on 3 Nov. 2006

This is the fourth example of the angular spiral.
AG200 has 4 fins with a constant interval fixed on each side-plate.
A plenty of Thermo-wool was placed in the triangle nearest to the driver as a damping material. Also, several small pieces of felt were glued to the wall of the air chamber for preventing standing wave.

Full range drivers used are Fostex's 16 cm FE166E with an affordable price and a low Q_ts (0.21) designed for a back loaded horn.

The sound is clear and crisp with well controlled and very powerful deep bass as if there is a high quality sub-woofer. The Higher region has a sensitive and exquisite tone unexpected from a relatively big full range driver.
This is the best speaker I have built so far.

15 Dec. 2006 : The damping material stuffed in the air chamber was taken out and, at the same time, rear opening was reduced to 25 sq. cm from 45 sq. cm by putting a temporary board with two holes. The diameter of the holes was 40 mm each, total area was 25 sq. cm (= 0.19Sd). By taking these measures, booming tendency on heavy bass was curbed completely witout damping materials.

20 Dec. 2006 : Frequency responses were compared on the different rear openings. There was only a slight shift to lower direction on the smaller one. But, the newly appeared impedance peak at 171 Hz indicates a change on the behavior of the cabinet.
ag200-holes

10 Jan. 2007 : The rear openings were reduced further to two 35 mm diameter holes, total area was 19.2 sq. cm (=0.14Sd).
The frequency and impedance responses indicated heavy bass was enhanced further, and sound was more pleasing with fulfilling bass. There were a harmful side effect, reverberation at higher range. By stuffing the damping material which was taken out previously, the problrm was solved.
ag200-35mm

Full-range	FE166E (Fostex)
Height	850 mm
Width	200 mm
Depth	230 mm
Air chamber volume; V	6.6 liters
Rotation number of spiral; n	3
Rotation number of sonic fins	4
Max length of sound passage; L	237 cm
Cross sectional area of mouth; S	45 32 sq. cm

Spiral passage (Unit of length: mm)
•Thickness of plywood is 15mm. Fins are 12 mm thick.

Helix-AG180

Uploaded on 18 Nov. 2006

This bookshelf cabinet is the fifth example of the angular spiral.
AG180 has 4 fins on one side plate and 3 fins on another side plate with a constant interval. The rotation number of spiral is 2.5.
A damping material was not used at all.

Full range drivers used are the same as AG150, Fostex's 12 cm FE126E with low Q_ts (0.25) designed for back loaded horn.

The mid and high range of AG180 has a higher resolution than AG200, although I prefer mildness of AG200. Its lower region is surprisingly powerful considering the size.
As a whole, AG180 is superior to AG150.

Full-range	FE126E (Fostex)
Height	380 mm
Width	180 mm
Depth	310 mm
Air chamber volume; V	2.6 liters
Rotation number of spiral; n	2.5
Rotation number of sonic fins	3.5
Max length of sound passage; L	256 cm
Cross sectional area of mouth; S	30 16 sq. cm

Spiral passage (Unit of length: mm)
•Thickness of plywood is 15mm. Fins are 12 mm thick.

Helix-AG140

Uploaded on 29 Nov. 2006

This bookshelf cabinet is the sixth example of the angular spiral.
AG140 has 3 fins on both side plates with a constant interval. The rotation number of spiral is 2.
A damping material was not used at all as same as AG180.

Full range drivers used are, Fostex's 8 cm FF85K.

The effect of the rear opening was checked by a varied opening attachment with a 3 cm hole (7 sq. cm = 0.25Sd). The result indicated the 3 cm hole was much superior to the original 4 cm hole. It may be possible to consider the shortness of the max length of sound passage is compensated with the narrowness of the rear opening.
This might be a proof of the "back pressure assumption."
Its lower region is surprisingly powerful considering the size.

Full-range	FF85K (Fostex)
Height	280 mm
Width	140 mm
Depth	210 mm
Air chamber volume; V	1.2 liters
Rotation number of spiral; n	2
Rotation number of sonic fins	3
Max length of sound passage; L	148 cm
Cross sectional area of mouth; S	7 sq. cm (3 cm hole)

Spiral passage (Unit of length: mm)
•Thickness of plywood is 15mm. Fins are 12 mm thick.

Helix-AG250

Uploaded on 4 Dec. 2006

Several people asked me to show a drawing for 20 cm (8 inches) full range.
Here, I upload a drawing of Helix-AG250 for Fostex's 20 cm full range, FE206E, FE208 sigma, FE208E sigma, FE207E, FF225K, FX200 and F200A. Its performance is not proofed yet.

Thickness of the plank is 20 mm for cabinets and 12 to 15 mm for fins.
The top plate and upper part of the cabinet should be reinforced because they are most likely to vibrate.

Helix-AG300

Uploaded on 10 Dec. 2006

Someone asked me to show a drawing for 10 inches full range.
Here, I upload a drawing of Helix-AG300 for Audio Nirvana Super 10. Its performance is not proofed yet.

Thickness of the plank is 20 mm for cabinets and 15 to 20 mm for fins.
The top plate and upper part of the cabinet should be reinforced because they are most likely to vibrate.

AG142 : The driver for AG140 was exchanged.

The driver for AG140 was exchanged to SA/F80AMG from FF85K.
SA/F80AMG has higher Q_ts than FF85K.
The sound changed to warmer and milder one, but the shift of frequency response was small.
The details are here.

AG145

The fins and the depth were increased than AG140 for investigating the effects of fins number.
The results indicated there was no sensible change except slight lower shifts on mouth output and impedance.
The details are here.

Tasuki Path

The angles of fins are altered so as to cross mutually as indicated in the left drawing.
A view from the side is a pattern called "Tasuki" in Japanese.

tasuki moyou

The sound passages created by the pattern "Tasuki" are far more complicated than the angular spiral, but, the sound quality is almost the same.

Helix-TP140

Uploaded on 27 Dec. 2006

This is the first example of "Tasuki" fins. The enclosure is the same as AG140 except the angles of fins.

The sound quality of TP140 is almost the same with AG140.

Helix-TP430

Uploaded on 27 Dec. 2006

Someone asked me to show a drawing for 38 cm (15") wide range, JBL D-130.
Here, I upload a drawing of Helix-TP430. Its performance is not proofed yet.

Thickness of the plank is 25 mm for cabinets and fins.
The merit of "Tasuki" path may be the mutual reinforcement of fins at the cross points.

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