Basic basshorn design questions

[Guest " "]

Mike,

Tractrix bass horn is not the way to go, per Edgar. He says "tractrix bass horn" is a contradiction of terms.

http://www.positive-feedback.com/Issue4/edgarinterview.htm

" ......so when I built a 70 Hertz Tractrix Bass Horn (Speaker Builder, 1983), I

was in for a surprise. The problem is that the Tractrix is a short horn. If you take the equivalent Tractrix and equivalent exponential horns (same mouths, same throats, same flare rates), the Tractrix horn is shorter. At the low end, the response on any horn is limited by the throat reactance, which peaks at the flare frequency. The exponential horn is long enough that if you can put on a back chamber and resonate it with your loudspeaker at the flare frequency, you can partially cancel out that throat reactance.

With a hyperbolic exponential horn, you can cancel it out exactly.

 With a Tractrix horn, you don't cancel it out at all, so the 70-Hertz horn rolled off at 100 Hertz. It sounded very good, but the problem is that the Tractrix horn response just does not extend to the flare point. There is no way that you can do it, so you have to live with the consequences. Well, for a midrange horn that's not too bad. The 300-Hertz horn that I make turns on at around 400 Hertz, and since its size is not huge, I can build a full-size

300-Hertz horn. It sounds very nice, but it won't turn on until 400 Hertz."

There is something here worth investigating furthur.

Any examples of a horn optimized for lower mid-bass?

[jwc]

Ok..lets go a little further. Read the above and Gil's throat riddle. Also see Dana's response.

jc

[jwc]

So to start with. Does my throat start here? Duplicated at 3 x 13".

jc

[jwc]

If so, I am gonna get about 14" in horn length from the throat to the edge of this motorboard (7" in both direction). This is just with an example of the La Scala motorboard which is 15.25 inches.

jc

[jwc]

The point above about the dead space in the la scala is not a good idea here. Will probably make the Horn wider than it need to be. Maybe I will consider the triangle like the belle except not as wide of a motorboard. Will ponder more on this once I get the throat concept clear as to where it starts. I guess it is official, 78 sq in it is.

jc

[ajsons]

For simplicity, yes, that's where I'll start, at the center. It gets complicated because of the 3 x 13 cutout. If the motorboard cutout is 6 x 13, then it is much easier to see.

Your horn length (total distance traveled, so far, is only 7", not 14. Yes the board width is 14. And you're on the right track as far as changing the dead space into something usable..

[ajsons]

The drawing shows a throat 6" wide, duct = 3". Effectively you now have two horns, one going to the left, one to right. Taking the center of the 3" path of the right horn, it is 1-1/2 if you start from the throat going up to the horizontal center. If you start at the center of the board, it is also 1-1/2. So it is the same.

Don't ask me what happens if the cutout is 3 x 13. Honestly I can't explain that one.

[Guest " "]

The drawing shows a throat 6" wide, duct = 3". Effectively you now have two horns, one going to the left, one to right. Taking the center of the 3" path of the right horn, it is 1-1/2 if you start from the throat going up to the horizontal center. If you start at the center of the board, it is also 1-1/2.  So it is the same.

Don't ask me what happens if the cutout is 3 x 13. Honestly I can't explain that one. 

point of very minor clarification. although there probally should be, there are no 45 degree angle inserts in the lascala. it's a sharpe 90 degree turn.

also my 1976 lascala's have a 3 inch wide slot at the face of the motorboard. I have never removed the woofers in my 1986 or 2004 lascala's, so I can't say for sure what thye have.

I think a 6 X 13 wide slot in a lascala would be helpful if the 45 degree inserts were in place and the section after the first turn did expand.

not sure of any needed changes to the depth of the first section to accomidate a wider deflection insert. if you did not widen it, there would be some bounce back.

I remember building a corner horn during the mid 80's that was more like a jubilee than a k-horn and decided to use expansion in both directions in the first section rather than the insert used in the LaScala.

[ajsons]

I know that. I'm trying to show how I will do it, unforunately I didn't clarify that. It just happened that I have a drawing of a La Scala handy, with some of the changes I'd like to see.. The truth is, I never liked the design. I don't know why I'm even on this thread.

I'll use a full Huygen reflector, though.

Edit: Actually, I know why I'm on this thread. I've seen most of JC's work and I'm impressed by his accomplishments, esp. the dual 15 corner bass bin. Great job, JC.

[Guest " "]

Rman, you have a PM waitng

[DrWho]

Just a thought...perhaps the approach of not using a full reflector on the first split was intentional...the 'interference' might work to reduce peaks at certain frequencies for example?

Doesn't 3" correlate to the wavelength of 4300Hz? So you've only got issues starting as low as 1kHz, which is right at the upper limits of the horn?

[jwc]

Rman. Thanks for the compliment.

Guys. I guess I was a little messed up on horn length. This may make me mess up on calculating the horn area at a certain "inch of the horn" if I don't get this right.

So you say with my previous sketch that my horn length is only 7 inches long so far. Ok. Now in order for me to calculate the area of the horn at that point...is it 7" x 3" or is it 7" x 1.5".

Next thing. I schetched this out on full size 1" graph paper so far. Top view like what you guys have just posted. The distance between the motorboard and the back wall is 3"...right. Now I ran a string thoughout the horn ON THE LEFT HORN and I got somewhere between 60-62". Now there will be only dead space at the first turn. I won't be doing the dead space like the scala but like the Bell. The 180 degree turn at the back of the "W shape" won't be dead space as I am gonna try and make a continous curve for tractrix or exponential. Don't ask me how I gonna do this...I will figure it out later. BUT. Eventhough the first 90 degree turn isn't like the scala, I will lose a little horn length there as I am going to keep at about 3" throughout the turn.

So does my horn length of 60" seem right? If so, I should be able to get a lower cutoff...right? I will figure out the height later. I'm shooting for total width of project ~40-42" and height ~38-40". We'll see what I come up with.

Couple of standards I am going to stick with:

1. Total 4 square foot mouth as like the scala, Belle and Khorn.

2. Slot 3 x 13.

The above seems to be liked by the K33.

So. You guys want to give me the data on a 60" horn with a 4 sq foot mouth (or 2304 sq in). Is it too soon for this? Tractrix?

jc

[jwc]

Can you guys (hell YALL, what's my problem?) shoot me a calculator that is in inches.

[Guest " "]

DrWho

I agree on the effect.

Part of the design of the heritage products was their qualities to use both the xovers and their horns to introduce a natural roll off.

So yes, having a LF horn that rolled off agressively above 400hz was just as much OK as having the mid horn play a key roll in rolling off at the mid and tweeter boundery rather than the tradtional use of a capacitor to ground in the mid circut to perform that function.

[jwc]

It is obvious I'm off somewhere. Look at this motorboard showing only the bottom left quarter. This was for an exponential horn with a 35Hz cutoff. I was trying to figure out the "wings". I'm using metrics for the moment not inches. Now, 78 sq in is equal to 503.22 sq cm.

The first 1 cm flare took me way down the board. The motor board height ended up right at 39 INCHES. That is OK. Can an exponential flare that quick or am I starting off with the wrong throat area?

jc

[jwc]

Here is the Horn calculation example.

Exponential Contour

Throat = 503.22, fo = 35.0, sizeFactor = 8

<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Distance Radius Area Contour Width

0.0 12.7 503.2 12.0

1.0 12.7 509.7 12.1

2.0 12.8 516.3 12.3

3.0 12.9 522.9 12.4

4.0 13.0 529.6 12.6

5.0 13.1 536.4 12.8

6.0 13.2 543.3 12.9

7.0 13.2 550.3 13.1

8.0 13.3 557.4 13.3

9.0 13.4 564.6 13.4

10.0 13.5 571.9 13.6

11.0 13.6 579.2 13.8

12.0 13.7 586.7 14.0

13.0 13.8 594.2 14.1

14.0 13.8 601.9 14.3

15.0 13.9 609.6 14.5

16.0 14.0 617.4 14.7

17.0 14.1 625.4 14.9

18.0 14.2 633.4 15.1

19.0 14.3 641.6 15.3

20.0 14.4 649.8 15.5

21.0 14.5 658.2 15.7

22.0 14.6 666.7 15.9

23.0 14.7 675.3 16.1

24.0 14.8 683.9 16.3

25.0 14.8 692.7 16.5

26.0 14.9 701.7 16.7

27.0 15.0 710.7 16.9

28.0 15.1 719.8 17.1

29.0 15.2 729.1 17.4 motorboard at 11.5" to one side

30.0 15.3 738.5 17.6

31.0 15.4 748.0 17.8

32.0 15.5 757.6 18.0

33.0 15.6 767.4 18.3

34.0 15.7 777.2 18.5

35.0 15.8 787.2 18.7

36.0 15.9 797.4 19.0

37.0 16.0 807.6 19.2

38.0 16.1 818.0 19.5

39.0 16.2 828.5 19.7

40.0 16.3 839.2 20.0

41.0 16.4 850.0 20.2

42.0 16.6 860.9 20.5

43.0 16.7 872.0 20.8

44.0 16.8 883.2 21.0

45.0 16.9 894.6 21.3

46.0 17.0 906.1 21.6

47.0 17.1 917.8 21.9

48.0 17.2 929.6 22.1

49.0 17.3 941.5 22.4

50.0 17.4 953.7 22.7

51.0 17.5 965.9 23.0

52.0 17.6 978.4 23.3

53.0 17.8 990.9 23.6

54.0 17.9 1003.7 23.9

55.0 18.0 1016.6 24.2

56.0 18.1 1029.7 24.5

57.0 18.2 1042.9 24.8

58.0 18.3 1056.4 25.2

59.0 18.5 1070.0 25.5

60.0 18.6 1083.7 25.8

61.0 18.7 1097.7 26.1

62.0 18.8 1111.8 26.5

63.0 18.9 1126.1 26.8

64.0 19.1 1140.6 27.2

65.0 19.2 1155.3 27.5

66.0 19.3 1170.1 27.9

67.0 19.4 1185.2 28.2

68.0 19.5 1200.4 28.6

69.0 19.7 1215.9 28.9

70.0 19.8 1231.5 29.3

71.0 19.9 1247.4 29.7

72.0 20.1 1263.4 30.1

73.0 20.2 1279.7 30.5

74.0 20.3 1296.2 30.9

75.0 20.4 1312.8 31.3

76.0 20.6 1329.7 31.7

77.0 20.7 1346.8 32.1

78.0 20.8 1364.2 32.5

79.0 21.0 1381.7 32.9

80.0 21.1 1399.5 33.3

81.0 21.2 1417.5 33.8

82.0 21.4 1435.8 34.2

83.0 21.5 1454.2 34.6

84.0 21.7 1472.9 35.1

85.0 21.8 1491.9 35.5

86.0 21.9 1511.1 36.0

87.0 22.1 1530.5 36.4

88.0 22.2 1550.2 36.9

89.0 22.4 1570.2 37.4

90.0 22.5 1590.4 37.9

91.0 22.6 1610.8 38.4

92.0 22.8 1631.6 38.8

93.0 22.9 1652.6 39.3

94.0 23.1 1673.8 39.9

95.0 23.2 1695.4 40.4

96.0 23.4 1717.2 40.9

97.0 23.5 1739.3 41.4

98.0 23.7 1761.7 41.9

99.0 23.8 1784.3 42.5

100.0 24.0 1807.3 43.0

101.0 24.1 1830.5 43.6

102.0 24.3 1854.1 44.1

103.0 24.4 1878.0 44.7

104.0 24.6 1902.1 45.3

105.0 24.8 1926.6 45.9

106.0 24.9 1951.4 46.5

107.0 25.1 1976.5 47.1

108.0 25.2 2001.9 47.7

109.0 25.4 2027.7 48.3

110.0 25.6 2053.8 48.9

111.0 25.7 2080.2 49.5

112.0 25.9 2107.0 50.2

113.0 26.1 2134.1 50.8

114.0 26.2 2161.5 51.5

115.0 26.4 2189.4 52.1

116.0 26.6 2217.5 52.8

117.0 26.7 2246.1 53.5

118.0 26.9 2275.0 54.2

119.0 27.1 2304.2 54.9

120.0 27.3 2333.9 55.6

121.0 27.4 2363.9 56.3

122.0 27.6 2394.3 57.0

123.0 27.8 2425.2 57.7

124.0 28.0 2456.4 58.5

125.0 28.1 2488.0 59.2

126.0 28.3 2520.0 60.0

127.0 28.5 2552.4 60.8

128.0 28.7 2585.3 61.6

129.0 28.9 2618.5 62.3

130.0 29.1 2652.2 63.1

131.0 29.2 2686.3 64.0

132.0 29.4 2720.9 64.8

133.0 29.6 2755.9 65.6

134.0 29.8 2791.4 66.5

135.0 30.0 2827.3 67.3

136.0 30.2 2863.7 68.2

137.0 30.4 2900.5 69.1

138.0 30.6 2937.9 69.9

139.0 30.8 2975.7 70.8

140.0 31.0 3013.9 71.8

141.0 31.2 3052.7 72.7

142.0 31.4 3092.0 73.6

143.0 31.6 3131.8 74.6

144.0 31.8 3172.1 75.5

145.0 32.0 3212.9 76.5

146.0 32.2 3254.3 77.5

147.0 32.4 3296.1 78.5

148.0 32.6 3338.5 79.5

149.0 32.8 3381.5 80.5

150.0 33.0 3425.0 81.5

151.0 33.2 3469.1 82.6

152.0 33.4 3513.7 83.7

153.0 33.7 3558.9 84.7

154.0 33.9 3604.7 85.8

155.0 34.1 3651.1 86.9

156.0 34.3 3698.1 88.0

157.0 34.5 3745.7 89.2

158.0 34.8 3793.9 90.3

159.0 35.0 3842.7 91.5

160.0 35.2 3892.1 92.7

161.0 35.4 3942.2 93.9

162.0 35.7 3993.0 95.1

163.0 35.9 4044.3 96.3

164.0 36.1 4096.4 97.5

165.0 36.3 4149.1 98.8

166.0 36.6 4202.5 100.1

167.0 36.8 4256.6 101.3

168.0 37.0 4311.3 102.7

169.0 37.3 4366.8 104.0

170.0 37.5 4423.0 105.3

171.0 37.8 4479.9 106.7

172.0 38.0 4537.5 108.0

173.0 38.2 4595.9 109.4

174.0 38.5 4655.1 110.8

175.0 38.7 4715.0 112.3

176.0 39.0 4775.6 113.7

177.0 39.2 4837.1 115.2

178.0 39.5 4899.3 116.7

179.0 39.7 4962.4 118.2

180.0 40.0 5026.2 119.7

181.0 40.3 5090.9 121.2

182.0 40.5 5156.4 122.8

183.0 40.8 5222.8 124.4

184.0 41.0 5290.0 126.0

185.0 41.3 5358.0 127.6

186.0 41.6 5427.0 129.2

187.0 41.8 5496.8 130.9

188.0 42.1 5567.6 132.6

189.0 42.4 5639.2 134.3

190.0 42.6 5711.8 136.0

191.0 42.9 5785.3 137.7

192.0 43.2 5859.7 139.5

193.0 43.5 5935.1 141.3

194.0 43.7 6011.5 143.1

195.0 44.0 6088.8 145.0

196.0 44.3 6167.2 146.8

197.0 44.6 6246.5 148.7

198.0 44.9 6326.9 150.6

199.0 45.2 6408.3 152.6

200.0 45.5 6490.8 154.5

201.0 45.7 6574.3 156.5

202.0 46.0 6658.9 158.5

203.0 46.3 6744.6 160.6

204.0 46.6 6831.4 162.7

205.0 46.9 6919.3 164.7

206.0 47.2 7008.3 166.9

207.0 47.5 7098.5 169.0

208.0 47.8 7189.8 171.2

209.0 48.1 7282.3 173.4

210.0 48.5 7376.0 175.6

211.0 48.8 7471.0 177.9

212.0 49.1 7567.1 180.2

213.0 49.4 7664.5 182.5

214.0 49.7 7763.1 184.8

215.0 50.0 7863.0 187.2

216.0 50.3 7964.2 189.6

217.0 50.7 8066.6 192.1

218.0 51.0 8170.4 194.5

219.0 51.3 8275.6 197.0

220.0 51.7 8382.1 199.6

221.0 52.0 8489.9 202.1

222.0 52.3 8599.2 204.7

223.0 52.7 8709.8 207.4

224.0 53.0 8821.9 210.0

225.0 53.3 8935.4 212.7

226.0 53.7 9050.4 215.5

227.0 54.0 9166.8 218.3

228.0 54.4 9284.8 221.1

229.0 54.7 9404.3 223.9

230.0 55.1 9525.3 226.8

231.0 55.4 9647.8 229.7

[jwc]

There is something weird here. I am off by a factor of 2. If I use throat are of 39 sq in, I get the below. Make the lines "match up". Also makes for a wide and short bass cabinet.

jc

[jwc]

Interesting. After doing all that. THAT IS WHAT THE BELLE IS. That second drawing is what the motorboard with the wings comes up to be. Same height and width of a Belle motorboard with the same angle flare/wings. Making the horn continue on in the "W" shape......is that going to give me the lower cutoff? Man this is weird.

jc

[D-MAN]

JC, you're scaring me! What are you up to?

1) choose an overall Fc for your horn. Calculate the wavelength for that.

2) choose an appropriate driver (this determines the throat size, which in turn determines everything else). Or choosing a specific throat size will dictate the driver, your choice...

3) determine the placement of the cabinet (full, half, quarter, eighth space). This determines the size of the mouth for the given wavelength.

4) determine overall length needed to follow exponential curve from throat (size) to mouth (size). Basically, using PWK's formula as described in the "Little B@stard" patent, that is a doubling point of 1/18.1 of the wavelength at the flare rate (Fc) in inches. That means the cross-sectional area at the throat doubles every length of whatever 1/18.1 of the flare rate resolves to. This also determines the length of the horn. Choosing an arbitrary length (1/4 or 1/2 wavelength) to start with is not really effective.

Do your design with the above information.

There you go in a nutshell. Ok, yes, it gets worse when you go for different flare rates along the horn path. Break out your calculator, cause you're going to need it!

I would recommend that you use a single flare all the way especially the first time out.

The LS/Belle/Jubilee/Khorn all have multiple flare rates. The calculations put forth by Olson are for determining the acoustic resistance at each "throat" section of the various rates - are you sure that you want to bite that off right away?

DM

[jwc]

Hey Dana. Yes, you ought to know by now I dive and dive deep.

Remember, this thread was meant to get some basic understanding of a few things so I could move forward. How far I will go? never know.

Anyhow, some of those questions of yours have been addressed but not written in stone. The thing is, I don't want to build too big of a monster and I am trying not to have a wierd shape. I definately can't visualize that.

Here is a few knowns that I will stick too because there is an "expected" outcome.

1. The Fc I would expect to be around 40-45Hz. Not solid on this.

2. I will use a K33 or Bob's woofer and the Slot and throat as the scala, belle and khorn

3. I was thinking 1/4.

4. You got me on that one. I last night was calculating the cross sectional area at every one centimeter (could of done it in inches) from the throat. My input numbers were just there for experimantation from software. You don't have a copy of the "little bastard" patent do you?

Dana. The above test of mine was to see if I could get the throat right. I can pretty much visualize in my head of calculating from throat to mouth the cross sectional area needed for a straight horn. I was thinking with the 1/4 wavelenth horn that I wouldn't have a monster.....Fc~40-45? However, not aware of the "That means the cross-sectional area at the throat doubles every length of whatever 1/18.1 of the flare rate resolves to".

My big hang up was the throat and its cross sectional area in the scala/K33 3 x 13 slot.

In my mind I was thinking of a horn "like" the jubilee with one 15 inch driver. In my head it seems the "wings" or "flares" from the throat from one woofer would give me a squaty shapped horn...like a super wide Belle.

jc