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Old 21st May 2013, 02:04 PM   #1
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Default DBLH

Hi. Weve moved house recently and the new listening room is much smaller than the old one. My BIBs with TB W5-1611 are sounding very different. No bass, all mids. No big surprice really since I tuned them specifically for the old room

So its time for a newer design Im quite fascinated with the Cornu. Two different length horns, big baffle, wall mounted. That plus wall + floor boundary for bass extension ie, making the horn much bigger. And minus the spiral since Im guessing the length would suffice anyway?

Heres some points that summarizes my ideas for the new speaker:

• Very thin and mounted on wall for practical reasons
• Wide baffle for nice transition of baffle step and horn output
• Back loaded horn with two different and offset length horns
• Wall, ceiling + floor boundary loading like Cornu/Klipsch
• Built mostly with styrofoam blocks for the weight. Plus its easier

Ive attached a sketch with dimensions. Chamber volume and design + the horn flare is completely arbitrary. I have no idea what would be good choice for that

What do you think? Would it work as planned?

Regards /Bo
Attached Images
File Type: png Speaker-Sketch1.png (39.0 KB, 388 views)
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Old 21st May 2013, 11:14 PM   #2
xrk971 is offline xrk971  United States
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Danerius,
Neat design. Give me some time to set this up in Akabak. I may go with conical horns at first and then progress to exponential. It should prove interesting. I am wondering if having the two horns end to end will present a full wave double open ended tube boundary condition rather than a 1/4 wave or 1/2 wave. Maybe the throat breaks it up? Perhaps a protrusion to prevent a direct line of sight may delineate the twohorn boundaries? I will keep you posted as soon as I have something. Are you really stuck on the W5-1611 driver?
Regards,
X
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Old 22nd May 2013, 06:13 AM   #3
xrk971 is offline xrk971  United States
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Default Sim of DBLH

Daneris,
Here are some results from my initial model of the DBLH given the parameters you specified. The nominal lengths for the horns did not yield very deep bass extension - only down to 100 Hz. I believe it is due to the concern I had that it would appear as a long double-open ended tube which is only a half-wave resonator, whereas a quarter wave resonator gets you down twice as deep. As a result the horn lengths essentially had to be doubled to get bass down in the 40 to 50 Hz region. This means that you will have to fold your horn line at least once. This is typical for double horns - which are folded many times to keep their size manageable.

The geometry I ended up with is as follows dimensions are in inches multiplied by meters/in (Depth was kept at 3.54 in or 90 mm):
Code:
| Define Horn Segments (need to multiply by Depth for area): S_Throat, S_Mouth, Length

| Shared Throat Segment

	S0T=4.2*0.0254;		S0M=4.21*0.0254;	L0=2.00*0.0254;  | Reduced throat to control HF escaping
	
| First Horn points up

 	S1T=3.00*0.0254;	S1M=40.0*0.0254;	L1=120*0.0254; 
	
| Second Horn points down

 	S2T=3.00*0.0254;	S2M=25.0*0.0254;	L2=95*0.0254;
So the upward pointing horn is 120 in long with a mouth of 40 in and downward is 95 inches long with a mouth of 25 inches. They both started with a 3 in throat fed by a common 4.2 in throat from a 3 liter driver volume chamber.

The sims are for 1 watt at 1 m and show freq response (red is long horn, green is short horn, black is combined with driver radiation), cone displacement, impedance, and impulse response. The impedance plots of double horns is very interesting - you can see the non-linear interactions of one horn with another. What is interesting is that lengthening the shorter horn decreases the frequency extension on long horn output - clearly showing an interaction of how this behaves like a double open ended resonator - which it is.

I did not have too much time to optimize for flat response - later...
Attached Images
File Type: png DBLH-Freq.png (26.3 KB, 325 views)
File Type: png DBLH-Displ.png (19.9 KB, 308 views)
File Type: png DBLH-Impedance.png (21.0 KB, 303 views)
File Type: png DBLH-Impulse.png (12.4 KB, 296 views)

Last edited by xrk971; 22nd May 2013 at 06:16 AM.
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Old 22nd May 2013, 01:17 PM   #4
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Quote:
Originally Posted by xrk971 View Post
Daneris,
Here are some results from my initial model of the DBLH given the parameters you specified. The nominal lengths for the horns did not yield very deep bass extension - only down to 100 Hz. I believe it is due to the concern I had that it would appear as a long double-open ended tube which is only a half-wave resonator, whereas a quarter wave resonator gets you down twice as deep. As a result the horn lengths essentially had to be doubled to get bass down in the 40 to 50 Hz region. This means that you will have to fold your horn line at least once. This is typical for double horns - which are folded many times to keep their size manageable.

The geometry I ended up with is as follows dimensions are in inches multiplied by meters/in (Depth was kept at 3.54 in or 90 mm):
Code:
| Define Horn Segments (need to multiply by Depth for area): S_Throat, S_Mouth, Length

| Shared Throat Segment

	S0T=4.2*0.0254;		S0M=4.21*0.0254;	L0=2.00*0.0254;  | Reduced throat to control HF escaping
	
| First Horn points up

 	S1T=3.00*0.0254;	S1M=40.0*0.0254;	L1=120*0.0254; 
	
| Second Horn points down

 	S2T=3.00*0.0254;	S2M=25.0*0.0254;	L2=95*0.0254;
So the upward pointing horn is 120 in long with a mouth of 40 in and downward is 95 inches long with a mouth of 25 inches. They both started with a 3 in throat fed by a common 4.2 in throat from a 3 liter driver volume chamber.

The sims are for 1 watt at 1 m and show freq response (red is long horn, green is short horn, black is combined with driver radiation), cone displacement, impedance, and impulse response. The impedance plots of double horns is very interesting - you can see the non-linear interactions of one horn with another. What is interesting is that lengthening the shorter horn decreases the frequency extension on long horn output - clearly showing an interaction of how this behaves like a double open ended resonator - which it is.

I did not have too much time to optimize for flat response - later...
Hi and a million thanks for doing a sim for this. I completely missed to include the depth of the styrofoam bits wich (at this point at least) are going to be 30 mm ie. 1.18". So three of them stacked is 90 mm and the horn has a depth of 30 mm. Sorry about that

Being a novice on horns I may have overestimated the boundary loading from wall + ceiling. Most of what I know Ive learned from reading Roy Allisons paper on speakers and room influence. I figured the wall + ceiling would be part of the horn giving a 6-9 dB of low end boost. If anyone can enlighten me on this. Please let me know

Regards /Bo
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Old 22nd May 2013, 02:42 PM   #5
xrk971 is offline xrk971  United States
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Danerius,
You are welcome. I wasn't very happy with the first simulation result as it requires such a long horn (10 ft!) and the impedance curve is a mess showing that there is a lot of horn-to-horn interaction going on. I decided to see what I could do to de-couple the two horns more to make the impedance and driver excursion plots behave better and reducing the horn lengths. It turns out that increasing the driver chamber volume is key as it provides the acoustic capacitance needed to de-couple the two horns thereby smoothing out the impedance and turning them into quarter-wave boundary conditions thus cutting lengths by about half.

The horn profile and chamber volumes are given here:
Code:
Vol_ch = (14.0/1000) ; | Volume of driver chamber in liters
Depth_ch = (3.54*0.0254);  | Depth of driver chamber
| Define Horn Segments (need to multiply by Depth for area): S_Throat, S_Mouth, Length
| Shared Throat Segment
	S0T=3.0*0.0254;		S0M=3.01*0.0254;	L0=5.00*0.0254;
| First Horn points up
 	S1T=2.5*0.0254;		S1M=18.0*0.0254;	L1=60*0.0254;
| Second Horn points down
 	S2T=2.5*0.0254;		S2M=26.0*0.0254;	L2=42.0*0.0254;
As you can seem the long horn length is now 60 inches (5 ft) and shorter horn is 42 in (about a meter) with an 18 in and 26 in mouth, respectively. I reduced the throats of the horns to 2.5 in and the common throat to 3 in with a 5 in duct connecting the driver chamber which has now been significantly increased to 14 liters in volume.

The depth of the chamber and horn is still kept at 90 mm (3.54 in). Your idea of making it only 30 mm is not good as the physical aperture size of the horn mouth determines the lowest frequencies that can get out. Making it 30 mm will reduce this and I believe the W5-1611 driver is 83 mm not leaving very much breathing room behind the driver even at 90 mm. I suggest using the three layers of 30 mm foam like you suggest but using all 3 for the horn and chamber and use thin 1/8 in or 1/4 in plywood for the back and baffle (face). The driver will mount better and it will look nicer. Be sure to use bracing ribs internal to the plywood every 3 or 4 inches to reduce the breathing mode vibrations in the horn.

The results are as follows: freq response (black is total, red is long horn, green is short), cone displacement, impedance, impulse response, all for 1 watt at 1 meter.
Attached Images
File Type: png DBLH-03-Freq.png (25.2 KB, 41 views)
File Type: png DBLH-03-Displ.png (19.8 KB, 36 views)
File Type: png DBLH-03-Impedance.png (20.9 KB, 16 views)
File Type: png DBLH-03-Impulse.png (12.4 KB, 17 views)
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Old 24th May 2013, 05:47 PM   #6
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A million thanks for takin ur time to do these sims Few questions though? How accurate are the response charts? Are they with or without damping?

Is there a point to separating the different horns as much as possible? And is there an ideal ratio ie 1/3, 1/4 etc for the horn lenghts? Thats better to shoot for?

I adjusted the sketch for two ”isolated” horns. The chamber volume is not accurate at all

Regards /Bo
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Old 24th May 2013, 05:49 PM   #7
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And the sketch
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File Type: png Speaker-Sketch-mk2.png (33.4 KB, 93 views)
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Old 24th May 2013, 08:35 PM   #8
xrk971 is offline xrk971  United States
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Danerius,
I don't know how accurate the response is as these are simulations. However, I have been able to confirm that many of my simulations using AkAbak of known systems that also have simulations using MJK's worksheets have provided similar results, albeit, the AkAbak doesn't have any damping effect modeled - so it will have sharp spikey peaks and dips which in all likelyhood will be smoothed out with stuffing. However, wider features in the frequency response curves will be real. The models I have presented only have a back and bottom wall so there is no reflection of the top wall horn - that may change things if it were considered. In your adjusted sketch of isolated horns, you lost some horn length due to chamber length taking up the horn length, and note that it is a different system than the previous one because the horns are now directly coupled to the driver chamber rather than sharing a common throat.
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Old 28th May 2013, 03:08 AM   #9
xrk971 is offline xrk971  United States
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Default PBLH? (5 unequal length BLH)

I ran a sim with 5 or Penta BLH case with a long 12 ft path and each successive one was 0.9, 0.8, 0.7, 0.6 X the length of the longest one. The mouths were all 5x8 in in cross section, and the driver chamber was about 1100 cubic inch (18 liters). It worked out pretty smooth. It would be a complicated build with 5 horn channels but very smooth and gets 30 Hz bass extension. If anyone is interested I will post the sim and design.
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Old 28th May 2013, 03:49 AM   #10
DrBoar is offline DrBoar  Sweden
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Why only 90 mm depth? Are you planing to build in inside a plaster wall with cc 600mm beams?
Crabbe editor of HFN&RR in the 1960s built wall horns somewhat similar to your design using Lowther drivers and a short front horn as well. As I recall they were build flanking a mantle piece so the depth was probably in the order of 300 mm or so.
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