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TH 15" flat response to 35Hz (-3dB) - By LORDSANSUI
TH 15" flat response to 35Hz (-3dB) - By LORDSANSUI
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Old 7th November 2016, 08:42 PM   #1
LORDSANSUI is offline LORDSANSUI  Brazil
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Default TH 15" flat response to 35Hz (-3dB) - By LORDSANSUI

Hello all,

Time to post some results, but before, I'd like to say thanks to all guys who have been supporting / teaching / encouraging me to learn more about TH design.

After some benchmark between lots of different cab I decided to choose TH one due to the large documentation available for design but also due to good results between simulation and real worlds.

The base design is the SS15 published by Jbell (He has one sheet build constrain, I'm not )

Single sheet TH challenge

or TH18 published by Xoc1 (designed for 18" drivers based on Danley's design TH118 that is also based on previous 15" design TH115)

TH-18 Flat to 35hz! (Xoc1's design)

They have the same base design in terms of fold.

Project targets:

Low frequency <40Hz for a single cab
High frequency > 100Hz
Volume < 300 L (reduced from 450L once my current T18 clone cab has 300L with 18” driver and I swapped from 18" to 15")
Single driver
SPL@1m > 98dB

I chose Brazilian driver Snake HPX2150 15” and I also forgot about 18” once I confirmed I could reach my target with 15” one with more compacted size.

Bellow you can find Thielle/Small parameters in comparison with SS15’s driver (Eminence) and also THAM15’s driver (B&C):

Click the image to open in full size.

The design was started using the image below to find the best targets for the cab.

Click the image to open in full size.

The S1 is a results of driver compression ratio (cone area dived by throat area).
Detail about the others parameters see here (credits to soho54):

Hornresp for Dum... hmm... Everyone - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

Like a DOE (design of experiments) I covered the ranged bellow:

Compression ratio: 1:1 till 2,5:1
Note: I didn’t went higher once the driver isn’t stiff enough and the motor strength (BL^2/Re) isn’t that high too.
Horn Length: 250cm till 350cm
Horn expansion angle: 0 degree till 5 degree

The best option I found was:

Compression ratio 2:1
Horn Length: 260cm
Horn expansion angle: 3 degree

Hornresp parameter for base design.
S1: 440 L12: 20 S2: 493,68 L23: 100 S3: 760,92 L34: 120 S4: 1081,71 L45: 20 S5: 1134,75

The next step was to install Solidworks to build the cab thru automatic folding process using parametric sketch.

Click the image to open in full size.

In sequence I also implement an automatic unfolding process. This is very important to guarantee reliability on the hornresp simulation. I used soho54 method that is called “advanced centerline method”.

Click the image to open in full size.

Using parametric CAD software makes things easier when they are well implemented.

Next, I tryed to add the second horn expansion:

Horn expansion angle: from 3 degree till 24 degree.

Click the image to open in full size.
Click the image to open in full size.

The best results condifering 2nd expansion was: 6 degree and 12 degree

Here are my proposals:

Proposal A (HxDxW 762 x 630 x 550 = 264,5L)

Click the image to open in full size.

Proposal B (HxDxW 776 x 625 x 550 = 267,1L)

Click the image to open in full size.

Proposals A and B over righted @ 600W

Click the image to open in full size.

Which one would you guys pick up to build?

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Old 7th November 2016, 09:38 PM   #2
Zero D is offline Zero D  United Kingdom
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Congrats. Excellent grasp of things in a short time Nice cad work too

Both appear good, but B just has the edge @ LF

Can you show Xmax @ full power ?
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Old 7th November 2016, 10:01 PM   #3
LORDSANSUI is offline LORDSANSUI  Brazil
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It's still not fully clear for me if the hornresp has accurate simulation for cone displacement and how this result can be linked to music wave once you don't play pure sine waves.

Proposal A - Cone displacements @ 800 W/4,7ohm

Click the image to open in full size.

Proposal B - Cone displacements @ 800 W/4,7ohm

Click the image to open in full size.
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Old 7th November 2016, 10:03 PM   #4
Brian Steele is offline Brian Steele  Grenada
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Both designs are missing "cone compensation", so the frequency response at the upper end of the passband (where the notch appears) is likely to be a bit different by a few dB.
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Old 7th November 2016, 10:59 PM   #5
LORDSANSUI is offline LORDSANSUI  Brazil
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Here an image to compare SPL@1w/1m the FR from SS15, THAM15 and SS15MOD-B (my proposal for HPX2150 drive).

Click the image to open in full size.
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Old 8th November 2016, 12:25 AM   #6
LORDSANSUI is offline LORDSANSUI  Brazil
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Quote:
Originally Posted by Brian Steele View Post
Both designs are missing "cone compensation", so the frequency response at the upper end of the passband (where the notch appears) is likely to be a bit different by a few dB.

Hi Brian,

Here are additional simulation with 3 different compression ratios.

The new question emerge: Is the HPX2150 drive able to manage 3:1 as compression ratio?

Once I'm no able to answer I was being more careful about compression ratio.

Note: Increasing compression ratio also requires to increase horn angle for the first expansion from 3 degrees to 4 degrees and 5 degree respectively to be able to keep reduced size. But even doing that, higher compression ratio will increase a little the cab volume to cover the same low frequency response. The good side is it will give a lot more high frequencies as you pointed and also helps to reduce max cone displacement.

Click the image to open in full size.
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Old 8th November 2016, 10:46 AM   #7
Brian Steele is offline Brian Steele  Grenada
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Quote:
Originally Posted by LORDSANSUI View Post
Hi Brian,

Here are additional simulation with 3 different compression ratios.
I'm not referring to compression ratios. I'm referring to either adjusting the model to include the volume of air contained by the driver's cone (Vtc and Atc), or adjusting the horn's layout so that the impact of this volume on the performance of the horn is minimized.
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Old 8th November 2016, 12:01 PM   #8
LORDSANSUI is offline LORDSANSUI  Brazil
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Quote:
Originally Posted by Brian Steele View Post
I'm not referring to compression ratios.
True, I worked too much yesterday and was publishing late at night so was my mistake. Anyway the CR = 3 looks good associated to 2nd expansion.

I'm planning to implement cone correction. Is there any guide for it? or it's just to add material with the cone volume aligned to the driver?

I think this design is the easiest one to implement.

Click the image to open in full size.

Anyone have idea to add grip? i think this cab will have more then 50kg so will not be easy to move it.
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Old 8th November 2016, 12:39 PM   #9
Xoc1 is offline Xoc1  United Kingdom
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Hi Lordsansui
Good work. This is the DIY forum after all and its good to see you are 'Doing It for Yourself'!
As for the cone compensation, I would not recommend the extra timber as it reduces volume and increases weight.
I have sketched out a quick mod of your layout. The cone correction line should be set out to suit your speaker cone, and relates to the cross sectional area of the air in the speaker cone. The volume also reduces the area at S4.
The cone correction is not to increase the compression ratio. It makes the ratio correct to your sim, therefore increasing the accuracy.
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File Type: jpg Mod Lordsasui TH15.jpg (86.6 KB, 189 views)
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Old 8th November 2016, 02:19 PM   #10
Zwiller is offline Zwiller  United States
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Nice design and write up! I look forward to seeing this develop.
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