Compact budget subwoofer: vented or TL/Horn? - diyAudio
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Old 29th January 2009, 09:37 PM   #1
mvangel is offline mvangel  Bulgaria
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Default Compact budget subwoofer: vented or TL/Horn?

Hello all,

I have started my first subwofer project some weeks ago with couple of clear objectives:
1. No time constrains to finish the sub
2. Limited budged and exposure to money risk in case of whole project going out of control: current budget 100 eur
3. Limited required external size of the finished enclosure: max external dimension should fit the maximum SAF (or WAF) and be less then 600x480x300 mm or 86 litres. The smaller, the better
4. Best case frequency response: F3 around 30-35 Hz

After quite some research (1 month already) and simulations with all the tools I could get hands on or evaluate, I have reached the following preliminary candidates for results:
1. Drivers: TVM ARN226/7 at 4 Ohms. Parameters:

Name: ARN226-07.1/4
Type: Standard one-way driver
Company: TVM
Serial No: ARN226-07/4
No. of Drivers = 1
Fs = 33 Hz
Qms = 4.443
Vas = 77.14 liters
Cms = 1173 m/N
Mms = 18.46 g
Rms = 0.926 kg/s
Xmax = 7 mm
Sd = 216.4 sq.cm
P-Vd = 0.151 liters
Qes = 0.494
Re = 3.452 ohms
Le = 1.021 mH
Z = 4 ohms
BL = 5.172 Tm
Pe = 70 watts
Qts = 0.444
no = 0.541 %
1-W SPL = 88 dB
2.83-V SPL = 93.13 dB

Here in Bulgaria this costs 14 Eur a piece. As the simulation showed significant improve, I've decided to go for a design with 2 drivers mounted in isobaric, push pull configuration, resulting in Vas for the drivers to reach 33 Hz of only 39 liters! (ok, I know this could be much better, but for the price of 28 Eur, this is a steal)

2. I've found a locally produced amp for subs. With integral design, hefty toroidal power supply, and rated 70W at 8 Ohms, I'd assume it would easily push the pair of ARN226 in the upper 90 SPL levels. Simulations show positive results.

3. Enclosure design.
This is where I would kindly ask for your help.

I have done the simulations with various sized of vented boxes. Attached bellow are the simulations:

My question is the following: Can I do better with this drivers and such amp?

Can I TL be implemented with such objectives in mind? The TL idea came into my mind after increasing the vent length and eventually I thought "what if it becomes very large", then I've read the theory on TL and started calculating. How should I chose the right ratio? I've read various options on, but how should I chose the right for these drivers?



http://www.t-linespeakers.org/design/taper.html


Quote:
These are all Classic lines from when designers were just guessing, cutting & trying.

Author Publication (/Sd) Comments
Atkinson 5-way Transmission-line 1.4 .6
Bailey A Non-resonant Loudspeaker Enclosure Design >=1
Bailey The Transmission-line Loudspeaker Enclosure 1.35 .6
V. Dickanson Loudspeaker Design Cookbook 1.25-2.5 1
Radford Studio S.90 1.66 .75
C. Rogers The Pro 9TL Domestic Monitor 1.5 1
C. Rogers HiFi Answers 1.5 .68
R. Sanders Electrostatic Loudspeaker Design Cookbook 1.25 1
"Classic Line" Seaford HiFi World 1.1-1.5 1
D. Weems How to Design, Build & Test Complete Speaker Systems 1.5-2 1
Attached Images
File Type: jpg simulation_arn226_v3.jpg (99.1 KB, 626 views)
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Old 30th January 2009, 09:28 AM   #2
mvangel is offline mvangel  Bulgaria
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Here is the most compact design I could find so far:
simple vented box
external dimensions : w/h/d: 25cm / 38cm / 60 cm

Volume: total 42 liters, Vb 30 liters
Vent dimensions: 30mm / 217 mm / 520

Simulated response:
Fb= 35.76
F3= 39.29 at 103 dB / 70 watts

Could I still achieve more with these drivers? so far my calculations for TL have shown min increase of volume needed is double!

Any suggestions?
Attached Images
File Type: jpg sub_enclosure.jpg (22.7 KB, 660 views)
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Old 30th January 2009, 01:38 PM   #3
GM is offline GM  United States
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Greets!

At a glance, an isobaric B@$3 WC might work well in as little as 28.3 L net Vb, but folding it up to make it compact will obviously increase total Vb, so probably at least as big as your best effort.

GM
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Old 30th January 2009, 07:46 PM   #4
mvangel is offline mvangel  Bulgaria
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@GM, I am sorry, but I missed your point: what does "B@$3 WC" mean?

What would be the most convenient way to calculate the needed parameters for a TL for these drivers? Once I have the parameters, I could put the dimensions through some scripts in CorelDraw I work with to measure the min required volume.
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Old 30th January 2009, 07:50 PM   #5
jbell is offline jbell  United States
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some people just can't say 'bose'
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Old 30th January 2009, 08:02 PM   #6
mvangel is offline mvangel  Bulgaria
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Thanks.

This is quite funny though

Actually, I would count bose as inspiration for such project: they succeed in making a decent sounding subs (lets not argue on the wording "decent") in a small volume with cheap drivers. As an engineering achievement they prove it is possible. However, considering they are profi and am newbi amateur, I am very fascinated to observe if I could achieve comparable results using internet forums instead of corporate know how.

P.S.Ok, B@$3 is bose, but what is WC? I am not used to the lingo yet...
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Old 30th January 2009, 08:04 PM   #7
jbell is offline jbell  United States
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wave cannon, 3:1 ratio pipes on each side of a driver. been looking at that lately, and I can see where the one note wonder bose sound comes from ....
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Old 30th January 2009, 11:57 PM   #8
GM is offline GM  United States
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Quote:
Originally posted by jbell
some people just can't say 'bose'
It's a matter of 'won't'. They have a history of using their legal power to go after anybody that has other than praise for their products.........

GM
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Old 31st January 2009, 12:16 AM   #9
GM is offline GM  United States
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Quote:
Originally posted by jbell
wave cannon, 3:1 ratio pipes on each side of a driver. been looking at that lately, and I can see where the one note wonder bose sound comes from ....
Yeah, below is a dual TB W6-1139SI BWC/2.83 V on axis in 1pi space since normally that's the way folds mount them if unfolded. A lower Qts driver would flatten it some, but not enough.

GM
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File Type: gif tb w6-1139si dual bwc.gif (21.4 KB, 534 views)
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Old 31st January 2009, 08:08 PM   #10
mvangel is offline mvangel  Bulgaria
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Very interesting to see another post of a simulated response. With bass box pro, I could see the following when increasing the port size to a 1/4 TL length of 2145 mm and the TL tuned to 33 Hz, as per the driver Fs (yellow line) . "normal" Vented box is in red"

It does not look better than the vented box and those peaks look quite bad in all the diagrams.

Despite all my good intentions to try a TL for the hack of it and the experience, it looks like for my objectives of compact sub the vented option would be better.
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