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Old 27th June 2010, 05:17 AM   #1
chaparK is offline chaparK  Luxembourg
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Default TS parameters & closed-box design

Hi all

I'm a beginner in loudspeaker design, and have in mind a 2-way closed-box with one SEAS CA22NRX woofer.

The woofer manufacturer published the following TS parameters:
- fs = 29 Hz
- Vas = 97 l
- Qms = 2.04
- Qes = 0.52

I cannot measure these parameters myself, but found here Poor Man' these numbers:
- fs = 38.5 Hz
- Vas = 51.84 l
- Qms = 2.27
- Qes = 0.51

If i take the manufacturer parameters, i could end with a 25l enclosure targeting F3 at about 60 Hz.

If i take the second set of parameters, the same procedure will lead to a 13l enclosure with F3 at about 80 Hz...

I can live with the imprecision on fs, but i'm more concerned about the value of Vas. If i make a small enclosure i might get a boomy sound, which i don't want. If i make a larger enclosure i might get really little bass...

Any advice on what i should do: trust the manufacturer, trust the independent measurements or look for some compromise?

Regards,

chaparK
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Old 27th June 2010, 08:43 AM   #2
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Hi

A second set of measurements.

Thiel & small CA22RNX
Fs = 38.55 Hz
Re = 5.80 ohms[dc]
Le = 1531.29 uH
L2 = 610.14 uH
R2 = 14.78 ohms
Qt = 0.42
Qes = 0.51
Qms = 2.34
Mms = 22.33 grams
Rms = 2.309682 kg/s
Cms = 0.000763 m/N
Vas = 55.23 liters
Sd= 226.98 cm^2
Bl = 7.820266 Tm
ETA = 0.59 %
Lp(2.83V/1m) = 91.23 dB
Closed Box Method:
Box volume = 65.00 liters
Diameter= 17.00 cm

Do not trust the manufacturer.
I think 30L for a closed box ? F3=64Hz. 25L also works .

Regards.
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Old 27th June 2010, 06:20 PM   #3
gedlee is offline gedlee  United States
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My advice is this. The two sets of measurements should have a decent cone mass calculation - average them. Then ignore the VAS and just use the box compliance. Set the F3 that you want from these numbers and you won't be far off.

"Boomy" is mostly the room and placement and has very liuttle to do with the enclosure design.
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Old 29th June 2010, 10:49 PM   #4
chaparK is offline chaparK  Luxembourg
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Hi Jerome, gedlee,

Thanks for your posts and sorry for answering late.

Given that there are two independent sets of measurements that are mostly identical, i'll go for these and discard the manufacturer data. Hope to post here soon more details as i'm going to need more advices

Regards,

chaparK
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Old 7th August 2010, 09:14 AM   #5
chaparK is offline chaparK  Luxembourg
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Hi all!

I haven't been onto this post for some time. I was busy with the amplifier for my project. It's a 4-channel with Tripath TA2022, one channel per driver.

I know it's not the right place for talking about amplifiers, but well i'm building my whole sound system consisting of DSP + Amp + Speakers, so it's a bit hard to split the project into separate topics.

Here are some pics of the amp (awful picture quality, gee )

I'll be back in a short while with a couple of questions regarding the speaker enclosures!

Best!

chapark
Attached Images
File Type: jpg front.jpg (59.0 KB, 531 views)
File Type: jpg rear.jpg (54.3 KB, 522 views)
File Type: jpg front_open.jpg (71.6 KB, 518 views)
File Type: jpg rear_open.jpg (66.8 KB, 514 views)
File Type: jpg top_open.jpg (66.3 KB, 513 views)
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Old 7th August 2010, 09:54 AM   #6
chaparK is offline chaparK  Luxembourg
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As i wrote in my first post, that's my first loudspeaker project so i'd like to keep it easy and concentrate on sound only.

That's the reason why i've selected a 2-way only design (rather than a 3-way) and that's also why i'm choosing a closed-box enclosure. Maybe that in the future the project will end into a 3-way vented - in the meantime the idea is more about learning some cool stuff about loudspeaker design rather than achieving from scratch the ultimate sound system (oh god where did i learn to flatter old experts like that? )

Here's a draft of what i have in mind. It's a basic symmetric bookshelf. The drivers are:
- SEAS CA22NRX
- Eton 25SD1

- Is there something fundamentally wrong with my design?
- I'm probably going to mount/unmount the drivers a few times, so i'm not too crazy about self-threading screws (parker style). What's an other good alternative?
- Finally, i heard that it's better for a closed-box not to be too air-tight, so that the atmospheric pressure can easily balance inside and outside. That makes sense to me. What does it mean practically? Where should the air leakage take place?

Thanks all for reading this post!

chaparK

EDIT: forgot to mention that the box will be built with MDF 18mm
Attached Files
File Type: pdf box.pdf (14.4 KB, 54 views)
File Type: pdf box4.pdf (29.1 KB, 39 views)

Last edited by chaparK; 7th August 2010 at 10:10 AM.
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Old 5th December 2010, 10:12 AM   #7
chaparK is offline chaparK  Luxembourg
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Hi all,

Here's an update of my little project with a few pictures.

Still need to cut the braces, then it will be time to glue it all.

Cheers,

chaparK

04122010_005.jpg

04122010_008.jpg

04122010_012.jpg
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Old 11th December 2010, 10:28 PM   #8
chaparK is offline chaparK  Luxembourg
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More work done this weekend, still need to cut the braces.

11122010_001.jpg

11122010_002.jpg

Anyone knows where i can find 5/32" screws like the one pictured below around Sydney?

screw.jpg
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Old 11th December 2010, 11:46 PM   #9
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Why not use Metric? Are these for T-nuts? Anyway most bolt and nut places should be able to supply. Try Coventry fasteners

Coventry Group
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Old 12th December 2010, 12:05 AM   #10
chaparK is offline chaparK  Luxembourg
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Quote:
Originally Posted by Moondog55 View Post
Why not use Metric? Are these for T-nuts? Anyway most bolt and nut places should be able to supply. Try Coventry fasteners

Coventry Group
Thanks Monndog, they even have a shop in Artarmon which is convenient for me.
Yes the screws are for the nuts and their bloody imperial thread (Hurricane nuts ordered from parts-express).
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