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Old 5th February 2011, 10:07 PM   #1
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Default The Acusticon: My first designed speaker

After researching and inspecting many DIY book shelve speakers, and unsuccessfully choosing at least one project, I came to the conclusion that I should design my own project rather then stay overwhelmed. It's already been a huge learning experience and I hope to maintain it, and I hope whatever I produce will influence someone. I've already begin choosing the drivers, this will be a simple two way system, hopefully I'll be able to work in a bass reflex into the front baffle too. I've picked out a couple of speakers so far, I've wanted to build a project with seas drivers, but because of cost restrictions I'll be willing to put up with what I can make due. The two drivers I've selected are:
- SB Acoustics SB17NRXC35-8
- Peerless XT25TG30-04

Considering the SB17, I have conflicted recommendations as to whether the SB17 should be used in a ported or sealed cabinet. Zaph recommends a sealed because of the highish Qts, but the simulations I did in Unibox said ported would be best. I favor the ported over the sealed so i decrease the likely chance of having to use a sub-woof. Could I get some opinions on this?

The target size for the enclosure is 20L, the front baffle dimensions will be different depending on sealed vs. closed.

I have also started modeling the frequency response in a Excel file, and this is what I came up with so far.
Click the image to open in full size.
This is with a First order parallel low pass filter (0.42mH) and a second order parallel Highpass filter (C: 6.02uf, L:0.67mH); it's crossed at 2,500Hz. I haven't added any Zoble Networks to manage the impedance, and I'm not sure if I have to.

I still need to:
1: Create two separate front baffles and model them in a diffraction
simulator
2: Model the frequency response in Speaker workshop
3: Continue reading though Rod Elliot's article for passive crossovers
4: Understand necessary information other people can use to help

I've still got a lot of learning to do!

Thanks,
Kurt

Last edited by KnightofAwesome; 5th February 2011 at 10:30 PM.
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Old 5th February 2011, 11:22 PM   #2
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Hi,
I prefer ported also.
You might want to consider another midwoofer for a vented box. The one you selected will need a very long port to get to the proper tuning.
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Old 6th February 2011, 12:50 AM   #3
6L6 is offline 6L6  United States
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The breakup on-axis starting at 4k on the manufacturers data-sheet (the blue line) is going to need some serious attention. It will sound really weird if you ignore it or get it wrong.

Trying to get deep bass out of this driver might sound muddy.
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Old 6th February 2011, 01:53 AM   #4
sreten is offline sreten  United Kingdom
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Hi,

Take a good look at : 2-way MT: SB Acoustics SB17NRXC35-8 and Vifa DQ25SC16-04 (Poor Man's High End) - Techtalk Speaker Building, Audio, Video, and Electronics Customer Discussion Forum From Parts-Express.com

rgds, sreten.
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Old 6th February 2011, 02:51 AM   #5
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I ran the numbers on my end....I got 88.88 for efficiency bandwidth product, putting it square into the ported camp. Ported box volume at 29.84 liters , Fb at 35.486 Hz. Rather deep bass for such a small enclosure! Yes indeed the tweeter response needs to be smoothed out..she's juking all over the map!
If you can push up that dip at 3700 Hz by 2 Db you should be OK.

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Last edited by Richard Ellis; 6th February 2011 at 02:55 AM. Reason: Additional thoughts
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Old 6th February 2011, 05:18 AM   #6
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First off, thanks for all the helpful posts

This is all I can do tonight, this crossover is not final. I've got an impedance trace but i don't think it's a good one. I've attempted to get another trace, but the auto SPL tracer is being difficult, I'll try it again tomorrow.

Since these will mostly be used as computer speakers, It's still possible that having a bass reflex will make being about 1m too bassy. but for the time being, I've got them highs tamed!
(I don't know the importance of the Total Frequency Graph, but none the less, it's there)
Click the image to open in full size.

Kurt
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Old 6th February 2011, 12:22 PM   #7
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Quote:
Originally Posted by MJL21193 View Post
You might want to consider another midwoofer for a vented box. The one you selected will need a very long port to get to the proper tuning.
Sorry, I had been modeling an isobaric and forgot to change from 2 drive units to one.
With that said, have you looked at peak excursion? Unibox shows:

VB Excursion SB.gif

At 20 watts, peak excursion is reached.
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Old 6th February 2011, 12:39 PM   #8
sreten is offline sreten  United Kingdom
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Hi,

The L-pad on the woofer is simply totally wrong.
Take a very good look at the design I posted.

rgds, sreten.
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Old 6th February 2011, 06:57 PM   #9
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Quote:
Originally Posted by MJL21193 View Post
Sorry, I had been modeling an isobaric and forgot to change from 2 drive units to one.
With that said, have you looked at peak excursion? Unibox shows:

Attachment 208600

At 20 watts, peak excursion is reached.
I'm at the stage that i know what peak excursion is, but i'm a little confused as to what i can do with it. I've ran the simulations myself after i saw this again, and noticed it's much better managed under a 15L closed environment; but that changes the impedance of the speaker. Do i have to change the impedance graph of the SB17 in speaker workshop to match that of the Unibox sims to get an accurate sim of a closed box in speaker workshop?

Quote:
Originally Posted by sreten View Post
Hi,

The L-pad on the woofer is simply totally wrong.
Take a very good look at the design I posted.

rgds, sreten.
Yes the L-pad does need to be altered, but any changes i make to it makes the frequency response graph turns all wonky. I don't see an L-Pad on the other XO.

As for the design you posted, I thank you. I've copied the woofer schematic into speakerwork shop, but since it crosses over at 1.9 Khz I'd have to rework everything. Zaph recommends the tweeter be crossed at 2Khz with a 4th order or a 2.5Khz 2ed order and no less.
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Old 6th February 2011, 07:05 PM   #10
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Quote:
Originally Posted by sreten View Post
The L-pad on the woofer is simply totally wrong.


Quote:
Originally Posted by KnightofAwesome View Post
Yes the L-pad does need to be altered
Never seen one on a serious speaker.
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