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Old 8th August 2013, 08:15 PM   #1
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Default Double Chamber Reflex - tips?

Hi,

Can I get some help with getting a useful design for one of these drawn up. I'm interested in investigating this design further as it seems to help reduce or eliminate some of the ML-TL draw backs for me, getting midrange output when its not wanted.

I am using MJK's sheet so it takes into account standing waves.

the standard 2:1 ratio based on the VB of a single bass reflex for the driver gives pretty poor results.

I keep getting a problem with the second 'hump', what am i doing wrong and how can i get a nicer flat bass shelf?

how can i move that peak at 100hz back to around 70-80hz?

thanks.

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Old 8th August 2013, 08:39 PM   #2
freddi is offline freddi  United States
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I don't have access to the sheets - are all three vents identical? (there's two external and one coupling vent in the classic DBR) - there's no restriction of mids.
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Old 8th August 2013, 08:40 PM   #3
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Quote:
Originally Posted by freddi View Post
I don't have access to the sheets - are all three vents identical? (there's two external and one coupling vent in the classic DBR) - there's no restriction of mids.
its fostex style 2 vents, 2 chambers.
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Old 8th August 2013, 08:57 PM   #4
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That's a double bass reflex (DBR), rather than a DCR. Somewhat different.

Depends on the design. Since you haven't provided any information, it's difficult to say. The secondary peak is a function of the box having two tuning frequencies, so depends on the volumes & vent dimensions. I can say they can be made to work well. For e.g. the attached.

Hmm. A properly designed MLTL should not have excessive midrange output since its behaviour should be akin to most other vented boxes in this regard. If it isn't, then there is a fault in either the design or construction (or both).
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Old 8th August 2013, 09:02 PM   #5
xrk971 is offline xrk971  United States
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So the driver is in between like a bandpass sub? I am not familiar with how to size a Fostex DBR. If you want flat bass shelf go with a Weems (?) DCR where design rule is this: size upper chamber as 1/3 volume of equivalent single chamber BR and size lower chamber as 2/3 of equivalent BR. Size 2 vents per single chamber BR and put one on each chamber, then connect two chambers with same dia vent but double the length of the external vents. Mount driver in upper (smaller) chamber. This usually gives pretty good baseline to start tweaking.
Hope that helps.
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Old 8th August 2013, 09:15 PM   #6
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Sort of. A Weems (actually George Augspuger got there about 2 decades earlier) style DCR has the driver in the larger chamber. Otherwise, the methodology set out was basically this:

1/ Design a BR tuned as desired, with 2 vents.
2/ Divide into 2 volumes, one being 2/3, the other 1/3 of the total internal Vb.
3/ Place driver in upper volume.
4/ Put a vent firing into the room in each chamber, and connect the two volumes with a third vent of the same dimensions.
5/ Lag both chambers per any BR.
6/ Job's a good 'un. Assuming you've done it right & like DCRs.

Last edited by Scottmoose; 8th August 2013 at 09:23 PM.
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Old 9th August 2013, 02:37 AM   #7
IG81 is offline IG81  Canada
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I built a dcr with the above method and it worked well.

TB W4-1320SIF double bass-reflex

The vent output you posted seems normal and similar to the Weems bottom vent output. The Fostex style dbr exhibits a larger dip, but I'd like to try it as well sometime.

Here is a neat calculator that can do both styles and lots more:

Lautsprecher Gehäuseberechnung mit Thiele Small Parameter

IG
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Old 10th August 2013, 03:57 AM   #8
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Try this for DCR info.Claudio Negro's home page, how to project and test a loudspeaker using Speaker Workshop
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Old 10th August 2013, 03:41 PM   #9
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by IG81 View Post
I built a dcr with the above method and it worked well.

TB W4-1320SIF double bass-reflex

The vent output you posted seems normal and similar to the Weems bottom vent output. The Fostex style dbr exhibits a larger dip, but I'd like to try it as well sometime.

Here is a neat calculator that can do both styles and lots more:

Lautsprecher Gehäuseberechnung mit Thiele Small Parameter

IG
Hi IG,

FYI,I've tested the calculator for another purpose, a T-QWP sub:

Lautsprecher Gehäuseberechnung mit Thiele Small Parameter

Semms to be a very usefull calculator as far as I can see...
b
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Old 10th August 2013, 03:50 PM   #10
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by gafhenderson View Post
...I am using MJK's sheet so it takes into account standing waves...

Hi Gaf,

Where is the rest of your simulated plots?

Here is an example (DBR) using one of your previously posted Drivers:

b
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File Type: jpg 2(2)_Gafhenderson-Driver-DBR.JPG (521.0 KB, 133 views)
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