Double Chamber Reflex (Silver Flute W17RC + Seas 17TDFC)

[Michael Chua]

I have earlier tested a 6-1/2" Silver Flute in a 15L BR. As expected, needs to be supported with subwoofer. On its own, bass is a bit "short" due to early roll off.

This is an attempt to design a 2-way that has bass extension down to 40-45Hz using the concept of DCR.

Components
=========
Woofer = Silver Flute W17RC38-S-8
Tweeter = Seas 27TDFC

Gross Box Vol = 40L (Internally divided to 2 chambers)
Smaller Chamber = 13L
DCR tuned with 3 PVC Tubes. One in each chamber and the 3rd one between the 2 chambers.
PVC Tube = 2" Dia x 3.1" Length
Chambers lined with R11 Fiberglass wool.

[Michael Chua]

T/S measurements done with LMS (20g Delta Mass). As can be seen, they are quite different from the manufacturer's specs.

In the box modeling, the black plot is how the response looks like when tuned to 37Hz in a BR of 40L. In a DCR, there will be a bass boost at F1 (37Hz) and F3 (80Hz). F3 is the port of the smaller chamber. F1 is in the bigger chamber where the woofer and tweeter are located.

There is another port, F2 (42Hz), that connects the 2 chamber within.

More information on Double Chamber Reflex can be found at:
Claudio Negro's home page

[mdynac]

hi,

first off, kewl project....

i too have a set of the silver flute 6.5" 8 ohm

i have them in a set of Parts Express BR-1S (99 bucks, could not pass it up!!!) i took the shielded woofer out and put in the SF with a new crossover 3500 hz 1st order. the cabinet is like 15 liters, i plugged the port with a sock....

sounds wonderful, at least the woofer does, and yes it needs a sub.


how did you decide on the tweeter?? and what are you planning for a crossover? i am tweeter hunting right now and your input would be appreciated.


i think the silver flutes have potential.

[Michael Chua]

Hi mdynac.

I've always wanted a 6-1/2" 2-way to go down low without having to resort to a 2.5 or a sub. I believe this DCR can do just that.

The Silver Flute W17RC is a nice woofer. Very reasonably priced and generally good performance. Flat response until some cone breakup which is not too drastic. I don't think there are any other 6-1/2 that has similar response at this kind of price.

When I tested out this woofer earlier, I had it mated with a Vifa D25AG35 in a 15L BR, just to have an idea of its character. I crossed them initially at 2K5. Unfortunately, I picked out some distortion in the D25AG, even with 3rd order HP. I am sure it has something to do with the rear chamber. Doesn't seem to affect others but drive me nuts. Moved the crossover to 3K5. Distortion disappear but lost the mids.

To cross at 2K5, I will have to correct the D25AG issues passively or even mod the tweeter. I don't want to go to all the trouble and complicate things. I rather keep this design as simple as possible so that its easy for diy.

The Seas 27TDFC has the properties that I am looking for. Flat response, low Fs and being a newer design, I hope none of the resonance issues with the rear chamber.

The SF W17 will be crossed at 2K5 to the 17TDFC. The LP for the W17 will be 12dB. This will keep the cone breakup farther away from the cross point.

The 17TDFC HP will be 18dB. I like to keep the lows away from the tweeter. They are always more comfortable.

[Michael Chua]

The DCR loaded with SF W17RC and Seas 17TDFC.

One port in upper chamber, one in lower chamber and last one connects the two chambers internally.

At the rear, top left, is an Altec Lansing CD912-8A Duplex. Not final yet but promising.

[Michael Chua]

Plot1 = DCR Impedance Sweep
=======================
As predicted, F2=44Hz and F3=85Hz.

Plot2
===
1) Purple = Raw Z of SF W17
2) Yellow = ZOBEL (11 ohms + 12uF) applied. Region of interest is from 1K - 10K.

Plot3
===
Raw Z of Seas 27TDFC. Fs is 550Hz, exactly as stated in the manufacturer's specs.

All plots swept with 2Vrms

[kelticwizard]

Which application models the double chamber reflex?

[Don Hills]

Originally Posted by kelticwizard

Which application models the double chamber reflex?

Any program that models reflex enclosures, plus the formulas from Claudio Negro's DCR page:
DCR

[Mosquito]

The third system (left to right) in C.Negro's page, is the one that work best with highish Qt, low Vas woofers. And as long as I know, can be modelled with LSPCad. But parameter insertion done manually, the automatic alignement routine will lead you off road. I suspect Leap can do the job as well...

[Michael Chua]

Originally posted by kelticwizard
Which application models the double chamber reflex?

I don't think there's any specifically for DCR. You can use any for BR programs to tune the box for your desired Fb. From the formula, you can calculate the F2 and F3.

Using LMS, I will measure the actual acoustic response of a DCR. It will give us an insight as to how different it is from a normal BR.