Hello & need help with Isobaric Design

[VSupe]

Hello,

My first post opening with a question on how to calculate the correct volume and port for a simple isobaric cabinet please?

I have used the search button, but with no luck!

I understand that as a rule of thumb you can half the volume of a normal reflex design.

That answers the cabinet size, but what about the reflex port dimensions?
Does this remain the same?

I’m looking to build a compact sub using a total of 4no. 6 1/2” subs.
2 speakers coupled together = 2 sets.
Therefore maintaining 4ohms.
Monacor SP-167C

Fs: 49hz
Qms: 2.89
Qes: 0.45
Qts: 0.39
Vas: 22L
Dia: 17cm

Which should give the expected results.

Reflex cabinet for single speaker (golden ratio)
L: 24.89cm
W: 40.32cm
D: 15.36cm

Vb = 15.42 litres
Fb: 49hz
F3: 57hz

As I’m putting 2 sets of coupled speakers in the same cabinet the volume will be the same as the single speaker reflex design.

Port for single speaker for reflex design:
Dia: 5cm
Length: 12.51cm

Port with 2 sets of coupled speakers (ie x2 of above):
Dia: 7.07cm
Length: 12.51cm

I’ve tried to the keep the port as small in both length & therefore dia to maintain the smallest cabinet possible.


Thank you very much!
Stephen

 

[VSupe]

I’ve been looking around a bit more it seem the port remains the same design as per a reflex design.

Using WinISD it suggests similar'ish cabinet size and similar'ish port size:
Dl: 16.13cm
Dp: 6.8cm

Looks like a bit of experimentation, but that’s half the fun!!

 

[Johnd]

You may do better with this thread in the DIY forum VSupe. annunaki, WmAx, Avaserfi and others are all pretty knowledgeable about subs.

 

[annunaki]

Honestly, those "subs" would not do very well as a subwoofer. They simply do not play low enough. If you need that small of a driver, I would look into the JL Audio 6W-0 as they will allow you to play significantly deeper. A single 8W7 in a vented enclosure will probably have more output and play deeper to boot. you could do that with an enclosure of probably no bigger than 1.5 cu.ft. or so.

 

[VSupe]

Hi, and thank you.

I used the word ‘sub’ very, very loosely. Too loosely I think, but was implying the end product, hopefully.

Monacor SP-167C
____.monacor.de/typo3/index.php?id=75&artid=1869&spr=EN&typ=u


I appreciate they’re not the best speakers in the world, by far, its just that I’ve them lying about so thought I’d use them and they’re going to offer some bass reinforcement to what I’ve got at the moment – which isn’t anything! (4x130mm).

Other wise I’ve got a 10” generic ‘proper’ sub (no stats)
Or
Monacor Predator-6/4:
____.monacor.de/typo3/index.php?id=75&artid=4913&spr=EN&typ=u
Impedance (Z) 4Ω
Resonant frequency (fs) 66Hz
Max. frequency range f3-2,500Hz
Music power 180WMAX
Power rating (P) 100WRMS
SPL (1W/1m) 91dB
Suspension compl. (Cms) 0.47mm/N
Moving mass (Mms) 12.4g
Mech. Q factor (Qms) 4.97
Electr. Q factor (Qes) 0.45
Total Q factor (Qts) 0.41
Equivalent volume (Vas) 10.6 l
DC resistance (Re) 3.15Ω
Force factor (BxL) 6.0Tm
Voice coil induct. (Le) 0.4mH
Voice coil diameter Ø 25mm
Voice coil former Kapton
Linear excursion (XMAX) ±3.75mm
Eff. cone area (Sd) 127cm2
Magnet weight 20oz.
Weight 1.55kg


Ideally I’m looking a cabinet size around 46x30x15cm (20.70L) so not much to play with at all.

Would i be best with the single 10" or trying an isobaric?