S8 Open Baffle using 6 Jaycar woofers

[gainphile]

Having a few drivers lying around and after acquiring $50 Aldi router I want to construct this one. For those down under, Jaycar is selling the discontined 10" CW2119 for buggerall ($14 each). This woofer has good FS and Qts for OB (33Hz and 0.7) but is limited in peak SPL.

I have also found out that tweeters "CT2009" at Jaycar is actually Hivi K-1. Very well tested by Zaph for its price.



The midrange will be Vifa P13WH which I will borrow from the S7

There are some design compromises here, namely the P13 will be operated on relatively wide baffle width, instead of the ideal < 2.2*diameter rule.

As I am already preparing to construct an 8-channel Gainclone, I will make it 10-channels now

[PeteMcK]

Hi Gainphile,

so your eq for the woofers wil be active?,
interested to see how this will sound (I've got the 12" Jaycars,
& I think Moondog has a bunch of 10"s).

Re: ''the ideal < 2.2*diameter rule'' - where does this come from? haven't seen it before (but then I'm lazy & skim rather than read anything in detail these days...)

[gainphile]

Hi Pete, I've pretty much convinced that active XO is the way to go both for sonic and cost reasons. I mean an audiophile-grade amplifier cost only $15 nowadays

There are plenty of discussion about ideal baffle width, from JohnK, SL, and a read here. Basically we want to avoid that massive dip after dipole peak. With wider baffle, the dip goes lower in the frequency and that means pushing down the tweeter xo. Although you gain bass response.

Progress so far: I've done the XO and mounted the Tweeters, mid, and one woofer on test baffle. It sound promising, but I have yet to take it outside for measurement. Hopefully weather will be good this weekend.

[ttan98]

Just curious what makes you choose 3 woofers instead of 2 or 4 units, which is normally the case.

[Rudolf]

Originally posted by PeteMcK
''the ideal < 2.2*diameter rule'' - where does this come from?

You want the driver to start beaming below the dipole peak frequency of the baffle.

Some explanation is in Consideration of Power Response: Looking at Fig.18 there you want a response like shown in red and not like in blue.

A mathematical derivation can be found in this treatise, equations (4)-(6).

[gainphile]

Originally posted by ttan98
Just curious what makes you choose 3 woofers instead of 2 or 4 units, which is normally the case.

I found that 30x115cm baffle is aesthetically pleasing. This will just fit 3 woofers per side, which will allow more SPL instead of 2x woofers in H-Frame.

Unfortunately this will cause impedance issue as wiring 3 woofers is not as simple as 2. That's why I'm planning to use 3 chipamps to drive them separately. But before going out building those amps, I may just try 2 first and wire them in parallel.

The issue with 3 woofers is vertical lobing. I think this will be more serious than others but without actually trying and making measurements it's difficult to judge.

The good news is while doing this iteration, I have a working OB for listening which I am very happy with, eliminating the need to "rush things" as in the past. I may even paint this one

[ttan98]

You can use 4 woofers in folded(W-shape) configuration, mounted vertically and housed in a H-frame, thereby reduce the height, improves impedance matching(series and parallel to get 8 ohm) as well as better SPL you gain 6 dB.

[gainphile]

The problem with H-frame and I suppose W-frame would be cavity resonance. Normally they would not be good to cross at 300Hz depending on the depth.

I have to cross at 300Hz, as any lower the P13WH would not be able to take the SPL level (tried down to 120Hz). Then I need MTM and that leads to different 'problems'

I also found from past experiments that H-frame and U-frame does not sound as good as simple baffle. I could be wrong.

So at the moment two additional chipamps is the path of least resistance.

[ttan98]

Try this, see attached picture. You may a second thought.

[gainphile]

Very interesting.

I wonder if this is how Beethoven sub is configured. I heard SL fitted 4 12" woofers, but could not find a pic without grills.