S9 Open Baffle Speakers

Early version of S9, circa July 2009

This build is to revisit the previous design which sounded most natural and smooth. So much that the further effort to obtain dipole bass quantity had to be scrapped.

Build process is discussed here.

Driver-baffle relationship is very important. If the inherent response is not smooth, no amount of EQ would result in natural sound.

The smoothness of this design can be summarised by differences of frequency response between on and off-axis measurements:

Update 23/8/2009
Finished dipole H-Frame woofers:




















Update 10/10/2009
Tidy up the prototype XO










Update 14/6/2010
Updated active crossover topology
W-M : 300Hz, 2nd order
M-T: 2.1kHz, 2nd order

Update 17/1/2011
- Converted Analog XO to DSP
- Changed H-Frame to W-Frame subs
- Measurement from recent GTG:











Normalised plot at 0 degrees, showing directivity pattern. Here we can see that the back to back dome tweeter is the achilles heel of such setup:







Update 29/5/2011
- Converted analog XO to DSP (MiniDSP)
- Use W-Frame woofer configuration. This opens the possibility of stacking 4 woofers/side.









Update 8/6/2011
Completed S9R, an "R" or rigid-cone version of this project. Fountek FW146 + Vifa DQ25. The phase shield of the tweeter needs to be removed to avoid resonance and stored energy.























Non-normalised sonogram of S9R, 0 - 90° taken with 11° increments.
I moved these loudspeakers in to my future "audio room" here: http://www.youtube.com/watch?v=RnaTs8oK8tA.
The iPhone does not record bass well unfortunately.

7 comments:

firestorm said...

Hi,
Very impressed with your speaker projects, good to see the your thought process translated into real speakers.

I tried to participate in the thread on diyaudio, but they're in an upgrade process till September.

My questions are :

Vifa P13WH midbass
Vifa TC20TD tweeters

seem to be not manufactured any more, do you have any suggestions for alternatives ?

I see that you are trying to follow the "SL rule of thumb to operate them at 1/2 wavelength of the cone diameter."

So for the midrange, the driver needs to be 130cm to 100cm. I've seen many desgins use 8" to 15" for the mid. Am I right in my understanding that these designs will be subject to more distortion and beaming ? Which is what oyu are trying to avoid?

Thanks
firestorm

gainphile said...

Thank you. It is a learning process, and yes, bit hard with DIYAudio being upgraded ;).

It's difficult to recommend something which I really don't have any personal experience. But given high value as a goal, I would try Zaph's new driver at madisound + Seas TBCFG tweeters. If cost is no object, it may be easier, just get seas excels ;)

I think 6.5" or 8" would actually work if the baffle-driver interaction is correct. Personally I would choose 6" over 8". Never 15"... tried that before.

btw. I currently use HiVi K1's, not TC20 tweeters.

firestorm said...

I'm looking at the following drivers :

HiVi K1 or Q1R
Eminence Alpha 6A - 165mm
Skytronic 902.222
(12", fs=29Hz,Qts=0.49,xmax=6mm) and cheap too, less than 20gbp each.

http://www.madisound.com/catalog/images/userimages/Image/alpha-6a-specs.png

What are TBCFG ?

I also plan to use a behringer DCX2496 to do the xo duties. I plan to cross it 5Khz and 1Khz too see which freq works best. Get the option of different filters and orders(?). The midrange low will be between 100-200Hz.

firestorm said...

Another thought, I wonder if I can get away with a different rear tweeter? If I can it to get it to work well, I'll consider upgrading the tweeter, something like a Beyma CP380M and put the cheaper HiVi at the back.

gainphile said...

I would stay clear of Q1R based on Zaph's measurement data. K1 is okay but not great, high imd distortion. Seas TBFC/G looks great but pricey.

DCX would be great as they are flexible and easy to configure. Unfortunately very pricey here in Australia.

I favour time-aligned LR4, but be careful it has to be acoustic slope, not electrical. Crossing woofer too near it's natural rolloff will not yield correct acoustic response.

firestorm said...

I didn't realise there are two slopes for filters, acoustic and electrical.

So if I use a digital xo, will it be electrical then ?

Theres a new Zaph Audio ZA14W08 5" Mid/Woofer, but I can see S&H being very expensive from USA to UK. Also the sensitivity is 87db/m which isn't so hot.

gainphile said...

Yes, acoustical response is what counts, as that is what we hear. All XO either digital, analog or even passive will only provide electrical response. They have to be matched with driver's natural rolloffs.

Seems like you have the same problem with us here down under re: shipping costs!