[matevana]

OB-GYN: “Open Baffle – Glassy Yet Neutral”.

Glassy yet neutral is perhaps the best description. Think Stevie Ray Vaughn on Little Wing or Knopfler on Sultans. These have a chimey, bubbly, and lively presentation.

Are they the last word in resolution? Nope. Do they produce bass you can feel in your chest? Not really.  Are they forgiving and fun to listen to?  You bet.

The OB-GYN is my attempt to build around drivers I had laying around. The crossover is purpose-built and the U-frame is pre-fab, sorta. In fact, the construction materials (less drivers and crossovers) were under a hundred bucks for the pair. The project was designed and built over a weekend.

More to come as time permits…

[JohnH12]

They look great.  Have you considered stuffing the box, ala cardioid?

[matevana]

They look great.  Have you considered stuffing the box, ala cardioid?

Thanks. That’s a great question. The premise of stuffing a u-frame, as I understand it, involves damping the rear resonance which in turn alters the internal propagation delay. Once properly damped, (by adjusting the quantity of stuffing) the front and rear waves are summed and the level is then only down about 6dB at half the system’s monopole frequency, or roughly half that (or twice as efficient) of its true dipole equivalent. At this point LFE is typically applied to bring the direct response close to the targeted alignment and flatten the curve. 

In an actively EQ’d system it sounds promising. This design however is passively crossed and the woofer that I had on hand is only about 5dB more efficient than the fullrange driver. Once you add passive components to the woofer for baffle step and low frequency equalization, the Alpair 10M requires about 12dB in attenuation to match the approximate output of the woofer. Shifting the LFE center point down another 20-30Hz, as a result of properly stuffing the box, would all but render the design useless from an efficiency standpoint.

I’d be willing to try damping the box w/o any additional compensation, but I suspect the response would be too irregular to be useful. What do you think? 

[matevana]

OB-GYN Crossover: A split series inductor topology shunted by a 4.7 ohm resistor provides the necessary LFE, in parallel with 130 mh of capacitance, providing a 175 Hz 2nd order electrical low pass on the woofer.

I tried to keep the Alpair 10M as vanilla as possible with a single, Mundorf 22 ohm M-Resist Supreme resistor yielding about 12dB of attenuation to match the woofer’s level post EQ.

While a high pass filter isn’t needed from a response standpoint (due to the drivers close proximity to the baffle edge and subsequent LF cancellation), you should use care and monitor the output level and subsequent distortion/excursion. For this reason, this system works best in a bedroom or den/office.

I experimented with adding capacitance to the Alpair 10M where greater SPL's are desired. Inexpensive electrolytic caps greatly detracted from the drivers sound, and midrange poly caps were only marginally better. If you choose to go this route, invest in premium quality metalized poly caps (i.e., Jantzen Z-Superior) and bank smaller values in parallel, or perhaps bypass larger value midrange caps with a single premium cap. You will require about 80 mh altogether. The top quality caps will really make a difference in this design but SQ-wise, it benefits from having no HP at all, provided reasonable output levels are observed.       

[Chicken Man]

 Not one for boutique capacitors, this quote from Jantszn makes me wonder if this is nothing more than marketing or there is something odd about this capacitor.


"With the Superior Z-Cap even the finest nuances can be heard. The sound never gets over-edged, really superb naturalness with a somewhat bright top-end.

Highly recommended for use as a high-end tweeter capacitor or as a coupling cap in an amplifier.

All Jantzen Audio Z-Caps are nitrogen filled, which means that you get more foil per capacitor and no risk of the evaporation that can occur in oil/dielectric fluid filled capacitors. "

C.M

[matevana]

LOL, sure sounds like hype! That being said, I think when you start with a quality component such as Clarity, Mundorf, etc., as you move up the line you generally get better materials and manufacturing technology, more attention to detail, consistent tolerances, etc.  These neo-metal cone full range drivers (Jordan, some Mark Audio, etc.) with their super thin/light cones can really sound compressed with lesser quality caps, and the affect isn't insignificant. I agree that some of the prices on boutique caps seem outrageous. In my case I chose to eliminate all filters from the 10M, and just keep an eye on the throttle.

[nicoch]

good caps is a must !

[soundbyte]

Hello matevana,

Interesting to read the comments re electrolytic capacitors and the effect of them in crossovers.

Has any one else tried "Battery Bias" with electrolytic capacitors?
C1 and C2 are electrolytics with the negatives connected together.

Both my wife and I thought we heard better results from adding battery bias.

Similar circuit to this.


Russell.

[nicoch]

Dc  on caps  work because fix the armature in position avoiding  the "pushpull" movement with ac signals

[Chicken Man]

Dc  on caps  work because fix the armature in position avoiding  the "pushpull" movement with ac signals

Could you explain what you mean ?

I'm at a loss as to how such a circuit could affect the voice coil position or for that matter why one would even bother biassing electrolytics for use in a crossover circuit. Signals from the power amplifier are easily going to exceed the 9 volt bias anyway, I can't image what benefit one could derive from it.   Just use a non-polar capacitor of 100 uf 100v, they're cheap enough.

Also, AC signals do not 'push pull' the voice coil, the single voice coil of a driver is driven in one direction and then the other, peak to peak in accordance with the average of the signal level.   

C.M

[nicoch]

just use google  "dc bias caps".......

here some info https://community.klipsch.com/index.php?/topic/79269-dc-bias-of-caps/

[Chicken Man]

 
Well I read through that waffle on the link you provided, it simply is nonsense.

Next some audiophile will be advocating a DC bias be applied to iron cored inductors so the signal isn't distorted by the B/H magnetisation curve when the core is being fluxed.   Look it up on google ......and gasp.

C.M