[MJK]

An off-topic question for Martin King:  You mentioned an H-frame dipole "with wings."  Can you elaborate on what you mean by this?

Can you point me to where I mentioned that idea, I think I have confused myself.

Martin

[dyohn]

Ack, looks like I am the one confused.  It was a comment by Richard describing a dipole baffle "with wings" by which I believe he means a standard H-frame alignment.  Sorry for the confusion.

BUT, while I have your attention can you comment on the likely behavior of an H-frame where the length is increased by "folding" the frame over the front and rear?  Something like this:



Would this effectively increase the length of the H-frame or would it convert the enclosure into a bandpass system?

[MJK]

Would this effectively increase the length of the H-frame or would it convert the enclosure into a bandpass system?

Off the top of my head I don't know how that arrangement would work. Depending on the driver properties and the design of the enclosure geometry I guess it might work but I don't know how well or what advantages or disadvantages would exist. If you think there is potential then by all means pursue the concept. I can't put any time into it at the moment.

Martin

[tubamark]

Would this effectively increase the length of the H-frame or would it convert the enclosure into a bandpass system?

Off the top of my head I don't know how that arrangement would work. Depending on the driver properties and the design of the enclosure geometry I guess it might work but I don't know how well or what advantages or disadvantages would exist. If you think there is potential then by all means pursue the concept. I can't put any time into it at the moment.

Martin

I've tried some arrangements like this.  It does increase the effective length, lowering the Fpeak frequency.  Also lowers Fs, presumably by increasing air load on the driver.  real small openings really lower Fs and efficiency - Ripole action.
The advantage is that one can offset the openings & use stuffing to reduce f-peak magnatude, all in a really compact 'enclosure'. 

I constructed U & H-frames this way (Credit for this idea goes to Larry Selmer):  Instead of open square(s), cover the opening and cut a well-offset round hole roughly equal to actual piston area, i.e.  15" driver =~13" hole.  Alternately could do some other hole shape, but an offset circle in a square box offers the greatest number of different path lengths for parmeter "D" - effective depth.
One can build a smallish 16" square x 8" deep U-frame this way that functions more like a 12"-15" variable-depth U-frame.   It works, but addition of some damping (or steep XO) is recommended.  Qts will increase & Fs decrease initially.  Still a dipole, unless you really go nuts with the stuffing.

I did not do advanced testing of this, but woofer tester, swept tones, and sound level meter confirm my assertion.  I'm sure Martin has the skills to better model these changes.

Easy to try!  let us know what you find out.

---Mark

[dyohn]

Thank you for the feedback Mark.  I am working on a few H-frame ideas and this sort of arrangement is one experiment I plan to try.  Using a circular opening is an intriguing idea, and easy enough to play around with several options since it involves simply changing out the front/rear "covers."  Thanks for sharing the idea!

[dewar]

You guys just reminded me of something I have been wanting to ask,

I'm using Behringer DEQ2496 into a power amp to drive my OB bass driver. I had been using a Reckhorn A-400 which worked fine but I had the power amp and DEQ sitting unused so I sold the Reckorn.

The DEQ works fine as a low pass filter, and the EQ is usefull, but the only thing it lacks compared to the Reckhorn is variable phase. Now it does have speaker delay, which I had thought would work the same as phase control, my thinking being that if acoustics waves around the XO frequency were say 20 feet, I would only have to delay the signal by 10 feet to get 180 degree phase, and roughly 5 feet for 90 degrees etc.

When I used to turn the phase knob on the Reckhorn while looking at a real time FR curve I could clearly see the a null point moving up and down the lower octaves, as one would expect. With the DEQ I can change the delay from 1 foot to 300 feet but strangely dont really see much effect on the FR curve. Its definitely working as I can easily hear the more delay. Is there something I'm not understanding re the difference between phase and delay. Can phase controls change phase without delaying signal, or are they one and the same?

Thanks for any input,

B.

[Davey]

The "delay" settings in the Behringer boxes implement a "pure" delay......a non-frequency dependent delay.

The "phase" control in analog processors (and the DCX2496 crossover) implement a frequency dependent delay with the phase shift of a second-order all-pass filter.  The phase varies from 0 degrees to 180 degrees...always.  When you adjust the "phase" control you shift the "turnover" point up or down the frequency range, but the phase response still looks the same.

Pretty much everything in the Behringer boxes functions in the same way as an analog equivalent.  The "delay" settings being the exception.

I have a nice analyzer plot on my computer somewhere that shows this visually.  I'll see if I can find it.

Hope that makes sense.

Dave.

[dewar]

Thanks Dave, that makes some sense. Perhaps the DCX would be better for my purposes, though luckily 0 phase shift seems to be near optimal for integrating my present drivers.

I dont want to take this thread too far off topic, but that has just raised another question for me, why anything other than 0 phase shift would be desired. I've used phase to target room nodes when I didnt have EQ, simply moving the out-of-phase cancellation point to the frequency of the room node, but apart from this I'm wondering why we shouldn't keep out drivers as in-phase as possible? Perhaps its that the XO puts everything out of phase anyway? Not my strong point this stuff.

cheers guys

B.