A Speaker that Kicks Butt in Large Spaces

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#801
Freddi,
That does sound like a fun experiment. Do you have a XO (Eminence 2.5k?) and which compression driver were you going to use?

One day, I just want to build a simple 0.25cu ft reflex box with a 3in dia x 4.6in long vent per recommended design by Eminence for a Beta 8cx with 100Hz XO. With a PRV D280Ti, it might sound quite nice. Maybe stick a K tube into the little internal horn?

This design supposedly hits 123dB and 200w limit but needs the -12dB/oct 100Hz HPF.
 
#802
I've got a homemade version of their 2K5 plus their old factory 3K5 board which actually works around 2K8 or a bit lower - not sure what compression driver - got thread on PV, B52, ASD1001 from Silver Iris, etc. and bolt-on Dayton DE250 clone, BM440.

Size-wise, that little reflex for Beta8cx would be tough to beat and should at least make a good speaker for small home theater fronts. I'm still thinking of XKi for Beta 8cx but not sure how the driver's depression coupled with vent interference would sound (?) - would you give it a go vs other K with the same driver?

a k-tube could be beveled and poked down the cx horn - might be good to keep the dust screen and just use as intended.

oh - Bob Crites did an interesting speaker with Beta 8cx with first order electrical networks and a Klipsch - type autoformer on the compression driver as the attenuator - that would allow some fancy caps to be affordable such as one 0.47uF film and foil Dayton "bypass" cap (or as he used, two 0.22uF caps in parallel) - with caps that small, it might be fun to make a homemade cap

https://community.klipsch.com/index.php?/topic/146074-eminence-beta-8-cx-8-inch-coaxial-driver/

Bob's crossover for Beta8cx - he used a Selenium D220 ti for the CD
XdMEF2r.jpg
 
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#803
How many mH is that autoformer ? Can I roll my own with some 20ga magnet wire and some ferrite toroid? Looks like a center tap - what is purpose vs plain inductor?

I want to play with making my own PIO using copper foil.

Regarding the Beta 8cx 0.25cu ft reflex. Yes, it's a natural for THX certified installs and I don't see how a regular woofer and dome tweeter can come close to it for the size.

The XKi can work - just need to scale vent to prevent it from having a harmonic at 1kHz. So basically vent needs to be less than 7in.
 
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#806
claimed to have lower output Z to the tweeter (guess that would depend on the dB attenuation Rs juggling - -
autoformer_vs_pad_646.png



finite inductance would run out on the low end might give some rolloff as Z goes towards coil resistance - Crites is a Klipsch Heritage type guy and autoformers were the way for earlier Klipsch products. Klipsch also mentioned lower transient modulation distortion (per Otala) as the reflected Z to the amp was high. For those who favor fancy caps, a reduction in value is good and could pay for the autoformer. 1dB steps on a Crites 3636 is nice - I think his autoformer goes high enough not to significantly choke off a tweeter's top end - modern mono L-pads aren't cheap. Transformer cores look cooler than two cheap resistors ;^)
 
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#808
- it would be interesting to see how your centertapped choke/autoformer performs - somewhere in my mess is a 3636 autoformer- been years since I mucked with it on a Klipsch type xover. DJK mentioned some years back that Madisound can tap an aircore for a nominal extra fee.
 
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#809
I will follow the topology of the diagram above in PCD software and see what I can come up with. I will put the Beta 8cx and D280Ti comp driver in the XKi for now. It will be interesting to see what I can come up with. The special thing about the Beta 8cx is that it has about the correct physical offset to get excellent time alignment for the drivers to be potentially used as a quasi transient perfect asymmetric XO. I got this purely accidentally before I knew what a Harsch XO is.
 
#810
if I get some XKi built for Beta8cx and use a sizable inductor on the woofer, do you think it would be ok for a steel core inductor to be in close proximity to the magnets? - there's not much room to escape if the xover board is mounted in the cabinet. What does a strong static magnetic field to to a steel core inductor carrying AC? Did you post an input Z graph for XKi/Beta8cx? - I'd like to get the duct best overall
 
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#813
I doubt it, but won't know until I get the FRD and ZMA data files uploaded to PCD and play with it. If I am going to follow Harsch XO, I need BW4 target for the low pass so will probably need two inductors on the woofer rather than just one. But if natural acoustic falloff is steeper then maybe BW1 can work - but I doubt it. This is actually where you can tune the vent resonance to cause the dip to aid in the falloff. The compression driver needs to follow a Bessel 2nd order target. Ususally I have found a 1st order BW1 combines with acoustic falloff of driver achieves the BES2 target. So I may end up completely different. I do want to try the EM XO though just to see where it leads and compare to my Harsch.
 
#818
Go miniDSP Freddi - you will then wonder why it took you so long and never want to go back. 🙂

It's like having an infinite supply of parts and the best designer to make you a custom XO at any named (BW, LR, Bessel) or un-named (via biquad coefficients) slope and any frequency you like with any notch and any shelf filter you like, and instantly.

What's not to like?
 
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#820
Yes, set amp to max volume and let miniDSP handle level matching. Plenty of bits as it is 28/56 bit processing internally and 24 bit DAC. The volume level match is done at the DSP level so 28 bits minimum - don't worry about running out of bits. You are talking about maybe a -10 to -14dB attenuation on the compression driver to match the woofer right?

User manual for you to see specs and how it works:

http://www.minidsp.com/images/documents/miniDSP 2x4 and Kit - User Manual v2.1.pdf
 
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