Pretty Persuasions - InDIY Coax Build Thread

[4thtry]

Excellent! Like your tip using masking tape around the corner to keep the flush trim bit from digging too deep. Good idea.
Can't wait to see how the alternating grain patterns pop when the finish goes on.

[JavadS]

Ok coming along, wrapping up the saw dust phase of the project! Time for some binding posts, I’m putting in binding posts for each driver as in the future I may consider going fully active on this.



I’ll be doing a recessed bowl cut for the binding posts, the recessed circular binding post provision has sort of become a little design detail on every build I do, and I’m taking it to the next level by doing a curved bowl cut. The binding posts are located between the two lower braces in the enclosure









The ID of the template is 4”, which is held securely with double sided tape





And the bowl cut



As you can see the bottom cut of the bit doesn’t leave the smoothest surface



Template removed



Surface irregularities are easily removed with a 2 inch sanding disc



After sanding with up to a 250 grit finish



And with binding posts temporarily put in place



Since the baffle for the woofer flange was so thick I wanted to put a relief cut to make sure the woofer can breathe easily, I’m not bothering doing anything with the mid as the baffle flange is only about 1/2 inch thick there, and there’s plenty of breathing room. The challenge with the kerf baffle like this is that I really didn’t want to cut driver holes before bending the kerfs as I didn’t want to weaken or put any extra flex in the baffle assembly, so this meant I wasn’t able to put any relief cuts from the outside so I’m doing it from the inside with this under round over bit for Magnate.









Woofer flange thickness



I lined the midrange enclosures with sorbothane, then lined that with 3/4” wool, then stuffed with poly fill





And ready for some crossover tuning





Thanks!
Javad

[scottvalentin]

Wow very nice idea with the rounded bowl cut for the binding posts, and as always, such attention to detail. Beautiful craftsmanship Javad!

[JavadS]

Wow very nice idea with the rounded bowl cut for the binding posts, and as always, such attention to detail. Beautiful craftsmanship Javad!

Thank you Scott and for the always encouraging comments =) Javad

[ugly woofer]

Very nice Javad! The grain should really pop when finished. Does the sorbothane have an adhesive side....peel n stick?

[JavadS]

Very nice Javad! The grain should really pop when finished. Does the sorbothane have an adhesive side....peel n stick?

Thanks man! No the raw sheets I buy don't have adhesive, I use 3M 80 adhesive spray for non load bearing attachment like this, and a special rubber adhesive from Lord if the panel needs to carry a load, like if it's a baffle attachment.

[JavadS]

Tuning for the Pretty Persuasions is coming along well, I have initial modeling done in Xsim and I’m waiting on some crossover parts which will be here Tuesday.

In the meantime I did a quick DSP tune using a MiniDSP 4x8 Sharc, really cool unit as it runs a digital coax input which I run directly out of my laptop for a fully digital signal path into the DSP. I’m running an Adcom GFA-2535 50watt x 4 to the mids and tweeters, and an Adcom GFA-545 to the 8” woofers giving them about 100 Watts each. Crossover points are approx 1000hz at 48db and 200hz at 24db, the amount of PEQ was minimal, I used about 10 filters total to create a response w/in a dB or two full spectrum, and it could be even flatter.

Bass response is flat to about 35hz, my initial impression with this woofer and enclosure are excellent, bass is tight and fast with a warm ported sound and no bloat or sloppiness. My only concern with this woofer (I need to test the other), is that at close to xmax it does make a small sound I can hear if I’m close to it, almost sounds like tinsel slap, I need to investigate further, worst case there are several other more high end woofers with 220mm frames I can use if I need to (I just need to mind a tight budget for the InDIYana event).

See attached for response charts, active makes it so easy to hit whatever response you desire, my passive crossover won’t be nearly this smooth. I also took a few videos, these won’t be winning any Golden Globe awards but they show the speakers, give you an idea that they don’t sound terrible, check them out.

Overall I’m thrilled with how this one speaker sounds in mono, if I have time tomorrow I’m going to assemble the second speaker and listen in stereo, that should be a treat. This is definitely a point source speaker and it sounds like it, I’ll write more about the sound as I spend more time with these guys. Thanks!



Response on axis no smoothing and 1/6, this is with the mic 20” from the tweeter



With individual driver responses



On axis, 22d and 45d



Video of one speaker playing in mono, also showing some of the DSP setup

[URL]https://youtu.be/OUETdkrbNUA[/URL]

[kenny_k]

Just heard the video............... could you make it longer................like a couple hours?

[xmax]

Beautiful! The frame of that mcm woofer looks identical to the Tang Band W8-2096.
What drivers are on the waveguide in the other speaker? Any luck with that blown amp?

[xmax]

On another note, I'm sure you are probably aware of this and I imagine you are not going 48dB slopes
in the passive domain. My experience with the mini dsp; the transfer function is nothing like the
passive version of the same filter, E.I. a Butterworth filter will have no bump at Fc and more
obviously the phase tracking is completely different. I only found it useful for acoustic center
alignment and roughing in how low tweeters could go before sounding like screwdrivers in
your ears and where cone break up could be avoided. Beautiful builds!!!

[dcibel]

xmax Still struggling with that whole "electrical impedance" hey? If you stop using the online filter calculator and design the passive filter properly, it can and will match the transfer function of the DSP. IIR filters have the same characteristics of a "matching" electrical transfer function. Your problem is only that you haven't desiged the passive filter well enough to match the simple textbook transfer function provided by the DSP.

[xmax]

I'm sure you heard a song in the last 24 hours my filters were involved with. I not only design passive speaker level filters.
I also design active, passive fully balanced line level and power supply filtering. As well as summing busses, Vari-mu
limiting amplifiers, make up gain amplifiers etc, etc etc. Again we are going to have to Agree to Disagree.

Just out of curiosity what City are you in?

[Wolf]

Beautiful! The frame of that mcm woofer looks identical to the Tang Band W8-2096.
What drivers are on the waveguide in the other speaker? Any luck with that blown amp?

Nope the TB have plastic frames. The MCM have cast Aluminum frames like that of Accuton. They are very different.
Wolf

[xmax]

Ah yes you are correct, it just looks very similar. from memory (clearly not very good)

[dcibel]

Just out of curiosity what City are you in?

You wanna come over and learn how to design a filter?