Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide

[ErnieM]

A pair of Marcel's waveguides please.

 

[xrk971]

New TL and Revised XO Tweaks

After listening to the new TL's for a day or so, I determined that the voicing was too bright and the measurements confirmed that it was too "flat" - I like the sound of my speakers to have a right downward "Harman tilt". It makes the sound much more balanced and cohesive. This required basically a large inductor and parallel resistor as a BSC as a shelf filter for the PTT6.5 at higher frequencies. I ended up using a 2.5mH (up from 0.68mH) paralleled with a 10R resistor to burn off the highs. For the tweeter, I decreased the high pass cap to 2.2uF and the XO frequency point remains at 3500Hz and is still a passive Harsch XO with a measured 55deg bump in the acoustic phase just to the right of the XO point. Here are photos of the setup, the new speaker, XO, and measurements.

Test setup:

Closeup of the TPA3255 Class D amp (my only amp capable of driving a 4ohm load) with BTSB Buffer and 800w LED SMPS (set to 50v):

Here is a closeup of the new TL cabinet utilizing lock-mitered joints:

Here is the new XO design schematic:

Photo of the new XO using components I happened to have on-hand from my XO development kit:

Here is the DATS impedance measurment of the new XO installed in the TL - we can see the TL box freq is about 28Hz:

Here is the measured frequency response and phase at 0.5m and 2.0Vrms (scaled to be equivalent for 2.83v at 1m) - the sensitivity appears to be 86dB at 2.83v and 1m, which gives a -3dB point of 39Hz, close to the 37Hz design frequency:

Here is the measured HD vs frequency - there may be some household noises contributing the the floor around the bass region:

Here is the measured Step Response - still transient perfect Harsch, but better (more right triangle-like) than DSP-based Harsch w textbook filters - I am not sure why that is:

I have been listening to it for about a day and maybe 30 songs - the sound is amazingly very similar to my larger 10F/RS225 TL's sitting next to it. Which is to say, excellent sounding. Very pleasing, full-bodied and great clarity and dynamics. The balance and bass extension are about the same as the larger TL's. The highs are a little better in reach, and the waveguide makes for a wider sweetspot. There are some dips and peaks in the midbass area that are not as smooth as before, and that was my experiment to see what happens when you do not line the labyrinth with eggcrate foam. It increases the TL ripple - so I would leave the eggcrate foam lining next time. The dips and peaks are not audible though and some of them are actually the result of interaction with the room modes and reflections.

If you want to see this TL moving some air, check this video out:
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Overall, I am very happy with how this turned out and will give a complete report once the crossover parts for the second channel arrives. I listened to the new voicing for a while first, and liked it and knew it was better before measuring it. I like to listen first befor measuring, so that I would make the final voicing through a listening-by-ear based process vs driven by measurements process. Happy to say my ears said they were great, and the measured tonal balance confirms this.

 

[Solve]

So you recomend this TL building but with eggcrates?

 

[sumotan]

You have my deepest respect XKR971. Though Im not into diy speakers yet, I've read some of your experiments. Always wonder how on earth do you find time to do all this & also what do you do with all these speakers after you've reach your findings. Lol & off course most important your generousity in sharing with forum members, bravo.

Cheers

 

[xrk971]

Yes, line the TL with eggcrate foam on one wall. Add melamine foam pads at the apex of the 180deg hairpin turns in the labyrinth. That will help reduce the parallel wall reflections and smooth the response out.

Thanks for kind words Sumotan. The speakers fill various rooms of the house - and some are gifts to friends. The foam ones sometimes get trashed eventually.

 

[xrk971]

I just built up the new crossover with the actual parts and not parts from my development kit. I thought I would try these new Dayton Audio Precision resistors (similar looking to a more expensive brand) - they are 1%, 10W, solid copper leads. Also added a Miflex KPCU 0.1uF cap to the 2.2uF 250V Dayton MKP for the tweeter. Woofer is using a Jantzen 2.5mH 0.88DCR 18ga air core. Excess leads on the Miflex are left in place in case I pull it off for use in another speaker. Everything is hot melt glued in place if not already tight to prevent rattle.

Will be assembling the second TL now and hopefully, will be listening to stereo later this evening.

 

[Vunce]

Looks real nice X, you “Fancy’ed” up the XO
Soon you’ll be listening in stereo!!

 

[maty tinman]

Bypass with Miflex KPCU 0.1uF capacitor

It would be interesting to know if you notice a difference and how much with and without the Miflex on bypass, but not listening to Beyoncé

 

[maty tinman]

BTW,

-> https://twitter.com/search?q=xrk971&src=typeahead_click&f=live

 

[xrk971]

Listening to stereo late last night. It sounds wonderful - the new speakers sound like much much bigger speakers and able to shake the house with their TL driven bass. I have them standing next to the 8in TLs which are about 3x in volume and have to say that I can’t tell that the sound is coming from the smaller TLs. Will listen more and give an update after a good long listen.

Regarding Miflex difference: I’ll build one XO without the Miflex but otherwise identical and set the two next to each other for a comparison in mono and see if I can hear a difference.

 

[xrk971]

I just built the second channel XO using identical components (the development XO parts went back to the development kit). I used a Dayton 0.1uF 250v MKP bypass cap in place of the Miflex so that both speakers would have at least the same capacitance value as 0.1uF is not tiny like a 22nF cap. Listening to them in stereo now. Very excellent sounding speakers. They can get quite loud yet play clean for a 6.5in 2-way speaker. Most rooms would find the sound level quite adequate.

 

[fedde]

Cool speaker! Nice pcb also...

Do you still have your speakers with Heil AMT? Are these better or do you miss something yet?

Fedde

 

[xrk971]

Hi Fedde,
Thanks! I still have the Heil AMT but they are not currently on any speaker. I am playing with a RAAL 70-20xr that belongs to a friend right now and really like it. I do not miss anything with the RS28F's as a tweeter. The highs are all there and very nice. When playing the RAAL - you definitely hear a difference in resolving power. Sort of like having a magnifying glass for sound. But I can't say if that makes it a better tweeter.

 

[danny_66]

Hi X,

Nice speaker !
That seem to be excellent drivers.

I noticed that in your test setup you used Wago clips,
I used them also, they're very convenient when tweaking the crossover.
But I just noticed that sometimes they don't make good contact,
I got inconsistent measurements in REW on my tweeter (-0.5 to -1db),
when I replaced them with a screw terminal my measurements were back consistent.

Regards,
Danny

 

[xrk971]

Hi Danny,
Thanks! Good to hear from you - the Wago connectors are very convenient and thanks for the warning about inconsistent connections. I have not noticed a problem for the setups I used so far as the measurement and predictions and final implementations on PCB seem to agree well. Are you still using the ALPHA amp on your RefSpeakers?
Cheers,
X

 

[danny_66]

Hi X,
Yes, I'm still using and enjoying the Alpha.
The Nirvana PCBs are almost done soldering, but since the Alpha is so good sounding I'm not in a hurry

 

[xrk971]

I have loaned the TLs to my cabinet maker for a week so that he can listen to them - he wants to know if he should build a pair for himself. I’ll get his impressions shortly and post an update. I do know that they sound like much bigger speakers. They could be mistaken for a speaker with 8in drivers.

 

[xrk971]

So after a week of listening, my cabinet maker had this to say about these speakers. He had also built some larger 10F/RS225 FAST TL’s for me which I consider my reference speakers and he had a set of those too:

As for me, I am falling in love with the small TL! What not to love? The size is perfect for any room. The more I listen to them, the more I realize that the vocal is far more superior than the big TL. With instruments, the bass may not be as deep as the big TL, but everything else is very, very close....Sometimes, I can even hear the high note clearer and more fully rounded, if there is such a thing.

I had a few friends came over the last weekend, and every single one of them love both pairs of speakers, especially when I set up my karaoke system so the big TL played music and the small ones for vocal. They all lined up to sing and they all agreed that their singing had never sound this good. It was one o'clock in the morning before the music stopped.

 

[zman01]

X,

That is high praise.

I am enjoying the RS225 FAST TLs (B80 mid-tweet version) for the last couple of days and they are sweet . Looks like your Purifi PPT6.5 and RS28F implementation is also a winner.

 

[xrk971]

Hi Zman,
Congrats on building your new 10F/RS225 FAST TLs. Those are some of the best speakers I have heard anywhere and you are the first lucky one to hear it with a Visaton B80 mid-tweeter variant. Both the PTT6.5 and the 10F/RS225 TLs are voiced very similarly that sometimes I have a hard time telling them apart. Given that the PTT6.5 TL is 1/3rd the volume and uses a 6.5in vs a 8in woofer - that is quite amazing.
Have fun with your new speakers.
X