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Multi-Way Conventional loudspeakers with crossovers

Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide
Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide
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Old 21st May 2020, 07:47 PM   #21
ErikdeBest is offline ErikdeBest  Switzerland
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Quote:
Originally Posted by xrk971 View Post
Hi Erik,
The Satori is perhaps one of the best 6.5in mid bass ever made. I donít have one, yet. It might work in this configuration - I donít know, but I think its response might take a few more components to get as smoothly rolled off. I think the main thing about the PTT6.5 is itís ultra low distortion - itís similar or even better than a dedicated midrange like a class leading 10F/8424 over the 1k to 4K range, plus it has 10m Xmax. This pumps a lot more air.

PTT6.5:
Click the image to open in full size.

Satori:
Click the image to open in full size.
Understood, thanks for explaining!

And it is correct that you use a 2nd order xover which combined with the natural rolloff off the Purifi makes for the 4th order acoustical slope needed for the Harsch XO? The Satori does not have the natural rolloff, so would need an actual 4th order electrical xover?

It looks as if the Purifi does indeed fit as a glove in this design!
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Old 21st May 2020, 08:04 PM   #22
Scottmoose is offline Scottmoose  United Kingdom
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Re the RS180P, the 2KHz 3rd harmonic is a product of the unsuppressed 6KHz breakup. The behaviour in this sense is more or less the same as you find in most rigid-cone drivers. If you cross sufficiently low and steep to shunt that breakup low enough (a simple notch is rarely sufficient to get rid of the distortion amplification products) you'll find it will go away. There isn't a hard & fast rule for what is sufficient -depends on the degree of the breakup and the baseline distortion level of the driver, but think minimum -36dB suppression, preferably -48dB or more.
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Old 21st May 2020, 10:24 PM   #23
xrk971 is offline xrk971  United States
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Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide
Yes, that H3 shape is the same in shape as the 6kHz breakup. So if one doesn’t bit the breakup - there is no 3rd harmonic generated from it. But that requires a steep filter and it’s associated phase wraps.
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Old 21st May 2020, 11:27 PM   #24
Scottmoose is offline Scottmoose  United Kingdom
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Right. Either that or it's purely used as a compact woofer crossing low. As always, name your poison. In this case, you've got a 4th order Butterworth low pass though, so speaking purely in the abstract, assuming you've got a tweeter / waveguide combination that can handle a low XO frequency with that relatively shallow slope, you should be able to cross sufficiently low to hammer it out of the way, albeit probably at the price of a couple of extra components relative to the current design here (nice job BTW).
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Last edited by Scottmoose; 21st May 2020 at 11:37 PM.
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Old 22nd May 2020, 02:23 PM   #25
phase_accurate is offline phase_accurate
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I have wondered many times whether Samuel is aware of how popular his proposal has become. I don't think that he is a member here (yet). Apart from that there are some very cool French audio forums that he might probably be frequenting. Should contact him again since a long time already.

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Old 22nd May 2020, 03:00 PM   #26
xrk971 is offline xrk971  United States
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Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide
Hi Charles,
If you know Samuel Harsch, please let him know! And please give him our thanks! Would love to hear his opinion on how his proposal has progressed and used on a daily basis by many DIYers here.
Cheers,
X
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Old 24th May 2020, 09:23 AM   #27
xrk971 is offline xrk971  United States
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Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide
Default TL Design

Here is the TL that I just came up with and simulated in Akabak. I am trying to keep it as a fairly compact standmount studio monitor rather than a floorstander. The design achieves between 36Hz and 42Hz -3dB depending on degree of stuffing/damping. Nominal sensitivity is 84.8dB at 2.83v ad 1m. Constructed of 3/4in BB ply on exterior panels and 1/2in BB ply on interior divider panels, box is 18.5in tall x 17.0in deep x 8.5in wide. Internal TL width is 7.0in.

Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide-ptt6-5-tl-design-sketch-jpg

Akabak predicted SPL for 2.83vs and 1m:
Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide-ptt6-5-tl-design-freq-2-83v-jpg
Attached Images
File Type: jpg PTT6.5-TL-Design-Sketch'.jpg (484.1 KB, 1344 views)
File Type: jpg PTT6.5-TL-Design-Freq-2.83v.jpg (103.9 KB, 1131 views)
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Old 24th May 2020, 02:28 PM   #28
xrk971 is offline xrk971  United States
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Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide
I think it is time to do a pathfinder build in foam core and XPS before committing to BB plywood.
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Old 24th May 2020, 03:01 PM   #29
camplo is offline camplo
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You are simulating in AkABAK now I'm jealous lol...I've watched a few videos (I've made a simple box and driver using a video tutorial), I think I can get close, I 'm sure If I understand how to place the driver. How do you feel about making a step by step for the process, while you attempt to model this as a TL?

One of the things I've learned from the modelling I've done is that the only way to keep great midrange at higher volumes not just a low relative volume, is to have sub bass and midrange on different drivers...Intermodulation distortion is a function of displacement, so when a two way is played loud enough, sub bass will displace the woofer far enough to create IMD in the midrange. These new woofers would be great as subwoofers with their ability to be displaced greatly without the harmonic distortion, since sub bass is about moving air, and I imagine that the box is small...3 ways have lower displacement within the midrange than MTM's even...Just something to consider.

Also to add to your idea tank, don't forget about the practice of low tuning a BR design...When I posted about it, I explained it in the terms of tuning like a horn, 1/2 the frequency of desired system cutoff, I came across a guy who tuned his woofers to about 23hz and used two woofers....the way he designed it, the second woofer drove down group delay around resonance, he was happy with it.

Last edited by camplo; 24th May 2020 at 03:16 PM.
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Old 24th May 2020, 03:21 PM   #30
xrk971 is offline xrk971  United States
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Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide
Akabak tutorial is a bit OT.

Look for stuff by member Don Hills. He is the one who turned me on to Akabak, and everything I learned I got from his tutorials and sample scripts. It truly is powerful and can model almost anything. But a steep learning curve - well worth it once you master the basics. Very similar to high level language like any programming language. But filled with audio specific things that make modeling speakers a snap.

Akabak Simulator

This one script of how to model a Cornu back loaded horn can be used as the basis to model any TL. The trick with typical TL is to model the turns as 45deg expansions followed by 45deg contractions as a “waveguide” element.

Download the software (you will need a WinXP emulator) and read the manual and try some sample code.

Start with a sealed box, then a bass reflex, then DCR, then a straight MLTL, then a tapped horn, then a 2 way with arbitrary driver placement and a XO, then the final crown of achievement would be a 3 way Synergy.

I still can’t model a compression driver ab-initio yet. However, I did model a Karson K-15 from scratch.

Compression driver throats: That’s for gonzo modelers.

Search for keywords “Akabak tapped horn” or “Akabak TL”. You will get lots of hits.
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Last edited by xrk971; 24th May 2020 at 03:24 PM.
 

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