Directive 3 way with flow slot mid and waveguide tweeter

[TasTinker]

Hi all
Inspired by the Directiva threads here's the outcome of my latest flow slot experiment.
Top end I'm using Sb26ADCs in Audiohorn 'ReShape' Tweeter Waveguides
Mid-woofers are Sica 6.5H 1,5 CP mid woofers, with Melamine foam pads in the slots and Twaron fill in the enclosure.
Bass are Visaton TIW250s in sealed boxes EQ'd flat to low 30's
xo varied in development between BW3 and LR variations, currently LR
DSP and amps by Hypex 253

Very very happy with the end result, pulled my LXmini clones apart for the components the improvement was so noticable.

Couple of things to share from the process:
With the flow slots I found damping choices were much more critical than precise slot size and placement. It affected both the response and H3 in particular.
A cubic chamber, despite the conventional wisdom of unequal sides, led to the easiest response/distortion combination.
If experimenting, making up a test box with adjustable dimensions and insertable slot panels enables quick concept checks.
The Sica mid woofer is a great option but does have a sharp response wiggle around 1500hz likely from surround resonance. With it's double roll design the options for edge coating to try and reduce it appear limited. OK if acceptable as is but might be difficult to address it without DSP.
Large cell melamine foam damping in the slots (dark grey acoustic panels) for some reason worked well in FR but resulted in high H3 measurements, the white fine celled 'magic eraser' blocks didn't result in the same F3 problem.

As noted I'm stoked with the oucome. Huge thanks to the ASR community for all I've learnt following various threads, so appreciated!
First image is without the NF bass measurements.

 

[TasTinker]

Test mule and final enclosure

 

[TasTinker]

Various sweeps developing the mid-tweeter combo (Bass units are from a previous project)

 

[jaakkopetteri]

Would you have normalized polars and a larger/more detailed graph just for the mid? Seems like pretty good rear attenuation throughout, most cardioid implementations tend do worse around 1kHz or so

 

[TasTinker]

Here's one of the development sweeps of the cardioid mid. Will have a look for a latter iteration on the weekend (midnight here at present)

 

[TasTinker]

Best I've got of just the mid, saved sweeps after this were with the tweeter

 

[TasTinker]

Hi all
Inspired by the Directiva threads here's the outcome of my latest flow slot experiment.
Top end I'm using Sb26ADCs in Audiohorn 'ReShape' Tweeter Waveguides
Mid-woofers are Sica 6.5H 1,5 CP mid woofers, with Melamine foam pads in the slots and Twaron fill in the enclosure.
Bass are Visaton TIW250s in sealed boxes EQ'd flat to low 30's
xo varied in development between BW3 and LR variations, currently LR
DSP and amps by Hypex 253

Very very happy with the end result, pulled my LXmini clones apart for the components the improvement was so noticable.

Couple of things to share from the process:
With the flow slots I found damping choices were much more critical than precise slot size and placement. It affected both the response and H3 in particular.
A cubic chamber, despite the conventional wisdom of unequal sides, led to the easiest response/distortion combination.
If experimenting, making up a test box with adjustable dimensions and insertable slot panels enables quick concept checks.
The Sica mid woofer is a great option but does have a sharp response wiggle around 1500hz likely from surround resonance. With it's double roll design the options for edge coating to try and reduce it appear limited. OK if acceptable as is but might be difficult to address it without DSP.
Large cell melamine foam damping in the slots (dark grey acoustic panels) for some reason worked well in FR but resulted in high H3 measurements, the white fine celled 'magic eraser' blocks didn't result in the same F3 problem.

As noted I'm stoked with the oucome. Huge thanks to the ASR community for all I've learnt following various threads, so appreciated!
First image is without the NF bass measurements.

and with merged NF

 

[Curvature]

and with merged NF

Really impressive. Top octave calls for some kind of phase plug, I would think.

 

[TasTinker]

Really impressive. Top octave calls for some kind of phase plug, I would think.

Thanks
The Audiohorn waveguide does have a 3d printed phase plug in the tweeter mount- beyond my expertise to modify though. They go plenty high enough for me personally however due to age and industrial hearing loss. Its a system that suits me and the reflective room.

 

[5150]

Very cool!

Any plans to share your cabinet design? Failing that, got some suggestions for reading to design an enclosure of this type for myself?

I actually found this thread by looking for someone who has used the Reshape waveguide... didn't expect to see cardioid mids along with it! Very very cool!

Edit: for others whose brains have been set afire by this thread, this looks like a great thread on the topic https://www.diyaudio.com/community/...ve-speaker-insipired-by-d-d-8c.369939/page-10

Another here which looks more helpful https://www.audiosciencereview.com/forum/index.php?threads/big-2-way-cardoid.20728/

 

[TasTinker]

Hi
There's no one site I found that has a definitive diy resistive cardioid instruction. I actually got started on this by the Directiva V2 thread and just searched widely to add to my understanding. (thx for the links

Id not recommend trying to duplicate this precise design, unless very confident in woodworking. Mainly due to that Sica driver being slightly too large for a straight extension of the rounding around the reshape WG so I ended up with a blended rounding below the WG. I also found that Sica in this implementation required a fair bit of dsp intervention.
I initially chose it as I was chasing max mid area / travel combination to help push the cardioid as low as possible. An easier cabinet option and cheaper would be one of the sb17's which is also what Nicolas at AudioHorn recommends with the reshape.
I tried 1, 2 and 3 slot arrangements with varying spacings and lengths. Not a massive difference but the final arrangement I chose for this drive and enclosure combination was 1 slot 170 x 15 20mm back then a second 150 x 40 spaced 40mm back from the first, with moderately tight fibre in the enclosure and 10mm thick white melamine foam in the slots.
Thickness and type of foam in the slots was moderately critical! Likewise the enclosure shape, where I strangely found a symmetrical cube gave most workable results. Foam choices also affected distortion, notably H3.

IMO not something to contemplate without a turntable, measuring capabilities and DSP implementation.

For the cabinet, unless you have good machining expertise if after a neat outcome I'd recommend getting the WG without the rounding and use a curved edge beading strip from hardware suppliers as illustrated on the AudioHorn site (orange edging shown on this page https://audiohorn.net/mid-range-beaming-and-narrowing/ You could then run the beading down the full cabinet length and no rounding over machining required. Note the rounding Nicolas offers from memory is not constant radius so likely wont precisely match cabinet roundings from commercially available rounding bits.

FYI I found Nicolas most helpful, worth contacting if you are contemplating the reshape. Depending on your listening distance and mid preferences, you might also consider the wg mid setup he's working on as an easier achievenet of fairly broad controlled directivity.

 

[5150]

Hi
There's no one site I found that has a definitive diy resistive cardioid instruction. I actually got started on this by the Directiva V2 thread and just searched widely to add to my understanding. (thx for the links

Id not recommend trying to duplicate this precise design, unless very confident in woodworking. Mainly due to that Sica driver being slightly too large for a straight extension of the rounding around the reshape WG so I ended up with a blended rounding below the WG. I also found that Sica in this implementation required a fair bit of dsp intervention.
I initially chose it as I was chasing max mid area / travel combination to help push the cardioid as low as possible. An easier cabinet option and cheaper would be one of the sb17's which is also what Nicolas at AudioHorn recommends with the reshape.
I tried 1, 2 and 3 slot arrangements with varying spacings and lengths. Not a massive difference but the final arrangement I chose for this drive and enclosure combination was 1 slot 170 x 15 20mm back then a second 150 x 40 spaced 40mm back from the first, with moderately tight fibre in the enclosure and 10mm thick white melamine foam in the slots.
Thickness and type of foam in the slots was moderately critical! Likewise the enclosure shape, where I strangely found a symmetrical cube gave most workable results. Foam choices also affected distortion, notably H3.

IMO not something to contemplate without a turntable, measuring capabilities and DSP implementation.

For the cabinet, unless you have good machining expertise if after a neat outcome I'd recommend getting the WG without the rounding and use a curved edge beading strip from hardware suppliers as illustrated on the AudioHorn site (orange edging shown on this page https://audiohorn.net/mid-range-beaming-and-narrowing/ You could then run the beading down the full cabinet length and no rounding over machining required. Note the rounding Nicolas offers from memory is not constant radius so likely wont precisely match cabinet roundings from commercially available rounding bits.

FYI I found Nicolas most helpful, worth contacting if you are contemplating the reshape. Depending on your listening distance and mid preferences, you might also consider the wg mid setup he's working on as an easier achievenet of fairly broad controlled directivity.

I'll reach out to Nicolas. I thought about kerf bending+steam to bend plywood for the corners, so I'll see what he says about the radius.

I'm surprised there isn't more math to help model out the slots in the box for the midrange. Everything I've seen so far is a trial and error approach, but it does seem like there's a good amount of leeway in how you solve it.

Im thinking of a 3 way tower with the purifi 6.5" "true midrange" and a subwoofer with a good motor for ~150hz on down. DSP certainly, was very impressed by the fusion amp I used for my IB subwoofer build

 

[Azrael]

I've also been toying with the idea of building a speaker with gills for the midrange. I have two 18sound 8MNB420s that I could use for this as mid woofers. But the whole thing seems to me to be a lot of trial and error. I wish there was a resource to help you tackle the whole thing a little more specifically.

 

[TasTinker]

Yes unless you have high level acoustic CAD expertise it will involve a fair amount of trial and error, IF you want to get every last bit of refinement out of the design.
However a general guesstimate starting point should still get you to a fairly good outcome with not too much tial and error, given even a conventional design will still need some test and adjust refinement.
My starting point if doing another in the 5.5 to 6.5" driver range would be:

• At the bass end it's behaving like an open baffle. Bottom end will drop like a stone so with the driver choice Sd, travel and EQ options will matter if pushing the XO lower.
• Total slot area around Sd for the driver
• Minimum x-y dimensions for the enclosure (edge of back side chamfer on the driver cutout)
• Personally Id go with the z the same as x and y. Others have good results with z a lot smaller than x-y
• One slot close to the front and another back about twice the width of the first. A net search will show some commonalities. My take is the multiple slots spread the cancellation effect over a broader range. Further back for lower frequencies but on this size range going further back didn't do anything useful.
• Fill the enclosure will your preferred damping. I prefer fairly tight due to the small enclosure
• Experiment with foam&/or mesh in the slots

 

[speedbad]

Hi,

Just to address a few points: If I can, the 18sound 8MNB420 I have tested is not the best driver for cardioid applications and has some distortion issues (see the 8" test on AudioHorn).

That said, the intersecting characteristics of a wavefront make 8" drivers generally more suitable and interesting for this use — but not all 8" drivers. Pairing it with a 10" woofer below like the Faital 10RS430 or Beyma 10NMFS, it can help maintain a compact design.

At some point, when the speaker gets large, I prefer to use a 15" in regular two voices + sub. It won’t be horizontally as controlled as a perfect 8" cardioid, but the difference isn’t that dramatic — and it offers better vertical control, which shouldn’t be forgotten, even if horizontal control is the priority due to the ear’s orientation and typical room geometry (wider than tall).

There is no strict mathematical modal model for cardioid behavior, because it's highly dependent on the nature of the wave-front emissions (yes, plural) from the back of the driver.

However, there is physical model based on advanced FEA — that's how I design my cardioid setups. For example, I get 90° coverage at crossover region (crossed with X-Shape X25 + 18S 1090), and still at 120° at 200 Hz (so quite "restricted" and controlled). The trade-off of a cardioid that's close to "100% efficient" is that it cancels sound very aggressively. It doesn't really use a slot — it's a DLCS (Dual Loaded Cardioid System), with both the front and rear wavefronts guided.

So SPL drop-off can be observed from 300 Hz, making a 200 Hz high-pass mandatory. Trying to push cardioid behavior lower generally means boosting the woofer (increasing H3 — which becomes audible above a certain SPL, cardioid or not), and/or reducing the cardioid effect to avoid excessive cancellation, especially in the low end. Some commercial systems run at just ~20% cardioid effect to keep a two-way design, but the result is often a "cardioid" that's not very effective, almost none in fact (except for marketing ^^).

This is due to the omnidirectional nature of the wavefront, at some point the two wavefront completely cancel each other, this appear progressively from 300 Hz. It also defines a top frequency limit as at some point both wavefront beam before meeting but it's depending on how the wavefronts (front and rear) are managed. A conventional method usually maxes out around 1 kHz, while more advanced approaches can easily reach 2 kHz very clean, it depends.

IMHO, the best approach is a true 3-way system, with a woofer crossing over around 200–250 Hz and a wave-guide cut not too high.

That’s not really a problem — in most rooms, the modal field begins around 250 Hz. The main benefit of guiding sound is in the reverberate field, so above 250 Hz. In the modal region, we stop trying to control directivity and focus more on distributing bass energy evenly, we need room gain, and avoiding masking effect. In this range, DSP/EQ combined with measurements at the listening position will be your best allies.

In professional environments, cardioid subwoofer arrays are still used in the low end, but primarily to control rearward radiation — typically by placing subs behind the stage to minimize noise pollution beyond the venue (e.g. neighboring residential areas).

The result with the 6.5" SICA is already very good here, and very compact/cost effective. For peoples wanted extended control at least horizontally in a small form 3 voices system factor there is no so much options.