Hoffman's Iron Law - How small can you go? 3 - Way build

[Efalegalo]

I'm itching to start a new build and wanted to gather fellow forum members' thoughts on the following 3-way:

• Tweeter: Peerless DA25TX00-08
• Mid: FSL-0512R01-08S
• Woofers: RSS210HF-4 (Pair In-Series).

All of the above are well tested by JonMarsh. I'm also choosing these as all of the above are already sitting inside my closet (for much too long).

Hoffman's Iron Law dictates that one can only choose two of the following:

• Small Size
• Deep Bass
• Efficiency

The above driver selection would lean towards Small Size + Deep Bass (we're definitely giving up efficiency), but I want to push the limits on how small I can go.

I'm personally not a fan of bookshelves, so this will 100% be a floor stander. I'm thinking of giving each of the Dayton drivers about 1.0 cubic feet or less -- perhaps as low as 0.5 cubic feet.

I'm looking to build a relatively small speaker that is rather unassuming in a modest living room - and can still pay (relatively) deep enough.

Thoughts --- am I headed in the wrong direction?

[Scareurpasenger]

Funny that I happen to have the same drivers sitting in my basement! I know JonMarsh was looking into such a build a while back and I had pre-purchased these based on that.

Time has not been on my side lately, otherwise I would have had a 3d model for this. I will be watching closely!

[JonMarsh]

Well, I think this is a very good direction, and one I've had in mind myself, if I alter the Kii inspired project and swap out the woofers.

Funny thing is, I have MF-HF basic test cabinets built, and it would be easy to take one of my full size Saint-Saëns V3 cabinet or stack two of the mono woofer cabinets being built to have the basis for trying this out- the only problem is TIME, or lack there of, with so many things on the table, including non-audio unfortunately.






I've been talking with ET about modifying the Kurosawa's to use that MF-HF combo, and have some new maple planks for updated front panels. Of course, the issue there is that the woofers in that project are hideously expensive, but since they're on hand, no worries.

Now, using the RSS210 and that MF and HF combo, my approach would probably be to use the tried and true home brew LR3 crossover topology (No, Linkwitz had nothing to do with that, though I did run it by him and explain the idea in a past California meeting.) Basically, an Ardent style crossover.

Because, of course, the combination you describe would work fine in a Wavecor Ardent style cabinet.

GO FOR IT!

[DaveFred]

"Of course, the issue there is that the woofers in that project are hideously expensive"

Which woofers are those?

[Efalegalo]

Because, of course, the combination you describe would work fine in a Wavecor Ardent style cabinet.

GO FOR IT!

JonMarsh - I do LOVE the look of Ardent cabinet. Any thoughts on how small an acceptable enclosure would be for the RSS210-HF?

[JonMarsh]

"Of course, the issue there is that the woofers in that project are hideously expensive"

Which woofers are those?

The woofers used for this project were/are the Accuton AS190-9-251. My recollection of the price when I bought them 10 years ago was about $500, through a European vendor. (no American vendor had the quantities- and were asking about $800 each). Now, I see pricing between about $1,250 and $2,100 each, depending on vendor and location. (that high one was probably after one of the recent egregious tariff bumps).

Pictures from 2016, that I'd sent to Michael Bell (HTG member and past collaborator)

[JonMarsh]

Looking at my records, in 2018 the AS190 were about $1,000 each at Madisound.

[WilZirkle]

That looks cool

[JonMarsh]

JonMarsh - I do LOVE the look of Ardent cabinet. Any thoughts on how small an acceptable enclosure would be for the RSS210-HF?

The HF version is the so-called high fidelity one, (different VC mechanics) and other bits, intended for larger enclosures. What you probably need is the HO version, Iike I'm using in the V3 of Saint-Saëns- I have both dual driver cabinets and now completing single driver cabinets, that could be stacked, of course, but mainly to ease the lift load of assembling the complete system in place. (the dual driver cabinets are about 100 lb each, and one could say a "kluge up" as I start with a PE MDF cabinet designed around the RS210HO and then build up a stronger shell around it using mostly BB ply. Transfer function for either version is about the same, but I have alternatives for both 4 ohm and 8 ohm version; dual driver is two 4 ohm parts wired in series, as the original intention was to parallel two of those cabinets for a net crossover load of 4 ohms.



Starting point after assembly from PE- their front panel thrown away.




This is one of the more extended LF alignments I was looking at for 28L, using Seas SL226R passive radiator (I think just one added disk- mass is in my XL files). Fully stuffed to adjust LF level in a room and system Q.

[JonMarsh]

The LF cabinet picture above is a rear view, showing the rebate panel depth, so that the cabinet can be laid on its back for assembly work, without worrying about the PR's. This could be built with RSS265PR, but the alignment winds up being different. I've analyzed both, prefer the Seas. YMMV.
DIYW.

[JonMarsh]

And of course, this isn't even discussing sealed alignments, which can be smaller, depending on the extension desired. I prefer a Qts of 0.6 sealed. Once again, this is starting to look (to me) a lot like a Wavecor Ardent, possibly a bit smaller. And it depends on your LF extension targets of course- as you well know, Unibox and VituixCAD are your friends, possibly also this new tool Amplion recently posted to HTG.

[JonMarsh]

One more reminder, a key reason for using the PE subwoofer cabinet for the RSS210HO is that it measures very much like how it models in software tools; the FRD style enclosure seems to induce standing wave amplification of the low mid bass, compared to individual cubes of the same volume, even when one completely stuffs it.

If one is familiar with the Peerless series they use, it has some curious characteristics, a lot like the SBS160 used in the Kii audio systems. It's long throw, but has a steady downward slope in the LF response below 100Hz, which the enclosure shape and proportions seems to compensate for. But this results in a bass boost peaking at around 50 Hz for the fairly flat drivers like the RSS210 series.

[JonMarsh]

Madisound is back up, and this is today's price, I think based on reduced EU tariffs

[JonMarsh]

Uh, brand new? As in, 2016 brand new?

Someone forgot to update their ad copy

[JonMarsh]

BTW, the point to the AS cell series (as I see it) is that response mechanism has two unique characteristics:

1. The acoustic Z axis origin is in the mounting plane, making it optimum for Duelund alignments or any other alignment where Z axis phase over a wide range is critical

2. The net frequency response accomplishing that combined with the optimum cabinet width gives the appearance of intrinsic baffle step compensation. Usually greatly reduces the primary inductor size in the crossover.

[JonMarsh]

witness this response plot in test enclosure, 28L if I recall correctly for one AS190, relatively long sample window (100ms) and 1/24 octave smoothing (low smoothing, IOW):

[JonMarsh]

This was a simple sealed test enclosure; LF roll off is due to low system Qts.

[JonMarsh]

BTW, something I forgot to mention yesterday, in regards to a possible RSS210HO Ardent, is that the sealed alignment for the Wavecor Ardent is 40L for the two 4 ohm 8-1/2" woofers connected in series- this would certainly be a good analysis position to start from. Or just use it!.

[JonMarsh]

A couple of graphs to compare- RSS210HO-4, 2x wired in series, in 22L and 37L

[JonMarsh]

Either cabinet combo is capable of a maximum of 100 dB at 30Hz at maximum rated excursion sealed. Placement can provide some LF balancing via controlled boundary reinforcement and of course there's the simple expedient of passive inline shelving EQ between preamp and power amp as described in other posts on the forum.

[JonMarsh]

Note that the power levels for the Unibox evolution are different for these two graphs; 1 watt versus 4 watts.

[Efalegalo]

In the top left, you have HO (pair, in series in 33 cubic liters, about 0.707 alignment) vs. HF (pair, in series in 46 liters, about 0.75 alignment). I'm trying to stick to the HF, as that is what I have on hand. You have a little bit of a bump, but that may not necessarily sound bad.

[JonMarsh]

Looks pretty reasonable to me! 46L is still a fairly petite size- just imagine the size you would need with two PuriFi PTT8.0 or two MW19TX-04!

(would have to be reflex due to their low Q; large due to the cone mass versus CMS.)

[technodanvan]

Looks really promising...and I have a ton of these tweeters, mids, even a few of these woofers sitting around. Tempting.

[Efalegalo]

Quick drawing -- just to see what the proportions may look like. This is roughly 950mm tall (37.4"), 240mm wide (9.44" wide) , and 420mm deep (16.5"). This is likely about as small as we can go. Right now, the side walls show one layer. This will likely be 1 layer of 18mm BB + 1/2 or 1/4 MDF.

My big concern right now is I suspect there will be possibly material directivity mismatch between the tweeter and mid.

[JonMarsh]

Classic!

[letiennam]

Looks really tempting. I have also these tweeters, woofer. Another option for the midrange is the SB15AC30, which I have, as Jon has also mentioned several times.

[JonMarsh]

This was my quick and dirty polar response check for the FSL-0512, in a plain box. Obviously, some implications regarding crossover frequency and slopes-

[Efalegalo]

Looks really tempting. I have also these tweeters, woofer. Another option for the midrange is the SB15AC30, which I have, as Jon has also mentioned several times.

The SB15CAC is also a great candidate.

Here is the SB15CAC vs FSL-0512 ---- these are simple traces from manufacturer spec sheets. Its easier to compare if you click on the images and use the left/right arrows to toggle between the measurements.



And here is the Peerless:

[Efalegalo]

And here is the directivity index of the SB15CAC (Blue - dotted) vs the FSL-0512 (Red - solid) ---- pretty much similar out the about 2.7Khz?

I suppose if you are crossing somewhere below that (e.g., 1.8Khz - 2.0Khz rage), then maybe the overall directivity index between the two options is not going that different?

I have the Peerless on hand. If someone is willing to ship me a single SB15CAC for some polar measurements, I'm happy to do it.

[Reet]

Of course, drivers of similar size will have similar DI, with only differences caused by breakup behaviour. Any sane designer will use the driver below the primary breakup region so those wild swings in response are well attenuated. That said, the view shown using manufacturer data is a lie as far as real-world DI is concerned, unless the design is for an in-wall speaker. First, response data all the way around the speaker is required, not just to 90 degrees, and then the DI through the midrange region will be defined primarily by the baffle shape, with DI increasing to 5dB level at 1kHz. Real-world DI in a cabinet can look a lot more like this:


To get a pulse on the effects of baffle shape and it's effects on DI, diffraction tool with directivity export will give some idea of reality for comparative purposes

[Efalegalo]

I 100% agree with your comments Reet. My post was more focused on the transition frequency range between the mid-tweeter (e.g., 2khz - 4khz), where I was expecting (possibly incorrectly) the baffle size/geometry to be less of an issue (from a directivity perspective - we can certainly expect it to still have diffraction impact).

[JonMarsh]

And here is the directivity index of the SB15CAC (Blue - dotted) vs the FSL-0512 (Red - solid) ---- pretty much similar out the about 2.7Khz?

I suppose if you are crossing somewhere below that (e.g., 1.8Khz - 2.0Khz rage), then maybe the overall directivity index between the two options is not going that different?

I have the Peerless on hand. If someone is willing to ship me a single SB15CAC for some polar measurements, I'm happy to do it.

A lot depends on the crossover approach you prefer. With the quasi LR3 (my made up alignment- not an official Linkwitz one but follows the gist of the concept with crossover point at -6 dB) one might have more flexibility than the fairly common 2nd order Butterworth three way. LR4 is nice and steep, but has intrinsic power response issues in the crossover reason- typically requires peaking the response through the crossover region if you want the power response fairly flat.

The Wavecor Ardent build is an LR3 and that works out fairly well. With careful choice of crossover frequencies, the Z-axis alignment is handled by the typical driver construction with tweeter in the mounting plane, midrange Z-axis source somewhat recessed, and woofers even more so.

[JonMarsh]

And, if it helps, a re-post of my basic concept explanation for the LR3 - IMO the best Linkwitz-Riley Crossover alignment that Sigfried had VERY little to do with, other than the - 6dB concept (it's not a square function of a lower order crossover, and it's an odd over crossover.)







Midwoofer offset delay is the difference in Z-axis origin. Front to back.





Three way is just an extension of the concept- of course, it requires a little bit of balancing of drivers with Z-axis offset in the right range, and usable response in the right range in consideration of the preferred crossover point based on the Z-axis offset.

Here is a Wavecor Ardent example crossover build with components available a few years ago. Refer to the Wavecor Ardent reference posts for more details.

[JonMarsh]

For those of you not mathematically inclined to generate a target curve for LR3, don't worry, VituixCAD can do that!

[technodanvan]

These Parts Express sales are killing me. First Wavecor, now the Reference line? Maybe these will have to stay on my radar... Just to confirm though, you're sticking with the HF woofer?

[Efalegalo]

These Parts Express sales are killing me. First Wavecor, now the Reference line? Maybe these will have to stay on my radar... Just to confirm though, you're sticking with the HF woofer?

Danny,

I'm inclined to stick with the HF series, not only because I have them on hand, but also because I don't think I need to go any smaller that 45 liter for the bass section -- and if I don't need to go any smaller, I don't currently see an advange of the HO series over the HF series (per VituixCAD simulation results). Jon has measued both --- so he may have more relevant (real-life) results to share.