Incorporating Natalie P MTM into 3 way tower

**JonMarsh** · 18 May 2013, 10:12 Saturday

What this does is change the baffle step frequency transition range, where the cabinet moves from 2pi radiation (equivalent to infinite baffle as regards the radiating wavelength) to 4 pi volume radiation (small point source, effectively, again due to the wavelength versus baffle size. Changing the cabinet without adjusting the crossover will likely result in a small bump up of the respond in the 300-450 Hz range. You could model the cabinet radiation differences using programs like the Edge or the FRD consortium BDS (Baffle Diffraction Simulator). Both are free, but the latter requires Excel to run. This will give you a clear idea what to expect.

If you have measurment equipment and can provide measurement files, the crossover design can be adjusted to your cabinet. Other than that, what you're planning should work nicely. I would change the NatalieP alignment from ported to sealed, though, and move the crossover point up to 80-100 Hz. You'll have better definition in the mid bass in that case, as ports are resonators, with several damped cycles of overhang.

**cjd** · 18 May 2013, 13:22 Saturday

What (sub)woofers are you planning? I've done a 3-way using the RS180 as a mid (RS28A as tweeter), though a 14" wide cabinet. It's substantially different than the Natalie P, etc. since it's a 3-way, so it's not a useful point of reference except perhaps in the RS180 measurements.

That said, I agree with Jon - you're really not building a 3-way here, but a two-way + sub. I cross my HT at 60Hz (WTMW mains) and 70Hz (TM surrounds) where the RS180 is the low end, but that's pushing things. I get away with 60Hz because I don't tend to push the system that loud (usually... :B) and the manifold-mounted IB sub starts to have issues much higher. I would choose different drivers were I to do this again (probably the RS225-4 instead of the RS180-4, but if I'm changing things why stop there...) The system starts to "fall apart" a bit sooner than I might like (~102dB) and this is in part due to the crossover frequency (bumping it to 80Hz helps).

C

**linguistisch** · 18 May 2013, 18:08 Saturday

I'm very humbled to be posting here and have responses from you both gentlemen, you are both part of a group of designers that I've read the most creative and helpful information from to date.

Originally posted by JonMarsh

If you have measurment equipment and can provide measurement files, the crossover design can be adjusted to your cabinet. Other than that, what you're planning should work nicely.

Unfortunately I don't have any measurement equipment. Although I do like the punishment of designing these speakers (it's an incredible problem solving experience, honestly), I can't say how many I will keep doing throughout the next few years to justify the expensive mics and software. I do own WT3 however, although I can't seem to find the USB dongle.

Originally posted by JonMarsh

I would change the NatalieP alignment from ported to sealed, though, and move the crossover point up to 80-100 Hz. You'll have better definition in the mid bass in that case, as ports are resonators, with several damped cycles of overhang.

You just touched on my original debate. When I first set out to design this tower I had everything vented (the subwoofer and MTM), but I realized that-that is what I have always done in my designs. I want to go acoustic suspension this time, I want something snappy and crisp. This newly changed sealed configuration in an MTM seemed to model a natural roll off at around 80-90hz as opposed to around 40-50hz in a vented design (not taking into account lower end room gain). These towers will be for stereo left right and strictly music in a different room, and with their onboard dedicated subwoofers the MTMs don't need to reach 40hz flatly like the Dr. K's approach because they will not be for anything like surround duty. So what you're suggesting is what I had originally wished for, a higher crossover point (80hz instead of 60hz) and more midrange punchiness. When I first started mocking these up again I did change my designs to be sealed enclosures crossed over at about 80hz. Others then suggested strongly (and probably rightly so) to stick to a proven design for the MTM. These designs I've mentioned are all ported as far as I can find (I've spent a few hours reading through Google searches but I haven't turned up sealed versions) and so I went back to a ported configuration to use the designs of the RS180-8/RS28F MTM. The benefit was at least I could cross them over at 60hz if I'd like but crossed over higher at 80hz or so in a sealed enclosure is very much what I'd like to try.

Hypothetically, if the baffles were 9" as intended, is it possible to use these proven crossover networks in a sealed enclosure as opposed to the vented they were modeled in? If so then I will gladly go back to sealed. I'm just uncertain what that means in terms of impedance (without the spike of the woofer/port at resonance) and the difference in enclosure volume. Following the impedance answer the second question is what the internal enclosure volume would need to be. I own Bass Box Pro, and I am beginning to think I should have just stuck with WinISD, because the things it models are not near what this serious audio community will come up with in their own modeling using the same stats.

Originally posted by cjd

What (sub)woofers are you planning? I've done a 3-way using the RS180 as a mid (RS28A as tweeter), though a 14" wide cabinet. It's substantially different than the Natalie P, etc. since it's a 3-way, so it's not a useful point of reference except perhaps in the RS180 measurements.

That said, I agree with Jon - you're really not building a 3-way here, but a two-way + sub. I cross my HT at 60Hz (WTMW mains) and 70Hz (TM surrounds) where the RS180 is the low end, but that's pushing things. I get away with 60Hz because I don't tend to push the system that loud (usually... :B) and the manifold-mounted IB sub starts to have issues much higher. I would choose different drivers were I to do this again (probably the RS225-4 instead of the RS180-4, but if I'm changing things why stop there...) The system starts to "fall apart" a bit sooner than I might like (~102dB) and this is in part due to the crossover frequency (bumping it to 80Hz helps).

C

The subwoofer I had in mind was the 12" RSS315HFA-8. It looked like it prefered a sealed enclosure with more volume, and ran a bit smoother/cleaner than something like a Titanic subwoofer that was after raw output. At 8 ohms it would be ~250w from the SPA500 plate amps. I could also decrease my subwoofer enclosure size and run a RSS315HF-4, which would draw out all 500w at 4 ohms. What I don't want is boomy.. I want tight, flat and powerful.

My design goals for this are two floorstanding towers fully incorporated without any other speaker in the room. I don't have a listening position and I probably won't be sitting and listening to these directly necessarily, so bass nodes and reflections won't be a primary concern. These will be in the spare bedroom/home office where I'll be working on design and music, sometimes sitting at a computer and sometimes moving around with projects in hand. I want an airy, disappearing sound that has power and clarity to tackle my wide ranging music tastes. I often will go from BBC style session recordings to Rap, Celtic/Bluegrass folk, Dubstep, Pop, Classic Rock, Hard Rock and back to orchestral movie scores all within the same listening period depending on my mood. I'm perhaps a little OCD and ADD

I think you're both right in saying that they're really a 2.2 setup and not a 3 way. Again my intention was to build a hybrid, in that I could use the RS180-8 with the SB29RDC now and have the ability down the road to swap out the crossover and the tweeter for the RS28F and be good to go with pretested designs without further modeling/engineering.

Thanks for your help, sorry for the word vomiting!

**cjd** · 18 May 2013, 23:09 Saturday

Ported to sealed is a straight shot, no changes to the crossover (unless a designer has attempted to deal with impedance spikes around resonance/tuning, but that's not the case for anything we're discussing here)

The RSS315HF is a mean sub, though as you've noted it sure likes its volume. It will happily play MUCH higher in frequency cleanly compared to most subs that size, so if you have a good pre stage you could definitely experiment with the crossover frequency. The amp may be the limiting factor at that point in SQ. Boomy is an artifact of how you tune things and room as much as anything else - most people (IMO) tune ports too high, and more importantly, undersize boxes significantly. Both of those will focus energy and create a bit more of a one-note-wonder (though that's the extreme.) The Ansonica is tuned quite low (I shot for mid-high 20's, think I hit around 30Hz) for a pair of 7" and isn't even close to boomy. The Garnacha is in a bit of an undersized box (for my preferences) and approaches boomy, but is still very articulate (that's a pair of RS180 as woofers FWIW, so relevant.) It's still a bigger box than most people build for this setup.

If you have access to MS Excel in a Windows environment, I highly recommend Jeff B's Woofer Box and Circuit worksheet for modeling - though sealed is pretty plain math; most of the differences between programs are end correction and other assumptions made in these programs. I typically target Q around .6 to .65.

The SB29 is a sweet tweeter, but so is the RS28(A or F). I used the SB29RDC in the Ansonica. Mmm. A pair of those built sealed, paired with a clean sub could get interesting!

I'll also say that of all the MTM designs with the RS180, the DrK is the one I would stay away from. Jeff B's or the Natalie P would be where I would be looking.

C

**peepaj** · 19 May 2013, 09:38 Sunday

Originally posted by linguistisch

Unfortunately I don't have any measurement equipment. Although I do like the punishment of designing these speakers (it's an incredible problem solving experience, honestly), I can't say how many I will keep doing throughout the next few years to justify the expensive mics and software. I do own WT3 however, although I can't seem to find the USB dongle.

WT3 or Dats doesn't use a USB dongle. Just plug it in and calibrate before using.

**linguistisch** · 21 May 2013, 06:10 Tuesday

Yeah not sure what to call it, I said dongle but what I meant was the usb adapter with the speaker leads and resistor. I found the box earlier today though so I'm back in business testing the RS180-8s once the drivers arrive in the mail.

cjd-
Lots of good information there. I downloaded Jeff B's WBC. Is this the spreadsheet you use for all your enclosures or is there also another popular program/spreadsheet I should look at in order to compare and contrast sims? I don't know what the community prefers and uses most often when comparing notes. I think I have Unibox, I should plug the numbers in there and give it a go as well... I think I'm done with BassBox. It's funny how PE sticks to it so much, they even list the "optimum" settings in their enclosure calculations from BassBox. But if you plug in the RSS315HF-4 into WinISD or Jeff's WBC you really come up with something around 3 times the size of the box they've put down as "optimum" (at least in the sealed variety).

Your Ansonicas are actually what I designed my revised tower after (in a way). I really fell in love with the layered plywood look and feel, I was at Home Depot tonight looking for voidless Baltic Birch or marine grade plywood. Originally after seeing yours I was going to use the plywood for the outside layer of the 1.5" cabinet walls (MDF for the inside), but I think I was getting too far ahead of myself. It's really more about proper bracing than building a 150lb tower, and the plywood should hold up better, look better, and sound just fine. So I've adjusted everything in Sketchup to reflect 3/4" walls and good bracing. At the same time I went ahead and modeled a sealed enclosure for the RS180s with WBC... they really want a small enclosure when it's sealed. Really small. For the Absorption I put down 40 because the cabinet will be lined with acoustic eggcrate and two Deflex pads (unless you have a good suggestion) and 20 for the Box Losses. WBC also modeled a 2.75ft3 sealed enclosure for the RSS315HF-4 which seems fairly big but it does keep the Qtc right where you were suggesting you like yours to be.

It'll be interesting to see how this all starts coming together. Before I forget to mention it, in this new redesign I also made the top cabinet 9" across the baffle. So now the front baffle portion with the MTM is externally the same height and width as the RS180 MTM setups. On the lower portion it adds 1.5" inches to the width, very similarly to the old Polk LSi25.

William

**linguistisch** · 22 May 2013, 19:25 Wednesday

Image not available

Image not available

Both subwoofer and MTM baffles are double layered (1.5"), everything else is 3/4". All wood will be void free marine grade plywood I'm planning.

Upper MTM cabinet is .292ft3 after brace and tweeter backing (but excluding driver displacement). WB&CD modeled the sealed enclosure at .27ft3 (7.59L), .641 effective Qtc. With the drivers in there and damping in place it should be right in the ballpark, perhaps a little lower Qtc with the walls damped. Driver placement and baffle width remain the same as the RS180-8/RS28F layout.

The lower subwoofer cabinet is 2.847ft3 (80.5L) after bracing (but excluding driver displacement). For this one WB&CD modeled the sealed enclosure at 2.75ft3 (77.91L), .669 eff. Qtc. Again, I think with the damping and subwoofer in place it should be right in the ballpark.

I may have gone overboard with the bracing but there's still room for the air to move around.

-W

**JonMarsh** · 24 May 2013, 18:18 Friday

There's no such thing as going overboard with the bracing for some of us! :W

It's looking good- when do you start making saw dust?

**CADman_ks** · 25 May 2013, 10:43 Saturday

This is an interesting thread.

I have thought about doing this very thing, BUT taking it even one step further, and building the amps for the subs into the speakers, thus having powered speakers.

My speakers sit in a HUGE room, but the only reason that it's huge is because it's part of an open plan design living/dining/kitchen/stairs. BUT, I would really want the sub in the living room, and in that "room", there really isn't the space for one, so the built-in subs into the towers has some appeal to me.

There are some commercial designs that utilize this very concept:

http://www.definitivetech.com/ - most of their speakers are bi-polar design. And while that may sound good on paper, I KNOW that there's no way that I could figure out the modeling of what would need to go on there to make that happen

http://www.goldenear.com/products/triton-series - they seem to win a lot of awards for that's worth

In doing more research on this, it appears that there aren't as many players in this arena as there were a couple of years ago. A lot of "opinions" on the WWW indicate that this is not the ideal way to go because you don't have control over the bass, and having two sub that you can't get "synced" may also be problematic. [ their opinions, not necessarily mine, but everything that you read on the WWW is true, so it must be true.

]

For me, I've actually thought about making the sub downward firing, but that makes for a lot wider box on the bottom, and getting that transition to the MTM part could be a little more problematic.

I'm not saying any of this to discourage the OP, as I still think that these type of speakers have a place, although I must admit that I've never heard them personally. I still like the idea.

**linguistisch** · 26 May 2013, 22:41 Sunday

Originally posted by JonMarsh

There's no such thing as going overboard with the bracing for some of us! :W

It's looking good- when do you start making saw dust?

As with the rest of life it's really a question of funds right now, but hopefully this coming month. I've just about finalized the design, I've figured out what I'm going to apply to the walls for damping, I've decided to return the SB29RDCs in order to purchase the RS28Fs (which means I can look into finalizing the crossover parts purchases), and I'll be looking at a local woodcrafting shop/specialty lumber supply outfit later this week to see what kinds of void free marine ply they can order in. Will still need both RSS315s, cabinet/building material/parts, so I'm a bit away but perhaps 2/3rds(?) with the subwoofer amps, RS180-8s and RS28Fs, and design aspects sorted.

On that crossover note, if you have any suggestions based on your Modula and Natalie P I would really like to hear it. I think I may start a thread and see what people's impressions are with the different RS180 MTM networks now available. Also if anything has changed parts wise and what the best types and brands are to order to get the most robust result. I've read through a lot of the MTM threads but they're still a couple of years old as far as I've seen.

Originally posted by CADman_ks

This is an interesting thread.

I have thought about doing this very thing, BUT taking it even one step further, and building the amps for the subs into the speakers, thus having powered speakers.

...

There are some commercial designs that utilize this very concept:

http://www.definitivetech.com/ - most of their speakers are bi-polar design. And while that may sound good on paper, I KNOW that there's no way that I could figure out the modeling of what would need to go on there to make that happen

http://www.goldenear.com/products/triton-series - they seem to win a lot of awards for that's worth

In doing more research on this, it appears that there aren't as many players in this arena as there were a couple of years ago. A lot of "opinions" on the WWW indicate that this is not the ideal way to go because you don't have control over the bass, and having two sub that you can't get "synced" may also be problematic. [ their opinions, not necessarily mine, but everything that you read on the WWW is true, so it must be true.

]

For me, I've actually thought about making the sub downward firing, but that makes for a lot wider box on the bottom, and getting that transition to the MTM part could be a little more problematic.

I'm not saying any of this to discourage the OP, as I still think that these type of speakers have a place, although I must admit that I've never heard them personally. I still like the idea.

It does seem like the design has gone a bit out of style, but it's still around. I originally started my design as a 3 way speaker box like they used to do in the 80's but then over different revisions it started slimming down and later subwoofer amps were incorporated to keep the avr powering just the MTM portion. At the same time that they were slimming down they were also slowly becoming taller until eventually it made more sense to put the subwoofer on the side of the tower and lose the whole "speakerbox" structure. Downfiring could work, but it would be a really wide cabinet like you mentioned and would be awkward to transition into something like the 9" I now have at the top for my incorportated MTM design. Definitely possible, but it just depends on your design craftiness. The two subwoofer amps were in the back of each tower since they were added to the design but with the 9" restriction in order to use the Modula/Natalie P crossovers the width of them would have forced me to forgo the 9" wide RS180 MTM crossover designs, so eventually they also had to go outside the box (I'll be building a separate shelf for them below my avr).

I'll post some updated photos soon. Keep the feedback coming, it's really helpful! Thanks!

Incorporating Natalie P MTM into 3 way tower

Incorporating Natalie P MTM into 3 way tower

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