Mass Loaded Transmission Line Speakers

[NeilBEN]

I have built two pairs of mass loaded transmission line speakers; both using 8" woofers. The bass and midrange clarity, and the bass extension are simply the best I have ever heard. I have been listening to hifi audio for over 32 years, and these speakers are as good as I could ever imagine.

I used an acoustic modeling program called Hornresp ( http://www.hornresp.net/ ) along with DataCAD, which I use in my day job, to settle on the designs, for the two woofers. The first used the Dayton Audio RS225P-4A, and the second has the SB Acoustics SB23RNXS45-4 - both are 92dB sensitivity, 4 ohm nominal, paper coned 8" woofers.

I have been using a miniDSP 2x4 HD active crossover initially. This is easy enough for me to refine the crossover to a fine level, and on the first speakers, I used the PEQ with a UMIK-1 calibrated mic and REW, to make custom filters to get very flat response.

On the second design, which I am calling MLTL-10 (after the Linaeum Model 10) I was able to use just the crossover and adjust the volume on the tweeters; as a model for an analog crossover. I have now done this, as well, and the parts are ordered. I used XSim to match the measured response of the speaker, using the individual driver response measurements. The crossover is 1st order on the tweeter, plus an L-pad to lower the level and balance the impedance - and 2nd order on the woofer.

 

[thirdicomplx]

I've been interested in speaker building for awhile but yet to have actually build a speaker. My woodworking skills, or lack thereof, hold me back. Wish I could build cabs like that. Both pairs look awesome! What tweeter is that in your first pair?

 

[raycarr00]

nice! the cabinets look like the kits partsexpress sells....the 'puter program.... nice woofer selections. the mids? interesting crossover choice. bet they sound fantastic. they appear to beat out the linaeum models 10's in sensitivity- per the stereophile article and your graphs. great job! thanks for sharing.

 

[thirdicomplx]

I know you were trying to pay him a complement but those cabinets are a big step up from what PE sells

 

[raycarr00]

To live and learn.... Was considering ribbon tweeters to add to Yamaha ns 1000's. Recall the sound was amazing. Chinese versions from the bay can handle a limited wattage,but are low priced. The good ones are half a grand each,but are the real deal.

 

[thirdicomplx]

You don't have to spend $1000 for real ribbons. PE has several models for under a $100 each

 

[NeilBEN]

I've been interested in speaker building for awhile but yet to have actually build a speaker. My woodworking skills, or lack thereof, hold me back. Wish I could build cabs like that. Both pairs look awesome! What tweeter is that in your first pair?

The first pair use the Linaeum TLS - True Line Source driver, that is a midrange/tweeter. It covers from ~440Hz on up. The horizontal dispersion is incredibly wide, because the way these drivers behave, they actually get more and more narrow an active area, as the frequency goes up. The mids on that speaker are jaw dropping - really clear and with every little nuance and detail. They are extremely rare - I happened to find a pair of the Linaeum LT1000 on eBay for $400, that were at a pawn shop in Danbury CT. My son and I drove down to get them the *last* weekend before the pandemic shutdown happened. We got them home and plugged 'em into my main system - and were blown away. So, my son looked online, and happened to find a pair of Linaeum LS2 speakers, that use the exact same drivers, for sale in a town about 20 miles away - for $400. I plan to build another MLTL for the second pair of TLS drivers - probably with the SB Acoustics woofer, or possibly with a 10" if I can find one with a lower Fs than the SB, which is 27Hz. Since the TLS covers the top 5+ octaves, the woofer can be higher Mms, as long as it can "keep up" with the ~3.5gm TLS driver ...

The Achilles Heel of the TLS driver, that is not terrible, is they have limited vertical dispersion. I wish I had the dipole version - and I may just remove the thick felt pad that is hot glued in behind the active leaves. It is operating as an open baffle, anyway. The reason I am doing the MLTL-10 is because there are a fair number of the Radio Shack made 1 1/2" high tweeters. These cover down lower than most tweeters - the acoustic crossover point is ~1.7kHz, and they are dipoles, so they *disappear*. And they have wonderful dispersion in all directions.

As far as cutting the Baltic birch - I found that the supplier I bought it from would do a straight through 90 degree cut for $1.50 each. So, this cost just $34 each to get the 12 panels cut. I only had to do a few more myself, though I could have had them do it. The Baltic birch only cost $69/sheet for the first pair, but the second was $129/sheet. I used a biscuit joiner and I really like how this process goes. You need about 10-12 long clamps - I have two 6", six 18", four 30", and two 48", and a couple of large C-clamps. The clamps are not expensive - I think I got sets of 6 for about $38? The 48" are my brother's.

 

[NeilBEN]

nice! the cabinets look like the kits partsexpress sells....the 'puter program.... nice woofer selections. the mids? interesting crossover choice. bet they sound fantastic. they appear to beat out the linaeum models 10's in sensitivity- per the stereophile article and your graphs. great job! thanks for sharing.

Yes, with 92dB sensitivity woofers, and the dipole tweeters having to be shelved down ~3.5dB, these are quite sensitive. I was amazed to se that the amp simulator in XSim was matching the response with just 1W, and 40W pushes them up well over 100dB. They have "jump" and they do sound really, really, good.

They are my last speaker - whichever one. I will go back an redo the active crossover PEQ on the first pair - which I think I will call MLTL-11 (these speakers go to 11!), and see whether I can come up with an analog crossover. I really like some of what the active crossover does - there is no interaction between the amp and the crossover - the amp only "sees" the voice coil.

Another less obvious but I think important advantage these Linaeum drivers have - in addition to their uncanny qualities of ease and clarity without any hint of glare or strain - is they are almost a perfectly constant impedance. The ET-8 and ET-5A tweeters are about 7.2 - 7.4 ohms across their entire spectrum. So, this means they are simple for the amp, and probably for the crossover. In this, they are similar to planar magnetic tweeters - but without the dispersion limitations of those drivers.

Since they are dipoles, it seems that the measured response from the front *seems* to be stepped down quite a bit, but with the "back wave" in the room, they are anything but dull. They do roll off the top of the upper octave, but many of us can't hear very well up that high, anyway.

These are my favorite tweeters, period. I want to a pair of the MLTL-10 to some reviewers - I ultimately hope that Paul Paddock - the inventor of the TLS drivers, who is still active, and has a 40th anniversary driver called the WBLS (wideband line source) that covers even lower than the TLS from ~1990, and are about 95-96db sensitivity. Oh, what I would do to have a WBLS atop a MLTL cabinet! Bass into the 20's that is the best I have ever heard, with the midrange and seamless integration all the way up ...

 

[thirdicomplx]

Very cool! I knew of the Radio Shack speakers but never knew these monsters existed. Do you find any issues with the dipole interaction and placement? I live in an apartment at the moment and don't have the room to give my speakers the recommended 3+ feet from the wall. The most I could get away with is probably about where you have yours placed. Open baffles would certainly be easier to build too .

Man, plywood has skyrocketed! I'll have to look into local lumber suppliers. I haven't had the best of luck getting my wood cut at the big chain stores

 

[NeilBEN]

Here's the Stereophile review of the Linaeum Model 10 speakers: https://www.stereophile.com/content/linaeum-model-10-center-channel-loudspeakers
It has illustrations of how the tweeters work, and suffice it to say, that with a mass loaded transmission line, there is far more bass extension - and clarity and "speed"; added to what they describe:

Overall, the Linaeums are among the relatively few speakers I've reviewed that sound so natural and uncolored, they are difficult to describe-but I'll try anyway. Their most noticeable traits are listenability, very respectable dynamic range (little compression), and the ability to handle realistic concert-hall volume levels without any perceptible strain.

The treble is very smooth, quick, and open, and it blends superbly with the lower range. The midrange is completely free from identifiable vowel colorations, and the bass is almost unbelievably deep, considering the modest woofer size.

Nothing seems to ruffle these speakers ...

And here's a review of the Linaeum LT1000 in the New York Times: https://www.nytimes.com/1991/11/03/arts/audio-a-new-concept-flexibility-and-fidelity.html Which I can't read at the moment ... but I read it a while back. Suffice it to say that even with an "old school" transmission line, it is a hidden gem.

Here are the LT1000 (with an 8 ohm Dayton Audio RS225P-8A) next to my MLTL-11. The stock woofer in both the LT1000 and LS2 is an 8 ohm Vifa poly coned 8" - which is a fine driver, but lacks the power and dynamics of the woofers I have used.

 

[NeilBEN]

Very cool! I knew of the Radio Shack speakers but never knew these monsters existed. Do you find any issues with the dipole interaction and placement? I live in an apartment at the moment and don't have the room to give my speakers the recommended 3+ feet from the wall. The most I could get away with is probably about where you have yours placed. Open baffles would certainly be easier to build too .

Man, plywood has skyrocketed! I'll have to look into local lumber suppliers. I haven't had the best of luck getting my wood cut at the big chain stores

Yes, many building products have TRIPLED or more ... At $69 the 19mm Baltic birch plywood was a steal. That is barely more than ACX 3/4" T&G subflooring. By the way, they had 18mm for the second pair.

I will be listening for reflection issues, but nothing seems obvious. The Model 10 had a "fern" shaped piece of felt on the top panel behind the tweeter - a solid band at the center, and arms/branches out to both sides, to reduce reflections. The image is huge and spacious, and deep with layers, too. There are vivid details that just effortlessly happen - you never heard sounds coming from the speakers or the driver. I have a room modes that is easy to "excite" at around 40Hz, and so far I have kept it to only about +4-5dB. These speakers have extension into the upper 20's - but most songs never go that low. A few get to the mid or low 30's.

 

[Akustic]

And how do they sound when you're listening to acoustic bass solo's ??

 

[wmgwizard]

Please pardon my ignorance but are they really Transmission Line enclosures or large ported enclosures with a well braced "chamber" ?

Your design look more like a 1/4 wave tube.
https://images.app.goo.gl/KPJ5LYu7EM4ERuVb7

I thought TL design channeled the back wave through a series of internal channels essentially creating a "vent" tube several feet long inside the enclosure.
https://images.app.goo.gl/k9eHSVJ6Hw5DcFPx7

Please, enlighten me to the errors of my thoughts.

 

[NeilBEN]

And how do they sound when you're listening to acoustic bass solo's ??

Better than any speaker I have heard in my over 40 years of hi fi listening. Bass was the initial reason I got into this - as I am sure it is true for many people. I listen to a fair bit of acoustic standup bass - bluegrass, some jazz, blues, folk. Edgar Meyer is one of my favorite players, with The Goat Rodeo Sessions, and Skip Hop & Wobble, and several other settings.

 

[NeilBEN]

Please pardon my ignorance but are they really Transmission Line enclosures or large ported enclosures with a well braced "chamber" ?

Your design look more like a 1/4 wave tube.
https://images.app.goo.gl/KPJ5LYu7EM4ERuVb7

I thought TL design channeled the back wave through a series of internal channels essentially creating a "vent" tube several feet long inside the enclosure.
https://images.app.goo.gl/k9eHSVJ6Hw5DcFPx7

Please, enlighten me to the errors of my thoughts.

There are a lot of variations and overlap in designs - and there has been significant changes in how transmission line speakers are designed. The older way of doing it, is like the Lineaum LT1000 - the woofer is all the way at the closed end. But with the decades of testing and development, it has been found to have the woofer moved away from the closed end, it makes the output much more even, by using the closed end as a resonance chamber. There are designs that are even size all the way along the TL, and some expand the size toward the terminus opening, and some like mine that taper the size smaller toward the terminus. This latter approach allows the woofer to operate under much lower pressures at the higher frequencies it covers (not unlike an open baffle - but obviously without the cancellation that an OB has). As the frequency goes down, more and more of the air along the TL gets "engaged" and this is were the mass loading comes in. This progressively adds mass until it reaches the terminus opening.

Where this is quite different from a typical ported box is the internal distance between the driver - and from the closed end - to the terminus opening is much longer, and it acts like a column of air. The actual length at the centerline of this speaker from the closed end to the terminus opening is 84" / 213cm. And the closed end is essentially folded back on itself - because sounds start at the woofer and go down to the closed end, and then reflect back up and then out to the terminus opening. This adds another nearly 20" / 50cm to the effective length.

To make things more complicated, there are TL designs the use a port (sometimes round, or rectangular) that is near the smaller/farther end from the woofer. This is called "restricted terminus". This has the same sort of effect as the closed end nearer to the woofer. The other gray areas are with tall floor standing ported speakers - the internal shape and proportion of the cabinet have an effect on how they behave. You can have two speakers with exactly the same internal volume - one may be closer to a cube and the other a long thin rectangle - and they may have the port located at various positions, and it all will change the way that the design resonates, and how it sounds.

To be clear about my design - the terminus opening is the size of the entire end of the transmission line, so it is a terminus opening; and not a port. As I said though - some TL designs do have a port or ports, and they are still considered as transmission lines. I think the distinction is in whether they are mass loaded TL, is the fuzzy area. All ported designs add the mass of the air IN THE PORT ITSELF. Mass loaded transmission lines add a *variable* amount of mass (depending on the frequency) and at their lowest frequencies, they add most/all the mass of the entire length of the path inside the cabinet.

But wait there's more: Hornresp also can account for the cancellations that occur because of the distance between the woofer and the terminus opening on the OUTSIDE of the cabinet. The effect of this is HUGE, and it accounts for the elimination or vast reduction of a whole lot of spikes (and dips) in the higher frequencies. To get this distance, you have to be doing the cabinet drawing of its actual design - at the same time as you are working on the Hornresp acoustic model.
The other thing that Hornresp can model, is the amount and placement inside the cabinet, of the poly-fil damping. It gives you the total weight in the design, and you can get the proportions of that total used in the various segments. Most designs that I have seen use a little damping in the closed end, and a lot more right behind the woofer - and almost never use any in the half closest to the terminus opening. Damping effectively acts like the TL is longer than its physical length - because it adds more mass - due to slight restriction of the motion of the air.

The Hornresp model is doing a MASSIVE amount of work. You can slide the sliders to change the size/areas, and the lengths, and the filling, and do trial and error, ad infinitum. And that is amazing - with the help of both the DIY Audio forum (which includes David McBean who is the Hornresp programmer), and the Facebook transmission line group (run by Martin King), that I can use this tool, to make a speaker that works so well. Using another amazing tool - XSim - I have ordered the crossover parts, that I will hopefully get to a complete speaker design - that would have been months and months and months of work for anybody in the past, before we got these tools.

 

[grindstone]

Did you use Martin's stuff, too? I've been out of touch with any of that really since he moved to yahoo let alone after that all folded (and am not a FB person). Fine work, at any rate, and thank you for posting.

And yeah as Neil stated, it's a continuum and there's a lot of gray. I just call everything "pipes" and it keeps life simple. There are closed-ended pipes and open pipes, each with different harmonics, but everything resonates. Increasing pipes trade bandwidth for gain, decreasing pipes trade gain for bandwidth. Unradiused corners lowpass because they're expansions. Mass-loading is another damping tool in a designer's box. It becomes about best-fitting a pipe for an era of driver manufacturing (eg very old big Vas stuff vs. more contemporary stuff) and cab goals. People are trying to get a lot of different things done in their differing designs and the semantics get in the way sometimes.

 

[NeilBEN]

Did you use Martin's stuff, too? I've been out of touch with any of that really since he moved to yahoo let alone after that all folded (and am not a FB person). Fine work, at any rate, and thank you for posting.

And yeah as Neil stated, it's a continuum and there's a lot of gray. I just call everything "pipes" and it keeps life simple. There are closed-ended pipes and open pipes, each with different harmonics, but everything resonates. Increasing pipes trade bandwidth for gain, decreasing pipes trade gain for bandwidth. Unradiused corners lowpass because they're expansions. Mass-loading is another damping tool in a designer's box. It becomes about best-fitting a pipe for an era of driver manufacturing (eg very old big Vas stuff vs. more contemporary stuff) and cab goals. People are trying to get a lot of different things done in their differing designs and the semantics get in the way sometimes.

From what I understand from my online interaction with Martin King - is that Hornresp is way better than any of the "rules of thumb" that had been how folks designed transmission line speakers, in the past. I read a lot of his writing before discovering the Facebook DIY Transmission Line Loudspeakers (if you are on FB, you can request membership in the group), and basically, his advice is to use Hornresp or another similar acoustic modeling program. Software can do the myriad calculations - way way way way way way beyond anything a person with pencil and paper, and even a calculator can manage.

 

[twiiii]

You may have great bass, but it won't be tight and accurate. High distortion levels and doppler distortion, too. Any time you port a speaker you will be having time arrival and increased distortion issues just so you can extend your bass a bit.

 

[Akustic]

Better than any speaker I have heard in my over 40 years of hi fi listening. Bass was the initial reason I got into this - as I am sure it is true for many people. I listen to a fair bit of acoustic standup bass - bluegrass, some jazz, blues, folk. Edgar Meyer is one of my favorite players, with The Goat Rodeo Sessions, and Skip Hop & Wobble, and several other settings.

Had a Fried transmission line once long ago .. didn't like the mid/high character but it produced the best bass solos that I've ever heard ..
A lot of work but if it sounds better, then it was worth it ..

 

[NeilBEN]

You may have great bass, but it won't be tight and accurate. High distortion levels and doppler distortion, too. Any time you port a speaker you will be having time arrival and increased distortion issues just so you can extend your bass a bit.

Well, I think that if you get a chance to listen to an MLTL speaker, you might be very surprised?

As I said, this speaker has the best quality bass I have ever heard. Anything but boomy or distorted ...