Transmission Line Bass Questions

[Ken Hicks]

Here's the deal - I think I am kind of a hybrid audiophile snob. A champagne taste on a beer budget kinda guy. I like good sound but there are many who would consider my taste in music (fairly heavy - running the gamut from Black Sabbath to newer progressive heavy stuff like Opeth) and "good sound" an oxymoron. I grew up with an audiophile step-father and in the past I've owned some high end stuff (for the average early twenties Marine), Nakamichi, JBL and the like. Being a lowly bicycle mechanic without a lot of disposible cash, my current system consist of an Onkyo A-9010 40wpc integrated amp, an Onkyo C-7030 CD player and a pair of 25 year old Pinnacle AC850 speakers.

Being a jack of all trades - master of none, I've built high-end cabinets and doors in the past which brings me to DIY Audio.

I want to build some speakers.

I am interested in a tall, slender MTM design which brings us to the crux of this post. I see a lot of DIY MTM speakers are of a transmission line design. My concern is the bass. It seems from some of the reviews and such on TL speakers that the bass is "different". I've never heard any TL speakers before so I don't know what this "different" is. I guess if I tell you what I want from a speaker you can tell me if a TL is the answer. I like solid, tight, punch in the chest type (double) bass. Not boomy, rattle the license plate frame, rollin' the dubs kinda bass. Also, I seem to have a sensitivity to the 1k range so if there is a mid-range adjustment or equalizer involved I usually knock that region down a bit. I guess I like bright, but not "bitey" top end. Basically I would describe what I'm looking for is distortion-free, smooth, yet hard-hitting. So, would I like a TL or do you think I would like your basic ported design.

BTW, I have a $400-$500 budget. I've been considering the Parts Express TriTrix but I'm leary of the TL design. I could be persuaded to spend a little more on the Murphy/Kittinger ER18s found on this forum if you could convince me that their sound is for me.

 

[ski2xblack]

Have you read THIS thread yet? I think they're available in kit form from Dayton/PE or Meniscus, may be above budget (haven't checked), but their bass would probably please you.

edit: never mind, after finishing your post I see that you have seen the thread. Yeah, they're probably worth scraping together the extra coin.

 

[TLS Guy]

Yes, TL bass is different. It is non resonant and very detailed.

That unit though is a cheap and cheerful design. The woofers are small and inexpensive with an Fs of 52 Hz. So the bass roll off will be about 60 Hz. However bass roll off will be 12 db pre octave rather then 24 for a ported box, so there will be more but still limited deep bass.

 

[Swerd]

I see a lot of DIY MTM speakers are of a transmission line design. My concern is the bass. It seems from some of the reviews and such on TL speakers that the bass is "different". I've never heard any TL speakers before so I don't know what this "different" is.

I guess if I tell you what I want from a speaker you can tell me if a TL is the answer. I like solid, tight, punch in the chest type (double) bass. Not boomy, rattle the license plate frame, rollin' the dubs kinda bass.

The short version of my answer is YES, I think you'll like the sound of TL bass. To my ears, it does all that you describe.

I've been listening to TL speakers for about 10 years now. First the Salk SongTower, and more recently the Salk Veracity ST. The ER18 MTM shares the same cabinet designer (Paul Kittinger) as do all the other Salk MTM tower cabinets. My first reaction to hearing the SongTowers for the first time was that I couldn't believe how potent and clean sounding the bass was. It was not exaggerated, boomy, or muddy sounding at all. Without the exaggerated boominess, there was more bass detail than I'd heard with other speakers. The bass was all there while remaining relaxed sounding – as if the speaker & amp were not straining at all. I've known the bass sound of sealed cabinets (tends toward over-damped, kind of lean & dry sounding) and ported cabinets (tends toward under-damped, more potent, less lean & dry sounding – the opposite of lean & dry is fat & wet, but that makes no sense at all). So I decided the TL sound was something totally different. Basically, I think Paul Kittinger gets the balance between over-damped and under-damped just right for bass, and he could achieve that same balance for TL, sealed, or ported designs.

The ER18 MTM design achieves an F3 frequency of 35 Hz. (F3 is the frequency at which the bass response has rolled off by 3 dB from the sound above that.) For music, that is good. For the bass effects in movies, you'll probably want a sub-woofer as well.

Also, I seem to have a sensitivity to the 1k range so if there is a mid-range adjustment or equalizer involved I usually knock that region down a bit. I guess I like bright, but not "bitey" top end. Basically I would describe what I'm looking for is distortion-free, smooth, yet hard-hitting. So, would I like a TL or do you think I would like your basic ported design.

The TL bass has no effect at 1000 Hz. In the ER18 MTM, that range is entirely due to the ER18 mid woofer. It's frequency response is very smooth across the whole mid-range. It crosses over to the tweeter at about 2200 Hz for the dome tweeter version, and a bit higher, about 2600 Hz for the ribbon version.

BTW, I have a $400-$500 budget. I've been considering the Parts Express TriTrix but I'm leary of the TL design. I could be persuaded to spend a little more on the Murphy/Kittinger ER18s found on this forum if you could convince me that their sound is for me.

The ER18 MTM is definitely in a class level above that of the TriTrix. Maybe two class levels above it. I think it's well worth the extra cash.

By now you have read the write up and realize there are two versions of the ER18 MTM, with different tweeters. One has a ribbon tweeter, and the other has a very good quality dome tweeter. The ribbon version is a bit more expensive. But you can save a bit if you get the dome tweeter version.

Meniscus Audio has done a good job with these. https://meniscusaudio.com/product-category/speaker-kits/page/2/ . They offer a variety of 'bare bones' and 'full kit' versions for both the ribbon and dome tweeter designs.

If you can build doors, you can probably easily build these cabinets. The trick is getting the cabinet edges to fit with the joints all tight and at right angles. I made the cut list with that in mind. I bought 4'×8' MDF sheets at Lowes' and had them cut at the store into 4' long×12" wide strips. Their panel cutting saw made that work easily. From those 12" wide boards, I used a sliding miter/chop saw to cut all the side pieces, tops, bottoms, and braces. Because they were all the same 12" width, I think things fit together more easily.

 

[Ken Hicks]

Thanks for the replies. I'm a little confused however. In the .pdf files that Swerd so graciously linked me to the ER18 MTM is described as a mass-loaded transmission line cabinet. But looking at the plans for the cabinet it discusses port dimensions and location. Am I missing something, or do I not fully understand the differences in bass reflex, ported, and TL?

 

[Swerd]

Thanks for the replies. I'm a little confused however. In the .pdf files that Swerd so graciously linked me to the ER18 MTM is described as a mass-loaded transmission line cabinet. But looking at the plans for the cabinet it discusses port dimensions and location. Am I missing something, or do I not fully understand the differences in bass reflex, ported, and TL?

Thanks to the pioneering work of Martin J. King and George Augspurger, the understanding of what is an acoustic transmission line (TL) has grown and changed in the past 15-20 years. I’m paraphrasing from https://en.wikipedia.org/wiki/Transmission_line_loudspeaker.

King, a physicist and DIY speaker builder, developed a mathematical model of acoustic TL behavior. Based on mechanical principles, his model allowed a designer to accurately predict bass acoustic behavior without the time consuming trial & error in sawdust previously required. At nearly the same time, Augspurger, an audio engineer, developed a TL model starting with electrical principles, and found it to agree closely with King's existing work. Both King and Augspurger agree that their independently derived models confirm each other’s work.

Both models showed that previous TL designs "did a good job of approaching what was possible in their day" but were "generally less than optimal". In addition to the ease of computer-based mathematical modeling, their work revealed new and previously unrealized variations of acoustic TL designs which could be built more easily. See Martin King’s web page http://www.quarter-wave.com/ for much more details.

Because of these developments, there is now a growing understanding that the so-called classical TL speakers, designed largely by trial & error, were generally decent designs, and were the best that was reasonably possible at the time. Thanks to King and Augsperger, better designs are now achievable based on modeled responses.

Among King’s new designs was the mass loaded transmission line (MLTL). It appears to combine both reflex port design and TL design into a hybrid. It works well given the right woofers, and is much easier to construct than classic TL cabinets. There has been much debate (pointless debate in my opinion) about whether the MLTL is a “true” TL.

 

[Ken Hicks]

Let's back up a little. It's obvious from my recent research that there are a lot of really smart people involved in DIY audio/speakers. This includes those that have taken the time to respond to this thread. I, however, do not include myself in the "really smart people" catagory (see avatar at left). I have always wanted to build my own speakers and I know I can pull the wood working aspect off with the tools I currently own but I have a very basic knowledge of electronics. What got the juices recently fired up on the speaker project was that about two years ago my 25 year old HK integrated amp crapped-out and with the combination of just living life and other interests I've been able to live with the audio stop-gaps at my disposal. But I recently purchased an Onkyo A-9010 based on the reviews of a prominent UK audio magazine. This magazine also recommended the Q Acoustics 3050 speakers. I've always been a "sweat equity" kind of guy so I thought "Build your own, dummy." Well, that ER18 is getting up in the price of the Qs so I could just buy the Qs and be done with it (without the hours of sanding the piano black finish would require).

Long story not much shorter, I kind of want to make an in between speaker. Something between the price of the Tritrix and the ER18. I've been futzing around and the Peerless 6.5" driver with nomex cone has piqued my curiosity. I really like the design of an MTM configuration so a couple of the Peerless drivers with a nice soft dome tweeter and Bob's my uncle. The pure TL design of the Tritrix has me leary but I like what I see (which is funny since we are working in the auditory realm) with the cabinet design of the ER18s. I realize that the ER18 cabinet and x-over are optimized for the drivers utilized but do you think (with the help of a gracious online community) I could achieve the sub-$400 results I'm looking for with an ER18 style box and the Peerless drivers?

 

[Swerd]

… I kind of want to make an in between speaker. Something between the price of the Tritrix and the ER18. I've been futzing around and the Peerless 6.5" driver with nomex cone has piqued my curiosity. I really like the design of an MTM configuration so a couple of the Peerless drivers with a nice soft dome tweeter and Bob's my uncle.

I realize that the ER18 cabinet and x-over are optimized for the drivers utilized but do you think (with the help of a gracious online community) I could achieve the sub-$400 results I'm looking for with an ER18 style box and the Peerless drivers?

You said it yourself, "the ER18 cabinet and x-over are optimized for the drivers utilized". If you substitute drivers, you have to start all over with both the cabinet design and the crossover. It requires having the drivers and a test cabinet in the hands of someone with the right type test rig and software, as well as the knowledge and experience to use it well. No online help can substitute for that. That's why so many DIY builders, like myself, are satisfied to build a tried & tested design from someone else who knows what they're doing.

There are many other assemble-it-yourself designs available at Meniscus Audio, Madisound, and Parts Express. What can you find in your price range?

Do you really want a glossy black finish? A glossy paint finish over wood is probably the most difficult type of finish to do well. It telegraphs the slightest imperfections that are underneath it. I once tried it, thinking paint would be easier than veneer. I'LL NEVER DO THAT AGAIN . Seriously, people have gotten much better results by taking their unfinished speaker cabinets to an auto body shop. Some, not all, body shops can do this at surprisingly reasonable prices. Something to think about.

… The pure TL design of the Tritrix has me leary but I like what I see (which is funny since we are working in the auditory realm) with the cabinet design of the ER18s.

I don't understand what makes you leary about the Tritrix cabinet design. From what I read (somewhere, but don't remember where) the Tritrix cabinet was designed using Martin King's software, and so was the ER18 cabinet. They are clearly different designs, but I'd trust them both to achieve what they promise in bass performance.

 

[Ken Hicks]

Wise words, thanks. I guess I'll do some more research and see if I can find a kit that's to my liking in that in between land. I'll keep you posted.

 

[Ken Hicks]

Hey Swerd,
I just read your JBL West Coast Sound post and it prompted the following. Please indulge me. Having a (wannabe) audiophile step-father as a teenager in the 70s sparked my love of Hi-fi. Most Marines don't have Okinawa Japan on their Duty-station wish list but I did. I couldn't wait to get to Japan to get me a killer stereo. I started out with a Yamaha C4 preamp and M2 power amp. Sources were a Denon DP60L turntable and a Nakamichi 680ZX tape deck. My speakers were JBL L-150As. I didn't like the sound of the M2 so I sold it and got a Yamaha B6 (remember that one, the truncated pyramid). I decided that I didn't like the B6 much either so I set my sights on the Onkyo M5090. A funny aside - the M5090 cost $1800 (in Japan) in 1982. It took me awhile to save that up and on the payday that gave me enough cash I jumped into a taxi to the stereo store and there was a sign on the door "Closed for Inventory". I could see people inside so I knocked on a the door and a little Japanese dude shook his head no at me. I pulled $1800 cash out of my pocket and fanned it out and pressed it against the glass door. He pulled out his keys and let me make the purchase. Money talks in every language.

Back to the original story. I really liked the sound of the Onkyo but something still wasn't quite right. Then I heard some JBL L-112s. I sold the L-150As to a Japanese friend and bought some L-112s and now life was complete. Sadly, that system went up in smoke so to speak. I know going from 250wpc to 40 is asking a lot but if I could make some speakers that hit like those L-112s I'd be pretty stoked.

Btw, I'm right there with you on the "outspoken audiophiles" thing. All that matters is if it sound good to its owner than it's all good.