Hello, so I am starting a design adventure where I'm going to try my woodworking and design skills with the hopes of designing a Transmission line 2 way designed to cover 60 Hz - 20 kHz in the style of PMC audio. I've built several speakers and several of those are transmission subwoofers but this is the first time I've called upon a transmission line to reproduce midrange. I want to post my thoughts here as I would like to know if hornresponse should adequately simulate what I'm trying to do. I'm specifically concerned with the 100-1000 range as that is where most resonances seem to lie. Here is a summary of what I'm looking for:
High fidelity (aka smooth), high output (enough to pair with a T60, Bill Fitzmaurice) 65-2000 Hz from the woofer, crossed most likely to Dayton Audio RS28F-4 1-1/8" Silk Dome Tweeter or similar
I was thinking of using FaitalPRO 5FE120 5" Professional Midbass Midrange Woofer 8 Ohm
Or Dayton Audio RS125-8 5" Reference Woofer
In single or multiples per side.
These appear to have high bang/buck and the size helps reduce the need for huge boxes. I'm willing to go as high as 500 in driver cost to make these speakers awesome (both speakers combined).
I know I'm going to need a combination of materials to properly damp the transmission line so if someone could link me to some materials (beyond fiberfill and similar, i have that) that could improve speaker response.
I've had trouble locating Mr. King's software for simulating transmission lines due to old links and currently am designing it in Hornresp using the filling capabilities in the Loudspeaker Wizard.
I'm specifically looking for a way to simulate the use of stuffing to smooth out the midbass/midrange as above 1k or so the driver cone itself determines the response more than the T-line.
Let me know if I'm on the right track, nuts, or have any comments/suggestions!
Thanks in advance.
High fidelity (aka smooth), high output (enough to pair with a T60, Bill Fitzmaurice) 65-2000 Hz from the woofer, crossed most likely to Dayton Audio RS28F-4 1-1/8" Silk Dome Tweeter or similar
I was thinking of using FaitalPRO 5FE120 5" Professional Midbass Midrange Woofer 8 Ohm
Or Dayton Audio RS125-8 5" Reference Woofer
In single or multiples per side.
These appear to have high bang/buck and the size helps reduce the need for huge boxes. I'm willing to go as high as 500 in driver cost to make these speakers awesome (both speakers combined).
I know I'm going to need a combination of materials to properly damp the transmission line so if someone could link me to some materials (beyond fiberfill and similar, i have that) that could improve speaker response.
I've had trouble locating Mr. King's software for simulating transmission lines due to old links and currently am designing it in Hornresp using the filling capabilities in the Loudspeaker Wizard.
I'm specifically looking for a way to simulate the use of stuffing to smooth out the midbass/midrange as above 1k or so the driver cone itself determines the response more than the T-line.
Let me know if I'm on the right track, nuts, or have any comments/suggestions!
Thanks in advance.
One more thing, I was also considering using a much larger pro woofer such as
Eminence Kappalite 3012HO Neo 12" Speaker Driver
and making a pseudo monitor, still transmission line, with about 115-120 dB of output (I would have to use a different tweeter obviously to keep up). I will have a DSP to aggressively cross whatever option I decide to go with and help smooth response peaks.
Can I achieve high fidelity with such a driver?
Eminence Kappalite 3012HO Neo 12" Speaker Driver
and making a pseudo monitor, still transmission line, with about 115-120 dB of output (I would have to use a different tweeter obviously to keep up). I will have a DSP to aggressively cross whatever option I decide to go with and help smooth response peaks.
Can I achieve high fidelity with such a driver?
Perhaps it is time to do some homework. You know what I am talking about.....
Transmission Line Theory
Learn how to fish, then you will eat for a lifetime.
Transmission Line Theory
Learn how to fish, then you will eat for a lifetime.
I just started getting serious about learning about what Martin King is teaching us from his works, and I tried modeling an Eminence Deltalite 12 in a simplified program that MJK has on his site. I was doing it just for the experience, and depending on how you wish your taper to go, I came out with a 92 inch length with the Deltalite. I have not got to the point of really contemplating a real build yet, but I think I will start with a smaller driver to keep the build a bit more reasonable for a first time try-- and probably a bit of a fiasco.
MJK software is no longer available but i understand that this is in the same league
http://www.diyaudio.com/forums/software-tools/220421-transmission-line-modelling-software.html
dave
http://www.diyaudio.com/forums/software-tools/220421-transmission-line-modelling-software.html
dave
If by hornresponse you mean Hornresp, and you want to simulate a damped tapered transmission line loudspeaker, then I can't see why not.
This sounds like fun. I have actually been working on my own TL monitor in a PMC like format. Should be very doable and one more thing to consider is use of dual smaller drivers so a MTM TL might be in order. But if you are willing to consider a 12in driver the design space is wide open. Are you leaning to max SPL and high sensitivity or compact footprint? Is design f3 only 60Hz? I think you can go deeper if considering larger drivers. We can handle the resonant mid bass peaks with 1/4-wave stubs so I am not worried. Just need a little more constraints and Akabak should be able to help fine tune a design.
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Some initial thoughts for drivers. The 5FE120 is an interesting choice and has a few great things going for it: good sensitivity, great 5mm xmax, a high Qms, moderate Qts to allow ML below fs, a small Vas for a compact box, fairly smooth midrange. One concern is the little dip in response around 250Hz. If this driver is doubled up in parallel, the sensitivity is 94dB, then take -5dB off for baffle step loss and we are at 89dB sensitivity for bass at 60Hz - this is a good match to an 88dB to 91dB sensitive tweeter. I am thinking of the Tymphany NE25VTS-04 1in silk dome Nd magnet tweeter. Partly because the response looks smooth and can probably cross at 2.5kHz just fine. I like Tymphany, Vifa, ScanSpeak tweeters also because full TS parameters are available for a simulation. These are my initial candidates going in. Now onto the TL design - probably a tapered one getting smaller at exit vent to provide mass loading to pull fb lower and keep compact.
Trigger warning: don't read any further if you can't stand a rant on transmission lines!
OK, here's the truth: TMLs are crap. Especially small ones.
Why? Because they resonate. Then a vented speaker is crap, too, you say? No, because a vented speaker only resonates on its tuning frequency (except you did something really stupid*), but a TML resonates on 1/4, 3/4, 5/4, and so on. What to do about it? Nothing! Well, not really, you can stuff the cabinet with absorbing foam/wool/sheets, whatever. And when you then measure again in the nearfield of the TML, you realize that you have just built a closed cabinet. Congratulations!
So you don't want a closed box? Then you will suffer from so many of these resonances, right in the speech and music frequency band, you must be deaf not to hear them. Compare the speaker to a well made closed cabinet then you'll know the difference.
Proof: look at the measurements of the small PMC bookshelves (can't provide scan for you due to copyright reasons, haven't found a link yet). Resonances whereever you like, a lot in one of the most important frequency bands.
What to do instead? Build a closed box. It's the best choice. Want more bass? Use bass reflex. It's a compromise for 2-ways, because it may also resonate like a TML when it is too long (then place the port on the back on the cabinet), or you will have snuffing noises.
*A transmission line IS a stupid bass reflex
Edit: the Faital driver is really great value for money! But don't use the 5FE100, it misses the demodulation ring.
OK, here's the truth: TMLs are crap. Especially small ones.
Why? Because they resonate. Then a vented speaker is crap, too, you say? No, because a vented speaker only resonates on its tuning frequency (except you did something really stupid*), but a TML resonates on 1/4, 3/4, 5/4, and so on. What to do about it? Nothing! Well, not really, you can stuff the cabinet with absorbing foam/wool/sheets, whatever. And when you then measure again in the nearfield of the TML, you realize that you have just built a closed cabinet. Congratulations!
So you don't want a closed box? Then you will suffer from so many of these resonances, right in the speech and music frequency band, you must be deaf not to hear them. Compare the speaker to a well made closed cabinet then you'll know the difference.
Proof: look at the measurements of the small PMC bookshelves (can't provide scan for you due to copyright reasons, haven't found a link yet). Resonances whereever you like, a lot in one of the most important frequency bands.
What to do instead? Build a closed box. It's the best choice. Want more bass? Use bass reflex. It's a compromise for 2-ways, because it may also resonate like a TML when it is too long (then place the port on the back on the cabinet), or you will have snuffing noises.
*A transmission line IS a stupid bass reflex
Edit: the Faital driver is really great value for money! But don't use the 5FE100, it misses the demodulation ring.
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BB:
Rant is ok - good points about resonances - but some TL's like mass loaded TQWT's and straight MLTL, do manage to get quite a smooth response. It won't be flat like a sealed box (which I really like as well if you look at my 10F/RS225 Ref Monitor thread. http://www.diyaudio.com/forums/full-range/273524-10f-8424-rs225-8-fast-ref-monitor.html). However, TL's have a distinct sound character. It won't be ruler flat but does squeeze more bass efficiency out of a driver vs a sealed box. I like them as they are a good design challenge and give you a good puzzle to solve.
Rant is ok - good points about resonances - but some TL's like mass loaded TQWT's and straight MLTL, do manage to get quite a smooth response. It won't be flat like a sealed box (which I really like as well if you look at my 10F/RS225 Ref Monitor thread. http://www.diyaudio.com/forums/full-range/273524-10f-8424-rs225-8-fast-ref-monitor.html). However, TL's have a distinct sound character. It won't be ruler flat but does squeeze more bass efficiency out of a driver vs a sealed box. I like them as they are a good design challenge and give you a good puzzle to solve.
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Using Martin King's software, I've designed and built many ML-TLs and tapered TLs for personal use and have modeled at least 50 TL designs for others around the world. To say they can't/don't work because of resonances at odd harmonics of their 1/4-wave resonance is just plain hogwash. If the TL is designed properly, meaning you've got to know what you're doing, and is built exactly according to the design, it will perform and sound very, very good and it won't end up just being a "sealed box". And, a 2-way TL is just as viable, having the advantage of the line's design mitigating reflections back through the cone of the midwoofer.
Paul
Paul
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I appreciate the feedback, although maybe my ears aren't very great, as the PMC monitors I've heard were some of the cleanest I've ever heard, without any hints of resonant peaks.
Perhaps it is time to do some homework. You know what I am talking about.....
Transmission Line Theory
Learn how to fish, then you will eat for a lifetime.
I've done some reading and will continue. Yesterday was baffle step learning day
.That is correct, I was referring to your software!
Thanks again for designing it.
Good to know that at least to start I can trust what I'm seeing, it appears quite tricky to remove/reduce all of the early peaks/dips even with varying stuffing. I look forward to the challenge.
I picked f3 of 60 Hz for an arbitrarily solid transition point. Mainly because all my other speakers cross at 80-120 Hz and the room acoustics of small rooms make it hard to effectively get flat bass and especially upper bass in any given listening position. I'm looking for something with enough 60 Hz to smoothly transition and handle power without fatigue, below that -> PA subwoofer. I figure that making the enclosure work with 40 Hz tuning would just be a waste of potential output. I also hope to learn Akabak with this experience as I feel it is the best suited to simulate the system in combination with Hornresp as a starter.
I'm leaning towards the dual 5 inch version because it allows for a really slick baffle and half the fun is making a really nice finish (once the acoustics have been tested out).
First Simulation
Here is a preliminary ballpark using Leonard's software: 1 cubic foot internal, tapered, .3 lb/cu ft stuffing. If the ripple looks this solid we're in business but something tells me it's smoothing out more than in real life. Simulation is done using a single driver because I don't know if it can handle multiple.
Here is a preliminary ballpark using Leonard's software: 1 cubic foot internal, tapered, .3 lb/cu ft stuffing. If the ripple looks this solid we're in business but something tells me it's smoothing out more than in real life. Simulation is done using a single driver because I don't know if it can handle multiple.
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