Transmission Line Riser Sub?

[Lindahl]

Thinking about that Danley that reaches 126db at 20hz with only a 12" in a transmission line-style box. I'm thinking I could take one of the many crowd-pleasing 15" or 18" drivers we all use, here, and throw it into my riser and snake a transmission line through it to get something pretty damn comparable. I'd want to model it using King's MathCAD worksheets, first, of course. Let's say I use a Ficaraudio Q18. 1210" sd, which means a cross-sectional area for the line of around 375 sq in. So, let's say a cross-sectional area of 2.75'x1' underneath the riser. I can't see the tuning being less than 15hz (could it be less?), giving a 1/4 wavelength of just under 20'. Given a riser 14'x6', this should be no problem. Using the Harman papers to guesstimate positioning for a normal listening room, you could place the upfiring driver in the rear-center, offset to the left, snake the line to the front, across to the right, and exiting out the rear, offset to the rear-center, offset to the right, like so:

--+ +--
|_____|

Does the Danley do something special, aside from a transmission line, to reach it's output with only a 12"? Granted, they call it a horn, but a transmission line gives you very similar properties that a horn does, right? Maybe less output, but using a good 18" driver, should more than make up for that?

Any thoughts?

[cjd]

Horn and transmission lines are not "very similar" particularly - a TL is more similar in some respects to a basic bandpass alignment.

I ran the numbers back before I installed my IB to see whether there were value in going TL - the difference is simple: you get a bit more SPL out of any given driver before it can't keep up, and it takes more power to do so.

You are making a LOT of assumptions when you say that a 14x6 riser "should be no problem" (how tall is that riser?) - I found a 5:2Sd taper with driver placed about a quarter way down to be the best response. That's pretty darned big. I have no idea where you get the number for the line cross-sectional area of 375 - on what do you base this number?

C

[Xmax BR]

Dears,

I love TL too, my last and fabulous project is this:

http://www.htguide.com/forum/showthread.php4?t=23522

To me, nothing is better for bass. This is my litle "Sublimes"

http://www.mrweb.com.br/fvm/sublimes/

and this, my old TOR

http://www.mrweb.com.br/fvm/tl2/

Tks,

Renato

[Lindahl]

Horn and transmission lines are not "very similar" particularly - a TL is more similar in some respects to a basic bandpass alignment.

Fair enough. I'll begin reading more about tapped horns. My preliminary reading lead me to believe there isn't much difference, see here. I'm sure someone out there is working on building their own, or at least working on HOW to build their own.

That's pretty darned big. I have no idea where you get the number for the line cross-sectional area of 375 - on what do you base this number?

Sorry, I'm getting 375 based on 2xSd of the Q18, based on an email with Dave of T-linespeakers(.org), saying that 2-4xSd is a good starting point.

[cjd]

Ok, that makes sense. Are you doing a straight line or a tapered line? You can get bigger or smaller - certainly, a "getting bigger" line shares a lot with a horn, and the "get smaller" is closer to bandpass. The math is not necessarily that far apart, but it's always hazy territory when you try to say "this is like that" - they're identified separately for a reason.

I'm assuming internal height of your riser is 1'? Which 18 are you looking at? You may not have enough volume...

[Xmax BR]

Dears,

http://www.diyaudio.com/forums/showthread.php?s=&threadid=79102

Tks,

Renato

[Lindahl]

http://www.diyaudio.com/forums/showt...threadid=79102

Perfect, thanks Renato! It looks like he's aligning the phases of the rear radiation and the direct radiation by manipulating the phases of both. Clever. Looks like a bit of experimentation will get me there. Create a square mounting board for the driver, and bolt it with a gasket to various divider sections until I find the optimum placement.

I'm assuming internal height of your riser is 1'? Which 18 are you looking at? You may not have enough volume...

Yes. It's not built yet, so I can adjust the height to whatever is needed (within reason, obviously). I was looking at the Ficaraudio Q18. Seems to be one of the best values out there.

[cjd]

Ahh, interesting.

I'm not sure how this would work in a riser with an up-firing 18" driver, given the requirements. It may also be one of those designs that demans the long-narrow shape to work.

C

[Lindahl]

I'm not sure how this would work in a riser with an up-firing 18" driver, given the requirements. It may also be one of those designs that demans the long-narrow shape to work.

Right, the driver certainly can't be upfiring if I go the tapped horn route. Given the size, I may have to go with a 15" driver. Though, the back row seating could be a sufficiently large couch that has a hollow-enough underbelly to allow a "bump-out" for a large driver - I think with the size of Sd x2? No matter what, I'd definitely have to rethink my riser dimensions. :B

I had been thinking about creating a floating floor. If I had a 6" floating floor, I could still keep my riser height around 16", which would allow 22" of space - probably sufficient enough for the tapped horn design for the Q18, and if not, the Q15.

This is another interesting diagram by qi that seems to show the idea behind a tapped horn a little better. It appears to essentially be double-driver transmission line, without the direct radiation into the room. Maybe Danley's design should really be called a tapped transmission line? I'm not seeing much relation to a real horn...

Note that with these designs, from what I've just read, if you tune low, you need to crossover to the subwoofer low as well. Several mentions of tuning of 15hz and crossing over at 40hz. This is to avoid the rough response in the upper frequencies, shown in Danley's white paper on tapped horns. This will be perfect for my application, since I had planned to have a seperate subwoofer in the front that would cover the upper frequencies (40hz-80hz) to allow better integration with the mains.

[cjd]

Well, the thing is, once you start looking at making huge huge boxes, it is worth considering a simple sealed system... if you can hit that 10x VAS number in volume you're close enough to call it "IB" - at worst a little low end boost might be needed but often little to none is required to be flat below 20Hz in-room.

C

[Lindahl]

Well, the thing is, once you start looking at making huge huge boxes, it is worth considering a simple sealed system... if you can hit that 10x VAS number in volume you're close enough to call it "IB" - at worst a little low end boost might be needed but often little to none is required to be flat below 20Hz in-room.

Need more drivers don't you? I'm doing this on the cheap, and since it's going in my riser, construction is essentially free. I'd probably plan on tuning the tapped horn to 10hz to 15hz. I don't think an IB could come near that sort of output with a single driver, but feel free to correct me.

Actually, the 15" TC-2000 looks like it might be a better candidate. It has a lower Fs, which, from reading, appears to be one of the most important characteristics when doing a low tune around 10hz-15hz - not sure, though. Then again, Ficaraudio offers custom drivers on the cheap...

[cjd]

Well, you need more drivers and less amp. It's a trade-off. I'm using a pair of 15" Dayton IB subs and a 240W amp, each picked up when they were on sale for $100 (so ~$300 total). The 15" TC-2000 does seem a better fit, though it may not have the excursion which is the other side of what you need for a low tune. You also will need to look at driver Q.

C

[Lindahl]

Well, you need more drivers and less amp. It's a trade-off. I'm using a pair of 15" Dayton IB subs and a 240W amp, each picked up when they were on sale for $100 (so ~$300 total). The 15" TC-2000 does seem a better fit, though it may not have the excursion which is the other side of what you need for a low tune. You also will need to look at driver Q.

For an IB in my space, the vas would be too high to go above 2 drivers, so I can't look at the cheaper drivers. With the drivers I'm looking at, it's cheaper to go with one driver in the tapped horn alignment and an EP2500 - I'm looking to get a ton of output, hopefully reference peaks at 10hz (probably can only do that at 15hz, though). And, I meant the TC-2000 being a good fit for a tapped horn sub. From what I've read, you shouldn't tune those below the Fs.

[Dennis H]

I'm looking to get a ton of output, hopefully reference peaks at 10hz (probably can only do that at 15hz, though).

You won't get that out of a TL or a horn with a single driver. Big sealed enclosures (IB) with lots of drivers are the hot ticket. Skip lunch a few days and buy more drivers. Look for sales. If you can build a box that's 4x Vas, that gets you pretty close to a 'real' IB so you can cram lots of drivers into the volume you have to work with.

[Dennis H]

Thinking about that Danley that reaches 126db at 20hz with only a 12" in a transmission line-style box.

He does that by placing the subs in a corner; it's part of the design. That gives any sub a theoretical boost of 18dB vs. free space. Of course room effects are much more complex than that but it's not fair to compare a corner loaded horn to a simulation of some other sub in free space.

[Lindahl]

You won't get that out of a TL or a horn with a single driver. Big sealed enclosures (IB) with lots of drivers are the hot ticket.
...
He does that by placing the subs in a corner; it's part of the design. That gives any sub a theoretical boost of 18dB vs. free space.

I'm not trying to be combative, but you seem to be contradicting yourself. Danley can reach 126db peaks in-room with a 12" driver, where the -3db point is 17hz. Yet I can't reach ~115db peaks in-room with a Q15/Q18 in the same alignment, where the -3db point is at least 15hz? I'm doing the math and that just doesn't make sense.

For a reference point, Steve over at AVS (swithey) had this to say about his 2 15" Soundsplinters in an IB alignment.

The sound level was hovering around 92-95db and peeked during a few scenes around 112db Freek’n unbelievable. The woofers did not sound strained or distorted at all – very clean the entire time.

Considering that a tapped horn effectively doubles your displacement by turning one driver into two at the tuning frequency, then I should be getting something pretty comparable (the Q15/Q18 has more displacement than the RPL15). He got pretty darn close to my goal - and he wasn't even reaching the limits of his output.

Maybe I'm missing something, though...

[Dennis H]

Maybe I'm missing something, though...

Yes. Lies, damn lies, and woofer specs. Compare apples to apples, i.e. same (corner) loading situatiions.

[Lindahl]

Yes. Lies, damn lies, and woofer specs. Compare apples to apples, i.e. same (corner) loading situatiions.

Do you have anything to back up such accusations? Perhaps measurements, experience or simulations? Also, what about Steve's experiences and measurements?

[cjd]

Lindahl, I am pretty sure Dennis has experience at the least. 92-95dB is a LONG way from 126dB. So is 112dB. But 112 puts that past where the single 12 might be in a similar configuration IF it didn't kill itself first.

[Lindahl]

Lindahl, I am pretty sure Dennis has experience at the least.

Well, I meant experience with the product (DTS20). From my brief stint here, I do know he has a lot of experience in audio.

92-95dB is a LONG way from 126dB. So is 112dB.

I'm not looking for 126db, just reference peaks to 15hz, which is 115db. Steve's 15s were cruising and hitting 112db peaks - normal output was around 92-95db. Who knows what they could have hit, had he pushed them.

But 112 puts that past where the single 12 might be in a similar configuration IF it didn't kill itself first.

How can you be so sure? This is a rather new configuration that not many have experience with. I'm just hearing "no way" without much else to back it up. I agree it sounds a little unbelievable, but still, you can't just say "no" without saying why...

[Dennis H]

Considering that a tapped horn effectively doubles your displacement by turning one driver into two at the tuning frequency

Right. 1 ported/horn/TL driver = 2 sealed/IB drivers. So that means a ported/horn/TL is about 6dB louder than the same driver in a sealed box placed the same way in the room, i.e. corner loaded in the case of the horn. If you want the most SPL for the number of drivers go ported/horn/TL. If you want the most SPL for a given box size, go sealed with multiple drivers. Regarding various measured SPL levels from different people, they're pretty irrelevant -- different rooms, different placement in the room, different measuring methods, etc.

[cjd]

I don't think anyone is saying "no way" - it's probably the combined skepticism that goes with ANY numbers published by manufacturers, and experience.

I can make a claim that my sub hits 120dB at 22Hz and it would be accurate.

I don't have to tell you it's a room node and that the average is about 110dB (pair of Dayton 15" IB subs with 240W behind them - the whole setup cost me $300). It does roll off and I probably only hit about 100dB at 15Hz, not sure. These drivers are only passable in this use and I have no EQ on them at all (which could dial in a little boost or cut above or whatever, to get it flatter).

C