Transmission line sub... ?

[GranteedEV]

Since I bought this driver I've been fairly broke combined with schoolwork taking up most of my free time so buying supplies and building has really been reduced into "planning, waiting, and debating". I've got a driver and proamp in place, but that's about it... high pass filters, cabinet materials, phase control, EQ, etc aren't things I've got yet. I was fairly set on the common low tuned extended bass reflex sonotube build until today, where the idea of building a transmission line for it piqued my interest. From my understanding though, a transmission line to match the driver's respective free air resonance would be "rather large", but I guess I'm not really comprehending just how long or wide we're talking about. So I figured I'd post here and

1) Find out if my driver seems suitable for a transmission line
2) What does the frequency response look like on one of these? One thing I read somewhere is that there would be a natural LPF around 75hz which ..well.. makes me wonder.. since my bookshelf surrounds want to be crossed over at 80hz... would I have a poor blend between my speakers?
3) Is it worth the effort of doing all the research and is it difficult to build?

I don't really know what I'm looking for in a sub. I realize there's no such thing as a perfect sub... some subs trade extension for output, others trade output for control and accuracy, and others seem to be a jack of all trades, master of none. I don't know what's important to me in a sub, but I guess I just want something that'll impress me with music and home theater... that's probably why I went with this driver in the first place because it seemed like good bang-for-buck. unfortunately this driver seemed to be modeling relatively well in different types of designs so it didn't make choosing any easier.

The only thing I've definitely decided is that I probably don't want to horn load or infinite baffle. Otherwise I think the speaker itself will be capable of sufficient raw output with any enclosure, so I just want to find the right balance between SQ, frequency extension, and box size. When I say box size, I guess some general max dimensions would be something like 28 x 28 x 76

I've been looking at a website called quarter-wave.com and it seems rather useful, but it seems like a lot of reading and that would only be worth it if this design is plausible(IT size, material, driver suitability, and low frequency extension) and reasonable.

 

[johngalt47]

I don't see why it wouldn't be. The only thing to consider in my opinion is the size of the box and whether or not you want a traditional line or a TQWT.

Take a look at the spreadsheet TL designer on quarter-wave.com. It was built by a guy named Keith or Kevin (or some other name starting with a K).

I'll see if I can work something up using Martin's MathCad worksheet but I'm not promising anything...

 

[johngalt47]

Wow! This driver is a beast!

Using the mass loaded "transmission line" mathcad worksheet, this driver will work as far as I can tell.

The cabinet length can be 60" while the area (width x depth) needs to be around 3 Sd (about 550 sq. inches).

Put a 6" diameter by 12 inch long port to start but you can play around with the length.

Just my 2 cents.

 

[TLS Guy]

Since I bought this driver I've been fairly broke combined with schoolwork taking up most of my free time so buying supplies and building has really been reduced into "planning, waiting, and debating". I've got a driver and proamp in place, but that's about it... high pass filters, cabinet materials, phase control, EQ, etc aren't things I've got yet. I was fairly set on the common low tuned extended bass reflex sonotube build until today, where the idea of building a transmission line for it piqued my interest. From my understanding though, a transmission line to match the driver's respective free air resonance would be "rather large", but I guess I'm not really comprehending just how long or wide we're talking about. So I figured I'd post here and

1) Find out if my driver seems suitable for a transmission line
2) What does the frequency response look like on one of these? One thing I read somewhere is that there would be a natural LPF around 75hz which ..well.. makes me wonder.. since my bookshelf surrounds want to be crossed over at 80hz... would I have a poor blend between my speakers?
3) Is it worth the effort of doing all the research and is it difficult to build?

I don't really know what I'm looking for in a sub. I realize there's no such thing as a perfect sub... some subs trade extension for output, others trade output for control and accuracy, and others seem to be a jack of all trades, master of none. I don't know what's important to me in a sub, but I guess I just want something that'll impress me with music and home theater... that's probably why I went with this driver in the first place because it seemed like good bang-for-buck. unfortunately this driver seemed to be modeling relatively well in different types of designs so it didn't make choosing any easier.

The only thing I've definitely decided is that I probably don't want to horn load or infinite baffle. Otherwise I think the speaker itself will be capable of sufficient raw output with any enclosure, so I just want to find the right balance between SQ, frequency extension, and box size. When I say box size, I guess some general max dimensions would be something like 28 x 28 x 76

I've been looking at a website called quarter-wave.com and it seems rather useful, but it seems like a lot of reading and that would only be worth it if this design is plausible(IT size, material, driver suitability, and low frequency extension) and reasonable.

That driver with the coils in series or parallel should have just about ideal number for a TL. I personally think the reverse tapered aperiodically damped line is best. Damp until there is just one peak of impedance.

It will take a lot of real estate, and yes it will be worth it. You will have deep smooth non resonant bass with support of the for the over 1.5 octaves.

The build is more difficult then for a ported box, but not by much as long as you can recruit help. Due to the length of the line you will need some assistance.

I'm behind on fall work, as I was unwell last week and just recovering again. May be I can look at it this weekend. Once you get the sub built you need to make the rest of the system TL.

I think the only commercial TL subs available are from PMC. Their largest pro TL I believe has an F3 of 15 Hz. They make the lines I suggest.

TQWT roll off 24 db per octave like most ported systems. The line I would suggest rolls off at 12 db per octave and so has a lot more deep bass.

Qt will end up around 0.5 so bass will no ooze all over everything, but that will make the effect all the greater when the bass is really there.

It is really hard to explain sound in words. Unfortunately very few have heard aperiodically damped TL systems. In Europe PMC are changing that. They are giving B & W a real run for their money and overtaking them in the studio monitor market. The BBC are switching to their designs pretty much exclusively. Their pro speakers are powered by Bryston and are active designs. They have formed a close partnership with Bryston.

They have also made an alliance with ATC and further improved their mid range driver. ATC had the best midrange driver around in any case.

 

[GranteedEV]

This sounds so exciting . Anyways I'm in no rush, I just last friday got paid enough to pay off the credit card bill for the tapco amp. I want to buy all the materials with debit or cash and avoid credit so it'll take me a few weeks; i'm on a 2-days a week part time liquor store job after all!

That 12db rolloff was one of the main reasons that the design interested me in the first place. However, rolloff aside, the main question I want to ask is how does a TL relate with excursion? The advantage of the shallower rolloff would seem less pronounced if I need to throw in a high pass filter

 

[johngalt47]

What is aperiodically damping?

 

[TLS Guy]

What is aperiodically damping?

It is nothing highly technical. A cycle in an resonant system is often referred to as a period of vibration. The term aperiodic just means to damp a vibration, in the case of a TL, what you are damping is an oscillating column of air.

 

[GranteedEV]

Okay, so let me just clarify a few things before I buy the martin j king worksheets:

1) I need a half wavelength closed line. What am I tuning it relative to?
2) I need it to be reverse tapered. What's the difference between an ordinary taper and a reverse taper? How does this usually relate to the driver
3) I need the driver placed about 3/4 or so of the way in or something along lines?
4) Aperiodically damping is to reduce resonance. When we talk about impedance peaks, will I need something to measure this or
5) Will it make a big difference in the final outcome if I use the supplied T/S parameters instead of measuring them myself? I don't want to mess up and end up with resonances is all but I also don`t want to measure them with less accurate devices and get a worse number. What do you recommend I pick up to do this, and test the box in general. Since it`s going to be rather large, I`m not sure I`ll be able to do much in terms of open area testing outdoors...
6) I`m leaning towards using baltic birch, especially if it ends up as large and heavy as I`m thinking. But on that note, does anyone know about this EFS stuff that elemental designs uses? If it's cheaper than 13Ply BB than I'd consider using it.

 

[TLS Guy]

Okay, so let me just clarify a few things before I buy the martin j king worksheets:

1) I need a half wavelength closed line. What am I tuning it relative to?
2) I need it to be reverse tapered. What's the difference between an ordinary taper and a reverse taper? How does this usually relate to the driver
3) I need the driver placed about 3/4 or so of the way in or something along lines?
4) Aperiodically damping is to reduce resonance. When we talk about impedance peaks, will I need something to measure this or
5) Will it make a big difference in the final outcome if I use the supplied T/S parameters instead of measuring them myself? I don't want to mess up and end up with resonances is all but I also don`t want to measure them with less accurate devices and get a worse number. What do you recommend I pick up to do this, and test the box in general. Since it`s going to be rather large, I`m not sure I`ll be able to do much in terms of open area testing outdoors...
6) I`m leaning towards using baltic birch, especially if it ends up as large and heavy as I`m thinking. But on that note, does anyone know about this EFS stuff that elemental designs uses? If it's cheaper than 13Ply BB than I'd consider using it.

You need this woofer tester and this software.

I use MDF, because the boards are long and plywood is generally too warped.

I have not had time to look at your driver. We have winter fast coming on, and I have had health problems lately, but I'm finally recovering. That has slowed up the fall work. I should have everything serviced by the end of this week. The boats and everything else winterized and under cover by Friday night. So next week looks more promising to get to your project. In the meantime please take a look at these pictures.

The reverse taper by the way gives the smoothest response.

It is a cold night and I'm typing this message by a log fire for the first time this season.