The Speedster Towers--A MLTL version True to the Originals

[Jim Griffin]

[joeybutts]

Re: The Speedster Towers--A MLTL version True to the Originals

This looks VERY enticing.

[thekorvers]

Re: The Speedster Towers--A MLTL version True to the Originals

Thanks Jim, this looks very interesting. Unfortunately I missed the sale on the TB's some time ago. I believe that they were $30 at one point (DOD?), a real bargain. I hope they go on sale again.

[Jim Griffin]

Re: The Speedster Towers--A MLTL version True to the Originals

I purchased my W4-1720s last summer at the MWAF for the normal 20% off (or about $40 each) on the Saturday tent sale. Makes visiting P-E worthwhile.

[Paul Carmody]

Re: The Speedster Towers--A MLTL version True to the Originals

This is cool. Thank you for the writeup Jim. An F3 of 35 Hz from little bookshelf speakers like the Speedsters is crazy!

[NickJ]

Re: The Speedster Towers--A MLTL version True to the Originals

This seems like a cool project. I admit that when it comes to transmission lines I am a little out of my depth, so if no-one minds I will use this opportunity to ask some questions.

1st. Paul recently released his MMt version of this speaker. I like the additional efficiency of that speaker, but imagine that the MLTL would need to be reworked. Is this true? Is it because one of the drivers would be relatively lower in the box? Is it dependent on the additional displacement? I can't think of a mathematical/physics reason why the second would be true…but as I said I am out of my depth a little here.

2nd. Box construction. I noticed you used .75 thick sides and ended up with a box slightly wider than the original. Additional thickness of material is not as useful in reducing vibrations as say, a ton of braces. How do braces work with a transmission line? Do they create detrimental in-box turbulence? Also in conventional boxes the vibrations are caused by the driver. In a TL design is there vibration that comes directly from the transmission line air movement? mdf is already pretty smooth, but could it be finished or treated in some way to reduce these ancillary vibrations (if they even exist in the first place)?

[Jim Griffin]

Re: The Speedster Towers--A MLTL version True to the Originals

Nick,

The Carmody MMT (MLTL box designed by Paul Kittinger) is twice the cross-sectional area of my box. That MMT and my design will be the same sensitivity over the majority of the frequency band but the MMT can supply 3 dB more output in the limit over the region of the frequency where both M's are working. Normally, MMT designs don't increase the sensitivity of the speaker as the sensitivity increase isn't over the entire mid bass range. I haven't seen Paul's sims for the MMT but I would not expect a lower 3 dB down point that I achieved. Paul box can achieve 3 dB more output at the extreme low end of the band before linear Xmax is reached.

Bracing normally helps a speaker but in this case you are talking about a 6.5" x 6" tube of 0.75" thick MDF. My experience is that this small of an enclosure will be very rigid and able to function without extra bracing. You could add some dowels between sides inside the box if you are concerned about rigidity but they are not required. Also the stuffing helps to damp the high pressure volume behind the woofer. I suspect that the MMT implementation would be less rigid than my MT version unless some bracing is added to that design.

Jim

[nikkoluvr]

Re: The Speedster Towers--A MLTL version True to the Originals

+1 NickJ, I too am out of my element when it comes to TL, MLTL designs. Looking forward to the replies to your question.
nikkoluvr

[Paul K.]

Re: The Speedster Towers--A MLTL version True to the Originals

The modeled F3 I achieved was 38 Hz, but my design was primarily based on the cabinet dimensions Paul C had for his non-MLTL MMT Speedster he brought to InDIYana. I may have increased the box depth some, but I purposely did not want to get a much lower F3 in order to keep driver excursion somewhat limited (I may have been a bit too conservative, however).
Paul

Nick,

The Carmody MMT (MLTL box designed by Paul Kittinger) is twice the cross-sectional area of my box. That MMT and my design will be the same sensitivity over the majority of the frequency band but the MMT can supply 3 dB more output in the limit over the region of the frequency where both M's are working. Normally, MMT designs don't increase the sensitivity of the speaker as the sensitivity increase isn't over the entire mid bass range. I haven't seen Paul's sims for the MMT but I would not expect a lower 3 dB down point that I achieved. Paul box can achieve 3 dB more output at the extreme low end of the band before linear Xmax is reached.

Bracing normally helps a speaker but in this case you are talking about a 6.5" x 6" tube of 0.75" thick MDF. My experience is that this small of an enclosure will be very rigid and able to function without extra bracing. You could add some dowels between sides inside the box if you are concerned about rigidity but they are not required. Also the stuffing helps to damp the high pressure volume behind the woofer. I suspect that the MMT implementation would be less rigid than my MT version unless some bracing is added to that design.

Jim

[NickJ]

Re: The Speedster Towers--A MLTL version True to the Originals

Nick,

The Carmody MMT (MLTL box designed by Paul Kittinger) is twice the cross-sectional area of my box. That MMT and my design will be the same sensitivity over the majority of the frequency band but the MMT can supply 3 dB more output in the limit over the region of the frequency where both M's are working. Normally, MMT designs don't increase the sensitivity of the speaker as the sensitivity increase isn't over the entire mid bass range. I haven't seen Paul's sims for the MMT but I would not expect a lower 3 dB down point that I achieved. Paul box can achieve 3 dB more output at the extreme low end of the band before linear Xmax is reached.

Bracing normally helps a speaker but in this case you are talking about a 6.5" x 6" tube of 0.75" thick MDF. My experience is that this small of an enclosure will be very rigid and able to function without extra bracing. You could add some dowels between sides inside the box if you are concerned about rigidity but they are not required. Also the stuffing helps to damp the high pressure volume behind the woofer. I suspect that the MMT implementation would be less rigid than my MT version unless some bracing is added to that design.

Jim

Thanks for this answer. A couple of followups.

1. MMT designs often do increase sensitivity when we are talking about a 2.5 design (which I believe the speedster mmt is), as the roll-off of the second mid bass is usually designed to compensate for the natural loss of baffle step. Am I missing something here?

2. I know that the MMT is bigger, but I am wondering whether the size and length of a MLTL has to adjust for speaker displacement in the same or similar ways as other vented boxes.

[Paul K.]

Re: The Speedster Towers--A MLTL version True to the Originals

When there are two drivers involved you'll always need twice the volume in order to have the same F3 as for a single driver. It doesn't matter what the box configuration is.
Paul

Thanks for this answer. A couple of followups.

1. MMT designs often do increase sensitivity when we are talking about a 2.5 design (which I believe the speedster mmt is), as the roll-off of the second mid bass is usually designed to compensate for the natural loss of baffle step. Am I missing something here?

2. I know that the MMT is bigger, but I am wondering whether the size and length of a MLTL has to adjust for speaker displacement in the same or similar ways as other vented boxes.

[NickJ]

Re: The Speedster Towers--A MLTL version True to the Originals

When there are two drivers involved you'll always need twice the volume in order to have the same F3 as for a single driver. It doesn't matter what the box configuration is.
Paul

Thanks Paul,

That is what I expected, I was just wondering if the MLTL had some rear loaded horn properties or something...

[Jim Griffin]

Re: The Speedster Towers--A MLTL version True to the Originals

Nick,

Paul has written a good summary of what a MLTL does on the Philharmonic Audio website. Read this:

http://philharmonicaudio.com/folio-me/html/Phil%20Pages/about.html

Jim

[infamous_panda]

Re: The Speedster Towers--A MLTL version True to the Originals

This is pretty cool. I wanted to do a quirky transmission line setup before I got set on my speedsters. I have some questions:

1. In a transmission line I had assumed the distance between the woofer and port is critical, Unlike say a speedster bookshelf where the port location has some flexibility. Is there truth to this or does the length of the enclosure mostly what matters?

2. I was considering a setup where a left floor standing speaker was on floor as normal, but the right speaker would be on my desk upside down. It would be made such that the tweeters would at the same height.

3. Does is matter if the woofer is above the tweeter in the right speaker? Would I need to have them reoriented in the upside down speaker?

Not saying I'm gonna do this but it solves some issues with my current furniture arrangement. Might give me an excuse to build something new.

[Paul K.]

Re: The Speedster Towers--A MLTL version True to the Originals

In an ML-TL the 1/4-wavelength resonant frequency of the line's length (which would be the cabinet's internal height for a simple floor-standing ML-TL) contributes to part of the system tuning mechanism, with the rest of the contribution coming from the port's dimensions. In addition there will be artifacts created in the system response curve caused by the distance between the woofer and port. These show up as peaks and dips in the response curve usually above 300 Hz. So, when modeling an ML-TL, one of the final steps is finding the optimum location of the port relative to the woofer's location and the line's length. The shorter the line (the shorter the cabinet), the less critical is the port's location usually.
Paul

This is pretty cool. I wanted to do a quirky transmission line setup before I got set on my speedsters. I have some questions:

1. In a transmission line I had assumed the distance between the woofer and port is critical, Unlike say a speedster bookshelf where the port location has some flexibility. Is there truth to this or does the length of the enclosure mostly what matters?

2. I was considering a setup where a left floor standing speaker was on floor as normal, but the right speaker would be on my desk upside down. It would be made such that the tweeters would at the same height.

3. Does is matter if the woofer is above the tweeter in the right speaker? Would I need to have them reoriented in the upside down speaker?

Not saying I'm gonna do this but it solves some issues with my current furniture arrangement. Might give me an excuse to build something new.