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

[Jim Griffin]

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

Trevor,

My Speedster MLTL uses Paul C's original crossover for the bookshelf speaker design. See the diagram at:

https://sites.google.com/site/undefinition/speedster

I don't have a photo of my crossover for the prototype build but you may find other Speedster builds with a crossover layout. Often in a small MLTL I will separate the woofer and the tweeter crossover networks and build the two networks on smaller boards. I place the tweeter board in the upper part of the cabinet while the woofer network is located behind the terminal plate near the bottom of the box. Wire from the terminal plate to both networks as evident in the crossover schematic.

I don't know of a specific center channel version of this speaker. If you have the vertical room (and don't mind the look), you could use a bookshelf Speedster box.

For another MT bookshelf application with a ribbon tweeter I laid the enclosure flat and rotated the tweeter 90 degrees. I suspect that this technique would work OK with the Speedster as the woofer and tweeter are closely spaced.

Jim

[trevor995]

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

Question for Jim or anyone who might be able to answer this. I am going to build these MLTL towers and had a couple of questions. One, do I use the crossover layout for the original Speedster TMM that was done by Paul (minus) the extra resister for the second woofer? (Does any one have a layout diagram of this crossover showing where what part goes where?) I am new to this and the crossover schematic is hard for me to understand. And second, Is there a matching center channel for these? I don't really have any size restraints so I was hoping for a plan that used the Fountek tweeter, Tang Band mid/woofers and 6 or 8" woofer. Thanks

[Jim Griffin]

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

Bob,

I used 0.75" thick walls (6.5" wide baffle) for my Towers vs. the 0.50" thickness of the original bookshelf units (6" wide baffle). I wanted the construction of the Towers to be more rigid than normally used for the bookshelf design. The extra wall thickness does have a slight impact on BSC but not enough to necessitate a change.

Now as you mentioned you can use flip the baffle to the 6" side of the box but I would caution that this may slightly intrude on the available air space around the rear basket of the woofer.

In fact Paul Carmody has addressed this baffle width question before and has stated that he did not think that it would significantly impact the performance of the speaker. Paul has said that the crossover will still work the same. See his comments on the first page of the MMT design write-up at:

https://sites.google.com/site/undefinition/speedster-tmm

You can use either the slot port or round port option in your build. I used a slot port that exits the front of the box for my prototypes but you can arrange for the port to emerge from either the front or rear of your enclosure.

Let me hear if you have additional questions.

Jim

[upsman]

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

Jim, Question regarding the baffle width.....you state " The width of this speaker is 6.5 inches vs. 6 inches for the bookshelf version which will slightly impact the baffle step correction"...........The dimension of your design is 6.5"Wide and 6" Deep.......why wouldn't you make the 6.0" side the front baffle and maintain the correct baffle step correction.....I not sure if this would change anything, maybe the design of the slot port. Using a round port would fit on a 6 inch baffle. Just curious.............

Thanks BobC

[Jim Griffin]

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

I use a piece of wire fencing (small mesh) wedged in the enclosure just below the woofer to retain the stuffing in the upper 1/3rd of the enclosure.

You likely would not need much, if any, bracing with this design as the internal dimensions are small. Five inches is the largest width or depth. Combine that with the wall thickness of 3/4" (18mm) and you have a rigid structure that needs little additional bracing.

[rhodesj]

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

How did you retain the stuffing in the top half of the speaker? I've gathered that one wants to be careful to not change the cross sectional area too much with braces.

[Jim Griffin]

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

nrg74,

As I stated in the first message in this thread the inside dimensions are 5 x 4.5 inches so the area is about 22.5 sq. inches. A round tube 4 inches in diameter would yield about 12.6 sq. inches so the cross sectional area is significantly less. My gut feeling is that the CSA reduction will be too much to work as I originally designed.

I'm on travel and away from my computer on which I have the Martin King MLTL worksheets for a few days so I can not give you a detailed answer until later in the week. Also the W4-1720 driver is more like a 5 inch frame size so I suspect that it would not fit 4 inch PVC adequately. If you have alternatives (larger pipe diameter, perhaps a larger pipe diameter with a half section, etc. which could be considered. Let me know if you have options that I can run when I return. The issue also becomes a crossover problem if we deviate much from Paul's 6 inches wide enclosure as well. Let me hear what flexibility you have.

Jim

[nrg74]

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

Very nice design. The tower is so slim, it is hard to believe that it can go that low.
Could it fit in a PVC tube of say 4inch? That would be a very futuristic look, especially in clear!
Well done, the thought is simple but very effective. I always prefer floorstanders over bookshelf speakers, simply because I don't have a shelf to put them on. Besides, everyone needs some bass in their music.

[Jim Griffin]

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

For this design the length of the line was selected to optimize the bass output and to place the tweeters at the best height for listeners. Paul covered the relationship between the woofer and the port locations and why they become important for this design.

These speakers work best when floor standing. But if Panda wishes to flip one speaker upside down and place it on his desk, it should function OK. I should add that you should not change the baffle layout but physically flip the whole box. As he suggests, the tweeters would be located at the same height. As built, the woofers cover the listener with good sound in a close listening situation. If your furniture placement changes, you can change the speaker orientation for your new situation.

[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.

[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.

[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

[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...

[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

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.