My First DIY MLTL Speaker Build

Jaybe

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Nov 6, 2011
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119
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Bangalore
Hi Folks,

I am happy to share my journey from germination of the idea to build the Speakers to its fruition.

Background:

In the thread http://www.hifivision.com/diy/22729-bug-has-bitten.html, I outlined the circumstances that prompted me to consider a DIY build of Speakers.


Considerations:

1. No Cross overs between 200 & 4000 Hz - the most sensitive hearing range.
2. Lowest Order Cross Over to retain the efficiency
3. High efficiency to enable use with Tube Amplifier
4. Frequency ranging from 40 Hz to 20 Khz. The lower one for smooth
integration with Subwoofer.


Choice of Drivers:

This almost necessitated a choice of Full Range drivers. I considered Fostex, Mark Audio and AER Drivers. Mark Audio Drivers though nice were ruled out because of lower efficiency compared to others. AER Drivers were priced more than 10 times those of Fostex . Fostex appeared to be a logical choice and relatively easy to procure from Madisound USA.

To suit the desired Frequency Range, I opted for 8 FostexFF225WK full Range driver. This Driver though has good Low frequency range, has been known to be lacking in higher frequency. Hence I decided to enhance the upper end using moderately priced Fostex FT17H Horn Tweeter. Fostex recommend using their Horn Tweeter with a single Capacitor to protect it. Generally the Full Range Driver is not applied any Cross Over but rather allowed to naturally roll over.

Choice of Enclosure:

I was tending towards building Metronome ML TQQT - Speakers . However over next few days the location where the system would be placed was changed and at nearly 65 tall, the Metronome Speakers were considered to be too tall. Thus began a search for an alternate design albeit using the Drivers already with me. I narrowed down the design to that of Decware and Bob Brines.

Steve Deckert of Decware confirmed that the Drivers I had were suitable to be used in his Decware NFX as well as HDT design. HDT design is a bit unconventional and uses multi ports with a number of passive Drivers. On the other hand, Bob Brines designs are more conventional. I ordered Plans of both Decware HDT and Bob Brines designs. After some consideration, I opted for Bob Brines MLTL Mass Loaded Transmission Line design.

This design is of a straight tower with fairly large cross section. So the enclosure was decided to be built with rounded edges and soften the In Face feeling of the straight tower by reclining them. In consultation with Bob Brines, I decided to incline the towers by 7 degrees.

Subwoofer:

The MLTL Towers with chosen Drivers go down to a frequency response of 40 Hz. To further augment this, a Subwoofer was needed. I decided to build a Subwoofer using locally available 12 Peerless Driver. I also ordered a Dayton 240 Watts Plate Amp to power the Subwoofer from Parts Express, USA.

- To be continued -

Jayant
 
Hi Folks,

I am happy to share my journey from germination of the idea to build the Speakers to its fruition.

Background:

In the thread http://www.hifivision.com/diy/22729-bug-has-bitten.html, I outlined the circumstances that prompted me to consider a DIY build of Speakers.


Considerations:

1. No Cross overs between 200 & 4000 Hz - the most sensitive hearing range.
2. Lowest Order Cross Over to retain the efficiency
3. High efficiency to enable use with Tube Amplifier
4. Frequency ranging from 40 Hz to 20 Khz. The lower one for smooth
integration with Subwoofer.


Choice of Drivers:

This almost necessitated a choice of Full Range drivers. I considered Fostex, Mark Audio and AER Drivers. Mark Audio Drivers though nice were ruled out because of lower efficiency compared to others. AER Drivers were priced more than 10 times those of Fostex . Fostex appeared to be a logical choice and relatively easy to procure from Madisound USA.

To suit the desired Frequency Range, I opted for 8 FostexFF225WK full Range driver. This Driver though has good Low frequency range, has been known to be lacking in higher frequency. Hence I decided to enhance the upper end using moderately priced Fostex FT17H Horn Tweeter. Fostex recommend using their Horn Tweeter with a single Capacitor to protect it. Generally the Full Range Driver is not applied any Cross Over but rather allowed to naturally roll over.

Choice of Enclosure:

I was tending towards building Metronome ML TQQT - Speakers . However over next few days the location where the system would be placed was changed and at nearly 65 tall, the Metronome Speakers were considered to be too tall. Thus began a search for an alternate design albeit using the Drivers already with me. I narrowed down the design to that of Decware and Bob Brines.

Steve Deckert of Decware confirmed that the Drivers I had were suitable to be used in his Decware NFX as well as HDT design. HDT design is a bit unconventional and uses multi ports with a number of passive Drivers. On the other hand, Bob Brines designs are more conventional. I ordered Plans of both Decware HDT and Bob Brines designs. After some consideration, I opted for Bob Brines MLTL Mass Loaded Transmission Line design.

This design is of a straight tower with fairly large cross section. So the enclosure was decided to be built with rounded edges and soften the In Face feeling of the straight tower by reclining them. In consultation with Bob Brines, I decided to incline the towers by 7 degrees.

Subwoofer:

The MLTL Towers with chosen Drivers go down to a frequency response of 40 Hz. To further augment this, a Subwoofer was needed. I decided to build a Subwoofer using locally available 12 Peerless Driver. I also ordered a Dayton 240 Watts Plate Amp to power the Subwoofer from Parts Express, USA.

- To be continued -

Jayant

I have reviewed this particular fostex drivers for my own TL designs and found them good only if you apply some kind of compensation at the mid and higher frequencies. That way you would have a better FR and would not need to go for a sub-woofer and super tweeter. Due to the harshness in these frequencies the lower and higher frequency get masked and need to be balanced. I found the FE series drivers to be better than the WK series and may plan to build them in the near future.

Please post some images of the speakers for the benefit of FM.

Cheers,
 
Hi Jayant

I built an MLTL using Bob Brines plans a few years ago using the Fostex 167E. The plans are very detailed, as you would seen by now, and it was an easy build.
 
Jaybe, I like the way you have described different things in your post like choice of driver, choice of enclosure and your thought process. Looking to know more about your build.
 
I have reviewed this particular fostex drivers for my own TL designs and found them good only if you apply some kind of compensation at the mid and higher frequencies. That way you would have a better FR and would not need to go for a sub-woofer and super tweeter. Due to the harshness in these frequencies the lower and higher frequency get masked and need to be balanced. I found the FE series drivers to be better than the WK series and may plan to build them in the near future.

Please post some images of the speakers for the benefit of FM.

Cheers,

Hi Hari,

FF225WK has received a good opinion from most designers using Full Range Drivers. While it is strong in low frequency it does behave erratically beyond 7 KHz frequency. So it does need to be augmented with a Tweeter. I am able to run these Speakers without a Subwoofer satisfactorily and indeed did so for several weeks. To my surprise, a Subwoofer below 50 Hz and with low gain, strangely seems to lift up high frequencies - There is no phase cancellation happening -.

Pictures coming up in continuation.

Cheers !

Jayant
 
Hi Jayant

I built an MLTL using Bob Brines plans a few years ago using the Fostex 167E. The plans are very detailed, as you would seen by now, and it was an easy build.

Hi George,

Indeed the Plans are greatly detailed and Bob is always forth coming. However I made my life difficult by wanting to incline back the Speakers.

Cheers !

Jayant
 
Jaybe, I like the way you have described different things in your post like choice of driver, choice of enclosure and your thought process. Looking to know more about your build.

Hi I audio,

The build process is coming up.

Cheers !

Jayant
 
II


Material of Construction:

Since we opted for a wood Veneer finish on rounded edge enclosures, it necessitated the use of 0.5 mm Veneer. This is known to faithfully reproduce any surface irregularity upon application. Plywood, though desirable would have given poor finish during rounding of the edges and thus, I opted for 18 mm MDF. However the internal braces were made of 19 mm Ply.

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I found it difficult to procure the recommended Armstrong 420 Ceiling Tiles in small quantity required. These are used for insulation. Instead Egg Shell Foam of 1 thickness was decided to be used.

Similarly, the subwoofer was built with MDF Panels and internal braces of Plywood for greater strength.

Flanged Ports were machined from high quality Black Nylon Tubes of suitable size.

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Building the enclosures:

Machining:

To obtain cleaner finish and accurate cut outs for Drivers, I wanted the panels to be cut on a CNC Router. Those I contacted were reluctant to take up such small work. Eventually a company whom a friend of mine gives significant work was persuaded.

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This did not turn out to be easy at all. The workshop needed Autocad drawings so that they could be used directly by them for cutting. Since the designers dis not supply drawings in this format neither in all details and that I had modified the design, the drawings had to made afresh. This ate up considerable time.

Further, the machines were not capable of making odd angles required on the edges to incline the speakers vertically. On the accuracy of cutting these angles, relied the final outcome of the enclosures. Thus the workshop was asked to cut at 90 degrees angles with oversized dimensions. These panels were than finished for final sizes and angles on an NC fitted, tilting head Milling Machine.

The Boxes were assembled with nails and Fevicol. The enclosure was lined with eggshell foam using a glue.

June2012774.jpg


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Jayant
 
Looks good so far.

I too had a hard time getting a couple of baffles( for an MTM build that is almost complete) done on a CNC router. My drawings were done using Corel Draw, and in the end the machining shop charged me an arm and leg for the job-I didnt have your leverage!
 
Looks good so far.

I too had a hard time getting a couple of baffles( for an MTM build that is almost complete) done on a CNC router. My drawings were done using Corel Draw, and in the end the machining shop charged me an arm and leg for the job-I didnt have your leverage!

Sorry to hear that. My experience with the CNC Router workshop remains unsatisfactory. I think we need to pull in resources and develop a good source for this kind of work.

Jayant
 
there is no need for a cnc router cutting for speaker builds. A jig saw m/c or a circular router is the best with necessary jig. In my sub build, the woofer cutout (2Nos) was done using a normal wood cutter (had to sacrifice a new blade though) total cost was 200Rs and effort and the cut was made perfect by slight sanding.
 
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III


Crossover:

The recommended Crossover consisted of a Baffle Correction Circuit and a capacitor to protect the tweeter from lower frequency. Natural Roll over of the drivers was relied upon instead of a cutoff filter. In Bobs opinion neither Zobel Circuit nor L-Pad correction was needed. I respected his judgment.

June2012778.jpg


The inductor needed was made by a local vendor who built it after much delay but did not measure to the values designed for. I decided to get it from Parts Express and was carried by a friend of mine returning home. While the designer recommends the Crossover to be fitted behind the Speaker for an access, I decided to mount it inside as, if needed the access would still be possible by removing the woofer.

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Finishing:

The choice of wood paper veneer as they are called is rather limited and expensive. I decided to use Zebrano Veneer available at a supplier. The gluing of the veneer needs to be carried out carefully in order to avoid imperfection. While I had been satisfied with all the work so far, this left me a little unsettled. I decided to avoid using Paper Veneer in future.

June2012782.jpg



The Supra Baffle to house the Drivers and the Plinth were painted matt black by a local auto body shop. The Enclosures were finished using a Polyurethane based coating. The process consisted of a total of three coats starting with a primer. After each coat, sanding was carried out. The final coat was a 50% mix of matt and glossy formulation.

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The painted Supra Baffle was attached to the polished enclosure using a Silicon adhesive. This is believed to isolate vibrations. The Plinth was fixed to the enclosure with screws. Spikes were fitted to the Plinth.

June2012785.jpg


Jayant
 
there is no need for a cnc router cutting for speaker builds. A jig saw m/c or a circular router is the best with necessary jig is enough. In my sub build, the woofer cutout (2Nos) was done using a normal wood cutter (had to sacrifice a new blade though) total cost was 200Rs and effort.

The design of Bob called for 45 degrees relief on the Supra Baffle on the Cut Out for woofers. That would have been difficult but possible using a conventional Router.

Jayant
 
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