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WalterPPK 15th July 2017 11:10 AM

Hi, a couple of years ago we built our own recording studio.
This week we sold our old monitors and I'm now looking at building PMC MB2 clones.
This is what I have in mind:

First I took a look at JamieMatrix's thread but didn't find any definite dimensions for his build.

The following units are on the list:

Volt RV3143
Volt VM752
Scanspeak D3004/6600

In the first stage a DCX is going to be used. Later on maybe a DEQX or something similar.

I made a fair amount of subwoofers but never a transmission line. I hope that I can get some help with the internal dimensions.

I made a 3D model based on the PMC 2D drawing found in Stargeezerme's thread with the cross section unfolded. The lines of the unfolded section are equal to the lines in the model of the cabinet. Changes in the cabinet will be reflected in the cross section automatically.

Cabinet width (internal): 344mm
Gross cabinet volume: 134L
Nett cabinet volume (-woofer,-mid, -ribs): +/-125L
Sd woofer: 479 cm^2
Offset center woofer: 27mm
Fs woofer: 34hz (or 31hz I read in another thread?)
Sl: 297cm^2 (copied from PMC drawing, including fillet)
So: 1204cm^2
I have a lot of questions but the the first one that came to mind is how do you incorporate the fact that the mouth is bend 90 degrees to the baffle in the unfolded cross section?
As seen on this photo.

This is the first sketch I made from some assumptions of the drawing and photo's found.

Hopefully, with some help from you, I can make this thing! :)

Mooly 15th July 2017 11:26 AM

Walter... we are experiencing some forum issues at the moment.

The reason your edited post disappeared is because as a new poster you are under moderation. Unfortunately we can't currently re-approve edited posts and so in this case I was able to paste your new reply into your following post.

WalterPPK 15th July 2017 12:01 PM

Would a few extra ribs placed in the right bottom corner and near the mouth improve the cross section and reduce internal volume and reduce the TL length?

WalterPPK 15th July 2017 12:03 PM

Thanks Mooly for re-posting it! Cost me some time to make the post. :)

WalterPPK 15th July 2017 12:36 PM

This also would be aesthetically more pleasing:

WalterPPK 15th July 2017 02:46 PM

Nett internal volume is now 120L

Bigun 15th July 2017 08:33 PM


wae 12th August 2017 01:00 PM

PMC Clone?
Hi WalterPPK,

I'm not sure you will find a specific detailed clone design here, for (my view) a number of reasons;

- We don't know what drivers they (specifications vary from the default drivers?) use, do we?
- SO, we don't know what we are designing. As you most likely are well aware, it starts with the driver. (The VOLT 3134 is a good driver for TL, but expensive. There are other very good drivers at half the price or even less). So we might think, Aaaha, they (PMC) use the Volt driver we can purchase, which might not be the case.
- Result, IF we would know in detail how the TL of PMC is designed AND use the standard Volt driver, we might still end up with a big misfit at "large" cost.
- I don't think that the forum members with detailed knowledge on this subject are willing to help you clone a commercial brand speaker, even if you just intend to use it for personal use only.
- There are some threads in the forum about these designs, I think the best would be
Transmission Line Question
- They use a spreadsheet from Martin J. King, who has published in detail how a TL works and can best be designed. This is no longer publicly available for reasons I'm unaware off. HOWEVER, there are VERY good articles from M.J. King on the internet explaining in detail how to design a TL

Which brings me to the following;

Why don't you use TL design software to build your own design, IF you like the appearance of the PMC and want to use the Volt, then THAT's your starting point.

I use Leonard Audio software (info on their forum as well) Transmission Line Modelling Software. If you read the King articles and use the basic principles for the TL design (derived from the T&S of the driver) you will be up and running in no-time.

I've also NEVER designed a TL, because "they say" it is a complicated animal. Now I dived into it, it seems that the damping could be a struggle. On the other hand, the LA software shows all detail about type of damping and volume of damping. I may post a new thread of these designs, ALSO found a nice theoretical design methodology for this damping questions (WHERE to place HOW MUCh of WHAT). The LA software tells me my methodology works. Don't have a clou how it will sound, that's future surprises (positive or negative).

I build a simpel spreadsheet myself (based on M.J. King design principles) to calculate the starting numbers for a TL for a given driver. ALSO modelled some PMC LOOK-ALIKEs. They come close to the dimensions of the real deal, although they differ, but I don't care, I want my own design.

Will start building 3 TL designs in very near future;
- A complete own design for a pair of Tannoy K3149 (as my personal home studio mid-fields)
- A PMC MB2 OR IB2 look alike, drivers to be decided but most likely low-end Dayton audio or Faital Pro. Look VERY promising on paper.
- A PMC look-alike 5" or 6" near field (as my personal home studio near fields).

I am planning to start a studio line / home recording speaker line in near future.

Which reminds me of your drawing for the control room, looks like you use those big MB2's as near fields? Are you SURE? :confused:

Any way, my first 5 cents:p

WalterPPK 12th August 2017 02:43 PM

Hi Wae, you are absolutely right. This is also why I decided to divert from the MB2 design because they are too big to use in near field operation. Second; the outcome is too uncertain because of the difficulty of designing the TL enclosure.
The plan is now to build a bass reflex monitor around the following drivers:

1x SB Acoustics TW29RN-B
1x Volt VM752
2x SB Acoustics W024P-8

The units are ordered and the design pictures will follow. Outer dimensions will be approximately HxWxD 650x400x440 Gross internal volume 90 liter. Tuned to 28hz.

C37 13th August 2017 12:08 PM

Just for Your information there is a thread here where a member has monted the Volt (or was it atc?) Midrange in a spherical enclosure and reported that a midrange dip he quite never managed to remove otherwise was gone and that it eased the filtering. Can't remember whom right now.

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