Vifa RB2 kit meets mini transmission line

Systems

A number of years ago I built these boxes in an atempt to replicate what PMC claimed as the worlds smallest transmission line speaker,the approx $1.5k model DB1 http://www.pmc-speakers.com/docs/147c7f79ded670_pmc.DB1i.pdf .They were able to achieve an effective line length of 5' within a compact 6"x11.4"x9" enclosure.As shown in the above link ( the pic under the heading ATL)you can see the line is created by 3 internal partitions and the channel is damped with foam.

For one reason or another I never completed the project but after seeing Madisounds Vifa Recession Buster 2 kit http://www.madisound.com/catalog/product_info.php?cPath=35_428&products_id=8525 I thought it would be perfectly suited for the project.

In fact the parameters of the 5" Vifa driver used by PMC(M13SG) are very similar to the ones of the Vifa M14 supplied with the kit.Therefore one can reasonably expect similar results as far as bass response are concerned. It will interesting to see if their claims of 50hz extension from this little box are realistic.

Systems

Ooops this was supposed to be the second pic.I tried to get it as similar as possible to PMC's ATL .

bikerboy

Thanks for the idea. Any input will be a great help. I looked around and didnt see anything like that for box designs. I thought I might build a full range single driver speaker first but the RB was too hard to pass up on. Down to 50hz would be amazing!

megasat16

GV#27 wrote: »

Ooops this was supposed to be the second pic.I tried to get it as similar as possible to PMC's ATL .

Wow! Open Baffled with Internal Wave Guide?

Systems

bikerboy wrote: »

the RB was too hard to pass up on.

Yeah I wasn't letting that deal go by even though I don't really need another set of speakers.

Down to 50hz would be amazing!

The vented box suggested by Madisound for the kit will get you near 50 hz ,but the box is bigger.However the quality of bass from a TL enclosure is reputed to be better damped and more detailed than that of a vented box.

megasat16 wrote: »

Wow! Open Baffled with Internal Wave Guide?

Yep I should patent it.;)or maybe I will just glue the other side panel on.:D

megasat16

GV#27 wrote: »

Yep I should patent it.;)or maybe I will just glue the other side panel on.:D

Yep! I thought it's a new design concept you are playing with. If it doesn't work well, you can always glue back the rear baffle and the side panel.

davidfmartin

Sweet! So are you planning on recessing the tweets?
How do they sound now?

We should start our own RB owners/builders thread

TECHNOKID

Thanks for sharing the info GV!

Cheers!
TK

Face

Very cool Fred!

zingo

Great project and great thinking.

Systems

davidfmartin wrote: »

Sweet! So are you planning on recessing the tweets?

I should and usually do but this time I'm not going to bother as I find it a PITA getting it right.

How do they sound now?

I still have some assembly to do before the auditioning can begin.

TECHNOKID

GV#27 wrote: »

I should and usually do but this time I'm not going to bother as I find it a PITA getting it right.
I still have some assembly to do before the auditioning can begin.

Keep us posted! I was thinking about buying a couple kits, would be nice to know how they sound.

Cheers!
TK

comfortablycurt

Damn...that's a killer price. I've been wanting to play around with building my own speakers for a while now. I might have to pick up one of those kits sometime.

Systems

Techno&Curt, you gents may not want to wait too long as Madisounds stock may run dry before you get in on the deal.You might shoot em an email to check.

Systems

For those interested in such things,here is a good pic of the inards showing how they partition and damp their TL's. http://www.pmc-speakers.com/company/technology.php There's also a technical description with a just smig of marketing hype thrown in for good measure.:D

Face

I recently heard a pair of their OB1i's. They had a pretty good amount of low end for a small woofer.

SCompRacer

Kewl project. I'm a fan of TL bass.

comfortablycurt

GV#27 wrote: »

Techno&Curt, you gents may not want to wait too long as Madisounds stock may run dry before you get in on the deal.You might shoot em an email to check.

I'd love to pick a kit up now...but my finances are tied up in a couple other soon to come upgrades right now. I'll just have to hope they still have them around afterwords, when I've got some extra coin.

If they don't...oh well. I'll figure something out one way or another.

Systems

I have them dressed up in some maple veneer with stands to match.They will be getting several coats of lacquer and the top and bottom plates of the stands will be painted black.

I'm kicking myself for not taking the time to recess the tweeter as it would have looked much better.:(



I must say that PMC's variation of TL loading works as claimed.The bass is definately more extended than would be the same woofer in a sealed box.I could have gained a few extra hertz of extension had I built the recommended (bigger) ported box,but I think the TL would win on SQ grounds.In direct comparison with another DIY speaker also utilising a 5" woofer in a ported box,the TL's bass was very natural and articulate sounding aswell as controlled , whereas the ported unit while it dug abit deeper sounded somewhat bloated and ill defined incomparison.
Interestingly even though both woofers have similar excursion capabilities,I am able to push the TL's harder before the woofers start to unload.


I did not mount the crossovers in the enclosures so as to give me a number of options to expierment.Mounting the passive networks outboard will allow easy access for trying different caps/resistors in the hi pass section ,or removing it entirely when I want to run them biamped with an active crossover.

The 3rd pic shows both the stock passive network and the active unit.
The passive unit has 12db HP/ 6db LP slopes at 3k with a decent Bennic PP cap in the tweeter section,air core coils and cheap sand cast resistors.

The active unit is from a previous project but will get some minor mods for use with this driver pairing.It has 24 db slopes at 2k,baffle step compensation and will when modded add 60us of delay to the tweeter for time alignment.Preliminary listening show the active setup superior even without the mods having been done to it yet.:D

megasat16

Looks Very Nice With Maple Veneers and on the Custom Stands.

Are you making the grille also?

Systems

megasat16 wrote: »

Are you making the grille also?

What are grilles?:D


Nah I prefer to leave them nude.

megasat16

It's a negative for you lave them naked. I prefer you get these. They looks awesome!

TECHNOKID

comfortablycurt wrote: »

I'd love to pick a kit up now...but my finances are tied up in a couple other soon to come upgrades right now. I'll just have to hope they still have them around afterwords, when I've got some extra coin.

If they don't...oh well. I'll figure something out one way or another.

They are still available but a much healthier pricing (original pricing I guess?).



GV#27, they look beautifull! Job well done! I guess you made the stands too?

Enclosed like this they look quite a bit like my Athena... the stands look as good if not better then the VTI stands I am using for my Athena. Again, job well done! :cool:

Systems

TECHNOKID wrote: »

They are still available but a much healthier pricing (original pricing I guess?).

You might be thinking of the Reference version that sells for $399.That kit has higher quality drivers and crossover components than the RB,RB2 but still a great bargain at the price.I believe the RB2 kits are now sold out.Maybe there will be an RB3?

.. they look beautiful! Job well done! I guess you made the stands too?

Thanks ,and yes I built the stands aswell so they would match cosmetically and to get the speakers at the optimum height.

bikerboy

Nice work on the cabinets and stands. This will be the first pair of speaker cabinets I will make. I want to do a tl type also. I never liked ported speakers much so I was going to do a sealed box. Can you give us some dimensions or do you think something different would be better?

ben62670

bikerboy wrote: »

.... I never liked ported speakers much so I was going to do a sealed box. Can you give us some dimensions or do you think something different would be better?

I like the range of ported speakers. They are easier to work with, and tunable, but after having PR's and sealed I have not had the urge to go back to ported designs. Sealed usually needs some boost down in the lower ranges which taxes the SPL output. Too many people shy away from PR's because they are very hard to model. After working with numerous custom speakers using all three styles with the same drivers, environment, and gear I have come to love PR's. Some people are under the impression that they actually boost bass in the lower regions, but this isn't really true. it helps the lower extension no more than a proper port. The big gains with a PR is that you lose next to no box volume, you have a larger radiating area, and no port noise. There is always trade offs. Sealed will hit harder and tighter than ported or PR's. Ported gains are deeper bass, and very easy to design with free programs, but again the SQ just isn't there.

Here are a few tips if you want to use PR's.

Try to build the box volume to approximately the size of what you would build with a ported setup. You can go with a smaller volume if you wish, but you will lose a bit of efficiency, affect the Q, and frequency extension in the lower regions. Deep bass with smaller ported boxes require ports that are way to long, and take up way too much internal box volume if you can even get them to fit.

So you have your box built and the PR is installed. Now run some test frequencies in the range you are going to use the sub, and more than double the high frequency. Say you are going to set your XO cut off to 80hz. You will want to test your response up to around 150(you may want to go higher depending on what kind of response you get(resonate frequencies rear their ugly heads sometimes pretty high)). So you have a chart that goes from say 15hz to around 250hz. Get a calibration chart that shows the actual DB's for the particular SPL meter you are using. SVS has that info on their website for some of the more popular meters. My rat shack SPL meter is down about 6db at 20hz IIRC. What you want to do is add more weight to the PR if the lows are not putting out the levels you want them to. Also when adding weight it helps bring down the peaks from room gain, and driver resonance that are in the higher ranges.
Another awesome thing about using a PR is you get to tune the bass for the environment you are in(room gains and nulls are a ****). You can test the response from where you sit if you like, but I have found that using the standard 1 meter from the driver setup is best(thats how the rest of the speaker is designed, and it just sounds more natural). I used to look at the speakers +_3db factory chart like nearly 99% of people do:o If you move the speakers around then your room gain, and nulls change. The manufactures specs don't really tell the truth in your listening area. You can pop the driver out and add or remove weight as needed. Another real nice thing about PRs if you are using mid drivers like Polk does you don't need to add more amplifacation for the subs, and the output is very linier the rest of the speaker. Very efficient:)

Face

http://www.aespeakers.com/PRFAQ.php

http://web.archive.org/web/20010128132400/lambdacoustics.com/library/whitepapers/diyprdesign.htm

ben62670

I like the first link(bookmarked). Also I like to tune to the room:) The calculation may get you close, but after a little measuring TBE(trial by error) works very well.
Thanks Bro.
Ben

Systems

bikerboy wrote: »

Nice work on the cabinets and stands.

Thanks BB

This will be the first pair of speaker cabinets I will make. I want to do a tl type also. I never liked ported speakers much so I was going to do a sealed box. Can you give us some dimensions or do you think something different would be better?

If you plan to eventually mate them to a sub then going sealed would be the easiest but for stand alone use I think the TL is a great option.I can draw a diagram and PM it to you if you are interested.

As for the PR they are great for subwoofers and bigger systems but we are talking about a 5" woofer in a mini monitor form factor and a first time build so IMO not practical.If bass extension is the priority then just build the ported option.Adjusting port lengths will give you the same tunability as a PR but you will have the very desirable benifit of being able to predict the resulting response with free software like WinISD.


BikerB if I can be of any assistance just ask.


Hey Ben long time no talky how are things?Is that Burr Brown DAC I sent you still singing sweetly?

ShinAce

I feel like there's some good port bashing going on without proper defense.

A ported box will have a 'Q' sort of like a sealed box, but it is changed by going with different box alignments. Box volume, box losses, and tuning frequency affect the 'Q' of the overall design.

You can't just build the smallest ported box possible, adjust the port until the response is nearly flat and call it a day.

bikerboy

Hi Fred,
I want to use these speakers for the computer or garage or as backups when I rebuild the xovers on my sda-2a speakers. I doubt that I will use the RB2 with a sub so I think your TL idea looks best for my use. I would greatly appreciate a diagram so I can get the TL cabinet built correctly. Do you use contact cement to stick the veneer to the box? I read some use elmers glue and iron it together. This will be the first veneer work I have done so it will be fun. Thanks, BB