Converting A7 cabinets into MLTL

[kwingylee]

[QUOTE=kwingylee;1962291]

Maybe I m asking too much. But then, this forum has offered a lot

There are multiple mltl designs with different cab volume for the 416b. I m asking if similar design is available for 515-8g. Once the line length, cross sectional area and terminus dimensions are known then one can see what is the best way to partition the 825/828 to achieve the design.

I see a lot has been written to tighten up the space behind the mid horn area and various ways to cross brace the a7 cabs. Why not put a simple 1/2 shelf between the bottom of the mid horn and the bottom of the cabinet to create a classic TL and provide the bracing? The front opening Can then be modified to the popular openings as suggested by many: from 48 to 85 square inch slot or 3" to 6" tubes?

I am still digging through many old threads, here is one that applies:

http://www.hostboard.com/forums/f700...t=A7+port+size

Where multiple individuals (drummerwill, aeyb701 and SD-50) suggested that 75 square inches is a good figure for a 515-8G in a 828 cabinet.... but that is not a MLTL, and its a good start for me.

[kwingylee]

Greets!


As a general rule and in theory, until the system Q [sysQ] exceeds ~0.403, then short of a horn alignment, the cab's net volume [Vb] shouldn't exceed the driver's suspension compliance [Vas], so with the 515-8G's ~12.4 ft^3 and likely to have a < ~0.403 sysQ, this would be the upper limit and since the pioneers of audio's electrical, mechanical engineers determined that the optimum net cab Vb is one that raises the driver's Fs 1.56x in a sealed cab, though have never read nor figured out how they arrived at this other than when I queried the late Prof. Leach, his assumption was that it probably was done empirically.


Considering his math, etc., skills, contribution to DIY audio, I took/take it as 'gospel' and considering how many successful vented speaker designs have been built over the ensuing decades by manufacturers, DIYers, I'd say they 'hit the nail square on the head' IME & NSHO.


Tuning was always to be actual Fs, which we do know has to do with the fact that they had to couple to a high output impedance, so no longer applies unless one's sysQ is > ~ 1/2 ohm: Damping Factor: Effects On System Response | Audioholics



Regardless, based on published specs, this equates to a ~8.611 ft^3 net Vb, which apparently by design [no doubt in my mind] happens to be 'close enough' to the 828's rear cab net Vb and has a sufficient acoustical path-length to meet the criteria that differentiates a mass loaded [vented] TL from a simple reflex; so again, all one needs to do is tune the vent to the driver's Fs or whatever lower Fb works best overall in your app/room same as others have done with apparently satisfactory results.


GM

Thanks GM I m pretty ready to just reinforce the cabs and reduce port size. One idea I have on bracing is to extend the woofer baffle vertically downwards and stopping 12" from the bottom to form a "transmission line" whose length is the height x 1.5 +depth of the dimensions of 825/828. Would that be beneficial? Or is the as build internal dimensions sufficient?

[Phil-G]

kwingylee, i have had a pair of scratch built A7s for a couple years now. ive managed to get a strong 38 hrtz by EQing and porting. but,, i've decided to quit fighting, and augment the A7s inherent limitations with a semistereo sub. i can post pics sunday. what i built is a 10.5cf ported cabinet with a pair of 3154s.
with a pair of electronic crossovers i can triamp the setup. breaking it down to 80-90hz on down, 80-90 to 1200, and from 1200 on up.

[GM]

Or is the as build internal dimensions sufficient?

You're welcome!

Not a good plan since this will change the pipe's aspect ratio, flare frequency too much, reducing bass output and adding some pass-band 'ripple'.

This was the problem with many early TLs that were based on driver Fs, effective piston area [Sd] with no consideration for the driver's upper mass corner [2Fs/Qts'] that the pipe must load to.

Qts' = Qts + any added series resistance: mh-audio.nl - Home

GM

[GM]

i just need to try a couple more box styles and hf pairing. i'm thinking MR994As with 800 or 900 series drivers.

Hey Phil,

Let's gather up the 411 cab musings into a fresh thread and if you still have any of our correspondence [sadly, I don't] let's get whatever might be relevant posted too and get this finished.

In the meantime WRT cab size, I don't recall mentioning its classical vented alignment, which is ~623 L [~22 ft^3] net tuned to Fs though don't have any speaker design software loaded yet other than Hornresp and haven't gotten 'up to speed' on all its new features, including vent mach speed, so not sure what the minimum size vent, length would be.

Hopefully, I'll get some more loaded this weekend, but first have to get this new OBIHAI phone system working, so I can finally finish getting 'customer no service' AT&T off my property.

GM

[VolvoHeretic]

Ok, I don't have a clue what a Transmission Line is or a Quarter Wave Transmission Line so I looked up those words, and found this Wikipedia link and figured that they where merely pipe organ pipes; Transmission line loudspeaker - Wikipedia, the free encyclopedia , which led me to this link: Organ flue pipe scaling - Wikipedia, the free encyclopedia .

So, don't I just need a diameter/area to length/volume ratio for a box tuned to really low C/16.4hz, slap any Altec into it and live long and prosper?

Any TL links for dummies?

[kwingylee]

Ok, I don't have a clue what a Transmission Line is or a Quarter Wave Transmission Line so I looked up those words, and found this Wikipedia link and figured that they where merely pipe organ pipes; Transmission line loudspeaker - Wikipedia, the free encyclopedia , which led me to this link: Organ flue pipe scaling - Wikipedia, the free encyclopedia .

So, don't I just need a diameter/area to length/volume ratio for a box tuned to really low C/16.4hz, slap any Altec into it and live long and prosper?

Any TL links for dummies?

Google Martin J King as he has one of the most comprehensive websites on the topic and sells his software to people interested in designing TLs.

I have not been interested in TLs for a long long time, when as GM mentioned, TLs were based on tuning the line based on driver Fs and Sd. As I recalled way back then, even the selection criteria for an ideal TL suitable driver was debatable (may be it still is )

My interest in TL and now MLTL was renewed last Oct at the RMAF when I heard and was impressed by GPA 604s in a MLTL cabinet. I never heard 604 bass that sounded this good and open. I m not sure if others in this site heard the same.

[GM]

So, don't I just need a diameter/area to length/volume ratio for a box tuned to really low C/16.4hz, slap any Altec into it and live long and prosper? Any TL links for dummies?

No, per what I posted earlier: "This was the problem with many early TLs that were based on driver Fs, effective piston area [Sd] with no consideration for the driver's upper mass corner [2Fs/Qts'] that the pipe must load to."

As kwingylee noted, MJK's work is the best, though sadly he no longer offers his MathCad worksheets due to way too many folks illegally using them for profit venture with the most 'hits'/DLs on his site from large manufacturers who should already know all that's necessary for proper TL/horn design as well as have the software to quickly design them, but apparently not. I would post some names, but they have apparently 'sanitized' the net of any reference as best I can tell, so my SWAG is this was the 'last straw' for him: http://quarter-wave.com/

Nowadays most folks use these:

Transmission Line

Download - Akabak

Others use Hornresp, but it can't do two offset 'drivers' [driver and vent], but fine otherwise.

To do 'foolproof' alignments without using any of the above, MJK still offers a design routine and another DIYer's Excel worksheet to do all its math if you prefer, then load it into one [or more] of the other programs to view its performance:

http://www.quarter-wave.com/TLs/Alignment_Tables.pdf

http://www.quarter-wave.com/TLs/Alignment_Tables_Calculator_3_3_09.xls

DIYer soho54's Excel worksheet is a more expansive one that encompasses other alignments such as tapped variants:

Eazy Horn Spreadsheet for Dum... Everyone - Home Theater Forum and Systems - HomeTheaterShack.com

GM

- - - Updated - - -

As I recalled way back then, even the selection criteria for an ideal TL suitable driver was debatable (may be it still is)

My interest in TL and now MLTL was renewed last Oct at the RMAF when I heard and was impressed by GPA 604s in a MLTL cabinet. I never heard 604 bass that sounded this good and open. I m not sure if others in this site heard the same.

It was well defined by the pioneers of audio as proven by their reactance annulled BLH alignments, though only published in the form of 'those practiced in the art' to use patent lingo . AFAIK, the reason they didn't bother to build/mass market simple TLs was due to their prime performance goal being the need for very high efficiency.

FWIW, technically, this is a flawed MLTL in that its vent is located per traditional reflex design dogma of keeping the vent acoustically very near the driver to maximize pass-band efficiency, which in turn creates a notch in a MLTL's mid-bass or lower mids BW depending on Fb[Fp] due to the extra eigenmode [reflection] between the bottom of the cab and vent as the trade-off for its increased 'bump' at Fb[Fp], but have never actually compared this alignment to one of my super smooth, etc., MLTLs; so for all I know, most folks might prefer its ~ Altec 'West Coast Sound' to mine's more 'HIFI' presentation.

GM

[juniper]

Google Martin J King as he has one of the most comprehensive websites on the topic and sells his software to people interested in designing TLs.

I have not been interested in TLs for a long long time, when as GM mentioned, TLs were based on tuning the line based on driver Fs and Sd. As I recalled way back then, even the selection criteria for an ideal TL suitable driver was debatable (may be it still is )

My interest in TL and now MLTL was renewed last Oct at the RMAF when I heard and was impressed by GPA 604s in a MLTL cabinet. I never heard 604 bass that sounded this good and open. I m not sure if others in this site heard the same.

Kwingy, 604's can be awesome with the right eq, and source material.. I prefer them on some recordings to my Jubs. I have a gentleman who builds my cables who has worked at, or built many a studio in CA and around the world. He has also done home studios for some of the greats, he says that some execs within the business build whole rooms around the 604 to this day. He says they cost around 70 to 100K and he has heard nothing like them...

[Altec Best]

kwingylee noted, MJK's work is the best, though sadly he no longer offers his MathCad worksheets due to way too many folks illegally using them for profit venture with the most 'hits'/DLs on his site from large manufacturers who should already know all that's necessary for proper TL/horn design as well as have the software to quickly design them, but apparently not.

I have Mathcad Explorer 8.. I got a copy from Martin when i joined his quarter-wave yahoo group couple years ago..But darn if i understand it Lol..