Converting A7 cabinets into MLTL

[Phil-G]

Altec recommends a 4.5 - 8 cubic foot sealed airtight enclosure for them... I would try that first.

there's a bit of room between 4.5 and 8. i tried 5 to start. it was ok but the 420s really liked it.

[bowtie427ss]

Why a flop? The [only] pair I messed with were fine for years after till they moved. Must have been a !@#$%^ to install though.

GM

There used to be a fairly lengthy post on this forum from i think a former Altec employee that explained how the cloth roll was not strong/stable enough to support the vertical force of the cone weight. Eventually, it allows the cone to sag and "trains" the damper into misalignment.

There are not as many photos on the net as their used to be. The majority of 411's with the old style surrounds used to show the tell tale creases in the 3 and 9 o'clock positions.

It might also have been Steve at GPA who enlightened me to watching for the creasing in the surround, and suggesting that many will require more than just a new surround to stop them rubbing and restore alignment. It's been a while(years), and i am not an archivist, my bad. But, this is why unless they go real cheap(like the ones above), i don't give wet edge 411's a second look.

[kwingylee]

alteca7a cemetary marker.jpg

The guy was probably telling you the truth as the HF drivers also in the picture look like 808-8A Symbiotiks.I should have posted this photo as well which is in the Altec is Now catalog.The Altec employee is doping the surround it looks like with some kind of glue.On the original 411's.

Congrats on the 411's.. I liked the 411's, they have some massive magnets on them don't they ?

The magnets are huge, remind me of the 421-8Hs that I also have. Are these Alnico magnets? In general, I am impress with the workmanship. They look very robust.
The reason I didnt buy the HF drivers is I already have a set of 808-8A symbiotiks. Different story if they were 802-8Gs....
and I dont need anymore 511B horns.

Any of you have the schematics for the N500C crossovers? and what are the differences between the C and the other varieties such as the G and Fs...

Including a sad/funny photo... hope we dont end up like this ...

[GM]

The majority of 411's with the old style surrounds used to show the tell tale creases in the 3 and 9 o'clock positions.

Interesting! Learn something new everyday! 'Mine' arrived pre-creased at more than 3-9 oclock, it looked downright wrinkled pretty much all the way around and assumed it was a new concept, but between a very stiff spider and powerful motor they had no trouble absorbing the amp's up to 225 W peaks [or whatever tripped its clip limiting ckt., but then maybe if used with a 500 Hz Vs 120 Hz XO it may have sounded a little distorted from the get-go since down low was pretty much uncharted territory; just know that feeding them pink noise right out of the box while propped up in the corners of my couch they sounded fine to us.

Another thing was that I was so used to regularly rotating gooped surround drivers that it de facto was included, so may have helped them to 'live' longer. Sometimes ignorance is bliss.

GM

[bowtie427ss]

Interesting! Learn something new everyday! 'Mine' arrived pre-creased at more than 3-9 oclock, it looked downright wrinkled pretty much all the way around and assumed it was a new concept, but between a very stiff spider and powerful motor they had no trouble absorbing the amp's up to 225 W peaks [or whatever tripped its clip limiting ckt., but then maybe if used with a 500 Hz Vs 120 Hz XO it may have sounded a little distorted from the get-go since down low was pretty much uncharted territory; just know that feeding them pink noise right out of the box while propped up in the corners of my couch they sounded fine to us.

Another thing was that I was so used to regularly rotating gooped surround drivers that it de facto was included, so may have helped them to 'live' longer. Sometimes ignorance is bliss.

GM

I'm thinking that environment(long term) HAS to also have an impact. There are some well preserved examples still out there, pair of Barcelonas on ebay right now with perfect looking wet surrounds.

The other problem for me is that the few that show up in these parts in working condition will have three generations of cat hair and other various debris embedded in the goop.

[GM]

Yeah, the downside, especially down here in the Deep South if you can't afford the high cost of AC ~8 mos/yr and dehumidifiers the rest of the time. Make great mosquito traps though.

Totally off topic; this was posted on another forum and never heard of such a thing, but never have bothered to learn much about driver assembly, so wondered. For sure, these drivers are so 'sharp' sounding that it doesn't seem likely: "Doesn't the 421 have silicone damping fluid around the dust cap to cone joint? Or is it just on the mid and bass surrounds?"

GM

[kwingylee]

[QUOTE=GM;1962177]You're welcome!

GM

Hi GM, I am going through the links, I am going to forego the ones that suggests adding 411-8A into a divided 828 cabinet for a subwoofer for now.

Instead, I want to focus on the various MLTL cabinets you designed for westend9, pano's A7-500 adventure, marshall's cabinets, marty's and so forth. These cabinets range from 10-16 cubic feet and designed around the 416B.

Will there be a big difference for the 515-8G? Assuming I use the 828 with an internal volume of 13^3, the main difference would be the port size? and the length of the line? Is there such a design available? Can you do one if not?

Also, in a previous post you mentioned the 828 is already a MLTL, I assume I will have to partition the cabinet in such a way as to obtain the line length, and then the line exit size will have to be adjusted. How would the partition be done If the cabinet needs to be divided in 1/2 like westend9's?
I would think that the 828 would be more easily adaptable to a traditional line?

Finally, in pano's A7-500 case, where there is a huge hump centered around 200Hz, if I understand correctly, that is strictly caused by the short horn? and can be ameliorated by the addition of wings (no way in my case) or active EQ'ed (very likely in my case) or a line line filter with a hi Q centered around 200 Hz (maybe)? So I would have this problem regardless of woofer type?

Thanks

Kwing

[valhallax]

[QUOTE=kwingylee;1962281]

You're welcome!

GM

Hi GM, I am going through the links, I am going to forego the ones that suggests adding 411-8A into a divided 828 cabinet for a subwoofer for now.

Instead, I want to focus on the various MLTL cabinets you designed for westend9, pano's A7-500 adventure, marshall's cabinets, marty's and so forth. These cabinets range from 10-16 cubic feet and designed around the 416B.

Will there be a big difference for the 515-8G? Assuming I use the 828 with an internal volume of 13^3, the main difference would be the port size? and the length of the line? Is there such a design available? Can you do one if not?

Also, in a previous post you mentioned the 828 is already a MLTL, I assume I will have to partition the cabinet in such a way as to obtain the line length, and then the line exit size will have to be adjusted. How would the partition be done If the cabinet needs to be divided in 1/2 like westend9's?
I would think that the 828 would be more easily adaptable to a traditional line?

Finally, in pano's A7-500 case, where there is a huge hump centered around 200Hz, if I understand correctly, that is strictly caused by the short horn? and can be ameliorated by the addition of wings (no way in my case) or active EQ'ed (very likely in my case) or a line line filter with a hi Q centered around 200 Hz (maybe)? So I would have this problem regardless of woofer type?

Thanks

Kwing

if I went to a engineer and asked these questions, I would glady offer a few hundred dollars for the answers.

[kwingylee]

[QUOTE=valhallax;1962290]

if I went to a engineer and asked these questions, I would glady offer a few hundred dollars for the answers.

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?

[GM]

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