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View Full Version : ALTEC A7 VOTT first timer build queries!!



oldbrowndog
06-23-2014, 12:55 AM
HI All, Im located in australia where we cant just hoover up Altec parts at garage sales so im doing a build fro scratch with parts i had to ship in from the states.. So it better be good!

Thanks in advance for all information i hope you provide..

So.. I am at the beginning of a build of some A7 cabinets to house the following Altec components


416 -16z speakers
806a compression driver
811B horns
Custom built N-800F crossovers (not yet made)
I am using the enclosure build plans listed in the bottom left corner at this link:
http://www.lansingheritage.org/html/altec/plans/1968-plans.htm


I am very interested to know 2 things..
1. How to achieve low frequencies (30hz) with the 416-16z in the cabinet.
2. Whether to add a bullet tweeter to the design for highs.


LOW FREQUENCIES
As i understand it with some modifications to the crossover & some to the size of the port it is possible to get 30hz frequencies out of the A7..
Can someone please explain what these modifications & any other necessary ones might be?


BULLET TWEETER
I had planned to have some N-800F schematic based crossovers built by a local speaker guru to suit the 16 ohm setup of woofer & tweeter..


My query is regarding the possible addition of a bullet tweeter to the A7 design to cover those really high sibilant frequencies & leave the 811 horn for the mids & highmids.. This would obviously require a different crossover design & a place to locate the tweeter physically so I ask:


a) how might the addition of a bullet tweeter (from a similar era) affect the overall efficiency of the design? Efficiency is paramount for me as i plan to use a valve amp to drive these babies.

b) which bullet tweeter might best suit the components I already have, I assume it also needs to be 16ohm to suit those components..?
Perhaps a pair of these JBL 075 16 ohm bullet tweeter?

c) Please see one of the attached sketched image for my idea as to where to place the bullet tweeter.. I think as close to the top centre of the 811 horn as possible is important? & I will not attach it to the top of the box until i have aligned it with the woofer & horn below..

d) is it a good idea to add the bullet, or do i not need to do it..? Id prefer to plan for it in advance rather than have to build a separate crossover later to add a bullet tweeter if i don’t do it in the beginning..

Thanks again happy to be on the journey..
62485

Lee in Montreal
06-25-2014, 06:33 PM
Your goal to get 30Hz out of an A7 will be a challenge. But an interesting one nonetheless.

You will need to build a much stiffer cabinet than originally and you will also want to increase the cabinet's volume. Consider this new cabinet as a bass reflex cabinet and calculate your volume, response and port as such. As for crossover, I wouldnt be shy to start with an active digital crossover with which you can test some good filtering. Once you have found the proper curves, then you can build a passive filter if it is what you want.

Or maybe you should simply build a pair of stock A7 and build a subwoofer in the middle ;-)

oldbrowndog
06-26-2014, 09:16 AM
Hi & thanks for your reply Lee, i have an older thread you posted in here
http://www.audioheritage.org/vbulletin/showthread.php?30915-Altec-voix-du-Theatre-A7-A5-anybody-done-this

& from what i can tell, particularly from what another forum user (altec best) mentions about the idea of changing the port size & crossover it is actually possible to get close to those 30hz frequencies out of the A7 cabinet. I agree stronger bracing is needed but I'd like to see evidence of a port design & crossover settings that might help me achieve this with the (already quite large) A7 cab....

heres a copy & paste from his post


Yes due to the port being too big.In Movie Theaters that was fine.With a few tweaks you can get the A-7 down near the 30-35 Hz range with a pair of 416's in them.If your running 515's you can still get them lower but not as much.There is a thread at the Altec userboard that Panomaniac started.He made several tweaks to the crossovers & box and got his down a lot lower.For one the port is too big to acheive a lower tuning.His thread is " My A7-500s. A journey " , if you can get the A-7 down near 30-35 Hz no sub will be needed IMHO ! There isn't much music below that (30HZ) anyway except for the occasional pipe organ notes and stuff like that. ;)

Smaller ports and adding length of 3" to those ports a long with XO tweaks will acheive a lower tuning is what he did IIRC



all that quite apart from my tweeter questions.. hehe..

Lee in Montreal
06-26-2014, 09:57 AM
... I'd like to see evidence of a port design & crossover settings that might help me achieve this with the (already quite large) A7 cab.... Well, you can use any simulation software and calculate the response based on cabinet volume and port dimension. Modify according to your tastes.

Altec Best
06-28-2014, 02:11 PM
The A7 is really a midbass horn 50 Hz..Getting it down to 30 HZ will be impossible IMHO.. You can get it down to maybe 37-42 HZ if your lucky.. You will need to stiffen up the box and make the port a lot smaller.Cut the port in half will help some.I sent you a PM.

You might want to read this thread..

http://www.hostboard.com/forums/f700/169115-my-a7-500s-journey.html

Lee in Montreal
06-30-2014, 02:14 PM
Any bass reflex cabinet can reach 30Hz. It all depends on size and port tuning. The original A7 was meant to be efficient. It offered a lot of midbass to match the low mids from the horn. That was the package. That being said, the cabinet can be remodelled and the big lower port reduced to a simple bass reflex port. But it will not sound anymore like an A7. The mid bass will be gone and the lower mid might become too prevalent. But now that active electronics can be used to reshape the output, I dont see why it cannot work. It will simply not be an A7 anymore.

Two years ago, I heard some Delta blues on a simple two-way A7 with a tube amp. No highs, no deep low. Who cared, as it sounded fantastic and lively for that type of music. So, my take is to make the lower front panel removable and tuneable.

rlsound
07-01-2014, 02:31 PM
Adding wings to the A7 might take it down a few cycles. Sure works well with the A4. :)

Lee in Montreal
07-01-2014, 02:42 PM
Adding wings to the A7 might take it down a few cycles. Sure works well with the A4. :) I am sure it works. On the horn section. The perimeter of the horn is half-wave of the cut-off frequency (or is that 1/4 wave).

rlsound
07-01-2014, 02:50 PM
I am sure it works. On the horn section. The perimeter of the horn is half-wave of the cut-off frequency (or is that 1/4 wave).

Wings are generally 1/4 wave.

oldbrowndog
07-03-2014, 06:53 PM
Adding wings to the A7 might take it down a few cycles. Sure works well with the A4. :)

what exactly are wings please?

Lee in Montreal
07-03-2014, 08:28 PM
what exactly are wings please?

No wings

http://xn--h6q16acwi80al42do4m.com/wp-content/uploads/2012/10/d_lucky_410jp-img600x453-1350010879iajjst72553.jpg

Wings. Great for the horn loaded part of the speaker. No impact on bass.

http://www.hifido.co.jp/photo/09/334/33455/a.jpg

Winged A7

http://www.melaudia.net/zfoto/RDS05/IMG_1155-640x426.JPG

http://pds.exblog.jp/pds/1/201001/19/71/f0198871_213185.jpg

Lee in Montreal
07-05-2014, 07:18 PM
My query is regarding the possible addition of a bullet tweeter to the A7 design to cover those really high sibilant frequencies & leave the 811 horn for the mids & highmids.. This would obviously require a different crossover design & a place to locate the tweeter physically so I ask: ]

If the bullet tweeter you have in mind is JBL's 2402, you will be disapointed. It cuts out at 14/15KHz and is nowhere are sizzling as the 2405 which reaches 20KHz

A7-Vott
11-30-2015, 05:14 AM
My A7 ownership spans 36 years and I have some knowledge of these. Before going wth Sub Woofers and tweeters etc .... my findings are to the contrary so to discuss these and their various components is long winded so its probably easier to find me by phone .... 0428 242024

James

NickH
11-30-2015, 01:02 PM
No wings

http://xn--h6q16acwi80al42do4m.com/wp-content/uploads/2012/10/d_lucky_410jp-img600x453-1350010879iajjst72553.jpg

Wings. Great for the horn loaded part of the speaker. No impact on bass.



Winged A7




Now Lee I've alway heard the exact opposite, that wings are there specifically to help bass response.


I spent a year with my a7's. I changed the port tuning. I used a rectangular port 2" tall and I think 9" or 10" wide and 1 1/2" deep. I believe the port was tuned to 30hz. I did double the thickness of the cabinet walls to 1.5" and braced the inside. It could also benefit from a decrease in volume. If you can fill the insides horn flares.

I was using GPA 416-8b drivers in mine. I eventually moved on to a different speakers. The drop in output from where the horn left off to where the bag reflex took over drove me nuts. If I were to do it again I would have kept the normal altec tuning and ran a really good sub.


Nick