Getting up to speed...
Hey all,
Read the rest of the thread...sorry about the duplications.
Panomaniac - Nice work on the Parisian Altecs. The pair I heard a few years ago had been carefully copied from the old plans but with beefed custom cabs, and then loaded with Altec 515s. A nice system with round wood horns for the mids/highs, twin 15s/side for low bass.
Cal - Good to hear that you are still hanging on to the vintage stuff.
Since summer's about here you'll be getting those out for the block party any day now, right? Still have the big VOTT cabs?
Bear - What woofer are you planning to substitute? I seem to recall an overall usable box volume of 7.5 or 8 cf. Sound about right? Unless he's in a desperate need to cash out the Altecs, I'd be tempted to try something like the Altecs used on the midbass horn in a sealed rear chamber, and a true bass unit added to the box for low bass run up to 60 - 80 Hz or so. Electronic crossover for the low to midbass xover, passive for the midbass to HF horn cross. More complexity, but might be worth the grief. I like the sound of the Altec midbass, although I've heard and used vintage JBL and EV, also horn loaded (80 Hz horn) to good effect.
Tim
Hey all,
Read the rest of the thread...sorry about the duplications.
Panomaniac - Nice work on the Parisian Altecs. The pair I heard a few years ago had been carefully copied from the old plans but with beefed custom cabs, and then loaded with Altec 515s. A nice system with round wood horns for the mids/highs, twin 15s/side for low bass.
Cal - Good to hear that you are still hanging on to the vintage stuff.
Since summer's about here you'll be getting those out for the block party any day now, right? Still have the big VOTT cabs?
Bear - What woofer are you planning to substitute? I seem to recall an overall usable box volume of 7.5 or 8 cf. Sound about right? Unless he's in a desperate need to cash out the Altecs, I'd be tempted to try something like the Altecs used on the midbass horn in a sealed rear chamber, and a true bass unit added to the box for low bass run up to 60 - 80 Hz or so. Electronic crossover for the low to midbass xover, passive for the midbass to HF horn cross. More complexity, but might be worth the grief. I like the sound of the Altec midbass, although I've heard and used vintage JBL and EV, also horn loaded (80 Hz horn) to good effect.
Tim
Lemme see... in no particular order.
Durham's wood putty is good stuff, but has some flaws, it like to crack and not stick in some situations. So, I'm not going to use it for stiffening the back of the thin plywood horn surfaces.
Pick-up bed liner - yeah, it is made in different formulations. There is a DIY version in the auto parts stores - two part I think. But again, there is the cost vs. benefit vs. grief/time thing. I'm looking for fast, simple, no-brainer.
The "bendable plywood" laid up - sure, but bendable ply ain't cheap, and it isn't that easy to find in the big box stores. Once could lay in "formica" too, for that matter - but again, messy to cut and ain't cheap either. If I had scrap of that, I'd use it in a second. Then damp the outer after say two/three layers.
Tim, yep, I thought about just that solution. But I didn't go that way here for two reasons:
- added expense for another driver
- won't get the same sensitivity in the bass end (if you can get it to go low, it won't be a high efficiency driver)
- the need for an extra amplifier
Ok three reasons.
But the idea does have merit.
Marche, I asked about the freq response because my nearfield measurements of the stock cabs w/Altecs loaded in was far worse than what you ended up with.
I am praying that after all this work, they will measure closer to "ideal" and not ratty like they did stock!!
Evenharmonics, yes the stock A-7 probably does not make 40Hz., it tails off around 50 with almost all of the available Altec drivers. There is one, iirc, that is an exception, and makes it all the way to 42Hz., iirc. But, that is because the goal is/was output level and to get as close to the horn in output as possible, not bass extension. They were PA cabinets.
The driver I'm using has somewhat less sensitivity than does the Altec drivers typically used in the A-7, but more than the typical "sub woofer" driver.
The specs are:
Fs = 20Hz.
Qts = .25
VAS = 16ft3
This gets you to -3dB @3Ohz.
If anyone cansuggest other suitable drivers, I'm interested in suggestions on that topic. Keep in mind the requirement is that it get as far below 40Hz. as possible and still have reasonably high 1w/1m SPL... For example, none of the TAD drivers will do it.
We'll see what really happens, maybe later today when I get the driver throat/mount assembly constructed and the thing gets tested.
_-_-bear
Durham's wood putty is good stuff, but has some flaws, it like to crack and not stick in some situations. So, I'm not going to use it for stiffening the back of the thin plywood horn surfaces.
Pick-up bed liner - yeah, it is made in different formulations. There is a DIY version in the auto parts stores - two part I think. But again, there is the cost vs. benefit vs. grief/time thing. I'm looking for fast, simple, no-brainer.
The "bendable plywood" laid up - sure, but bendable ply ain't cheap, and it isn't that easy to find in the big box stores. Once could lay in "formica" too, for that matter - but again, messy to cut and ain't cheap either. If I had scrap of that, I'd use it in a second. Then damp the outer after say two/three layers.
Tim, yep, I thought about just that solution. But I didn't go that way here for two reasons:
- added expense for another driver
- won't get the same sensitivity in the bass end (if you can get it to go low, it won't be a high efficiency driver)
- the need for an extra amplifier
Ok three reasons.
But the idea does have merit.
Marche, I asked about the freq response because my nearfield measurements of the stock cabs w/Altecs loaded in was far worse than what you ended up with.
I am praying that after all this work, they will measure closer to "ideal" and not ratty like they did stock!!
Evenharmonics, yes the stock A-7 probably does not make 40Hz., it tails off around 50 with almost all of the available Altec drivers. There is one, iirc, that is an exception, and makes it all the way to 42Hz., iirc. But, that is because the goal is/was output level and to get as close to the horn in output as possible, not bass extension. They were PA cabinets.
The driver I'm using has somewhat less sensitivity than does the Altec drivers typically used in the A-7, but more than the typical "sub woofer" driver.
The specs are:
Fs = 20Hz.
Qts = .25
VAS = 16ft3
This gets you to -3dB @3Ohz.
If anyone cansuggest other suitable drivers, I'm interested in suggestions on that topic. Keep in mind the requirement is that it get as far below 40Hz. as possible and still have reasonably high 1w/1m SPL... For example, none of the TAD drivers will do it.
We'll see what really happens, maybe later today when I get the driver throat/mount assembly constructed and the thing gets tested.
_-_-bear
Altec 416-8B is a safe bet.
http://www.lansingheritage.org/html/altec/specs/components/416-8b.htm They are often listed on ebay.
As for A-7 enclosure, as far as I know, the rectangular port opening at the front is designed for 40 Hz. Unless someone had a satisfactory audition of it playing below 40 Hz, I'm not sure if it would work well.
http://www.lansingheritage.org/html/altec/specs/components/416-8b.htm They are often listed on ebay.
As for A-7 enclosure, as far as I know, the rectangular port opening at the front is designed for 40 Hz. Unless someone had a satisfactory audition of it playing below 40 Hz, I'm not sure if it would work well.
Well actually, afaik it doesn't quite cut the mustard.
Assuming you get one that meets factory specs, ur a whopping 11dB down at 30Hz., and minus 3db at 42Hz. starting to roll at ~60Hz, and that is assuming you get a full 7.9cuft out of the cabinet (you won't).
If you take the cabinet as 6.5cu ft (closer to the real world usable volume, imho) then it hits -3dB @46Hz., and that in my view is the problem with the A-7 in a nutshell.
And, no, the stock "port" isn't tuned to much of anything at all. I'm presuming that everyone knows that you have to check the real T/S parameters of the driver, run the simulations, and then actually iterate the tuning of new ports until you get a reasonable result.
So, the short version of my modification is that I want usable output down to ~30Hz. which I am willing to trade for 3-6dB of sensitivity, given that using a high power amp for the bottom end in this home application is not an issue.
_-_-bear
Assuming you get one that meets factory specs, ur a whopping 11dB down at 30Hz., and minus 3db at 42Hz. starting to roll at ~60Hz, and that is assuming you get a full 7.9cuft out of the cabinet (you won't).
If you take the cabinet as 6.5cu ft (closer to the real world usable volume, imho) then it hits -3dB @46Hz., and that in my view is the problem with the A-7 in a nutshell.
And, no, the stock "port" isn't tuned to much of anything at all. I'm presuming that everyone knows that you have to check the real T/S parameters of the driver, run the simulations, and then actually iterate the tuning of new ports until you get a reasonable result.
So, the short version of my modification is that I want usable output down to ~30Hz. which I am willing to trade for 3-6dB of sensitivity, given that using a high power amp for the bottom end in this home application is not an issue.
_-_-bear
Preliminary Listening Report
Preliminary Listening Report!
Good!
Maybe even very good!
The rear panel isn't exactly solid on yet, since once on it won't come off due to the Mortite putty for sealing will hold it on very well once squished fully by the screws.
I have decided to build in "screw jacks" on the panels so that the panels can be pulled without screwdrivering the cabinet in futile attempts to get them off... insert 1/4-20 (US Coarse thread) bolts and tighten, it pushes the panel up and out...
Anyhow, the thing goes low now. Thank goodness!
After a minor adjustment to the secondary rolloff on the xover for this driver, it sounds very very nice indeed.
Measurements indicate the -3dB point with (gasp) 4 x 4"dia x 16"long ports to be smack dab on the predicted 30Hz. point.
The response seems nicely smooth, +/-3dB from 30Hz. up to the tarket freq of ~275Hz. whereupon it dives like a stone, as it should due to the very extreme xover slope.
Stanley Clarke sounds very articulate and solid. Warm without being heavy or thick. So far nothing has sounded bad or problematic. Which is a great relief actually. Drums sound fast and dynamic.
And, the cabinet panels are not fully screwed in and sealed, the ports are friction fit, some absorptive material is yet to be installed (about 10% worth), the flares are not yet stiffened and damped, and technically speaking the throat adapter plate is not sealed to the mounting surface either (although it is a dead flat fit now).
For the stiffening, after much thought and staring at the inside of the flares, I decided that the way to go was cast-in-place stiffening, which then gets glued in place, the edges finished after gluing with more cast-in-place compound. I went with a 4:1 mix of sand to "floor leveling" compound (which is a hard gypsum material I believe), water mix. Dries hard as a rock. Stiffness is my main criteria on these thin plywood flares. After they are stiff, damping is simple, if needed. I want the bass energy going out the port and out the front, not modulating the walls of anything, or leaking out gaps.
The foam surrounds on these woofers have been doped with professional compound made for foam. I may have some available... fyi. Check my website soon, or email me.
So I can safely expect only improvement. <sigh of relief>
This is a night & day change from the stock unit.
The client will be happy...
pix of the saga will come soon on my website... fyi.
_-_-bear
Preliminary Listening Report!
Good!
Maybe even very good!
The rear panel isn't exactly solid on yet, since once on it won't come off due to the Mortite putty for sealing will hold it on very well once squished fully by the screws.
I have decided to build in "screw jacks" on the panels so that the panels can be pulled without screwdrivering the cabinet in futile attempts to get them off... insert 1/4-20 (US Coarse thread) bolts and tighten, it pushes the panel up and out...
Anyhow, the thing goes low now. Thank goodness!
After a minor adjustment to the secondary rolloff on the xover for this driver, it sounds very very nice indeed.
Measurements indicate the -3dB point with (gasp) 4 x 4"dia x 16"long ports to be smack dab on the predicted 30Hz. point.
The response seems nicely smooth, +/-3dB from 30Hz. up to the tarket freq of ~275Hz. whereupon it dives like a stone, as it should due to the very extreme xover slope.
Stanley Clarke sounds very articulate and solid. Warm without being heavy or thick. So far nothing has sounded bad or problematic. Which is a great relief actually. Drums sound fast and dynamic.
And, the cabinet panels are not fully screwed in and sealed, the ports are friction fit, some absorptive material is yet to be installed (about 10% worth), the flares are not yet stiffened and damped, and technically speaking the throat adapter plate is not sealed to the mounting surface either (although it is a dead flat fit now).
For the stiffening, after much thought and staring at the inside of the flares, I decided that the way to go was cast-in-place stiffening, which then gets glued in place, the edges finished after gluing with more cast-in-place compound. I went with a 4:1 mix of sand to "floor leveling" compound (which is a hard gypsum material I believe), water mix. Dries hard as a rock. Stiffness is my main criteria on these thin plywood flares. After they are stiff, damping is simple, if needed. I want the bass energy going out the port and out the front, not modulating the walls of anything, or leaking out gaps.
The foam surrounds on these woofers have been doped with professional compound made for foam. I may have some available... fyi. Check my website soon, or email me.
So I can safely expect only improvement. <sigh of relief>
This is a night & day change from the stock unit.
The client will be happy...
pix of the saga will come soon on my website... fyi.
_-_-bear
Several years ago I had new 825s built by a pal who is a cabinetmaker. They were built with high grade 3/4" plywood with extra bracing for solidity.
They were built with substantial braces between the horn flares and the sidewalls.
They were loaded with 515B woofers. I never worrried about bass response because I valued VOTs for their reproduction of 100-10,000hz, below 100hz i simply augmented them with a pair of JBL Pro bassbins.
In my experience the 511 horns are amply damped by application of non-hardening modeling clay to the lips.
They were built with substantial braces between the horn flares and the sidewalls.
They were loaded with 515B woofers. I never worrried about bass response because I valued VOTs for their reproduction of 100-10,000hz, below 100hz i simply augmented them with a pair of JBL Pro bassbins.
In my experience the 511 horns are amply damped by application of non-hardening modeling clay to the lips.
Attachments
Evenharmonics said:
Even----That's a 550hz horn. But with tractri you should crossover higher than the theoretical cutoff so I did 700hz.
The horn with the 2420s had even response and with it's narrowing dispersion with increasing frequency had pretty extended highs, measured flat out to 16khz as I recall.
They can be quite natural sounding horns, depending on the things that must be depended on.
Fun times in Canadaland!
Some people think those are the best sounding horns Altec ever made. I love the 1505s and got to hear the 1803 only a couple of times. Was very impressed.
So you already have the 288s, or are they coming with?
It would be great fun to try other drivers on those horns. The 1808s will not be the limiting factor, the driver will. Could be very informative. I may want to come up to Canada and play in your garage some day. Some summer day.
Some people think those are the best sounding horns Altec ever made. I love the 1505s and got to hear the 1803 only a couple of times. Was very impressed.
So you already have the 288s, or are they coming with?
It would be great fun to try other drivers on those horns. The 1808s will not be the limiting factor, the driver will. Could be very informative. I may want to come up to Canada and play in your garage some day. Some summer day.
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