ALTEC Model 15 Project - Now with JBL and Fostex parts!.

[mhardy6647]

There beautiful - (as only an Altec fan could say unironically)

Are those CD cabinets behind them? Whatever they are -- I really like them!

 

[hjames]

There beautiful - (as only an Altec fan could say unironically)
Are those CD cabinets behind them? Whatever they are -- I really like them!

Yes - they are shipped flat snap-pack cardboard CD cases. I used to have the CDs just lined up across the shelves (IKEA Bondi in Beech finish),
but after a while I ran out of shelf space and there was a lot of space behind the front row. So I got a few of these and played with them, liked them and bought more,
and eventually had all the shelves filled with them. I shot one box so you'd have an idea of the versatility
The trick is to be sure there is expansion room in each box for future buys. I think the boxes were about $3.50 each.



Okay, back-filling the thread. The JBL woofers were a REAL TIGHT FIT in the routed holes on the Altec Cabinets - The didn't quite drop into the holes, even with some hand sanding. Then it hit me - I have a dremel tool I got a few years back, don't use it often but it did come with some coarse sandpaper cylinders! Dug it out of the basement and made some passes around the edges of the routed spaces - made some nice sawdust in the process - and - now the JBLs drop all the way down in the routed area - tightly, but they do settle down nicely!

 

[mhardy6647]

Hey look, a Frankenaltec thread! There oughta be a forum for that...

I'm diggin' the funky new avatar there, @mhardy6647

Thanks! It's -- exciting.

 

[hjames]

Okay, Christmas package came in today - Altec plastic 32 horns and Model 15 crossovers ...
Found out you can't install the bent horns with the 908-8A drivers mounted (!)

Pulled the JBL 2214 woofers for an access hole - Assembled the horns on the baffle board.
Pulled out the soldering iron 'cause I was using heavier gauge wire - soldered the new wires into the crossovers.
Did the cabinets one at a time. First one sounded pretty good - on to cabinet #2 ...

Played some tunes (Jolida tube amp)
Its a bit shrill - I may have to pad the Altec horns down for a bit -
I expect the JBL woofers are less efficient than the original ALTEC woofers -
but I had figured the JBLs would be a temporary compromise until I could afford the (proper) Altec woofers ...

Yeah, its messy - I still have tools out - but the music is playing - more fun later!

 

[LoStrings]

You can take the horns out with the drivers attached. I have a pair of 15's that I had to change a diaphragm on, and when pulling out the horn, there is a cutout in the middle of the horn opening for the driver to fit thru with the horn.

 

[mhardy6647]

Found out you can't install the bent horns with the drivers mounted (!)

Heh, it's like a ship in a bottle!

but, in all other respects...
Congratulations!

 

[hjames]

You can take the horns out with the drivers attached. I have a pair of 15's that I had to change a diaphragm on, and when pulling out the horn, there is a cutout in the middle of the horn opening for the driver to fit thru with the horn.

I saw those notches, but I'm using the 908-8A drivers I got from ictwoody - they apparently fit differently ...

But ... In A Silent Way sounds Great!

Hilliard Ensemble is a bit harsh ...
Who's Next has its moments ...

 

[LoStrings]

I saw those notches, but I'm using the 908-8A drivers I got from ictwoody - they apparently fit differently ...

But ... In A Silent Way sounds Great!

Got it...different drivers.

 

[hjames]

Pulled the 908-8A drivers saturday, opened them up and had a look (took pix). Thick felt pad in the end caps, no internal plastic cap like some drivers have.
So in summary - the system has stock Model 15 crossovers and (plastic) 32 horns, the nonstock 908-8A horn drivers and JBL 2214 woofers (both 8 ohm drivers).

I got this schematic from the Lansing forum - it does show typical LR values of the two drivers in the circled areas on the schematic -
but if you ignore that, I traced the schematic and confirmed that is the components and values of the crossovers in my speakers.
Note the woofer runs full-bandwidth, and is not low-passed in any way.

I'm off for the MLK holiday today, so I planned to do a view of system response. I loaded the $5 Octave RTA app to my phone and played with it last week,
so I loaded it to my wife's iPad today, put that in a tripod mount I got for it last year, and played a Delos test tones record with stereo pink noise.
Yes, the room is not empty, yes, I should clear more space here - but we live here - its not a display space.

Anyway, the display charts height is dbfs and shows levels in 6dB blocks.
Vertical axis is freq 20-20k, tho it rolls off on both ends, the bass roll isn't bad,
tho you can see the highs rolloff from 8k, ...

 

[Goodwill_HiFi]

You have trees indoors!

 

[gdmoore28]

Looking good, Heather.

I'm thinking that you should be able to dial out the "shrill" qualities of those drivers by dialing back on the mid frequency control. Did you experiment with it? If needed, you can modify the mid control elements to cut even more in those frequencies, because that is typically where the objectionable harshness tends to originate. (Hopefully Tom, Mark and the other Altectistas will make up for my ignorance here.)

And you are certainly right on the need to attenuate the HF driver. In my Altec build, it became readily apparent that the horn needed attenuation - which I accomplished with a simple L-pad inserted after the crossover network. Once the mids were tamed and the overall level issues were dealt with - bringing the horn's output in line with the woofer - the magic I'd hoped for happened.

GeeDeeEmm

From the Amazing Interweb: Altec Model 15 crossovers.

 

[hjames]

Yep - my Model 15 crossovers I bought from GaryL look pretty much just like those!

I did have the HF level at 9 o'clock, and the MF level at 12 o'clock - but
I set them both to the midpoint (12 o'clock position) before I did the RTA tests today.

I'm planning to swap out the stock caps with more audio- supportive cap-arrays ... in a stock config at first, and experiment with the circuits afterwards

You have trees indoors!

Why yes - it is a Norfolk pine we got 20 years ago - was a little Charlie Brown christmas in a small pot, live -
and since we're too far north for it to live outdoors ... well, there is is.The Corn plant on the left was much the same.
We took it over at maybe 4 foot tall when a church member died - and- with the cathedral ceiling, and three sky lights,
its grown to maybe 17 foot tall there by the stairs. The Banana trees by the windows go outside in the warm months,
and come in around October. We also have a rosemary bush thats just nice when we want some herbs for cooking ...
We try to manage them, and they give us oxygen!
Dunno if they like the music ...?

 

[hjames]

One of the audio gurus I've been following shared this tip with me, and it actually made a real difference improving the sound.
While I had the horn drivers out, I drilled 2 relief holes in the rear caps. (!)

These drivers are the 908-8As i got from ictwoody - they already had nice felt packing to reduce ringing within the back cavity,
apparently a customizing trick he said a previous owner had done. So I opened them and drilled 2 1/8 inch holes through the back cap.
Blew out the aluminum shards and scrap, reassembled them, and - shaZAM!
Great improvements with sibilance, and similar shrillness from certain sounds.
(I figured if I didn't like the change I could always plug the holes with silicon RTV or JBL-Weld).

My wife had heard them before, so I asked her to have a listen - she went through parts of 12 or so songs she likes,
and said on a scale of 1 to 10, she rated the improvement as a 5.

I'm not really here to argue - try it or don't, its your choice.
but it was an impressive improvement and the cost is excellent!

 

[gdmoore28]

Never heard of this. Did your correspondent say what the theory behind the holes is supposed to be? It'd be very instructive to measure the drivers' response before and after the addition of the two holes.

GeeDeeEmm

 

[faber12]

JBL Weld

LOL I find that really funny for some reason.

 

[Tom Brennan]

Some people run compression drivers without the rear cap; I tried it with some 1” Altecs and heard no difference one way or the other.

 

[bowtie427ss]

Or, significantly over-sized rear chambers. I've seen a number of attempts to outwit the engineers over the years. For the most part, the physics used by the original engineers hasn't changed, they largely knew what they were doing.

There's still a fella out there promoting the removal and discarding of the horns in your 604's.

In this instance it should be kept in mind that these drivers were engineered for high power handling/pro-sound applications. Smooth, extended hifi response was not the main engineering goal, and the design of the diaphragm makes significant compromises in smoothness, and extension of frequency response in order to meet the main goals of high acoustic output/high power handling.

 

[hjames]

Never heard of this. Did your correspondent say what the theory behind the holes is supposed to be? It'd be very instructive to measure the drivers' response before and after the addition of the two holes.

GeeDeeEmm

My understanding was that its a way to relieve back pressure so the diaphram moves faster without the trapped air causing a "spring" effect, which could sound like mild ringing.
The guy that shared the tip with me say it came from JBL and Polk - and I'll admit his home speakers sound amazing.
My pair of 908-8A drivers had already been modified with shorter screws, the added felt pad, and had no internal "loading cap."
All I did was remove the back, drill them, and reassemble them.
My wife and I heard the difference. Feel free to give it a chance and see what you think. Its a cheap mod either way.

 

[hjames]

Just an update. I keep playing the Model 15s as my main speakers in the plant room.
They sit just inside the Von Schweikert VR4s, where the L212s used to sit (they're over on the side).

Some friends were arguing on Facebook over the weekend if LedZep was still relevent.
Truthfully, tho I own most of their releases, I was always more of a Who fan than a Zep fan -
I did see their Who's Next Tour at Merriweather TOO MANY years ago ... sigh!
Anyway, Emma was away Sunday afternoon - so I pulled my trusty Radio Shack Sound meter out,
cranked up the level into the Jolida Tube amp, and played a few tracks in the low 90dB range (OMG!)
Dazed and Confused, of course, Battle of Evermore (just a bit), Stairway (Gawd - just a bit) and
The Immigrant Song - where is that freaking Viking Kittens Video!!
And a few other things -
Tho stupid loud isn't really my style, I can see why the Model 15s were popular to that crowd!

 

[toddalin]

The "Zep" must be heard at loud volumes to sound right. I attribute this to them mixing at loud volumes, as bands tend to do. If you don't listen at the recorded/intended volume, the F-M curve doesn't let the music sound as intended.