newbie to Altec's

[David Yost]

Here you are, my friend. Babble fish should help -- unless you already know French.

http://monsite.wanadoo.fr/acoustique...in/index.jhtml

I have used 416B loaded 817s under EV9040/288Hs and loved the combo. Please let us know what woofers came in the 817s.

For crossover duty, btw, you cannot beat the Behringer digital gear for value.

Congrats!!

[Old Guy]

Originally posted by oface1:
O G


A question on measuring DCR, they say 16 ohms, I really doubt if they will read that high after all this time? what is the margin -/+ they should be reading,,,, I have seen 8 ohm speakers read around 6-8 ohms and still be fine..

<font size="2" face="Verdana, Helvetica, sans-serif">We need to go to Sound 101 here...

Lots of people confuse DC resistance and inpeadance- they ain't the same.

The resistance of the speaker really does not change much throughout its life- those 8 ohm speakers were 6 ohms when they were new.

Impedance is always higher than DCR. 16 ohm units often read 12 ohms.

Impedance takes in a number of factors.

For instance, I play with bass horns. It is not uncommon for an 8 ohm speaker to go up to 10-12 ohms impedance in the horn..this is due to the loading the horn places on the unit.

Impedance is quoted as a "nominal" figure and varies with frequency. It helps to have the "curve" showing these changes when designing a passive crossover.

For instance- a diver that is 8 ohms at 800 Hz may be 9.2 ohms at 1200- if you wanna cross at 1200 take into account the 9.2 figure if you want to be exact...

The beauty of active xovers is all these calculations go out the window...The Behringer DCX 2496 is the best bargain in cheap crossovers IMHO.

There are European guys modding the outs of the Behringers to make them friendlier to home use..I wouldn't bother.

If you just want crossovers short term, basic SR units will at least get them up to listen to..

A "textbook" unit just assumes 8 ohm impedance and goes from there...not fine tuned to the speaker or box.

There are some decent textbook units to be had cheap, but for long term home use, custom or active is the way to go.

[oface1]

O G ,,

Thanks for the insight, I should know better , but were never really measured speakers in the navy,, I just looked at o-scopes and analyzed equipment and tweak stuff away....,,

David , the drivers are 921-8a's .... I have read a bit here and there that some say they are good for clubs/venues, but I might not enjoy them for home use....any experience with these drivers?

[Old Guy]

Originally posted by CONVERGENCE:


I would make it a 3 way TRI AMP the bottom part
from 20 to 250 second half 250 to 500 and horn
500 to 20kHz.

<font size="2" face="Verdana, Helvetica, sans-serif">Not sure I see the benefit in rolling off the bass in the upper cabs...

I would run all the bottoms down to their lower limit...and start rolling the mids out of the lower set an octave or so below where I crossed to the horn...

The reason for rolling the mids out of the bottom cabs is to create a smoother transition in sonic image at xover.

Your mileage may vary.

[Old Guy]

The 921 is an updated 421. Used tons of them in the 70's.


Good strong mid-bass. Louder than stink.

They don't go as low as say, 416's.

I would consider a set of subs with 3184's as the easiest way out if you wanna keep it all Altec.

A user here was lucky enough to get a set- just search the board, it was recent.

with subs you don't have to apologize for anything.

Kinda hard to get from down around 20 all the way up to mid bass with one unit...

You could gain a little with different 15's in the 817's, but the 817 is basically a mid bass box. the original intent of this stuff was to punch the sound thru a screen to the back of a theater, remember...

[Old Guy]

8 or 16 ohm frams interchange , magnets are the same.

So NP if you want 8 ohm drivers...

Mainly be careful with the screwdriver when replacing frams- in the beginning I would recommend holding the tip of the screwdriver and guiding it onto the screw then transferring grip to handle- that's the chief hazard is the mag yanking the driver in a direction you didn't plan on...

I changed my first diaphragm at age 18 without instructions, but I always scored well on the mechanical ability charts...sounds like you are the same, doubt you will have problems. It ain't rocket science...

[David Yost]

Hello,

I don't have any experience with the 921's, but judging by the specs, it looks like it would not go as deep as a 416 but could handle considerably more power. If you are contemplating a sub woofer anyway, try them and see for yourself -- they have a very low Qts with a highish res. frequency( .25 and ~ 35 Hz according to my literature) so they could be excellent upper bass/mid drivers.

If you haven't done so already, download WinIsd and play with the box size and tuning to simulate the response of your 921 loaded 817s.

[oface1]

Well finally rechecked and opened all the drivers up. the one that wasn't giving any readings, continuity and ohms had a bad diaphragm.

I am guessing whoever had this one last replaced the diaphragm wrong with the leads crossed (L1-red/ L2-blk), which was there was a caution in the instructions that someone posted a link to (thanks).

I will, in the future, order some 288 phrams to have a pair of those in order to compare to the 291's. In the meantime I wondering about going about maybe building a xover for the current setup I have now.

I am gonna use the drivers I have now currently to try and get up and running now when I build a xover( MR 64),driver(291-16k), and (4 each side) mid-bass driver (291-8a)in 817a cabs. The reference material says that the 921-16's can go down to 500hz, the 921-8a's can go up to 3.5khz. Is there a simple xover to build for this?

Right now my funds are a bit limited and I think for the time being the dcx2496 is out of my reach. Anyone have a suggestion for a type of xover to get me going till I can afford the dcx? Would it be cheaper for me for me to build one now or just suffer and wait to save for the dcx? Would build a xover be cost effective for now?

I am able to sling solder and troubleshoot.So i look forward to building.I just want to get some sounds going for now and see how this set up sounds. I promise to post pics along the way and I am up too any amount of criticism and suggestions that comes along the way.


thanks.....

[Old Guy]

Do you want a recommendation on a cheaper used active unit? Lots of Pro sound xovers get retired to home use.

Or do you want to build something?

Martin has input plates and boards, plus caps and inductors. Site has a calculator for "textbook" crossovers.

http://www.martinsoundpro.com/item.asp?id=322

[oface1]

A cheap recommendation would be nice, but I am not afraid to build either. Which one would do less damage to my wallet?

If I was to build a xover, what type do you suggest? I saw there was 1st,2nd,3rd, and 4th order xovers. I guess I need to study up on this.

<font color="#FFFFFF" size="1">[ May 22, 2008 03:19 AM: Message edited by: oface1 ]</font>