825 Build Questions

[gil393]

I recently picked up 3 empty 825 cabinets and have started working on them. I could not afford Altec woofers but I did find 2 AE TD15M woofers for a very reasonable price. I installed one with a 511B and 808A driver on top playing mono. I am using active crossovers with 18db slopes run through Ashly FET amps.

At low volumes they sound pretty good. As they get louder they get mushy which I attribute to all of the cabinet and horn ringing coupled with my concrete vault basement. I'm pretty sure that this can be made to go away and have read many posts about this. Also once they get moved out of the basement into the barn/theater and once deadened they will hopefully sound better.

My question concerns crossover points. After much experimenting by ear, but no measurements, I have settled on about 2000 as a good crossover point. The driver plays flat up to 4K but above 2.5K I start hearing changes in the sound as I move from side to side and around the room. Clearly at this point the off axis response from the 15" falls off and becomes audible. What surprises me is that the driver can play up to 2K without hearing off axis issues. Is this a side effect of the short horn on the woofer? Is it better to use the higher crossover or a lower crossover? Once dialed in I can listen to the same vocals over and over and even change the crossover mid note and not hear much, if any, difference from 800-2K. Below 800 the vocals seem a bit grainy, less smooth. The reason I ask is that I am looking at trying a compression driver (Radian 475) that wants to be crossed 1200+, preferably, 1600+ from what I read. Before trying that I wanted to see if there is any issue with using such a high crossover.

Thanks,
Greg

[Phil-G]

sheesh nobody had any advice to give greg here?
all i could say in my VERY limited altec experiance is: greg break down and get a pair of altec 3156 16s. they run for about 100 bucks each. i'm not even going to look up the specs on the lf drivers your using but theres a 99% that they're not designed for a loaded horn enclosers. the night and day difference will amaze you. as far as the 808 drivers they usually cross over at WAY less than 2000. try something like 800.
now if some real altec guys would chime in greg would probly appreciate it.

[GM]

Hmm, I wrote a response days ago and thought I posted it, but apparently I did it either during one of the times the board disappeared or 'customer no service' AT&T dropped my DSL due to the high traffic demand during the 'final four' basketball series being held here. Now all I have to do is remember where I saved it.

GM

- - - Updated - - -

all i could say in my VERY limited altec experiance is: greg break down and get a pair of altec 3156 16s.

When did the 3156 become suitable for the 825/828 cab? With its high inductance and relatively low Vas it's a prosound vented cab or scoop bin woofer.

GM

[rontec]

No expert here either....but I would stay between 800-1000 crossover frequency. I've used Altec 421's with this type cab with approximately 54 sq in ports with good results. Diffinitely pad down the 808's with an L-pad and series resistor. And use a bypass cap of 1-2 uf to eq the horns. I would also listen to each of the drivers independently of one another. This may help to reveal any anomalies within the system and the drivers themselves.

[Phil-G]

When did the 3156 become suitable for the 825/828 cab? With its high inductance and relatively low Vas it's a prosound vented cab or scoop bin woofer.

GM

well notice i did lead that off with "VERY limted experience" someone else suggested that to me as an alternative, seeing as how i'm on a budget.

[bowtie427ss]

well notice i did lead that off with "VERY limted experience" someone else suggested that to me as an alternative, seeing as how i'm on a budget.

A readily available, brand loyal, value retaining, "compromise" that gets sound coming out of your boxes. Probably wasn't suggested as the "ideal" driver.

i'm not even going to look up the specs on the lf drivers your using but theres a 99% that they're not designed for a loaded horn enclosers.

FWIW, the Acoustic Elegance TD-15M is a highly regarded woofer in the DIY and HE(high efficiency) interest groups. As with many niche market products, they're only produced to order which can cause some frustratingly long delays(you can read about this on other forums).

http://www.aespeakers.com/

Personally, i'd love to have a pair of non-used ones complete with proper phase plugs. However, the snail's pace at which buyers of new product are serviced is likely to ensure that i'll never own any.

Just another kudo's to Bill and GPA for maintaining the Altec level of quality with very reasonable turnaround times.

[fpitas]

Since you're using active crossovers, you have to be careful to get the horn and woofer into phase alignment, which usually requires woofer delay. The job is done for you if you use an Altec passive crossover and mount the drivers with the factory specified offset; otherwise you're on your own. As an example, I need 0.97msec of woofer delay for the midbasses I use with 511 horns, with a voice coil offset of about 17 inches. I determined that delay by inverting the horn polarity and tuning for a good null at the 800Hz crossover.

[Phil-G]

FWIW, the Acoustic Elegance TD-15M is a highly regarded woofer in the DIY and HE(high efficiency) interest groups. As with many niche market products, they're only produced to order which can cause some frustratingly long delays(you can read about this on other forums).

AE Speakers --- Superb Quality, Unforgettable Performance, Definitely.

Personally, i'd love to have a pair of non-used ones complete with proper phase plugs. However, the snail's pace at which buyers of new product are serviced is likely to ensure that i'll never own any.

Just another kudo's to Bill and GPA for maintaining the Altec level of quality with very reasonable turnaround times.

yeah i probly should have at least looked them up before opened my mouth. so how does phase plug apply to a LF driver? thats definately a new one for me.

[Alien_Shore]

FWIW, the Acoustic Elegance TD-15M is a highly regarded woofer in the DIY and HE(high efficiency) interest groups. As with many niche market products, they're only produced to order which can cause some frustratingly long delays(you can read about this on other forums).

+1
I've not yet heard these, but some expert builders whose opinions I trust have spoken very highly of these woofers. I was just looking at these a couple of weeks ago for a project I'm doing for a friend to replace some old woofers in Altec 816 cabinets. You can find a measurement a DIYer made in this thread:

Ugly LP Filter

And some pro measurements of the "beefier" TDM15H can be found here:

Best woofer for a 2-way using Altec Mantaray

[GM]

well notice i did lead that off with "VERY limted experience" someone else suggested that to me as an alternative, seeing as how i'm on a budget.

Yes, I noticed, but my 'involvement'/interest WRT Altec products had for a variety of reasons dropped to near zero by mid ?75, so even though I couldn't find anything to support it in a quick search, I still wondered if more current versions of this driver had been 'upgraded' to horn driver status.

Just because someone has "VERY limted experience" doesn't mean that they haven't learned some useful tidbit that other, more knowledgeable overall, folks didn?t know.

GM