My A7-500s. A journey

Starting here a running account of my "new" Altec A7-500s
I'll document my findings and the work I do one them. I've been wanting a pair of A7 or A5 speakers for many year, now thank to forum member "old Guy", I have a pair. And at a very reasonable price, too!

These belonged to a fellow who ran a music store in Ohio.

Here's what I got (see photos below).

825 cabinets (I think) in 3/4" ply. Looks like A/C grade, lots of knot holes on the inside. But pretty solid and in nice shape. They have been taken care off.

416-8A drivers in the 16" frame. Don't know if they have been reconed. It looks like the cabs had 15" woofer originally, as the bolt circle is so small that it just barely fits the 16" cast frames. There is window screen in front of the 416s, as you can see in the photo. Don't know if it's to keep bugs out or beer bottles!

On top of the cabs, bolted on, are the horn houses. More 3/4" ply with a 511 horn + 802-8 ohm driver. The 802s have the symbiotic diagrams and loading caps. They appear to be from 1971. I've never seen the horn house before, Todd W says they may be from the 50s.

Crossovers are the stock N-501-8A type. Nominal 500Hz, 2-way with L-Pad on the HF side. I will post schematics and photos later.

OG said that one of the compressions drivers was bad, but it turned out to be an easy fix. The spade terminals were touching the inside of the back cover causing a short. Bent them down and it works!

So I have a fully working pair of A7-500s. Yeah!

Part two, the sound.
Well of course I fired them up to hear the glorious "Voice of the Theater" sound.
And how do they sound? Well, they work....
To be honest, I do not like the sound. No bass, very midrange heavy, a bit muffled. I can see why a lot of folks don't like these old girls. Maybe great for dialog behind a movie screen, but not great for music. I've heard a horn + 15" sound much better. Much.

I spent a few hours carefully measuring, listening to and adjusting the the horn level to get it set right. Better, but not great. :(

At the moment I am running 1 A7 on the right and one of my "Big Ugly Speakers" on the left. The do sound different. The A7 sounds midrange heavy and closed in compared to the B.U.S.* I am mixing all signals to mono and going back and forth between the 2.
The big 803 multicell horn sounds so much more open and live than the 511. Voices seem to come from the area of the speaker, but can't be pinned down to the speaker. The A7 on the other hand, is definitely "speaker" sounding. The horn is there, no mistake.

I did a lot of EQ work (DEQ-2496) to get each as flat as possible. They still sound different. The BUS is bigger and more open, the A7 closed and midrange heavy. But the 803 seems to have a slightly annoying edge that the 511 does not. The 511 may sound like a horn, but it is not fatiguing or edgy.


*Altec 604-8K in a 14 cubic foot box topped with an Altec 803 horn driven by a 291 1.4" driver (Symbiotic fram). Passive crossover of my design crossing at about 450Hz, 2nd order.

Next - crossovers.

Thanks and good work. I will be following your thread closely, as I too am a recent A7 Voice of the Theater owner. I too agree that it doesn't have much bass and sounds muffled.

Compared to my Klipsch La Scala....the La Scala blows the A7 away in bass and clarity of sound.

But if I drag the A7 out of the garage and crank up the volume....watch out...geeze...it has absolutely stunning sound and clarity at higher volume.

Which leads me to believe....they might not be suitable for in home use.

Hey Leland. Yep, that sounds about right. Just got off the phone with my friend John who had the Klipsch when he was in high school. His buddy had the A7-500. Johns says his buddy coveted the bass of the Klipsch, while John coveted the smooth detail of the A7.

There are some things to try.

1. Put them against the wall. This should help with bass. Maybe add wings
2. Change out the symbiotic frams for all aluminum. May reduce the horn sound. Should be better overall. I'll try my 806 drivers.
3. Damp the horn. The 511 does ring (my 811s ring much less). Damping the horn should also kill a lot of the "horn sound."

My goals:

I hope to bring these old girls up to date. I know they can sound better with proper care.
Damping, tuning, crossover work, etc.
The reason I know they can sound better is because my favorite speakers ever are the pair of A5s that I helped rebuild in Paris 22 years ago. They are the only speaker I've heard that had NO speaker sound, none. Others I've heard were close, but none disappeared the way those did. Even with different amps - everything from 300B SET to Halfer, to Krell, vintage Scott, Dynaco or MacIntosh - all the way to a Luxman integrated. All sounded great on these speakers. Different, more or less colored, but great. No speaker has ever sounded more "real" to me. Like real people playing music on real instruments in a real space. Changing the electronics was simply like putting on a different pair of sunglasses looking at the rand Canyon. A different tint, but still obviously the real thing. Beautiful. :Red heart:

That's were I hope to go with this pair.

Panomaniac, Thanks.

Yes, I have done nothing to work on the sound or modify the Altec. Mine has a 515-16G and an old 288B Driver with an 805 horn. N-500-C Crossover. It is old school, perhaps late 1940's except for the Woofer. Don't get me wrong...I love it....but just not as refined as the La Scala for my uses.

I know so little about the Altec....it could be an A5 and not an A7.....

I've played around with the antenuator on the crossover...that is about it.

THe Altec is a true Professional Audio unit....for pro audio applications. At "Volume" it is stunning.

By the way,,,Yours look GREAT...congrats on the new speakers. Do you have a pic of the 803 horns?

Hi Guys,
I own a pair of Magnificents for my two way stereo, and have a pair of A-7s in my home theater with the equivalent of a 9844 for my center channel, JBL surrounds. [ I know, but they came out of a theater in Oklahoma]. After having lived with these speakers for at least 25 years, the one thing I have found is that they sound a lot better when they are EQ'd, anything but flat. I boost low bass up to about 100 Hz and then start a gentle climb on my EQ from about 1000 Hz up. Not a lot but, but just a gentle climb. Augment the Maggies with a def tech supercube one, and the HT with a supercube reference. I mix sound on a regular basis and I can almost guarantee all the live sound you hear anywhere has been EQ'd for the venue. I do it for my boards and I do it to the great big speakers with the mildly ugly horns that we all know and love as this company named Altec. And I might add, that anyone that listens to these giants of audio in my house, and HT all say that they sound amazing.
It thrills me to this day that I have not grown tired of their sound. Can't say that about the multitudes of speakers that they replaced.
side note: was at a festival relatively recently that had an old school sound guy running four 825 cabs with larger horns on top fed by 288's. there was a great big "honking" ugliness to the midrange. I got to talking to him for a while about his speakers and how he EQ'd and he said there set the way his RTA said to set them. I gently suggested he listen to the mids and he started pulling them down. all of a sudden he started smiling and said I knew my ears were telling me something just wasn't right but I couldn't find the problem. problem was solved when he just listened for a little bit. the sound got much much better. and the old altecs sounded a lot better than the shrill stuff guys are using now, although
the altecs are always a lot bigger!!!
just my .02, but anything but flat!
regards,
scott in nc

Hi Mike, They look Fantastic though it's a shame about the sound but I have no doubt once you get the acoustics right on the room,tuning,crossovers,etc... you will have that smile on your face that all Altec owners will have once project complete.Once you get your Altec's set right that smile on your face will be PRICELESS !!! Kinda like this guy right here to the right > :D You are doing a great job on the evaluations and providing great info for everyone Thanks !!! :)

Try the later N1201 crossovers. Or the model 19's. Way better than the originals.
Remove the screens over the woofs.
416-8B's are better woofs. The -8a are a bit wooly.
Use 802-8G or 902-8a drivers with the bug screens removed.
Do damp the horns.
Brace the cabs per Jim Dickensons article.
They will come around.
BTW, EQ the low end only, a 1/3 octave EQ below 500hz will work wonders.
I actualy added 1/4" plywood spacer rings at the woofer mount to keep the cone from hitting the cab on big excursions.

Remember, these are theatre speakers, not home. But with work and patience, they can be quite nice.

There is a reason M19's were better for home use.

ron

Hey John - yes, I'll get them there. And I'll be smiling! :D

Scott. Right on. Flat just does not sound right. That's one of the reasons my "home made" Altecs sound better. I tuned the passive x-over by ear and pulled the mids down. Doing that makes listening to them close up a lot more pleasant. I just wanted to start the A7s as flat as possible for a reference. Doesn't sound like they will end up there.

I'll post x-over schematics, photos and impedance curves tomorrow for the technically minded reader - and those who just like pretty graphs. =)

Here is the stock N-501 crossover schematic. There is a typo in it. That should be 3mH, not 30! I'll revise and repost.

I found this crossover schematic but I don't know where it came from.

Possibly from here:My latest DIY speakers - Club Polk

Pano,
Thanks for this thread. I have just completed my A7-500 project. I posted some of the restoration in another post. Mine have 416-b, 902-8t, 511B, and 800HZ Eminence XO.

I had the 416-8B's re coned by GPA. They also recommended that I reduce the port size for home use. This tuned the port to the 416. The size now is 26 in. X 3 1/4 in. or 84.5 cu in. This does help the bass, but you really have to crank them up. I also have boosted the bass on my amp by about 4db. Someone also told me the cabs are actually too large volume wise for good musical sound reproduction. (I hope not)

I have heard that "bracing" the cabs also helps the bass although I have not seen any detailed description or pictures. I have also used Redux acoustic insulation in pretty much the same manner as the original Altec design. Could more insulation help? I don't know.

The 511 on my cabs was mounted inside. I moved it back to the top. I used steel angled stock with the holes in it I got at Lowes for mounting. The holes line up perfectly with the bolt holes in the 511. I also used rubber grommets, also from Lowes to mount the 511 to the angel stock. Rubber washers were used between the 902 and the rear stand off bracket. this makes the 511/ 902 assembly completely rubber mounted. I have detected NO ring. Striking the horn only gives a dull thud.

As the others have noted, I am not satisfied that my A7's sound as good as they could. I will pay close attention to your progress. Please don't leave anything out.
Thanks and good luck.
Marvin

Thanks for the info and the encouragement, guys! It very nice.

OK, going to start talking crossovers. This is just the beginning. Crossovers can make or break a speaker. They are a full 1/3 of the speaker - drivers, box, crossover. All equally important. Many speakers do not live up to their full potential because of poor crossover design. There has been a lot of progress in the past decade on computer crossover design, but it only helps, it does not do the whole job - at least not well. It takes a lot of experience, time and effort to design a great crossover. I'm a novice, but learning.

So here we go!

My A7-500s came with the stock N-501-8 crossover. This is the 500Hz crossover for 8 ohm drivers. I have attached a schematic that I drew from the actual part. I measured all values. The inductors measure 2.7mH outside the crossover, but probably rise to ~3mH when mounted in the steel frame. I have called them 3mH. Also included is a photo of the insides. The caps are marked 28uF 125V and measure spot on. L-Pad is 24R & 5.6R Just a basic 2nd order crossover with L-Pad. No Zobel, no traps, no EQ.

The values for a nominal 500Hz, 2nd order Butterworth filter are 28uF + 3.6mH. So the N-501 has slightly smaller inductors than "textbook." The problem is, although the drivers are nominally 8 ohms, they are not 8 ohms at the crossover frequencies. (See impedance graphs in the next post.) So the frequencies are shifted a bit. Simulations show the 416-8A electrically crosses a bit higher, the 511/802 combo pretty close to 500Hz. Electrically speaking. I will try to measure both the electrical filter function and the acoustic points for further reference.

Here is the schematic I drew from the actual crossover and pix of the guts. Nice big L-Pad!

When doing box tuning and designing crossover, driver impedance curves are a great help!
One of the best audio gadgets I ever bought is the WT3 woofer tester from Parts Express.
Just a little USB gadget, it makes measuring drivers very fast. Only a couple of seconds to measure everything but Vas. And that only takes a few seconds more.

Plots show here are from the WT3.

Below we see 2 graphs, 3 plots. One is the woofer in the A7 box. This is a 416-8A. You can see the single peak at resonance (~23Hz) and the rising impedance typical of a woofer. Also obvious are some small bumps that indicate box resonances. I'll work to get rid of those.

Do notice the single peak. Does not look like the classic twin peak bass reflex curve, does it? More like infinite baffle. Maybe that's because of the big port. Currently 206 sq. inches or about 160% of cone area. We can see why Marvin brought his port size down!
I'll do the same and run a sweep.

The other graph is the impedance of the 802 driver on the 511 horn. One is with loading cap, the other without. As the peaks come near the crossover point, this makes things a little tricky. An LCR trap could be used to flatten this peak, might be worth trying.

Just for fun, I tried running the drivers with an active crossover. 3rd order at 610Hz. It works well and certainly sounds better than the stock crossover. Worth investigating further.
FWIW, the way my 511s are mounted, there is only 4 cm of depth offset between the acoustic centers of the woofer and horn. Very close to time aligned. Just a small fraction of a wavelength. Nice!

Altering the xover point will alter the sound a lot.

500, what you have, results in a more mid heavy, very "up front' aggressive sound.

This can be very desirable with a straight bass reflex, but the 828's short mid bass horn tends to boost that area too.

Going up to 800 will mellow them a lot. To 1200 even more...but how much is good is personal preference.

An electronic xover can help , play around with crossover points till you get the sound you like, then design your passives for that point...or just stay electronic.

Personally, I will never go back to passives. Never.

And this from someone who insists on never saying never...:D

Really glad the horn worked out for you, in the old days would have had a spare fram to send, but those days are gone...

Quote:

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Originally Posted by RonSSS

Remember, these are theatre speakers, not home. But with work and patience, they can be quite nice.

There is a reason M19's were better for home use.

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Hey Mike, I think Ron brought up a good point. These were designed for large areas not a small room inside a home.So it will take some tweaking to get them right but you do good work very thorough.I thought your port was too big also for the 416 I would even try reducing it even more to what the M19 uses a 2 1/2" x 11" port you can always enlarge it.Also the 802 symbiotik with loading caps, most people I have talked to don't like the loading caps so they remove them and stick in a thick piece of felt in the end cap instead.And the symbiotiks are more or less for power handling replace with a all aluminum diaghram. :I don't know: Well anyway nice job Mike you are no novice :Sad no: we all can learn more each day for sure.I learn something new every time I come to this forum isn't it great !!! :Clap: Those A-7's look to be very nice shape though. Regards :)

Thanks guys, lot's of good feedback. I didn't know this thread would get so much interest. Yep, a get a nice set, thanks to O.G.

Some more playing this afternoon. Just FWIW.

• Putting the A7s in the corner or right against the back wall helps the bass a lot. Certainly seems to be the way to go in a room like mine.
• Adding a wing to one side also helps the bass. The A5s I used had wings in both sides.
• Rolling the crossover point up and down from 450Hz to 1.8KHz does not change the sound nearly as much as I thought it would. The 511 seems to blend well with the woofer all thru this range. Above that and the mids start to drop away (woofer roll-off) and below that the low mids go away (horn roll-off). Things do change, but it's fairly subtle. Good drivers, I suppose!
• Pulling out some mid with EQ does help the horn shout. A dip of about 3-4dB centered at 1.5K is a good starting point. Overall or just on the horn.
• Vibration. The woofer horn vibrates like crazy. It's the worse part of the cabinet. And it's pointed right at you. Mine are not kerf cut in the back, but are a solid bent piece. Damping material and some bracing back there ought to work wonders.

I agree about the symbiotic frams and the loading caps. They can't be helping. Will swap in an 806 driver tomorrow for a listen. That may smooth things out a lot.
OK, back to the music (Carlos Santana).

Note, just a quick swap to a 811/806 made a BIG difference. So much smoother, better balanced and more top end. Gives the 803/291 a run for its money. Eager to hear what the 806 does on the 511.

Quote:

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Originally Posted by Panomaniac

Do notice the single peak. Does not look like the classic twin peak bass reflex curve, does it? More like infinite baffle.

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The little bump is the reflex's upper impedance peak which is highly damped due to the cab being tuned so much higher than the driver's Fs, ergo if tuned a similar amount below Fs it would become the ~single peak with the lower one just a small bump and of course equal in amplitude if tuned to the driver's Fs.

Anyway, if you recall my remarks about driving vintage speakers with the type of high output or matching impedance sources they were voiced with, this high tuning relative to Fs is desirable since it yields much better woofer control/higher low distortion SPL while still having extension to slightly below Fs same as if tuned to Fs with the trade-off being it sounding a bit 'loose' due to the amp 'stalling out' against the high impedance.

This same high output impedance source would also flatten the HF horn's 'hot' mids somewhat while adding scharron's 'gentle climb' EQ to flatten it out with increasing frequency due to increasing driver inductance.

GM

Hi GM, I was hoping you would "tune in."

Yep, I will be working on the port tuning, for sure. Will aim for equal peaks to test how that sounds. And for sure, a high output impedance or resistive network on the horns sounds better. Not quite sure about it for the bass, yet.

Sorry to report no real progress over the weekend, too busy with yard work and other chores. Mostly just listening. =)

But I did try to figure out the internal volume of the box. I have read and heard various numbers, but nothing definitive. So I started measuring. I figure this:

Gross internal volume = 15 cubic feet
Horn section + woofer = 3 cubic feet.
Net volume = 12 cubic feet = 340 liters.
(for box with horn flares open in back)

Actually did all my calcs in cubic centimeters then converted. Years ago I had figured 11.5 feet going from published plans. So pretty close to my measured results. I sure looks like the horn and woofer should take up more than 1/5th the volume, but I measured and calculated 3 times. Anyone have an opinion?

Given an Fb of 340L, and the port size I have, my cabs must be "tuned" to about 65Hz. Or about an octave too high. A starting point!

Well did a little tuning and testing today. I pulled off the top board from the port and made 3 others boards of different sizes for various port areas. Easy to swap out the boards and change the port size. Or course all were "flat ports" - just 3/4" deep. And all where full width - about 28.5".

Closing down the port definitely extends the bass, no doubt about that. Easy to hear as the port plates are switched in and out. I was trying to get the box tuned to about 35Hz for max flat response. Never sure what tuning I got. Could not tell be the impedance curves.

But about 57 sq in. seemed to work best to my ear. Nice solid bass, less midbass. Listening with a signal generator says that the boxes now play strongly into the mid 30s. Drop fast under that. Tried both more area and less (down to 17 sq inches) but liked the mid 50s best. Will need more time to fine tune.

One thing I can say for sure. Bracing and damping the woofer horn flare is going to be VERY important! They buzz like crazy. I put one hand on the flare while running the sine waves up and down. Real easy to feel the resonances. And they don't all happen at the same points, that was easy to feel with my hand. All the bad stuff seems to be between about 120-200Hz. In fact just pressing my hand on the flare at 200Hz made the fundamental rise a good 6dB! The horn flare must have been vibrating in opposite phase, canceling the fundamental. Super easy to hear. So you A7 owners, get those flares under control! :eek:

Sounding pretty decent now. Good port and the 811/806 combo running at 800Hz, 3rd order. Still the dip at ~2K to pull back the midrange. Getting nice. And can only get better!

Hi Mike,

Well that didn't take to long I can see a half smile almost there :D good deal....

You're right John. :D
Just a little work and they already sound much better. In many ways better than my home made Big Ugly Speakers.

The right crossover, the right horn and the right port take them a long way. Very promising for the future improvements.

One of my DIY audio projects - Altec Lansing A5
Configurations are as follows:-
Cabinet - 825
Woofer - 515B
Horn - 1005B
Driver - 288C
Crossover - DIY

For details, go to link showed in my signature.

You could probably Fleabay the 511's and replace them for not a lot of cash difference...

Ditto the Symbiotik frams...

I had a friend who poured the horn curve on the A7 full of plaster...I generally just used high density urethane foam...you can get small amounts mix and pour, or use a bunch of the cans...

Not sure I want to dump the 511s, yet. Am willing to work with them, they may have hidden talents. But I guess I don't really "need" 3 sets of horns - 811-511-803 and drivers 802-806-291 =)
Gotta find what works best for me.

By foam, do you mean the light brown stuff they use in boats? Does it stick well to the walls? It's heavier than the isolation foam in cans, yeah?

ec188 - nice work! Those cabs are beautiful. The wood is so thick, it makes the boxes look smaller. Crickey, those must be heavy. Nice work bracing the horn flares. I want to do something similar. Inspiring work, thanks.

Yes it's used for flotation, house insulation, and tons of things.

Comes in different densities. There is even tooling foam for making fiberglass molds, it can be machined.

I suggest one of the heavier densities...

Well I did try the 806a driver (aluminum diaphragm) on the 511 horn in place of the 802 with symbiotic 'fram.

Much better. More balanced, less shouty, better overall. I still think the 811/806 combo sounds better, but the 511/806 combo is not bad. Works OK down to 500Hz, but seems a bit cleaner at ~700Hz. So better frams in the 802 ought to sound nice.
FWIW, the 802 with no horn makes a nice tweeter. ;)

Also played with the 803B/291 horn/driver combo in top of the A7 - which would make it an A5. I like it! Looking forward to hearing what the aluminum 'fams will do in the 291. Will change it into a 288 and should sound a lot better. If there is as much improvement as in the difference between my 802 & 806, I'll be a happy camper. Many say that the symbiotic 'frams don't sound great. Now I've heard it for myself.

Also did some EQ work just for fun. The 803B/291 combo is far from flat, but I knew that. The big surprise was that the bass cabinet with the smaller port is almost flat. It's the flattest response I've yet gotten at the listening position. Flattest of any speaker I've had in the room. Just needed to pull down about 2dB at 60Hz. No big deal.
Very happy with that.

Beware (my) good-intentioned rambling to follow. Sorry to stray OT.
Caveat to all suggestions being 'of course you may have already tried it' :-)

Quote:

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Originally Posted by Leland

...a 515-16G and an old 288B Driver with an 805 horn. N-500-C Crossover.
...but just not as refined as the La Scala for my uses.

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I found the Plywood 828/825 (whichever they were) cabs with the 416-8A to have a better/wider FR than the La Scalas.
You might wish to make sure that you are comparing them @ the same location in the room (swapping). Corner placement certainly came into play with mine.

Interesting that 'more bass' was attributed to the la scala, not generally known for it's (quantity of) bass reproduction. (unless perhaps turned around to face the corner... which was also kind of neat!) Mine however were industrial, so had a slightly different (iirc) K43 model woofer. Some have said the K33 has more bass in the LS, but that was/is highly contested.

IMO, the LS's folded horn seemed more accurate for (some) lower frequencies compared to the smoother BW of the 416/BR Altec. Whether the altec is horn on floor or port on floor may also come into play, given the size differences involved.

You might investigate whether the 16g is suitable for the N-500-C, or whether it should be an 8ohm woofer. That might be affecting things.

Mine were 416-8A's w/N-500-C's, though rather than recapping, I bi/tri/amped and found this combo most pleasing:

416-8A -> ~500hz (828/825 port = ~80 in2)
808-8A (old, symbiotik afaik) -> ~6000hz (511b)
902-16A (gpa, aluminum) -> the rest (511b)

I liked the 808-8a for MR.
Sounded more natural/compliant to me than the 902's there.
Maybe it was the alnico though.

Alas, did not get to the point of setting up a passive between the 808 and 902... which I think would've been the best scenario for me at the time (using one amp for MF and HF).


*Since you like it - your LS bass section with the Altec multicell on top might be the best of both worlds.

IIRC the K-55/K-400 MR combo crosses to the LS's FH @ 400hz.

If 'daring', you could try to keep them 3-way and just insert the Altec horn into in the klipsch network in lieu of the K55, but impedance differences (K-55=16ohm) may make that less than ideal (?). You'll want to run it at lower levels and/or read up on opinions about danger to running the Altec below 500hz.

Gear freak, thanks for the good info. Looks like you tried a lot of stuff.

As Ron said earlier in the thread, I'll get there. =)

Also rereading Leland's post. What you have are A5, because of the multicell horns. I would love to compare your 805 horns to my 803s. I suspect the 805 will be better. The length of the 300Hz horn rolls off the highs a good bit. With my 291s they roll off second order at about 5K. Not what you would call "extended." All aluminum 'frams (288) should help, but I doubt they'll go very high on that horn.

If I could recover on the low end and really cross at 300Hz, I'd be happy. But the 291 just does not play that low. Neither do my Radian drivers. 500 is about it. So maybe the 500Hz horns are popular for a reason.

Getting the bass cabinet right will help the bass, for sure. Just tuning the port makes a big difference. Damping and bracing will be a big help, too.

----

At the moment, things are sounding rather nice. Here is the system as it stands today.

• Source: HP laptop. CD, Flac or MP3 files. ASIO drivers (no resample, no K-mixer) -> USB
• M-Audio Duo USB: -> SPDIF
• SPDIF to AES transformer - 75:100 -> CAT5 cable
• Behringer DEQ2496 Digital room EQ and touch up. -> AES out
• Behringer DCX2496 Digital crossover. AES in. 3rd order at 500Hz. Delay for woofer, mid dip for horn. Analog out via custom transformers.
• Highs & mids: Virtue Audio TWO class-D amp. 24V battery supply. 291/803B combo 500Hz-5Khz. Selenium 1" horn 5K up. (passive off same amp)
• Lows: IcePower 65W class-D amp. Altec 416-8A in 825/828 cab.

Getting there.

Quote:

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Originally Posted by Panomaniac

If I could recover on the low end and really cross at 300Hz, I'd be happy. But the 291 just does not play that low.

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Hi Mike, From research I did the only Altec driver of the large format capable of going that low is the 288C maybe something to keep in mind when using the 803's I'll try and find that info for you. :)

Quote:

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Originally Posted by Panomaniac

If I could recover on the low end and really cross at 300Hz, I'd be happy. But the 291 just does not play that low.

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This is primarily what dual driver adapters are for. ;)

GM

Quote:

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Originally Posted by Altec Best

Hi Mike, From research I did the only Altec driver of the large format capable of going that low is the 288C maybe something to keep in mind when using the 803's I'll try and find that info for you. :)

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HMM..curious where that's from.

All of the big Altecs should go to 300 at realistic living room levels.

Especially the 290.

They won't handle full rated power at 300.


But lots of 290's were run in public address with only capacitors to protect them.

Hi Panomaniac,

This is really a great detailed kind of a thing from your side....and many many thanks for this. I was really wanting to see something like this as I am in the process of hand building a pair of A7s for myself. Pls keep it up.

Quote:

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Originally Posted by Panomaniac

The values for a nominal 500Hz, 2nd order Butterworth filter are 28uF + 3.6mH. So the N-501 has slightly smaller inductors than "textbook.".............

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Pls correct me if I am wrong.

I think iron-core inductors are like that. Unless a sizable amount of current passes thru them, they will be less than the prescribed value. They are not linear in the graph. But for the VOTs it was not a setback as they were meant to pump away at very high & constant volumes. Also the reduced resistance of the iron-core inductors were an added bonus.

Another interesting point to note here is that, in a standard 12db crossover, if the value of the inductor is a little reduced (as is the case here) while the capacitance value is alright, it will infact put a slight bulbous rise (IIRC...nearly 2 db), at around the crossover point. Which is probabely why the A7 sounds much better at high levels compared to lower ones. Also as they are very efficient units, the mismatch becomes much more apparent.

For home use, IMHO one should either go for air-cored inductors or active X-overs.

Thanks again for the great thread.

Hey guys, thanks for the kind words and good ideas.

I did a little work and measuring and found that the 291/803 will actually play flat down to ~250Hz. Roll off under 250 is 6th order Butterworth. I.E., it drops like a stone. To get this, the midrange has to be pulled down about 7dB. That flattens it out.

Trouble is, phase has gone wacky at that point, so good luck matching phase at the crossover point. Distortion is higher at the bottom of the range, too. So minimum 400Hz, or 500Hz to be safe. Would be interesting to see if the "Giant Voice" drivers could do a better job down low.

So happy Thanksgiving. See you soon!

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Originally Posted by Old Guy

HMM..curious where that's from.

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Hi OG, I was looking for that,can't find now :confused:. That is a good question.I think it was one of those sheets from Altec on their 803 Multicellur horns where they say recommended drivers. 288C,290,etc.... Mike if you have a spare 288 maybe you can try it to see if it helps. Regards ~ JOHN

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Originally Posted by Altec Best

Hi OG, I was looking for that,can't find now :confused:. That is a good question.I think it was one of those sheets from Altec on their 803 Multicellur horns where they say recommended drivers. 288C,290,etc.... Mike if you have a spare 288 maybe you can try it to see if it helps. Regards ~ JOHN

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I can see where that is confusing.:)

Altec likely just recommended the driver that was current at the time of the sheet. Why recommend old drivers if you are in the business of selling new ones? And of course you can't recommend 288D's if they don't exist yet.

Well the 288 and 291 (I think) were spec'd for 500Hz. I thought that might just be because of being spec'd on a 500Hz horn. But even on the 300 horn they drop like a stone under 250Hz, so crossing them an octave above that is a good idea. Keeps it out of distortion, phase problems, excursion, etc.

I may try to get them down to about 425 acoustic, but if they don't sound good down there, no point in it. Will be interesting to find the sweet spot.

But that is the fun part isn't getting to play with all the different horns,drivers,etc..:D let me pose this question which driver did Altec recommend for the 803 multicell all of their large format drivers are 500 hz the 803 is 300 hz horn so they have no driver that goes to 300 hz does that make sense :Can't belive it:

A good question! The 290 driver, AKA "Giant Voice" seems to be what was meant for the 300Hz horns. I'm sure someone here can verify. They can play low and had a phenolic diaphragm. Could handle a lot of power.

Almost bought a pair, but I'm sure the 288 is much better for my app.

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Originally Posted by Panomaniac

The 290 driver, AKA "Giant Voice" seems to be what was meant for the 300Hz horns.

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The 300 Hz horns were originally for voice paging.
And Altec did recommend a 300 Hz driver.

This sheet states the 288 to handle 10 watts from 300 hz up. Just a little hard to read.
http://www.lansingheritage.org/image...1947/page3.jpg

The field coil 287 was rated to 300, and the permanent mag 387 also, at 20 watt "peaks" when less than 12 dB/octave, ie just a protection capacitor...

http://www.lansingheritage.org/image...943/page07.jpg

I suspect somebody had an attack of honesty and changed the 20 watt "peaks" to 10 watts for the 288 spec.

Of course at 98 db from 1/10 watt, you don't get a lot of volume at full power, but note the dual driver adapters as GM mentioned...and things weren't as loud in those days.

As the need for volume went up so did the need for power handling, therefore the 290. But the Aluminum frams were used regularly from 300 for voice paging early on.