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421-8H Series II in an A7/VOT cabinet + 511B / 807-8A — real-world experience wanted

28Hz

28Hz

New Member
Hi everyone,

I’m working on a project based around an Altec Voice of the Theatre system, and I’d really like to hear from people who have actually lived with this combination, rather than simply repeating the published specifications.

The system I currently have is:

  • Altec VOT / A7-type bass cabinet
  • Altec 421-8H Series II
  • Altec 511B horn
  • Altec 807-8A compression driver
  • Active DSP crossover rather than the original passive network
I have two complete systems, one for each stereo channel.

The ultimate goal is not maximum SPL, nor is it to create a museum-correct restoration.

I’m trying to build a system where the loudspeaker eventually disappears and the recording itself becomes the event.

STAGE. DEPTH. EMOTION.

Width and height of the soundstage.
Depth behind the loudspeakers.
Layering of instruments.
Realistic scale.
And ultimately that moment when you stop listening to the equipment and simply listen to the music.

The 421-8H Series II

This is the part I’m particularly interested in.

I understand that the 421-8H was used in various VOT/SR applications and that there are many different opinions about how it should be used.

For those who have actually used a 421-8H or 421-8H Series II in a VOT/A7-type cabinet:

  1. What frequency range did you find worked best in practice?
  2. At what frequency did you normally cross from the 421 to a 511B?
  3. Have you tried several crossover points — for example 400, 500, 600, 700, 800 Hz or higher?
  4. What happened sonically when you moved the crossover point?
  5. Did you find that the 421 became noticeably less convincing, congested or distorted below a certain frequency?
  6. Did you ever measure the 421 in your actual cabinet? If so, I would be very interested in seeing the measurements.
  7. Did you use EQ on the 421? If yes, how much and over what frequency range?
  8. Did you ever use a separate low-frequency section below the 421?
511B + 807-8A

I’m also interested in the real-world lower limit of the 511B / 807 combination.

  1. What crossover frequency did you find gave the best combination of smoothness, dynamics and low distortion?
  2. Did you prefer around 500 Hz, 600–700 Hz, 800 Hz, or higher?
  3. Which diaphragm did you use in the 807-8A?
  4. Did you ever compare the 807-8A directly with an 808, 802 or 806 on a 511B?
Active DSP

The system will be actively crossed and time/phase aligned using measurement rather than simply choosing a “classic” Altec crossover frequency.

So I’m particularly interested in experiences with:

  • acoustic crossover slopes
  • phase alignment
  • time alignment
  • EQ
  • driver protection
  • distortion
  • and what actually sounded better after the measurements were taken
I’m not trying to achieve the prettiest graph possible.

A measurement is useful to me because it helps explain what I hear.

And perhaps the most important question...

For those of you who have spent years with VOT/A7 systems:

What change made the biggest difference to the emotional experience of the music?

Not the biggest change on a frequency-response graph.

Not the change that made the system louder.

I mean the change that made you sit back and think:

“Damn... I’ve never heard this recording like this before.”

Did it come from:

  • crossover frequency?
  • cabinet bracing?
  • damping?
  • driver selection?
  • alignment?
  • room treatment?
  • subwoofer integration?
  • EQ?
  • removing the passive crossover?
  • something completely unexpected?
And finally:

If you were starting again with a 421-8H / 511B / 807 system today, what would you do differently?

I’m very interested in both successful modifications and failures.

In fact, the failures may be even more useful.

If you have measurements, photos, old crossover designs, cabinet information or simply 10+ years of experience with these systems, please share it.

I’m trying to separate:

“I think...”

from

“I tried it...”

from

“I measured it...”

and ultimately:

“I lived with it for years, and this is what actually mattered.”

Thanks in advance.

28Hz
 
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malden said:
how are you going to find someone who "tried it" in the exact same room as yours, especially when we know nothing about it?

this looks to be some AI nonsense
Click to expand...
Fair point. I'm not looking for someone who has used this exact combination in my exact room — that would obviously be impossible.

What I'm really looking for is experience with the 421-8H II / 511B / 807-8A combination itself: what crossover points people actually tried, what measurements showed, what worked or didn't work, and what they eventually preferred by ear.

The room and final crossover will obviously be determined here by measurement and listening.

I'm deliberately trying not to design this entirely from theory or datasheets.
Measure first, listen, then decide.

That's why real-world experience with the components is useful, even if the room is completely different.
 
Tom Brennan said:
For awhile I had 825s with 421s and with 511s with 808s, crossed at 500 with an Altec crossover. They sounded pretty good; big Altec tone, excellent dynamics and clarity.
Click to expand...
Thanks Tom — that's exactly the kind of real-world experience I was hoping to hear.

The 500 Hz point is particularly interesting, as that's where I'm currently planning to start with my 421-8H II / 511B / 807-8A combination.

I'll be using active DSP, so I'll be able to experiment around that point and compare measurements with what I hear.

Good to know that 500 Hz has worked well in a real-world Altec system.


28Hz
 
28Hz said:
Do you remember what crossover slope you were using at 500 Hz?
Click to expand...

I am not Tom, but I would recommend a pretty steep slope at 500Hz. Even though a 511 is RATED to 500Hz, it doesn't seem to LIKE playing much of ANYTHING below that. Distortion starts to rise pretty steeply below 500Hz, by measurements I've seen and done. In fact, the 511 just didn't seem to "maintain load" well below 800 Hz as well as it does above that- I can start hearing more "artifacts" to the sound at lower frequencies from a 511.

I'd probably recommend starting with a third order slope or so. Tom may have other info, but to be safe, for the 511, I would be inclined to "get it out of there" as fast as possible, below 500Hz. And don't be afraid to try nudging the crossover point up in frequency a bit- you might like it. The 421 certainly isn't going to mind playing up to even 1KHz, though I probably wouldn't go TOO much higher (above 1200Hz is kind of the tipping point where things can start to not sound as good- you start getting close to the woofer breakup-mode region pretty soon, above that).

Regards,
Gordon.
 
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As usual I'm going to agree with Gordon here. I love the 511 but 500hz is really optimistic, even with a capable driver. Just doesn't sound that excellent. Maybe if I had 50' of throw it would smooth out, but 800hz definitely was much smoother to my ears.

Now I'm crossed at 1200 and honestly don't really miss it. I think i was trying to get too much out of the horn for no good reason. Absolutely try it out at 500, 800, 1k, and everything in between. Taming big horns is about getting that sound, not where the knob is at.
 
GordonW said:
I am not Tom, but I would recommend a pretty steep slope at 500Hz. Even though a 511 is RATED to 500Hz, it doesn't seem to LIKE playing much of ANYTHING below that. Distortion starts to rise pretty steeply below 500Hz, by measurements I've seen and done. In fact, the 511 just didn't seem to "maintain load" well below 800 Hz as well as it does above that- I can start hearing more "artifacts" to the sound at lower frequencies from a 511.

I'd probably recommend starting with a third order slope or so. Tom may have other info, but to be safe, for the 511, I would be inclined to "get it out of there" as fast as possible, below 500Hz. And don't be afraid to try nudging the crossover point up in frequency a bit- you might like it. The 421 certainly isn't going to mind playing up to even 1KHz, though I probably wouldn't go TOO much higher (above 1200Hz is kind of the tipping point where things can start to not sound as good- you start getting close to the woofer breakup-mode region pretty soon, above that).

Regards,
Gordon.
Click to expand...
Thanks Gordon, that's very helpful.

The point about the 511B producing increasing distortion below 500 Hz is particularly interesting. I definitely don't want to force it to do something it doesn't like.

I'm using 511Bs with 807-8A drivers and active Lake DSP, so I'll be able to experiment with both crossover frequency and slope.

One question: in your experience, does the diaphragm in the 807 make a significant difference to how comfortably the 511B can be used around 500–800 Hz?

I'm currently checking exactly what diaphragms are fitted to my 807-8As before I decide whether to replace them.

If you have a particular diaphragm/driver combination you'd recommend for this application, I'd be very interested.

Thanks again,
28Hz
 
28Hz said:
Thanks Gordon, that's very helpful.

The point about the 511B producing increasing distortion below 500 Hz is particularly interesting. I definitely don't want to force it to do something it doesn't like.

I'm using 511Bs with 807-8A drivers and active Lake DSP, so I'll be able to experiment with both crossover frequency and slope.

One question: in your experience, does the diaphragm in the 807 make a significant difference to how comfortably the 511B can be used around 500–800 Hz?

I'm currently checking exactly what diaphragms are fitted to my 807-8As before I decide whether to replace them.

If you have a particular diaphragm/driver combination you'd recommend for this application, I'd be very interested.

Thanks again,
28Hz
Click to expand...

It's mostly the horn geometry (mouth area, flare length, flare rate and such) that determines the effective cutoff frequency of a horn, on the low end.

A driver can have a small effect- some drivers can handle unloading a bit more gracefully than others- but, I have never really seen that "save" a horn from its normal cutoff point behavior, in a significant way. Maybe if one went to something like a phenolic diaphragm instead of metal, that could help it "cope", but that's going to be with a HUGE loss in high frequency extension. I don't think that's a viable tradeoff.

Regards,
Gordon.
 
GordonW said:
It's mostly the horn geometry (mouth area, flare length, flare rate and such) that determines the effective cutoff frequency of a horn, on the low end.

A driver can have a small effect- some drivers can handle unloading a bit more gracefully than others- but, I have never really seen that "save" a horn from its normal cutoff point behavior, in a significant way. Maybe if one went to something like a phenolic diaphragm instead of metal, that could help it "cope", but that's going to be with a HUGE loss in high frequency extension. I don't think that's a viable tradeoff.

Regards,
Gordon.
Click to expand...
Thanks Gordon, that's very helpful.

The point about the horn geometry determining the effective low-frequency limit is particularly useful. It makes sense not to try to make the 511B do something it fundamentally doesn't want to do.

I'll definitely be experimenting with 500–800 Hz and different slopes using active DSP, and let measurements and listening decide where the system works best.

One thing I'm curious about: with the 421-8H II on the other side of the crossover, would you personally lean towards keeping the 421 relatively low and crossing around 500–600 Hz, or do you think there is a real advantage in letting the 421 run higher, say 700–900 Hz, before handing over to the 511B?

I'm particularly interested in what you've found by ear, rather than just what looks good on a measurement.

Thanks again,
28Hz
 
In my past experience with the 421’s in some big pa cabinets
Was they were better than the 416’s at deeper bass, but lacked the ability to play higher
As most Altec 15’s are known to be the best to come up and meet the horn smoothly
Whether 800 or 1200 hz.
What say you Prosound guys bowtie427ss? Twiii?
Bobhorn
 
Nyjblbob said:
In my past experience with the 421’s in some big pa cabinets
Was they were better than the 416’s at deeper bass, but lacked the ability to play higher
As most Altec 15’s are known to be the best to come up and meet the horn smoothly
Whether 800 or 1200 hz.
What say you Prosound guys bowtie427ss? Twiii?
Bobhorn
Click to expand...
Thanks Bob — that's very interesting.

Your comment about the 421 having better/deeper bass but not wanting to play as high is exactly the kind of real-world experience I'm trying to understand before I start setting the DSP.

I'm using 421-8H Series II in an A7/VOT cabinet with 511Bs and 807-8A drivers, and I'll be able to experiment with the crossover actively.

So here's the question I'm really curious about:

If you had a 421-8H / 511B combination in front of you today, would you personally start around 800 Hz and work down, or would you still try 500–600 Hz with a steeper slope?

I'm less interested in what the textbook says and more in where you found the 421 actually sounded best in the real world.

Thanks again,
28Hz
 
Ask any Vintage Altec collector-Audiophile, what their favorite woofer is?
Most would pick the 416. or the 515 if using Huge cabinets.
The bigger problem IMHO is pushing the 807-806 or even 802's
down to 500Hz .
Not a smooth response. the bigger 1.4" 288 drivers,with 311's or any of the big multi cells,
sure in a domestic system.
you can try it with a higher slope. after all it's your ears!
 
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I have a strong hunch that the goodness will lie somewhere in the middle. Probably 600 to 800 Hz or so. Again, since it's active- it's going to be pretty simple to experiment with various slopes and frequencies, to see what sounds best. Don't even be afraid to try different slopes on the woofer low-pass and the horn high-pass. As long as you keep track of polarity (if you hear cancellation or a "drop out" in the crossover region, try reversing polarity of either the woofer or the horn), there's an opportunity to find what's best here, that would be harder to do with passive crossovers.

Regards,
Gordon.
 
Nyjblbob said:
What say you Prosound guys bowtie427ss?
Click to expand...
I'm sure there were a handful of folks muttering "don't call him out on this" there'll be more after i respond. ;)


28Hz said:
For those of you who have spent years with VOT/A7 systems:

What change made the biggest difference to the emotional experience of the music?

Not the biggest change on a frequency-response graph.

Not the change that made the system louder.

I mean the change that made you sit back and think:

“Damn... I’ve never heard this recording like this before.”
Click to expand...
Large format on a constant directivity horn, lower distortion, and micro-dynamics that no small format Altec driver and horn combination can do.

28Hz said:
One question: in your experience, does the diaphragm in the 807 make a significant difference to how comfortably the 511B can be used around 500–800 Hz?
Click to expand...
Yes, if it's a properly installed symbiotik diaphragm, it will tolerate and perform better at those lower frequencies at the cost of some HFE.
28Hz said:
If you had a 421-8H / 511B combination in front of you today, would you personally start around 800 Hz and work down, or would you still try 500–600 Hz with a steeper slope?
Click to expand...
Personally, i wouldn't for any reason cross a small format Altec below 1khz on a 511.

28Hz said:
The 421-8H Series II
Click to expand...
Heavy cone, stiff suspension, series II replaced the paper coil former with an aluminum one for increased heat dissipation/power handling.

It's a bit forward right in the range where the mid-bass horn of an 825/828 provides the most gain. Great for SR and PA, maybe not so much for hifi.

I'll probably repeat this more than once, it's a great bass guitar speaker or LF driver for stage monitors.

28Hz said:
Altec VOT / A7-type bass cabinet
Click to expand...
Eventually, hopefully sooner than later, you'll have to define with a bit more precision exactly what you have.

It matters.

Sometimes a picture is worth a thousand...
 
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Zilch

Thread 'Z19 Crossover'

Express interest in a variant of the Altec Model 19 crossover I developed nearly three years ago has motivated me to build up a pair. It was originally posted on Lansing Heritage Forum here:

http://www.audioheritage.org/vbulle...-Altec-9844-8B&p=197971&viewfull=1#post197971

Since then, the design has been built and used successfully by Skywave-Rider, Similost, Dc270, and others. Here's my version, from the original schematic:

attachment.php



Shamefully, I myself had no data on how...
  • Like

This might be worth reading thru. Loads of actual data, even if it might be heading in a different direction than you. Definitely helped my decision making.
 
bowtie427ss said:
I'm sure there were a handful of folks muttering "don't call him out on this" there'll be more after i respond. ;)



Large format on a constant directivity horn, lower distortion, and micro-dynamics that no small format Altec driver and horn combination can do.


Yes, if it's a properly installed symbiotik diaphragm, it will tolerate and perform better at those lower frequencies at the cost of some HFE.

Personally, i wouldn't for any reason cross a small format Altec below 1khz on a 511.


Heavy cone, stiff suspension, series II replaced the paper coil former with an aluminum one for increased heat dissipation/power handling.

It's a bit forward right in the range where the mid-bass horn of an 825/828 provides the most gain. Great for SR and PA, maybe not so much for hifi.

I'll probably repeat this more than once, it's a great bass guitar speaker or LF driver for stage monitors.


Eventually, hopefully sooner than later, you'll have to define with a bit more precision exactly what you have.

It matters.

Sometimes a picture is worth a thousand...
Click to expand...
This is why 288s and 311s exist.
 
About 25 years ago I used 802s on 511s with 1st order crossovers and they worked well even at high volumes. I suppose they weren't used ideally but I liked them. However JBL 2420s on the same horns crossed at 500 first order clacked. Now I use the active FIR filters of my Acoustas AC-650 DSP amplifier and am currently crossing JBL 2425s on 2370 horns to D-130s in C35 cabinets at 630hz, 48 db per octave slopes, practically brick wall.

IMG_0521.jpeg
 
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