The 1803 is quite large in comparison with the 15 series. I run mine with 288C's.
I'm not too concerned about the bass extension as they aren't for critical listening and they are coupled with the big boxes for bass. Here you see the 828's when they were a two way. Standard beer mugs for relativity.
I'm not too concerned about the bass extension as they aren't for critical listening and they are coupled with the big boxes for bass. Here you see the 828's when they were a two way. Standard beer mugs for relativity.
Attachments
Decreasing the size of the port reduces the box tuning frequency. Part of Pano’s gain could well come from room gain as well.
<rant> It should be noted that F3 is a meaningless number to the human ear/brain (ref Toole) and only useful with reference to an electrical filter. If you want to get a measure of the low frequency extention using F6 or F10 is much more meaningful. </rant>
Dave
Yes, what GM says about the wings. It mostly helps the crossover region with the horn.
"Plump" was being polite. Boomy, flabby, bloated would be more direct terms.With the standard port there as nothing below 60Hz, and a peak above that. With reduced ports and some corner placement, I was getting an f3 in the lower 30s. The Hiraga A5 didn't go much below 50 Hz, but did everything above that with smooth elegance and ease. Not the least bit boxy.
As GM states, the horn flare in front of the woofer makes that range louder than the lower registers. What I did to combat that was to cross the woofer lower than the horn, and that works out the better match levels all around. E.G. low pass woofer @ 500 Hz and high pass horn @720 Hz resulted in the best blend. Don't remember the exact points, but may be able to look them up. They would vary with different horns and drivers anyway.
Pano, perhaps this looks familiar, and understanding French wouldn't hurt either.....these images and text are from June/July of 2005.
MELAUDIA :: écoute Revue du Son - juin/juillet 2005
You can clearly see the reduced reflex port area that you and Jean had installed in these cabinets. The shock absorbing feet look interesting too, and I wonder what kind of effect they had on the sound, aside from decoupling the speakers from the floor. And the wings appear to be around only 12 inches wide or so. I thought they would have been wider, and making them wider (within limits) could only serve to improve the mid-bass response further.
Best Regards,
Bruce
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It certainly did, and corner gain added some extension too.
Since I really didn't know what to do, I just measured the port response as best I could and went with a port area that gave the best match to the woofer response. In my case it worked out well and allowed the boxes to play down into the mid to lower 30s. There was some calculation involved to get near the target, but it was measurement at the port for the final stretch.
Bruce I know those Meluadio photos well. IIRC, there were no feet while I had them. And there was no carpet pad stuffing between the cells, tho Mr. Hiraga had talked about doing something like that with wool or similar. We did have something wrapped around the neck to dampen it a bit. Don't remember what. Later on, I used ace elastic bandage.
FYI, it's very important to stiffen and dampen the horn flares in front of the woofers. In stock form they sing along with the woofer, and they don't have the prettiest of voices. Easy to hear with a tone generator.
That should work well, along with a brace. In France I used a product called Blackston (from the UK I think) a messy non-hardening tar. Sticky!! In the US I used bituminous paint with sand. I think the ductseal is a much better idea. 
The woofer flares are usually thin ply and kerf cut so that they will bend. Some have a brace, many do not.
The woofer flares are usually thin ply and kerf cut so that they will bend. Some have a brace, many do not.
Greets!
You're welcome!
Hmm, can't recall ever having to explain this and while I'm sure there's probably a nice tidy way to do it, can't think of it ATM or could find it in a quick search, so going to load you up with a few facts that will hopefully help you visualize it..........
A point source driver has an acceleration [rising] bandwidth [BW] that's slowing down with increasing frequency up to its lower mass corner [Flc] where its curve has slowed enough [flattens out] based on its [Qts'] and at some point higher up in frequency its moving mass becomes too great relative to the shrinking frequencies, so begins rolling off its highs [Fhm] based on its voice coil [Vc] inductance.
All box design theory peters out at [Fhm], so pretty obvious that as one lowers box tuning to below a 'max flat' alignment, it must be following the Qts' and acceleration slope downward, hence the oft used phrase that one is always 'trading [acoustic] efficiency for [extended] BW'. The only efficient way around it is using room gain [as Pano did] and/or rear horn loading [BLH], which has its own set of trade-offs limiting usable BW, i.e. size, delay between horn, driver output; otherwise some form of EQ is required to shelve down all the BW above the cab's tuning to tonally balance it out.
Flc = Fs*Qts'/2
Fhm = 2*Fs/Qts'
Qts' = Qts + any added series resistance: mh-audio.nl - Home
'max flat' alignment = tuned for flattest response, i.e. a 0.707 box alignment Q [Qtc for closed, Qtb for vented and sometimes see Qtp for TL]
Haven't read it per se, only an Altec internal tech memo version of it many decades ago, but may help too: http://www.xlrtechs.com/dbkeele.com/PDF/Keele (1975-07 AES Published) - New Set of VB Alignments.pdf
GM
Spacing up a cab also impacts vent efficiency, reducing it, so will '[further] 'tighten up' the [mid] bass line at the expense of [further] rolling it off, which is principally what causes the perceived improved transient response.
Spacing up a cab also impacts vent efficiency, reducing it, so will '[further] 'tighten up' the [mid] bass line at the expense of [further] rolling it off, which is principally what causes the perceived improved transient response.
Assuming the wings are Altec spec, they're 10" wide and as I previously noted, only meant to fill in the area directly below the mid horn's roll off BW, i.e. 'feathers'/fills in somewhat down to ~65 Hz when setting on a very rigid floor to maximize floor boundary gain [+3 dB]. If a HF horn baffle is added then you have a really solid ~45 Hz before any room gain is added, so normally have to tune lower in a HIFI/HT app to keep from having too much [mid] bass.
Anyway, the original small Vott, the A800 before the 'bean counters' got to it, turning it into the baffle-less A7-8 [click to enlarge]: 800 VOTT
GM
It certainly did, and corner gain added some extension too.
Since I really didn't know what to do, I just measured to port response as best I could and went with a port area that gave the best match to the woofer response. In my case it worked out well and allowed the boxes to play down into the mid to lower 30s. There was some calculation involved to get near the target, but it was measurement at the port for the final stretch.
Bruce I know those Meluadio photos well. IIRC, there were no feet while I had them. And there was no carpet pad stuffing between the cells, tho Mr. Hiraga had talked about doing something like that with wool or similar. We did have something wrapped around the neck to dampen it a bit. Don't remember what. Later on, I used ace elastic bandage.
FYI, it's very important to stiffen and dampen the horn flares in front of the woofers. In stock form they sing along with the woofer, and they don't have the prettiest of voices. Easy to hear with a tone generator.
Hi Pano,
Yes, when I first got my 828 cabinets in the early 1990s, I coated the inside of the short horn flares with a lot of marine-grade epoxy. It was a pain to apply smoothly and in even coats, and it was expensive, but it worked. The short horn is dead as a rock as a result. I must have used close to a gallon or more of that stuff. In retrospect, the other materials described here for deadening of the short horn would have probably worked as well, would have been easier to apply, and been less costly.
I certainly don't doubt Mr. Hiraga's extensive experience with the A-5 and it's related hardware, but I'm not sure about the effectiveness of stuffing that material between the cells of the 1505B, or draping it over the top of the compression driver. The Aquaplas coating as applied by the factory is fairly effective at damping each of the individual cells, although probably not as effectively as the tar-filled 1505. I also would question how much ringing is present in the 30166 single-driver throat between the driver and the horn itself, as the bronze and aluminum throats Altec used with the 1505-series had a lot of mass. If Jean had the appropriate acoustical test and measuring equipment, he was probably well aware of any artifacts that were present in the HF horn structure, and he could have objectively measured the effect of these kinds of fixes.
Reading the Melaudio posts, it confirmed that Jean was indeed using some kind of E-V cone on the Westrex bass driver frame. This was news to me, and was not reported by John Stronzer in his classic SP article about the modifications Jean had made to his A-5s. Again, he had definite reasons for doing so, and I'd be curious as to his logic for making this change, vs. using a stock 416, 515, or other driver.
Best Regards,
Bruce
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Hi Cal,
Thanks for the photos of these cabinets, and the 1803. Very impressive! I wonder how the 1803 would sound compared with the 1505, while crossing the 1803 at 500 Hz???
I can also see the reduced port area you employed on your modified 825 cabinets. As I had mentioned in my earlier post, I am using about the same port area (80 square inches), but the jury is currently out on my feelings of the effect of the reduced port area with my A-5s. I have to do some serious listening, which I have been unable to do since I made this modification.
Best Regards,
Bruce
Hi Dave,
Thanks for the input!
Yes, reducing the port area should improve the extreme low frequency response of the 825/828 cabinets. I have to do some serious listening to hear if this did indeed improve the low bass performance of my A-5 system. I clearly hear improved transient response as noted, but I hope this was not at the expense of a loss of the lowest octave of bass output.
BTW, my A-5s are located in the corners of my listening space, so they do get the benefit of corner enhancement.
Best Regards,
Bruce
GM, thanks very much for the very detailed reply. Much appreciated!
At the risk of being a PITA, can you clarify for me what "Spacing up a cab" means? The "spacing up" term is unclear to me.
Are you suggesting that the reduction in port area did not improve the loading and damping of the bass driver, and as such did not improve its transient response? My logic here is that the reduced port area had better tuned the bass reflex mode of the enclosure, and as such, the control or damping of the woofer was much improved. Are you further suggesting that what I am actually hearing in this regard is not improved transient response, but rather the bass response was actually rolled off in the region where I had heard the boominess with the stock 210 square inch port area, and the reduction in port area to 80 square inches has significantly rolled off the low bass? This would appear to me to be contrary to what Pano had noted when he reduced the port area on Mr. Hiraga's A-5s.
If I could get reasonably flat acoustic output (below the short horn cut-off of around 150 Hz or so) to 45 Hz, and with improved damping of the woofer by virtue of the reduced port area of 80 square inches, I would be very happy.
Again, please forgive my lack of knowledge about these kinds of things.....my expertise is more towards the electronics.
Thanks for your patience here!
All the Best,
Bruce
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As for the details of stuffing and damping to horn, hard for me to say as mostly wasn't in place when I used them. They sounded amazing with out it, FWIW. IIRC, the first woofer was a 416, but changed later. Mr. Hiraga had a few mix and match woofers that I never really understood. That was way above my pay grade, at least at the time. I wish I had written down details, but it was Paris and I was young, too busy and foolish. Who knew those speakers would live on for decades. 
The bass reflex changes could be difficult for you, as you've lived with your A5s for 25 years. For me it was all new the first time as I'd not heard an A5 or A7 before.* When I bought a pair of A7-500 years later to be turned into A5, I was shocked at how bad they sounded. Nothing like the Hiraga A5s I had known and loved. The journey to transform them was fairly straight forward, with not too many twists and turns, other than crossover work.
*I had heard them many times in a theater I worked in - but didn't realize it.
The bass reflex changes could be difficult for you, as you've lived with your A5s for 25 years. For me it was all new the first time as I'd not heard an A5 or A7 before.* When I bought a pair of A7-500 years later to be turned into A5, I was shocked at how bad they sounded. Nothing like the Hiraga A5s I had known and loved. The journey to transform them was fairly straight forward, with not too many twists and turns, other than crossover work.
*I had heard them many times in a theater I worked in - but didn't realize it.
As for the details of stuffing and damping to horn, hard for me to say as mostly wasn't in place when I used them. They sounded amazing with out it, FWIW. IIRC, the first woofer was a 416, but changed later. Mr. Hiraga had a few mix and match woofers that I never really understood. That was way above my pay grade, at least at the time. I wish I had written down details, but it was Paris and I was young, too busy and foolish. Who knew those speakers would live on for decades.
The bass reflex changes could be difficult for you, as you've lived with your A5s for 25 years. For me it was all new the first time as I'd not heard an A5 or A7 before.* When I bought a pair of A7-500 years later to be turned into A5, I was shocked at how bad they sounded. Nothing like the Hiraga A5s I had known and loved. The journey to transform them was fairly straight forward, with not too many twists and turns, other than crossover work.
*I had heard them many times in a theater I worked in - but didn't realize it.
Thanks very much, Pano!
Your experience with the stock A-7 is dead-on. There is zero comparison sonically between a stock A-7, and an A-5 system modified to the Hiraga configuration. I acquired a pair of A7-500s about 4 years ago, and I found them to be almost unlistenable, as I had become so used to the sound of my A-5s with the Hiraga crossover.
You make a good point about my being so accustomed to the A-5's bass performance with the standard reflex port area, after listening to this speaker system for the last 25 years. I will continue to listen to them with the reduced port area for a while, and if I really think that to my ears, the original 210 square inch port sounded better, it is of course an easy thing for me to go back to that.
I was looking at a technical book I have had here for many years, specifically the section on the design of bass reflex enclosures. The author of this book recommends a minimum port area equal to a minimum of 75% of the total radiating area of the driver, and up to a maximum of 100% of the radiating area. In the case of a 15 inch driver, the minimum port area would be around 95 square inches; my reflex port has an area of 80 square inches. The port area apparently impacts the radiation resistance of the port, which makes good sense, and there is an optimum value for this.
Altec had some very talented engineers who were responsible for designing the A-5 and A-7 enclosures, (John Hilliard being one), and I must assume that there had to be valid engineering rationale for the 210 square inch port area used with these cabinets. I think it had nothing to do with being able to locate the 500 or 800 Hz sectoral horns within the A-7 enclosure, when the speaker system was used in that configuration. I would really like to know why the Altec engineers designed the 825 and 828 enclosures with such a large reflex port. Perhaps the program material limitations (i.e., very limited low-end content) of the 1940s-era cinema soundtracks were a consideration, but this changed substantially in the early 1950s with the introduction of magnetically-striped cinema soundtracks having much greater low frequency content, but not yet with subterranean bass. That said, you would assume that Altec would have modified the port area to enhance the low-frequency performance of the 825 or 828 cabinets due to the improvement in low-frequency content this new cinema recording media now provided, if indeed the port area would have a significant impact on the ability of these enclosures to reproduce frequencies cleanly much below 60 Hz or so. And of course with the advent of LP records and magnetic tape recording in the early 1950s, you would assume Altec would improve the low-frequency performance of the 825 and 828 to be on par with this newly introduced audio storage media, as many A-5 and A-7 systems were utilized in recording studios for playback purposes. But perhaps these enclosures, by their inherent design limitations, could not be modified by Altec to do so.
By the same token, the reflex port area on the large 210 cabinet (as used in the A-1, A-2, and A-4 systems), with its much greater enclosure volume, appears to be roughly the same area as on the smaller 825 and 828 enclosures, so go figure...….
I would like to speak with an Altec engineer who was really knowledgeable about the 825 and 828 cabinets, and the theory behind their design. And of course, there are a lot of very knowledgeable people nowadays, such as yourself, Cal, and GM that can provide excellent technical rationale for the use of the reduced area port, based upon the testing and experience you have had with this.
Best Regards,
Bruce
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Bruce,
The answer is (the short version):
They didn't know any better!
These designs came long before Thiel-Small Parameters, so the approach back them was more cut and try than mathematical.
Also the big open "reflex" saved them money - their goal was to make the box as inexpensively as they could. Things like wall resonances were not considered very much if at all. Neither were seals or leaks, or stiffness...
The deal behind the front loaded horn was to make it possible to meet the HF horn in amplitude as closely as possible. In other words better than just a basic "reflex" box, more output per watt input. The goal was speech intelligibility, not fidelity.
Few speakers of the day had any real bass response. Especially in PA speakers.
Home speakers before the AR-1 with LF response were few and far between, despite what any printed specs said. Exceptions were things like the JBL Paragon and the Klipsh corner horns - both expensive and large.
It's really that simple.
The answer is (the short version):
They didn't know any better!
These designs came long before Thiel-Small Parameters, so the approach back them was more cut and try than mathematical.
Also the big open "reflex" saved them money - their goal was to make the box as inexpensively as they could. Things like wall resonances were not considered very much if at all. Neither were seals or leaks, or stiffness...
The deal behind the front loaded horn was to make it possible to meet the HF horn in amplitude as closely as possible. In other words better than just a basic "reflex" box, more output per watt input. The goal was speech intelligibility, not fidelity.
Few speakers of the day had any real bass response. Especially in PA speakers.
Home speakers before the AR-1 with LF response were few and far between, despite what any printed specs said. Exceptions were things like the JBL Paragon and the Klipsh corner horns - both expensive and large.
It's really that simple.
What I did is pure heresy.
Here's a partial list/rundown. From memory. It's over 20 years now.
- Move to a 300Hz horn
- this permits reasonable flatness overall, and improves the upper mids (takes them off the 15" driver
- Use an elliptic LP filter for the LF driver, 1st order for the (non-Altec) HF driver
- The elliptic LP is designed to precisely counteract the rise in amplitude of the front loaded LF driver, flattening the response with a <3dB rise between 150Hz and rolloff
- rolloff to the HF horn measures like a cliff
- stiffened all walls by outer lamination
- stiffened interior with struts
- stiffened horn flare with very hard "concrete-like" poured in compound
- replaced LF driver throat piece with something substantive (not cheesy plywood)
- used highly absorptive wall treatment on all interior walls (it's dead in there)
- changed out "reflex" opening for sealed ports - simulated and tested, ample area.
- used modern JBL 15" equivalent to the "Paragon" driver, permitting actual 35Hz tuning.
- necessary to biamp now, higher power amp on the bottom, and can now nice tube SE or other amp without ANY attenuator between the amp and speaker on the HF!!
Obviously, this is no longer a true "Altec".
But it solves or resolves a number of real problems that the original design has for our applications.
It's not really good for PA use like this.
Advantages:
- true LF tuning, pretty darn flat to 35Hz. (awesome in a large space like that barn!!)
- able to use full sensitivity of HF driver, can use much lower power amps than stock; aka 109dB/1w/1m typically, not 100db/1w/1m
- LF speaker can handle more power than the Altec designs
- no midrange or midbass "blow through" from the "reflex" opening
- much much cleaner midbass than stock
Disadvantages:
- heretical
- takes WAY too many hours to pull this off - not going to do THAT again!
_-_-bear
PS. Imho, it is impossible to get "bass" out of the stock drivers given the cabinet volume. Run the simulations.
So, forget about low bass, that's the conclusion I drew, and moved to a different driver and the above solutions.
Here's a partial list/rundown. From memory. It's over 20 years now.
- Move to a 300Hz horn
- this permits reasonable flatness overall, and improves the upper mids (takes them off the 15" driver
- Use an elliptic LP filter for the LF driver, 1st order for the (non-Altec) HF driver
- The elliptic LP is designed to precisely counteract the rise in amplitude of the front loaded LF driver, flattening the response with a <3dB rise between 150Hz and rolloff
- rolloff to the HF horn measures like a cliff
- stiffened all walls by outer lamination
- stiffened interior with struts
- stiffened horn flare with very hard "concrete-like" poured in compound
- replaced LF driver throat piece with something substantive (not cheesy plywood)
- used highly absorptive wall treatment on all interior walls (it's dead in there)
- changed out "reflex" opening for sealed ports - simulated and tested, ample area.
- used modern JBL 15" equivalent to the "Paragon" driver, permitting actual 35Hz tuning.
- necessary to biamp now, higher power amp on the bottom, and can now nice tube SE or other amp without ANY attenuator between the amp and speaker on the HF!!
Obviously, this is no longer a true "Altec".
But it solves or resolves a number of real problems that the original design has for our applications.
It's not really good for PA use like this.
Advantages:
- true LF tuning, pretty darn flat to 35Hz. (awesome in a large space like that barn!!)
- able to use full sensitivity of HF driver, can use much lower power amps than stock; aka 109dB/1w/1m typically, not 100db/1w/1m
- LF speaker can handle more power than the Altec designs
- no midrange or midbass "blow through" from the "reflex" opening
- much much cleaner midbass than stock
Disadvantages:
- heretical
- takes WAY too many hours to pull this off - not going to do THAT again!
_-_-bear
PS. Imho, it is impossible to get "bass" out of the stock drivers given the cabinet volume. Run the simulations.
So, forget about low bass, that's the conclusion I drew, and moved to a different driver and the above solutions.
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Hi Bear,
Thanks very much for the information you had provided!
You are right; that is a lot of work to get that system to do what you wanted it to do.
I have no plans for incorporating any kind of active corrective EQ within my system. I plan on continuing to use the Hiraga crossover network, and the passive EQ it provides to the 1505B horns I am using with my A-5 system.
My quest is to improve the bass performance of the 828 enclosure/416-A bass driver combination, below the cut-off of the short horn. I realize that the acoustic output of the shorthorn rolls of at around 150 Hz, and that the bass reflex mode of the enclosure cannot match the short horn's acoustic output. That is an inherent issue with the A-5 and A-7 systems.
Take a look at my post above, with regard to my thoughts on the stock 210 square inch bass reflex port as used in the A-5 and A-7 systems. I'd be curious to hear your thoughts on this.
I did reduce the bass reflex port area on my enclosures from the stock 210 square inches, to 80 square inches. A lot of A-5 and A-7 users have commented that this does improve the bass performance. My jury is currently out on this; I am not sure if what I am hearing is improved damping of the bass driver and less boominess, or a roll-off of the bass output.
I had posed the following questions to another participant on this forum, and perhaps you can provide your input here. I believe (but I am not sure) that he was suggesting that the reduction in port area did not improve the loading and damping of the bass driver, and as such did not improve its transient response. My logic here is that the reduced port area had better tuned the bass reflex mode of the enclosure, and as such, the control or damping of the woofer was much improved. He may have further suggested that what I am actually hearing in this regard is not improved transient response, but rather the bass response was actually rolled off in the region where I had heard the boominess with the stock 210 square inch port area, and the reduction in port area to 80 square inches has significantly rolled off the low bass? This would appear to me to be contrary to what Pano had noted when he reduced the port area on Mr. Hiraga's A-5s.
If I could get reasonably flat acoustic output (below the short horn cut-off of around 150 Hz or so) to 40 Hz, and with improved damping of the woofer by virtue of the reduced port area of 80 square inches, I would be very happy.
Again, please forgive my lack of knowledge about these kinds of things.....my expertise is more towards the electronics.
Thanks & Best Regards,
Bruce
Thanks very much for the information you had provided!
You are right; that is a lot of work to get that system to do what you wanted it to do.
I have no plans for incorporating any kind of active corrective EQ within my system. I plan on continuing to use the Hiraga crossover network, and the passive EQ it provides to the 1505B horns I am using with my A-5 system.
My quest is to improve the bass performance of the 828 enclosure/416-A bass driver combination, below the cut-off of the short horn. I realize that the acoustic output of the shorthorn rolls of at around 150 Hz, and that the bass reflex mode of the enclosure cannot match the short horn's acoustic output. That is an inherent issue with the A-5 and A-7 systems.
Take a look at my post above, with regard to my thoughts on the stock 210 square inch bass reflex port as used in the A-5 and A-7 systems. I'd be curious to hear your thoughts on this.
I did reduce the bass reflex port area on my enclosures from the stock 210 square inches, to 80 square inches. A lot of A-5 and A-7 users have commented that this does improve the bass performance. My jury is currently out on this; I am not sure if what I am hearing is improved damping of the bass driver and less boominess, or a roll-off of the bass output.
I had posed the following questions to another participant on this forum, and perhaps you can provide your input here. I believe (but I am not sure) that he was suggesting that the reduction in port area did not improve the loading and damping of the bass driver, and as such did not improve its transient response. My logic here is that the reduced port area had better tuned the bass reflex mode of the enclosure, and as such, the control or damping of the woofer was much improved. He may have further suggested that what I am actually hearing in this regard is not improved transient response, but rather the bass response was actually rolled off in the region where I had heard the boominess with the stock 210 square inch port area, and the reduction in port area to 80 square inches has significantly rolled off the low bass? This would appear to me to be contrary to what Pano had noted when he reduced the port area on Mr. Hiraga's A-5s.
If I could get reasonably flat acoustic output (below the short horn cut-off of around 150 Hz or so) to 40 Hz, and with improved damping of the woofer by virtue of the reduced port area of 80 square inches, I would be very happy.
Again, please forgive my lack of knowledge about these kinds of things.....my expertise is more towards the electronics.
Thanks & Best Regards,
Bruce