Pete Riggle (maker of my crossovers) says he improves bass on his (and others) A7's by attaching a large dual thickness plywood plate to the front of the 825B bass cabinets from the bottom of the forward facing bass horn to the bottom of the cabinet, bisecting the front port so that two 4" wide openings result (on either side of the plate), reducing the front port area to 64 square inches (32 each), and reinforcing the front panel at the same time. He also advises raising speaker off the floor. The DIY forum alternatively recommended both 80 square inches, and 90 square inches, also not reducing the 220 square inches (argues the Altec 416-8B Alnico driver not up to it?). Which is it? The DIY forum also suggests wings on the sides and placement in corners to help bass. Your opinions welcomed.
The top of the line Songer speaker does look interesting in design. I like the idea of the speaker being supported from behind at the magnetic structure, so that less energy is transmitted to the front baffle. I also like the nice taper at the back so that the back wave is smoothly reflected and guided rearward. The price is also quite reasonable. The major downside is its lowish efficiency (93 db/w); something closer to 100 would have been better. I hope it shows up at the Capital Audiofest.
Yes and no... Reducing the port area will lower the -3 dB. point. Maybe you will lower is from 47 Hz. down to 44 Hz. A still smaller port will lower it another 1 or 2 Hz. However... there is no such thing as a free lunch! When you lower the -3 dB. point you also change the drop-off slope. Altec has a reason for keeping the port the size it is. Yes, the bass does drop off below 47-Hz. That is due to the size limitations of the cabinet. After which, it will drop off gradually. It can still reproduce bass frequencies down to the low 40's, just at a lower, but not that noticeable, volume. The best approach is to leave the port and the cabinet alone, except for the adding additional internal bracing. The A7's are a time proven design. Let them do what they are designed to do and do well. For lower bass frequencies, add a sub at and below 40-Hz.
I have experimented with reducing the port size of my Altec A7-500s but in the end go with the stock port opening. The sensitivity hit is too severe when giving up the large port. Also, I use subwoofers with the A7s (four 18" JBLs in stereo, two to a side), which fills in the bottom octaves which is pointless to try to get out of the Altec cabinet, which was never designed to go much lower than 40-50Hz. Stiffening up the stock cabinet helps a lot to achieve better clarity.
Thank you, I expected as much, but do I trash the resale value by stiffening up inside with 1” x 2” bracing?
Why on earth would you want to resell them? Regardless, if you are concerned about resale value, I'd leave them stock, so the next lucky bastard can stiffen them up if that's what they want to do.
Not so much concerned about resale, but don’t want to ruin then out of ignorance like I did with a samurai sword once by filing off the rust under the handle
Please elaborate on what modifications must be performed on A7's. I wrote, asking A7 owners if attaching 1"x2" beams on narrow edge in irregular patterns on inside of the cabinet to stop resonance and standing waves would be a good idea and was told that any changes would lessen resale value (implying not a good idea). Have any of you with A7's ever done this, reinforced cabinets with beams glued/screwed to the inside walls where it wouldn't show? I would like to know, but I have been confused by what some say on this thread. Overall the point seems to be that stock A7's, in vintage state, are up there with the very best speakers available from any time, however: Some argue that the crossover must be changed. One suggests using Klipsch crossovers on Altec speakers, while another argues against that and suggests Hiraga style crossovers (which were designed for the A5). As the stock crossovers are mounted in the back panel by a thin board covering a hole, which resonates in low frequencies, does that mean changing from stock crossover to new with a new solid rear cabinet panel as well? Some on this thread dispel the notion of adding sub-woofers as they can not be fully coherent in speed/immediacy as the bass in the A7's, that instead of using subwoofers, one should attach wings to the sides of the 825B bass cabinets to improve the bass response (does the addition of wings include placement in the corners of the room to add walls as final extension of horn?), yet most of the video examples of A7's playing music on this site, utilise sub-woofers. Last, adding super-tweeters to A7's. I read on this thread that doing so was trying to turn a vintage speaker (with acceptable good sounding limitations) into modern speakers, and even saying that when added, they didn't add much to the sound ... but left them on anyway. The above is not intended to criticise in any way, only to show where what contributors have said, and then done, is confusing. We are comparing vintage speakers with modern speakers and some have argued that the Altec A7 is highly competitive, some say as it comes, some imply (by their own mods) by making certain changes. I would like to run mine without sub-woofers or super-tweeters, and do not like the looks of them with wings attached either. I have already replaced the back panel with solid ply and two external braces when I changed crossovers to Pete Riggle's "Hiraga" style crossover (I kept the original Altec crossovers, one friend whose ears I trust likes them better). I replaced the cheap large gauge multi strand hookup wire placed by a previous owner with Duelund 16Gauge tinned-stranded copper in cotton and oil insulation. I did not reduce the front port opening to 90 square inches/80 square inches/64 square inches as has been advised to me elsewhere as I am told it will lower bass response, but also sensitivity (and I didn't like the looks of those I saw with this modification). I am planning on stapling Marshall-style guitar amplifier grill cloth to the inside to cover the port as I do not think it will harm the sound but might help the appearance. I do not want to stuff the inside with fibre glass insulation as that stuff breaks off and gets aerosolised in the listening room, not good for lungs! Instead, I want to attach 1"x2" hardwood beams to the inside walls of the cabinet to reinforce and hopefully stop internal standing and interference waves. Being inside, and hidden by the grill cloth, I am hoping I can keep the original appearance while improving the performance. I would like your opinions.
I've listed the modifications I've made on my A7s before, but I'll repeat them here. I was a former Altec Lansing engineer from their original factory in Anahiem, CA. I bought my A7s a few years before working there and took the opportunity of being around the people who designed these speakers to pick their brains to improve my own pair. I also just loved the history of Altec. It was a great place to work, but unfortunately they went belly up in the early 80s. Anyway, there are a number of problems which must be dealt with to bring the A7 up to today's standards. Most of these problems have to do with resonances, both of the low frequency cabinet and of the high frequency horns. Also, the stock Altec N-500 and N-800 crossovers do not go nearly far enough to 'voice' the speakers to modern HiFi standards. They were voiced for efficiency, not the finest sound quality to audiophile standards. The good news is that the basic components such as the compression drivers, woofers, low frequency and high frequency horns are exceptional - I would go so far as to say they are the best available, even today. The high frequency compression drivers went through several iterations, even as I worked there. There were two main changes; the change to ferrite 'mud' magnets from the previous Alnico, and the change from radial to tangential 'Tangerine' phase plugs. Myself, I prefer the old style 802D compression drivers which have both Alnico magnets and radial phase plugs because of their smoother sound quality. I had quite a bit of experience with the ferrite magnet 902 drivers with their Tangerine phase plugs and I found them extremely harsh sounding compared to the old style 802. Your mileage may vary, but I would seek out the 802 over the 902. Also, it is extremely important that the proper diaphragms be installed. The 34647 diaphragm (8 ohm) was considered the 'HiFi' version. There were other versions for higher power applications - don't use these. Luckily the 34647 diaphragm is still available from Great Plains Audio. It is pricey, but mandatory. Radial Engineering also makes a replacement diaphragm which I have on a set of 802 drivers. They have nice, flat response but require more extreme voicing to get there - this might be too difficult for people without a lot of technical capability to construct the required voicing filters. The high frequency 811 and 511 horns have a problem with resonance. Under some circumstance they will ring like a bell, which is obviously not great. Mounting these horns onto a baffle helps somewhat but this does not alleviate the problem completely. The solution is to apply a thickness of about 1/2" of damping material to the entire exterior of these horns. The factory used Aquaplas for their sectoral horns and on later 511 horns, though not of sufficient thickness in my opinion. By the way, Aquaplas is the substance which was sprayed on the older JBL woofers and this made them their signature white color. I use Aquaplas on my horns but unfortunately it seems to no longer be available. Fortunately there is a readily available alternative - Bondo automotive putty which is sold in any auto parts store. Apply about 1/2" of Bondo to the entire exterior of the horn, even the front portion of the horn in front of the mounting flange. Be careful to work quickly because Bondo has a fast set-up time. You might want to work up thinner layers so that the Bondo doesn't start to set up before you're done spreading it out. When done, spray painting the exterior with Krylon Satin Black improves the appearance. After applying the Bondo, rapping the horn with your knuckles will reveal an absolute lack of any resonances. The low frequency horn has several problem areas. These are the sides, the upper and lower rear, the boards which form the bass reflex port, the top of the cabinet, and the sides and bottom of the bass horn. The sides of the cabinet can be stiffened by applying edge-wise 2x4s diagonally on each side. Likewise the lower back. Apply new fiberglass batting over these boards. I have applied a 3/4" thickness of Baltic Birch plywood to the back of the port boards. For the removable upper back, I constructed a new one by laminating two thicknesses of 3/4" Baltic Birch together. The sides of the low frequency horn are so thin that they seem more like the body of a guitar. While not absolutely mandatory, you might wish to deal with this. Apply a 1/2" thickness of Bondo to the inside walls of this horn. I followed up by applying a couple inch thickness of a mixture of sand and plaster on top of the Bondo, then fiberglass on top of this. The sand/plaster is more optional however. The lower side of the horn can be stiffened by placing a 2x4 on edge across the middle, inside the cabinet, and fiberglass over this. For the top of the cabinet, anything you do here will degrade the cabinet visually, so what I do is place a couple of 5 or 10 pound sand bags on top. These can be purchased from photo supply shops. I absolutely recommend the use of active crossovers with these speakers! This will allow the easy voicing of the low frequency and high frequency horns and also allow optimum selection of power amplifier for each half. The high frequency horn works best with a low power SET. The low frequency woofer section works best with a push-pull tube amp of about 40 watts. DO NOT USE SOLID STATE AMPLIFIERS OR CLASS D AMPLIFIERS ON THESE OR ANY HORNS! Just don't. Also, for the high frequency horn, you do not need much power at all - my SET amplifier uses sweet sounding 2A3 tubes and outputs around 2 1/2 watts which is perfect, and more than enough to drive you out of the room. A 300B amp will also work very well. Elliot Sound Products makes a suitable electronic crossover. Linkwitz-Riley Electronic Crossover The crossover frequency should be 800Hz when using the 811 horn and 500Hz when using the 511 horn. I would seek out the 511 horn since this allows the higher sensitivity high frequency horn to cover the range from 500Hz to 800Hz. This provides better projection in this range than when the woofer horn covers this range. The reason that Altec designed the 500Hz crossover version (the A7-500) was to provide this extra projection. I've found that this substantially increases the sense of realism from these speakers. In the late 70s, Altec changed the crossover frequency to 1,200Hz. I tried it then, and I've tried it since, and my conclusion is just do do this. The projection of the woofer horn in this range just isn't there. I have tried every possible crossover slope with my A7-500s - 1st order (6dB per octave), 2nd order (12dB per octave), 3rd order (18dB per octave) and 4th order Linkwitz-Riley (24dB per octave). I have found that the best, smoothest transition from high frequency horn to low frequency horn is achieved with a 2nd order 12dB per octave Linkwitz-Riley crossover. The crossover board I linked above is 24dB per octave; if you want to go 12dB per octave, just use one section. There is a resistor value calculator on the project page for calculating the values needed for a 2nd order Linkwitz-Riley crossover. The high frequency compression drivers have an 'efficiency hump' in their response in the vicinity from the crossover point to around 3kHz. This MUST be equalized out to achieve anything resembling flat response and to bring the speakers up to current standards. By the way, this hump is not unique to older Altec compression drivers; most all compression drivers, old or new have it. Below is the basic response of my voicing filter. I add a couple passive filter sections on top of this to correct for my specific room, but these would be different or not needed at all for different situations. On the matter of subwoofers, the Altec bass horns only go down to around 40Hz to 50Hz which is typical of all bass horns. I use four 18" JBL subwoofers which have been tuned to 12Hz to extend response to the vicinity of 15Hz. You will need multiple, large subwoofers to keep up with the Altec bass horn section. Just warning you..... Hopefully I've covered everything. Properly sorted out, these classic Altec Lansing Voice of the Theater speakers can hold their own against the biggest and baddest and newest speakers made today. They will certainly have better dynamics and sense of realism than any non-horn speaker made today.
This is the in-room response of my left channel A7-500 taken at the listening position which is 11 1/2' away from the speakers. The subwoofer is included.
Hey Ampexed, Thank you for this, most helpful. I am wondering if you would kindly take a look at my situation a bit closer? First, the crossover, I replaced rebuilt stock with Pete Riggle's "Hiraga" style crossovers (crossed over at 500 Hz), which use large oil-filled capacitors which have increased bass considerably, but that has unveiled cabinet reflections that smear the notes. I am planning to reinforce the cabinets with internal bracing, but would like to avoid using fibre glass wool padding as I do not want to breathe the microscopic fragments expelled from the front port. Will that work (RCA metal horns have no padding and they sound great)? Second, the compression drivers. I too have read that the 802D(G etc) with the (34647) aluminium diaphragm and radial diffuser sounds better than my 902-8B ferrite's. I searched for used 802D (in 8 Ohm) on the internet and the best I could find was a single beat up 16 Ohm example (one) in pieces for parts or serious rebuild. Great Plains Audio has released a modern remake of the 802 with Alnico magnets, however the diaphragm is different (don't know if the phase plug is tangerine too, or not). I contacted them and asked if these new remakes would sound much better than my 902's and was told they would not! A friend suggested replacing my 902's with TAD (TD-2001, beryllium diaphragm, 1kg Alnico magnet, 500~22,000 Hz range), but their web-site warns never to crossover lower than 800 Hz! I wrote them to see if they would work at 500 Hz crossover, just not optimally, or will I need to exchange my recently bought crossovers for a pair that crossover at 800Hz? Also I would need to change the mounts to my Klugghorns (two rows five) currently being built for a 1" mouth, two-bolt connection 902. I have employed Markus Klug to replace my 511B horns with his 1005 (2 rows of 5 discrete horns, made of wood, cork applied to outer surface) horns in hopes that these will eliminate any ringing and improve sound stage. As they will not have the Altec bug screens (See Sound Practices Summer 1993), that should improve definition as well. Any comments? Mark
All I can say is that if you want results identical to mine, follow the guidelines exactly. Feel free to experiment, but you're on you own there, as I can't speculate what the performance will be. What I have done reflects several decades of experimentation and personal conversations with the other Altec engineers at the factory when I worked there. I had access to their test lab, anechoic chamber, and all the production facilities. These are old speakers with original parts which are difficult if impossible to get in good used condition. Luckily some of the parts are still available at Great Plains Audio.
It doesn't sound like he's changing the port in any way, just adding thickness to the front baffle. Most vintage speakers respond well to this.
If you are concerned about fiberglass, there are many alternatives that you can experiment with to see what works. A local custom builder uses a variety of materials, such as acoustic foam and thick wool felt (the felt is somewhat expensive). I believe Hiraga used medium density thick wool felt in his speakers. My local dealer likes Kimsul, but that is very hard to find as it has not been in production for well more than 50 years.
He was asking about changes in the port area that he had read about. Some people like to reduce the port size. Doing this will "tune" your port and give you a deeper bass, but it is a trade-off. The guy in California that did the restoration and modifications of my main pair of A7's, did add some internal bracing to the cabinet and behind the port boards. I understand that he added some foam to the inside of the wooden horn area. I have never opened the cabinets so I don't know exactly what these changes are. I made a screenshot of his description of them. He had bought a few 828 cabinets at a good price. Mine are not even a matched pair. This guy does some first class work and is very knowledgeable when it comes to speaker audio. I have played these A7's at all volume levels, from a bare minimum to naxing them out and I have not experienced any issues with cabinet resonances. Though they no doubt do exist, being that these are large mostly empty plywood boxes. As they are, they are pretty solid!
I have found a site in the UK that sells “wool insulation” rolls, the thinnest being 50 mm thick, and “acoustic wool carpet underlay”, which is 10 mm thick. I know the thinner one would be easier to staple over reinforcements to the side walls of the cabinets but would it work? The 50 mm thick wool insulation roll would probably deaden internal reflections more, but be much more difficult to cut to shape and install (how do I attach it to the plywood cabinet walls). Since the RCA horns have no internal wool/glass but sound great, is it needed after I reinforce the cabinets?
Always wanted to try out a pair of horn speakers and was offered this pair locally for $200 by an elderly man who has gotten rid of most of his equipment. I'm told they work perfectly, but I couldn't give them a listen. Tempted to give them a try to get a feel for what horns will sound like in my system, though I have no experience with them and am pretty ignorant of the technology. I'd be driving them with a pair of Carver Cherry 180 tube monos. Am I wasting my time/money or would these give me some good sense of horn sound?
Chances are that you won't like the sound of these. They can be made to hold their own with anything made today, but these look stock and will likely sound 'like horns' in the pejorative sense.
I've written what is required in some other thread on this forum. You might do a search. The crossover network is great as a doorstop. Let's just say that making these presentable is not a plug 'n play proposition.
I disagree with the idea these are a waste of time but they will need to be properly set up…gonna need a recap, drivers checked, make sure bass enclosure is right size, right amounts of insulation, etc. mount the horns the right way and you will have an amazing set up for a ridiculous low amount of money…this is a no brainer…
