I'd be interested to know the external dimensions of your ported enclosure, and also what the internal diameter and length of the port are. I'm just a little curious about what sort of tuning has been used for these Altec 409-8c drivers.
There are vented-box tuning tables that are used when calculating vented enclosures for drivers. They are based on particular "alignments", but it's definitely possible to create ported designs that don't exactly fit a particular alignment. I liked your comment that "in some way it works", but that's the nature of loudspeaker design and listener preferences. What might be a "bad" design to one listener, might be a "good" design to another listener; welcome to the world of subjective evaluation.
@newbie802 Do you have a more complete set of Thiele–Small parameter data for the Altec 409-8c driver? What's needed for an enclosure design program is at least Fs, Qts, and Vas, and you've only mentioned Qts=1.54.
Even when new, the Polk Audio PSW111 isn't a very expensive subwoofer. Its low-frequency cut-off performance, as you've noted, seems to be very similar to that of the Yamaha YST-SW45. However, with a 150W amplifier driving its 8-inch woofer, it might be expected that the driver in the PSW111 might have a greater excursion capability than the driver in the YST-SW45. In any case, either of these two subwoofer models will augment the bass in your system very well.
That does make sense, as I believe that the Altec 409-8c has a free-air resonance frequency 10–20Hz above that.
As the Altec 409-8c is a relatively old driver, its excursion capabilities are likely to be a little bit limited by modern standards. Hence, it might be worth considering blocking the port and turning the ported enclosure into a closed-box enclosure. This would benefit the driver by greatly reducing its excursion at low frequencies below the port tuning frequency when it is being driven full-range. This would leave the Altec 409-8c with more linear excursion capability above 90Hz or so, reducing distortion at higher power inputs.
The enclosures are 23 cm deep, 30 cm wide, 44 cm high, and the front baffle is receded by 1 cm. The material is particle wood 2 cm thick. The port is a cardboard tube 7 cm wide. I haven't measured the lenght but it should be about 15 cm long. There's no removable baffle. They put a cloth on the external part of the tube. I don't know why. (Not to get pieces of fiberglass outside?) Here you can see the the cardboard tube. If I open the speaker again I will measure the tube lenght.
The material inside is yellowish. I don't know if this is polyfill turned yellow of fiberglass, but it is probably fiberglass. It was only on the back wall and on top. The enclosure was built around 1973, so perhaps you understand yourself what kind of material it is.
With an online calculator I got 0.66 cubic feet of internal volume, not taking into account the driver's volume. But I don't know if the figure is correct. You'd better calculate it yourself.
This is the Altec Lansing 409-8C manual:
https://www.manualslib.com/manual/365635/Altec-409-8c-Ceiling-Speaker.html
These are the Altec Lansing T/S parameters:
http://alteclansingunofficial.nlenet.net/Thiele-Small.html
On this list you will find T/S parameters of two other versions, the 409/8d and 409/8E, I havent' found the parameters for mine. They must be of course very similar but probably not identical. For example, on the 409/8c manual, the Fs is 84 hertz and on the T/S parameters of the other two Fs is 91 hertz.
I have tried blocking the port and I got a tighter bass but I also got fewer low frequencies.
The enclosure had internally fiberglass on the back wall and on top. It sounded like it needed a tiny little tuning. Since there were a few resonances on the mid-high, maybe amplified by my room, I tried adding a thin layer of Dacron on just one side wall. The resonance are gone but I also got a tighter bass. Must be the luck of the beginner. Perhaps I can try removing a thin layer of the Dacron I added to get a better tuning.
On another forum some people talked about an aperiodic enclosure for this driver. But they didn't seem to know how to calculate the internal volume. I read that there are some aperiodic vents sold by scanspeak . Or that you can make them yourself with fiberglass. I also read that these lower the Qts of the driver and that with these you can get away with a small internal volume. But I don't know anything about this.
I can't tell you more because I have never built a speaker myself.
Maybe when they deliver the subwoofer and I connect it I can try again to block the port of the enclosure to see if it sounds better.
The material inside is yellowish. I don't know if this is polyfill turned yellow of fiberglass, but it is probably fiberglass. It was only on the back wall and on top. The enclosure was built around 1973, so perhaps you understand yourself what kind of material it is.
With an online calculator I got 0.66 cubic feet of internal volume, not taking into account the driver's volume. But I don't know if the figure is correct. You'd better calculate it yourself.
This is the Altec Lansing 409-8C manual:
https://www.manualslib.com/manual/365635/Altec-409-8c-Ceiling-Speaker.html
These are the Altec Lansing T/S parameters:
http://alteclansingunofficial.nlenet.net/Thiele-Small.html
On this list you will find T/S parameters of two other versions, the 409/8d and 409/8E, I havent' found the parameters for mine. They must be of course very similar but probably not identical. For example, on the 409/8c manual, the Fs is 84 hertz and on the T/S parameters of the other two Fs is 91 hertz.
I have tried blocking the port and I got a tighter bass but I also got fewer low frequencies.
The enclosure had internally fiberglass on the back wall and on top. It sounded like it needed a tiny little tuning. Since there were a few resonances on the mid-high, maybe amplified by my room, I tried adding a thin layer of Dacron on just one side wall. The resonance are gone but I also got a tighter bass. Must be the luck of the beginner. Perhaps I can try removing a thin layer of the Dacron I added to get a better tuning.
On another forum some people talked about an aperiodic enclosure for this driver. But they didn't seem to know how to calculate the internal volume. I read that there are some aperiodic vents sold by scanspeak . Or that you can make them yourself with fiberglass. I also read that these lower the Qts of the driver and that with these you can get away with a small internal volume. But I don't know anything about this.
I can't tell you more because I have never built a speaker myself.
Maybe when they deliver the subwoofer and I connect it I can try again to block the port of the enclosure to see if it sounds better.
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Blocking the port will definitely reduce the bass output due to the higher low-frequency cut-off frequency. It's good that things are working as expected in that department. 🙂
The aim is to get the subwoofers to blend-in/integrate with the closed-box low-frequency output, and this should be possible to do without too much trouble. With the driver's Fs=84Hz, we can probably say that the resonance frequency in a closed-box enclosure will be in the 90–100Hz region. You could try setting the low-pass filter on the subwoofer to 90Hz and listen to the results.
If you have a microphone and a laptop you could use REW to perform a near-field low-frequency measurement of the driver's low-frequency response in the closed box enclosure. Alternatively, you could use an app on your mobile phone to measure the near-field response using white noise as a test signal. These measurements would give you some idea of the –3dB frequency of the closed-box low-frequency response, and knowing this would then help greatly in selecting the initial value of the low-pass filter frequency on the subwoofer.
The aim is to get the subwoofers to blend-in/integrate with the closed-box low-frequency output, and this should be possible to do without too much trouble. With the driver's Fs=84Hz, we can probably say that the resonance frequency in a closed-box enclosure will be in the 90–100Hz region. You could try setting the low-pass filter on the subwoofer to 90Hz and listen to the results.
If you have a microphone and a laptop you could use REW to perform a near-field low-frequency measurement of the driver's low-frequency response in the closed box enclosure. Alternatively, you could use an app on your mobile phone to measure the near-field response using white noise as a test signal. These measurements would give you some idea of the –3dB frequency of the closed-box low-frequency response, and knowing this would then help greatly in selecting the initial value of the low-pass filter frequency on the subwoofer.
Thanks. I haven't got any gear to measure speakers. I can try using my smartphone as you said. The amplifier is connected to my computer through a usb dac. No CD Player or Record Player. How do I get white noise? Can I get something online that generates white noise? Is it reliable?
I know that people put these altec 409 drivers in DIY Altec 618c cabinets, especially in Japan.
This is a video of a 409 driver in Altec 618c:
It sounds like this doesn't need a subwoofer.
On this Jelabs blog the guy talks about the Altec 618c enclosure. He says that it is a sort of boombox.
https://junkyardjukebox.blogspot.com/2012/10/wealtec-755a-thinking-inside-box.html
This is a video of a 409 driver in Altec 618c:
It sounds like this doesn't need a subwoofer.
On this Jelabs blog the guy talks about the Altec 618c enclosure. He says that it is a sort of boombox.
https://junkyardjukebox.blogspot.com/2012/10/wealtec-755a-thinking-inside-box.html
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That value seems reasonable.
I've taken a guess at the Thiele–Small parameters based on the value Fs=84Hz and the other data. I used a 20-litre enclosure for both ported and sealed enclosure simulations. Below are the frequency response plots: the green line is the sealed enclosure, and the black line is the ported enclosure. The port seems to be tuned to about 53Hz or so.
The port adds a bit of extra low-freqeuncy output in the range 40Hz to 80Hz. Note the quite high excursion levels at around 35Hz with just 1 watt of input power for the ported enclosure.
The enclosure really needs lots of absorption material on all the internal walls. That's where by using a sealed enclosure it can be filled completely, resulting in a cleaner midrange sound quality.
I don't think that an aperiodic enclosure can be attained with this driver. Its Qts value is too high. Going smaller in terms of internal volume is probably not a good approach to take with this particular driver. It would be better to double the internal volume and use a sealed enclosure.
I have every expectation that the sealed enclosure will sound much better, as long as the subwoofer's low-pass filter frequency is carefully chosen and an appropriate amount of gain is dialled in.
@newbie802 Below is an exploratory simulation of the Altec 409-8C in a sealed enclosure with a subwoofer added. It's based on a lot of assumptions, so its accuracy may not be all that great. Hopefully, it can help clarify a few things.
The low-frequency response of the vented subwoofer has been chosen to represent the Yamaha subwoofer that's at your disposal. The low-pass filter is modelled as a 90Hz 4th-order Linkwitz-Riley filter. The subwoofer here is connected with reverse polarity. As can be seen, the integration is reasonable, considering the +5dB peak in the Altec driver's response due to the Qtc=1.77 of the enclosure response. The gain on the subwoofer model is set to +1dB, but it can be dialled up and down and the bass shelf will simply go up and down in unison.
The low-frequency response of the vented subwoofer has been chosen to represent the Yamaha subwoofer that's at your disposal. The low-pass filter is modelled as a 90Hz 4th-order Linkwitz-Riley filter. The subwoofer here is connected with reverse polarity. As can be seen, the integration is reasonable, considering the +5dB peak in the Altec driver's response due to the Qtc=1.77 of the enclosure response. The gain on the subwoofer model is set to +1dB, but it can be dialled up and down and the bass shelf will simply go up and down in unison.
Witwald, you were right.
You suggested I turn the cabinet of the Altec into a sealed box. I decided to try again. There were still two bare internal walls into the cabinet and I thought that a sealed box needed more sound-absorbing material, so I first added Dacron to those two walls. Then I bloked the port and the bass response had improved.
Then I tried another option. I made a roll of Dacron same diameter as the port, about one third of the port's lenght, and stuffed it inside.
This way it sounds even better.
I don't know if it is a sort of aperiodic enclosure now, but that dacron into the port added some mid-bass warmth which is very pleasing. The bass response has improved a lot. I'm still trying the two options, sealed box and stuffed port.
I have bought two Yamaha yst-sw45 subs and am still waiting for the shipment. I think the result will be very similar to the model you posted
Is there anything wrong with stuffing a port with Dacron? May this cause damage to the speaker?
You suggested I turn the cabinet of the Altec into a sealed box. I decided to try again. There were still two bare internal walls into the cabinet and I thought that a sealed box needed more sound-absorbing material, so I first added Dacron to those two walls. Then I bloked the port and the bass response had improved.
Then I tried another option. I made a roll of Dacron same diameter as the port, about one third of the port's lenght, and stuffed it inside.
This way it sounds even better.
I don't know if it is a sort of aperiodic enclosure now, but that dacron into the port added some mid-bass warmth which is very pleasing. The bass response has improved a lot. I'm still trying the two options, sealed box and stuffed port.
I have bought two Yamaha yst-sw45 subs and am still waiting for the shipment. I think the result will be very similar to the model you posted
Is there anything wrong with stuffing a port with Dacron? May this cause damage to the speaker?
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There shouldn't be an issue with filling the port with Dacron. It would be expected to provide a high resistance to the airflow through the port, hence reducing it to being more of a leakage than a Helmholtz resonance. As you mentioned, this setup tends to become like some sort of an aperiodic enclosure. The resistance to flow will depend on the packing tightness and extent of the Dacron that is placed in the port tube.
Thanks anyone. I received two used Yamaha YST-SW45 active subwoofers. I used speaker level inputs and outputs to connect them to the Altec 409. They sound good together. These are two 60 watt subwoofers and are barely enough in my room, just because the tube amplifier has only got 3+3 watt.
As Witwald predicted in his model the right cut-off frequency is 90 hz.
But I have one last question:
If I forget to switch on the subs before switching on the tube amp, will the output transformers read any impedance? Could the output transformers fail?
As Witwald predicted in his model the right cut-off frequency is 90 hz.
But I have one last question:
If I forget to switch on the subs before switching on the tube amp, will the output transformers read any impedance? Could the output transformers fail?
@newbie802 You do ask the difficult questions!
As I'm not an electronics engineer, and neither am I privy to the circuit diagram, I can't answer your question with 100% confidence. I would guess that it would be okay if the subwoofers were switched off at the point where the tube amplifier was switched on. I expect the Yamaha electronics designers would have had that situation clearly in their set of use-case scenarios. As you are using speaker level inputs and speaker level outputs, there would be some reasonable expectation that the subwoofer might not always be switched on. I would tend to leave it switched on all the time, as it has an Automatic Standby function, which also happens to be defeatable. You may, of course, prefer the alternative approach from a power-saving perspective.
You could try using an electronic multimeter to see what the impedance across the subwoofer's terminals is when the subwoofer is switched off. That would be interesting to know.
As I'm not an electronics engineer, and neither am I privy to the circuit diagram, I can't answer your question with 100% confidence. I would guess that it would be okay if the subwoofers were switched off at the point where the tube amplifier was switched on. I expect the Yamaha electronics designers would have had that situation clearly in their set of use-case scenarios. As you are using speaker level inputs and speaker level outputs, there would be some reasonable expectation that the subwoofer might not always be switched on. I would tend to leave it switched on all the time, as it has an Automatic Standby function, which also happens to be defeatable. You may, of course, prefer the alternative approach from a power-saving perspective.
You could try using an electronic multimeter to see what the impedance across the subwoofer's terminals is when the subwoofer is switched off. That would be interesting to know.
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I can only pontificate on the YST unit I worked on in da previous Millenium which IIRC was only for the UK market.
On that design, the 'speaker' connections were straight through. ie unaffected by whether the YST unit was on or off.
You can check this on your own unit with a multimeter.
On that design, the 'speaker' connections were straight through. ie unaffected by whether the YST unit was on or off.
You can check this on your own unit with a multimeter.
I have found another couple of these '70s Altec Lansing Cervino with the coaxial speakers Altec 409-8c. They are really cheap. I'm thinking about buying them for another tube amp I have but also for spares.
But I was wondering....These 409 coaxial speakers have an advertised nominal impedance of 8 ohm and minimum impedance of 6 Ohm. With a multimeter I got 0.7. If I buy another pair of these and connect them in parallel to the one I have, the impedance will go to 4 ohm nominal and 3 ohm minimum?
Can I have problems driving them in parallel with a single ended tube amp with that impedance? The amplifier has got 8 ohm and 4 ohm taps.
I have no background in electronics, so I ask: Is there any way of bringing the impedance back closer to 8 ohm? A resistor? Something else?
Thanks
But I was wondering....These 409 coaxial speakers have an advertised nominal impedance of 8 ohm and minimum impedance of 6 Ohm. With a multimeter I got 0.7. If I buy another pair of these and connect them in parallel to the one I have, the impedance will go to 4 ohm nominal and 3 ohm minimum?
Can I have problems driving them in parallel with a single ended tube amp with that impedance? The amplifier has got 8 ohm and 4 ohm taps.
I have no background in electronics, so I ask: Is there any way of bringing the impedance back closer to 8 ohm? A resistor? Something else?
Thanks
That may mean that they have a short circuit and unusable unless you restore the speaker coil if possible at all.