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Thread: 2 way using Altec 3156 drivers

  1. #1
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    2 way using Altec 3156 drivers

    Was able to get my hands on a pair of Altec 3156 drivers , As per the original recommendation enclosure is 8156. And few have tried loading with 816 cabinets.

    So want to know what is best suited for duties below 800-1000 Hz. This will basically be a LF stage of a 2 way setup, with HF managed through 288 or 802.




    Thanks
    Altec_fan

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    Quote Originally Posted by Altec_fan View Post
    Was able to get my hands on a pair of Altec 3156 drivers , As per the original recommendation enclosure is 8156. And few have tried loading with 816 cabinets.

    So want to know what is best suited for duties below 800-1000 Hz. This will basically be a LF stage of a 2 way setup, with HF managed through 288 or 802.




    Thanks
    Altec_fan
    Greetings -

    With an efficiency Bandwidth Product of 131, It's best to use the 3156 in a vented enclosure versus a horn enclosure. A lot of folks put speakers with low EBP figures in horn enclosures. It doesn't mean they will always perform optimally. A judicious calculation of volume is critical for horn loaded designs.

    Per the catalog, the 8156 loaded with the 3156 will provide "good low frequency response", what ever that means. The 3156 has an fs of 38 Hz. The box fb is at 57 Hz. Perhaps not "good" low frequency response. I would at the least, double the volume if you wish to use the system for HiFi. A larger box tuned accordingly should give you "good low frequency response". If you're planning to use the system domestically, perhaps the 511E horn would be a good choice with the 288. The 511E is hard to find, and go for a small fortune when they can be, but Bill Hanuschak at Great Plains Audio can modify a 511B as ALTEC did.

    Good luck,

    HF

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    Quote Originally Posted by Horn Fanatic View Post
    Greetings -

    With an efficiency Bandwidth Product of 131, It's best to use the 3156 in a vented enclosure versus a horn enclosure. A lot of folks put speakers with low EBP figures in horn enclosures. It doesn't mean they will always perform optimally. A judicious calculation of volume is critical for horn loaded designs.

    Per the catalog, the 8156 loaded with the 3156 will provide "good low frequency response", what ever that means. The 3156 has an fs of 38 Hz. The box fb is at 57 Hz. Perhaps not "good" low frequency response. I would at the least, double the volume if you wish to use the system for HiFi. A larger box tuned accordingly should give you "good low frequency response". If you're planning to use the system domestically, perhaps the 511E horn would be a good choice with the 288. The 511E is hard to find, and go for a small fortune when they can be, but Bill Hanuschak at Great Plains Audio can modify a 511B as ALTEC did.

    Good luck,

    HF
    Thanks for the detailed reply.

    Yes, this will be for domestic use driven by a low powered SET in range of 3-8 Watts, so tuning fb lower will help , as reaching the xmax may not be a problem.

    What volume do you think would be good enough for this driver (one driver per channel). And do you think fb of 25-28 Hz will be practical for this driver ?

    and for 288, procuring a 511 is almost impossible, so i will be leaning more towards diy wooden horns.

    Thanks
    Altec_fan

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    Quote Originally Posted by Altec_fan View Post
    Thanks for the detailed reply.

    Yes, this will be for domestic use driven by a low powered SET in range of 3-8 Watts, so tuning fb lower will help , as reaching the xmax may not be a problem.

    What volume do you think would be good enough for this driver (one driver per channel). And do you think fb of 25-28 Hz will be practical for this driver ?

    and for 288, procuring a 511 is almost impossible, so i will be leaning more towards diy wooden horns.

    Thanks
    Altec_fan

    I recommend using at the minimum a 5 cubic foot enclosure. Not wise to tune the enclosure below fs. Best to tune the enclosure fB at fs. Some manufacturers tune their cabinets slightly above fs which gives a bump in the bass response, but does not offer proper damping.

    Wooden horn? Perfect. Try this chap. He ships all over Europe.

    https://klughoerner.com/

    Regards,

    HF

  5. #5
    Senior Member RMC's Avatar
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    Hi Altec Fan, and Horn Fanatic

    An Altec 3154 with foam surround, rated response 30-2000 hz and mid-band (100-1,000 hz) sensitivity of 95 db 1W/1M, in a recommended 8154 6 cu. ft. (170 L.) enclosure (F3 40 hz) would have been a better driver choice for Hi-Fi use. However, I do realize that one finds what he can find. Can't blame you for that.

    As per Altec's 1989, 8000 series boxes spec sheet, the 8156 has a Vb 3 cu. ft. (85 L.), Fb 57 hz and F3 of 65 Hz. On the other hand, as per the 1986, 3156 driver data sheet, one can see this driver has a cloth surround suspension, a rated response of 50-2,000 hz, a driver sensitivity rating of 99-100 db 1 W/1 M (100 hz-1,000 hz), according to driver and box spec sheets). This gives right away SOME indication about the 3156 LF capabilities. NOT subwoofer material, but rather for general purpose bass cabinet, with Fs 38 hz, Qts 0.24, Vas 8.7 cu. ft. (246.4 L.) and Xmax 0.15 in. (3.81 mm). These are about the essential numbers for how low/loud can you go with a box in LF. High mid-band sensitivity, such as here, is another indicator for what purpose that driver was optimized for: high level reproduction, not for low frequencies as for 3154.

    If Altec recommended, in the driver spec sheet, a 3 cu. ft. (85 liter) box for that 3156, there's a good reason for this: "When used in the 8156... full capability of the 3156 is achieved." That's the cruel reality for LF capability, though other box sizes may be used. But one reaches fast the "limit" in increasing box volume with that driver. I know a thing or two about this since the 3156 driver is somewhat similar to my JBL 2205H.

    Even though I have high respect for HF's contributions and most of what he wrote here, I tend to disagree with him regarding the box sizes he suggested for 3156 ("I would at the least, double the volume..." which would mean 6 cu. ft. (170 L.) and "I recommend using at the minimum a 5 cubic foot enclosure." (142 L.).

    To satisfy my own curiosity, I also did a quick vented box modeling in Winspeakerz v. 2.5.2 with a Vb of 5 cu. ft., Fb at 38 hz ("Best to tune the enclosure fB at fs." HF wrote) using this 3156 driver. The low frequency limits of the driver appear pretty fast with Vb increase/lower tuning: it cannot maintain flat LF response. A good dip starting early in LF range (100 hz going down). Tuning too low also puts more strain on the woofer, though I understand your expexted input power and sound level would be low.

    The result isn't satisfactory in my view, unless you plan to locate the speaker box at the junction of TWO boundaries (floor AND wall) to get LF 3 db increase compared to floor location alone(*see below). From about 125 hz and up you get a rising response to +2.5 db from 500 hz to 1 khz, and in the low end you get a progressively falling response from 125 hz going down, -1 db 100 hz, -2 db 70 hz, almost -3 db at 50 hz and -4.5 db at 40 hz... That means your output level at 50 hz would be about -3 db and at 800 hz about +2.5 db. This is quite a difference, as such this speaker is prone to sound very mid-bassy. Increasing tuning to 45 hz would improve bass to about -1 db at 50 hz and tuning at 50 hz would mean +1 db at 60 hz. If not floor/wall located, then I would forget that box and the even larger 6 cu. ft. ...

    Another option would be a 4 cu. ft./Fb 40 hz box which I also modeled quickly: -3 db 50 hz and -6 db 39 hz. Same type of response. For Fb 45 hz -2 db 50 hz, if Fb 50 hz then flat at 60 hz and -3 db 48 hz. As can be seen, this driver begs for smaller volumes/higher tunings, not the opposite. This explains Altec's 8156 box...

    Regards,

    Richard

    (*) In both of his following books, John Eargle (JBL) mentions that in the modeling of a system's response with T/S parameters, enclosure mounting in half-space (2 Pi radiation) is already assumed (so a 6 db room gain in LF from full space to half-space is also already assumed here): Handbook of Sound System Design, ELAR, 1989, P. 106 and 295; Loudspeaker Handbook, Chapman & Hall, 1997, P. 58.

  6. #6
    Senior Member RMC's Avatar
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    In my post # 5 here I forgot to mention that I also did model response of the 3156 in Altec's 8156 box (Vb and Fb) to see the result. It fits like a glove on the 3156! Not really surprising. This one has the flattest LF response of the three boxes I modeled (3, 4, 5 cu. ft.). It confirms the folks at Altec had it right in the data sheet stating a precise recommended volume of 3 cu. ft., instead of a range of recommended volumes as JBL usually does (e.g. 3-8 cu. ft.). However, even with that 3 cu. ft. flat LF response box, there remains the issue of mid-bass/midrange rising response of the driver (+2.5 db from 500 hz and up) and its possible effect on perceived driver sound if used in a two-way system crossed over at 800 hz for example...

    RE "I know a thing or two about this since the 3156 driver is somewhat similar to my JBL 2205H." in my post # 5 here, the 2205 has its own issue too, but less critical than Altec's 3156: box volume being much more "forgiving" for the 2205, but not box tuning frequency in my view. Some relevant T/S of the latter are: Fs 30 hz, Qts 0.21, Vas 10.5 cu. ft. and Xmax 0.14 in. (3156: 38 hz, 0.24, 8.7 cu. ft., 0.15 in., in the same order). I think what saves the 2205 for use in larger boxes compared to Altec's 3156 is the higher Vas number (used in calculating box volume). The lower Fs on the JBL can't hurt also. In case you wonder how things turned-out for me with the 2205H in a vented box, here's an overview...

    When I purchased the 2205s in 1981, I called JBL Pro Tech. Services and discussed my box options with Applications Engineer Nat Hecht. I was offered three box choices: 7.1, 4.2 and 3.0 cu. ft. The first one seemed way too large for available space, more so considering the gross volume required to get to 7.1 net, and the third one appeared small to me for a 15" driver. So, at the time I settled for the middle of the road 4.2 cu. ft./Fb 50 hz cabinet. In these days, speaker design software was not as easily available to amateurs as today, but manufacturers such as JBL and E-V had their own in-house box design programs based on T/S parameters. E-V also modeled a box for me many years ago, and I still have those too.

    I can report that my choice of box among those offered by JBL, looks like a good compromise for the 2205, after having done my own simulations with a few speaker design computer programs years ago. Even if a 3 cu. ft. box, Fb 50 hz, wasn't bad, response being reasonably flat (though a bit on the negative side in LF) and F3 @52 hz, similar response shape to 3156/8156 combo, with JBL F3 result better than Altec's. The 4.2 cu. ft./Fb 50 hz boxes, show a little edge for me on response since the lows are not in negative territory where it counts (e.g. + 0.5 db @ 60 hz) and F3 @ 47 hz. The slight 2205 driver rising response of 1-1.5 db above 250 hz or so is not an issue in my application considering these bass cabinets are one-way only, and always used in a bi-amp mode (active X-over around 200 hz) with a pair or two of smaller speakers from my lineup.

    BTW, the JBL Pro Enclosure Guide, providing GENERAL GUIDELINES for enclosures, does suggest a 4 cu. ft. box with Fb 40 hz for that 15" driver, and many others. However, modeling this 4/40 combo in Winspeakerz design software shows a progressively falling LF response from 200 hz and lower, by almost - 3 db @ 50 hz, with a curve of similar shape to that of Altec's 3156 driver in a 5 cu. ft. box mentioned in my post # 5. Not my cup of tea. Here, that lowering response is purely the result of too low tuning frequency (40 hz) for such a driver/box duo. Based on my simulations, response would be much flatter at Fb 50 hz in that 4 cu. ft. box.

    As a Sound Reinforcement driver, the 2205 was primarily designed with rear loaded folded horns in mind (4520, 4530), but it may well be used with good results for general purpose low frequency reproduction in vented enclosures of 3, 4, 5 or even 7.1 cu. ft., as long as box tuning frequency remains around 50 hz for each (about 45 hz for 7.1 enclosure) according to my simulations. An Fb 40 hz is just too low for this woofer and puts more strain on it, unless one uses floor/wall junction placement to boost the deeper low-end by 3 db. That driver, at 97 db sen., as for the 2225, is a middle of the road between max efficiency/lower fidelity (e.g. E-140, 2220 at 100-101 db) and max fidelity/lower efficiency (e.g. 2235 at 95 db).

    JBL's 2/80 data sheet recommended enclosure volume of 6-8 cu. ft. appears somewhat overly optimistic or exagerated, in real life, for the 2205. It sure can be used in a large box size, but the useable spl output below 50-60 hz drops rapidly, since it was not engineered to be a subwoofer type driver (i.e. limited Xmax). I wouldn't try to mount this driver in a larger box than I have, since that would mean trying to extract from it lower frequencies than what the woofer was made for. It can only provide some VLF at a reduced output. It can still "rattle the silver" with 120 db @ 60 hz because of amplitude, not LF bandwidth. In fact, at high LF levels, the bandwidth should be high-pass filter limited around 45hz to minimize the risk of over excursion.

    Bottom line, some drivers, even if large in size, are not necessarily designed for very low bass reproduction, but may rather be optimized for higher level sound reproduction, excluding deep bass...

    Richard

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    Quote Originally Posted by RMC View Post
    In my post # 5 here I forgot to mention that I also did model response of the 3156 in Altec's 8156 box (Vb and Fb) to see the result. It fits like a glove on the 3156! Not really surprising. This one has the flattest LF response of the three boxes I modeled (3, 4, 5 cu. ft.). It confirms the folks at Altec had it right in the data sheet stating a precise recommended volume of 3 cu. ft., instead of a range of recommended volumes as JBL usually does (e.g. 3-8 cu. ft.). However, even with that 3 cu. ft. flat LF response box, there remains the issue of mid-bass/midrange rising response of the driver (+2.5 db from 500 hz and up) and its possible effect on perceived driver sound if used in a two-way system crossed over at 800 hz for example...

    RE "I know a thing or two about this since the 3156 driver is somewhat similar to my JBL 2205H." in my post # 5 here, the 2205 has its own issue too, but less critical than Altec's 3156: box volume being much more "forgiving" for the 2205, but not box tuning frequency in my view. Some relevant T/S of the latter are: Fs 30 hz, Qts 0.21, Vas 10.5 cu. ft. and Xmax 0.14 in. (3156: 38 hz, 0.24, 8.7 cu. ft., 0.15 in., in the same order). I think what saves the 2205 for use in larger boxes compared to Altec's 3156 is the higher Vas number (used in calculating box volume). The lower Fs on the JBL can't hurt also. In case you wonder how things turned-out for me with the 2205H in a vented box, here's an overview...

    When I purchased the 2205s in 1981, I called JBL Pro Tech. Services and discussed my box options with Applications Engineer Nat Hecht. I was offered three box choices: 7.1, 4.2 and 3.0 cu. ft. The first one seemed way too large for available space, more so considering the gross volume required to get to 7.1 net, and the third one appeared small to me for a 15" driver. So, at the time I settled for the middle of the road 4.2 cu. ft./Fb 50 hz cabinet. In these days, speaker design software was not as easily available to amateurs as today, but manufacturers such as JBL and E-V had their own in-house box design programs based on T/S parameters. E-V also modeled a box for me many years ago, and I still have those too.

    I can report that my choice of box among those offered by JBL, looks like a good compromise for the 2205, after having done my own simulations with a few speaker design computer programs years ago. Even if a 3 cu. ft. box, Fb 50 hz, wasn't bad, response being reasonably flat (though a bit on the negative side in LF) and F3 @52 hz, similar response shape to 3156/8156 combo, with JBL F3 result better than Altec's. The 4.2 cu. ft./Fb 50 hz boxes, show a little edge for me on response since the lows are not in negative territory where it counts (e.g. + 0.5 db @ 60 hz) and F3 @ 47 hz. The slight 2205 driver rising response of 1-1.5 db above 250 hz or so is not an issue in my application considering these bass cabinets are one-way only, and always used in a bi-amp mode (active X-over around 200 hz) with a pair or two of smaller speakers from my lineup.

    BTW, the JBL Pro Enclosure Guide, providing GENERAL GUIDELINES for enclosures, does suggest a 4 cu. ft. box with Fb 40 hz for that 15" driver, and many others. However, modeling this 4/40 combo in Winspeakerz design software shows a progressively falling LF response from 200 hz and lower, by almost - 3 db @ 50 hz, with a curve of similar shape to that of Altec's 3156 driver in a 5 cu. ft. box mentioned in my post # 5. Not my cup of tea. Here, that lowering response is purely the result of too low tuning frequency (40 hz) for such a driver/box duo. Based on my simulations, response would be much flatter at Fb 50 hz in that 4 cu. ft. box.

    As a Sound Reinforcement driver, the 2205 was primarily designed with rear loaded folded horns in mind (4520, 4530), but it may well be used with good results for general purpose low frequency reproduction in vented enclosures of 3, 4, 5 or even 7.1 cu. ft., as long as box tuning frequency remains around 50 hz for each (about 45 hz for 7.1 enclosure) according to my simulations. An Fb 40 hz is just too low for this woofer and puts more strain on it, unless one uses floor/wall junction placement to boost the deeper low-end by 3 db. That driver, at 97 db sen., as for the 2225, is a middle of the road between max efficiency/lower fidelity (e.g. E-140, 2220 at 100-101 db) and max fidelity/lower efficiency (e.g. 2235 at 95 db).

    JBL's 2/80 data sheet recommended enclosure volume of 6-8 cu. ft. appears somewhat overly optimistic or exagerated, in real life, for the 2205. It sure can be used in a large box size, but the useable spl output below 50-60 hz drops rapidly, since it was not engineered to be a subwoofer type driver (i.e. limited Xmax). I wouldn't try to mount this driver in a larger box than I have, since that would mean trying to extract from it lower frequencies than what the woofer was made for. It can only provide some VLF at a reduced output. It can still "rattle the silver" with 120 db @ 60 hz because of amplitude, not LF bandwidth. In fact, at high LF levels, the bandwidth should be high-pass filter limited around 45hz to minimize the risk of over excursion.

    Bottom line, some drivers, even if large in size, are not necessarily designed for very low bass reproduction, but may rather be optimized for higher level sound reproduction, excluding deep bass...

    Richard
    Thanks Richard for simulations and the explanations.

    So i will try to build test enclosures and measure, do you think 4 cu. ft. is a good balance to start, as for testing we can always reduce the volume ?

    Thanks
    Altec_fan

  8. #8
    Senior Member RMC's Avatar
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    Hi Altec Fan,

    As per your last post, I have done another quick check in Winspeakerz design software with a 4 cu. ft. box (113.28 L. net), but this time with different tuning frequencies of 40, 45 and 50 hz. That box size could be not only a good starting point, but also a good finishing point! Providing box tuning frequency choice is done right. Therefore, no need for test boxes or to reduce the volume!

    With that box volume, 40-45 hz tuning shows a pretty dropping LF response like I mentioned in post # 5 about the 38 hz tuning box, and a pretty mid-bass sounding speaker because of driver mid rising response, plus more strain put on the woofer when tuning too low. However, at 50 hz tuning your low frequency response is flat (60-100 hz) with an F3 at 48 hz. Not bad, quite close to my own 2205 cabinets! As long as you were not expecting subwoofer bass range performance (in any case 3156 is NOT the driver for that).

    If driver mid-bass emphasis (rising above 100 hz) is still a pain in the neck for you when listening to it, then you may try, as I mentioned before, placing the speaker at the junction of TWO boundaries (floor AND back wall) to increase bass output by 3 db to sort of "balance" bass output with mid level, which may sound more appropriate. Another option would be to tune the box higher (Fb 55 hz = + 1.25 db @ 65-80 hz and F3 51 hz; Fb 60 hz = + 2.5 db @ 70-80 hz and F3 53 hz). I would probably prefer to take advantage of speaker placement option first if space permits... Another possibility is to take advantage of an Equalizer to correct perceived response problems.

    The Winspeakerz minimum recommended vent surface for the 4 cu. ft./Fb 50 hz box is 20 square inches and this is related to bass output capability but also in relation to the driver's rated input power of 250 W.

    As for box volume displaced or taken by driver, JBL 15" drivers usually take about 0.2 cu. ft or 6 liters according to JBL, so I would assume its about the same for Altec, though I don't have a precise number for Altec drivers. Moreover, you'll also have to consider in your gross box volume the space taken by bracing and vent. I hope this helps you. Have fun! Regards,

    Richard

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