AR 12" Woofers as Subwoofers

[Guest bocoogto]

Has anyone tried using AR1/AR3 vintage woofers in a larger acoustic suspension enclosure as a subwoofer for home theater? I know enough about sealed enclosures to realize that a larger enclosure will lower the resonant frequency of the system but allow higher cone excursion for a given power input. Infinity had a problem with the Quantum systems from the late '70's where the same Watkins dual-drive woofer was used (acoustic suspension) in various sized cabinets. The larger cabinets yielded better low frequency response, but cone bottoming was a problem on the larger ones. The Fs (bare speaker resonant frequency) of these woofers must be somewhere in the 28-30 Hz range?

I have three pair of speakers using these woofers with various problems with the mids or tweeters. One alternative would be to use them in the OEM cabinets as subwoofers. The only problem with this is that the usable low frequency range is limited to about 30 Hz in my experience.

As a side note, my main home theater speakers, AR9LSi's, with their 12" and 10" woofers don't seem to be as strong around 30 Hz as the AR3's with their single 12" woofer. Is this true or just my perception?

I have installed a 15" IB (infinite baffle speaker from Parts Express) woofer driven by a Hafler DH-500 in my listing room in the floor using the basement as the back side of the enclosure. Low frequency extension is great as is quality of sound, but output level is limited with this single speaker. There is a web site devoted to IB fans called the "Cult of the Infinitely Baffled" at http://f20.parsimony.net/forum36475 that is very interesting. Usually, people end up using four drivers to provide adequate output.

[johnieo]

>Has anyone tried using AR1/AR3 vintage woofers in a larger

>acoustic suspension enclosure as a subwoofer for home theater?

No, but I have constructed a standard 1.48 cu ft enclosure for an AR 12" woofer and it performs quite well. One is not advised to increase the volume, or attempt to increase the throw, as this woofer was not designed for that (mis)use.

Some hints...

--it is the *interior* cabinet volume that is critical, not its shape. If you have a spare cabinet, solidly seal the tweet and mid holes.

--If you do not have a cabinet, construct your own with dimensions to fit the space available. Mine is about 18"x18"x12". Forgot exact dimension--whatever yields the exact interior volume.

--Your home theater AVR will have an adjustable upper frequency cuttoff for its "sub" woofer; you do not need a crossover--set the upper limit to ~150-to-200 Hz.

---Remove both the #9 inductor in series with the woofer and the 150 uF capacitor in parallel with the woofer. At 25 Hz, the impedance of the #9 coil is X=(0.8+j0.3) Ohms, so the coil is not doing anything except wasting input power.

--If you read the threads on the 12" woofer's low frequency response, you might learn that the oldest style, the Alnico magnet woofer, has the best bass response, and the newest, the Tonegen replacement, has the poorest. Best to choose the oldest spare woofer you own for that application.

John in Tucson

[Guest bocoogto]

John,

Thanks for the response to my post. Yes, I have a couple of older 12" AR woofers still in the AR3 cabinets. If my wife will OK it, I could place them in the listening room--one placement would be under the single AR3a rear surround, which is 29' from the front speakers. That would raise the rear surround about 14" to improve the path for high frequencies to the listening area. The other one could go immediately behind a couch in the center of the listening area. I would use my Hafler DH-500 to power these two AR subs.

The system then would have five 12" and four 10" AR woofers (two AR9LS's, one AR3a, two ARLSTII's, and the two "AR1W's" as subs). Very low bass extension would be limited to just below 30 Hz, but output level should be great even for the large listening area (30' X 15' with a 17' high ceiling).

It's interesting to see other people's home theater systems, especially Bose, which they KNOW are the best speakers you can buy. These people are quite surprised when they hear my system with the vintage speakers.

[Guest palomar]

I have a pair of AR11 woofers, and I was actually thinking at one point of mounting them in 5 cubic foot vented cabinets to see what would happen. (I never got around to doing it.) I had some simulation software which, based on my estimates ('wags' is more like it) of the Theile-Small parameters of the AR woofer, seemed to show that with the cabinet tuned to about 22 Hz, the bass would be flat (+/- 1 dB or so) to 25 Hz or so.

I'm sure that the fullrange bass would suffer, since, as mentioned in another response, they were never designed for this. Most probably the mid-bass would be weak, and there probably would be some ringing at about 25 Hz (which is so low I doubt you'd hear it as such). You'd have to be more careful driving them, since with less of an air-spring, they'd bottom more easily. And with the porting, there is no air-spring at DC, so a loud transient (hot-plugging a cable with the volume turned up, for example) could be a disaster.

But as pure subwoofers, and with some care and restraint in driving them, it might be worth trying.

Gary

[ninohernes]

>I have a pair of AR11 woofers, and I was actually thinking at

>one point of mounting them in 5 cubic foot vented cabinets to

>see what would happen. (I never got around to doing it.) I had

>some simulation software which, based on my estimates ('wags'

>is more like it) of the Theile-Small parameters of the AR

>woofer, seemed to show that with the cabinet tuned to about 22

>Hz, the bass would be flat (+/- 1 dB or so) to 25 Hz or so.

>

>I'm sure that the fullrange bass would suffer, since, as

>mentioned in another response, they were never designed for

>this. Most probably the mid-bass would be weak, and there

>probably would be some ringing at about 25 Hz (which is so low

>I doubt you'd hear it as such). You'd have to be more careful

>driving them, since with less of an air-spring, they'd bottom

>more easily. And with the porting, there is no air-spring at

>DC, so a loud transient (hot-plugging a cable with the volume

>turned up, for example) could be a disaster.

>

>But as pure subwoofers, and with some care and restraint in

>driving them, it might be worth trying.

>

>Gary

The problem with placing an AR woofer in a vented enclosure is there is no restoring force. Even at a low volume, the woofer would bottom out. The spider, and surrounds supply essentially no restoring force. Running an AR woofer in a vented cabinet would destory it.

[johnieo]

> The other one could go immediately behind

>a couch in the center of the listening area.

I am not sure what this would accomplish. It is my understanding that the Dolby subwoofer preamp output signal is designed to feed an amp/spkr located in *front* of the listening area, to provide the lowest frequencies, which you do not hear from your left/right speakers. Were it to be placed behind the viewer, would it not destroy the spatial relationship between audio and images? I believe Dolby 7.1 has the two channels (L-rear, R-rear), which go behind the viewer.

My video sits diagonal near the room corner; a single subwoofer--the ".1" in the Dolby 5.1--sits in the corner. The corner provides added amplification by confining the power to half the solid angle it would fill when located on a long wall.

Some 5.1 layouts show a single sub in a nearby corner when the system is in the middle of a long wall.

[Guest palomar]

You actually do get the restoring force in a vented cabinet until you start dropping below the tuning frequency. This is because the air in the port is actually moving in phase with the woofer. (In fact, if you take a ported system, run a signal into it near its tuning frequency, you can actually see the cone excursion decrease as you cover up the port.

The problem is that as you drop the below the tuning frequency, the air in the port begins to move out of phase with the woofer, and by the time you low enough in frequency, there is no restoring force. And as you indicate, the woofer can be easily bottomed out at this point.

But it is certainly true that in a 5 cubic foot cabinet, the restoring force is far less than what it would be in the 1.48 cubic foot cabinet that the woofer was designed for, so you would definitely have to be careful. Again, maybe the whole thing wouldn't be a good idea, but what the heck. Sometimes you just never know.

Gary

[soundminded]

The AR9 places two AR 12" woofers in an enclosure approximately 3 1/2 to 4 cubic feet. The fiberglass is apparantly restricted to the upper half of the enclosure while the speakers are mounted on each side near the bottom and the bottom half of the cabinet is empty air. The resulting bass when properly positioned and equalized is nothing short of frightening in my 4000 cu ft room with a good 60wpc amplifier. The upper frequency cutoff is limited to 200 hz which makes it a true subwoofer. It is hard to see why anyone would want or need more bass than this system can deliver and it is also unlikely IMO that you will find a better subwoofer but if you do, it is sure to be very expensive. If you want to build one, there are many interesting drivers between the Madisound and Parts Express catalogue. Look also at the 18" woofer I cited in the thread PeteB started. In a 4 cu ft enclosure, it might be a very powerful subwoofer but I have no idea how much it costs. As for the limited output of the 15" IB woofer from Parts Express, I am quite surprised it didn't do better. Insofar as Bose is concerned, the original and series II 901 will give AR3 more than a run for its money when properly equalized and powered assuming that the units are tightly sealed and the drivers all work properly (they have cloth surrounds which do not deteriorate with time.) I haven't determined the maximum output because I don't have sufficient electrical power but I could predict that with two pairs in parallel powerered by a Crown CE-1000, they will likely challenge AR9s bass output. The pair I do have is connected to a Marantz SR930 receiver which I think was mostly marketed in Europe. I don't know how much power it can deliver but its meters redline at around 120 wpc and it's main powerline fuse is 8 amps. It isn't nearly enough power for the 901s to show the limits of their bass capabilities.

[Guest bocoogto]

The position of the subwoofer is not critical to the surround effect in any home theater system that I've ever heard. My plan would be to cross over at 50 Hz into these two "AR1" subwoofers so these subwoofers would be outputting all completley non-directional sound. Try it for yourself--move the subwoofer to the opposite side of the room from where it is now with a temporary long lead--with your eyes closed, you CANNOT tell where a good quality subwoofer is located in the room.

The reasoning for placing one subwoofer next to the main listening position is for low frequency intensity only. When the subwoofer is located in front (in my case 18 feet away), while you cannot locate the sub position with your ears, there certainly is less intensity of bass 18 feet away. That's why some people like those bass shakers that mount in seats--Disney uses these in their special-effects theaters.

Your comments on no center channel are not true. I have a Pioneer 1014 Receiver which allows selecting "no center channel speaker" and directs this sound to the left and right speakers. I've tried center channel speakers with no audible improvement in center fill, dialogue, or any other aspect of surround sound. Beca7use my main listening position is 18' away from the left and right front speakers, and they are separated by 10', the center fill is just fine.

[Guest palomar]

Oops. In my discussion of the restoring force of a ported system, I mentioned that as you cover up the port at the tuning frequency, you can see the woofer excursion decrease. What I meant to say was that as you cover up the port, you see it increase. I know this seems counter-intuitive, but the air in the port at this frequency is running in phase with the woofer which actually resists the cone movement.

(I'm no expert on the physics of the system, so I welcome those who know more about this than I do to either expand on it, or correct me if I've misled anyone on this.)

Gary