Two different sized woofers in the same enclosure

[ligs]

Recently I refurbished a pair of AR TSW 410s. Each speaker has two woofers(8 and 6 inches) shared the same sealed enclousure of 1.14 ft3 and spec says –3 db at 46 Hz with an effective Q of 0.9 at resonance. My questions are: Is it pretty rare to use two different sized woofers in the same enclosure? And Any Pros and cons to this arrangement?

[fitzwaddle]

Re: Two different sized woofers in the same enclosure

You sure the 6 isn't a mid?

[OlderMongrel]

Re: Two different sized woofers in the same enclosure

I plan to play around with this concept at some point. I have an old pair of Speakerlab Super 7s that a friend gave me. They used a 10" and a 12" woofer sharing the same cab, sealed. I still have not decided if the old drivers are worth re-surrounding (all have foam rot, including the 6" 4 ohm mids, which might be the best of the bunch).

When Stereo Review tested the original 7, which used the same approach, slightly different drivers, they were puzzled because the output of the 10" was 2db below the 12. I'm not sure that's a problem, but they did not elaborate.

I was thinking of trying a 2.5 way with 4 5.25" woofers and 1 10" as the 0.5. I might even try this vented, just to be contrary, and to try something new. I think it would work with careful driver selection and measurements.

John

[billagee]

Re: Two different sized woofers in the same enclosure

Rare? It should be. The mid is also acting as a PR for woofer. There's no good reason to do that aside from cost.

Bill

[ligs]

Re: Two different sized woofers in the same enclosure

You sure the 6 isn't a mid?

Both the 6-inch and 8-inch share the bass in the same cavity. The 8-inch rolls off earlier than the 6-inch. This is a 2.5-way design as can be seen from the XO schematic.

Interestingly enough, the earlier top-of-the-line AR 9 LS also had 10-inch and 12 -inch for the bass. But I never owned a pair of AR 9LS's so I don't know if there was a partition between these woofers inside the cabinet.

[ligs]

Re: Two different sized woofers in the same enclosure

I plan to play around with this concept at some point. I have an old pair of Speakerlab Super 7s that a friend gave me. They used a 10" and a 12" woofer sharing the same cab, sealed. I still have not decided if the old drivers are worth re-surrounding (all have foam rot, including the 6" 4 ohm mids, which might be the best of the bunch).

When Stereo Review tested the original 7, which used the same approach, slightly different drivers, they were puzzled because the output of the 10" was 2db below the 12. I'm not sure that's a problem, but they did not elaborate.

I was thinking of trying a 2.5 way with 4 5.25" woofers and 1 10" as the 0.5. I might even try this vented, just to be contrary, and to try something new. I think it would work with careful driver selection and measurements.

John

I happen to have an old Catalog from SpeakerLab which has several models(30, 50) using the similar design as your Speakerlab 7. I copied a page about Speakerlab 30 below. It does mention this so-called Nestorovic Woofer System for these advantages: 1. accurate transient response, 2. extended low bass response, and 3. modest enclosure size!

Could someone try to SIM this to see what is really happening?

[OlderMongrel]

Re: Two different sized woofers in the same enclosure

I happen to have an old Catalog from SpeakerLab which has several models(30, 50) using the similar design as your Speakerlab 7. I copied a page about Speakerlab 30 below. It does mention this so-called Nestorovic Woofer System for these advantages: 1. accurate transient response, 2. extended low bass response, and 3. modest enclosure size!

Could someone try to SIM this to see what is really happening?

All of the Sevens just used two standard woofers in parallel, a 10 and a 12. They stopped using the old W1208R in the later Super Sevens. The ones I have are the later ones, the woofer looks quite a bit cheaper. I think the bean-counters were beginning to take over. Can't measure it until I replace the surrounds, not sure if these woofs are worth the trouble.

Looking at my old catalogs, the Nestorovic bass in the 30 and 50 was indeed different. They had another variation on this later on called "Delta I Hybrid". Some of these used a deliberately weak motor on the larger woofer to produce what they called an "active hybrid radiator", which became progressively passive at lower frequencies. Apparently the 30 did this via crossover tweaks, which I did not know. (Maybe they both had XO tweaks, not sure.)

From the catalog, on the Delta I Hybrid Type 5: "The AHR employs a unique high-impedance voice coil which draws only a specific proportion of the current...supplied to the upper driver. This allows the massive 12" diaphragm to remain in phase with the 10" woofer as if the system were a sealed box. This provides the advantage of gradual roll-off slope, better transient response, tightly controlled cone motion, and higher power handling below the system cutoff frequency. The AHR device also furnishes the advantages inherent in a passive radiator system of lower tuning frequency, reduced cone excursion, and greater system design flexibility."

Some related patents, although they are not the Speakerlab stuff (you might need to register, which is free, to see these):

http://www.freepatentsonline.com/3984635.pdf

http://www.freepatentsonline.com/4403112.pdf

John

[LouC]

Re: Two different sized woofers in the same enclosure

I had the SpeakerLab 30's for 15 years. The Nesterovic crossover was quite sophisticated for the day. (25+ components) I think the designer is still selling them. The principle was to gradually roll off the 10" and turn it into a passive radiator at lower frequencies. (Based on my limited recall) They were awesome boxes BITD.

Sealed designs shouldn't present much problem with two different woofers assuming roughly the same sensitivity. Not sure how you'd model the boxes ported.

[ligs]

Re: Two different sized woofers in the same enclosure

I am pleasantly surprised about the positive information that is turning up. While most of it is over my head but there seems to be real technical merits for doing this mixed-woofers approach.

[billagee]

Re: Two different sized woofers in the same enclosure

So it's a 2.5 way design. That's what keeps the mid from acting like a PR for the woofer. Interesting! I don't think I have seen that before.

Bill

[FredT]

Re: Two different sized woofers in the same enclosure

Vandersteen Audio uses this configuration in their Models 2 and 3, with an 8" modwoofer and a 10" woofer in the same enclosure space. In their design the larger driver appears to act as an electrically coupled passive radiator, covering a narrow deep-bass range. http://www.vandersteen.com/2cesigii_specifications.pdf