[BrunoB]

Hi OB fans,

I might need some advice ...

I have a pair of VMPS 626R. I  remove the back of the enclosure to have U shape open baffle (see my signature link).
I have a problem with bass: with the track #12 from Roger Waters's CD  "Amused to death", my current woofer (6.5' megawoofer from VMPS) makes some loud bangs. I suspect that the VC bottoms out due to the removal of the closed box air spring  (not sure if this is the right terminology here - feel free to correct me).

Therefore, I am looking for a woofer with longer excursion. I came accross the Extremis 6.8 web page:
http://www.adireaudio.com/Home/ExtremisMidwoofers.htm .

I have the impression that this woofer might solve my problem: it has one  inch of peak-to-peak linear excursion and should fit onto my enclosure.


What do you guys think? Any good or bad experience? Any recommendation for another driver?

Thanks in advance,

Bruno

PS: This track #12 is tough bass  test!

[Rafal]

Here is the link to the OB kit using extremis woofers:
http://www.adireaudio.com/Home/KITDDR.htm
It may give you the info you need.

CHeers,

Rafal

[audioferret]

The guys at diyaudio.com have been experimenting on this design for a while now.

http://www.diyaudio.com/forums/showthread.php?s=bd3c920cf2b5fd7012e69d760ac20220&threadid=89491&highlight=

The results with this design are very promising.  I am using the extremis in a vented configuration on a pair of RawAcoustics HT3s - excellent bass.

[tdangelo]

Therefore, I am looking for a woofer with longer excursion. I came accross the Extremis 6.8 web page:
http://www.adireaudio.com/Home/ExtremisMidwoofers.htm .

I have the impression that this woofer might solve my problem: it has one  inch of peak-to-peak linear excursion and should fit onto my enclosure.


What do you guys think? Any good or bad experience? Any recommendation for another driver?

I have 4 Extremis in each of my RAW Apex II.  I get excellent bass - the drivers are VERY fast and together produce chest pounding bass when need and in my room are never boomy.  Highly recommended.

Tony

[JohninCR]

I'm not sure any single 6" or 7" driver is going to get you where you want.  I understand the Extremis is a fine driver, but you're likely to end up with an efficiency mismatch, and a single Extremis is only capable of a max SPL of about 85db at 40hz in your open backed exclosure.  The first thing I would suggest if you haven't already done so is to stuff that open rear cavity.  That will reduce resonance and gain up to 6db at the bottom end, because you now have a variation of a U-baffle.  Since you're hitting max excursion, you'll want some type of rumble filter to filter out the lowest frequencies to protect your current drivers.  Then if you need more extension add a sub. 

If you were able to go with 2 Extremi (sp) per side, with biamping, and an adjustable active XO, then I'd say go for it.  In your case I'd be hard pressed to recommend cannibalizing a good speaker.

[BrunoB]

Thank you all for your input. It looks like that the Extremis will be the right driver.

I'm not sure any single 6" or 7" driver is going to get you where you want.  I understand the Extremis is a fine driver, but you're likely to end up with an efficiency mismatch, and a single Extremis is only capable of a max SPL of about 85db at 40hz in your open backed exclosure.  The first thing I would suggest if you haven't already done so is to stuff that open rear cavity.  That will reduce resonance and gain up to 6db at the bottom end, because you now have a variation of a U-baffle.  Since you're hitting max excursion, you'll want some type of rumble filter to filter out the lowest frequencies to protect your current drivers.  Then if you need more extension add a sub. 

If you were able to go with 2 Extremi (sp) per side, with biamping, and an adjustable active XO, then I'd say go for it.  In your case I'd be hard pressed to recommend cannibalizing a good speaker.

I think that a single driver will be OK.  There are two reasons :
      - listening distance is only 5.5 feet
      - the open back of the speakers  will be firing in another room section such that the there will be no cancellation between front and back wave.

Redline is a standing wall of foam+fiberglass.


However, I like your suggestion to add a filter and a sub since I plan to use a home theater digital amplifier anyway.

Bruno

[Duke]

I think the Extremis uses a Tang Band motor. 

Assuming you don't need smooth response well up into the midrange, a more cost-effective route might be the Tang Band 6.5" subwoofer.  I use 'em (in a reflex enclosure tuned to 27 Hz)  and like 'em.  Similar excursion capabilities to the Extremis, a different surround, and lower thermal power handling.  In an OB application, mechanical limits will set in long before thermal limits become an issue.

http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=264-832

Duke

[audioferret]

Does the Tang Band use the XBL motor patented by Adire Audio?  You may want to check.

The motor that the extremis is detailed here: http://www.adireaudio.com/

[BrunoB]

I think the Extremis uses a Tang Band motor. 

Assuming you don't need smooth response well up into the midrange, a more cost-effective route might be the Tang Band 6.5" subwoofer.  I use 'em (in a reflex enclosure tuned to 27 Hz)  and like 'em.  Similar excursion capabilities to the Extremis, a different surround, and lower thermal power handling.  In an OB application, mechanical limits will set in long before thermal limits become an issue.

http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=264-832

Duke

Thanks for the suggestion. The Tang Band 6.5" subwoofer is a 4 ohm driver. For my QSO series XO, I prefer to use a 8 ohms driver. Furthermore, the  Adire has a  flatter impedance curve, which simplifies the XO.

Bruno

[JohninCR]

Bruno,

Re your wall partitions, what kind of foam & fiberglass?  Bass waves go thru a lot of stuff, so you may not be getting the almost IB response that you think.  Cool idea though, your own audio cocoon.

[Kevin Haskins]

I think the Extremis uses a Tang Band motor. 

Assuming you don't need smooth response well up into the midrange, a more cost-effective route might be the Tang Band 6.5" subwoofer.  I use 'em (in a reflex enclosure tuned to 27 Hz)  and like 'em.  Similar excursion capabilities to the Extremis, a different surround, and lower thermal power handling.  In an OB application, mechanical limits will set in long before thermal limits become an issue.

http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=264-832

Duke

No... the motor structure is completely unique for XBL^2 designs.   In a typical underhung or overhung motor in a high excursion design requires a relatively large VC (higher inductance).   The BL curve you get is parabolic and the inductance of the unit is FAR higher than an equivilent XBL^2 design.    Seeing that the three major mechanisms of transducer distortion are BL nonlinearities, Le nonlinearities and Cmx nonlinearities using a properly designed XBL^2 motor helps to minimize two of those parameters (BL & Le).

The disadvantage is in power handling (smaller coil also translates to less ability to handle transient heat) and cost/weight of a larger motor in some cases.   

 

[Duke]

Thanks for the additional information, Kevin.

I was basing my guess about the motor on having eyeballed the two woofers side-by-side; the motor assembly looked identical from the outside.

However the flatter BL curve of the XBL technology is a significant advantage and makes the Extremis worth the price difference.  I definitely agree with you on the value of minimizing BL nonlinearities.  I don't see the lower Le as a significant advantage in a subwoofer application, but maybe it is.

Duke

[Kevin Haskins]

I think they both us Neo magnets.   The difference between XBL^2 & non-XBL^2 designs really is only visible in on the inside profile of the motor (not visible). 

Whether it is worth the price difference or not depends upon your application I suppose.    I'd say both the lower Le and flatter BL curve are important.   Most people think of Le problems only causing additional IMD at higher frequencies but the system is fairly complex.   In general, anytime you can lower Le effects you get closer to the "ideal" transducer.    Wiggins or Dr. Klippel would be better than I at explaining the effects.

For low frequency applications the suspension of both drivers is probably the limiting factor.   The Extremis will have better distortion figures but you have to also consider that you can buy two of the TB drivers (and get corresponding lower distortion) if your application will support the extra driver.

[BrunoB]

Bruno,

Re your wall partitions, what kind of foam & fiberglass?  Bass waves go thru a lot of stuff, so you may not be getting the almost IB response that you think.  Cool idea though, your own audio cocoon.

I do agree. However, I had a "Sound Cocoon" when I was living in NC. My speakers were not open baffle at that time. Even with a two inch foam thick hanging wall, the improvement on bass was tremendous: both in quantity and quality (actually, by far the best bass I have ever heard). IMO, the most important factor for bass reproduction is the room.

Bruno

[Kevin Haskins]

Bruno,

Re your wall partitions, what kind of foam & fiberglass?  Bass waves go thru a lot of stuff, so you may not be getting the almost IB response that you think.  Cool idea though, your own audio cocoon.

I do agree. However, I had a "Sound Cocoon" when I was living in NC. My speakers were not open baffle at that time. Even with a two inch foam thick hanging wall, the improvement on bass was tremendous: both in quantity and quality (actually, by far the best bass I have ever heard). IMO, the most important factor for bass reproduction is the room.

Bruno

I absolutely agree.   You cannot ignore the drivers, acoustic system and electronics either though.    The room is certainly the largest uncontrollable variable from a design standpoint though.