SVS Driver turned into IB use. Clacking away. (1 Viewer)

[Steve G]

I purchased this driver a few months ago and finally got around to posting about it. I'll post questions in order with numbers so as to make it easier to answer and help me out or tell me what i'm doing wrong. First of all the driver was received in perfect condition with packaging that would have made Santa proud. Thanks Dave VT.

1: The driver makes some very serious clacking noise as if bottoming out when volume gets a little high. At low to moderate levels it sounds great.When I say high I'm only using an older Pioneer 60 wpc receiver to push it and only turned up to 3/4 volume with the sub output on my receiver only 1/2 up.This is nowhere near reference level.
I've thought about getting the Parts Express 250 sub amp but I'm afraid of what that would do. Any ideas on whether that would help or make things worse.

2: I have the driver mounted firing forward into the room. All the SVS drivers [I believe this one was out of a 20-39]that I have seen were bottom mounted and down firing. Is it possible that mounting it vertically could be doing damage or just not right for what this was designed for. Thanks for any help or comments.

 

[Edward J M]

The IB application has virtually no back pressure and the woofer operates in "free air" (hence the term infinite baffle).

Since there is no air piston to damp the woofer, you will reach the mechanical excursion limits of the driver FAR before you reach the thermal power handling limits of the voice coil.

A driver's power handling limits are always "de-rated" in an IB application. It doesn't surprise me it can be driven to bottoming with a 60 watt amp, and this should in no way be construed as being reflective of a poor woofer design.

That woofer was specifically designed and optimized for application in an SVS vented enclosure. It is unwise to assume that driver is optimal for an IB application.

An IB application typically needs larger multiple driver to produce the same type of SPL as a vented design. Twin 15" is often considered the minimum for an IB, and I can attest from personal experience that driver array works fine in a 3000ft3 basement. Many people go crazy and add 4, 6, 8, etc. 15" drivers and really belt out some clean SPL. I think the Tempest is a good choice, as is the Dayton driver specifically made for IB applications.

Regards,

Ed

 

[Chu Gai]

Succinct and excellent comments.

 

[Steve G]

Thanks for clearing that up for me Ed. I guess I'll pull it out and put it in a box or sonotube design.

Ed said:
A driver's power handling limits are always "de-rated" in an IB application. It doesn't surprise me it can be driven to bottoming with a 60 watt amp, and this should in no way be construed as being reflective of a poor woofer design.

Ed,I meant nothing bad at all about the driver or its design. I do apologize to the SVS company and its fans.If anything it was me using it for a purpose for which it obviously was not designed. As I said at low and even moderate levels it sounded fine. I was obviously doing something wrong and am glad that you pointed it out.
Hopefully someday I'll be able to join the ranks of the real SVS folks.
Thanks Steve

 

[Seth_L]

You need more than 1 12" driver in an IB. Something like 11 more of them

 

[SVS-Ron]

Steve,

Keep in mind too that in the configuration you are using, it'd be a cinch to drive that low powered receiver to clipping (square waves).

A bad thing as they say, and just another reason the bottoming isn't much of a shock.

I would imagine this is a old first gen woofer (before the more capable ISD's were introduced) and in a ported tube or box it will do very well still indeed.

Ron

 

[Edward J M]

No, I didn't think you were bashing the driver per se, I was just noting that your ability to bottom a 12" woofer in an IB application with 60 watts is normal, and that it doesn't mean anything is wrong with the woofer (in case you were wondering that).

IB is a cool application, and I had fun helping build/design one (dual AV-15). I wouldn't give up on it necessarily, you just need more/bigger drivers.

 

[Geoff L]

Add 3 more of the same First gen SVS drivers (MIN) and then you'll be getting into some spl..
All tho ~{not knowing the room size or where the IB is located in room}~ limits what you might need in terms of driver SD & power.

Ed already covered everything quite well and if you only have the one driver, a clone of a 2531 or 2039 as you mentioned, would make best use of the 12 and get you the most room performance.

Regards
Geoff

 

[Joey_V]

guys, what is an IB? sorry to sound dumb. :b

 

[Steve G]

Well,thanks for all the replies. Time to go back to the drawing board again.As I said,someday I'd love to get an SVS. But this thing seemed so easy to build,I thought I was going to be in subwoofer heaven As the saying goes though"If it SOUNDS to good to be true it probably is".:wink:
Thanks again
Steve

 

[Steve G]

Joey V asked

guys, what is an IB? sorry to sound dumb.


Joey I'll let one of the other guys answer it for you.As you can tell I didn't exactly understand it to well either or you might try doing a search in the DIY and Advanced project area.BTW as the saying goes Joey There are no dumb questions only dumb answers.Thats why I'll leave the answer to those who know much more than I do.

Steve

 

[ChrisBee]

Dumb answer? :b

An infinite baffle is a loudspeaker design where the pressure waves coming from the front of the cone cannot meet the pressure waves coming from the back.

Cancellation would otherwise occur when the out of phase waves meet each other. This calls for a very large baffle. Or a very long path between the front and the back of the drivers. Usually by using the house structure to seperate the pressure waves for as great a distance as possible. Remember that with falling frequency wavelength increases dramatically.

Avoiding back pressure on the drivers is important. Only very large enclosures (or open air spaces) allow the drivers to keep their natural resonant frequency. Raising the resonant frequency lifts the frequency of the roll-off point of the system. So frequencies below this point are lost.

Here is one website which explains it clearly. There are others. But that picture of the 18" driver has to be worth a thousand words:
Click on William's "home page" then on "infinite baffle" to see the construction details. It looks simply awesome!

http://diy.cowanaudio.com/frontier.html

 

[Edward J M]

Here's some pics of the IB we built. Fires into the living area of a basement. The adjacent space is a fruit cellar. It just begged for an IB application. Running off one side of a Samson S1000. Good SPL, good FR, good SQ. We recently upped the Q to about 0.8 to add a bit more slam to the HT experience.

Check out the Cult of the Infinitely Baffled for more info on IB designs.





Ed

 

[EdNichols]

How is this different from the subs that have a passive radiator design. Does IB have no radiator, just a driver into a sealed enclosure?

 

[Dustin B]

Here is a link to the Cult of the Infinitely Baffled FAQ. It pretty much answers any question you have.

http://home.comcast.net/~ttriff/

Subs that use passive radiators are in the same class as those that use ports, bass reflex. A port and a passive radiator do the same thing in different ways.

An IB is, as stated above, essentially a sealed sub with a really, really large box. Typical subs have net internal volumes of 40-150L. Typical IBs have boxes measured in the thousands of litres range.

There are 4 keys to getting great performance out of an infinite baffle sub. As mentioned above, the front and back waves need to be issolated. The location has to be carefully choosen (this is a design you don't what to have to move). So make sure you test the location with a normal sub before you start cutting holes. The volume on each side of the driver(s) should be 10x the combined Vas of the drivers used. In the case of the most common IB design, 4 Tempests, that means 12800L is the ideal. The last point is you need to choose an appropriate driver(s). Low Fs, mid Qts, good displacement. 5L is about where you should start to get great results (the original SVS driver is less than 1.5L). Using multiple less expensive drivers with the appropriate specs works best when going after the ultimate in price/performance value for subs.

 

[Mike SJ]

"just a driver into a sealed enclosure? " no, the driver sits in no enclosure. the params for an IB are
1: waves created by the rear of the woofer NEVER reflect back to the driver.
2: waves created by the rear of the woofer NEVER come into contact with the sound created by the front of the driver.