Driver diameter and hitting hard

[PHT 0]

I am hoping that all of you with more experience in the car audio world can help me out.

I am designing a home theater installation for a friend. My friend has never heard an I.B. (Infinite Baffle) sub but he plays guitar and has mucho experience with car subs. He is of the firm opinion that 15" and 18" subs cannot hit like 10" and 12" subs.

I am recommending an I.B. sub installation, using 4 Q18's in 2 manifolds mounted in the attic, with each manifold having 2 drivers mounted on opposite sides but facing in the same direction and wired out of phase, for that extra 2nd harmonic cancellation.

I had to sell my house (divorce) and am leasing now so I can't demo an I.B. sub for him. Sigh...

He loves the sound of sealed subs over ported. I explain that an IB sub is just one biga$$ sealed sub but he goes back to his experience with open baffle subs in cars ??? and thinks lower sound quality and less hard hitting.

I tried to explain the difference that small sealed boxes in small spaces like cars make to the transient response and that in an IB, with multiple drivers sharing the load, the lower excursion of each individual driver keeps them more linear, lowering distortion and improving transient response.

It would really be great for his confidance in the I.B. route if I could get some expert opinions about the larger diameter drivers' performance in the car audio sub world. Then maybe I can get his mind around the IB concept.

Is it a myth or true that the smaller diameter subs hit harder or have sharper transient response?

Any help appreciated!

=>><<=robobob

Edited June 2, 2007 by robobob

[///M5 2,833]

He is of the firm opinion that 15" and 18" subs cannot hit like 10" and 12" subs.

??? is he a mongoloid? wtf?

Either way subs don't "hit" they play the low end of the musical spectrum.

[JimJ 11]

Transient response is much more a function of a driver's inductance than its cone area.

[DevilDriver 28]

For a subwoofer, I think the perceived accuracy of the driver has a lot more to do with the damping characteristics of the speaker and the enclosure it is coupled to. I agree that inductance has an effect, but not a particularly noticeable one throughout most of the average subwoofer's bandwidth. If it's below the inductive rolloff corner frequency, you won't see much effect.

[PHT 0]

Thanks for the replies.

"He is of the firm opinion that 15" and 18" subs cannot hit like 10" and 12" subs."

Well, opinions are like arsehos....

Re transient response:

I agree that in the sub operating range, voice coil inductance is usually less of a factor than the damping factor of the enclosure and the power of the magnet to stop the ringing after the note.

I think his experience is with older technology subs where the larger diameter drivers with their greater mass and lower powered magnets (lower Bl) relative to the total mass would ring badly or keep on moving long enough past the signal to smear the quality.

He mentioned having heard "open baffle" car subs and not likiing them. Is this just an install where the trunk or back of the cab is walled off with a baffle instead of building a box? If this is not sealed off well, that would explain why he thinks that the sound quality and clean hitting suffered. I am trying to clear up the confusion in his mind of open baffle and infinite baffle. They both have the word "baffle" in them, yeah they both must sound the same!

In an I.B. installed properly in a house, there is little chance of the back wave leaking around the baffle and lowering the SPL and muddying up the quality.

Anyone think that higher magnet strength (Bl) is a must for 15" and 18" subs to have clean transient response or to hit cleanly?

[DevilDriver 28]

Well, higher and lower BL (more specifically, BL^2/Re) most definitely relates to damping, as it manifests itself in Qes. Whether higher or lower is required is dependent on the intended application. The fundamental issue at hand is not an argument of whether high mass sounds sloppy or high inductance sounds sloppy, but rather that a poorly engineered speaker will sound like a poorly engineered speaker. There is nothing inherently better or worse about any speaker size or even any speaker material if the design is well engineered to compensate.