IB questions?

[vaughan]

Hi,

I'm a newbie and I have some questions that I hope can be answered for me, but before I get there, just a few things. I have heard nothing but good things about infinite baffles so far. The sound quality is what I am after but also the output (and extension).

I just would like some clarifications, if possible. I have been talking to my manager (I'm an audio specialist) and he tells me that infinite baffles are sealed subwoofers. So what I understand is that infinite baffels are very large sealed subwoofers. But there must be differences in how they operate.

What are they?

Is an acoustic suspension sub (like an M&K) the same thing as an infinite baffle? My manager, who has 40 years in the trade, and a billion certificates, tells me that it is. I don't believe him though. Is he correct ?

Also, what exactly makes an infinite baffle, infinite? Why use this terminlogy?

Right, I am from South Africa, and down here, no one knows what a true infinite baffle is. I have a few SVS subwoofers and I am impressed with them, don't get me wrong, but the bass is a little "thick" sounding. There also is a bit of bass overhang.

I want the best quality bass that I can get. From what I've been reading, you don't need to spend outrageous amounts of money in order to achieve it. Which has led me here. I want very loud output in the range of 115 db's down deep (in the range of 20hz-15hz), and strong output below that.

My room size is 3500 cubic feet and I was thinking about building a manafold and using 4 Tempest drivers (with the ability to mount an additional 4 more) and using around 150 watts per driver (using one of Adires pro amps, or something similiar).

Do you think 4 Tempests would give me the kind of output that I want? And would the Tempest drivers give me great quality bass, or are there better options out there?

I posted in another forum and I said there that I was worried about having an IB installed because another member here had his IB system bottom out and he has 18 15" drivers.

I obviously don't want to damage the drivers in my IB setup when I eventually build it . Please, if you have the time available to answer my queries, I would really appreciate it.

Thank you.

--Sincerely,

[ThomasW]

Okay, thanks for moving this discussion.

Small sealed subs are called 'infinite' baffles because technically the front wave never interacts with the rear wave. In reality they are more appropriate called "acoustic suspension".

Now our use of the word 'infinite' refers to both the size of the box and the size of the baffle the driver is mounted on.

Once the box size reaches approx 10 times the summed Vas of the drivers, there's no interaction of the rear wave and the box containing the rear wave.

Why do our IB sub have the particular sonic characteristics that make them better than small sealed boxes?

First the small sealed box acts as a high pass filter, second there's no interaction of the rear wave with the 'box'

Engineering types think that all subs with the same Qtc sound the same. Well it's just not so. A "true" IB that has a "Q" of 0.5 sounds much different than a small sealed (acoustic suspension) box with the same "Q".

One can blame most of the sonic differences on the size of the 'box' and the interaction of the rear wave with the 'box'.

For your installation I think drivers with a higher Xmax than the Tempest should be considered

[vaughan]

Thank you for answering my questions.

So if I am getting this straight, in small sealed enclosures, there is a certain amount of back pressure that the driver is working against. The enclosure acts as a spring to control driver moment.

Infinite baffles have no rear waves interfering with the front waves, and the driver is using it's own suspension to control it's movement. Am I correct so far?

Which driver would you recommend to me that would give better sound quality (and output) than the Tempest? I don't want to break the bank or anything, but I would like to know which would be the most effective driver to use.

I don't want to skimp on SQ to make up for output. Thank you very much for having the time to answer these queries.

--Sincerely,

[ThomasW]

Yes that's correct...

Currently there are limited options since both Adire and Ascendant haven't released new drivers.

One of the 'best' drivers out there is the 15" TC2+ from www.Oaudio.com.

Another option would be the RL-p 15" from www.SoundSplinter.com.

Both these drivers are made by TC-Sounds.

I know SoundSplinter will ship to you since they've been willing to ship to Australia. I think Todd at Oaudio would do the same if ask.

The down side is that all these drivers are relatively heavy, so shipping 4 will be $pendy .....

[vaughan]

Thank you for the advice, Thomas. As a matter of interest, how do small sealed subwoofers act as high-pass filters?

I would like to know the how behind these things. Sorry to be a nuisance.

--Sincerely

[ThomasW]

The smaller the box the higher the resonant frequency, and the higher the "Q".

It functions as a high pass filter since it physically can't reproduce low frequencies at any significant SPL

[vinculum]

Hi Everyone...

First post for me. I'm pretty new to the infinite baffle concept, so I hope my posts are appropriate to this thread!

From what I understand, a sealed enclosure also helps protect from over excursion of the drivers. How does the infinite baffle setup protect against this since there is no pressureized box to fight against? I've read about running a certain percentage of power below the normal rating. Is this the only protection relied opon? Is this the weak link in this type setup?

I was planning on building a stage from wall to wall under my projection screen, 12 feet long x 22" high, about 28" deep. It was originally going to be for looks, but now I see I can do more! The one end can be open thru the wall to the other half of my basement. So basically my stage could be my manifold with some forward facing drivers. Does this sound like it would present any problems?

Will I get a comparable transient responce to a sealed design with an infinite baffle?

I currently have a SVS PC-Ultra. It sounds great, don't get me wrong and I could easily be happy dropping the tuning down to 12Hz and adding a second one. But I like the idea of having them integrated into my stage. If i can get the "dynamic punch" of a sealed design and the high SPLs down deep, it seems like a value to me to do an infinite baffle over a sealed or ported design.

Thanx,
Dr V

[ThomasW]

We use multiple drivers (higher displacement) to protect the drivers. If you're worried about this use a rumble (high pass) filter.

Stage mounted IBs work very well and are becoming more popular as more people make dedicated HT's.

The transient response of an IB is the same as any large sealed box, since an IB is simply a VERY large sealed box.

An IB won't 'sound' like your SVS design, since unlike your SVS, with an IB there's no box to color the sound. An IB will of course play much deeper than the PC Ultra.