Infinite Baffle and/ or high xmax 12 incher: 50-200 Hz?

[rick57]

Anyone know the maths/ formulas for Infinite Baffle resonances,
how IB performs in * upper bass* (50-200 Hz); or use
the Peerless XLS (or another high xmax 12 incher) up to 200 Hz?

– or Anyone have a theory or a hunch??

(Lambda would be good up higher, but too dear to ship here).

There are lot sof arguments about what alignment produces best bass . . . Sealed is tighter than vented, but less full, etc.

Linkwitz opts for the Peerless XLS 830500 in a sealed box in his sub design the Thor
http://www.linkwitzlab.com/thor-intro.htm
This driver has Fs of 18 Hz, but in a modest box size has an Fb 35 Hz.
It’s only intended to run up to 40 Hz, for home theatre.

Linkwitz states there:
“Above resonance the moving mass, Mms = 166 g, dominates the driver motion according to force = mass x acceleration”

So above 35 Hz in a sealed, the sound is a little slow.

I’m looking for a sub +bass to go from about 20 – about 200 Hz, in a stereo pair.

A transmission line that goes down to 20 Hz will be too bulky.

Linkwitz has an excellent compact dipole bass design, but it requires two Peerless XLS a side, and for the application in mind, I don’t want the xepnse.

Infinite Baffle (IB), with roof mounted drivers seems the best option – no vented boxes to upset the wife!

The “Cult of the Infinitely Baffled FAQ” has a basic FAQ:
http://t-3.cc/users/audioworx/page101-IB-FAQ.html

Anyone on this forum have experience with either IB and/or
a good high xmax 12 incher running up to 200 Hz?

TIA

 

[mikee12345]

if u mean IB as in a large sealed box perhaps just use the normal sealed box equations with the size eg-3000litres


i get the idea that some ppl use their ENtire attic space???
if so those equations dont count.

the shiva is another similar driver.15mm excursion.,
titanic...xxx drivers at > http://respl.com/home.html

if u can put it in a large box up in the attic.perhaps just choose ur box size to what u want the resposne to be

the only difference is u get a much larger sized box if u want :-D
and then the driver is more thermally protected.

eg fit in that sealed box of 6cu ft u cud never fit in ur lounge.

forgive me if im wrong i dont know about IBs

 

[rick57]

large box in the attic: but with a Peerless XLS?

Yes mikee, the idea was to use the entire attic space, often that's what IBers do.

It wouldn't be too hard to measure & calculate the entire space.

I wonder if I plug that volume into the box size of say Unibox, how valid the answers would be, with an unusually large volume?

Building a large box up in the attic could be the way to go.
Finish becomes a non-issue J

I think the Shiva is excellent as a sub, but more of a sub-bass driver than a bass.

 

[mikee12345]

oh yes i just realised,, u said 50hz + not 20hz lol

www.eminence.com (high resonance high efficiency ones)

18sound





personaly i would prefer to build a large box in there-eg www.diysubwoofers.com > EBS

i dont know any other drives designed for sealed boxes i prefer ported.

have protection
rather than have an truelly almost infinite baffle! 25watts rms ? lol>perhaps that would be rather loud anyway.

with a eminence 100db speaker in a large box it would be fine altthough those are generaly ported.

 

[phase_accurate]

Linkwitz states there:
“Above resonance the moving mass, Mms = 166 g, dominates the driver motion according to force = mass x acceleration”

So above 35 Hz in a sealed, the sound is a little slow.

The same applies for every direct radiating speaker. But this does not mean that a speaker is "sounding slow" above resonance !
It means that diver excursion is decreasing with increasing frequency which in turn leads to a flat frequency response with the help of the increasing radiation resistance of the driver's diaphragm.

Regards

Charles

 

[rick57]

‘sub-oriented’ driver up to 200 Hz?

Encouraging
So do you, or have you heard anyone run a good high xmax ‘sub-oriented’ driver up to 200 Hz, with good results?

 

[mikee12345]

200hz is fine
perhaps some alignments mite go up in Db at that zone...

i crossover at 70hz so that i dont boom my voices loudly otherwise i would crossover higher. :-D

(this probably shows that i have a speaker that rolls off at a high frequency so the higher stuff is abit too loud and i try making it louder making the higher stuff louder anyway hahahaha)

 

[f4ier]

rick57, an IB is simply a very-very large sealed box, so you can use your favorite sealed box software to calculate the theoretical bass response. As with any box type, you'd need to consider the subwoofer(s) + room acoustics + placement to really get an idea of the response. But why such a high cutoff frequency of 200Hz? Apart from higher modulation distortion, the drivers would easily be localized at such a high operating frequency.

In this case (and in most cases IMO), the Shiva is a better driver compared to the XLS since it is more efficient.

Cheers

Isaac

 

[mikee12345]

when i do IBs in winisd the response isnt that amazing
what is the typical response of a large IB?

i have seen some good jbls,they needed 300litres but wud go to 20hz with 95db efficiency :-D

 

[rick57]

> Shiva is a better driver than the XLS since it is more efficient.

f4ier, well yes a little more efficient, but IIRC Linkwitz in testing for new drivers for the Phoenix, found that the XLS had less distortion

> why a high cutoff frequency of 200Hz? the drivers would easily be localized at such a high operating frequency.

Yes I would need to locate the bass as close as possible to the rest - if IB, considering mounting mid & treble up near the ceiling.

> Apart from higher modulation distortion

Are you referring to the doppler affect?
20 - 200 is 3.25 octaves.
Many mids might do say 180 - 3000, which is more than 4 octaves. Two ways will of course do more.
There is a trade -off, e.g. if you only run the bass the say 120 Hz, the mids must cover more.
(First breakup mode on the XLS is at 470 Hz).

Does anyone think that IMD is more of a problem with a bass driver?

 

[sfdoddsy]

The problem with the Shiva versus the XLS when SL tested them was that noise from the rear of the Shiva. In a dipole you really need an open basket.

If you are thinking IB, I suspect the Adire DPL12 would be another good choice due to the really low Fs.


Steve

 

[Coolin]

xls=slow

Hi

I have tested the 12" xls with and without a passive radiator in about a 100 liter cabinet (german design) and fount the bass plenty but a very mushy punch to the sound. It could not keep up with the higher frequencies. Even with the crossover set to about 30 hz you could still hear it was slow.
I even used another amp but this didnt help.
Maby in a much larger volume or IB it would be better?

Coolin

 

[f4ier]

Thanks for pointing out SL's tests. I had a look at the relevant pages and it looks like SL had tested an old model Shiva. Shiva Mk. III has different T/S parameters (but [probably] has the same basket as the old model). For the same power level, SL mentions the Shiva has lower distortion... Until power is increased to the level at which aerodynamic drag becomes apparent. Anyway, the new Shiva may/may not be better than the one SL tested. Since this is an IB setup, the noise from a driver's stamped-steel basket should be negligible. (The primary breakup of the Shiva is at 780Hz btw.)

I was refering to the sub's modulation distortion only. I don't think the sound of ~200Hz + sub bass signals from the same woofer would sound good. And at 200Hz, even when the driver units are close together, it can be a little disturbing noticing the sound jump between the mains and the woofer(s)

 

[rick57]

jump between the mains and the woofer(s)

f4ier
> noticing the sound jump between the mains and the woofer(s)

Could you explain this?
Are you referring to where the mains and the woofer(s) are not adjacent? You would definitely want them close to each other.
Or something to do with the XO?

To return to your earlier thought, do you think that IMD is more of a problem with a bass driver?

 

[f4ier]

Are you referring to where the mains and the woofer(s) are not adjacent? You would definitely want them close to each other.

Exactly. When I commented, I was assuming the mains were on the floor or at least mid-way up on pedestals when you mentioned having the IB sub up on the ceiling.

Depending on the closeness of the drivers, I would still think a sub driver operating up to 200Hz can be quite obvious. Initially I set my Shiva sub to crossover at > 100Hz and placed it right beside one of the two main bookshelf speakers. Even with the sub placed less than a foot away from one of the mains, the transition from mains to the sub was too noticeable. I had to lower the low-pass filter. Eventually I settled for a XO frequency of 50Hz and moved the sub 3m away from the nearest mains speaker (to counter my room's acoustics). Even though my bookshelf speakers have to go lower given the lower XO frequency, the "invisibility" of the sub made for a more enjoyable listening experience. And if there are some audible distortion due to the lower cutoff frequency, at least they're coming from the mains -- not from 3m away from the sub.

But given that you're planning to have stereo subs, the transition from sub to mains may/may not be so obvious as a 2.1 speaker set (at such a high cutoff frequency).

To return to your earlier thought, do you think that IMD is more of a problem with a bass driver?

I have to admit that I haven't given this much thought. But since our ears are not so sensitive at low frequencies, I would say distortion is more apparent at higher frequencies, so I would say no.


Cheers,

Isaac