IB Speaker Specs

[MorfiusX]

I have been trying to figure out why some subs are recommended more often than other for an infinite baffle configuration. I have read some articles stating Qts should be above .5, and optimally above .6-.7. Many people recommend the IDQ12 v2, but the spec show the Qts at .259. I would think that this speaker would not have enough dampening for an IB setup.

The other sub line I was looking at is the Hertz HX 300 which has a Qts of .47. I would think that this speaker would be better suited for an IB setup, but I have yet to find anyone who is running them in this configuration.

Can anyone shed some light on what makes a speaker a good choice for IB for a speaker specs newb? Thanks!

[amitaF]

edit

[amitaF]

Acoustic Elegance IB15 4ohm car version (Idmax comparison)

good reading here

[tinctorus]

I check out that acoustic elegance site and they aren't very descriptive about there subs I mean they essentially list the same exact specs for every speaker from 10' through 18's

Are they ALL meant as as IB sub or what I was getting kinda confused as to the workding on there website

[fish]

Amita, what was the wait time between placing order & the subs showing up at your door?

[amitaF]

3 months...but they had [frame]supplier issues at the time

[amitaF]

edit

[schmiddr2]

To answer your question---

As quoted from MTX: "An infinite baffle design is defined as an enclosure that contains a greater volume of air than the Vas of the driver. An infinite baffle system can easily be applied to an automobile. This is accomplished by mounting the speakers on a board and using the trunk of the vehicle as the other walls of the enclosure. It is important that there be no leaks that would allow air to move from the front to the back of the cone. Look for speakers where the Qts is greater than .6, and a Vas lower than the volume available when selecting a woofer for an infinite baffle system."

[alachua]

It took a little over 5 weeks for my order to ship. The reason you see the same specs on many of the drivers is because they share the same motor assembly. The IB15/12/10 are all essentially the same aside from the size of the cone.

Take a look in their forums, there is a bunch more info in there.

[MorfiusX]

Originally Posted by schmiddr2

To answer your question---

As quoted from MTX: "An infinite baffle design is defined as an enclosure that contains a greater volume of air than the Vas of the driver. An infinite baffle system can easily be applied to an automobile. This is accomplished by mounting the speakers on a board and using the trunk of the vehicle as the other walls of the enclosure. It is important that there be no leaks that would allow air to move from the front to the back of the cone. Look for speakers where the Qts is greater than .6, and a Vas lower than the volume available when selecting a woofer for an infinite baffle system."

I have read that definition before. Given this definition: Why is a IDQ sub with a Qts of .259 considered a good choice for IB around here? That's where I'm confused. I have read many posts saying how well the IDQv2 subs perform in IB, but yet to figure out objectively why.

[amitaF]

dang..sorry , i mis-read your initial question ..
failed attempt at multi-tasking

[fish]

Amita, have you put up a review for your trio of 12's? If not, how about a mini review now(if you don't mind)? What would you guess the total weight(baffle/subs) came to?

[schmiddr2]

Originally Posted by MorfiusX

I have read that definition before. Given this definition: Why is a IDQ sub with a Qts of .259 considered a good choice for IB around here? That's where I'm confused. I have read many posts saying how well the IDQv2 subs perform in IB, but yet to figure out objectively why.

The 12" IDQ has a Vas of 2.98cuft and the Qts is .397 . I don't consider these to be good specs for IB, but I don't know enough to say for sure it will not be good/great for IB.

[squeak9798]

You can not look at Qts individually. You need to consider both Qts and Fs. With these two, you can quickly guesstimate what the final response will look like. Ultimately that's what we are aiming for, a certain final response.

We have a particular advantage in a vehicle, and that is cabin gain. Home audio doesn't benefit from room gain nearly as much as we benefit from cabin gain. So typically in home audio to have good low end response from an infinite baffle driver, you need a high Qts (.6-.8) and a low Fs (~20hz, +/-). Why? Because that will provide a really low F3 with a reasonable rolloff thereafter.

In car audio, we don't have to have such a low F3 because we benefit from cabin gain. We can have a higher F3 and a little shallower roll off and still have good low end response because of the boost in output we receive from the cabin gain. And really, having too much low end from the driver itself could result in an exaggerated or bloated low end response once placed in the vehicle due to the addition of cabin gain.

So why does the original IDQ with a Qts of .259 work well IB? Because it has a really low Fs of 19hz. This will keep the F3 at a reasonable point so that when combined with the cabin gain we still get good extended low end response. Another option would be a driver with a higher Qts and a higher Fs. Something like a Qts of .5 and Fs of 30hz has a fairly similar response to that of the IDQ infinite baffle. A high Qts and low Fs can work also depending on the response of your vehicle and your ability to EQ out the low end if it is overbearing.

The main thing to AVOID is low Qts and high Fs. The F3 is too high for cabin gain to make up the low end, so the bottom end will be anemic. For example, when I won the SSA Dcon I tried it IB simply because that's how my car was already setup so it was a simple drop-in installation (among other reasons). And guess what? The low end sucked. But I knew that would happen before I even installed it. Why? Low Qts, high Fs. Bad combination for IB. You could try to EQ in the low end in this situation, but you may run out of driver excursion before you get to where you want to be depending on the driver.

The other thing I would look for is excursion. Output in IB is a function of excursion. It doesn't have to have 30mm of Xmax, but if Xmax is fairly limited you may need to use multiple drivers to achieve satisfactory output depending upon your output requirements.

I use(d) an Exodus Audio Shiva-X infinite baffle in my vehicle and loved it.

[amitaF]

Originally Posted by fish

Amita, have you put up a review for your trio of 12's? If not, how about a mini review now(if you don't mind)? What would you guess the total weight(baffle/subs) came to?

my job has had me travelling away from home for most of the past year.
i have not had the chance to power em up yet. a review is in order for sure.

back to the subject

[amitaF]

squeak has pretty much condensed the bits of information that i have found, digging through diyma's threads on the subject and more...thanx

[thehatedguy]

What he said minus having used a Shiva-X. There is a pair of Mal-Xs on DIYA though. Should be a nice driver IB in the car.

It seems as if whatever the Qts is, you can add about .1-.15 for a single driver IB in the typical trunk and .2-.25 for a pair of drivers in the trunk to get you an idea of what the Qtc would be...provided the Vas isn't something dumb like 100 cubic feet per driver.

In the house, Qts=Qtc and you can have large Vas numbers because the space is great. In the car that isn't necessarily the case, and why some drivers intended for the house might not work so well IB in the car (think Fi IB3 line).

Originally Posted by squeak9798

You can not look at Qts individually. You need to consider both Qts and Fs. With these two, you can quickly guesstimate what the final response will look like. Ultimately that's what we are aiming for, a certain final response.

We have a particular advantage in a vehicle, and that is cabin gain. Home audio doesn't benefit from room gain nearly as much as we benefit from cabin gain. So typically in home audio to have good low end response from an infinite baffle driver, you need a high Qts (.6-.8) and a low Fs (~20hz, +/-). Why? Because that will provide a really low F3 with a reasonable rolloff thereafter.

In car audio, we don't have to have such a low F3 because we benefit from cabin gain. We can have a higher F3 and a little shallower roll off and still have good low end response because of the boost in output we receive from the cabin gain. And really, having too much low end from the driver itself could result in an exaggerated or bloated low end response once placed in the vehicle due to the addition of cabin gain.

So why does the original IDQ with a Qts of .259 work well IB? Because it has a really low Fs of 19hz. This will keep the F3 at a reasonable point so that when combined with the cabin gain we still get good extended low end response. Another option would be a driver with a higher Qts and a higher Fs. Something like a Qts of .5 and Fs of 30hz has a fairly similar response to that of the IDQ infinite baffle. A high Qts and low Fs can work also depending on the response of your vehicle and your ability to EQ out the low end if it is overbearing.

The main thing to AVOID is low Qts and high Fs. The F3 is too high for cabin gain to make up the low end, so the bottom end will be anemic. For example, when I won the SSA Dcon I tried it IB simply because that's how my car was already setup so it was a simple drop-in installation (among other reasons). And guess what? The low end sucked. But I knew that would happen before I even installed it. Why? Low Qts, high Fs. Bad combination for IB. You could try to EQ in the low end in this situation, but you may run out of driver excursion before you get to where you want to be depending on the driver.

The other thing I would look for is excursion. Output in IB is a function of excursion. It doesn't have to have 30mm of Xmax, but if Xmax is fairly limited you may need to use multiple drivers to achieve satisfactory output depending upon your output requirements.

I use(d) an Exodus Audio Shiva-X infinite baffle in my vehicle and loved it.

[MorfiusX]

All of this really helps.

Using the calculator here, should I input a Vb equal to my trunk size (11.5 cubic feet)? What F3 is a good number to aim for?

[jimbno1]

I have a set of each (8,10,12) of the jl IB4's The QTS is .63 - .77, VAS 1.8-4ft3, FR 37.5-40.5, xmax 7.3-8.6mm, depending on size.

I was hoping to use the 10 or 12 as a sub in one of my installs. But this thread has made me wonder if a single 10 or 12 will be enough. Specifically the xmax figures.

If you double or triple the number of subs I assume you will need double or triple the VAS inthe trunk. Correct?

[thehatedguy]

1 wouldn't be enough for me. But you should be approaching IB even if yo double the Vas figures.

I wouldn't worry until you got into a Qtc of like .9 or in the 1s. You can fix a lot of the "problems" with an EQ.

Originally Posted by jimbno1

I have a set of each (8,10,12) of the JL IB4's The QTS is .63 - .77, VAS 1.8-4ft3, FR 37.5-40.5, xmax 7.3-8.6mm, depending on size.

I was hoping to use the 10 or 12 as a sub in one of my installs. But this thread has made me wonder if a single 10 or 12 will be enough. Specifically the xmax figures.

If you double or triple the number of subs I assume you will need double or triple the VAS inthe trunk. Correct?

[thehatedguy]

Given cabin gain, around 45-55 hertz is what most "good" sounding sealed boxes are tuned to.

Originally Posted by MorfiusX

All of this really helps.

Using the calculator here, should I input a Vb equal to my trunk size (11.5 cubic feet)? What F3 is a good number to aim for?

[huckorris]

Originally Posted by jimbno1

I have a set of each (8,10,12) of the JL IB4's The QTS is .63 - .77, VAS 1.8-4ft3, FR 37.5-40.5, xmax 7.3-8.6mm, depending on size.

I was hoping to use the 10 or 12 as a sub in one of my installs. But this thread has made me wonder if a single 10 or 12 will be enough. Specifically the xmax figures.

If you double or triple the number of subs I assume you will need double or triple the VAS inthe trunk. Correct?

I would probably worry about the cone area and resonance frequency. X max isn't great either. I bet 2 12's would be okay. It also depends on your tastes, like bumping hip hop.

[jimbno1]

Yeah I don't lsten to a lot of hip hop. The 91 Lexus LS400 has only a 8 in the center of the deck and the gas tank is directly behind the rear seats. I am not opposed to opening the existing hole up some but cutting two new holes might weaken the structure too much.

This plan to do a simple system in the Lexus keeps getting more complicated by the hour. Gonna cost me more than the car is worth. GRRRRR!

[thehatedguy]

I wouldn't think opening up the hole some is going to hurt. Remember as long as you have about 75% open area for the speaker to fire through to cone area, you should be fine. And keep the volume between the speaker and the opening as small as possible to prevent it from acting like a bandpass.

[jimbno1]

Yeah I was worried about the band pass too just visualizing the install. Would it help to fill the area between the deck and the baffle with something like non-expanding foam or that not dense enough to prevent the band pass effect and sub freqs? I was also thinking of using a 12" concrete form and sealing both sides between the baffle and the deck. Or am I way off base?

One other thing I am probably stuck with small front mids (4-5.25") so I was hoping to raise the crossover to compensate. And the IB4s have a good rep for midbass duty. Hopefully I can get away with the sub playing up to 150Hz or so.