IB Mid-bass Output - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 18 Old 10-24-16, 06:01 PM Thread Starter
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Thumbs down IB Mid-bass Output

I have had my 4 x 18" FI sub in place for 4 years now.

Here is the build thread: It is the Christmas Build: http://www.hometheatershack.com/foru...mas-build.html

Nobody has been able to answer this question and I have not seen an answer for it anywhere.

It just does not have the mid bass oomph as other super high quality subs with less drivers and smaller drivers. I am a bass SNOB and I can't stand even a tiny bit of boom in my bass. So - explanations that start with - other sub woofers just boom away and just sound louder and with IB subs they are quieter because of no boom are not expected as I have had a large IB sub for years now. I a fully taking this into account. I have Magnepan speakers and can't stand boxy sound either...

I understand that drivers where the volume of air behind and in front of it is greater than 10 x VAS are limited by excursion and not by heat.... I understand that you can't pump as many watts into and IB sub compared to non-IB all things equal...

OK, so... so what? Assuming an IB sub is following the wave front and rising and falling based on the current going through it... Assuming a SEALED sub is doing the same thing....assuming that this test would be within the limits of both the subs. I am thinking that if you took a super slow motion video of them side by side - they would both be moving in unison - when one is up the other would be up - responding to the current....therefore essentially making the same sound pressure differences in the room...

So..... as you turn it up - eventually one of the subs hit it's excursion limits. So, let's only turn it up to just before that happens. I would still think both the sealed sub and the IB sub would be giving out similar sound pressure....

BUT this appears not to be the case. The sealed sub is much louder. I just can't figure out the mechanical reason why my IB sub with twice as much xmax as a sealed sub does not play as loud and does not seem to pressurize the room in the same way. Again, I understand that the sealed sub has the air pressure to help control the cone.

Basically, assuming the an IB sub as a larger xmax - what is the mechanical reason why an IB sub needs more drivers than a sealed sub with smaller xmax? Please don't just say - because a sealed sub can handle more watts because of the back pressure and because of thermal reasons. That does not give me a mechanical reason why that is the case.

Am I being clear? I have just been considering going back to non-IB because of this. I have borrowed a JL audio f113 that has a single 13.5" driver that is boom free, but gives me a ton more mid bass.

The only think I can think of is that the sealed sub's cone may start moving up a curve that would lead it to a much greater xmax...but the air pressure or the voice coil restricts it so it does not complete it's journey to match the voltage going through the voice coil the same way it would in an IB sub. This would mean that the sound is essentially clipped, so to speak, because the driver does not go as far out as it should. Basically, a plot of a sinewave of a sealed driver would cause the sinewave peaks to be flatten out, but have a much faster rise time between and THAT would account for the increase in loudness?????

This has been bugging me for years!!! Please help.

-Brent


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post #2 of 18 Old 11-25-16, 09:21 PM
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Re: IB Mid-bass Output

Could it be that the front and back wave are both in the room when using a sealed enclosure but with an IB the backwave goes into another room?

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post #3 of 18 Old 11-25-16, 10:07 PM
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Re: IB Mid-bass Output

To be a bit simplistic, the design rules of a Sub say you can choose any two of the following:-

Size of enclosure.
Output Volume/Power Handling.
Bass extension.

With an IB you are getting maximum bass extension in a very large box.

You really need to measure what you are getting in your room to see what is happening when you run the IB as compared to the JL audio f113 and observe the differences in output and bass extension.

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post #4 of 18 Old 12-23-16, 09:50 PM
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Re: IB Mid-bass Output

Maybe I missed it but when you are comparing sealed and your IB setup you have been using different subwoofers. Is that correct? Or are you removing one of your IB woofers and putting it into an enclosure and comparing that way?

Long story short the reason for lack of midbass punch and ouput is high inductance. The reason you do not have the midbass punch from your Fi subwoofers compared to the JL that you borrowed is inductance. The ratio of Re:Le is lower on the JL subwoofer than the Fi unit. For example click this link to see Data-Bass's measured Fi Q that supposedly has the internal shorting ring option. Re of the driver measured is 2.8 Ohms and Le is 6.19 mH which is quite high. The high ratio means the driver starts rolling off earlier as the frequency increases comapred to say a driver with an even Re:Le ratio (Re of 3.0 and an Le of 3.0) or even a lower ratio (Re of 3.0 and Le of 2.0), etc.
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post #5 of 18 Old 12-25-16, 01:41 PM
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Re: IB Mid-bass Output

If it makes you feel any better, my big sealed sub doesn't have diddly for midbass, either. It is rolling off fast above about 90 Hz


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post #6 of 18 Old 10-26-17, 12:31 PM
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Re: IB Mid-bass Output

Subwoofers should not be reproducing midbass frequencies...

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post #7 of 18 Old 10-26-17, 03:48 PM
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Re: IB Mid-bass Output

Here's an idea. Volume is a product of driver sensitivity, number of drivers, total watts into the subwoofer system and the distance between you and the drivers. You may not be factoring all of those things. If your sealed sub is closer, more sensitive, powered with a better or more powerful amp then sure it'll be louder. The other thing to think about is sub location and room acoustics. The location of the sealed sub may have a peak at a frequency you associate more with what you think is mid bass. The IB may have a null at the same frequency and the same seated location. The answer is near field subs .

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post #8 of 18 Old 10-31-17, 10:28 PM
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Re: IB Mid-bass Output

Just to clarify things, when you say IB, are you referring to a large closed box as an or just a driver in a large baffle open at the back (dipole)? In a dipole you get cancellation when the distance between the front and rear is in the order of the wavelength, thus you need much more volume displacement to produce the same SPL as the frequency gets lower. There should still be spreadsheets to compute that on Linkwitz Lab.

Last edited by dgmartin; 10-31-17 at 10:30 PM. Reason: ambiguous
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post #9 of 18 Old 12-05-17, 06:51 PM
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Re: IB Mid-bass Output

I have had this same complaint with mid-bass and my ib. I recently swapped out my old equipment (ep4000 and Pioneer Rx) for new equipment (Yamaha Aventage, and Inuke 6000) with no other changes to speakers or ib subs and to my surprise it fixed my mid-bass. It seemed like the Yamaha helped to fix the room/ crossover and the Inuke seems to have more even power.
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post #10 of 18 Old 12-05-17, 08:35 PM
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Re: IB Mid-bass Output

Quote:
Amplidood wrote: View Post
I have had this same complaint with mid-bass and my ib. I recently swapped out my old equipment (ep4000 and Pioneer Rx) for new equipment (Yamaha Aventage, and Inuke 6000) with no other changes to speakers or ib subs and to my surprise it fixed my mid-bass. It seemed like the Yamaha helped to fix the room/ crossover and the Inuke seems to have more even power.
What drivers do you have and how many watts does each driver see?

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