Richard1

iTrader: (1)

I will be installing a 10" or 12" sub under the sealed rear deck for an "IB" setup. The installer recommends a Hertz ES300D. My readings have led to me to understand that a minimum Qts of .7 is required. The Hertz sub has a Qts of .42 although I sense that other factors come into play. Does anybody have any experience with this sub, input regarding my approach, and/or recommendations?

Thanks,
Richard

df.dima

iTrader: (12)

Aim for the qts that you want the qtc to be. i don't have experience with IB, but from my interest and research I've found recommendation to go by that.

.42 might be too low. try finding a driver in like .5+ range at least, would work, still might be too bottom heavy.

question is what other equipment you are running, ie what you are integrating the sub into?

Richard1

iTrader: (1)

The sub will receive 180 watts from a five channel Audison amp. How do assess my Qtc needs? Thanks for your interest.

Richard

2deep2

.7 is not required. In fact I prefer 0.53 qtc because it represents a critically damped system. Any Qtc between 0.577 and 0.7 will sound good.

A lower 0.53 Qtc will sound dry. 0.7 Qtc and higher will go from full to fat to boomy. Qtc higher than 0.7 represent a system that has ringing or some would call it overhang.

This is not to say 0.8 and 0.9 or even 1.2 Qtc systems will not sound good to most people. That's why many boomer brand subs have Qts of 0.7
(also many think 0.7 is what they need and don't know that when 0.7 Qts is mounted the resulting Qtc is higher than 0.7).

When you mount a sub IB its Qtc will be very close to the Qts but the Qtc will always be higher than the Qts. How much higher depends on how true you are to being IB, 3 X VAS. Any air volume larger than VAS should be IB but most use the rule 3 X VAS to make sure the air volume does not effect the sub. The sub complance is lower than the IB air volume complance is required to claim you have a true IB. You also need consider the fc/fs.

0.42 Qts will work IB for 0.57 to 0.7 Qtc.
If you want more fat to boomy sound, go for a higher Qts.

I'm not familiar with the Hertz Sub but you need make sure you don't run into control problems. Things like not enough motor or xmax for the given sub complance can result in mechanical noise. Too high of a Qt will result in excessive ringing or flutter like sounds.

At 180 watt in a an IB set up.... Hope your sub is super effecient and you like to listen at low volume levels.
In an IB set up the effeciency will go down, less out put for input over that of a sealed, ported or band pass enclosure. 180 watts is about the lest amount of watts I have ever put on a sub, and that was a 10" in a sealed box. I can't say if the output will be enough or not. My 10" sealed would do 120 dB with about 180 watts.

Richard1

iTrader: (1)

Thank-you for your very informative answer Ant. At this point, however, I am pushing the bounds of my knowledge - and confidence. Hence, a few more questions. But first more specifics. My undetermined IB sub will be mated with Rainbow's 6-1/2" Vanadium Kick drivers powered by Audison's LRx5, sourced by Eclipse's 8454, and Audio Control's Three.1 (whew!). The vehicle is a 1991 Mercedes 300E where the trunk is already well sealed by its' vertical gas tank. I intend to MDF/seal the underside of the rear deck, install the 12" sub which will fire through the modified first-aide kit cover into the cabin. I will also Dynamat the trunk lid and front doors. As I mentioned, the sub will receive 180 (clean) watts and I am more focused on SQ than SLP or boom. The Hertz Energy ES300D (dual v/c) sub has the following specs: Fs 30.2Hz Qts 0.42 Qtc n/a Qes 0.49 Vas 85.57 litres SPL 97 db Remaining questions: Why and how should I consider the Fc and FS, as you suggested? Do the specs, mentioned above, affect your suggestion not to use this sub? Do you have any recommendations regarding IB specific subs I CAN use? Again - with thanks, Richard

2deep2

I'm coming from the Speaker Design Cook Book.

Let's say you want a Qtc of 0.707, well the Cook Book says fc/fs should be 1.683 given a Qts of 0.42 for an Infinite Baffle configuration.

fs is the resonance of the driver, 30.2 Hz.
fc is the resonance of the system (speaker in Box), which needs to be 50.83 Hz.

This will give an fc/fs = 1.683, which should make for a good IB configuration given a Qts = 0.42 and the desire for Qtc = 0.707.

Richard1

iTrader: (1)

Thanks again Ant. But how do I ensure the Fc is 50.83 Hz? Is this an inherent characteristic of the driver itself (not posted) or something to aim for with the enclosure. If it's the latter, I have no control over the size of the trunk in an IB setup.

Richard

2deep2

I normally use the enclosure volume. Like Matt and Image Dynamics says, we are really doing a TB (Trunk Baffle) and the trunk is a very large enclosure.

I've read of 2 other ways to effect Qtc but I can't recall them at this moment.

Still what I normally find is you need to know what fc you have now before you think about changing things.

I normally measure the impedance of the driver installed like it would be once the installed is completed and the frequency that gives you the max peak is the fc.

Use this with the Cook Book table and if the Qtc is 0.577 to 0.7 I would not change anything.

Question: how do you determine fc before doing any testing?
Answer: I'm sure there is a way, but now all the information I have found to date says just measure it in a mock up install. IMO, The idea behind IB volume being 3X VAS is to have Fc close the Fs, meaning Qtc will be closure to Qts. However, Qtc is almost always higher and this I've reviewed with several speaker testers.

Richard1

iTrader: (1)

Another informative response - thanks again. Now that I'm (over)loaded with the technical side of an infinite baffle setup, can anyone offer their experience with various brands of 12" subs? I am after SQ primarily, noted above.

Richard