Enclosure for a 1800 GTi

[Lee in Montreal]

I have this 1800Gti driver and would want to use it as a sub, under 60Hz.

I initially wanted to build a sealed bandpass box for its reduced group delay, but it seems the excursion at 28Hz is over the top. Second choice is a 12cubic ft bass reflex, but group delay is very high... So, what have you successfully done with your 1800 GTi?

TIA

Lee

[Eaulive]

So, what have you successfully done with your 1800 GTi?

Strip it and turn it into a 2241? :dont-know:

[pos]

I think 1audiohack is using them as subs and likes them a lot.

[1audiohack]

Strip it and turn it into a 2241? :dont-know:

Oh hell no!!!

Skipping past the first three rules of subs and real-estate, comes the creative design process of coupling smoothly with the room for a reasonably accurate overall response.

I built the big 12ft3 box, then another, stacked them, separated them, retuned them, made 9ft3 boxes and did all the same things. Here is what I have ended up with, and after other tunings and drivers come back to this time and time again.

Two separate GTI1800 subs in 9ft3 boxes tuned to 22 Hz with a single 8" SonoTube port that is 23.5" in length.

OK here is where the creative part comes in, yes the tuned frequency is below the resonant frequency of the driver, what's more the port is only 1.5" from the back wall of the box. Here's why:

1 Tuning below the driver Fs gives you a softer curve on the bottom, this was done to match the room gain to obtain flat response without EQ. I brought this up once a year or two ago and was immediately characterized as an ignorant beginner and never brought it up again. Recently Rob "confessed to this sin" and was not ostracized so I will admit it again.

2. When I really started modeling seriously in Leap, and measuring with LMS with a VI box at small and large input power, and TEF on the acoustic side, it becomes apparent that a small port loads the driver well at low level and port noise aside behaves more and more like a sealed box with a leak as the drive power increases. On the other end, most of the SR subs seem tuned to load and protect the driver at full rated power and I think that's PART of the reason why they sound thin at home listening levels. Anyway I experimented with in box port end boundaries to find a best compromise alignment that gives great loading at low level and noise free, meaning un-audible to me, operation at high levels and that I am pleased to say has been achieved to a very high degree. It is one of he things most people note when hearing this system is it's very full and smooth bass at very low levels and level contour correctness through very high listening levels.

One sub is in a front corner and one is front and center, this provides a very homogenous LF field all around the room. That brings us back to the first three rules, location location location.

Remember, you asked for it. :p

[grumpy]

:D Nice post. Holistic room/speaker design... what a concept. Thanks!

[badman]

1 Tuning below the driver Fs gives you a softer curve on the bottom, this was done to match the room gain to obtain flat response without EQ. I brought this up once a year or two ago and was immediately characterized as an ignorant beginner and never brought it up again. Recently Rob "confessed to this sin" and was not ostracized so I will admit it again.


Hopefully those members are not still giving people a hard time. Tuning below Fb is perfectly fine, it keeps group delay to the lowest frequencies where it's inaudible (or nearly so), and does a better job of protecting a driver for home use. One might even skip a rumble filter for movies in this case. My own subs use an overdamped alignment similar to yours but with passive radiators.

[FE3T]

Oh hell no!!!1 Tuning below the driver Fs gives you a softer curve on the bottom, this was done to match the room gain to obtain flat response without EQ. I brought this up once a year or two ago and was immediately characterized as an ignorant beginner and never brought it up again. Recently Rob "confessed to this sin" and was not ostracized so I will admit it again.

I simulated your tuning suggestion, and as expected the curve was pretty similar to the curves i get when i sim Wayne Parham`s use of the 2226H in his Pi 4 speakers, and i have not seen anyone complain about them being tuned below fs ;)

[4313B]

Second choice is a 12cubic ft bass reflex, but group delay is very high... So, what have you successfully done with your 1800 GTi?For home use this high Q, low Bl driver likes a really big box tuned low and the Fb will always be lower than the Fs. That's just how this particular driver plays out. 12 to 20 cubic feet tuned in the 27 to 23 Hz range, give or take a few Hz, and group delay is going to be high, but centered around 20 Hz.

It was designed for automotive competition applications. Smaller boxes tuned higher to give it a ton of power handling and punch.

Compare and contrast with a traditional low Q, high Bl JBL driver such as a 2245H.

[badman]

I simulated your tuning suggestion, and as expected the curve was pretty similar to the curves i get when i sim Wayne Parham`s use of the 2226H in his Pi 4 speakers, and i have not seen anyone complain about them being tuned below fs ;)

Yep :)


Fs and Fsb (Fs with box) are two different things- tuning at Fs means tuning significantly below Fsb, similar to the arrangements we're discussing. 'taint a bad idea, a more "banana" curve vs. a "knee" curve, helps keep box unloading less of an issue and group delay lower in frequency. For a higher Q driver that might like a sealed box, I'd rather live with a little more low-end rolloff and be able to skip the high-pass filter by going sealed.