Discussion about LT versus Vented subwoofer designs...

[simon5]

Hi, I want to know your opinion about this.

I modeled the Adire Audio Tumult, a very high excursion subwoofer in three configurations, Sealed, Vented and LTransformed.

I used a 5.032 cu.ft enclosure (142.5 liters) tuned/transformed to 18.34 Hz with Q=0.707, sealed it gives a Qtc of 0.539 with Fc of 29.18 Hz.

In this simulation, I used the maximum power the Tumult could get continuously over 20 Hz if maximum excursion was not reached (1600W for vented, 1520W for sealed and 300W for LT).

Do you think the 7 dB of efficiency/headroom lost over the whole subwoofer range is worth it to get the low group delay advantage?

My opinion on this is even the group delay is obviously better (11.2 ms at 20 Hz LTransformed versus 27.5 ms at 20 Hz vented), I think it will not be audible much and the significant loss of efficiency/headroom is too important to offset this. You will need two subwoofers with LT to have the same output as one vented. It cost more to do LT subwoofers so the price will be more than two times the cost of one vented to achieve the same output.

What do you think?

I included the sealed enclosure as a reference. The group delay is even lower, the midbass is louder and the deep bass is the same as the LT enclosure.

I include here the graphs (Excursion with the box tab clicked) :

[simon5]

Here's the group delay graph with the filter tab clicked :

[simon5]

Here's the SPL graph with the signal tab clicked :

[richie00boy]

Good idea. The group delay on the transformed design is bound to be worse (neglecting where in the band the delay is for a minute) because the Q you are transforming to is much higher than the plain sealed box. I think a better comparison would be to transform to the same Q, or use a smaller box to get the natural Q up to 0.707.

You can also get more SPL out of a LTd speaker than the simulations suggest, if the music content is not bass heavy. You get the advantage of low group delay and phase change and great transient response by transforming down low with low Q. The reason you can get good SPL with lighter music is that the simulations are relative and keep within the headroom for the lowest frequency signals, thus if these signals are not present or low in amplitude naturally, their operating point can be shifted up with a consequent upshift in the midbass.

Using the specific designs you have presented I think you are right -- the vented design is the best to go for. However, the point of an LT is to obtain fantastic performance from a small box. This is likely to come with a cost impact and so you must trade your design to get the balance that is right for you. I simply do not want a 5 cu ft monster in my living room. I'd be happy with 2x 1.5 cu ft subs that cost twice as much.

[simon5]

You are right about the sealed versus LT part, but I want to discuss here about LT versus Vented. I used a Vented curve designed to match room gain well, then used a LT in a sealed box to achieve the same response in a box of the same size.

I would like to have your opinion on this, would you take 7 dB of headroom/efficiency over 16.3 ms of group delay advantage at 20 Hz?

[richie00boy]

See above, I was editing my post whilst you submitted your reply.

[simon5]

Originally posted by richie00boy
You can also get more SPL out of a LTd speaker than the simulations suggest, if the music content is not bass heavy. You get the advantage of low group delay and phase change and great transient response by transforming down low with low Q. The reason you can get good SPL with lighter music is that the simulations are relative and keep within the headroom for the lowest frequency signals, thus if these signals are not present or low in amplitude naturally, their operating point can be shifted up with a consequent upshift in the midbass.

Using the specific designs you have presented I think you are right -- the vented design is the best to go for. However, the point of an LT is to obtain fantastic performance from a small box. This is likely to come with a cost impact and so you must trade your design to get the balance that is right for you. I simply do not want a 5 cu ft monster in my living room. I'd be happy with 2x 1.5 cu ft subs that cost twice as much.

You could also get more SPL out of a Vented speaker using the same principle you used in the first part of this quote.

Now, I understand you don't want a 5 cu.ft monster hehe!
The point is, you would need TWO! to achieve the same output.

Thanks for your imput.