BillFitzmaurice.info

Hi Folks,

Im mid-build of a pair of 20" T39's with a 3012LF in each, and im looking at amp options.

the 3012's are 8 ohm, but i'm sure i read somewhere on the forums that in a horn loaded enclosure, the effective impedance is reduced. anyone know how much by? I will not always run them as a pair - sometimes just one will be enough, so my amp option needs to be flexible.

I'm going to use Hypex UcD class-d modules to run the pair. if i were buying bits from scratch, i'd just go a single UcD-700 and run the pair in parallel. *but*, i already have a UcD 400 module sitting here. so the cheap option would be to get another one, and run them bridged, with the T39's in parallel. or i could run one module per sub. then if i'm just using one sub, i can just use a single UcD400 channel. I could always sell the UcD400 and buy the 700 tho.

I'm also wondering how much power a 20" 3012LF T39 can take. Ive also read somewhere that the T39 design is the limiting factor, not the 3012LF. is that the case?

too many options!!!

anyone got anything to say that might help me make the decision?

cheers,

ben

but i'm sure i read somewhere on the forums that in a horn loaded enclosure, the effective impedance is reduced.

Where did you read this?
Consider the air between the front of the woofer ( at the throat ) and the mouth adds impedance.
If you want to err of the side of conservancy, uses the nominal impedance rating

anomalous wrote:i'm sure i read somewhere on the forums that in a horn loaded enclosure, the effective impedance is reduced. anyone know how much by?

Horn loading adds to the driver impedance. How much ?
:iitp:

I'm also wondering how much power a 20" 3012LF T39 can take. Ive also read somewhere that the T39 design is the limiting factor, not the 3012LF. is that the case?

:iitp: :iitp: :iitp: :iitp: :iitp:

Bill Fitzmaurice wrote:

anomalous wrote:i'm sure i read somewhere on the forums that in a horn loaded enclosure, the effective impedance is reduced. anyone know how much by?

Horn loading adds to the driver impedance. How much ?
:iitp:

ah ok my mistake. increase, not decrease. like i said, had a vague memory of reading it somewhere... hence the question

Bill Fitzmaurice wrote:I'm also wondering how much power a 20" 3012LF T39 can take. Ive also read somewhere that the T39 design is the limiting factor, not the 3012LF. is that the case?
:iitp: :iitp: :iitp: :iitp: :iitp:

mmm. ok. Indian Institute of Technology Patna. no. International Information Technology Professional. mmm. no. Internet Investigations Training Program. nope.

right. at any rate, none of these was the straight up one word answer I was after, but I'm getting the distinct impression that perhaps the information i'm looking for ought to be somewhere obvious. I'll keep looking.

It's In The Plans!!!!!!!!!!

tammojsmit wrote:It's In The Plans!!!!!!!!!!

AHA! thanks.

that said, I looked in the plans, and on the last page is "even if your driver is rated at 1000W, power compression prevents anything over 500W from adding any additional output anyway..."

I did see this, but wasnt sure if this 'power compression' was a factor of the driver or the box, and if the box, presumably it would vary with box width. thinking about it, it couldnt be the driver. but that still leaves the question of how the t39 width affects it.

and I just found the "impedance" section , so guilty as charged there.

Ben

Power compression is a factor of the driver. Adding power does not linearly increase volume output. It takes 10 times the power to double the output of a driver. 1W to 10W doubles volume, 10W to 100W doubles volume, but the next step is 100W to 1000W(!) which drivers simply can't handle. Above a certain level, power starts turning into heat instead of volume, and when you reach 500W, you are getting so little extra output that it's negligible. The phenomenon happens gradually, which is why there is a school of thought to limit RMS input to half of rated power, leaving plenty of headroom. More volume requires more boxes (which is part of why line arrays work so darn well, among other more complex factors).

This applies to all speakers, too, by the way. It's why you can drive the snot out of a box and only get more distortion, without more volume.

Hope this helps!

High pass T39 at 46 Hz, 24dB/octave or steeper.
Apply 450w maximum, have 225w at 42 Hz which is critical excursion frequency.