Best Sub for approx. 200.00?

[Forte_II]

O.K. I have approx 14cu. ft. and 1200real watts. to work with and need to choose a driver. I want infrasonic performance. I am considering the Daton TIT MKIII 15", the Mach 18.4, 2 Mach MJ18 or tempest 15. What would be a good value? I want the best possible performance within the price range. If there are other drivers you think are better let me know.

[Paul H]

Given a choice between 1 or 2, the common answer on this forum would be 4.

How big is your room and how loud do you listen?

[Forte_II]

Sorry I changed the post on you. My room is approx. 2880cu. ft. Do I include the vol. of the dining and hall area?One corner opens into the dining area and a hallway. The sub will be in a sealed off brick fireplace centered on the wall behind the tv.

[ThomasW]

The Tempest-X is your best bet.

[chasw98]

Tempest

[Forte_II]

Thanks. The Tempest is better than a Mach 18.4?

[ThomasW]

Thanks. The Tempest is better than a Mach 18.4?

At this point in time the Tempest-X is the driver to buy.

[Forte_II]

Thanks, I think you both know what you are talking about so I will give the Tempest a shot. Besides even with shipping it is cheaper than its competitors.
Now since this is a fire place with all its angles and tapers plus chimmy It will be hard to get exact vol. So what is a good way to test tuning? Impedance or Mic at the port? Maybe both...Can someone tell me the best/acurate way to do this? I know not to push the driver until this is done properly.
Since this is a massive brick fireplace and I am useing a 3" baffle is there any need for fiberglass damping?
also based on room size and approx. vol of enclosure what would be a good HT tune for the Tempest X15?
Thanks again.
P.S. this is a great forum.

[mazurek]

You are planning on sealing the fireplace well right? The fireplace is one of the weakest points in my room, I can hear it resonate when I do a frequency sweep. The vibrating things are the chain mail curtain, and the flue valve. I'm assuming yours is better built than mine though.

[Forte_II]

LOL... the flu is gone and there isn't any curtain. The chimmey was capped with concrete and the whole thing is air tight.

[ThomasW]

I would build a wooden box and insert it into the firebox. That way you have a known volume (easier to tune) and you're guaranteed it's air tight

[warnerwh]

You may want to go outside and listen to it. A friend did that and used the chimney for the back wave of the sub. Many complaints from neighbors and one guy who had been in Nam said the first time he heard it he hit the floor(seriously). You may want to block the chimney to outside.

[Forte_II]

It is capped with 4" of concrete and it is a massive brick thing. the bass will travel through the walls first.
It is already set up for a sub. I had a Daton series II 15 in there before. I know it was the wrong app. for the Daton but I had it laying around. the baffle is 3" thick and well sealed. It already has a precision flared port and the cutout. So what is the best way to determine actualport tuning?

[Kevin Haskins]

The best way is to measure it. The impedance graph will give you a good idea or a close-mic measurement of the port shows you where your getting a hump in the response from the port.

If you don't have measurement gear a test-disc with a stepped sine wave for different tracks will allow you to play it and you can watch for when the cone excursion gets real small, that is effectively your port tuning frequency. the port will have lots of output and the driver little. On both sides of that point the cone motion will be noticeably higher. You need the sine wave disc though. Ethan Winer used to have a test track you could download. I'm sure there are other sources on the web. You just need a disc that plays a sine wave stepped in 1 Hz increments. You have to keep track of which track is playing to know what frequency your at and watch the cone dance.

[ThomasW]

So what is the best way to determine actualport tuning?

That's covered in detail in this thread. Sorry but it contains drawings that your reader probably can't translate...

http://www.htguide.com/forum/showthread.php4?t=17794

[Forte_II]

Thanks Kevin and Thomas. I have the test gear...I just need to learn how to use it! LOL
Can't wait to get the correct tuning and hear a real LLT with a real hi excursion sub! All I have heard are cheap subs and one note car subs.

[Forte_II]

Kevin, What tuning freq would you suggest for this setup and your tempest x15 sub?

[Dennis H]

Thomas, you may want to go back and edit your article on measuring impedance. The way you have the diagram wired, measuring the voltage across the series resistor, higher speaker impedance will give a lower voltage across the resistor. You seem to suggest the opposite in the text.

Forte, a sealed box will have a single impedance peak at the tuning frequency and lower impedance above and below there. A ported box will have two impedance peaks above and below the tuning frequency. The tuning frequency is at the minimum between the two peaks.

[Forte_II]

Hi Dennis. Thanks, that makes sense. Now I am unsure of how to wire for testing...I think I put a 20ohm resister inline on the + side. Then measure at the + and - speaker terminals with the DMM. If I understand Thomas the voltage will drop as the impedance goes down. But you are saying the voltage will increase as the impedence drops?
Please clarify.

[ThomasW]

The drawing I used as a visual guide showed wiring different than I described in the text, so I deleted the drawing...

[Dennis H]

Forte, the way you describe it is correct. Thomas's diagram showed measuring across the resistor rather than measuring across the driver. Most of the software packages do measure across the resistor but they do some math to account for bigger voltage equals lower impedance. If you don't care about exact impedance, just want to find the frequency of a maximum or minimum, it's more intuitive to measure across the driver where bigger voltage equals bigger impedance.

[Forte_II]

Got it. thanks.

[Dennis H]

By the way Forte, Kevin's suggestion of looking for the frequency where the cone moves least is a good one for finding the tuning frequency of a ported sub. It doesn't require any test gear or software, just some test tones. I know you can't see the cone but your sense of touch should be better than sight anyway for this job. Just play the tones quiet enough that you won't damage the cone by touching it.

[Forte_II]

I am going to try both... the "touch" method then the impedance method just to see how close I got. Besides I like to play with test gear. I have my son to read things I can't.