Need help, designing TH sub with 2x12" drivers.

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Hi!

My good 'ol Paradigm PS1000 need a replacement, it cannot keep up with the lower frequenzies watching movies and music.


I got two barely used Cadence Beastmaster 12" subwoofers, BM122C, dual 2Ohm voicecoils.

Specs:

Z=1
Fs=32.5
Pe=1500
SPL=95.27
Re=0.8
Le=1.63
BL=11.99
Xmax=0.0063
Cms=0
Qms=8.1
Qes=0.37
Qts=0.35
Sd=0.048
Vas=23.9
Type=0

Link to spec: MODEL BM12-2C DVC 2-OHM SUBWOOFER 12 DRAG RACE BEASTMASTER - BEASTMASTER - Cadence Acoustics, LTD


Do anyone want to help me design one or two cabinets for these drivers that can create a stable volume down low,

OR

am I better of selling these drivers to get better suited ones. In that case, what drivers?

Also, I need suggestions on what amplifiers needed to power this subwoofer setup.


I am in the process of replacing my front speakers with horns, looking hard at the Lowther DX2 fullrange drivers, possibly going with a tube amp setup over time.

This sub need to match the new setup.


Due to lack of knowledge, I need to ask for help on this. How small can we make the cabinets and keep the puch down low?


After some reading, my current opinion is that a Folded tapped horn cabinet design should be it?


I hope someone have the time to help me out a little..


Thanks,

John

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Hi again.

Tried out the Hornresp program, entered the info on the drivers. I didn't get the flat spl response other people do on their projects. I'm not able to alter the enclosure data to fix the peaky SPL response when simulating a tapped folded horn.. More reading is required!



I'll come up with the data used when I get home to my computer..

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Hi!

The picture from my previous post was moved. Here it is:



I have been reading a little, tried different stuff in Hornresp to get my drivers to respond differently to simulated enclosures, without too much luck, because my lack of knowledge.

Tonight I tried a known enclosure, I found the The Eminence TH from the Tapped Horns site to see how one of my drivers simulate in that one with my parametres for the driver.




Look what happened! The lower corner dropped to 20Hz! Atleast I got a change in the SPL response..



But there is a 15Db drop from 20Hz to 28Hz, I want a more smooth response than that? What can I do to smooth things out a little?

Is it a good idea to try to fold this horn to save some space(WAF improvement)?

Do I need two drivers? Will I benefit from two when watching movies and listening to music, or is it overkill for a set of Lowther DX2 loaded horns?

If I want to decrease the size, where is a good place to start, I want to keep the low corner close to 20Hz. The upper corner doesn't have to be more than 70Hz if I get the good fullrange Horn fronts I want.

[littlemike]

You're still not simulating a tapped horn, but you're close.

See the Nd on your input screen? That box should say TH for a tapped horn simulation.

Here's a little writeup I did:

Tapped Horn Tutorial

It is by no means complete, but it will get you started.

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Originally Posted by littlemike

You're still not simulating a tapped horn, but you're close.

See the Nd on your input screen? That box should say TH for a tapped horn simulation.

Here's a little writeup I did:

Tapped Horn Tutorial

It is by no means complete, but it will get you started.

Thanks for the tip! I'm onto it, but need more time.. Trying different stuff to get rid of the major drop at 30Hz.. Not very successful at the moment..

Amplifier:
I have been a little worried about powering these babies inside a house.. But any conserns about power just went out the window! The price is good too!

Someone gave me the link to this amplifier, THE T.AMP PROLINE 3000, 2x 1500W @ 4 Ohms, 2x 1100W @ 8 Ohms, 2x 1800W @ 2 Ohms.. Weight 37kgs.

If I decide to run only one of the two Beastmasters, it can run 1800W into each coil @ 2ohms. Better WAF with only one driver..

My first concern is sound quality on a PA amp like this? Anyone with experience? Will the sound quality be good enough for a subwoofer setup?

Will it fit a setup with the Lowther DX2's and Acousta 116 cabinet like my plan is to do before summer?

I don't want rumbling ugly loud bass at all times. Accurate and precise bass into the ground is the target, but want the overall SPL response to be somewhat linear.

Any advice appreciated..

John

[brsanko]

Try this on for size!

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Thanks!

Hmm.. I live in a concrete house with 8" reinforced walls.. Was not planning on reinforce it further!

Is it possible to tune this thing lower? I can see it drop from 30Hz down, where the fun begin when watching movies!

Or will a lower window make that much bigger of a box and kill any WAF, if there is any from the start?

Thanks for your help.

John

[littlemike]

These woofers should be able to play a bit lower - one of the rules of thumb with a tapped horn is that you can design them for response that is lower than the drivers Fs. With the right drivers, you can get response to 1/2 the Fs.

Unfortunately, these aren't really the right drivers in that regard. With this particular driver in a simple conic taper, once you lengthen the horn to get to 20 Hz, the passband response starts to get a bit too lumpy unless S2 is set rather small (high compression ratio).

Hoffman's Iron Law applies though - as the response gets lower, cabinets get bigger or efficiency drops. No free lunches here

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Originally Posted by littlemike

These woofers should be able to play a bit lower - one of the rules of thumb with a tapped horn is that you can design them for response that is lower than the drivers Fs. With the right drivers, you can get response to 1/2 the Fs.

Unfortunately, these aren't really the right drivers in that regard. With this particular driver in a simple conic taper, once you lengthen the horn to get to 20 Hz, the passband response starts to get a bit too lumpy unless S2 is set rather small (high compression ratio).

Hoffman's Iron Law applies though - as the response gets lower, cabinets get bigger or efficiency drops. No free lunches here

Hmm.. To keep things smaller, I'm considering only one driver, keeping the other as a spare if something bad happens.

What is the "best" cabinet size and lengths from your point of view?

How much can be done with stuffing?

Can I expect some kind of quality bass from it? These drivers are incredibly hard or got a stiff suspension compared to other drivers I've played with. But they sound very accurate. Mabye a sealed box is better?

1001 questions, but it's easier to modify the design now than later.

Thnxx

[littlemike]

In all honesty, with respect to tapped horns, though I am a ways down the path, I do not feel that I am not that far off the vertical part of the learning curve. As I figure out some things, I learn of dozens more that I need to learn about.

They are not a bad driver, they are just not a truly optimal driver for use in a tapped horn (honestly - I think the truly optimal tapped horn drivers could be counted on one hand....). It is my understanding that that series is designed for car SPL competition, so they probably like small sealed or ported cabinets, tuned relatively high to take advantage of cabin gain. A 25 Hz. tapped horn for this driver is actually a fairly small cabinet, you'll probably have a hard time fitting the driver into it. It appears that 25 Hz is within reach without getting too esoteric. Keep S2 to no less than Sd/4 and you should be OK. Make L12 as short as possible (1/2 the driver diameter) to keep the impulse response accurate. Adjust things slightly to get the phase right, and you're set for sawdust.

Don't worry too much about the ripples in the modeled passband response if they are less than 3 dB. My experience has indicated that they will be there, but 3 dB is not that big a deal. Room issues will likely be much bigger. As it is a horn, stuffing is a bad idea. Batting stapled to the walls has been shown to help, but it is truly a try it and see approach as each build is different. I'd suggest that you concentrate on the throat and the area near the driver on the mouth side first.

Though they can be simply described, these actually are pretty complicated cabinets. Bracing is a must. Good cabinet material is a must. Accurate layout and construction is a must. Cutting corners and using cheap materials will lead to problems. Long designs (single-fold) may experience cancellation issues. Additionally, more folds attenuate the high frequencies, within reason.

The box I just built as a test (though fairly well-braced) had visible resonances in the access panel with only 10 watts applied. Admittedly, I used cheap 1/2" plywood and 1/2" MDF, it was never designed as anything other than a proof of concept so that I could get some more measurements and try a few more things out.

Imagine what a kilowatt would do to a cabinet like this. There is a reason Danley uses 3/4" birch plywood.

Tapped horns can be accurate, and can be musical, you just have to design and build them right. It is all in the design and implementation, the devil truly is in the details.

Mr. Danley said something like this first, but I can't repeat it enough:

Measure what you plan to model (measure the actual Thiele-Small parameters for your drivers)
Model what you've measured (get the data into Hornresp accurately)
Build what you've modeled (translate the areas and taper rates into an enclosure accurately)
and you'll actually measure pretty close to what you predicted.

If not - it is not the model's fault.

The only time I did not get reasonably close to the predicted result was due to a building error on my part.