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8" sub cabinet

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odc04r View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 28 February 2017 at 2:04pm
You can implement it with any cabinet, it is just a question of implementing the filter boost to be the inverse of the cabinets natural roll off. In a sealed cab this will be slower roll off than a ported cab below resonance. It is a lot easier to implement in a sealed cab as driver and cabinet combine to give one resonant peak as opposed to 2, and that resonance is what you would tune the filter to.

Rod Elliott offers a project based on for sealed subwoofer equalisation I think, and would probably sell PCBs too as he does for quite a few of his pages. It is just active low pass filter using an op amp with 0db gain in the rest of the passband.

The downside to this technique is that your driver is going to have very large excursion at the lower frequencies. So this is a technique normally used with sealed subwoofers capable of large excursion but that are not intended to be used with a lot of power. So then even at the lowest frequencies the driver can take the excursion. They are also often used with a steep high pass filter set low to make sure nothing too ridiculous gets through.


Edited by odc04r - 28 February 2017 at 2:06pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Padde298 Quote  Post ReplyReply Direct Link To This Post Posted: 01 March 2017 at 7:31am
A few pics of the cabinet for tests..:





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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 01 March 2017 at 11:41am
for Linquitz Transform info, try:

http://sound.whsites.net/linkwitz-transform.htm

This will give you the basic info

Mik
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Padde298 Quote  Post ReplyReply Direct Link To This Post Posted: 01 March 2017 at 11:44am
Thanx...Thumbs Up
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 01 March 2017 at 11:52am
Padde298

PM me if you need further info and I can reply with a phone number as I've done a number of these boxes with reasonable success

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Padde298 Quote  Post ReplyReply Direct Link To This Post Posted: 01 March 2017 at 12:09pm
Dear Mik.
Having read some of the material, I stumble on this section, which maybe makes the use of my drivers less than suitable..:

Guidelines

With the explanation and examples out of the way, you might be wondering what kind of specs to look for when choosing a driver. Here are some guidelines that should help you.

  • Look for a driver with a BIG linear Xmax. The driver should have a one-way Xmax of over 12 mm (0.5").
  • Look for a driver that is 300 mm (12 inches) or bigger. Remember, that producing low frequencies is all about displacing large quantities of air.
  • The driver should have a high power handling capability, in my opinion at least 300 watts RMS. The driver will need a lot of power to hit those low frequencies.
  • The driver should also have a low Fs. It should be the lowest you can find. The reason for this is because you want the transform to use as little gain as possible to reach the lower frequencies. The lower the Fs of your driver, the lower the Fc of the closed box system will be and the lower overall gain the circuit needs to apply.
  • And finally the driver should have a high sensitivity rating, unless you have a really big amp to power it. The higher the efficiency rating of the driver is, the less power it will take to reach those insanely low frequencies. If you have a driver that is 89 dB sensitivity and a driver that is 92 dB sensitivity, the 92 dB driver will require half as much power as the 89 dB unit, for the same sound pressure level.
My drivers are only 8", they can only handle 150 watt, Fs is relatively high: 48 Hz and the sensitivity is 85 dB...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 01 March 2017 at 12:58pm
Generally it is only used for low frequencies and that usually means drivers such as the descriptions you highlight. The key is that you are using a lot of extra excursion headroom to deliver the lower performance so having as much headroom as possible helps.

That is not to say you cannot use it with less than ideal drivers - as long as you understand the limitations of the technique and design properly. For example you find that your final design has closed box resonance of 200Hz, but you want to to extend down to 150Hz as that is the highest you want to crossover to the cabinet below based on listening tests. A Linkwitz transform will allow you to do that, it dies not have to extend to 10Hz. The tradeoff is always amplifier power and excursion for the extended bandwidth. A bass driver might be moving 10mm to get the same SPL at 20Hz than at 1mm for 100Hz, maybe a 200Hz driver is moving 1mm and a 150Hz signal for the same equalised enclosure is 2mm (for a given SPL). As long as that SPL is in your design specification life is good.

Consider it as an option going forward once you have measured the final item and are making your next decisions about where to go.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Padde298 Quote  Post ReplyReply Direct Link To This Post Posted: 01 March 2017 at 2:09pm
It certainly makes good sense to do the equalization that the Linkwitz Transform is doing, especially when aiming for a SMALL box. As for my project, I'm in bit of a doubt as to what I have to reconsider when it comes to the amp. IF using the LT, I would think I had to step my initial choice for amp up a nudge...
Here's the amp in the project so far..:

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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 01 March 2017 at 3:01pm
Yeah maybe, see how it sounds and measures first of all - then consider your options.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 01 March 2017 at 3:09pm
Looking at your 'Speaker specification table earlier in this thread, a suitable power amplifier as in your list will be around 300 Watts, so with the 300 watts rating quoted in the 'speaker specification table, then this will be more than adequate for your proposed use. Various modules providing this are readily available as program signal should be well within this rating.

As in my earlier post, something suitable should be easy to find.

I would suggest that you build one channel to start with so as to try things out first. I'm sure that a modular power amplifier to deliver 300 watts into the 4 ohms load of your loudspeaker which can be fairly easily found with a suitable power supply.

See the PM I will send you shortly for possible Amplifier types,,,,,, so that you are then able to set up one amplifier channel to test things.

Hope this helps!

Mik

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Padde298 Quote  Post ReplyReply Direct Link To This Post Posted: 06 March 2017 at 8:13am
Got the first drawings for the SUB cabinet made this weekend. Getting the MDF cut to measure during the week. Assembly in the coming weekend (maybe... #wifefactor)
Any comments..?





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