What woofer for low profile HT sub? - diyAudio
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Old 25th October 2005, 07:42 PM   #1
xcortes is offline xcortes  Mexico
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Default What woofer for low profile HT sub?

I'm designing a system that will be enclosed within a wall. All the speakers will be based on Jordan JX92S drivers. The front wall will have the plasma tv, the three front speakers and ideally one or two passive subwoofers.
The driver characteristics are:

1. Efficient drivers. At least 88dB per watt.
2. That they go as low as possible and they will be crossed over below 80/90 hz.
3. That don't need much space behind them in their enclosure. I don't have any restriction in the other two dimensions and can make then as wide or tall as needed (within reason!) but don't want to make them deeper than 20 cm (external dimensions).
4. I'm willing to pay up to $200/$300 per driver.

Any suggestions?
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Old 25th October 2005, 08:17 PM   #2
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Here is a driver specifically designed for low profile, subwoofer duty. It is the AE Speakers SL10, which uses a patent-pending motor design incorporating Neodymium magnets. John also uses two of these in the Acoustic Elegance in-wall subwoofer. Available in 8 or 4 ohms, this seems to be just what the doctor ordered, except that you are going to need to find them some different power - they are only 83dB sensitive. http://www.aespeakers.com - click on the 'store' link. The woofers are $150 through an introductory period but once that's up, then the price goes to $200.



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Old 25th October 2005, 08:24 PM   #3
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Default More about the woofer

This woofer is not your typical low profile woofer. Most low profile woofers have a flat or slightly inverted cone diaphragm which bends and flexes all over the place, and buckles under the force of the motor's action. But the SL-10 is revolutionary in that it incorporates a smaller-diameter poly cone that transmits its force to the outer edges of a reinforced poly dome. Since the force is applied evenly around the perimeter of the dome, the driver moves as a more perfect piston. And that M-shaped surround is designed to give the most linearity in a slim profile. It's no overstatement to say that the SL-10 is the beefiest 'slim' woofer around because of its design. As to concerns about the mass of the dome/cone assembly, this driver actually has an Mms that is less than that of the AV12 woofer that has been developing quite a good reputation among DIY enthusiasts.
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Old 25th October 2005, 10:47 PM   #4
simon5 is offline simon5  Canada
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Since you want to pay 300$ per driver, so 600$ total, just get 4 SL10s and there you go, nothing will beat those for in-wall operation.
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Old 26th October 2005, 03:43 AM   #5
xcortes is offline xcortes  Mexico
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These drivers look like they can help me. Any idea of how low do they go in the 1 cubic feet enclosure?

About how heavy are they? If I buy them it would be four or maybe even eight! maybe four for the front wall and four for the back wall!

How would these integrate with the Jordans?

thanks
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Old 26th October 2005, 04:10 AM   #6
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Well, I say go for one cubic foot per driver, for a QTC around 0.7. You can run your own simulations with box programs but you won't make it below Qts, which in this case is 0.64. I think you will be impressed with the woofers, because they have a nice low moving mass for the motor structure. Shipping to Mexico might be a bit more but this is what you are looking for, to be sure. Don't just drill holes in the wall and put the driver in, however. Just cut holes and build boxes to fit between the studs, and then patch up the plaster around them. That is what John (proprietor of AE Speakers and developer of the SL-10) suggests. It is possible to build a box that fits within the wall structure and yet is the correct size to fit the SL-10 drivers. It may be a tall box, however. Internally, it should be 2.5" deep, 4.8 feet tall, and 12" wide. That's 6.4cm deep, 146cm tall, and 30.5cm wide. Use bracing along the narrow dimension of the box so that the front and back panels do not vibrate. Finally, you will need a 1.9cm protrusion out of the wall to mount the woofer to so that there will be enough depth to fit the woofer. Then on top of that, you can build a grille frame and cover it with grille cloth.

I just sent John Janowitz an IM alerting him to this thread. He should be able to give you plans for a dual-woofer in-wall subwoofer called the IW-10D. Put one of these on each side of the screen (assuming this is for a home cinema application). The enclosure of the IW-10D is designed to fit within the structure of American walls.
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Old 26th October 2005, 02:22 PM   #7
xcortes is offline xcortes  Mexico
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There's something I'm not getting right. I'm using the T/L parameters on the page on two different box design spreadsheets and in both cases I get a Qtc of 1.0 with a 1 cubic feet box. To get a 0.7 Qtc I need a box larger than 8.5 cu ft.

I will be powering my HT with a seven channel LM3886 gainclone. I will require five channels for the speakers and can use two for the subwoofers. I could use two drivers on each subwoofer connected in parallel to get 4 ohms and 86 dB efficiency. The LM3886s should give me around 60 Watts continuous on 4 ohms so I could go up to 104 dB per subwoofer, 107 dB adding both. Is this enough for HT? (room will be about 5 x 4 meters).

Thanks again
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Old 26th October 2005, 02:43 PM   #8
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You will need to look into excursion and power together to get an idea of whether or not it is sufficient power. Why chip amps?

My experience is that they are more costly than buying budget amps, but ymmv in your country.

50w chip amps sound a bit light for the task.

I'd suggest using a linkwitz transform to get the Qts and F3 desired, then you will have to simulate to see how many you need to get your target SPL and how much power is required to achieve it.

When you ask questions like "how low will it go?" and "how well will they integrate?"

My answer is "it depends." They can go as low as you want with eq, then the question becomes "how much power do I need?" and "how much SPL can I achieve" or "how much displacement do I need to achieve my target SPL" ... the way to find out is with some sims ... I suggest WinISD.

How well it integrates should relate mostly to getting the filters right, making sure that your mains can get down low enough so that your subs don't have to work higher than they are capable of doing with accuracy.

Quote:
The LM3886s should give me around 60 Watts continuous on 4 ohms so I could go up to 104 dB per subwoofer, 107 dB adding both. Is this enough for HT? (room will be about 5 x 4 meters).
1 sub = 104 db
2 subs = 110 ... 3db due to efficiency and 3db due to twice the power

If you can actually achieve this at your listening position down to at least 25 Hz then you should be happy. I have a similar sized room with two sealed AV12 subs driven with 650w each. I can get enough output out of them to measure in room over 110 db. You could probably achieve this with four of those 10" slim drivers if driven with sufficient power.

I think you are probably underestimating the amount of power required to get some clean, dynamic bass. Bass is very dynamic and requires generous power and an amp with some reserve. Chip amps aren't designed to be pushed hard, and I'm not sure they are a good choice for subs. I'd say a better choice would be a pro amp with some brute force power - say 450w or more. The Behringer EP2500 is a good bang for buck amp with 650w/ch into 4 ohms, or a much cheaper amp is the A500 which is VERY cheap. If you go for the bigger amp, you will have fan noise, but if you can put subs in the walls, then you can put the amp in another room.
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Old 28th October 2005, 09:03 PM   #9
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When you order the woofers, send an email asking John (Proprietor of AE Speakers) for plans for the IW-10D subwoofer. He doesn't build the cabinets anymore but they are simple enough that you could build it.
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Old 29th October 2005, 01:35 PM   #10
xcortes is offline xcortes  Mexico
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thanks for your suggestions. looks like the sl10 AND a behringer amp is the way to go.
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