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Class D Switching Power Amplifiers and Power D/A conversion

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Old 4th February 2009, 02:52 AM   #261
col is offline col  Australia
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I think you need to rename your version to the NoBassinator

maybe try a P-Audio 8" neo.

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Old 4th February 2009, 03:13 AM   #262
MartinQ is offline MartinQ  Canada
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8NMB420
http://www.eighteensound.com/index.a...roduct&pid=256
Net Weight 1.7 kg (3.7 lb)

8.50NdW
http://www.usspeaker.com/ciare%208.50ndw-1.htm
Net Weight 1.41 kg (3.1 lb)

W8N8-150
http://www.usspeaker.com/faital%20pro%20w8n8150-1.htm
Net Weight 1.7 kg (3.74 lb)

W8N8-200
http://www.usspeaker.com/faital%20pro%20w8n8200-1.htm
Net Weight 1.8 kg (3.96 lb)

8NDL51
http://www.usspeaker.com/B&C-8NDL51-1.htm
Net Weight 1.8 kg (4.0 lb)
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Old 4th February 2009, 04:42 AM   #263
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Martin,

those look like awesome speakers, but they're $130+ each

Col,

I looked at that speaker, but couldn't find it for less than $90 each in the US

Do you really think the bass will be that lousy using 8s instead of 10s?
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Old 4th February 2009, 04:57 AM   #264
col is offline col  Australia
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It depends, pro-audio 8" drivers are usually used for high power midrange, not bass and even then you would still want them in around a 15-25ltr enclosure.

If you use a HiFi 8" driver with a large enough enclosure you might get some bass but it won't be as efficient and not very loud and certainly won't be small enough to be carried with a shoulder strap.

I think if you go back to the first few pages of this thread there is someone with a pair of P-Audio 8" neos in a ghetto blaster (post #21).

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Old 4th February 2009, 01:40 PM   #265
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I have for some time been working on a smaller version, not a mini but a micro. Based on 4 5" pro drivers from Dayton running full range.

http://www.parts-express.com/pe/psho...10&ctab=2#Tabs

The cabinet I'm working on to fit them in is 500x150x150mm using 8mm plywood, and the target weight is under 10kg still using a SLA battery.

The volume for each speaker box is 2.9l when the drivers own volume is included. Qbox would be 1.0 and F-3 would be 160Hz. Naturally this would require electronic compensation to get acceptable output to 100Hz.

A +6dB notch at 120Hz would do the trick, and you could achieve that amplification for free using a neutrik (or other) 1:4 input trafo. This would/should give a -6dB at 90 Hz and a 3dB lift in the 160Hz area like the Boominator and a even sharper roll-off. Off course at the expense of dynamic headroom but alas there's laws of physics at play here that I haven't yet been able to cheat.

It's basically finished on the drawing board but I have not have the time nor the cash lately to actually complete it.
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Old 4th February 2009, 04:42 PM   #266
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Saturnus,


Wow, that sounds really cool! I didn't think about doing it with speakers that small - figured it would be too tiny to make decent sound.

I have the time and money to build something like this. Is this something you would send me the plans for and help me along with? I'd be ecstatic to be your guinea pig for the micro build! However, I understand if you want to complete this project before anyone else does.

Thanks again for all your design help thus far!
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Old 4th February 2009, 07:50 PM   #267
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Just as another data point, my homemade bopombox uses a pair of CSS Fr125S 4" drivers and a pair of Audax mylar tweeters with a simple cap crossover fairly high, just for a little more sparkle. Box is 8" high, 9" deep and 16.5" wide and about 30 lbs w/ a 5AH SLA battery. It's not a bass monster, but it sure fills a room with sound. Amp is an Amp 32 (Tripath 2021B) and I am planning on installing a second amp with a connector for an additional pair of speakers when I want to make more noise. As much as possible, I like a modular approach.

I have a simple adjustable low-pass filter on the input and a coil and cap on the output to tame some of the small-speaker "shoutiness."

On a lead-acid battery, at least, it's possible to just plug in the solar cells in parallel with the battery as a booster when you're outdoors. FYI, there are newer generation solar cells (look at what Brunton offers) that are efficient as well as flexible and lightweight. I have a 6 or 7 watt model that weighs just a few ounces. Having it separate also means you don't have to position the box for maximum solar cell exposure.

--Buckapound
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Old 7th February 2009, 05:40 PM   #268
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Saturnus,

Due to being a new forum member, I cannot message you. I guess my only hope is to bump this thread in hopes that you see it I'm just curious regarding the questions I have above.

Thanks!d
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Old 7th February 2009, 07:51 PM   #269
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Default Boominator Speaker mounting

Saturnus,

Can you explain about mounting the speakers magnet to magnet? If you DON'T do it that way, will they tend to cancel?

Also, should there be some tension on the speakers pushing against each other slightly, or should they simply be touching lightly.

Does the magnet to magnet mounting make the speakers MORE efficient?

I am currently doing a project where right and left speakers share the same air space, and I am wondering if I will lose efficiency.

I'll be using a Tripath 2024 based t amp for the mains, then running a Dual Voice Coil Subwoofer with at Tripath 2020 based chip amp.

Any tips are appreciated!
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Old 8th February 2009, 10:57 AM   #270
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aphelion, I've been reviewing my build, and I'm not completely satisfied. I'll be adding tweeters to the build, and since I am already using the same drivers as the podzuma I might as well just use the same tweeters as it does but just double up on them. I'm also working on an extremely clever solution for the bass compensation. It might take a week or two before I have a ready-to-go build, though.

In effect you and your friend could try this almost for free by just adding another tweeter pair of the same tweeters as in podzuma. So for you it's almost a free build.


p-macaudio, I think I have thoughroughly explained the reasons for the magnet-to-magnet setup but to recap here's the main reasons:

- slightly increased sensitivity. You get around +1dB free on the drivers I use with other drivers it might be less but generally you will see a slightly incresed sensitivity because of the magnets of each driver working as a bucking magnet for the other driver.

- automatic magnetic shielding. Since the magnet of driver works as a bucking magnet for the other magnet, you get the same benefit as a regular bucking magnet which is to severely reduce stray magnetic fields. This will have some influence when used near other electronic devices.

- structural strength. With the drivers connected internally and each driver connected to each front baffle, the drivers themselves work as an extremely effecient brace on the baffles. With a center brace running down the middle and connected to the drivers to support the top/bottom and ends, what you end up with is a structure that by design is extremely rigid. In effect this design is as strong and resistant to vibration as a cabinet made of at least 50% thicker wood.

- bipolar design. By very nature a bipolar design has many advantages in outdoors speakers. First one is baffle step; it's gone, it doesn't exist in bipolar speakers. Second one is automatic bass compensation; try placing a normal speaker outside on a grass field and play something, now as you walk around it you will find that on the opposite side of where the speakers are facing treble and midrange will be lower than directly in front of it, this is because the air works as a gentle acuostic filter of higher frequencies but letting lower frequncies pass. Now in a bipolar design you add the response of the front facing driver with acoustically filter back facing drivers and thereby get a completely free bass boost.

There's tension on the baffles, not on the magnets per say, with you stack two drivers like this it takes consirable force to pry them apart again but I have explained elsewhere in the thread how to build it in detail.

In principle you could use the center brace to divide the cabinet into two seperate chambers, each with it's own reflex port and have a Boominator Mini of half the originals size plus a little for electronics. Just with each side playing the left and right signals instead of the same signal.
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