EQed array of midwoofers for sub - diyAudio
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Old 30th April 2010, 08:58 AM   #1
tresch is offline tresch  United States
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Default EQed array of midwoofers for sub

Aaaahahahaha

Okay! So, this is me being goofy.

I like being goofy and thinking of odd things. I also like striking visual designs that are (potentially) also functional.

I built a set of home theater speakers for a friend recently. They're a set of sealed-box MTMs with MarkAudio Alpair5s running in a woofer/midtweet configuration. The MTM mains and center are all actual speakers which I actually built, and actually sound good.

Beyond that the goofyness begins.

He still needs a sub. Those MTMs actually put out a fairly serious amount of bass when you get right down to it, but they don't quite have the Xmax to handle much in the way of EQing and still get proper dynamic range.

I've been thinking of various things to do for him for subwoofers, and recently I've been reading about the whole column speaker thing, and line arrays in general, which lead me think... what about, instead of using big arrays of full rangers to get bass, use big arrays of woofers to get SUB bass?

The nice thing about the DA175 woofers is that, for the price, their harmonic distortion at the low end is pretty clean. at $25 they're pretty cheap. I calculated that 6 of them is about 30% more surface area than a 15" subwoofer, and runs about the same price. Granted, a subwoofer at that price ought to have significantly more xmax and thus more output potential, but we're being silly here, okay?

Think of the efficiency! Well, the midwoofers are actually a lot less sensitive in the first place than a big sub (85 vs. 91) so in this configuration they might only be slightly more efficient.

And I have no idea what the distortion properties would be like.

BUT C'MON. IT LOOKS CRAZY! Look at all the shiny silver cones! Also, instead of crossing them over to the mains, the system could be set up where they just add to the mains, which play full range, and thus have 8 WOOFERS PER SIDE cranking out bass!

In fact, if you positioned them really close to the mains, like in this picture, you could cross them to the mains pretty high and just have really efficient, ultra low distortion bass up to like 300hz.

Now that I'm getting into the EQing thing, if I were to do something like this again, with these same drivers (which work REALLY well together, btw), and a bigger budget... I'd just make them MTMMM or MMTMMMM

aaahahhaha it's late, okay? Face it though. YOU LOVE THIS IDEA
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Old 30th April 2010, 11:06 AM   #2
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but driver to driver distances are aproaching the wave legnth of the sound at midrange frequancies so your sub will cause peaks and nulls in the midrange frequancy response when it adds to the mains. Due to the waveform been out of and in phase dependent on distance from the two speakers. This isn't an issue for wavelegnths are so long they can't add out of phase. So you can't run your sub at midrange frequancies. Apart from that it seems interesting and visualy striking, by running many drivers you should reduce distortion, however the best position for the subs may not be right next to the mains so traditional cube subs may offer more placment opertunities.
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Old 30th April 2010, 12:07 PM   #3
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Can't help but to post this.
HiFiForum.nu - Spelglädje med 10W ?
Half of them are PR in this setup though.
You'll have to translate with Google if you want to know more.

You also have the benefit of minimized floor to ceiling mode when using vertically tall subs.
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Old 30th April 2010, 05:37 PM   #4
tresch is offline tresch  United States
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Quote:
Originally Posted by kipman725 View Post
but driver to driver distances are aproaching the wave legnth of the sound at midrange frequancies so your sub will cause peaks and nulls in the midrange frequancy response when it adds to the mains. Due to the waveform been out of and in phase dependent on distance from the two speakers. This isn't an issue for wavelegnths are so long they can't add out of phase. So you can't run your sub at midrange frequancies. Apart from that it seems interesting and visualy striking, by running many drivers you should reduce distortion, however the best position for the subs may not be right next to the mains so traditional cube subs may offer more placment opertunities.
Of course this would have to be taken into consideration when choosing the "crossover" point!

Also: Upped to a proper 8-driver line!
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Old 30th April 2010, 05:46 PM   #5
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Fun project, only thing that could be a problem really is that you may need massive levels of gain to get the response down low.
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Old 30th April 2010, 06:08 PM   #6
tresch is offline tresch  United States
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Originally Posted by richie00boy View Post
Fun project, only thing that could be a problem really is that you may need massive levels of gain to get the response down low.
Yup! "Linkwitz Transform" is the idea. 12db/octave of gain to "undo" the falloff of the sealed box.

However, these speakers play pretty low, naturally. In this box, SEALED, their F3 is at 63hz!

ultra-quick measurements in winISD show that a single stack of 8 of these could hit 93db at 20hz (limited by xmax)

16 of them firing together would be managing about 99db@20hz, and 93db@15hz!

That's all simulated anechoic, of course. "Room gain" would help boost things up a bit, too. In this case, it's in a basement home-theater, and it's not that huge, so this would be significant.

Granted, you could definitely get more output for the price with big subwoofer drivers, but there are other advantages so this. I calculated that a single 8-way stack would be running an efficiency of 94db and 4ohms. Or, if you just want to use a single channel of amp or prefer 8ohm loads, wire the two stacks in series and you're at 97db efficiency! We're talking upwards of ONE TENTH the power requirements of a lot of subwoofers!

Have a 7.1 receiver and only a 5.1 speaker system? That extra channel or two on the amplifier could run this to fairly insane levels with ease!
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Old 30th April 2010, 08:29 PM   #7
tresch is offline tresch  United States
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100 watts would run this at 95db flat to 20hz, or 102db flat to 30hz with normal falloff after that (just running through some numbers for fun)
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Old 1st May 2010, 04:18 AM   #8
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If you wanted to try it without a lot of financial risk, do a stack of 6 of these buyout drivers - you would be at just under $50 for each stack !
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Old 1st May 2010, 06:34 PM   #9
tresch is offline tresch  United States
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Whoah, that's cheap!

And actually has almost identical Qts and Vas measurements to the DA175, though slightly higher FS. Thanks for the find!
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Old 2nd May 2010, 02:47 PM   #10
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with drivers that cheap seems like a good idea, how about a super high output version with lines on all sides of the box :O
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