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Old 13th August 2003, 07:52 PM   #1
octopus is offline octopus  England
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Default Subwoofer in a floorstander

I'm addicted to DIY AUDIO, now I want to add subwoofers to my speakers. (Currently they are a 2-way floorstander with a 3000Hz xover, which were commercial Eltax cabinets. I am modifying them)

The woofer of choice is a Vifa C20WJ-19-08
[8ohm,Fs:36Hz,91dB,20cm dia]


I want to add them to a sub-cavity in the floorstanders (20litre), will add bracing and it will be sealed.

I've done most of the math, 15mH inductor, crossover at 80Hz, downfiring, and, sag 2.4% of xmax.

Problems:

Should I go for a series alternative, this would help the low 3.6ohm DC impedance I got? Could I just add it onto the end of the current mid-woofer with an inductor before it? If so, could I take away the series inductors in this ciruit (and midwoofers') from the 15mH 1st order?

I cannot find any info on how high off the floor a downfire sub should be, any suggestions?


This is the present xover...
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File Type: gif xoover.gif (14.5 KB, 432 views)
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Old 13th August 2003, 09:19 PM   #2
SimontY is offline SimontY  United Kingdom
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Adding bass drivers to two-way speakers like this is something I've often tossed around in my thoughts, so I'd love to know what comes of it.

Sorry I can't help with the x-over, I'm no expert here.

The distance from the bass driver to floor probably wants to be at least 7 or 8cm, going by my downward firing sub and similar things. But I guess this depends how much gain you want, from the room. Also, if you are crossing over at 80hz, isn't there a danger the midbass might sound muddied and 'detached' in this position?

How did that zobel filter affect the sonics? I think there may be one in mine, but I'm too ignorant/stipid to know!

Like the site btw
Good luck with the upgrades!


-Simon
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Old 13th August 2003, 09:23 PM   #3
SY is offline SY  United States
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80 Hz xover? Biamp. Watts are cheap.
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Old 13th August 2003, 10:16 PM   #4
octopus is offline octopus  England
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Quote:
80 Hz xover? Biamp. Watts are cheap.
Well I wouldn't find a power amp for 75, ditto a compact sub.

Quote:
Adding bass drivers to two-way speakers like this is something I've often tossed around in my thoughts, so I'd love to know what comes of it.
Sorry I can't help with the x-over, I'm no expert here.
The distance from the bass driver to floor probably wants to be at least 7 or 8cm, going by my downward firing sub and similar things. But I guess this depends how much gain you want, from the room. Also, if you are crossing over at 80hz, isn't there a danger the midbass might sound muddied and 'detached' in this position?
How did that zobel filter affect the sonics? I think there may be one in mine, but I'm too ignorant/stipid to know!
The zobel made a significant improvement, better midrange punch. But the tweeter/crossover upgrade was better than I expected!

I guess 80Hz, could be lowered, perhaps to as low as 50 or even 40Hz.

What I am trying to create is a boost to the low end rolloff, so the two drivers combine, but impedance could be a drawback in parallel..
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Old 13th August 2003, 10:43 PM   #5
SY is offline SY  United States
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Big, low DCR inductors aren't cheap. Neither are big banks of quality capacitors. You can put together a chip amp and chip-based electronic XO/EQ easily for the price of the passives- or you can be a cheapskate like me and find used gear (I just paid $100US for an old Crown DC150, which will work perfectly well for a bass channel).
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Old 13th August 2003, 11:37 PM   #6
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Quote:
Adding bass drivers to two-way speakers like this is something I've often tossed around in my thoughts, so I'd love to know what comes of it.
I've done it before..at times the performance was stunning! Remember listening to a Hendrix song ...and just heard tremendous bass lines engulfing the room...

Was a slim tower. With an infinite baffle 17l for an butchered Wharfdale 505.2 woofer with a Focal tc90tdx on top of the box...
And below the Wharfdale woofer a bandpass subwoofer based on a the SEAS triplet subwoofer.(8" CA21RE4X/DC )..But now a subwoofer for each speaker.

Was fun and weight 60kilo's per side made of 28mm MDF...

But they had a horribly low WAF factor so they had to go.

Cheers,
Bas
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Old 14th August 2003, 08:14 AM   #7
octopus is offline octopus  England
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Quote:
Originally posted by SY
Big, low DCR inductors aren't cheap. Neither are big banks of quality capacitors. You can put together a chip amp and chip-based electronic XO/EQ easily for the price of the passives- or you can be a cheapskate like me and find used gear (I just paid $100US for an old Crown DC150, which will work perfectly well for a bass channel).
I know that the coils are going to be most expensive, but they are still cheaper - if I go with iron core - than a separate amplifier. And not forgetting I'd need two, so its out of the question.

I was hoping to go for a 1st order, a 25-30mH coil perhaps for 40-50Hz 6dB rolloff.

As I said I need info on the idea of a series network, as the impedance is very low.
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Old 14th August 2003, 10:36 AM   #8
SimontY is offline SimontY  United Kingdom
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Why do you need to run it in series? With a big inductor, won't that be adding enough resistance to make it ~4ohms anyway? 4ohms is good for bass, and as you have a largeish Nad amp, why should it matter?

I know this is more complex, but would the ideal solution not be to make your speakers 2.5 way, crossing over at ~150hz, as per B&W DM603 (s2/3) and Monitor Audio GR20. This would free up the mid-bass driver and maybe make the mids cleaner, with more maximum output/less distortion. Plus I think you wouldn't need such a large inductor.

Of course, x-ing over here, you'd want the lower bass driver not too far below the original one, or it might sound crap.

Hmm, just thought, maybe the driver you have in mind won't fit on your front baffle... so many complications! baffled...


-Simon
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Old 14th August 2003, 01:13 PM   #9
octopus is offline octopus  England
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Fortunately I am putting them on the bottom side of the speaker, not the front , and they are 26x30cm (WidexDeep) with 2.5cm walls, so I think they will fit.

Impedance is a bit of a worry, I don't want my amp overheating at relatively high volume and shutting down.

The 2.5way idea seems good, and I may consider it. At the moment the woofers stay distort free to 70% volume. But adding a cap doesn't sound cost effective, I'd need at least 500uF...

There's still plenty of time to work on this...and save up!
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