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Old 10th February 2009, 04:27 PM   #1
freddi is offline freddi  United States
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Default moderate Qts and OB?

know it s not "full-range" but might apply to some woofer helpers - FWIW I only had a small baffle ~24x36 inches to try a SN15C P-Audio for a quick run - bass was warm and adequate -- if anything it sounded a bit "thick" on some bowed bass viola and appeared to have more clean power than a BK20 which I don't think could play "car bass" tracks- Qts was about normal for bass reflex -- has anyone had the perception of usable bass from low-moderate q drivers with open baffle and no EQ? did anyone here mess with open baffle for 15" P-Audio coax?

SN15C woofer alone o baffle
Click the image to open in full size.

heres what the coax's basket looks like - don't make fun of me for playing with coax - they were $70ea new
Click the image to open in full size.
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Old 10th February 2009, 04:42 PM   #2
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Freddi, you have a museum of Karlsons. I like the coax idea and always think about getting a pair to play with.

I wanted to email you the other day but you don't accept emails...

email me at Godzilla3@hotmail.com

Godzilla
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Old 10th February 2009, 09:19 PM   #3
freddi is offline freddi  United States
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my wardrobe
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Old 11th February 2009, 06:37 AM   #4
CLS is offline CLS  Taiwan
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Hi,

I'm using woofers of Qts=0.3 on OB and very satified with some EQ and most important - T-bass circuit.

'T'-bass drive for OB LF drivers.

Please don't turn down EQ. EQ's are everywhere, be it electrical or acousitcal, or even psychological.... Electrical EQ is not the most evil, and it works. So why not?
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Old 11th February 2009, 12:08 PM   #5
freddi is offline freddi  United States
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hi - - regarding the T-bass circuit - is yours tuned to the driver/baffle fs so the input impedance isn't dragged down low? -- with simple C-L passive underdamped 2nd order highpass filters I've had one amp "ratchet" at very low spl levels due to the low Z load with vented systems and one 21" open baffle,

I'd like to see some input Z graphs for this circuit (or good simulation) - - seems like there would be no free lunch - but - there might almost be if its tuned to drive more voltage right into the Z peak region.

what transformer or autoformer are you using?

here's example of Z - a little K-coupler with aobut 2 cubic foot rear chamber loaded with JBL tuned in high 40's
with 500uF/20mH. Going up to 30mH made it a bit easier to drive but still touchy with a Samson F1200 amp.

No network
Click the image to open in full size.

No free lunch network added
Click the image to open in full size.

and some network effects on a baffle
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Old 11th February 2009, 12:40 PM   #6
freddi is offline freddi  United States
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and one more graph - too bad I don't have input Z for these - some amps can handle low Z loads - others can't
Click the image to open in full size.

if amplifier source impedance is high then it won't work
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Old 12th February 2009, 01:04 AM   #7
CLS is offline CLS  Taiwan
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Quote:
Originally posted by freddi
[B]hi - - regarding the T-bass circuit - is yours tuned to the driver/baffle fs so the input impedance isn't dragged down low? ...

...

No free lunch network added
Click the image to open in full size.

...

This is new to me! Wouldn't that inductor in parallel with woofer eat up much of the low frequencies? So, even though the system impedance is low here, much of the dirving current goes to inductor instead of woofer, doesn't it?


This is the impedance plot of my woofer (Eminence SigmaPro18) on baffle (120cm H x 90cm W):
Click the image to open in full size.

And this is the same woofer on same baffle but with T-bass circuit:
Click the image to open in full size.

T-bass circuit drags down the impedance big time! At some frequcies it approaches 1 Ohm. My tube amps previously used were unhappy with that. Luckily my old Halfer SS amp is doing fine.
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Old 12th February 2009, 03:04 AM   #8
freddi is offline freddi  United States
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-- cap's ireactance is offsetting some of the choke's falling inductance at LF - at some point there resonance - Cool graphs and WoW ! - that T-bass looks tuned nice but that load would likely elicit cracks and clicks from my wimpy Samson (I've got other solid state which might (?) drive it. This brings the question of active EQ vs trying to pull more current. I think the Erse choke I used got pretty saturated - it would pull pliers strong on drum beats and make them jump

what is the voltage and VA rating of your transformer? what are your woofer(s)? - this is fun stuff and I couldn't see well enough to follow that thread
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Old 12th February 2009, 04:21 AM   #9
CLS is offline CLS  Taiwan
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I'm using 400VA toroid transformer and 4.2mH iron core inductor for each channel:

'T'-bass drive for OB LF drivers.
(I changed the caps later, but all irons remain the same... )


The woofer is Eminence Sigma Pro18. And this is the entire OB:

Click the image to open in full size.

Click the image to open in full size.

It's a very simple build and I'll redesign the baffle in the near future....
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Old 12th February 2009, 10:40 AM   #10
freddi is offline freddi  United States
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cool baffles! - whats the size and offsets? what do you intend to change?

my apologies for missing the driver description text above your Z graph - - -

love your midrange size - are there more guitar speakers which are suitable? (10" Buddy are sometimes used). Are there stock drivers which are close to what Bastanis builds?

I've used 18 pretty close to Sigma in Karlson-type and they're durable - not much low bass but high impact and low cone excursion with 200-400W peak

was there much discussion of Graham's circuit price of low impedance tradeoff? ---using an autoformer like that would reflect a lower Z.
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