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Old 27th May 2011, 07:22 PM   #11
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A normal vent will raise the Q. An aperiodic vent can lower the Q. What is the volume of the box?

dave
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Old 27th May 2011, 07:47 PM   #12
IG81 is offline IG81  Canada
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Most of the M7 1218 woofers I measured have an Fs~49Hz and Qts~0.31 (check out their hefty magnet!). Both a low Fs and Qts is the way to get away with a small sealed box. These TB will definitely sound different in there. The normal M7 Qtc is somewhat under 0.707 IIRC. The TB's might give the illusion of more bass if there is a bump in the response, but the original woofers will go deeper and be smoother.

M7 Vb ~1.8 liter IIRC. Makes sense if I sim that with the measured specs I have for 1218. An aperiodic vent will lower the Q, but there will now be no semblance of bass.

IG

Last edited by IG81; 27th May 2011 at 07:51 PM.
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Old 27th May 2011, 07:51 PM   #13
von Ah is offline von Ah  United States
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I was using them daily in my office until I started breaking in 4 EL70s (free-air) in their place a few weeks back. I recall seeing that high-Q when playing with WinISD... But my cabinets are actually the 'Optimus Pro7' which have a port in the back.

The port is ~3/4" diameter and ~2 5/8" deep, which nearly touches the back of the tweeter magnet...

The cabinet is 1.5-2 Liters.

I thought they sounded fantastic and well balanced from ~150 Hz up. While breaking in these EL70s, I've brought back the foobar Electri-Q EQ to dial them in to taste (roughly 3-5 db cut from 400 to 7k). The Minimus 930s were run without any EQ.

Click the image to open in full size.

Note I use a 10" powered sub under my desk in this arrangement. So I haven't really cared about true bass response from these. I plan to return the 930s to the desk after I move ahead on building the Castle EL70 system.

Last edited by von Ah; 27th May 2011 at 08:01 PM.
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Old 27th May 2011, 08:10 PM   #14
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Quote:
Originally Posted by IG81 View Post
M7 Vb ~1.8 liter IIRC.
It wouldn't go as low, but a vented (or sealed) Alpair6M would fit that box (with better mids & top). Vent might need to be external thou if one aims for max bass.

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Old 31st May 2011, 05:32 PM   #15
rongon is offline rongon  United States
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Quote:
Originally Posted by planet10 View Post
A normal vent will raise the Q. An aperiodic vent can lower the Q. What is the colume of the box?

dave
I assume you meant to write 'volume'...

Somebody wrote that the internal dimensions are (in inches) 7 x 4.5 x 4, which equals 126 in3, or about 2 liters. I got that number off the web, so can't vouch for its accuracy.

Would like to know more about aperiodic venting. Is that the one the old Dynaco A25 used, basically a port covered with acoustically absorptive material? Or is that the dual-chambered cabinet design, as in the old Dynaco A40?

With the Tang Band W4-930SF in such a tiny cabinet, I imagine I'm looking for a way to lower the Q from that of a sealed box.

- Ron

Last edited by rongon; 31st May 2011 at 05:46 PM.
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Old 31st May 2011, 06:00 PM   #16
rongon is offline rongon  United States
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Quote:
Originally Posted by IG81 View Post
Most of the M7 1218 woofers I measured have an Fs~49Hz and Qts~0.31 (check out their hefty magnet!). Both a low Fs and Qts is the way to get away with a small sealed box. These TB will definitely sound different in there. The normal M7 Qtc is somewhat under 0.707 IIRC. The TB's might give the illusion of more bass if there is a bump in the response, but the original woofers will go deeper and be smoother.

M7 Vb ~1.8 liter IIRC. Makes sense if I sim that with the measured specs I have for 1218. An aperiodic vent will lower the Q, but there will now be no semblance of bass.

IG
Thanks, I missed your post at first, now I see it...

OK, 1.8 liters sounds more Realistic .

I'm not looking for bass much below 150 to 200 Hz from the M7+TangBand. My hope is to smooth out the low-end roll-off so I can couple these with a pair of woofers using only -6dB filtering without too much problem. I want to experiment with a simple RC x-over network at line level. Perhaps a -6dB hi-pass in the input of my homebrew PP-2A3 amp (6wpc, nice Tango OPTs) and a cathode-follower buffered, -12dB lo-pass to a woofer amp with volume control. I have a 110wpc Hafler MOSFET amp I can use for this, which is more sensitive than my 2A3 amp and has its own input level controls.

High volume and big bass are not as important to me as mid and high frequency purity. That's what I like about the PP-2A3 amp.

Once I've figured this setup out, I figure I might try a final version with Alpair CHR-70 drivers and proper cabinets. This M7-TangBand project is a sort of trial run.

thnx
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Old 31st May 2011, 06:43 PM   #17
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Quote:
Originally Posted by rongon View Post
I assume you meant to write 'volume'...
Yea, when i was going to high school i was not going to need to know how to type, so took grade 11 math instead of Grade 10 typing.

Quote:
Would like to know more about aperiodic venting. Is that the one the old Dynaco A25 used, basically a port covered with acoustically absorptive material?
Yes, fiberglass insulation and rain gutter mesh works well. Or a series of small holes with an appropriate open cel foam covering the holes on the inside. The former is more appropriate for the box we ar etalking about.

Quote:
With the Tang Band W4-930SF in such a tiny cabinet, I imagine I'm looking for a way to lower the Q from that of a sealed box.
You don't want to start with too high a Q, 1.1, to 1.3 is likely a good maximum target.

I think i may try Fountek FR88ex in my spare set of M7 boxes.

dave
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Old 31st May 2011, 07:00 PM   #18
rongon is offline rongon  United States
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Quote:
Originally Posted by planet10 View Post
You don't want to start with too high a Q, 1.1, to 1.3 is likely a good maximum target.
I found this freebie online calculator and plugged in the T/S parameters -- http://www.mh-audio.nl/CBC.asp.

Tang Band W4-930SF specsheet: https://www.madisound.com/store/manuals/w4-930sf.pdf

If I put in a 1.8 liter box, I get

Qtc = 1.135
Fc = 169 Hz
F3 = 127 Hz
it predicts a +2dB peak at 216 Hz.

Re: aperiodic loading -- Have to look up how to stuff the cab and how to calculate size of opening(s). It would be nice if one or two 3/8" or 1/2" round holes could work. I happen to have that size hole saw bit.

-=|=-
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Old 31st May 2011, 07:02 PM   #19
rongon is offline rongon  United States
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and then a little Googling yielded this:
Aperiodic loading to lower qt

!
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Old 1st June 2011, 02:39 AM   #20
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Quote:
Originally Posted by rongon View Post
Thanks, I missed your post at first, now I see it...

OK, 1.8 liters sounds more Realistic .
hahaha REALISTIC....The irony....Just like the ads for 'Mr Muscle'(kitchen cleaner), featuring possibly the skinniest man alive.

I seem to remember the minimus range being sold when i was a child, in Tandy/RadioShack.

Almost ANYTHING should sound better than these did in original form........ I like the Alpair idea though...its a pity those Hivi or aura 3" are probably too small a frame size to fit.
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