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Old 12th June 2010, 10:33 AM   #11
Arnulf is offline Arnulf  Europe
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I found some time to rig things up for a practical test. Armed with Rod Eliott's article on the subject I have calculated parameters except for Vas (I don't own precise enough a kitchen scale).

Results are:

Qms = 1.98
Qes = 0.83
Qts = 0.59

Now these results are interdependent, if one is wrong, they are all wrong. I hope I got everything right, I used the spreadsheet provided by Rod for error-free calculation

Do these figures bring me any closer to determining most suitable box volume or am I still stuck without Vas parameter ?
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Old 12th June 2010, 03:36 PM   #12
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You can get Vas using a small test box. I always keep a 1ft^3 box around just for that purpose. Heck, I'm still using the equations from the old Weems book, plus the classic issue of Speaker Builder magazine that had the first decent T/S article, but the numbers work fine. I have a DOS program I've never bothered to convert to Windows that leads one through the measurement process. PM me if you want a copy.

Conrad
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Old 12th June 2010, 04:57 PM   #13
GM is offline GM  United States
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Quote:
Originally Posted by Arnulf View Post
Now these results are interdependent, if one is wrong, they are all wrong.

Do these figures bring me any closer to determining most suitable box volume or am I still stuck without Vas parameter ?
Correct.

What is the measured Fs?

Well, going back to my 5.5 ft^3 minimum cab net Vb, with this Qts it only needs a ~1.5687 ft^3 Vas to fill it up in a maximally flat alignment assuming a 35 Hz Fs, ergo if it's a higher Vas, then it will need to be larger for the same F3/Fb. Anyway, this calculated Vas is well within the range for vintage 8" drivers, so absent any more, accurate, specs I stick by my recommendation.

GM
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Old 9th November 2010, 11:36 PM   #14
Arnulf is offline Arnulf  Europe
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Hi guys,

Thank you for your replies ! I haven't paid attention to this thrad for a while now since the focus of my project has shifted - these drivers will find a new life as guitar amplifier speakers which I think they are perfectly suited for (they will sound nice at 80+ Hz and well into KHz range, guitar won't go ver far from there), quite the opposite of what I had in mind earlier on (mid-fi replay duty).

I realize this is hardly a subwoofer subject anymore but I figured you might be interested in the follow-up - as I see it I owe you that much at least, so here it goes:

Since I'm after 8R load impedance I'll be using two of these drivers (4R apiece) in series (and in phase). My plan is to use 30 liters per driver (60 liters total) sealed enclosure for two of these; set side by side it should result in a rougly 30x40x50 cm box (HxDxW), built from 19 mm MDF board material. Yes, I realize inside volume would be lower thann my target with above measurements so I plan to enlarge each side accordingly to get me somewhere in the vicinity of 60 liters.

My only concerns left are:

1: Shiould I split the box in half with a wall n the middle (isolating each driver from the other) ?

2: How to attach the backside of the speaker ? Glueing it in place would provide the best attachment but if I screwed something up I'd have to break the box down and I'm not very fond of this idea. OTOH if I merely screw the backside on there I am going to lose compression, so my sealed box is not going to be sealed anymore

Any pointers greatly welcome !
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Old 10th November 2010, 05:16 PM   #15
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If you use plenty of screws and some sticky foam strips, you can screw it together while you play with enclosure volume. That said, a ~7" hole would likely be enough to make some ammendments (if you were to glue it). I'd also suggest playing with stuffing/lining the enclosure. This would help to prevent internal reflections.

Chris
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