TH-18 Flat to 35hz! (Xoc1's design) - Page 20 - diyAudio
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Old 22nd June 2011, 05:27 AM   #191
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^You're correct I'm not arguing with that at all. And if you can get it for $30 more go for it!
but from what I read in another thread I don't think the B&C driver is really capable of 14mm xmax...that firgure is with 10%thd. I could be wrong this is going off memory, but thats what I got out of it....

Last edited by m R g S r; 22nd June 2011 at 05:31 AM.
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Old 22nd June 2011, 12:24 PM   #192
Xoc1 is offline Xoc1  United Kingdom
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Quote:
Originally Posted by m R g S r View Post
Why didn't we make the brace come all the way out to the front of the mouth? Wouldn't that have helped with the deformation of the front part of the bottom panel?
Extending the brace would help of course but would of probably involved another sheet of material.
The doubling of the bottom panel is an option more than a requirement - The amount and sizes of bracing is always going to be an individual decision.
If a reinforced grille is used then the doubling of the bottom panel is probably not needed, but not everyone will have the resources or funds to source a reinforced steel grille. Without a grille doubling the base will improve things without additional cost.

Djim have you got any particular mesh material and construction in mind for a grille for this project.
Most mesh materials have a very low open percentage ratio, or are very weak.
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Old 22nd June 2011, 02:17 PM   #193
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If I just read it correctly it is a matter of B&C's Xmax (14mm) and Xvar (16mm) specs for this driver. Xmax should be fine while Xvar figures for distortion while still working within the physical limits of the driver?

Quote:
Originally Posted by m R g S r View Post
^You're correct I'm not arguing with that at all. And if you can get it for $30 more go for it!
but from what I read in another thread I don't think the B&C driver is really capable of 14mm xmax...that firgure is with 10%thd. I could be wrong this is going off memory, but thats what I got out of it....
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Old 22nd June 2011, 02:37 PM   #194
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**** I could have made the brace come all the way to the front i had enough wood to do so (because of the way i cut the pieces from the third sheet), i just figured you designed the brace the way you did on purpose! (I guess it was because of wood limitations)
Ohh well, I will on the second one.

Martin, quick question. What was the original target "knee" (frequency in which it starts to roll off) for this box? I mean before all the bracing, corner reflectors etc? All of these which take up volume inside the cabinet reduce the cabinets ability to play lower, correct? I know your original design only included one corner reflector and didn't have any bracing in place.
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Old 22nd June 2011, 03:36 PM   #195
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by Xoc1 View Post
Djim have you got any particular mesh material and construction in mind for a grille for this project. Most mesh materials have a very low open percentage ratio, or are very weak.
I know, so don't use perforated steel. Look in the industry for weaving-wire. It is used in filter technique a lot. Here in the Netherlands we have Averinox in Haarlem.
Click the image to open in full size.



Another option is concrete mesh with small openings (10x10cm). On the ends you iron rings for attachments. It's very cheap and very strong.
Click the image to open in full size.



As a third option, at gardening shops they sell steel plant-holders for wall attachment. It doesn't have the relief on the steel like concrete mesh but it is more expensive.
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Old 22nd June 2011, 06:03 PM   #196
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Quote:
Originally Posted by m R g S r View Post
^You're correct I'm not arguing with that at all. And if you can get it for $30 more go for it!
but from what I read in another thread I don't think the B&C driver is really capable of 14mm xmax...that firgure is with 10%thd. I could be wrong this is going off memory, but thats what I got out of it....
In the Keystone sub, which is similar in size and path length to the Xoc1 TH, the BC18SW124-4 took 77.5 v (1500 watts) of sine wave and worst case distortion was 8% at 45 Hz.

Post # 12 goes into detail.

Keystone Sub Using 18,15,&12 Inch Speakers

Art
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Old 22nd June 2011, 06:33 PM   #197
Djim is offline Djim  Netherlands
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Art, do you have an impedance chart?
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Old 22nd June 2011, 08:49 PM   #198
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Art, do you have an impedance chart?
No.
An impedance plotter is one of those tools I would love to own, but can't quite justify buying, as I only seem to rebuild about every five years.

You can probably figure impedance curves roughly from the excursion readings.

The Crest CA-9s have been happy driving the BC18SW115-4s bridged mono.
IIRC Hornresp showed impedance minima to be about the DC resistance of the driver .
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Old 22nd June 2011, 09:41 PM   #199
Xoc1 is offline Xoc1  United Kingdom
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Quote:
Originally Posted by m R g S r View Post
**** I could have made the brace come all the way to the front i had enough wood to do so (because of the way i cut the pieces from the third sheet), i just figured you designed the brace the way you did on purpose! (I guess it was because of wood limitations)
Ohh well, I will on the second one.

Martin, quick question. What was the original target "knee" (frequency in which it starts to roll off) for this box? I mean before all the bracing, corner reflectors etc? All of these which take up volume inside the cabinet reduce the cabinets ability to play lower, correct? I know your original design only included one corner reflector and didn't have any bracing in place.
I tried extending the bracing to the front today. Although it makes a difference it is not much. To make it work it would need to be a lot heavier than the current brace.
I have tried out a few options and still the best performer for stiffness would be a V shaped bracing to the front of the horn. I will keep on plugging away at it to come up with a decent solution. Hopefully one that pushes the boundaries a bit with TH design! See pics for the way I am thinking about at the moment. Note the scaling factor compared with previous postings. Maybe I can make this work with the tube & threaded studding construction if I design some sturdy brackets??

My original design Posted here
C/E/X PA Flat to 30 (FT30) PA TH Awesomeness
was not really designed to any target values. Instead it is the result of setting out a fold and tweaking. This at least avoids the endless hornresp fantasy sims that will never be folded into a usable box.
Don't forget that the cabinet that you have is probably closer to the actual hornresp data than most TH cabs built before. How often have we seen claimed hornresp sims that are a bigger volume than the actual box.
In past discussions adding reflectors has been a bit of a black art with some claiming they are not necessary. No doubt in this case though they are stiffening the cabinet, which could be handy given the high sound pressure levels that we are going for.
Can't wait to see what results you get - You must be very close now.
Regards
Martin
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Old 23rd June 2011, 12:32 AM   #200
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How well would something like this help the strength of the mouth in sims? I really want to get my hands on that stress analysis software. Made from 1"x1" 1/8" angle iron, shouldn't take very long to tack something like this together!

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