Horn/TL enclosure for 2 8 inch woofers - diyAudio
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Old 21st October 2013, 07:30 PM   #1
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Default Horn/TL enclosure for 2 8 inch woofers

I am trying to calculate a box for 2 8 inch woofers for my car. It is a smart fortwo, so not a lot of room in the back. The largest measurements i can fit are 30x35x95cm. And I converted these to inches for some of you: 11,8x13,8x37,4 inches
The woofers I am planning to use are these: http://www.hifimotive.nl/files/produ...da0b65a70c.pdf
Maybe an unknown brand for the most of you, but they sound great in a ported enclosure! I once built a tapped horn for a 12 inch woofer and a transmission line for a 6 inch and they sound really good. That is why I want to build something like this for in my car.
I am starting to learn hornresp quite a bit. But I cant get a good frequency response in a horn. Maybe one of you can?
Sensitivity and max spl levels are not very important for me. I am trying to get the best sound quality and to make them play as low as possible.
The transmission line I built was not really calculated. It was just a line from 1,5x sd to 1x sd with a length of 300/4/fs (in meters).
I was hoping that one of you can calculate something for me
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Old 21st October 2013, 09:53 PM   #2
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Well, without doing any sims, it appears the cab is big enough, but from just looking at a picture of the car it seems like cabin gain would be very high, so considering the driver's specs it seems like a well damped sealed cab of your max dimensions would be best overall for high SQ, extension.

Heavily stuffed with acoustic fiberglass insulation, you can in theory get down to almost a transient perfect 0.5 Qtc, which with cabin gain would give you the most extension, SQ if the published specs are fairly accurate.

GM
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Old 21st October 2013, 10:01 PM   #3
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VAS is a little bit small so you might have to mount the drivers in a chamber that fires into the line.

Click the image to open in full size.

mike
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File Type: png SQ8Dual.png (117.6 KB, 584 views)
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Old 22nd October 2013, 09:41 AM   #4
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Looks nice! And I could fit a box this size I think!
But this is a offset driver in Hornresp I see. When I looked at the schematic diagram I noticed it looks something like a tapered TL with drivers at 1/3 of the length. Or am I totally wrong?
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Old 25th October 2013, 10:23 PM   #5
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That is correct.

mike
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Old 9th December 2013, 08:19 PM   #6
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I made a few adjustments to mashaffers simulation so it will fit in my car and it is amazing! I expected a lot but this is even better. I didn't test it in a car yet, only in a listening room of a local car audio shop.

The owner of the shop asked me to calculate something for his car. I am trying to calculate a TL and it is done. But I have 1 question.. It needs to be as small as possible, 1,25cu ft will work well for a 10 inch woofer according to simulation. But the end of the TL needs to be a bit different so it will play through the 'ski hatch' in his car (not sure if it is a word, but I roughly translated it from dutch :P).

I was wondering if the end of the line can be like the image in the attachment.
The top picture is the inside of the box and the bottom picture to show how I would like to have the end of the line
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File Type: jpg tl.jpg (44.8 KB, 157 views)
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Old 10th December 2013, 09:36 PM   #7
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And 1 more question: is there a minumum for the surface area of the open end compared to the sd of the driver? For example: sd is 300cm2, can the surface of the open end be 60cm2?
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Old 11th December 2013, 12:37 AM   #8
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You've eliminated the driver offset. I built a bunch of these in the 80s, when we didn't know about getting flat response with a TL. It'll work.

Last edited by phivates; 11th December 2013 at 12:40 AM.
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Old 11th December 2013, 01:24 AM   #9
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Quote:
Originally Posted by Michelp89 View Post
And 1 more question: is there a minumum for the surface area of the open end compared to the sd of the driver? For example: sd is 300cm2, can the surface of the open end be 60cm2?
It depends on the taper ratio, amount of damping used, driver peak excursion at Fp, but lacking the math skills to calculate it, I empirically determined that an ideal bass reflex's Sd/4 rule to work well, but high Xmax drivers didn't exist back then, so best to use MJk's or similar software to calculate a low vent mach for drivers with an Xmax > ~5 mm.

GM
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Old 11th December 2013, 05:45 AM   #10
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Sd of the woofer is 366cm2
Xmax is 10mm, don't know if it is one-way or p-p
And for the simulation I made the taper ratio was 10:1 (seems a bit high when i type it )

And I can still get a offset in it. The image was just for showing the end of the line
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