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Old 24th September 2008, 09:30 AM   #11
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I'm sure if the set is for parties with rap music the TH can be compromised with the low end cut out around 35-40Hz to make up for efficiency.
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Old 26th September 2008, 01:06 AM   #12
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the calculations you posted will work. the port may be a little off but it seemed to be close enough to 28hz it really depends on the TS.
The biggest problem you should run into with this box is being evicted. I got evicted for an oldschool kicker comp 15" also tuned to 28hz, It shook the washing machines in the laundry room next building over from my towne house.
If you go with the horn configuration it will surely be louder, and you can expect police at your parties!
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Old 26th September 2008, 01:30 AM   #13
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Quote:
Originally posted by TravisDigital
the calculations you posted will work. the port may be a little off but it seemed to be close enough to 28hz it really depends on the TS.
The biggest problem you should run into with this box is being evicted. I got evicted for an oldschool kicker comp 15" also tuned to 28hz, It shook the washing machines in the laundry room next building over from my towne house.
If you go with the horn configuration it will surely be louder, and you can expect police at your parties!

We ended up making a "proof of concept" out of some 3/4" ply so we could mess around with the port geometry. Neither of us has any experience with tuning ports and so we wanted to get some experience before we cut into the $60 1" MDF.

It took me a week and a half to get the 1" MDF to start with, as I am in the northern penn. of michigan and it had to be special ordered. I only have one sheet, so that pretty much rules out building a TH.

We tried the port using the dimensions I had mentioned for a 28hz tune and then we took it apart and reconfigured it for supposedly a 35hz tune. I liked the 28hz a lot more, with the 35hz port the base lines of most of the music hit some crazy spl and seemed very out of proportion with the rest of the notes.

Is 28hz all that uncommonly low? or is that pretty reasonable?

Test Box (AKA: Ghetto Sub1):
http://mattodoom.com/hosted/101_0237.JPG
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Old 26th September 2008, 01:59 AM   #14
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Quote:
Originally posted by MattODoom



We ended up making a "proof of concept" out of some 3/4" ply so we could mess around with the port geometry. Neither of us has any experience with tuning ports and so we wanted to get some experience before we cut into the $60 1" MDF.

It took me a week and a half to get the 1" MDF to start with, as I am in the northern penn. of michigan and it had to be special ordered. I only have one sheet, so that pretty much rules out building a TH.

We tried the port using the dimensions I had mentioned for a 28hz tune and then we took it apart and reconfigured it for supposedly a 35hz tune. I liked the 28hz a lot more, with the 35hz port the base lines of most of the music hit some crazy spl and seemed very out of proportion with the rest of the notes.

Is 28hz all that uncommonly low? or is that pretty reasonable?

Test Box (AKA: Ghetto Sub1):
http://mattodoom.com/hosted/101_0237.JPG
it might be a little low for 1 12" but for 2 it seems ok. I generally tune ports to the drivers fs, but I usually use 15"s which are most commonly 28hz or lower. The test box at 35hz is probably closer to the fs of some type r's. I don't think 28hz is that uncommon for a pair of high excursion 12"s , Try the happy medium at 30hz that should give you everything you're looking for.
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Old 26th September 2008, 03:31 AM   #15
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The spec sheet says that the type Rs have a Free Air Resonance (Fs right?) of 29hz.
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Old 26th September 2008, 04:45 AM   #16
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If the fs is 29hz your original plans for 28hz should perform very well with these woofers.
You said you tried 28hz and liked it more right? Was it "proportionate" with other frequencies, or did that problem only occur with the 35hz port?
Wait a minute... you said the original plan was 1"mdf, but you're testing with 3/4ply, so did you adjust calculations for different size wood? I personally would have forgotten to adjust most likely, that's why I asked. So if you pulled a me and forgot, your test box would have a slightly larger inside volume. You wouldn't notice in the box, but the port would give/take a few hertz.
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Old 28th September 2008, 01:21 AM   #17
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Quote:
Originally posted by defwing
I have been contemplating a tapped horn for my Alpine Type-R 12".
Not too shabby, 200W/2 ohms or 400 W/4 ohms, ~316.249 L, half space:

GM
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File Type: gif alpine swr-1221d 13.5-135 hz th (parallel vc).gif (18.8 KB, 245 views)
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Old 28th September 2008, 01:36 AM   #18
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Quote:
Originally posted by TravisDigital
If the fs is 29hz your original plans for 28hz should perform very well with these woofers.
You said you tried 28hz and liked it more right? Was it "proportionate" with other frequencies, or did that problem only occur with the 35hz port?
Wait a minute... you said the original plan was 1"mdf, but you're testing with 3/4ply, so did you adjust calculations for different size wood? I personally would have forgotten to adjust most likely, that's why I asked. So if you pulled a me and forgot, your test box would have a slightly larger inside volume. You wouldn't notice in the box, but the port would give/take a few hertz.

Yeah we did account for the dimensional differences in the construction material. The 28hz sounded much better I think, the 35hz hit really really hard at one note, and sounded lackluster at the others. Also, with some songs that hit really really low notes ("I Put On" for instance) the low end response was compromised.

We're going to lug this 1" MDF up to the woodshop at school and do it up real nice. I'll be sure to take pics, but it could be a week plus!
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Old 29th September 2008, 10:26 AM   #19
defwing is offline defwing  New Zealand
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GM,

Could I bother you for the Input specs sheet on that please? I have spent the last few days playing in hornresp and understand it and tapped horns a bit better. I have got two good configs already but yours looks better,

My go at replicating it is

s1 114cm^2
s4 1000cm^2
l12 30cm
l23 530cm
l34 45cm

Although mine is closer to 125dB, must be something different or wrong with mine.

Thanks for your time,
James.
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Old 29th September 2008, 04:10 PM   #20
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Greets!

Yours looks fine, mine is larger so looks a bit 'fuller'. I assume that any big differences are due to mine being in 2 pi space and possibly you not inputting the driver correctly due to it being a dual VC.

Parallel and series VC sims will look different, but adding inductance and its associated series resistance to the series sim evens out the difference as shown, though all things considered, probably not worth the extra cost.

Parallel VCs:

GM
Attached Images
File Type: gif alpine swr-1221d 13.5-135 hz th (parallel vc) - specs.gif (13.6 KB, 190 views)
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