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Old 30th August 2008, 09:44 PM   #21
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Quote:
Originally posted by Patrick Bateman


Here's a pic of the response in a single reflex bandpass tuned to 63HZ:

Click the image to open in full size.

It's being fed 1000 watts; with 25db of cabin gain at 20hz and 15db of cabin gain at 40hz, it will be basically flat to 20hz inside a car.

Looking at the graph I'd say you'll be -8dB at 20Hz compared to 40Hz if your cabin gain figures work out correct for your car.

Rob.
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Old 31st August 2008, 12:23 AM   #22
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Here's a tapped horn using the same woofer as the bandpass box above. The volume of the two is practically identical. This one uses up 2.3 cubic feet of air space.*

Here's the SPL response. You'll note it's been carefully tailored to work with a car's cabin gain to yield output flat to about 25hz. Not too bad for a woofer with an FS of 51hz!

Click the image to open in full size.

Here's the displacement. Here's where we see some serious improvements. Even though the box size is comparable, the bandpass starts having displacement issues at 50hz, whereas this box is safe to about 30hz. Having said that, the *overall* displacement of the tapped horn is worse. There's no free lunch; we're trading one variable for another.
Click the image to open in full size.

Last but not least, here are our parameters. Note there's a coupling chamber. Just for the heck of it, all dimensions are based on the golden number. It might help to spread out the resonances, who knows?

Click the image to open in full size.

* To be specific, the volume of S1 through S3 is 2733ci, S3 through S4 use up 887ci, and the coupling chamber is 346ci.
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Old 31st August 2008, 02:25 PM   #23
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Quote:
Originally posted by Patrick Bateman


I cloned an autotuba and had it in my car for a few months.
...
I was feeding it something like 500 watts IIRC. I believe it's rated for 100 watts, and it's from MCM, so it's probably more like 50 watts IRL
...
As for corner loading a sub in a car, I really doubt it would make a worthwhile difference. I tried this myself with the autotuba clone I made, designing it so that mouth exited through the passthrough of the rear seats. The idea was that the rear deck would extend the mouth flare. When I measured it in car, my measurements didn't indicate that the rear deck was helping out the low end at all.
Thank you very much for your answer! I was thinking more along the lines at feeding it 10 (NO typo ) watts, provided I can get around 105dB efficiency over the desired passband. 500 watts would have me buy separate amps which I rather wouldn't.

I am not sure I understand your "passtrough of the rear seats". Is that like a hole for putting fishing poles?
My idea was to make a hole in the "hat-shelf" (translated from dutch, don't know how it is in english) and have the rear window and the "hat-shelf" extend the horn from the cornered mouth. My experience with my bdeap also made me sure to have the horn length at 280cm to make it get as low as needed with a 10dB slope from 30Hz till 100Hz. It would make for an enclosure around 100 liters so I still have trunk space over.

I could do with less by making a bdeap, so the mouth of the cabineth exits at the bottom of the trunk and the external airpath then goes from there till the hole in the "hat-shelf". Road noises from the wheel and the trunklid would then enter the interior more than ever, so I binned the idea.


Anyway, to get a little more on topic: I would still prefer a horn over a bandpass. I tried some simulations in hornresp and to me a horn is a better spot on the spectrum than a bandpass box if you want effeciency over a wider bandwidth.
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Old 31st August 2008, 08:44 PM   #24
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'hat shelf' = parcel shelf in the UK.
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Old 3rd September 2008, 02:51 AM   #25
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Quote:
Originally posted by Cordraconis


Thank you very much for your answer! I was thinking more along the lines at feeding it 10 (NO typo ) watts, provided I can get around 105dB efficiency over the desired passband. 500 watts would have me buy separate amps which I rather wouldn't.

I am not sure I understand your "passtrough of the rear seats". Is that like a hole for putting fishing poles?
My idea was to make a hole in the "hat-shelf" (translated from dutch, don't know how it is in english) and have the rear window and the "hat-shelf" extend the horn from the cornered mouth. My experience with my bdeap also made me sure to have the horn length at 280cm to make it get as low as needed with a 10dB slope from 30Hz till 100Hz. It would make for an enclosure around 100 liters so I still have trunk space over.

I could do with less by making a bdeap, so the mouth of the cabineth exits at the bottom of the trunk and the external airpath then goes from there till the hole in the "hat-shelf". Road noises from the wheel and the trunklid would then enter the interior more than ever, so I binned the idea.


Anyway, to get a little more on topic: I would still prefer a horn over a bandpass. I tried some simulations in hornresp and to me a horn is a better spot on the spectrum than a bandpass box if you want effeciency over a wider bandwidth.
ugh 10 watts? why?

As for the pass-thru, in my car the entire seat back folds forward, but it's not a hatch back. So there's an opening that's about 2250 sq cm.
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Old 3rd September 2008, 04:20 PM   #26
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Quote:
Originally posted by Patrick Bateman


ugh 10 watts? why?

As for the pass-thru, in my car the entire seat back folds forward, but it's not a hatch back. So there's an opening that's about 2250 sq cm.
Aha, I understand now.

Just to elaborate: with about 10 watts I should get 115dB (or at least one acoustical watt) which is enough for me ... and for now, héhé.
I have small horn-loaded tweets of 100dB, and mids of 98dB - aldough they look more like 95db in the band I'll be using them - and I want to power these with a passive crossover I still have to solder together when I find time.
The headunit I want to buy has a "direct sub drive" feature that allows to filter the bass from the front outputs and bridge the rear outputs to give 70 watts. The catch is that it's only in a 2 ohm load, and the driver I'll put into the basshorn is the same 8 Ohm driver that is now in my bdeap. 17 watts or a little less should suffice dough. I think if I would buy an amp, there is much chance it will be for the mids (who will probably be the limiting factor of the system.)

It'll be a true high sensitivity system and by sparing out on a handfull of amps, it'll be on the cheap too!
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Old 3rd September 2008, 05:27 PM   #27
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Amps are so cheap these days! Two days ago I picked up a pair of Class D monoblocks that were marked down at a labour day sale. Original price was $300 for 500w into 2ohms, the sale price was $54

$108 for 1000watts ain't to shabby!

Also, these power levels were RMS, not maximum, and adhered to CEA standards.
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Old 1st October 2008, 09:32 PM   #28
grecon is offline grecon  United States
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Default autotuba alternative

My nephew wants me to help him replace his 2x12" car sub with an autotuba. We have the plans but I'm not convinced even with cabin gain that it will be the deep sound the younger crowd likes. I see in message #22 Patrick Bateman offers up a tapped horn using two Audax HT240G0 woofers. I'm the old carpenter type and all the numbers are greek to me. Are there plans available for this box?
On a similiar note would William Cowans 60hz TH + cabin gain be a viable alternative for the autotuba? Old dogs learn slowly;-)
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Old 1st October 2008, 10:14 PM   #29
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Default Re: autotuba alternative

Quote:
Originally posted by grecon
My nephew wants me to help him replace his 2x12" car sub with an autotuba. We have the plans but I'm not convinced even with cabin gain that it will be the deep sound the younger crowd likes. I see in message #22 Patrick Bateman offers up a tapped horn using two Audax HT240G0 woofers. I'm the old carpenter type and all the numbers are greek to me. Are there plans available for this box?
On a similiar note would William Cowans 60hz TH + cabin gain be a viable alternative for the autotuba? Old dogs learn slowly;-)
I think you are right. The autotuba is a really cool design, it has great "slam.' It's not that I think it's a bad box by any means, but even Bill's graphs show that it's efficiency is WAY higher at 60hz than at 30hz.

If I had a friend who listened to a lot of hard rock, I'd happily recommend it, but for a teenager who probably listens to music with a lot of bass, there are better alternatives.

I'm totally slammed at work at the moment, but I'll dig out my notes on the Audax box later, cool?
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Old 2nd October 2008, 03:09 PM   #30
Blotch is offline Blotch  United States
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Well...i made a 38hz tapped horn and put it in my suburban - hows 133Db with 200 watts from a generic 10" sub sound(45hz)? Only bad thing is it cut off steeply at 30 hz so musically I was kinda dissappointed. It was a fun build though. Recently replaced it with a huge dual 15" kicker L5 box tuned to 24 hz. Same amp - 138Db @ 45 hz AND 134 Db @ 25 hz If I can find my charts I'll post em.
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