Dear all,
I have decided upon a subwoofer with following dimensions (internal) excluding the port volume
20”x 15”x 24” = vol. 4.17 cubic ft / 118 liters tuned at 15Hz
1. For round (Single) port : dia. 4” port length = 33.17” volume = 416.61 cubic inch = 0.241 cubic ft
2. For round (Two) ports : dia. 4” each, port lengths = 69.26“ volume = 870 x 2 = 1740 cubic inch = 1.00 cubic ft.
3. For slot port B= 15” H= 2” length = 81.64” volume = 2449 cubic inch = 1.5 cubic ft.
Are my calculations right ????? do I make any sense ?????? if so which design should I go with ????
If I go for the first option will the port noise be high ?
And if I have the box tuned to 15 Hz what will be the upper limit of frequency reproduced with good quality?
Warm regards,
Alex
I have decided upon a subwoofer with following dimensions (internal) excluding the port volume
20”x 15”x 24” = vol. 4.17 cubic ft / 118 liters tuned at 15Hz
1. For round (Single) port : dia. 4” port length = 33.17” volume = 416.61 cubic inch = 0.241 cubic ft
2. For round (Two) ports : dia. 4” each, port lengths = 69.26“ volume = 870 x 2 = 1740 cubic inch = 1.00 cubic ft.
3. For slot port B= 15” H= 2” length = 81.64” volume = 2449 cubic inch = 1.5 cubic ft.
Are my calculations right ????? do I make any sense ?????? if so which design should I go with ????
If I go for the first option will the port noise be high ?
And if I have the box tuned to 15 Hz what will be the upper limit of frequency reproduced with good quality?
Warm regards,
Alex
Depends how loud you listen, but probably yes. The port is too narrow and too long.
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Same answer. To make 15 Hz audible you need to move a lot of air. Ports with sufficient area will invariably lead to extreme length with high losses. You should consider passive radiators instead of ports or use a transmission line.
By the way, here is a simulation with your 118 l box tuned to 15 Hz. Compare it to the closed box. You get nearly the same frequency response, but the closed box is only half the size, has better step response and group delay. The black line is the theoretically ideal bass-reflex alignment. Bigger box, tuned higher, but the frequency response is flatter and goes lower. The port is still too narrow and too long, but already less so.
Loudspeaker enclosure calculating with Thiele Small parameter
By the way, here is a simulation with your 118 l box tuned to 15 Hz. Compare it to the closed box. You get nearly the same frequency response, but the closed box is only half the size, has better step response and group delay. The black line is the theoretically ideal bass-reflex alignment. Bigger box, tuned higher, but the frequency response is flatter and goes lower. The port is still too narrow and too long, but already less so.
Loudspeaker enclosure calculating with Thiele Small parameter
Regarding your last question (yes!),
do you have the space for bjorno project (post #80)? who was so nice to bother to take from his time to give you a fantastic calculation/simulation that you can't find anywhere else adapted to your "special needs" driver and application. If so what are you waiting for?! If not you have to go with the smaller foot prints BR's (or sealed) as was already mentioned in this thread. Take your time and be careful and cautious but also don't start going back and forth, like other members do, ending with high difficulty in further discerning their moving forward.
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Hi Alex,
FYI:
1. Look at the Picture again.
2. Yes: The Port is partitioned to decrease the Reynolds Number for the Pipe in order to prevent a non laminar Air Flow.
This design should work fine despite the very long Port System.
I've calculated the flow induced attenuation becoming equal to the viscous-thermal counterpart at a frequency of ~46 Hz, and the sum of these will add up to a negligible loss of only ~ 0.1 dB, IE. the attenuation due to the Port losses is solely defined by the amount of added Flow Resistance.
The preferred Pillow-fill that have the lowest Absorption characteristic of all commercial Stuffing types and will show the lowest FR attenuation above 46 Hz.
Be very careful to tease all Port stuffing and the weight of Port fill should be measured to be equal in each of the partitioned Volumes.
b
Attachments
http://www.diyaudio.com/forums/subwoofers/168737-night-living-bassheads.html
This sub was a lot of fun. I used a 350watt plate amp and when watching movies it could make the walls flex.
On the downside, the box rattled a lot (should have made it stronger) and I found that music just doesn't have enough bass under 30hz to justify using this thing.
I ended up throwing it away, due to the size and the lack of infrabass in the music I listen to.
That's a great thread with a lot of info for us noobs, thank you very much
I was interested by the part discussing tuning dictated by driver Fs:
http://www.diyaudio.com/forums/subwoofers/168737-night-living-bassheads-2.html#post2233053
Going from that calculation, the SI HT18's Fs of 17Hz:
Stereo Integrity | HT Subwoofers
or maybe even 15Hz (!):
Data-Bass
would seem to infer a possible Tapped Horn tuning of 12Hz or 10.6Hz, if I'm correct?
Would that be where you set the HPF or would it be possible to capture a few Hz more below that before cone excursion got crazy?
I am noob and have never tried Akabak or Hornresponse but I'm guessing either of those designs would be monstrously big and potentially destroy your home...
lol
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Yeah I think that's why Danley is using car audio subs in some of his products. The car audio subs tend to have an efficiency that's lower than a prosound driver, but also more displacement and a lower FS. It's a nice combination for a home theater tapped horn.
Here's the specs, note that it gives you a F3 of 20hz in the right TH:
Specifications: *Power handling: 1,000 watts RMS *VCdia: 4" *Impedance: 4 ohms per coil *Re: 1.71 ohms *Frequency range: 32-150 Hz *Magnet weight: 260 oz. *Fs: 31.9 Hz *SPL: 93.8 dB 2.83V/1m *Vas: 2.474 cu. ft. *Qms: 3.78 *Qes: 0.79 *Qts: 0.655 *Xmax: 25.65 mm *Dimensions: Overall Diameter: 15.74", Cutout Diameter: 13.85", Mounting Depth: 10.74".
Get 'em while you can, MTX is running out:
t9515-44-mtx-car-subwoofer MTX Audio
Here's the specs, note that it gives you a F3 of 20hz in the right TH:
Specifications: *Power handling: 1,000 watts RMS *VCdia: 4" *Impedance: 4 ohms per coil *Re: 1.71 ohms *Frequency range: 32-150 Hz *Magnet weight: 260 oz. *Fs: 31.9 Hz *SPL: 93.8 dB 2.83V/1m *Vas: 2.474 cu. ft. *Qms: 3.78 *Qes: 0.79 *Qts: 0.655 *Xmax: 25.65 mm *Dimensions: Overall Diameter: 15.74", Cutout Diameter: 13.85", Mounting Depth: 10.74".
Get 'em while you can, MTX is running out:
t9515-44-mtx-car-subwoofer MTX Audio
Yes, tunings that low are possible, but since the usable range of a TH is only a couple octaves with flat response, tunings that low end up going to only around 50-60 Hz before the nasty upper peaks and dips rear their heads.would seem to infer a possible Tapped Horn tuning of 12Hz or 10.6Hz, if I'm correct?
Would that be where you set the HPF or would it be possible to capture a few Hz more below that before cone excursion got crazy?
The HPF can be set a few Hz below Fb, but usually response is around 3 dB down at Fb for tunings below the driver's Fs, so little or no boost can be used below Fb without seeing excessive excursion.
And yes, 10-15 Hz can resonate wall panels, working nails loose, and cracking sheet rock mud and plaster, as well as making for a general feeling of unease.
The unease becomes more after you see picture frames have fallen and broken glass is littering adjacent rooms
.
Thank you for the info, both, it sounds like the voices of experience lol
I am unsure how my 4x18" sealed build will sound in my room when it gets finished but I am hopeful it will be 'adequate'! I heard an 8x18" the other week - utterly crazy, so much more than you could realistically use everyday but lots of fun nonetheless
lolI am unsure how my 4x18" sealed build will sound in my room when it gets finished but I am hopeful it will be 'adequate'! I heard an 8x18" the other week - utterly crazy, so much more than you could realistically use everyday but lots of fun nonetheless
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Hi Alex,
The load never will go below 9 Ohm from 8 - 80 Hz if a 2 x 24V Transformer with the 2 Amps in bridge configuration:
Maximum available Output Power will be ~89 W/ 8 Ohm and returning ~105dB /1m when placed near Room Corner.
Rec. It's still safe to increase the Transformer to 2 x 28 V (2 x 39.6 V Peak (Bridged Mode/ 9 Ohm Load==> ~107.7W==>~106 dB/1m)).
If I were you I would use two Chips: Each Paralleled then Bridged to allow a low Impedance Load and making it possible to add another Sub(Smaller flanking) in Parallel(>9 Ohm(Easy if a TL type)).
b
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