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Help for Project: Horn OR 6 Order Bicycle 12V Sub?

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studio45 View Drop Down
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    Posted: 06 August 2018 at 9:21pm
I've been advised in the past to swap my MTH30 bins for reflexes, but every time I try to simulate something I end up with less sensitivity and output for the same sized, and often heavier, box. 
Like I could load 2x bass-oriented 12" into a similar volume ported enclosure, but it would end up at least 1.5x as heavy and with only about the same available output when driven from my amps. The benefits would be proper response to 35-40Hz instead of 50Hz, and higher possible maximum crossover point, but those factors are less important than weight and sensitivity for me. I've got to be able to tow it a long way and the battery's got to last a good amount of time, otherwise there's no point in it being on a bike trailer ;)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mr. doom Quote  Post ReplyReply Direct Link To This Post Posted: 06 August 2018 at 4:04pm
When I did the maths a 4X10" reflex rig in sonotubes had a better DB to weight ratio than any of the horn designs. I had 6  ferrite 10"s on a trailer and had to push the rig up hills and that was made with lightweight plywood (reflex cab). 

My 2X 10" neo rig made with sonotube fit on a rear rack and was light enough to ride up mountain passes. I think it was around 7kg./15lbs.  

Rolling bike parties were more fun than hauling the trailer to a location and camping so my design priorites may be different than yours. (weight>SPL>cost>efficiency>size) 

There is a company in my town building industrial trikes/pedicabs and trailers that can haul 600lbs+ which would be interesting to see show up at a SPL contest with a pair of M-force boxes bolted to it. Cops would probably show up in SWAT gear to shut down that party.
 




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Post Options Post Options   Thanks (0) Thanks(0)   Quote bitSmasher Quote  Post ReplyReply Direct Link To This Post Posted: 09 June 2018 at 1:12am
For reference, here's my bike in its current state:


(without battery, amp and lighting which fits behind/beside the tops)
It's built to be loud, for Bike Rave and other street parties... and when loaded up I can still ride at a reasonable speed and distance. 

MTH30 is a good option for belting out the bass, my friends use them on their bike rigs. It is not small, and weighs ~25kg (15mm ply and ferrite driver), which works well to have a single one in a trailer or perhaps two on a 3 wheeled trike. I did consider building two for bike my but that'd be an over-commitment for a 2 wheeler.

If you wanted to consider refolding a design, have a look at the Tapped Horn design sheets by Brian Steele - can tweak dimensions then export to HornResp.
http://www.diysubwoofers.org/sheets/

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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 08 June 2018 at 9:03pm
I've added information to my post above.

Adding: Large surface areas in horns are often many times that of a reflex port, meaning lower losses, when the volume gets turned up. So at whatever the horn is tuned, right in that smallish frequency area its way more powerful/ efficient then a reflex cabinet at it's particular tuning.

As this is specifically aimed at 12V PA (usually a few drivers in small cabinets, with little power) the relation between the Sd and cabinet size, becomes of way other proportions than 6 drivers stacked, with plenty of power, in large cabinets. The larger the cabinet becomes, the smaller the effect of the driver Sd is. In my opinion those are 2 very different design strategies (for cabinets and drivers)then this particular case.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 08 June 2018 at 8:34pm
Yes that makes sense, I had always assumed the horn coupling was responsible for the extra boost in Hornresp.

In which case though, surely the efficiency benefits of large horn systems vs reflex are greatly exaggerated? Or even literally the opposite! If the baseline efficiency is only whatever the first driver offers, then lower power handling and greater power compression would make horns almost always a worse option once you get above 6 drivers or so, before even taking cabinet size into account.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 08 June 2018 at 8:04pm
Quote You're right, the Volvotreter design is modelled misleadingly, I didn't spot that, but if I model a tapped horn in 2pi the efficiency tends to be around 5dB less than if I model it in 1pi. So doubling the enclosures increases efficiency by 5dB not 3dB, surely?
If you halve the boundary loading (so from 2 Pi to 1Pi), you have created a 'mirror cabinet' that acts as if it's actually a secondly introduced cabinet in every way (without the boundary loading implied on that too). Just like in adding a single cabinet does +3 dB due to coupling (within a maximum of 1/4 wavelength apart). Then +3 dB due to double the power handling (going from 8 to 4 Ohm). Both the coupling and the double power aren't usually up to the theoretical 6 dB together, do to losses basically.

Sd of the drivers combined is very important for small 12V PA, as well as the cabinet size. A single 15" has say 855 cm^2 Sd, whereas 2 x 12" has 2 x 530 = 1060 cm^2. Two times 6,5" might have 300 cm^2 together IIRC. All those drivers are awesome if the size of the cabinet and the tuning become right. As the size of the enclosure decreases (for space and weight saving reasons) the influence of the driver Sd on the outcome of the overall sensitivity increases, so you'll get a high balancing factor there.

I like the idea of 2 small cabinets opposite sides of the bike (2 x 10" or 2 x 12"), or a single 15" minimum (think Sd). Bas reflex for easiest depth extension, tapped horns for up to twice a as intense (+ 5 dB) output with a single driver, at the cost of cabinet size. So if you make the tapped horn at least twice the size of the reflex cabinet, expect double intensity for the same power given.

I would go for the middle way in this case, 40 Hz extension. 30 Hz is going to be large or not loud. 50 Hz is gonna be loud but some music styles like you mentioned suffer 'vibe-wise'.

This setup would compare to 2 THAM 12's, powered with 25 - 50 Watts each (high pass at 50 Hz). Those 8"/1" coax cabinets, up till 250 W a piece (get large Sd or suffer ;). Standing near a wall helps tremendously with impact of the system, as opposed in the middle of a field.



Etc. etc.

Johan


Edited by mobiele eenheid - 08 June 2018 at 9:05pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mini-mad Quote  Post ReplyReply Direct Link To This Post Posted: 08 June 2018 at 6:58pm
..or even have a shot at slicing the MTH30 in half width ways!! The MTH folding seems to kick better (which is a nice strong energy point for dance music) and would be worth a bit of experimenting slicing it width was and loading up two 6.5inch drivers and see what it does!! The THAM12 sliced in two has been proven to work by one or two other on the internet so why not make some saw dust and have a go at a MTH15
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 08 June 2018 at 3:26pm
I'm having great success with the MTH30 design and a lightweight 200 watt woofer (Fane Sovereign but have tested it with even cheaper drivers and it still works great) plus 2x6.5" P.Audio coax, all mounted on/in on a Carryfreedom/"Bamboo" style trailer. 
I really think you should abandon your goal of getting good performance to 32Hz though - you will either end up with a heavy box that goes low but won't play loud, a large box that goes low and plays loud but doesn't fit on the bike, or a small light box that plays loud but doesn't go super low - that 3rd option is where people generally end up.
The idea using two 6.5" tapped horns seems like a winner to me. If I was building my rig again, I would unfold the MTH30 to make it half the height but twice the length - this would work better in a bike trailer. You want a nice low centre of gravity to avoid the thing tipping over round corners.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 08 June 2018 at 2:20pm
You're right, the Volvotreter design is modelled misleadingly, I didn't spot that, but if I model a tapped horn in 2pi the efficiency tends to be around 5dB less than if I model it in 1pi. So doubling the enclosures increases efficiency by 5dB not 3dB, surely?

Submeditation: the 1/10 power idea is based on the idea that decibels are logarithmic, so +10dB takes 10 times as much power.

In reality it's not easy to achieve an extra 10dB efficiency but even three or four times less power means three or four times less batteries required, so it's not just efficiency that should concern you as much as relative efficiency.

Multiple enclosures effectively increases your low frequency potential by increasing the system efficiency overall, so if one system is 97dB/Watt at 50Hz but it's never higher then 97dB at any point, another system which is 105dB at 60Hz but still 97dB at 47hz will be a better option for bass extension, assuming the overall size and weight is close enough.


Edited by Hemisphere - 08 June 2018 at 3:52pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SubMeditation Quote  Post ReplyReply Direct Link To This Post Posted: 08 June 2018 at 1:59pm
@mobile eenheid: Ah, sry, i wasn't sure what was the meaning of "band pass" but i was thinking of a paralell version. Or do you think (as we started speaking about 2x12" in multible systems are more efficent than 1x15" now) one or two 12" series 6th order bandpass version (one side each) could be better than the 2x6,5" 38hz tuned taped horn hemisphere posted above?

Thanks for the clarification about batteries!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SubMeditation Quote  Post ReplyReply Direct Link To This Post Posted: 08 June 2018 at 1:52pm
Greetings Hemisphere, 

all right, someone mentioned the 1/10 advantage of 2x12 instead of 15" here aswell - i guess i have to read more about that because i fell i don't have a clue what is the reason for that. Thanks for the hint!

The trailer is not that big, it's this one https://www.weber-products.de/products/monoporter/ - so i thought a cubo could be all right as it's not that high, and exactly 62cm at the smales part - what is the max lenght of a load. Considering your 1/10 efficiency point i have to rethink that, but i would not get more than two of the plan you posted next to each other. But the disign you posted really looks interesting, the duble folded version would be the way that would fit - https://volvotreter.de/downloads/TangBand_W6-1139SC_38Hz_TH_Rev_1.pdf

So you think two of this would deliver more 40hz than a single 12" 6th oder tuned to 40hz?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 08 June 2018 at 1:45pm
Quote That's 97dB/Watt. The 6.5" horn I linked to is 98.5dB, 3 of them on a trailer will be ~107.5dB and be comparable in weight and size to the sub18 with similar frequency response


Unfortunately, that simulation is incorrect for a comparison with an enclosure outside. The registered 98.5 dB is comparable to what 2 of those enclosures, with 2 W each would reach. After that it's +3 dB per doubling of enclosures, + 3dB for every doubling of power (it's simmed in 1,0Pi with 2.83 V instead of in 2,0 Pi with 2 V).

Tapped horn vs band pass

A tapped horn is a sixth order band pass, just in series and not parallel (like the ones normally referred to as 6th order band pass). Also, the much larger cross sectional areas used in tapped horns have benefits to typical 6th order bandpass ports.

I've been building 12V systems for quite some time now, I'm mostly down to using 9 mm Baltic birch these days, for that 100 W or so that they'll see that's plenty.thickness.

Car batteries

Car batteries are made for high currents for short periods of time, leisure batteries are made for low to medium currents for long periods of time. That's mostly down due to the difference in porosity, thickness and surface area of the Pb in the battery.

Edited by mobiele eenheid - 08 June 2018 at 1:46pm
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