Bl is "motor strength," of course. Isn't that basically how powerful the magnet is?
- Or does it actually reflect the overall "control factor" ?
This is something I'd definitely like to understand better.
Regardless, again, my info above comes from many reliable sources. - Meaning, at the least it should not be disregarded as marketing hype. (And what marketing? Companies selling the same driver (or headphones) in two different impedances have nothing to gain by lying about this.)
Higher impedance also increase the damping factor of the amp itself. (So they all say.)
Also, from what I've read, (not personal knowledge) A 16 ohm driver typically has a lower Q and less resonant peaking than its 8 ohm counterpart.
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As for HF drivers, just ask B&C.
Other things I've read, (specifically about HF drivers) but cannot personally confirm:
A 16 ohm driver can allow for a tighter gap on a different magnet structure than its 8 ohm counterpart. When built with the tighter gap this lowers Q and increases efficiency.
A 16 ohm driver has a lighter voice coil than an 8 ohm driver so is a better mechanical match to the diaphragm portion of the driver. Ideal is voice coil/bobbin assembly mass should equal effective diaphragm/air load/surround assembly mass. This matches mechanical impedance of the two parts and moves toward ideal coupling of the voice coil to the diaphragm.
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If you were right, there would be nothing but 2 ohm drivers in the world, no?
Free decibels, weeeeee ! Also, in the winter, you won't need to turn the heat on as all your amps will be cooking away..... It's a win - win !
(Again, I am only going by what I've read. It wouldn't be the first time 95% of the internet, and a few high level techs, got something wrong.)
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Now let's talk about subwoofer throw !
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If you're looking for something that represents "control" of the driver due to the motor, then Qes is what you should be looking at. Qes is directly related to BL. The "B" in BL refers to the flux strength, the "L" refers to length of any wire carrying current through the magnetic field. True, if you double up the number of turns, then L doubles, but then so does BL. So if BL remains unchanged, then its impact on Qes remains unchanged. So when someone claims that "more turns" makes a difference, just look at if that translates to a higher BL figure. No change = no difference.
It won't increase the damping factor of the amp (that's set by its output impedance). It WILL increase the damping of the system (amp, cables, speaker), but by a minute amount, because the amp's output impedance is typically significantly smaller. Once the amp has a DF that's approaching or exceeding about 30, no listener is going to be able to hear a difference between a 4 ohm driver and an 8 ohm driver playing at the same SPL level, all else being equal. It would be like trying to hear a difference between a system that goes to 50 kHz and one that goes to 100 kHz
. On paper one might look better, but there will be no audible difference IRL.Some equations might help to throw some light on the matter.
DF = Zs/(Za+Zc) (Zs=speaker impedance, Za=amp output impedance, Zc=cable impedance).
Qes'=Qes*(Za+Zc+Zs)/(Zs)
For longer cable runs, Ic could become an issue, a lot more than Ia, the amplifier's output impedance. It may make sense to use higher-impedance drivers when long cable runs are involved.
Example, for an amp with a DF of 100@4 ohms (suggesting an output impedance of 0.04 ohms) and a cable run with an impedance of 0.1 ohms
For a 4 ohm speaker,
DF (4 ohms) = 4/(0.04+0.1) = 28.6
For an 8 ohm speaker under the same conditions:
DF (8 ohms) = 8/(0.04+0.1) = 57.1
I doubt anyone would be able to hear the difference between those two, if playing at the same SPL level with the same FR.
Lower Qes can also be a result of lower moving mass. 1/Qes is basically the motor to mass ratio. If you just look for low Qes, you often find low mass cones that can't take the pounding.
For a given motor strength, BL will go UP with a higher impedance coil. The figure of merit to look at for motor strength is BL over the square root of Re. You get more L (length) with a longer skinny wire (higher impedance). The force of the magnetic interaction is proportional to BL * I, and you do get more current with the lower impedance so you don't need as much BL to get the same force.
For a given motor strength, BL will go UP with a higher impedance coil. The figure of merit to look at for motor strength is BL over the square root of Re. You get more L (length) with a longer skinny wire (higher impedance). The force of the magnetic interaction is proportional to BL * I, and you do get more current with the lower impedance so you don't need as much BL to get the same force.
IMO BL has no dependence on impedance.
A "4 ohm impedance" for example can be achieved by two 8 ohm windings in parallel, one on the inside of the former, another on the outside. That's DOUBLE the windings (and therefore double the BL) of an "8 ohm" driver that turns out to have one 8 ohm coil that's wound just on the outside of the same former.
Qes IS dependent on Re, and as I mentioned before, is a pretty good indicator of how much control the motor has over the moving mass of the speaker. It will of course be lower if the moving mass is low. But it will also be lower if BL is higher.
As for a low Qes suggesting a low mass motor, have a look at the IPAL drivers. Or the original Aurasound 18" drivers. High mass AND low Qes.
Hi Brian, just added everything to cart, about to make the order
Question: I have no measuring equipment. Nor do I know how to. But would like to learn. Will the iMM-6 work with a laptop running REW be all I need?
Dayton Audio iMM-6 Calibrated Measurement Microphone for Tablets iPhone iPad and Android
Also slightly off topic, how would the PA460 do in your "B1" compared to the 18TBX100? Just out of curiosity. This would be a different project for a different time.
Question: I have no measuring equipment. Nor do I know how to. But would like to learn. Will the iMM-6 work with a laptop running REW be all I need?
Dayton Audio iMM-6 Calibrated Measurement Microphone for Tablets iPhone iPad and Android
Also slightly off topic, how would the PA460 do in your "B1" compared to the 18TBX100? Just out of curiosity. This would be a different project for a different time.
I'd second the suggestion of going with the UMM-6, if you're going to use a laptop. And perhaps add a USB extension cable to the mix. However, if you're going to be doing measurements, consider purchasing the DATS v2 as well, or build an impedance measuring jig to use with REW. Measuring impedance curves is a lot easier to do than measuring FR (especially for bass horns), and comparing the measured impedance curve against the one predicted by Hornresp can tell how close your build came to the sim.
The PA460 isn't a good match for that box. With a PA460, I'd likely go for a simple vented design, or an offset TL.
The imm6 is a fraction of the price! and from the description I thought it does the same thing, but instead of USB its an audio jack. Having the option to measure with my phone is also nice?
I also have a DAT as well, though I don't think I ever got it to work properly. Recently I took it back out and I couldn't even calibrate it with the supplied resistor. Its just a big mess, I googled it a bunch and seems like a common problem, some say its windows 10 compatibility, some say its the driver, no one knows whats wrong with it if it decides to act up. So I just called it a $100 loss.......
Does that really work?
I've seen mention of USB-OTG used for external storage devices, but never as an audio input. Will it support stereo input?
Thanks,
Chris
For a given magnet and gap, the BL is fixed. One can go for a lower number of turns of a thicker wire and get lower Re or go for higher number of turns of thinner wire and get higher Re. Other things being equal, both will integrate the same flux.
The Re does play a role in Qe (and hence Qts) but thats another story. The flux integration is dependent on the amount of copper in the gap irrespective of the turns, assuming that the full gap has been utilised.
So I built them
No photos for you because they're ugly. And i used OSB that I already have on hand, because I see this as more like a practice run. No leaks as far as I can tell (a lot of PL premium), and I am still going to add more bracing in the mouth.
They are loud, obviously, and I haven't had the chance to play them outside yet. Frankly I don't know where I can do that, until we all head to the desert in September. I can immediately tell (listening to the music I plan to use these subs for) that they don't go as low as my "run of the mill" 12" ported and even sealed subs at home. But so so so much more efficient, only a fraction of amp gain to reach about the same levels - which is the whole point of this design for me - max runtime with a 12V battery. So I'm fairly satisfied. They are as big as I asked for, though a bit more pain in the *** to move than I expected And one *might* be loud enough.
Which makes me wonder - this one horn, compared to 2 ported or TL (which takes up the same space as the 1 horn), driven to the same db, will the horn still have a longer run time on the same battery? (i.e. 1 horn more efficient (per W) than 2 ported?)
Whats the max Wattage each horn can take before I hit x-max? 200W per horn? (not that I'll feed them that much power on battery, but useful to know)
All in all I'm pretty happy with this "prove of concept", the performance I got from the money I spent is incredible ($200 total wood and drivers without amp). Now I have some time to think about all this while playing with it and think of optimizations that would benefit my application.
Thank you brian for the design. Your spreadsheet and instructions were great. I just had to go buy a metric ruler!
No photos for you because they're ugly. And i used OSB that I already have on hand, because I see this as more like a practice run. No leaks as far as I can tell (a lot of PL premium), and I am still going to add more bracing in the mouth.
They are loud, obviously, and I haven't had the chance to play them outside yet. Frankly I don't know where I can do that, until we all head to the desert in September. I can immediately tell (listening to the music I plan to use these subs for) that they don't go as low as my "run of the mill" 12" ported and even sealed subs at home. But so so so much more efficient, only a fraction of amp gain to reach about the same levels - which is the whole point of this design for me - max runtime with a 12V battery. So I'm fairly satisfied. They are as big as I asked for, though a bit more pain in the *** to move than I expected
And one *might* be loud enough.Which makes me wonder - this one horn, compared to 2 ported or TL (which takes up the same space as the 1 horn), driven to the same db, will the horn still have a longer run time on the same battery? (i.e. 1 horn more efficient (per W) than 2 ported?)
Whats the max Wattage each horn can take before I hit x-max? 200W per horn? (not that I'll feed them that much power on battery, but useful to know)
All in all I'm pretty happy with this "prove of concept", the performance I got from the money I spent is incredible ($200 total wood and drivers without amp). Now I have some time to think about all this while playing with it and think of optimizations that would benefit my application.
Thank you brian for the design. Your spreadsheet and instructions were great. I just had to go buy a metric ruler!
Depends on the drivers being used, but typically that is the case, yes.
Theoretically just a little over 200W. Practically I'll bet that it will be quite a bit more than that before the driver starts to complain.
LOL - no probs. Nice to know it's worked out for you.
They should be around 6dB down at 40 Hz, maybe slightly more if the box isn't properly braced. It is possible to obtain a bit more output down to 40 Hz, but that would require making the box a bit larger as just over 37 l of extra volume is required. About 3dB of EQ @ 42 Hz will accomplish about the same thing.
Hi Brian,
I spent more time with my new horns, inside the house! The more I listen to them the more I like them. they remind me of the "clubbing" sound I experienced when I went to college in London, and the funktion one system in Beta, Denver. This is not my first tapped horn. I've built lilmike's T6 (10" car driver, tuned to 30Hz) and anarchy (tang band w6, 25Hz). Those "work" (as in all that "oh it does dig low and got decent output for such a small driver"), But nothing that I've built myself that has anywhere close to the output of these 2 new horns. Once I have gotten used to the sound (and the experience of the high output), I forget the few notes it misses in the 30s. Initially I worried that I should have gone for a "flat to 40Hz" horn (so a 35), but now that I've spent more time with these 2, I think I made the right choice. To go 5Hz lower it'd be a bigger box, that won't fit inside the SUV with passengers. And I probably have to spend 2-3x more for a different driver. Though apparently the PA380 models well in the keystone which does go lower but bigger? Maybe in the future I can build some keystone cabs for these drivers and use them as HT subs at home when I'm not throwing parties outside!
I've powered it with a PE plate amp, 240W into 4ohms, and now its hooked up to my HT system, a XLS1500 that was powering a ultimax 15 (which recently died, cone ripped etc. didn't think I over powered it but I guess I did). The XLS1500 puts out 1500W into 4ohms, 1000W into 8, and I have it wired in series so its 16ohms. I have no data for the amp at 16ohms so I assume its doing 500W or so into 2 horns, so 250W each, about the max of what you just said. And they sound great. (gain knob only half way to 70% is as loud as I can handle inside)
I was also on the fence of just planning to take just 1 to the outdoor party, having seen just how big and difficult they are to move (I should probably add handles etc). Now that I am used to having that kind of output indoors, it would be a shame not to make use of both of them. I might have to convince my friends to let me bring them in the car though, they are going to think I'm crazy!
Every time I think I wish I have another 5Hz, I remember how there is no way to get anymore performance out of $200 total. Just no way. I think with my shoestring budget
(and low power from battery) I've hit the sweet spot. And its not like I can't spend more. I just get such a kick out of extreme value designs such as this.
I'll be using a D car amp with DSP:
Kenwood Excelon KAC-X40 4-channel car amplifier 70 watts RMS x 4 at Crutchfield.com
its actually the amp i've been using in my car for the last 10 years. But since its the only one I have with time delay and subsonic filter, I'm going to take that out of my car and use it for the horns. I assume a 30Hz HP will do? (it has 20/30/40/50). Should I delay the fronts? If so by how much? It also has EQ which I'll play with when I get the chance.
Thanks again for guiding me through all this, and getting a design that fit my dimensions perfectly (though I have not actually put it in the car yet...fingers crossed!!)
Like I said I've done some smaller horns. I'm now hooked for big horns now. May have to pick your brains for some HT full size horns down the road!
I spent more time with my new horns, inside the house! The more I listen to them the more I like them. they remind me of the "clubbing" sound I experienced when I went to college in London, and the funktion one system in Beta, Denver. This is not my first tapped horn. I've built lilmike's T6 (10" car driver, tuned to 30Hz) and anarchy (tang band w6, 25Hz). Those "work" (as in all that "oh it does dig low and got decent output for such a small driver"), But nothing that I've built myself that has anywhere close to the output of these 2 new horns. Once I have gotten used to the sound (and the experience of the high output), I forget the few notes it misses in the 30s. Initially I worried that I should have gone for a "flat to 40Hz" horn (so a 35), but now that I've spent more time with these 2, I think I made the right choice. To go 5Hz lower it'd be a bigger box, that won't fit inside the SUV with passengers. And I probably have to spend 2-3x more for a different driver. Though apparently the PA380 models well in the keystone which does go lower but bigger? Maybe in the future I can build some keystone cabs for these drivers and use them as HT subs at home when I'm not throwing parties outside!
I've powered it with a PE plate amp, 240W into 4ohms, and now its hooked up to my HT system, a XLS1500 that was powering a ultimax 15 (which recently died, cone ripped etc. didn't think I over powered it but I guess I did). The XLS1500 puts out 1500W into 4ohms, 1000W into 8, and I have it wired in series so its 16ohms. I have no data for the amp at 16ohms so I assume its doing 500W or so into 2 horns, so 250W each, about the max of what you just said. And they sound great. (gain knob only half way to 70% is as loud as I can handle inside)
I was also on the fence of just planning to take just 1 to the outdoor party, having seen just how big and difficult they are to move (I should probably add handles etc). Now that I am used to having that kind of output indoors, it would be a shame not to make use of both of them. I might have to convince my friends to let me bring them in the car though, they are going to think I'm crazy!
Every time I think I wish I have another 5Hz, I remember how there is no way to get anymore performance out of $200 total. Just no way. I think with my shoestring budget
(and low power from battery) I've hit the sweet spot. And its not like I can't spend more. I just get such a kick out of extreme value designs such as this.
I'll be using a D car amp with DSP:
Kenwood Excelon KAC-X40 4-channel car amplifier 70 watts RMS x 4 at Crutchfield.com
its actually the amp i've been using in my car for the last 10 years. But since its the only one I have with time delay and subsonic filter, I'm going to take that out of my car and use it for the horns. I assume a 30Hz HP will do? (it has 20/30/40/50). Should I delay the fronts? If so by how much? It also has EQ which I'll play with when I get the chance.
Thanks again for guiding me through all this, and getting a design that fit my dimensions perfectly (though I have not actually put it in the car yet...fingers crossed!!)
Like I said I've done some smaller horns. I'm now hooked for big horns now. May have to pick your brains for some HT full size horns down the road!
These drivers have an Xmax of only 5mm. The lower you try to take them, the less mechanical power-handling they would have within the passband. 40 Hz is probably about as low as I'd go with a design for these drivers. If I wanted to go lower, I'd start looking at the new neo PA series from Dayton, or start looking at the B&C pro TBX and TBW series of drivers.
A 30 Hz HP filter should be fine, though that does depend on how sharp that HP filter is (i.e. is it 12dB/octave or 24 dB/octave). As for delay, I'd start around 6ms on the mains, but this is something you'll have to experiment with to get the best results. And if you can provide any EQ at 42 Hz with the amp, try around 3dB to see if that makes a nice difference.
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