The real reason you don't want high inductance drivers

what you have to understand is that a high inductance driver is very different than a low inductance driver in series with an inductor.

VC inductance is an electromagnet that modulates the magnetic flux of the permanent magnet in the pole piece potentially producing unwanted weirdness

this is why shorting aluminum and copper coils are called " flux demodulation rings " and not " inductance reducing rings "

induction can be equalized out. flux modulation can’t. well not electronically anyway - it can be equalized out with shorting rings - but those cost money.

shorting rings are one of the things separating high end drivers from entry level ones.

one other method to stabilize the flux in a driver is to saturate the gap with flux. if the flux is saturated it can’t really change much. but saturating the flux in the gap is only really feasible for high end tweeters and compression drivers where magnets are larger and gap is small. it is cost prohibitive in any driver that requires a sizeable VC gap.

once again though multi-way designs come to the rescue. since most energy in music is between 40 and 250 hz or so with a peak around 50-60 hz ( basslines and kick drum fundamentals ) we can isolate that energy to the subwoofer so that it only modulates the flux in the subwoofer’s pole piece. this way it won’t be able to modulate anything in the vocal range.

my philosophy is:

subwoofer handles kick drum funamentals

woofer handles kick drum harmonics

midrange handles the vocals

compression driver handles detail / intelligibility

by moving the energy of kick drum ( and similar power hungry sounds ) out of the driver responsible for the vocals we can enjoy unstressed vocal reproduction with the coil centered in the gap and the magnet’s flux remaining relatively unperturbed, especially if the midrange also features a shorting ring which the 8" Eighteen Sound Bucket does.

i mean just check this impedance curve:

it’s almost an impedance curve of a tweeter. there is virtually no inductance. and this is a 8" driver !

just saying …

the other benefit of such a bucket driver is you don’t need to make an enclosure for it. it already has internal foam damping. and it can dissipate heat through the aluminum basket whereas if you make an enclosure for a regular driver out of MDF it won’t dissipate heat as well. of course that may only matter at extreme SPLs for extended periods of time.

buckets like this tend to cost a lot but they tend to have smoother upper midrange and higher efficiency than regular drivers, better heat dissipation and don’t require you to build an enclosure.

most people are wary of such “closed back” midranges because their experience is with stamped steel ones. it is hard to get optimum chamber volume by stamping and cheap drivers have cheap magnets which combined with low chamber volume result in high QTS sometimes over 1.0 …

but cast aluminum buckets don’t have those issues because chamber volume is calibrated and motors are more than powerful enough to completely control resonance …

aside from cost and availability issues the only reason not to use such a bucket would be that its optimum frequency range somewhat overlaps that of something like a Coaxial compression driver, or a large compression driver in general …

it would only make sense with a smaller compression driver that needs a higher crossover point … but at that point the question becomes does it make sense to use an ultra high end midrange with a more pedestrian compression driver ?

i suppose this is where things start to get complicated and i don’t have the answer for this :slight_smile:

actually i just noticed that 8" bucket has a serious resonance around 2.7 khz or so that you can see on the impedance curve - not so much on FR curve

they probably applied a bunch of smoothing to the FR

if you want to avoid this area you could cross over lower at around 1.5 khz which is still comfortable for any good compression driver

you would then be running this bucket from about 400 hz to 1.6 khz or two octaves. you would need a combination of waveguide and DSP to lift up that lower end a bit around 400 hz but this is actually where the driver is most efficient which you would see if you modeled it in HornResp.

at 400 hz the driver just needs volts - it doesn’t need watts. with a good amp and DSP you can give it what it needs without generating any sort of unwanted mechanical of thermal stresses.

here is an example compression driver you could mate to this 8" mid at 1.6 khz or so:

it is a very interesting relatively new driver with exceptionally smooth top end.

only downside is it’s a 1.4" driver rather than 1" so very top end dispersion will be less.

also you will obviously need DSP to raise the top end, but that’s fine.

here are some pics of internals from DiyAudio

i think compared to BMS, Faital Pro has inferior phase plugs but superior membrane material …

i would rather have a better phase plug but BMS doesn’t have an equivalent to this particular driver, in fact no company does. it is NOT a coaxial - it is a SINGLE ring that is 3.5" in diameter VC and it strikes a near perfect balance between between midrange and top end extension and is exceptionally smooth.

this is one of the Unicorn drivers that probably shouldn’t exist. it may be a good choice for a state of the art home audio system. you can find discussion of it on DiyAudio.

BMS is smarter than Faital Pro when it comes to compression drivers and would have been able to better optimize this driver to produce way more top end and at half the price and weight. but as i said they don’t make an actual equivalent.

anyway i am not married to this driver or anything it’s just an interesting relatively new relatively high end driver using relatively modern design approach, though still behind what BMS is doing, but may be good enough for home use.

the combination of that 8" midrange and that 1.4" compression driver would give you pretty much flawless vocal reproduction. you would sacrifice some performance at the very top end but 100 db at 10 khz i think is still OK especially as this driver is able to avoid the typical compression driver horrors in the 15 khz or so area …

AudioExpress tested other Faital Pro compression drivers so that can give you an idea of how close Faital’s posted measurements are to real honest measurements.

This driver is not that different from other Faital Pro ring radiators - it’s just larger and more high end, so it will sacrifice some of the very top end for better vocal range performance, which is arguably more important.

there are definitely other ways to design a system i just thought these two drivers were interesting and wanted to mention them …

My problem with these bucket midranges is that they have to be mounted in huge horns to achieve the advertised sensitivity. If your design doesn’t call for that then they aren’t very useful.

B&C calls this 100dB. It doesn’t hit 100dB until around 1200Hz. How is that a 100dB midrange?

This is another 6.5" midrange that doesn’t use a closed back and you can see that it has way higher sensitivity for actual midrange frequencies. 96dB at 400Hz vs 91dB that the bucket has.

you’re looking at output per volt ( sensitivity )

the more important parameter is output per watt ( efficiency )

if you can’t make a waveguide you can use DSP to correct this dropoff and still be more EFFICIEINT ( not more sensitive ) than the regular driver.

you will see this once you plot it in HornResp. the reason being buckets have much higher impedance at low frequencies so they pull very little wattage and are actually very efficient even without a horn.

however you will want a waveguide anyway just to equalize off axis response to make sure the beam angle gradually tightens from bass to treble without any abrupt steps.

if given an option with such buckets perhaps go for the lower impedance version because once you EQ the the effective impedance will be pretty high as you will mostly be pushing against back EMF rather than RE.

it’s the same concept as what iPal is doing for subs only it’s for midranges.

obviously if you think this is too complicated and not worth it that’s up to you.

ultimately as we keep making things simpler eventually you will arrive at just a single woofer connected directly to the amp and a dome tweeter with only a single capacitor and resistor on it in parallel with the woofer.

it’s really just how fancy you’re willing to get versus how much performance you need.

doing a primitive low performance design isn’t necessarily bad - maybe low performance is all you really need ( most likely the case ). you just need to understand the trade offs then make the call.

Isn’t a bucket just a sealed enclosure for the driver?

yes but by limiting the range of applications to only a dedicated midrange the designers can focus on optimizing the driver for that purpose.

whereas if it was a normal open back driver somebody might try to use it as a woofer so designers would have to do a more balanced rather than focused tune.

basically open back drivers are jack of all trades master of none. bucket is master of midrange. it isn’t due to the bucket itself, but rather once you do such a focused optimization for a single purpose ( midrange ) at that point it makes zero sense NOT to build it as a bucket to make the lives of people using it easier.

in other words if you drilled holes in that bucket and tried to use it as a regular woofer it wouldn’t work due to the tuning. so since it will only work as a bucket might as well make it a bucket.

the sound isn’t due to the bucket - it’s due to the motor, VC and cone. the bucket is just there to make your life easier building cabinets.

it just so happens that the most highly optimized midranges will all be buckets and vice versa - open back drivers will not be midrange focused, but designed to handle a variety of scenarios.

anyway i’m out to sleep. TTYL. i’m so sleepy i’m not sure what i even wrote above.

I see. Yeah modeling it in Hornresp it is the most efficient midrange that I have found. With the 2" voice coil it also has the most power handling. It should have more output than anything else out there.

B&C doesn’t specify xmech. How hard do you think it can be driven without breaking? Pushing subwoofers/woofers past xmax for high voltage peaks isn’t such a huge deal as long as there is no mechanical contact with moving parts and the coil doesn’t leave the gap. Do you think the bucket driver can handle voltage peaks that push it beyond xmax?

efficiency is: ((Bl^2)/Re)*(Sd/Mms)^2

where (BL^2)/Re is motor force while Sd/Mms is basically how thin the cone is ( notice it is squared )

this only applies to pistonic and non-resonant behavior of course.

you can verify this formula through mental experiments such as adding two motors electrically in series and in parallel to the same cone ( without increasing moving mass ) and observing that you’re now consuming 3db more power but outputting 6db more power, so ((BL^2)/Re) works in both series and parallel.

for (Sd/Mms)^2 the mental experiment is you either half the moving mass or double the cone area and observe 6db gain.

i’m sure there are more scientific explanations and if i was the guy who made HornResp i would probably know what they are LOL

the Eighteen Sound bucket i linked has 3" inside and outside voice coils, so it would be more powerful.

but honestly when you’re talking about 100 db / watt and you only need 100 db total what difference does it make how many hundreds of watts the driver can handle ?

i think if you use a decent DSP crossover the bucket will handle anything you throw at it for home use short of any sort of accidents. now if you have some some kind of accident like Direct Current or 60 HZ AC hum going into the driver that might damage it perhaps if it is full scale and not some low level DC offset or hum … and frankly even low level DC offset would not be great, but i don’t think quality equipment would have that.

a film capacitor at such low frequencies ( like 200 hz ) would be too expensive, but what you can do is either use an electrolytic crossover capacitor at say 200 hz and bypass it with a smaller film cap OR you can use an electrolytic cap to complete all your testing and then once you are confident you won’t have any bloopers that send high amplitude low frequency to the driver then you can short that capacitor and run the driver directly to the amp thus eliminating any unwanted contribution from that capacitor to the sound.

electrolytic caps are not expensive but some audiophiles refuse to use them. for testing purposes though it should be fine.

i mean some cheap electronics will have a turn on thump or my behringer DSP would sometimes have super loud pops - with a cap in series the driver should survive all that but you couldn’t brag about a system that uses an electrolytic cap in signal path.

so what you can do is swap components ( amps, DSPs ) until you get something that you are confident will not send any of those loud pops to your speaker and then you can remove that cap.

you can consult the folks at DiyAudio when it comes to this. you wouldn’t be the first person worrying about blowing up a delicate driver directly connected to a big amp without any passive crossover. some people sleep better with a cap and some take the risk. but i think it may be wiser to do what i said which is keep the cap long enough to test out and or swap out all your electronics until you trust them and yourself.

you might also want to consider the event of power loss, though i probably wouldn’t test that scenario with a delicate and expensive driver. i would probably hook up a cheap subwoofer instead and then pull the wall plug to see what happens.

by the way i just had a thought - my JBL EON tops have 55 hz tuning and 55 hz is right between US AC mains frequency ( 60 hz ) and 50 hz used elsewhere in the world:

if somebody accidentally sends 60 hz or 50 hz to that speaker the resonance of the port will limit cone excursion so as long as you turn it off before the VC burns up the speaker might survive …

i always assumed the 55 hz tuning was to enable a proper 80 hz crossover, but maybe it is also for mechanical protection against accidents.

I’m looking for a 6.5" midrange

not going to try to change your mind but …

i think 8" is more common midrange size in prosound. you may still be able to find smaller drivers because Arrays drive the demand for those …

but for point source 3-ways, the 6.5" is mainly for PA stuff ( PA is like gateway to prosound ). 8" seems more standard.

you may also want to consider the waveguide. for example this 8" horn:

comes with measurements for B&C 8NSM64 and RCF MR8N301

have to say, it looks pretty much perfect with the RCF for about 400 hz and 2.5 khz crossover points

by the way this horn is 15.3" wide so same width as a 15" woofer so it won’t make your cabinet wider if you’re going with a 15" woofer anyway.

i don’t know what other products limmerhorns have ( they seem to have quite a few ) i just knew about this particular horn.

you should probably be able to find some discussion of limmerhorns on DiyAudio ( haven’t checked )

in fact probably a good idea to do so ( find such a discussion )

if that horn introduces any sort of problems like being honky or whatever then it would obviously defeat the entire purpose of spending more to try to get better sound.

anyway i have a flu so i’m going to go …

It has too narrow directivity. If narrower directivity is desired then a larger midrange can be used. However with a 2000Hz crossover and wide directivity being desired a 6.5" or even a 5.25" midrange would be better.

directivity has to be matched to the tweeter

if you’re going to use a compression driver it will be in a horn and also have narrow directivity due to the horn

in my opinion this is why prosound midranges are larger. a 1" dome in a regular home speaker pretty much radiates equally in all directions at crossover frequency. for a midrange to match this omnidirectional pattern up to the crossover point it has to be pretty small. like 4 inches or so.

but if you’re crossing over to a compression horn that is maybe 40 X 60 or 60 X 90 degrees dispersion …

you can use much larger midrange … perhaps twice the size.

i see this as a benefit rather than detriment. why bounce sound all over the room when you can direct it towards the listener …

from the Limmerhorns page linked previously:

directivity: 70° x 55° at 1,6 kHz

this is right between 40X60 and 60X90 which are the most common compression driver horn directivities

for example my beloved JBL VTX F35 comes in two version - the 40X60 and the 60X90 versions …

depending on crossover frequency or size of compression horn you may want to go one way or the other but certainly the guys who made this horn have though about it …

one thing i don’t really like about it is that it’s fairly small. there may be some kind of sound quality penalty for this. on other hand it keeps speaker size to where you won’t feel the urge to throw the speaker out just to free up space in the room.

I prefer the sound of wide directivity speakers.