multiple drivers smooth response by how much?

[will33]

Is there some formula for this as far as doubling or quadrupling drivers as related to some db difference in higher valleys and lower peaks?

Talking peaky midranges here, it's hard to find ones who's curves don't either look like a sawblade or have some more general rise or drop in the response somewhere that would equate to an eq boost or cut voiced into it. Looking at 6" mostly. A lot of the 8" drop off a little too early in the highs if you're leaving a tweeter out of the equation.

Eminence has a couple lowerish SPL offerings that look pretty smooth and yes, I know you can always drop $150 on an 18sound (but hey, you only have to buy one.)

Thanks.

 

[fourstringburn]

All I can say is my past experiences with both small and large drivers.

Large drivers definitely give you a deeper bass sound because the ones I used were spec'd to deliver low frequencies at 30Hz. The trade off is they are boomy and the sound seems to be projectional and has a narrow sweet spot. That is to say they sound good when standing in certain spots and the low frequency seems to drop out when you start moving around. This is characteristic with all drivers but it seems to be less noticeable with smaller drivers.

Since I am now using smaller drivers, my sound seems to be more consistent where ever I stand. You can use a combination of small and large drivers, but I wasn't really satisfied with the results when I used them.

As for midrange frequencies, I think smaller drivers give a better mid EQ curve and you can always use a cab with a tweeter/horn to extend them.

As for db( volume gain) the perception seems louder using a 810 cab as opposed to a 2-15 cab. Many manufacturer's claim this also, though I believe it to be true because again my sound is more even and consistent.

So the best advice is use your ears and not the hype to determine what works best for you!

 

[rpsands]

Couple things-
-I believe Bill Fitzmaurice uses a horn to smooth the response of the alpha 8MRA to quite some effect.

-I don't know of multiple drivers smoothing mids out at all, but could just be something I've not heard yet

-B&C makes a nice midrange (the 6md38) that is kind of in between the alpha 6a and the 18 sound 6nd410 that may be suitable for some higher spl applications

-The Alpha 6a is quite smooth in the mids and so multiples of those seem like a good option.

I can't say anything much to the above except that smaller drivers beam less, but only if they are vertically arrayed, and large drivers do not innately give you deeper bass (everything depends on the drivers' specs. Lower frequencies are omnidirectional pretty much so not sure what is meant by the low freqs dropping out.

 

[will33]

The alpha6 is a smooth one but a little low in SPL.

That B&C looked pretty good with the exception of a big 5k spike in the top end, kinda a like a very narrow treble boost. Not sure what that might sound like. SPL "might" still be an issue there requiring 2 of them, putting the cost above the 18sound. Maybe not if incorporated with a single woofer.

Not trying to be a total cheapskate but wondering if using multiples of cheaper drivers could be a solution. Been reading up on notch filters to possibly "fix" a less expensive mid with a few dollars worth of parts.

 

[billfitzmaurice]

Is there some formula for this as far as doubling or quadrupling drivers as related to some db difference in higher valleys and lower peaks?
Thanks.

You get smoothing with increased driver count, but less than four drivers won't do all that much. As for how smooth response really needs to be, take a look at the response curve for an average MI woofer, they aren't the least bit smooth at all. As for how high you need to go, 6kHz is sufficient. That does leave most eights out, as even if they will go that high on-axis they won't be worth much above 4kHz off-axis.

 

[will33]

Most woofers do have peaks in the midrange but many of them don't look too bad below where you would normally cross them at. Trying to maintain some of that up higher in frequency.

How smooth do they need to be? I'm not sure. When a steep dip is immediately followed by a steep spike with no "level" spot in between like in the top end of the la6cbmr and alpha8mra, that translates to a 8-10db difference that's close together.

For those particular 2 drivers I'm thinking it may have to do with the sealed back? Among other things.

Goofing around with my PA and eq to mimmick that type of stuff and see if I can deal with.

Thanks for the info, I don't think I'll be putting 4+ mids in anything anytime soon.

 

[billfitzmaurice]

When a steep dip is immediately followed by a steep spike with no "level" spot in between like in the top end of the la6cbmr and alpha8mra, that translates to a 8-10db difference that's close together.

That also translates to a plus/minus 5 dB response, and for MI use that's not half bad. The LA6CBMR is more like plus/minus 3dB from 500 to 5.5kHz, and that's hi-fi quality. A pair of them vertically aligned will give a very good result, especially off-axis. You can extend their usable response to 7kHz using a 2nd order Chebychev low-pass filter with a 6kHz corner frequency, though if you run a tweeter I'd cross them at 5kHz.

 

[greenboy]

A couple things I've found: the sealed basket midranges were designed as a quickie solution for some content up higher. But the sealed basket is so close to the cone that there's not room for any damping but a liner. A decent amount of damping makes a huge difference in perceived sound quality. Take a look at the Faital midranges if you must have a sealed back - there's probably enough room in there that they might have damped the backwave down better, and at the very least the distance it travels is further.

I prefer to do a chamber and stuff it with polyfill for the increased distance and damping. It becomes a noticable improvement. Large enough (dependent on driver) it also rolls the response off smoother and gives a little more control over the resonance.

Breakup peaks near the top of the driver's useful range are unavoidable, especially with MI drivers. The Eminence datasheet FR are a little misleading as they are smoothed a lot more than what some of the other manufacturers publish, but they give you the gist of the general response. If you look around at some point you'll see near field data with only 1/12 octave smoothing and it's quite revealing how crazy acoustics/audio really is.

I don't worry too much about peaking in a two-way (after all, people hear scads of it in woofer-only and conventional woofer-tweeter bass cabs). But some drivers will give you a different voicing, with all response jumps arranged differently, some quite enormous. For three-way I want the central area of response to have less variation, with enough room to get the worst of the peaking minimized without too complex of a crossover.

Though lately I'm looking at Zobels more for midranges than woofers ; }

 

[billfitzmaurice]

Though lately I'm looking at Zobels more for midranges than woofers ; }

A zobel is a waste of parts. Well designed crossovers don't need or use them.

 

[greenboy]

And yet I'm seeing them in so many designs by guys with tons of experience. And their FR data does seem to travel well through each axis. Anyway, the design I'm contemplating adds one component - a small cap - since otherwise the shunt would still be there as part of an L-pad - the difference being that the top end is more balanced yet still edgy.

 

[DukeLeJeune]

A zobel is a waste of parts. Well designed crossovers don't need or use them.

It depends. Direct radiator woofers are more likely to need a zobel than are horn-loaded woofers due to the horn's bandpass characteristic.

If sound quality rather than parts count is the top priority, then it depends on the specifics. Sometimes using a zobel is the most efficient way to meet the target transfer function. And for some applications severe impedance peaks in the crossover region are undesirable (tube amps and solid state amps behave differently into a severe impedance peak).

 

[billfitzmaurice]

It depends. Direct radiator woofers are more likely to need a zobel than are horn-loaded woofers due to the horn's bandpass characteristic.

Even with direct radiators IME all of the problems addressed by a zobel are also addressed by a low-pass filter that is optimized for the specific driver and box combination. Even if you're running the filter corner frequency close to the break-up mode of the driver a 3rd order slope will take care of it, more often than not giving a better result than a 2nd order filter with zobel. A zobel is of course useful if you're doing a cookbook filter alignment that requires a set load impedance.

 

[greenboy]

Sure looks like it's going to be nice on the mid driver in conjunction with a switchable pad ; }

 

[will33]

That also translates to a plus/minus 5 dB response, and for MI use that's not half bad. The LA6CBMR is more like plus/minus 3dB from 500 to 5.5kHz, and that's hi-fi quality. A pair of them vertically aligned will give a very good result, especially off-axis. You can extend their usable response to 7kHz using a 2nd order Chebychev low-pass filter with a 6kHz corner frequency, though if you run a tweeter I'd cross them at 5kHz.

So you're looking at it as distance above or below the "average" line and not distance from point to point, that makes it not so bad. These applications would be adding mids to current 212 and 1 or 215 bass cabs, no tweeter. All this other info will come in handy when it comes to making improvements to the PA.

The eminence sealed backs can be crossed high enough here to eliminate the 500hz bump on the lower end, just trying to imagine what the top will sound like before the $'s spent and looking around for possible alternatives.

Your talk of zobels and chebychev's requires more reading on my part to really ask any somewhat intelligent questions. Extending topend response to 6 or 7k without a tweeter sounds "cool". The only stuff I've read on zobels thus far is about presenting a known ohm load to the crossover when you don't have an impedance chart for the speaker you have.

 

[rpsands]

The Alpha 8MRA I can speak to from experience, does not sound quite as nice as the 18 sound 6nd410, but it does a very good job for what it costs. Definitely superior to the midrange of a 3015LF

 

[will33]

There's some practical experience, thanks. Any bump between 500 and 1k sounds much worse to my ear than choppiness on the top end. The plan for the 212 all along was an alpha8mr and an L-pad. If you look at the impedance curves, they're close enough where eminences 800hz pre-built crossover would probably work fine. (woofers ride at about 7ohm, the mid about 9). Cheap, easy and would sound much better than it does now. I may be over-thinking this.

 

[rpsands]

One thing you may want to do is, even if the volume is a match, try to pad the 8MRA back by 2-3 db. I run mine down a db even with two 3015LF's and it provides enough mids for my tastes. Of course, mine is crossed over a bit higher (around 1.2khz) which is contrary to popular wisdom I guess.

Again that's definitely contrary to the popular method, but I am pretty happy with the sound of the 8MRA padded back a couple db with the pair of 3015LFs - it's dark, but that's what I was after. Still more mids than most cabs, off-axis.

 

[will33]

Hence the commonly available, cheap and easy, 8ohm/100watt L-pad. I wasn't sure how much I'd like all those mids so the ability to dial it to taste is important. If I was to have the cabinet "voiced" any certain direction, it would be to have the mid driver a little bit less than the woofers to bias the cab towards the lower end of things. Would make it's initial sound not too "modern", just better and take away any inkling to boost a bass knob thus making life easier on the woofers and keeping headroom in the amp.

 

[will33]

To be clear, I'm coming at this stuff from the angle of using "medium" power bass amps, 200-300 watts @ 8ohm, 400-500 @ 4ohms and higher SPL cabs. That's why I'm not considering going the 3015LF/18sound mid route and buying a bunch of power to make them do what they can do. I already have enough regular bass amps, any purchase of more/increased power will be in the PA rack.

 

[will33]

A couple things I've found: the sealed basket midranges were designed as a quickie solution for some content up higher. But the sealed basket is so close to the cone that there's not room for any damping but a liner. A decent amount of damping makes a huge difference in perceived sound quality. Take a look at the Faital midranges if you must have a sealed back - there's probably enough room in there that they might have damped the backwave down better, and at the very least the distance it travels is further.

I prefer to do a chamber and stuff it with polyfill for the increased distance and damping. It becomes a noticable improvement. Large enough (dependent on driver) it also rolls the response off smoother and gives a little more control over the resonance.

Breakup peaks near the top of the driver's useful range are unavoidable, especially with MI drivers. The Eminence datasheet FR are a little misleading as they are smoothed a lot more than what some of the other manufacturers publish, but they give you the gist of the general response. If you look around at some point you'll see near field data with only 1/12 octave smoothing and it's quite revealing how crazy acoustics/audio really is.

I don't worry too much about peaking in a two-way (after all, people hear scads of it in woofer-only and conventional woofer-tweeter bass cabs). But some drivers will give you a different voicing, with all response jumps arranged differently, some quite enormous. For three-way I want the central area of response to have less variation, with enough room to get the worst of the peaking minimized without too complex of a crossover.

Though lately I'm looking at Zobels more for midranges than woofers ; }

One of the reasons for this is to see what else is out there and why, other than the simple sealedback fix. What does the damping do to "percieved" sound quality? Mid reflections/cancellations I assume but how can I accurately model stuff like that in WinISD? I do have the boundry cancellation chart, can dig in there and do some math next. Will likely lead to more questions than answers but that's how I learn, man.

For now, I'm just staring at graphs and counting costs, wondering why is this one a little better than that one but costs twice as much.

I'm fine with building sub chambers and doing a little more tweaking to the thing if there is a noticable result, noticable to someone other than myself, like the audience, the other bandmembers.


Or maybe someone else with $ or influence. yeah...right.