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Argh!!! Choosing Drivers


Deadeye
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I've known for a while exactly how my DIY speakers will look - in every way.  I know what I want them to sound like and I know the first song I'll play when I demo them to my friends. I'm eve 10% of the way to having the first clue how to build a crossover.  I know I want 3-way.

How in god's name do you go about choosing the drivers!!!???

Pretty sure the tweeter will be the Morel Excel - in my opinion, the tweeter is the most important to get right.

the rest? pff, I must have built 30 frd files and still none the wiser.

 

I know 8" is the biggest I can go and from my car subwoofer box building days (25 years ago) I prefer a couple of smaller drivers than 1 big one for more "punch".

 

Passive Radiator? Port? Sealed?

 

These will probably be crosseded over at 80Hz anyway so why agonise so much!?

 

How do you choose your drivers?


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TVOR-Ceasar
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This is a highly personalized part of the hobby. Some want to only look at the highest of the high end, some are open to the mid priced stuff, some look to find a real bargain or diamond in the rough, and others are looking to see if they can at least make costume jewelry out of canine feces.

There are a couple of ways to go, but really, you should start with assessing the equipment you will be hooking the speakers to (amp power/ohm capability), the room size (LxW) or nearfield / desktop use, and overall general acceptable size of the speaker for it's intended placement, so you can get a rough idea of internal volume you have to work with. 

Obviously, the amp's power needs to be considered when choosing a driver. Too low of a driver power rating and you run the risk of frying the voice coil. So keep that in mind, and especially for the lower frequency drivers.

The bigger the room, the more SPL you'll need to fill it, so higher sensitivity or higher power handling. Nearfield and desktop don't generally need as much power or sensitivity.

Overall maximum size will be important when doing rough calcs to see if a bass or midbass driver will be able to be used in that box. Try to stay a bit flexible here.

Now that you have a few key parameters, you can go to a site like Parts Express and dial them in to narrow the search. Remember to give yourself a range to look for, otherwise you might miss that one driver that would possibly be "the one."

For me, I end up with several QBasic windows open and my old programs running to help narrow down the choices. The absolute minimum you need for both sealed and ported is Fo/Fs, Qts, and Vas. Transmission Line uses Driver Diameter (equivalent if not a round driver) and Fo/Fs. I can run a calc in less than 10 seconds to see if it's worth considering. Then I can download the full info and files for something like WinISD to run a better analysis.

For crossover info, you'll need to look at the resonant frequency of the driver that will be the next in line (up frequency), double it, and see if the driver below it will work with it.

So say you have a woofer that goes from 30-2000Hz, a mid-range that goes from 800-6000Hz, and a tweeter that goes from 2400-22000Hz.

As you can see, 800x2=1600Hz. This "fits" within the 2000Hz limit, but you may want to consider a mid-range that goes a little lower to better fit the overlap. Now the tweeter at 2400x2=4800Hz, so you are fairly good there, but may still consider a tweeter with a slightly lower Fs. Ultimately, you'd need to chase down the graphs, FRD and ZMA files to put in a XOver software, just to make sure, but this will give you a starting point.

Don't forget to keep an eye on the SPL ratings. They are easiest to compare when they are of the same impedance and designation, like 1W/1M or 2.83V/1M. If you have questions about this, please ask. I've gone over it a few times, but I don't mind doing so again. Mixing differing impedances makes it harder to easily match levels and tends to make the XOver design more complicated, though it can be done. 

The more you do it, the better you'll become. And maybe, just maybe, you'll find that jewell you never knew you were looking for.

-Charlie
https://www.youtube.com/user/TheTrueVoiceOfReason


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Deadeye
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Thans for this, it's so tricky choosing.

 

I really like the Seas Excel stuff but it's expensive and I don't know yet if what I build will be any good.

I am tempted to just use the drivers Nick used in the uglies.  I'm 80/20 films and a 2-way is easier than 3-way.  Maybe

 

Thing is, I'm supposed to be building speakers that are better than my PMCs.  The PMCs are amazing.

 

I've got an Arcam recevier with Dirac Live for room correction and I'll have enough power to drive whatever I build.  I have a JL Audio E112 sub with 1500watt built-in amp so that can keep up with anything and break your house. I might even build new ones to match my mains.

 

I need to choose quickly as I've had my templates waterjetted in 6mm aluminium (I'm building the cabinets from sandwiches of 18mm MDF) so I need to know volumes to pick which sandwiches to make.

 

I didn't really want to port the cabinet so I would be putting the Tangbands W8s in a sealed box which according to the part-express website would tun to 75Hz which is great as I'd probably still cross them at 80Hz for movies.


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123Toid
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Posted by: @deadeye

How in god's name do you go about choosing the drivers!!!???

 

I know 8" is the biggest I can go and from my car subwoofer box building days (25 years ago) I prefer a couple of smaller drivers than 1 big one for more "punch".

 

Passive Radiator? Port? Sealed?

 

These will probably be crossed over at 80Hz anyway so why agonize so much!?

 

How do you choose your drivers?

This is a really good question.  There is no real wrong way to do this, but I will give you my advice.  And the basics of what I do.

 

First, I would start with the woofer or mid (assuming two or three way).  Make sure that whatever alignment you choose it will be able to go to the frequency you want it to.  So if you want it sealed and crossed over at 80hz, you will want to find a driver that can do that. 

Once you have this narrowed down, not it's size.  Ever driver will start beaming by a certain point. That means that the driver will start to deviate from it's on axis response. this is completely dependent on the driver size chosen. For example if we take a look at an 8 inch woofer were going to see that it starts to deviate from its own axis around one kilohertz. And it starts getting a lot worse around 3 KH. that means that if we take this driver and crossover during this area, are off axis response will suffer. So you typically want to crossover closer to the one kilohertz with a 8 inch driver. That doesn't mean you can't go later, just means that you're off axis myself for a little.  Another thing you wanna look at when you're looking at the driver is it cone break up. you're gonna notice that with some pretty sharp peaks in the response. this should be well after your usable frequency range. you wanna make sure to get that down as far as you can come and see don't get distortion in your final build.

Once you have the woofer or mid picked out you want to move onto your tweeter. you'll notice I didn't start with the tweeter, because I didn't know where I would want to crossover yet. If I have the idea of doing a 2 way with an 8 inch driver, I'm gonna need a tweeter that can crossover relatively low. so I probably don't wanna crossover any later than 1500 Hertz if I can help it. for this wanna take a look at 2 things. I wanna check the sensitivity of the tweeter and I want to check out it's FS. Typically a good rule of thumb to follow is not to crossover any higher than 2 times the FS of the tweeter. so you'd be looking for a tweeter with an FS around 750 Hertz or lower. You would also want to look free tweeter that is more sensitive then the woofer or mid that you've chosen. let's do the fact that you wanna be able to attenuate it to match the mid. You do not want attenuate the mid in a 2 way build.

What I have mentioned are basic rules of thumb.  But it should help as you learn.

https://www.youtube.com/123toid


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Deadeye
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@123toid

The W8s in the uglies are the first 8 inch drivers that go that low. Why wouldn’t they be good for music?

or would they ideally need a mid between them ate the tweeter?


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123Toid
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@deadeye

They are good for music.  I listen to music with them all the time.  The reason I used the Peerless Corundum was in part due to the fact that I could cross it over low enough not to worry about the off axis response in the crossover region. 

https://www.youtube.com/123toid


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Deadeye
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@123toid

 

have you thought about what mid you might use if you would go 3-way?

I’ll start a build thread tomorrow

(I’m in England) 

I finally got PCD to work thanks to you videos and with those two drivers in the uglies have a good flat response but I can’t help think a good mid in between would finish things off nicely.

morel do a big soft dome mid like the mid in my PMCs. 


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Deadeye
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123Toid
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@deadeye

The Uglies don't' need a mid, so I have never looked or thought about it. But that is only due to the fact that both drivers can integrate well together and keep distortion down. You could add one if you wanted to.  I just haven't thought about it. 

https://www.youtube.com/123toid


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ajc9988
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@deadeye - I actually spent a lot of time compiling data and making my impressions of the data from the frequency response graphs, including off axis. Some companies were excluded due to them not having off axis data (looking at you Tang Band; just give more info because I "hear" you are great (horrible play on words)).

As such, for midrange, there are two groups of speakers you would want to look at: mid woofers and lower ranged tweeters. Make no mistake, you will need a tweeter above those, as they both only go up so far.

For lower ranged tweeters, I primarily found Peerless and Wavecor to have a LOT of offerings in this frequency range worth considering. I have my spreadsheet setup so I can see which frequency range I would use it at, which the company recommends, the SPL (two columns, one for 2.8V, one for 1W), the Nominal Impedance, the Pe RMS rating (not to be confused with Rms, which is a different category), the diameter (both baffle hole and overall) and then the calculated beaming frequency according to the equation F=(2*c)/(pi*D) with the frequency equaling 2 times the speed of sound divided by pi multiplied by the diameter (with the diameter, if not provided, being the baffle cut out, not the overall woofer size, as that includes non-moving metal). Considering 343.68 is in meters and I am using mm for the speaker dimensions, I divide the cone diameter by 1000 to get the beaming frequency. You could also multiply the 343.68m for speed of sound by 1000 to get the same result.

I then also use a cheat sheet I found ( https://www.jdbsound.com/art/frequency%20wave%20length%20chart%202013.pdf ) to figure out the number of inches for a full wavelength. I then use the radius (diameter divided by two) of each driver added together to check if I can get them close enough to cross them within one full wavelength.

Arguably, you might look more at the Morel MDM 55 and CAM 55. Half the price, similar frequency response.

image
image

Aside from those, I have a couple midrange woofers tucked in accidentally to the Woofers tab of my spreadsheet, but generally, those are the mids that I would consider that are not too expensive, but still great performance (if their graphs are correct and in the ranges that I figured for them).

In fact, if you want you could create this as a 3-way and add the Dayton Audio ND13FA-4 (granted, 4 Ohm instead of 8 Ohm, so you will have to deal with that), you could fill out the areas above the Peerless if you feel the highs are not enough. This would be around 6,000Hz crossover. Otherwise, you could use an ND20FB-4 as well.

But evidently the frequency will also depend on the order of the crossover, just to avoid the Fe on the fall (which avoids overheating and overworking the tweeter).

So start with a spreadsheet of driver specs. Separate them into their categories like this

image

 
Once you have the information mentioned above (mine also has all the information needed to be added to WinISD for modeling, meaning the T/S factors from the mfr), you then start with looking for your main woofer. Then look for a midrange tweeter or a mid woofer that would cross well with the woofer (if possible over 1200 to avoid higher voices playing out of one speaker and lower voices driven by the woofer, but that isn't a real rule and 800-1000 is realistically fine), while having a high enough range before the off axis splits to cross with the higher ranged tweeter. Then, when you have this, you can start designing the box size by figuring out the volume the Woofer(s) need. I still do not know how to calculate having woofers of different sizes for the necessary volume (tweeters are often sealed and/or do not have large requirements on volume, etc., so less worried of those in the same enclosure space in a cabinet). In any case, then check baffle diffraction with the front shape and figure out the dimensions from there.

If there is anything I missed, please let me know.

Edit: on those lists I still need to move some drivers around, so, for example, the 5 3/4" Wavecore WF146WA05 needs moved to the woofer tab, as does possibly the WF118WA07. I am still debating is low 2000s is enough for the mid or just call that a woofer if the lower frequency is enough. If it hits (or is serviceable on off-axis) to 3000+, then it is a good mid. Lower playing tweeters really fill that role well.


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Deadeye
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@ajc9988 Thanks for this.

I've made significant progress since my post.  There are so many drivers by so many manufacturers.  It's easy to whittle a lot of them out as they naturally have a rubbish frequency response.

 

I actually have two working speakers and I've finalised a crossover design that works.

 

DATS V3 arrived this week and I have a UMIK1 so it's time to measure the drivers in the cabinets to make sure the crossover works in real life before I buy parts.

I bought a cheep pair of 3-way crossovers and use Dirac Live in my amp to "fix the issues" and they sound great.

 

I went with Scanspeak 70003 tweeter - flat to 20KHz and goes to 30kz+ (eyewateringly expensive)

SB Acustics Satori MD60N-6 soft dome mid. (Not cheap)

2 x Dayton RS225-8s (got them cheap in the UK)


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ajc9988
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@deadeye - I'm still in the design stages on a couple different things. I am looking at the on sale Dayton Audio ES104AMT-4, the Foster E100T10, and other high range tweeters to figure out the highest part. I really like the Freq. Response of the ND13FA-4, which has a great 45deg at -3dB to 16,800 and 30 degree is good to 20,000. But, depending on crossover type and order, you may need to cross at like 6000 with that (and the 88.5dB means it needs matched roughly with the driver and mid or you need more than one, etc.).

I may need to redesign my Dayton/Peerless 3-way, as I just learned about the crossover and Fs of the tweeter AFTER I designed it. But it is what it is. Except for the Peerless Fs, the rest would have been fine. Either that or I can make it taller, swap a different Peerless in like the DA25BG08-06, double check the wavelength distance, then reduce the depth accordingly (which also means changing the volume of the braces, which then also reduces volume), but should not be too hard (and I have some room to spare on the distances from the center of each driver, so it should be fine with those changes). Makes me think if I'm changing the mid-tweeter, might as well change the small tweeter to the ES104 AMT, except for the wavelength possibly making it too large a distance for crossing properly.

But glad you found what you are looking for.


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Deadeye
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Here's my crossover mock-up:

Using Optimizer Stock Values

And here's a speaker:

 

RightHumpy

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ajc9988
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@deadeye - Thought you might enjoy this quote from Audioholics:

Editorial Note by Steve Feinstein on Crossover Frequency Selection

A basic, ages-old but still true, rule of thumb states that a designer is usually safe when he crosses a driver over at double its resonant frequency. If a tweeter has an Fs of 1500 Hz, use a 3000 Hz crossover, minimum. If a midrange is 300 Hz, use 600 Hz.

Another good rule of thumb says, “18 dB down at resonance.” If a tweeter’s resonance is 1500 Hz, the voltage curve of the crossover should show the tweeter section being down 18 dB from “0 dB.” That kind of conservatism all but assures no tweeter burn-out.

This was the “rule” at a major speaker company I used to work at, and the engineers all hated it, because it was so conservative and resulted in very high tweeter crossover points. But we almost never lost a tweeter and our warranty costs were vanishingly low. ‘Real world’ vs. ‘theory.’

https://www.audioholics.com/loudspeaker-design/crossovers

So the doubling of the resonant frequency, which coincides with the peak impedance, which is the hottest and hardest for a tweeter to play, is to protect the tweeter from being rode too hard and dying prematurely.

I like the second rule, though, which is another way to check for it: 18dB down at resonance. Now, the reason I like this one is in the event you are using a third or fourth order crossover (rare and takes into account issues that can happen in phase if you go out that far), you have another measure as you may wind up being fairly close to the double Fs or just barely under, but you can look at the resonant frequency, make sure it is down 18dB, and see if the tweeter is being rode too hard.

As was put but the editor, the engineers believed that was way too conservative. But depending on your price range and the amount spent on your tweeters, what is being a little conservative for a little peace of mind on something that brings you this much joy.

Thought you might like that reference.

Edit: also, for ribbon tweeters (i.e. AMT and planar), do you calculate the distance from the center like normal speakers or, because of the origination coming from the entire area, can you use the lowest point of the opening. Basically, trying to figure out how low I can cross the Foster mentioned above.


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123Toid
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@ajc9988

It is to help protect it, but in the same token it is also there to cut down on distortion. Having said that, that rule of thumb is for a second order crossover.  You can switch to a third order and crossover later if the driver allows it.  And although the rule is 18db down at FS, I try to be closer to 24db if I can and 20 minimum. But a lot of this will show up on your graphs when you take distortion measurements. It's one of the main reasons you can't just go for a linear response.  You have to account for things like this.  

https://www.youtube.com/123toid


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