Tech Talk 10: Loudspeaker Measurements

0:01 [Music] [Applause] [Music] hey everybody welcome back it's time for another Tuesday's Tech Talk and this is a follow-up from last week it was kind of a two-part episode about loudspeaker measurements and last week we talked about all the measurements that really don't tell us anything about how a speaker sounds we looked at power handling or watts and we looked at distortion measurements and talked about

0:47 that this week we're gonna talk about the measurements that actually tell you more about how a speaker is going to sound no measurement is going to tell you exactly how a speaker sounds two speakers can have the exact same measurements but sound very different you can't really measure everything that we hear there are a lot of things that are not in the measurement because you're not measuring that thing it's like walking around your car looking at your car and realizing one of your tires is flat that tells you an awful lot about the performance of your car and how it's going to handle or drive and but that's just one aspect of the whole car it doesn't tell you everything about the rest of the car and the rest the car

1:34 performs measurements are the same way each measurement will give you insight as to how that speakers gonna sound in a particular way but it's not gonna tell you everything about the speaker a case in point I once picked up a little pair of behringer studio monitors not a great sounding speaker but it was an inexpensive speaker that measured relatively well and I took the crossover out and I replicated the crossover with the exact same values value provide you but used higher-quality parts I used sonic apps use some earthy larger gauge air core inductor is used mils resistors and I used some higher-quality wiring to

2:19 it and put both networks in the box and put toggle switches on the back so you could turn all the switches down and use the stock Network and all the switches up and use the upgraded network if you measure the speaker and any way you wanted to measure the speaker with either Network it measure is exactly the same but they sounded very different and we took those speakers and we sent around on a little tour and people got to listen to them and talk about the differences in the way they sound and you know a lot of that had to do with the capacitors then all the rest of the parts still contributed a tremendous amount to the difference in sound there's differences in clarity difference in resolution different things like that and how things imaged even stuff that you just

3:07 can't measure very well but there are a group of measurements that we look at and there's a group of them that I use regularly I look at frequency response I look at the vertical and horizontal off axis responses I'll look at the impedance curves and I'll look at a spectral decay looking at each of those from discussing each of those specifically the frequency response tells you what it's doing on axis so it's it's giving you a level of accuracy over a frequency range and that tells you a lot about how accurate the speaker is if you see dips and peaks and things like that in the frequency response you know that's deviation from accuracy you see a linear response you know that that's speakers gonna reproduce some

3:53 level of accuracy which is what you're looking for the other thing I look at very closely is the affects response a lot of guys look at the horizontal off axis you're just looking at maybe on axis 10 20 30 and 40 degrees off axis that's fairly common and it's fairly common for the top end of the speaker to start dropping off as you move further off axis but I I spend more time looking at the vertical off axis that means I'm moving the microphone up and I'm seeing how well the speaker maintains the consistent response over a wide range and and that's what you're really looking for you want a speaker that will sound the same regardless of where you are and load this room with the same

4:41 sound if you move up vertically and the difference between the distance of the tweeter versus the woofer has now created a time delay so that there's a cancellation effect as you move up you're getting a big suck out that's gonna contribute to what you hear that's gonna contribute to the overall room response your ceiling reflection is going to reflect that it may be hot in the top hot down low and where they're out of phase there's a huge hole so you're getting reflections at some frequency ranges but not reflections at other frequency ranges so you get an uneven reflection it could be the same with sidewalls and your rim of course can be contributing to any uneven reflection you can have flat surfaces in

5:27 the room that are causing reflections that are a problem so always look at all the horizontal and vertical effects just that tells you a lot about you know how well that speaker is gonna load the room how it's gonna how the room response is gonna be you know it's gonna sound looking at the output the other thing to look at it's very important it's look at the impedance curve then peens curves gonna tell you how well the speaker's balance from one into the other versus how it's loading new amplifier you know is it an easy load or a hard load is it demanding current on one end and not the other also in the penis curve you can see cabinet resonance as you can see internal standing wave resonances and you know when you see those resonances

6:13 and the penis curves then that gives you a pretty big clue that hey there's there's a problem here and that problem is gonna be an audible problem but the most telling of all the measurements as far as telling you how speaker is gonna sound is they'll look at the spectral decay the spectral decay gives you response as far as the amplitude of the response across the frequency range and it shows you how fast it dissipates stored energy notice how quick does it does it die you know you want that speaker to reproduce the signal and then once the signal is over you want it to stop you don't want it to reproduce the signal and then take some time for it to settle you want to reproduce it and stop quickly and you see that in a spectral

7:00 decay and if there's ringing or breakup in the cone or things like that you'll see it in the spectral decay you'll see long traces where they're stored energy where it's taken longer to dissipate that energy that's really easy to hear when it's you know the rest of the speaker's stopping within a couple of milliseconds and you got something there that's four or five milliseconds longer in stopping time just within a certain band you hear that ringing really easily I mean that's a time smear it's just dragging out of the signal it's it's a distortion and it's gonna show up in that spectral decay if it's clean you see a flat line that drops off

7:46 immediately that tells you a lot about how that speakers consent if it drops off really fast that's indication of speed and speed is speed your friend you know when it comes to reproducing sound you want it to play and stop playing stop you want to hear space between notes you don't want to hear it dragging that stuff out long decay times that's a blur of everything you know just looking at that spectral decay and on how to read it that's probably the one measurement it's gonna tell you more than any other measurement as far as how is that speaker in a sound it's gonna highlight problems or it's gonna show you greatness so what we're gonna do next we're gonna look at a bunch of measurements really look at

8:33 measurements of bunch of full-range drivers real look at speakers and mainly I'm just gonna look at drivers and speakers that are out of production I'm not going to pull up a lot of speakers that are you know commonly in production I don't want to try and hurt anybody's business by showing what their measurements look like when they don't want them out there I'm just gonna show you drivers out of production stuff speakers that we've upgraded so you can see some before and after measurements and you can see how those measurements of the before and after gives you an idea of the improvement in the sound quality so let's do that I'm going to move the camera over to the computer and we're

9:21 gonna pull up some measurements I want to walk you through I'm going to send those measurements over to Ron he's gonna just drop them right on the screen so you can just see the measurement as clean as possible and give you a narrative on all that stuff and let's see if we can learn something about it all right we're looking at some measurements here this first measurement that we're looking at is a found tech FR ATX full range driver the frequency response you see here in green is a response after I've put in correction filter for it the red line that you see here is the output of it before correction so what we've done is

10:07 I've gone in and put in a baffle step compensation that's dropping the output above 1k hurt down to where it's level with the output down in the lower frequency range so it's a smoother response the first spectral decay we're going to look at is the spectral decay with no filter on it and the peaks up top are so extreme they're so hot that they've kind of pushed the level of everything else down so if we look at it pulling it up a little higher we get a better idea of what's going on in a spectral decay you can see there's a considerable amount of ringing going

10:55 on across the board from about seven or eight hundred Hertz and up there's a lot of breakup a lot of ringing after the filter compensation network it leveled everything back out there's still a lot of ringing there you can't get all of it out with a filter you can get some of it out with the filter but it's just impossible to get all of it out this next measurement we're going to look at is a Jordan Jordan econia model and this is the spectral decay on that unit and you can see there's a lot of stored energy there in the 1k hurt region it's

11:41 in fact it splits into a couple of different wringing points so in listening to that it's going to be a little aggressive and a little harsh and a little hard to listen to in that range so you can you can clearly see it in the spectral decay this next one is actually a production speaker so let's just call it el stock production el is just the letter of the what the speaker's names begins with but you can see at around 2200 Hertz there there's a long ridge line there where you see a lot of stored energy a lot of ringing you see a lot of ringing again over in about five key hurt Rangers a little smaller trace

12:27 there but quite a bit of breakup that was actually just due to the woofer playing up so high that there was a lot of ringing and break up there in that range this next measurement is the exact same speaker the crossover point was lowered so that the tweeter was covering those ranges and as you can see it's actually pretty clean there's some small traces that you still see across the the lower section of the graph there where you see some little bits of ringing going on sitting you know in quite a few areas but overall pretty good pretty good after the upgrade this next one a spectral decay of one of the little lgk drivers we sell it's a little three inch driver little three inch driver is low

13:14 mass it's very fast and dissipates its energy really quick really quickly and the frequency response is a little rough up top there but the spectral decay and that all through the whole range is really clean next we're going to compare this to another three inch driver from mark audio company that little driver has a lot of cone breakup and ringing as you can see and about the twelve hundred hurt range you see a long ridge line that extends out there that's a very aggressive ringing that would be very hard to listen to and up top you see

14:01 even blowing off the graph there there's a tremendous amount of ringing and the upper ranges again that would be extremely harsh and hard to listen to so if you see things like that if you can if you can get ahold of spectral decays the spectral decay really tells you a lot about a speaker here's one that was really popular in its time this is the Merlin VSM speaker this was when somebody brought by to me for measuring and testing as you can see the the woofer has a considerable amount of stored energy and about the 1k heart reagent it it continues to continues to play several milliseconds longer than it

14:46 should that makes it a little harder to listen to little harsher but that's common you see that and a lot of speakers the next one I'm going to show you is a as one of our models we sell as a kit this is the the in one kit and this is just the on axis response this is the same response ten degrees off-axis that kind of designed it to be played a little bit more in the off-axis so I tilted the top up just a little bit at the very top but overall it's a really flat response that's a high level of accuracy if you look at the crossover plots of the drivers you see super smooth wolf or roll-off super smooth

15:32 tweeter roll-off they some really well they're in phase over a wide range overall that's about as good as you can see if you look at the horizontal off axis this is another thing I mentioned this gives you an impression of what it's doing in the room the red is on axis orange yellow green to blue those are all 10 degree increments moving off axis you see a little bit of a raised area there that's come up in about the m20 2600 of K her range not 2600 K range a little bit of a hump terrier there but

16:18 overall from 15 K Hertz and down there's still plus or minus 2 DB so still super smooth over that whole range the one of the most impressive things about the speaker the vertical off axis look at the vertical off axis you'll see that as the microphone is moved up four inches per measurement the frequency response to the speaker's stays almost unchanged so that's a speaker that's going to load the room really consistently really evenly you know it's going to have a very balanced overall in room response and then we see the the impedance curve that's that's a real good impedance curve there you see a minimum at 219 Hertz you see 6.20 minimum impedance dip

17:05 it's it's pretty smooth across the board we don't see any resonant peaks or anything that would point to any issues at all then the most impressive thing about the speaker is the spectral decay this these are this a small five and a quarter inch driver dissipates the stored energy really quick the planer magnetic tweeter dissipates its stored energy real quickly as well it just plays and stops real immediately you see nothing beyond just 1 and 1/2 milliseconds it's pretty much clean probably one of the most impressive speakers that I've seen in that regard let's contrast that with another speaker this was one that was

17:50 brought in the company no longer exists the owner passed away this was one that was called a recital the Green Line is the output of the woofer the blue line is the output the tweeter the red line is summation of the two you'll see that in some areas there the red line is above the green line and that's where it's getting additional output from the tweeter over on the tweeter side you'll see the red line actually dips below the blue line of the tweeter which means they're they're not in phase in that area so they're not summing you're not getting any additional gain in the crossover region and they're out of phase so the measurement in this case is

18:36 going to tell you that it is not gonna have a very coherent sound they're just not not in phase drivers and if you look at the impedance curve you'll see issues there as well you'll see the the impedance rise between the drivers at the crossover point completely blows off the graph it goes up to 80 ohms right there at that point so your amplifier is going to see that as an uneven load rather than a consistent load also there's two resonances that are popping up there 146 Hertz where the green dotted line is that little bump is either an internal standing wave resonance or cabinet wall residents and there's another one at the tuning frequency which is over around

19:23 sixty Hertz there there's another resonance bump there and those are things that you will hear in the playback of the speaker you're going to hear those resonances and you can see them right there in the impedance curve so like I said the the measurements are a tool they can tell you certain things that you're going to hear in the speaker they're going to point out problems but they're not and overall going to tell you how it's going to sound here's the same speaker in a spectral decay you can see at that upper range of the woofer where it was allowed to play up too far you see a lot of stored energy there where it's where it's ringing or breaking up energy from about 3k Hertz to 5k Hertz that's fairly aggressive

20:08 ringing that's going to be hard to listen to and it's going to be pretty pretty harsh over time it's not a speaker you'd want to listen to over a long time here's a spectral decay of our little studio monitor this one's pretty clean especially on four six and a half inch woofer that drops off really fast there's a few little traces there on the tweeter in pretty clean overall though that one's pretty exceptional this is an impedance curve that's pretty exceptional this is the Super seven that we designed it's all planar magnetic so you've got four neo tens and a neo three and so those are pure resistive loads you see the impedance curve it's it's almost completely balanced from one end to the other there's very little

20:54 variation there so that's something that's impressive to see in the measurement this next one is a spectral decay of a twelve inch full range driver it's called the super 12 and as you can see it's got a lot of stored energy in a lot of areas it's pretty rough flicking over to the frequency response same-same speaker the Green Line is the actual frequency response of that speaker the red line is the same frequency response after we compensated for the rising responses we put I think it was an eight or nine component count filter that we put on it

21:39 to bring the levels down to where they're within reason to where you can actually listen to it without it taking your head off and the impedance curve or the spectral decay that we're looking at is after the compensation filter so you can imagine before the compensation filters were added this was most twice as bad so definitely a really tough one to listen to by contrast this one's a supermini it's a new speaker we've designed it's a single neo tenon neo 3 in an open baffle and the planar magnetic drivers are super fast the decay rates are are really clean especially for the larger diameter driver you see it just just dropping off immediately

22:25 that one looks exceptionally well this is a measured frequency response of a TB it's a TB w8 1808 it's an 8 inch full range driver the red line is the actual frequency response you get from that driver when you put it in a box the green line that you see there is after compensation so you can see a lot more linear response after the compensation filter is put on I think it was a baffle step loss and a notch filter that it took to smooth that out and then this is the spectral decay if you're looking at the spectral decay you see a little bit of ringing in about six or eight different areas there you see the traces

23:12 that carry out a little longer that's kind of indicative of what you get with a lot of these wideband drivers so you're getting a lot of ringing but not well I would say a lot of rain but you're getting ringing across the board in that thing here's another full range driver this one was from a company up in Canada I don't think they're around anymore either this is a Unity audio as you can see there's some peaks in the upper frequency range there from about 4 K Hertz to 7k Hertz there's some pretty aggressive if you look at the off-axis response because it's a single wideband driver it does it's not gonna have as good off

23:58 access response to something with a tweeter you see the frequency response as you move further off access just completely drops off that's pretty indicative of those four range drivers if you look in the impedance curve there's a couple of blips there's one right at the tuning frequency there's another one up at about 1700 Hertz that little bump in the impedance is indicative of possibly some breakup or some ringing the one down is low at the tuning frequency around 80 Hertz it may be a port resonance but there's from that measurement you can definitely gather some information that tells you a little bit about how that speaker is going to sound and if you look at the spectral decay you'll see

24:43 quite a bit of stored energy and ringing up in the upper frequency range where that where those Peaks are that's definitely gonna be pretty rough to listen to the next speaker it's a bit unusual speaker this is also a speaker that's no longer production the owner of the company has passed several years ago this was a VM PS 626 R and this speaker had a a well I guess what they call a waveguide over the mid-range driver it was really a restrictor plate I guess you could say it's it reduced the surface area down to a little slit and it was designed to kind of help control

25:29 off-axis response it really jacked up the frequency response that's that's a pretty rough frequency response so you're looking at that you can tell it's it's in and it's out it's it's 6 or 10 DB louder than it should be in some areas and not so in others this next measurement is the same speaker with the cover taken off of it so that's with all of the driver exposed you can tell it improve the response considerably that was the best curve I can get out of it including all the adjustments that were made if you look at the spectral decay this is uh this is with the front cover on and the so called waveguide you'll see lots of stored energy here the

26:15 woofers got a lot of long decay rate on the woofer in this configuration and right in I'd say around 3k Hertz you're seeing an internal resonance that was caused from the waveguide or the baffle that was placed on it that's internal reflections with it you know from behind it and it caused a lot of ringing the next measurement we'll look at is the best measurement I can get out of it which is the red line and then the green line I think it's I just wanted to make sure something wasn't wrong I threw one of our speakers up there Oh just to get a idea of the sensitivity

27:02 and make sure the sensitivity wasn't wrong because sensitivity was so low on that speaker this is actually the same speaker it's the same VM PS speaker with an actual crossover designed for it that takes into account the acoustic output of the drivers so much cleaner response each drivers within its own range they're in phase and looking at the spectral decay you'll see it's it's much cleaner the woofer still has a little bit of energy down there in the lower range there that's a little bit of a story energy that's just within the driver that can't be gotten out of it you can see it back in the original MP or an original spectral decay but

27:48 pulling it back much further notice I didn't let it play up as high it crossed at around 500 Hertz that took some of that breakup away from it if you look in the frequency response even with the filter I had on it at 1k hurt you see a little bump there down low I've moved that breakup down pretty low to try and get it out of it but still it's a little bit there so in the spectral decay you still see a little bit of that there it's a little bit of stored energy you just can't get all of it out of it the next thing we'll look at here the this is a spectral decay of the XLS encore it's a kit that we offer six and a half inch woofer and a dome tweeter

28:34 again this is another one that's very exceptional a lot of speed no stored energy that's it for the measurements I just want to throw a few of these up here walk you through these things and let you guys get an idea of how to read that stuff and what things matter and maybe you'll have a little better idea when you look at measurements then getting a more useful information from it that's it for today thanks for dropping in and I hope this was useful let us know in the comments section see you guys next week