Out of curiosity I was plugging some of the smaller Fostex very low Xmax drivers into Linkwitz's SPLmax spreadsheet. The results show that drivers such as the FE126E with an Xmax of 0.35mm and the FE108EZ with an Xmax of 0.28mm can't break 90db at 300hz, much less 100hz or lower.
I've used these drivers and I know for a fact that these predicted results are not correct, but where is the error? Do these types of drivers have linear operation far past Xmax? Visaton, eg, claims linear operation for the B200 up to +/-3mm, yet the Xmax is only 2mm, as determined by the VC dimensions. How can we determine the true performance limitations of such drivers?
I've used these drivers and I know for a fact that these predicted results are not correct, but where is the error? Do these types of drivers have linear operation far past Xmax? Visaton, eg, claims linear operation for the B200 up to +/-3mm, yet the Xmax is only 2mm, as determined by the VC dimensions. How can we determine the true performance limitations of such drivers?
They are very dynamically limited. Horns help quite a lot. But this sort of thing puzzled me too.
I asked awhile ago what sorts of bass energy one could expect whith different types of prgram material at various listening levels. Nobody knew, and instead of doing a decent experiment, I played some various music at 90-95db A weighted at the listening seat (radio shack meter), and measured my drivers (8" with 2mm xmax) excursion in both sealed and vented enclosures. In sims, neither of my enclosures approaches 90db at 80hz without hitting xmax. However, with all of the program material I tried (everything from chamber music to rock), 95db in either enclosure didn't exceed .5mm of excursion (P-P) as measured at the whizzer edge with a ruler. On the contrary, an 80hz since wave at 90db get's 'em shakin'.
Outside of special effects (HT) there just isn't that much energy down there. Music is not linear. It's my opinion that the sims are telling the truth, but playing music and sine waves at 90db are completely different things.
Paul
I asked awhile ago what sorts of bass energy one could expect whith different types of prgram material at various listening levels. Nobody knew, and instead of doing a decent experiment, I played some various music at 90-95db A weighted at the listening seat (radio shack meter), and measured my drivers (8" with 2mm xmax) excursion in both sealed and vented enclosures. In sims, neither of my enclosures approaches 90db at 80hz without hitting xmax. However, with all of the program material I tried (everything from chamber music to rock), 95db in either enclosure didn't exceed .5mm of excursion (P-P) as measured at the whizzer edge with a ruler. On the contrary, an 80hz since wave at 90db get's 'em shakin'.
Outside of special effects (HT) there just isn't that much energy down there. Music is not linear. It's my opinion that the sims are telling the truth, but playing music and sine waves at 90db are completely different things.
Paul
John,
This is something I posted on the Madisound forum back in 2002 that attempted to explain why I am not that concerned about Xmax when music is being played.
One last thought, when using a bass reflex or a TL the situation with Xmax gets even better because the driver motion is significantly attenuated at the tuning frrequency. For an OB the situation is as described above. I have been running Fostex and Lowther full range drivers in ML style of enclosures for the past few years and have not had any real problems with a driver exceeding the 1 mm Xmax value specified by the manufacturer and producing audible problems or even worse damage to the driver.
Hope that helps,
Martin
This is something I posted on the Madisound forum back in 2002 that attempted to explain why I am not that concerned about Xmax when music is being played.
One last thought, when using a bass reflex or a TL the situation with Xmax gets even better because the driver motion is significantly attenuated at the tuning frrequency. For an OB the situation is as described above. I have been running Fostex and Lowther full range drivers in ML style of enclosures for the past few years and have not had any real problems with a driver exceeding the 1 mm Xmax value specified by the manufacturer and producing audible problems or even worse damage to the driver.
Hope that helps,
Martin
Paul,
I'm not really even thinking about bass. I see the little drivers exceeding Xmax with bass content in music. I'm talking about 200-300hz or more where the alignment isn't helping, and we're left with the driver only output. If my little 108's are Xmax limited to 84db at 300hz at 1m, how can I possibly play any semblence of good music from only a pair of them at 95db+ at my listening position? Yet I'm able to do so. We're looking at 1/4 the surface area and 1/7 the Xmax of your 8's.
Martin,
Thanks, I need let your explanation soak in.
I'm not really even thinking about bass. I see the little drivers exceeding Xmax with bass content in music. I'm talking about 200-300hz or more where the alignment isn't helping, and we're left with the driver only output. If my little 108's are Xmax limited to 84db at 300hz at 1m, how can I possibly play any semblence of good music from only a pair of them at 95db+ at my listening position? Yet I'm able to do so. We're looking at 1/4 the surface area and 1/7 the Xmax of your 8's.
Martin,
Thanks, I need let your explanation soak in.
Just a quick note. The term Xmax has different interpretations. Some manufacturers spec Xmax as excursion in one direction only while others reference the total positive and negative throw of the driver. This can present problems when modelling, and for all I know, different software may assume one convention or the other. There needs to be one standard, everyone agrees on that, but yet................
Best Regards,
TerryO
Best Regards,
TerryO
John,
xMax as calculated by pole piece / voice coil dimensions is a worst case scenario, assuming that magnetic energy is "chopped off" as soon as the vc starts to leave the air gap. Fact is, however, the magnetic field reaches further out and the vc still gets some shove - the decline is gradual, not sudden.
Pit
xMax as calculated by pole piece / voice coil dimensions is a worst case scenario, assuming that magnetic energy is "chopped off" as soon as the vc starts to leave the air gap. Fact is, however, the magnetic field reaches further out and the vc still gets some shove - the decline is gradual, not sudden.
Pit
johninCR said:
I just guess, Martin actually knows stuff.
Let's say I play whatever pitch has a fundamental of 300hz on my trombone (about an F?), and the SPL meter registered 95db. When I play that note, then second harmonic (600hz) is nearly as strong as the fundamental, and the third is a little less strong that the second. They'll trail off, but you could still measure the eight or ninth. All of them would sum to 95db. If you could isolate the 300hz fundamental, it would be well below 95db (if I'm right.) 300hz is awfully low for a trumpet, but at 600hz, there is a good chance the 3rd harmonic would be louder than the fundamental!
Now, to match the acoustic power of my trombone playing, you'd have to have some serious kit. The 108's wouldn't come close. But many speakers can sound something like hearing me from an orchestra hall balcony. I've got some little old fullrangers in an open back cabinet. They don't sound like an orchestra, but they get closer than I thought they would. My big speakers come pretty close in my not-too-large room.
My point is that music is not a sine wave, nor made of anything that looks like them.
Again, I might be absolutely full of it. I'm an M.M., not an E.E.
Paul
Hi,
I had build a BLH for my Coral Flat 6B. The Flat 6B's have small Xmax too. Yet, they actually produce bass.
From visual observasion, you hardly see any cone movement even the window is rattling...
Is this the result of the cone being "loaded" and "pressure on both sides of the cone being "equilised?
Cheers
A_I
I had build a BLH for my Coral Flat 6B. The Flat 6B's have small Xmax too. Yet, they actually produce bass.
From visual observasion, you hardly see any cone movement even the window is rattling...
Is this the result of the cone being "loaded" and "pressure on both sides of the cone being "equilised?
Cheers
A_I
even large drivers in direct radiator can have more excursion than I like and when reach say 4mm peak to peak can "gargle" with say sustained bass and flute passage. do some FR not gargle?
the reflex here is "equivalent" to the K15 sans front section and Z input looks similar other than K's 3rd z peak.
the reflex here is "equivalent" to the K15 sans front section and Z input looks similar other than K's 3rd z peak.
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Hello audio idiot. You are not living up to your name. I think you are spot on. Cone excursion in a sealed enclosure is far greater than that of a BR at box res. The energy from the port loads the cone, and the area of the cone is added to the area of the port, so the radiation resistance is improved.
Paul, music isn't sinewaves, if it were we wouldn't listen to it, and muso's would be erradicated. Be careful comparing your speakers to a live trombone. It's the ultimate test, and could become very frustrating.
Sound reproduction at it's finest will not compete with a live instrument, especially a horn. Your observation with the harmonics is very valid. Thats why instruments have their unique sound. Take some measurements of the horn on the trombone, and look at some horn designs and you'll see why the 2nd harmonic is louder than the fundamental. Try that with a sax.
It's not good to try to match SPLs from speakers with live music. A conductor in front of a 75 piece orchestra is subjected to over 115db SPL (at 15ft, but they don't say where that starts) That's about 130db at 1 metre. Lot's of speakers will protest and emit strange noises followed by nasty smells trying that.
Paul, music isn't sinewaves, if it were we wouldn't listen to it, and muso's would be erradicated. Be careful comparing your speakers to a live trombone. It's the ultimate test, and could become very frustrating.
Sound reproduction at it's finest will not compete with a live instrument, especially a horn. Your observation with the harmonics is very valid. Thats why instruments have their unique sound. Take some measurements of the horn on the trombone, and look at some horn designs and you'll see why the 2nd harmonic is louder than the fundamental. Try that with a sax.
It's not good to try to match SPLs from speakers with live music. A conductor in front of a 75 piece orchestra is subjected to over 115db SPL (at 15ft, but they don't say where that starts) That's about 130db at 1 metre. Lot's of speakers will protest and emit strange noises followed by nasty smells trying that.
Geoff & all,Geoff H said:
it's no effing good to match ANYTHING against live music. Even trying to reproduce an acoustic guitar in your living-room means boxes that will take up the space your furniture (and your wife - we're talking facts, not hopes) feel currently at home in.
And even if you are a bachelor with unlimited space and funds, there's the wee problem of getting proper recordings - and as any honest sound engineer will tell you, that's a dream he shares with us.
Lads, I'm not talking about the rubbish the mp3 generation deafen themselves with - even a lower-class LP recording's 40dB dynamic range can clobber most of that ****. But have you ever lived in a town with a music academy? Out on the lawn in summer, somebody plays the violin and two trombones and a snaredrum take up the theme...abandon hope, all ye who enter here, there's just no way to reproduce that amount of goosebumps.
OK- long oratory, little sense...all I wanted to say is we'll never get there, but we try and we have lots of fun sniffing sawdust and sharing results.
Pit
el'OL,
Even if the useable excursion of the FE126 was 2mm vs the quoted Xmax of 0.35 , the predicted limits still don't make sense with a max of 92db at 150hz. The explanation must lie in what Martin and some others have touched on, that music is different and somehow the summed output of the complex mix of difference frequencies enables a driver to play music much louder than it's limits playing simple tones would suggest. I guess I'll just high pass at 300hz and worry only about thermal limits.
Now I'll hijack my own thread and change the subject. Who wants to take a shot at explaining why the sound from a large driver is different than a small driver. I'm not talking about tonal difference, and I don't believe it's just a difference in polar response. There seems to be some audible spatial difference in a wave launched from a large cone vs a small one. I'm fairly sure that it's not just a psycho-acoustic difference.
Even if the useable excursion of the FE126 was 2mm vs the quoted Xmax of 0.35 , the predicted limits still don't make sense with a max of 92db at 150hz. The explanation must lie in what Martin and some others have touched on, that music is different and somehow the summed output of the complex mix of difference frequencies enables a driver to play music much louder than it's limits playing simple tones would suggest. I guess I'll just high pass at 300hz and worry only about thermal limits.
Now I'll hijack my own thread and change the subject. Who wants to take a shot at explaining why the sound from a large driver is different than a small driver. I'm not talking about tonal difference, and I don't believe it's just a difference in polar response. There seems to be some audible spatial difference in a wave launched from a large cone vs a small one. I'm fairly sure that it's not just a psycho-acoustic difference.
I was thinking...
Any driver can produce bass, even a tweeter. Only thing is it won't reach far and won't go anywhere near loud.
A bass frequency wave only has more wavelength, a low excursion driver only can't produce the bass very loud, but can go just as deep as a similar high excursion driver. (unless it can handle mechanical torture very well and Qts is high, the swing the motor adds to the cone (regardless of voice coil winding height) is in some cases responsible for very high efficiency).
Surface improves sensitivity...
Many low excursion, low fs bass drivers have higher Qts and therefore tend to sound more bass heavy. The relative sound reproduction can be bass amplified due to boundary effects and enclosure Q too offcourse.
Manufacturers sometimes show x-max, sometimes x-nominal. X-max I think is due to mechanical properties of the driver and x-nominal rather shows upto which point the cone is being displaced by the motor.
Just some assumptions, I'm not a theory expert...
Any driver can produce bass, even a tweeter. Only thing is it won't reach far and won't go anywhere near loud.
A bass frequency wave only has more wavelength, a low excursion driver only can't produce the bass very loud, but can go just as deep as a similar high excursion driver. (unless it can handle mechanical torture very well and Qts is high, the swing the motor adds to the cone (regardless of voice coil winding height) is in some cases responsible for very high efficiency).
Surface improves sensitivity...
Many low excursion, low fs bass drivers have higher Qts and therefore tend to sound more bass heavy. The relative sound reproduction can be bass amplified due to boundary effects and enclosure Q too offcourse.
Manufacturers sometimes show x-max, sometimes x-nominal. X-max I think is due to mechanical properties of the driver and x-nominal rather shows upto which point the cone is being displaced by the motor.
Just some assumptions, I'm not a theory expert...
Most of the Fostex drivers with low xmax are low Qts drivers meant for use in rear loaded horns.
Horns are acoustic amplifiers - the back loaded horns ramp up the bass response acoustically, bringing up the bass without the driver having to move very far at all at those low frequencies. Without the horn, you'd have to use a baffle step correction circuit to compensate which lowers the efficiency and I'd venture the driver would run out of steam faster as well.
Compression drivers are another perfect example. They're very small and move very little yet can produce a lot of dynamic SPL because they have horns in front of them that improve the efficiency with which the driver couples with the air. There are bass compression drivers and they're quite small in comparison to large, high excursion woofers, but they need enormous horns to work.
I'm planning on building a BIB for a pair of FE206E drivers that I have on hand and I hope to experience this low bass amplification in a big way!
Horns are acoustic amplifiers - the back loaded horns ramp up the bass response acoustically, bringing up the bass without the driver having to move very far at all at those low frequencies. Without the horn, you'd have to use a baffle step correction circuit to compensate which lowers the efficiency and I'd venture the driver would run out of steam faster as well.
Compression drivers are another perfect example. They're very small and move very little yet can produce a lot of dynamic SPL because they have horns in front of them that improve the efficiency with which the driver couples with the air. There are bass compression drivers and they're quite small in comparison to large, high excursion woofers, but they need enormous horns to work.
I'm planning on building a BIB for a pair of FE206E drivers that I have on hand and I hope to experience this low bass amplification in a big way!
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