hi,
Most of the comercial hifi subs use single 12 or 15 inch drive units some use double. And they all claim to go very low in the region of 15hz. What size drive unit and enclosure do we really need to get a flat response to say 17hz?
How accurate are the manufacturers claims?
How does the room size affect the response?
Most of the comercial hifi subs use single 12 or 15 inch drive units some use double. And they all claim to go very low in the region of 15hz. What size drive unit and enclosure do we really need to get a flat response to say 17hz?
How accurate are the manufacturers claims?
How does the room size affect the response?
Low frequency waves are very long compared to high frequencies ,and to complete a full cycle it takes time ,and space .As a 20 Hz tone needs about
10 meters to complete 1 cycle ,you'll understand why room affects the reproduction.
Depends . Large scale production makes sure that a project has to pass many stages before exiting the factory. Advertising is another thing.
The larger the driver ,the easier it reproduces bass freq .That is related to wave length . But there are other issues , like cone excursion and power compression ,and heat . Once you solve these ,the box and the amps are bonuses !
With subwoofers like that, they'll never go very loud and that low (displacement limited), even with the 1kW of amplifier power.
The power is needed to overcome the deficiencies of trying to run a sealed box as a subwoofer. They're not very efficient, but at least they go low. It's basically Hoffman's Iron Law in effect - small size, efficiency, low frequency extension. Pick two. In this case, they've left out efficiency, which is understandable as amplifier power is cheap nowadays.
I know B&W have switches to pick between maximum LF extension and maximum SPL. And the claims are usually either in-room, or the -10dB point. In the case of the latter, my sub will go to 21Hz, using a pair of 8" drivers and 100w.
The power is needed to overcome the deficiencies of trying to run a sealed box as a subwoofer. They're not very efficient, but at least they go low. It's basically Hoffman's Iron Law in effect - small size, efficiency, low frequency extension. Pick two. In this case, they've left out efficiency, which is understandable as amplifier power is cheap nowadays.
I know B&W have switches to pick between maximum LF extension and maximum SPL. And the claims are usually either in-room, or the -10dB point. In the case of the latter, my sub will go to 21Hz, using a pair of 8" drivers and 100w.
By default i never trust manufacturer's claims. Those measurements could have been made in a smallish room with optimal placement of the sub and the mic. They are usually pretty good at giving you an estimate but i never ever trust them. There are just too many ways to play with the numbers and room to get what marketing wants.
I am pretty pessimistic arnt i...
I am pretty pessimistic arnt i...
The trouble with most FR specs is they are made at low power. You could probably design a 5" driver to do 15Hz, but as SPL capability at a given frequency is determined by driver volume displacement (Sd x Xmax) then the theoretical 5" driver will be limited in output. There are quite a few modern sub drivers with good motors and large diaphragms and Xmax capability.
What's well worth reading are Illka's sub tests, to see what some commercial and DIY systems are actually capable of, then figure out what you want/need and start modelling. His tests are a couple of years old now so don't include some drivers like the Maelstroms.
These test would be the most interesting though, has anybody else tested them? I would like to know how much of the excursion can be used with <10% THD. One good rival would be BMS 18N860. BMS's drivers have very linear motor, which I know from experience
Kevin has posted Xmax is specified at 70% Bl and the curves of Bl/X have been very good.These test would be the most interesting though, has anybody else tested them? I would like to know how much of the excursion can be used with <10% THD. One good rival would be BMS 18N860. BMS's drivers have very linear motor, which I know from experience
The BMS looks good but they are designed for 2 different markets and it has 19mm vs 33mm Xmax so which would be better will be determined by application.
Yep, the conservatively calculated (lengh of the VC - magnetic gap height) xmax of 18N860 is +/- 19mm. In maelmstoms the xmax is not stated the same way.
The cone of 18N860 can be moved approx +/- 30mm before the suspension starts to limit the excursion: YouTube - BMS 18N860 20Hz sine tone#3
In maelmstoms the biggest possible (not actual) source of distortion could be, I think, that the medium-BL motor has to move/drive very heavy cone against the air of a closed box. In this vid 18 inch Mael makes strange noise at quite moderate excursion (approx half of the specified +/- 32mm): YouTube - maelstrom 18 gen II 20 hz testtone bass test.MP4
According to Hifimaailma's (Finnish hifi magazine) test, SDX15 which also has XBL^2-motor, can move approx +/- 8mm in 150l@20hz bass reflex and +/- 7mm in 100l closed box before it hits 10% distortion limit. In BR the woofer generated 110dB pressure at 40Hz in half space and in closed box 106dB (limited to 10% distortion). Maximum pressures according to WinISD would have been 118dB and 115,5dB accordingly.
One can look the distortion performance of 18N860 at 1000 watts from the manufacturer's spec sheet. In the distortion graph the THD% is approx -20dB/10% at the whole spectrum, while the SPL at 40Hz is approx 122dB (the 170l@32Hz box is far from being optimal since the response starts to drop so early).
It's true that XBL^2 motors have very long excursion indeed. I'm however only interested of the linear excursion (THD% <10%), which can be, and usually is, quite a different story than calculated or claimed xmax (I'm not saying that this is the case with Maels).
From these points of view I would be very interested to see actual measurements of Maelmstroms. Measuring is fairly easy, one can do it at back yard with laptop, measurement mic, mic preamp and ARTA/Holm Impulse.
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I shall await your tests then. The M18 is available from the UK and the BMS is distributed through the EU. I cannot get the 18N860 as the US distributor does not return calls and the EU distributors are expensive both in price and shipping (yes I understand to consider VAT). When I got my 4590 directly from BMS I paid more in fees/charges at this end than I did for the drivers. The 860 does not fit into any of the construction plans I have either.From these points of view I would be very interested to see actual measurements of Maelmstroms. Measuring is fairly easy, one can do it at back yard with laptop, measurement mic, mic preamp and ARTA/Holm Impulse.
Found one comment regarding TC Sounds LMS Ultra 5400 from here: TC Sounds LMS Ultra 5400 18" DVC Subwoofer | Parts-Express.com
I think many people do measure their woofers but the results rarely end up on the Internet, which is a shame.
Well there's no data in the form of measurements to back it up, so it's still no more than assertion. And, it's not an 18N860.
FWIW, I'm not arguing either way particularly, but the quoted comment above gives me no more confidence than a 6moons review that it's accurate and fair.
Show me the measurements using the same methodology (why I linked Illka's) and there may be a case. I have no doubt about the performance of the LMS because I've seen several different measurements that show it is excellent. By the same token, random youtube videos constitute no more than entertainment
Still for what one would cost me landed to my door, I could probably get 3 M18. Put two in a push-pull manifold loaded sub a la djk, and it may be a better overall system. As I said earlier, depends upon implementation.
FWIW, I'm not arguing either way particularly, but the quoted comment above gives me no more confidence than a 6moons review that it's accurate and fair.
Show me the measurements using the same methodology (why I linked Illka's) and there may be a case. I have no doubt about the performance of the LMS because I've seen several different measurements that show it is excellent. By the same token, random youtube videos constitute no more than entertainment
Still for what one would cost me landed to my door, I could probably get 3 M18. Put two in a push-pull manifold loaded sub a la djk, and it may be a better overall system. As I said earlier, depends upon implementation.
Interesting assertions of the two different standards for the same thing Xmax. Many manufacturers don't even mention it sometimes. That's a good case for a new post or for a future Audiophiles/diyAudio article.
One, the first, is calculated (from a pseudo Xlim or Xmax.limit of movement). As in AE Speakers.
The other, second one, is measured (where THD=>10%). As for Selenium.
An interesting article for the Professor
Trading SPL for Extension in Subwoofers - A Current Trend? — Reviews and News from Audioholics
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Inductor said:
Btw., magnetic flux's changes, due to coil's movement, changes also inductance. Quantity of inductance's variance correlates with intermodulation distortion (IMD%).
Nominal inductance (= inductance value when the coil is at it's resting point, which in Maels is very high compared to other advanced motors, 4mH) affects directly to middle and upped bass distortion, in closed systems above Fc.
Both nominal inductance and inductance's variance due to coil's movement should be should be low if shorting rings are applied properly. AS's page does not work at the moment, but if I rememeber correctly Lambda motor has very low inductance despite that the voice coil is quite large. Also BMS (with 4" in diameter and 2" in height voice coil) has 0,81mH inductance due to three shorting rings. edit: AE TD18H+ has 2,5" inch voice coil, which lenght is maybe 40mm(?) and an inductance of 0,42mH.
Cone's movement also lowers suspension's compliance (Cms).
Ilkka stated at a finnish ht forum that he had measured SDX10 and SDX15 woofers:
SDX15's useful excursion is between 8,1 - 12,4mm according to his test which is quite interesting because it correlates fully with Hifimaailma's actual SPL measurement, from which I simulated what the cone movement was at given SPL and got +/-8mm. Woofer is actually ~8mm limited in (linear) xmax regardless the specified +/-28 mm.
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Hi,
I doubt BMS´s claim of +-19mm of linear stroke as I doubt most manufacturer´s claims about the stroke capability of their drivers. At least with its smaller brother the 18N850 (claiming +-13mm, but otherwise beeing nearly identical) You can feel by hand how the spider stiffens above ~8mm of excursion. Both, the 850 and 860 feature rather small diameter spiders with a strong progression. The voice coils are wound linear, so they are not able to counter the loss of BL-product nor the spider´s progression. On the good side I found that they perform quite silent, which is a sign of good venting.
jauu
Calvin
I doubt BMS´s claim of +-19mm of linear stroke as I doubt most manufacturer´s claims about the stroke capability of their drivers. At least with its smaller brother the 18N850 (claiming +-13mm, but otherwise beeing nearly identical) You can feel by hand how the spider stiffens above ~8mm of excursion. Both, the 850 and 860 feature rather small diameter spiders with a strong progression. The voice coils are wound linear, so they are not able to counter the loss of BL-product nor the spider´s progression. On the good side I found that they perform quite silent, which is a sign of good venting.
jauu
Calvin
The decreasing compliance of the suspension is not a problem at all at those excursions.
FR and THD graph (click) in the specs show that the 18N860 plays ~10% THD at 1000 watts. When simulating these parametres (170l, 32Hz tuning, 1000w power) in WinISD, the program shows that the cones moves 11 -12,1mm between 55 - 40Hz. However the THD in the spec sheet does not alter between different excursions, but stays constantly at approx. 10%. Note that the box is/might be far from being optimal for 860...
The same phenomenom can be seen even with 18S430v2, which has specified xmax of 7,5mm but can actually move +/- 11,5mm (or more) linearly according to manufacturer's THD sheet (which is nearly identical with 860)! Simulating 430v2 in 170l box@32Hz@1000W in WinISD shows thaty the longest excursion is approx. 11,5mm at 45Hz, but it does not show in the THD graph at all.
Here is my excursion test of 18S430v2: YouTube - BMS 18S430v2 20Hz sine tone . That excursion is not suspension limited; one could push it more but I did not see any point in that. The THD rises towards the last millimetres, but 30mm p-p movement comes quite easily, propably stays below 10% THD in a box, or at least is completely usable in a movie's bass transient. One can also find excursion videos of 860, vid #3 is the real deal. In vids #1 and #2 the amp clipped because I drove two 860's.
These are my experiences with these two woofers, which I bought four of each kind after testing 18S430v2, PD186, Faital Pro 18HP1020 and 18sound 18NLW9600. BMS's 18S430v2 were the quietest of these four and could make as long of an excursion while sounding as good as or better than 18sound, which has xmax of 14mm and x-damage of 35mm and costs nearly 550 euros.
18N860 has bigger spider (one roll bigger) than 18S430v2 so it can move more easily than it's little brother, that can already move linearly much more than the calculated linear xmax is. Based on my experiences, the 860 can make an excursion of approx. +/- 20mm while sounding as bad as 430v2 at +/- 10mm excursion.
If you feel that the suspension it too tight, maybe you should give them some "sine tone treatment". The suspension loosens up in the burn in and suspension related noises at high excursions drop significantly.
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Hi,
THD must alter between different excursions....The datasheet shows a rather constant THD vers frequency-behaviour.
What could You possibly prove with excursion videos at Youtube? Noise maybe, but anything else??
Longthrow or superlongthrow drivers therefore need vey large diameter spiders and which are not easyto source (BMS experienced problems with spiders which delayed introduction of the driver to the market considerably).
The BMS features quite small diameter spiders and progression of the spider sets in way before the claimed linear excursion value is reached.
Since the voicecoil is wound in a simple linear fashion there is nothing to counter the progression of the suspension system.
jauu
Calvin
THD must alter between different excursions....The datasheet shows a rather constant THD vers frequency-behaviour.
What could You possibly prove with excursion videos at Youtube? Noise maybe, but anything else??
The problem is not the driver´s excursion capability but it´s linear excursion capability. That´s why I talked about the progression in stiffness of the spider and not its initial stiffness. I always do 2 measurements. The first with the new driver and a second after at least 24h of a burn-in cycle with shaped sines. While the suspension mostly hast softend slighty after the burn-in, the spider´s behaviour over excursion remains the same. Every spider runs into progression sooner or later (meaning that stiffness increases non-linearly). The smaller the spider diameter the sooner this must happen.
Longthrow or superlongthrow drivers therefore need vey large diameter spiders and which are not easyto source (BMS experienced problems with spiders which delayed introduction of the driver to the market considerably).
The BMS features quite small diameter spiders and progression of the spider sets in way before the claimed linear excursion value is reached.
Since the voicecoil is wound in a simple linear fashion there is nothing to counter the progression of the suspension system.
jauu
Calvin
Hi,
THD must alter between different excursions....The datasheet shows a rather constant THD vers frequency-behaviour.
What could You possibly prove with excursion videos at Youtube? Noise maybe, but anything else??
The problem is not the driver´s excursion capability but it´s linear excursion capability. That´s why I talked about the progression in stiffness of the spider and not its initial stiffness. I always do 2 measurements. The first with the new driver and a second after at least 24h of a burn-in cycle with shaped sines. While the suspension mostly hast softend slighty after the burn-in, the spider´s behaviour over excursion remains the same. Every spider runs into progression sooner or later (meaning that stiffness increases non-linearly). The smaller the spider diameter the sooner this must happen.
Longthrow or superlongthrow drivers therefore need vey large diameter spiders and which are not easyto source (BMS experienced problems with spiders which delayed introduction of the driver to the market considerably).
The BMS features quite small diameter spiders and progression of the spider sets in way before the claimed linear excursion value is reached.
Since the voicecoil is wound in a simple linear fashion there is nothing to counter the progression of the suspension system.
jauu
Calvin
I ment that it does not show in the THD plot, that the 430v2 exceeded it's linear excursion between ~80-37Hz. 1) The linear excursion was exceeded and 2) the suspension got stiffer, but THD% did not rise. In other words, the excursion stayed linear.
Stiffening suspension is a bad thing once it starts to affect the linearity of the stroke. Before this point, I don't really care what the suspension does. According to your measurements, how does the stiffening suspension affect the linearity of the stroke? At what excursion does the THD% exceed 10%/-20dB threshold (which is usually considered the audibility threshhold of the bass frequencies)? How much is the THD% at extreme > +/- 25mm excursions like in my vid?
I think one should be more worried of the flux modulation that the voice coil's movement causes, which causes Bl and inductance variation. Have you measured how BMS's motor fares in this regard? With triple shorting rings and very low nominal inductance, I'm prone to believe that woofers have very linear motor system. Given manufacturer's THD plot supports this "belief".
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Calvin said:
Here's the simulated cone excursion and manufacturer's THD plot. It shows also rather constant THD versus excursion behaviour because there is no correlation between excursion and THD - even though the woofer had exceeded it's calculated linear xmax between 80 - 37Hz.
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Hi,
if You want to proove the THD behaviour over power, then show us a THD versus power diagram! The amplitude response of SPL and THD versus frequency at one(!) certain power value doesn´t tell You what You want to know. That the THD stays nearly constant over frequency is an indicator that they put some effort into the drive system and that the BR-alignment fits the driver and is very effective inTHD-reduction within its working range.
The true driver behaviour would become obvious when measured in an IB, or very large CB, not in a BR. To see how the spider behaves we needed the K(m) curve.
jauu
Calvin
if You want to proove the THD behaviour over power, then show us a THD versus power diagram! The amplitude response of SPL and THD versus frequency at one(!) certain power value doesn´t tell You what You want to know. That the THD stays nearly constant over frequency is an indicator that they put some effort into the drive system and that the BR-alignment fits the driver and is very effective inTHD-reduction within its working range.
The true driver behaviour would become obvious when measured in an IB, or very large CB, not in a BR. To see how the spider behaves we needed the K(m) curve.
jauu
Calvin
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