Definitive Technology Descend DN15 15" Subwoofer Review

TLS Guy

TLS Guy

Seriously, I have no life.
Do you think Def Tech's drivers & DSP tuning are responsible for its middling performance numbers? Surely if they added a 1000W amp it would've brought much greater headroom in the mid-bass region like REL's HT/1510 Predator II, there is absolutely no excuse for them to charge $1799 only to include a 500W amp, it's understandable for their smaller DN12 12" variant to have 500W like REL's 1205 MkII or the Monoprice M-12 V2 but the other companies had the smart sense to employ more powerful 1000W amplification for their 15" counterparts, it truly is amazing that the Monoprice SW-15 @$300 with a 600W amp offers greater punch even if it isn't as refined sounding as the DN15.
You are recent member, and welcome. We cover this often. There are hard and fast laws of physics with audio reproduction and that is especially crucial in considering subs.

First is that amp power can not be considered in isolation. A sub driver with 3db higher sensitivity will have the same acoustic output with 500 watts as one with 3db lower sensitivity which will require a 1000 watt amp for the same output.

So, you may ask why are all subs not designed with high sensitivity? The reason is that there is an inverse relationship between sensitivity and bass extension. That is why pro subs used in cinemas and live theater performances have relatively low bass extension as sensitivity is paramount.

How the sub is loaded makes a difference, in general the bass output is highests for horns, then pipes and ported/passive radiator close seconds. Sealed are way at the bottom of the heap, and will have native f3 in the 40 to 60 Hz range, and require a 12db per octave boost below their native F3. That amounts to a massive acoustic efficiency penalty, and why they require such monstrously powerful amps. One other point is that a sub will not go significantly lower than the driver fundamental resonance known as Fs. Only sealed subs can be boosted below F3 that is the 3db drop in output point. The reason is that the driver decouples from the loading of the enclosure abruptly in other designs. So response falls off like a rock.

The take home is that you can have enormous bass output from an efficient design with comparatively little power. That is true in my approach, but the enclosures are very large.

As far as high frequency extension that is not usually of great concern in sub designs. That is because subs are often placed away from the main speakers and you don't want localization. However there are other issues. As Shady pointed out, heavy cones, which tend to a lower Fs, are not going to have much top extension as a rule. Even more to the point big heavy cones are likely to break up, which means the cone does not move as an entity. These break up modes result in nasty frequency peaks which you don't want, and require higher frequencies to be smartly rolled off.

However, you do have a point about the power of music for a couple of octaves above where subs are crossed over. You are correct if you are trying to point out there is a lot of power in that range. To make matters worse it is where speakers with smaller drivers and narrow fronts will be transiting from monopole to omniole. This is known as the baffle step response and has to be equalized for, with a 6 db boost below that transition frequency.

To compound the problem you can't really test speakers like you can other components like amps, where you can drive with as much power as the amp can take and measure the distortion. Speakers on the other hand have wildly different power and output capabilities at various frequencies, which are always totally unknown except from careful listening. In my view this is the largest confounding factor in choosing a speaker system and you won't get much clue of that aspect from standard speaker measurements.

When I design, I look carefully at the frequency power ranges of the music I listen to, which is pretty much classic, opera and choral music. This program material has massive power demands below 1500 Hz down to 80 Hz. Yes, you have it right, above sub range.

So in my main system, I don't actually use sub drivers, but four powerful 10" SEAS Excel drivers, with an Fs of 20 Hz. With active drivers I can also supplement the mid drivers below the transition frequency. The design is integrated in the main speakers, to make seamless full range speakers, with no sub in the traditional sense.
But that results in room spl. than you could ever use across the whole frequency spectrum. The system uses modified stopped pipes known as transmission lines. The system is not commercially viable due to size, and what would be enormous production costs. But is gives me a powerful unique system.
 
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oniiz86

Enthusiast
Thanks so much @TLS Guy for the highly informative post, I was just curious as to why the high frequency response discrepancy between the smaller DN12 12" only managing 100Hz compared to the DN15 managing 300Hz, I thought it being a smaller lighter cone compared to the DN15 15" it would have been much higher in frequency response but I guess Def Tech have used lower sensitivity drivers for the 12" variant.
 
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shadyJ

Speaker of the House
Staff member
Thanks so much @TLS Guy for the highly informative post, I was just curious as to why the high frequency response discrepancy between the smaller DN12 12" only managing 100Hz compared to the DN15 managing 300Hz, I thought it being a smaller lighter cone compared to the DN15 15" it would have been much higher in frequency response but I guess Def Tech have used lower sensitivity drivers for the 12" variant.
Deftech may simply be measuring it differently or are characterizing it differently than how we are. My guess is that the DN12 would have a similar high-frequency extension to the DN15.
 
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oniiz86

Enthusiast
Deftech may simply be measuring it differently or are characterizing it differently than how we are. My guess is that the DN12 would have a similar high-frequency extension to the DN15.
Thanks for that, I was referring to @haboscio 's measured frequency response of his DN12 that he shared below,
"However, I have never managed to measure upwards of 90hz to 100hz (or 110hz) before it rolls of completely. So I am very surprised the DN15 can go up to 300hz or more.

Always thought my DN12 had a "short response runway" (18-100) because they were mean to be xo at 80hz... That how I convince myself that was the expected :).

Now I wonder why I get such limited response on the DN12"
 
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Danzilla31

Audioholic Spartan
Thanks for that, I was referring to @haboscio 's measured frequency response of his DN12 that he shared below,
"However, I have never managed to measure upwards of 90hz to 100hz (or 110hz) before it rolls of completely. So I am very surprised the DN15 can go up to 300hz or more.

Always thought my DN12 had a "short response runway" (18-100) because they were mean to be xo at 80hz... That how I convince myself that was the expected :).

Now I wonder why I get such limited response on the DN12"
Did you measure it in room or out in the open for an anechoic response like Shady is doing

I guarantee you that once you put that DN15 into your room that room is going to mangle that beautiful response curve Shady is showing in his measurements and it won't be extending out as far as you see it doing here in his tests

In my bedroom I have had quality subs that extend well beyond 100hz but in my room, in the best spot for placement, measuring with REW the response drops pretty sharply after 90hz no matter what.

The room is going to affect your subs measured response in a huge way which is why as I'm sure you well know room eq is so critical in the bass region
 
AcuDefTechGuy

AcuDefTechGuy

Audioholic Jedi
Class D amplifiers are highly efficient (greater than 90%), allowing for cooler operation, smaller physical size, and lower power draw than Class H amplifiers.

Class H amplifiers are a variation of standard AB amplifiers that use two power rails operating on an overlapping portion of each input cycle to achieve very low distortion. However, they sacrifice efficiency by requiring more power and heat sinks to run cool. They also draw more energy to get to the same level of loudness as a Class D amplifier.

The Class H amplifiers use multiple power rails, which kick in when output-signal peaks would otherwise exceed the maximum voltage available from the Class AB amplifiers voltage rails. The result is even greater linearity (smoother, more natural sound reproduction) with extremely low distortion.

The Class H amplifiers have larger size requirements and draw more power than Class D, which is why they are used for the larger 12-inch (DN12) and 15-inch (DN15) subwoofers in the Descend Series. If your objective is to fill a large room with deep bass for low-frequency effects on movies and tight bottom-end music enjoyment - where size is not a constraint - then the Class H models produce excellent sound quality.

The Class D amps in the smaller subs are just as fast and make a proper LFE impact when watching movies. Your only limit with these is the size of the room you will be pressurizing"
I will only use $5,000 Class A/B Amps that weigh 100-Pounds for all my subwoofers. :cool:
 
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shadyJ

Speaker of the House
Staff member
Thanks for that, I was referring to @haboscio 's measured frequency response of his DN12 that he shared below,
"However, I have never managed to measure upwards of 90hz to 100hz (or 110hz) before it rolls of completely. So I am very surprised the DN15 can go up to 300hz or more.

Always thought my DN12 had a "short response runway" (18-100) because they were mean to be xo at 80hz... That how I convince myself that was the expected :).

Now I wonder why I get such limited response on the DN12"
He might have left some kind of low-pass filter on when he measured that. Also, like what Danzilla said, the room acoustics will boost the lower stuff but not the upper bass stuff, and can make an in-room response look low-pass filtered too.
 
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oniiz86

Enthusiast
@shadyJ In regards to the DN15's distortion that mostly stems from Induction as was noted in your review, I know it was difficult to determine as you couldn't remove the DN15's driver but is it safe to assume they didn't employ dual Aluminium shorting rings to greatly inhibit Induction in the DN15 as is typically used in motor designs?

"It’s interesting to see that the majority of measured distortion is even-order. That tells us that most of the distortion is originating from only one side of the driver’s excursion. I would guess, from the steady rise in 2nd-order harmonics, that the distortion comes from induction. I am not sure what measures Definitive Technology has taken to reduce induction, but there are a lot of measures that can be taken to inhibit induction. There may be room for Definitive technology to do more here and get even cleaner output, although the results may be more a technical achievement than anything that is audibly beneficial."
 
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shadyJ

Speaker of the House
Staff member
@shadyJ In regards to the DN15's distortion that mostly stems from Induction as was noted in your review,

"It’s interesting to see that the majority of measured distortion is even-order. That tells us that most of the distortion is originating from only one side of the driver’s excursion. I would guess, from the steady rise in 2nd-order harmonics, that the distortion comes from induction. I am not sure what measures Definitive Technology has taken to reduce induction, but there are a lot of measures that can be taken to inhibit induction. There may be room for Definitive technology to do more here and get even cleaner output, although the results may be more a technical achievement than anything that is audibly beneficial."

I know it was difficult to determine as you couldn't remove the DN15's driver but Is it safe to assume they didn't employ dual Aluminium shorting rings to greatly inhibit Induction in the DN15 as is typically used in motor designs?
Firstly, dual shorting rings aren't typical in driver motors. A lot of drivers don't use shorting rings at all, and many that do might only have a single aluminum or copper ring, or maybe a copper or aluminum pole piece cap. There are many different ways to implement Faraday shorting in driver motors.

Second, I would guess Deftech did use some kind of shorting in the driver motor. It's not perfect, but it is still a fairly linear system. Shorting rings/caps can inhibit induction, but they don't get rid of it entirely. There are still some effects from induction in these measurements, and my comment meant to convey that Deftech might have room to go a bit further and suppress induction effects even more, although it would be more for academic perfection rather than anything that would do any good in real-world listening.
 
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luis1090

Audioholic Intern
Do you think Def Tech's drivers & DSP tuning are responsible for its middling performance numbers? Surely if they added a 1000W amp it would've brought much greater headroom in the mid-bass region like REL's HT/1510 Predator II, there is absolutely no excuse for them to charge $1799 only to include a 500W amp, it's understandable for their smaller DN12 12" variant to have 500W like REL's 1205 MkII or the Monoprice M-12 V2 but the other companies had the smart sense to employ more powerful 1000W amplification for their 15" counterparts, it truly is amazing that the Monoprice SW-15 @$300 with a 600W amp offers greater punch even if it isn't as refined sounding as the DN15.
Look closely at the driver they are using, even with 500w the are limiting the output to prevent damage to the woofer. The woofer in use here have no place in a $1800.00 subwoofer; I'm sure that if an amplifier of 1000W is used it will overdrive the speaker and even damage it. The REL Predator subwoofers have the same compromise a cheap budget speaker that limits the true potential of the design. The REL subwoofers low frequency performance suffered even though is a sealed design, the low frequency output is very limited; I think that when Audioholics tested the Predator 1510 it barely broke 100db at 25hz, that is using a 15" driver with 1000w amplifier. REL mid-bass, fantastic and excellent for music but for movies not so good, keep in mind that is my opinion. My subwoofer is an SVS PB3000 pro, what a beast!
 
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shadyJ

Speaker of the House
Staff member
Look closely at the driver they are using, even with 500w the are limiting the output to prevent damage to the woofer. The woofer in use here have no place in a $1800.00 subwoofer; I'm sure that if an amplifier of 1000W is used it will overdrive the speaker and even damage it. The REL Predator subwoofers have the same compromise a cheap budget speaker that limits the true potential of the design. The REL subwoofers low frequency performance suffered even though is a sealed design, the low frequency output is very limited; I think that when Audioholics tested the Predator 1510 it barely broke 100db at 25hz, that is using a 15" driver with 1000w amplifier. REL mid-bass, fantastic and excellent for music but for movies not so good, keep in mind that is my opinion. My subwoofer is an SVS PB3000 pro, what a beast!
Every commercial sub with ports or passive radiators will have limiters to prevent overdriving. It doesn't take much power to damage the driver below the tuning frequency. Your PB-3000s have similar limiters. My guess is, given its very low distortion, the Deftech driver could have easily taken more power. The REL 1510 25Hz output was decent for a sealed 15".
 
William Lemmerhirt

William Lemmerhirt

Audioholic Overlord
A friend of mine has 2 of those. One sub needed the woofer driver replaced. The other sub needed the amp replaced.
Seen lots of those reports, surprisingly. BUT, since everyone pays the premium for the bill of rights, the minority can get exemplary customer service. For those that never need it, they just end up overpaying.
 
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luis1090

Audioholic Intern
I only buy Lexus LX600 SUV. :D

Well good luck, the Lexus LX 600 use the same engine that you'll find in the Tundra ans Sequoia. Make sure you take it to the dealer for every scheduled maintenance. Toyota(Lexus) have a problem in their hands with this engine with a lot of catastrophic failures requiring in most cases full engine rebuild or replacement. Obviously this isn't the forum to discuss cars and engines but in your case is good to be aware since my neighbor is dealing with this issue since January.
 
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luis1090

Audioholic Intern
Well good luck, the Lexus LX 600 use the same engine that you'll find in the Tundra ans Sequoia. Make sure you take it to the dealer for every scheduled maintenance. Toyota(Lexus) have a problem in their hands with this engine with a lot of catastrophic failures requiring in most cases full engine rebuild or replacement. Obviously this isn't the forum to discuss cars and engines but in your case is good to be aware since my neighbor is dealing with this issue since January.
...by the way my original Tundra comment in case you missed it is related to perceived reliability. Toyota/Lexus are supposed to be the most reliable car brands on the market and even them from time to time have "Lemons". SVS to me so far has been very reliable with amazing performance to price ratio.
 
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Kevin C

Audiophyte
Why would someone pay 1700 for this sub. I own 2 rsl speed woofers mk2 and 2 12s speed woofers. I would put 2 of the rsl 12s against this on all day. And you get to have your bass spread out in your room for less money then just one definitive sub.
 
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shadyJ

Speaker of the House
Staff member
Why would someone pay 1700 for this sub. I own 2 rsl speed woofers mk2 and 2 12s speed woofers. I would put 2 of the rsl 12s against this on all day. And you get to have your bass spread out in your room for less money then just one definitive sub.
I would say that the RSL 12S is a better value in terms of performance, but people would only have room for one large sub, and in situations where you have more money than floorspace, the DN15 would be the better buy.
 

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