Velodyne CHT-15: Could this sub pass the THX Ultra certification?

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tk2001

Active Member
Seeing as the HGS-15 & HGS-18 has recently been given the THX Ultra II certification without Velodyne having to make a single alteration to their specifications, could the CHT-15 pass the THX Ultra certification? If so, then why aren't Velodyne willing to pay for the THX Ultra certification when they have for the HGS-15/18?

BTW, does anyone know the subwoofer requirements needed to obtain a THX certification i.e maximum distortion level, frequency response, etc?
 

Ian J

Banned
Originally posted by tk2001
Seeing as the HGS-15 & HGS-18 has recently been given the THX Ultra II certification without Velodyne having to make a single alteration to their specifications, could the CHT-15 pass the THX Ultra certification? If so, then why aren't Velodyne willing to pay for the THX Ultra certification when did have for the HGS-15/18?

On the very dubious grounds that this is a serious question (which I doubt) you are asking why, if Velodyne's two subs in the £2,000 and upwards range have been ceritified at THX Ultra, the cheaper range costing hundreds of pounds have not.

On a general commercial note, if the cheap range could also achieve THX Ultra certification, how many people would bother buying the top of the range equipment
 

baileych

Standard Member
THX requires "an accurate in-room response down to 20 Hz". The HGS are rated at 20Hz-120Hz +/- 3dB and 15Hz-120Hz +/-3 3dB so I guest they pass easily.

The CHT-15 "only" does 23Hz-120Hz +/- 3dB. I'm sure with funky room positioning you can get a solid in-room response at 20Hz but I'm guessing that you loose out on accuracy. I get the impression that the THX sub spec is one of their most difficult specs to achieve.

As Ian J says, more importantly, why add a premium to your best lower midrange sub and at the same time make your high end subs look less valueable?

Can't wait for my CHT-15, don't mind that it doesn't have THX earthquake approval. (When does it come, uncle eric? :D)

Charles.
 

tk2001

Active Member
Originally posted by Ian J
On the very dubious grounds that this is a serious question (which I doubt) you are asking why, if Velodyne's two subs in the £2,000 and upwards range have been ceritified at THX Ultra, the cheaper range costing hundreds of pounds have not.

On a general commercial note, if the cheap range could also achieve THX Ultra certification, how many people would bother buying the top of the range equipment

Pioneer's AV Receivers, the Pioneer VSX-D2011 and the Pioneer VSX-D101, which are around the same price as the CHT-15 are THX Select but that doesn't stop people from buying Pioneers flagship Pioneer VSA-AX10. .:confused:

Yes, I am aware that the THX Select & THX Ultra are two different certifications but if the CHT-15 received a THX Ultra certification, do you really think thats gonna stop people from buying Velodyne's flagship subwoofer? I mean, from buying a less than one grand subwoofer to a more than two grand subwoofer is a big difference in terms of money.

Anyway my main question was, is the CHT-15 good enough to gain a THX Ultra certification? Keep in mind that uncle eric has the opinion that the CHT-15 simply kills the MX-150 MK II in terms of performance, and that sub IS THX ULTRA. :D

"The Servo powered Velodyne is twice as powerfull and has 10-15 times less distortion than the M&K due to its patented Servo controlled technology." - uncle eric.
 

Jase

Distinguished Member
I believe the original specs for THX Ultra subwoofer cetification were less stringent and the sub only had to go as low as 35hz +/- 3db with a certain output. There are a few subs that will do this but presumably the manufacturers didn´t want to pay for the THX Certification.

THX Ultra 2 is harder to achieve as it requires output at lower freqencies (20hz) with low distortion etc etc.

I would assume that the CHT15 would pass THX Ultra specs but not meet THX Ultra 2 specs (only the HGS 15 & 18 have in their current form).
 
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uncle eric

Guest
Originally posted by baileych
THX requires "an accurate in-room response down to 20 Hz".
The HGS are rated at 20Hz-120Hz +/- 3dB and 15Hz-120Hz +/-3 3dB so I guest they pass easily.

The CHT-15 "only" does 23Hz-120Hz +/- 3dB. I'm sure with funky room positioning you can get a solid in-room response at 20Hz but I'm guessing that you loose out on accuracy. I get the impression that the THX sub spec is one of their most difficult specs to achieve.
Charles, this is where the confusion lies. Having spoken to both THX and Velodyne USA some weeks ago to clarify this, the figures required are Anechoic (dead chamber) measurements not room loaded (magnified)

TK,
Along with the £2000 M&K 350 subwoofer, many more have fallen flat on their faces trying to pass the Ultra II spec. The notable points of this new spec being that the sub must have the ability to go down to 20Hz at 105dB at no more than 4% distortion.
This doesn't sound like much at all, and in fact countless subwoofer manufacturers have been quoting lows of 20Hz for years.
However, these quotes have been in room (room loaded or magnified) measurements which really don't count for much particularly when a prospective buyer is trying to compare differing subs from various manufacturers.

The figures quoted by THX for the Ultra II spec are "Anechoic" chamber measurements. This is a special sound absorant "dead" room which obviously offers the sub no help in achieving higher figures.

There are only a handful of subs that have passed the very tough Ultra II spec and these are new designs specifically built for this purpose. Producing something to this level is not a cheap excercise and you'll find that these subs all cost many times more than the CHT-15.
Going back to the spec, as you rightly said, the Velodyne HGS-15 and 18 were the only subs in their original state that passed the spec. Godzilla achieved the distortion figures (doing the required) at less than 1% distortion hence going more than 4 times lower than the distortion threshold.

Regarding the £684 CHT-15 , as per Velodynes Anechoic figures, this great sub goes to 23Hz at -/3+dB which is an admirable figure that I know for a fact that the M&K150THX sub at £1500 simply cannot match. Does this mean the CHT-15 would pass the original THX Ultra spec? Almost certainly. However, THX certification is not free and the price would almost certainly go up.
Going back to the 23Hz figure of the CHT-15, in an attempt to illustrate the effects of room loading (and forgeting for a moment that much of it was harmonics) our own Dom H measured a 16Hz figure with his 50 watt (8 inch driver) MJ 50 subwoofer.
If this little mid-woofer can achieve the figure quoted by Dom, imagine what the 300 watt servo powered 15incher will do in room ???

Velodyne have been making and selling the HGS range for some time now and have not altered the price of the HGS-15 and 18 to match its new found status. I spoke to Velodyne USA a few weeks ago and asked why they submitted the subs after all this time. There are 2 reasons both of which I am not allowed to reveal yet. Stay tuned!!!
 
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Timmy B

Guest
Velodyne have been making and selling the HGS range for some time now and have not altered the price of the HGS-15 and 18 to match its new found status. I spoke to Velodyne USA a few weeks ago and asked why they submitted the subs after all this time. There are 2 reasons both of which I am not allowed to reveal yet. Stay tuned!!!

Being a hgs-15 owner (well, soon anyway!) I hope its not bad news!:)
 

baileych

Standard Member
Originally posted by uncle eric
Charles, this is where the confusion lies. Having spoken to both THX and Velodyne USA some weeks ago to clarify this, the figures required are Anechoic (dead chamber) measurements not room loaded (magnified)

---snip---

So when the THX website said "an in-room response" they were obviously talking rubbish (unless you live in an anechoic chamber which, so I'm told, is such a deeply spooky experience you'd probably go mad!). To be honest the bit I found didn't make it clear which spec they were talking about. While it was under "Technical information" it had very little information, and almost none of it techincal. Sigh :( .

Charles.
 
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EvilMudge

Guest
If you close your eyes/turn out the lights in a proper anechoic chamber you pass out - seen it happen - very funny.:D
 

Matt F

Active Member
Originally posted by baileych
The HGS are rated at 20Hz-120Hz +/- 3dB and 15Hz-120Hz +/-3 3dB so I guest they pass easily.

Charles.

Just on a point of correctness, the HGS15's figures are actually 18Hz-120Hz +/-3dB.

Sorry to be picky, I mean it's not as if I own one or anything.... hang on a minute, I do own one :D

Matt.
 

baileych

Standard Member
Apologies - read the wrong column :rolleyes:

20Hz - ... for HGS-10 and HGS-12 according to Velodyne website.

Charles.
 
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Tom Vodhanel

Guest
Sometimes it can be very tough for the consumer to try to figure out which manufacturers "speccing" method most accurately relates to the real world. Rather than depend on those specs(which can be on very uneven playing fields to begin with---As Eric noted)...I would suggest looking for independent reviews of the products in question. If you can find both products reviewed by the same person,in the same room ,using the same test equipment...regardless of what any *spec* might try to claim...you now have a INDEPENDENT comparison of the two products.

One example is Tom Nousaine's extension database of subwoofer performance. TN uses a 10% THD limit and finds the maximum clean output capability of the subwoofer at various real world HT frequencies(mainly 20-80hz. TN never reviewed the MK150 AFAIK, but he did review the smaller,less expensive MK125 mkII. In his published data reports...

at 20hz, the MK125 Mkii had 91dB of clean output, the CT150 had 82dB. Or, the MK had 3x the clean output capability as the VEL.

When he averaged the clean output capabilities from 25-63hz for both models, they were dead even...105.3dB. Response wise, the VEL had relatively flat in room extension to 32hz, the MK down to 25hz. I have no idea how any of this relates to each manufacturers claims...but both performed well.(nearly even) with the MK only gaining the advantage in the deepest bass capabilities.


Tom V.
SVS
 

Matt F

Active Member
Originally posted by Tom Vodhanel
TN never reviewed the MK150 AFAIK, but he did review the smaller,less expensive MK125 mkII

Yep, me again, correcting people I'm afraid ;) . I presume you are talking about the MX150 and 125 as opposed to MK. In which case it should be noted that these two subs are identical in size and both use the same 150 watt amp. The only difference, as I understand it, is that the 150 is THX certified which may explain why it costs more (and has less connection options?).

As for comparisons with Velodyne, you seem to be talking about the older CT150 which, I believe, is somewhat different (less power) to the current CHT15 which many members here have purchased.

Matt.
 
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Tom Vodhanel

Guest
Hi Matt,

I think you are right, the MKs are the same size...I'm not sure if they have the exact same amp or drivers though. On the CT150/cht15 differences. I thought VEL said they were identical except for a minor amp tweak for the cht15s...bumping it from like 250w to 300w or something like that? I could be wrong on that. Regardless, my point about having a industry professional independently validate any manufacturers claim stands. I still think that is much better than listening to a dozen manufacturers all claim their methods are the best and their *specs* are the msot accurate...and then trying to figure out the what and whys of it all.

Tom V.
SVS
 
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uncle eric

Guest
Originally posted by Tom Vodhanel
I'm not sure if they have the exact same amp or drivers though. On the CT150/cht15 differences. I thought VEL said they were identical except for a minor amp tweak for the cht15s...bumping it from like 250w to 300w or something like that? I could be wrong on that.
Sadly you are Tom. Velodyne did quite a bit more than you suggest. In fact quite a fair number of changes went into the CHT-15.

Originally posted by Tom Vodhanel
Regardless, my point about having a industry professional independently validate any manufacturers claim stands.
Which is where THX comes in.
And is in fact one of the reasons Velodyne submitted the HGS-15 and 18 for Ultra II certification. It's a sort of shut up or put up if you will. There are no buddy buddy reviewers involved with this certification. You either pass or you don't. Products at the top of their leaugue are always open to bashing and competitors of Velodyne have aspired for years to attain the highest standards as set by Bruce Hall and Co.
We know that THX certification is not the be all and end all of subjectiveness but it is superb as an unbiased "standards" organization. Which brings me right back to your point regarding industry professionals. I think having industry standards is just as important and perhaps even more so. While some measurements and methods as taken by THX could be pushed and pulled by various folks, basically, its of no consequence as ALL subs are as tested by THX are done in the same exact way.

Going back to the old Velodyne CT-15, it was a great product even before the alterations.

Quote from John E Johnson from Secrets of Home Theatre which typifies Servo Controlled subs,
" Bass is kind of a funny thing in audio. There can be lots of distortion, and some people will like it. Nothing wrong with that. However, the CT-150 is not one of those kinds of subwoofers. It produces powerful deep bass, but because harmonics are not a big part of its profile, there can be sounds that you feel and not hear, as opposed to hearing bass all the time with subs that produce lots of harmonics. For example, the lunch scene in "Jurassic Park" has some extremely deep sounds. With a subwoofer that has significant harmonics, the crunching sounds will seem more powerful than they actually are. I prefer clean bass, which is what the CT-150 produces. It won't play as loud as the Velodyne HGS-18, but within its range of power, the CT-150 sounds like a much more expensive product. Plus, it has all the features on the amplifier panel that just about any subwoofer possibly could

What surprised me most about this subwoofer is that it is so clean and tight. No boominess or chestiness (two things that are extremely irritating to hear). Each deep note is musically distinguishable. There is also an uncanny amount of dynamics, meaning that it has punch (responds quickly), which is unusual in a 15" driver. This product has obviously been very, very carefully engineered"
 
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Tom Vodhanel

Guest
>>>Sadly you are Tom. Velodyne did quite a bit more than you suggest. In fact quite a fair number of changes went into the CHT-15.<<<

Really?

That is interesting. I have measured both and didn't note any specific performance differences.(nothing that common assembly line tolerances wouldn't explain). Are all these changes something you are allowed to discuss? I would be interestd to hear what they are exactly, thanks.

I suppose we will begin seeing the newer *cht* series reviewed soon enough though and we can compare those numbers to the old CT numbers easy enough then.


quote:
--------------------------------------------------------------------------------
Originally posted by Tom Vodhanel
Regardless, my point about having a industry professional independently validate any manufacturers claim stands.

--------------------------------------------------------------------------------


>>>Which is where THX comes in.
And is in fact one of the reasons Velodyne submitted the HGS-15 and 18 for Ultra II certification. It's a sort of shut up or put up if you will. There are no buddy buddy reviewers involved with this certification. You either pass or you don't.<<<


I wouldn't label Tom Nousaine as ANYONE's *buddy,buddy* reviewer. He is an honored member of the AES and has an industry wide reputation for really putting subwoofers though some torture testing. The measurement methods used are available for all to see, and all the data is published for both peer and consumer review. There is simply NOT a more realible source of information available anywhere.




>>>Products at the top of their leaugue are always open to bashing and competitors of Velodyne have aspired for years to attain the highest standards as set by Bruce Hall and Co.
We know that THX certification is not the be all and end all of subjectiveness but it is superb as an unbiased "standards" organization. Which brings me right back to your point regarding industry professionals. I think having industry standards is just as important and perhaps even more so. While some measurements and methods as taken by THX could be pushed and pulled by various folks, basically, its of no consequence as ALL subs are as tested by THX are done in the same exact way.<<<


I agree, Velodyne has a great reputation(well deserved!). But I'm not sure what you mean by THX measurements being *pushed* and *pulled*?




>>Going back to the old Velodyne CT-15, it was a great product even before the alterations.

Quote from John E Johnson from Secrets of Home Theatre which typifies Servo Controlled subs,<<<


The ct/cht15 isn't servo controlled...at least not active servo controlled as most folks think of the term. While I highly respect John Johnson's opinion...anecdotal praise isn't really the issue I was trying to highlite here(or even talking about specific subs). I only read this thread because of the THX issue. They are a lot of questions about the THX testing no one seems very clear on. If I've understood you correctly...you need to produce 105dB/20hz/4% THD/1m true anechoic to be THX-2. But when Tom Nousaine maxxed out the HGS15 he measured about 95 or 95.5dBs max clean output. And that was with the unit corner loaded(measuring at a 2m distance)...so something definitely isn't adding up at all. If we knew more about the THX testing facility(and their "anechoic" chamber) it might make more sense. Are we SURE they are measuring at 1m? if it was 1/2m or even nearfield to the sub...that would explain a lot.How large is the anechoic chamber they use? Tom Nousaine uses a ramped pulsed 20hz burst...what type of input signal does THX use?


Tom V.
SVS
 

Stuart Wright

AVForums Founder
Staff member
I am not happy with Uncle Eric's comments which sent this thread off in a tangent, so I have deleted them and everything afterwards.
Eric is pro Velodyne - he is a dealer.
Tom is pro SVS - he makes them.
I have reopened this thread because it is interesting. Lets keep discussion as reasonable, factual and friendly as possible.
 

tk2001

Active Member
Originally posted by Tom Vodhanel


The ct/cht15 isn't servo controlled...at least not active servo controlled as most folks think of the term.

Tom V.
SVS

Can you please explain to me what this means in English?

What exactly is "active servo controlled"?

According to Velodyne's website, it clearly states that the CHT-15 is the only sub in that range which uses "Current Sensing Servo circuitry"

Is the CHT-15 servo or isn't it?
 

Flimber

Distinguished Member
Originally posted by tk2001
What exactly is "active servo controlled"?

Is this not the thing what Yamaha uses ? Philips (?) developed active servo speakers some time ago and Marantz used to market a pair (which used a three core cable). "Helmholtz Resonance" is your Google keyphrase, IIRC.

Mike.
 
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EvilMudge

Guest
Philips had servo controlled speakers about 30 years ago, according to my PIE Big Book of Audio (circa 1973).
It's only with the advent of seriously good DSPs that proper servo controlled subs have come of age.
:lesson:
The HGS, the ML Descent and the Paradigm Servo-15 all use accelerometers to measure the acceleration of the cone and then compare this to the rise and fall of the signal that was playing at the time. This information is then used to correct input to the magnet in order that the movement of the cone matches that of the input signal. Without being privy to the design specifics I cannot say whether this is done in the analogue or digital domain.
The CHT-15 attempts to determine what the cone is doing by measuring the current drawn by the voice coil and comparing this to the voltage of the input signal - any non linearities indicating that the cone is not behaving in the correct manner, and therefore a correction is applied.
If anyone would like to tell me how to beat the distortion figures of the above subwoofers without using some kind of measurement-correction system I would love to know how to do it.
If anyone would like to know how to build (theoretically) a better DIY sub then I can tell them what they are going to need!:D
 

tk2001

Active Member
Originally posted by Tom Vodhanel


at 20hz, the MK125 Mkii had 91dB of clean output, the CT150 had 82dB. Or, the MK had 3x the clean output capability as the VEL.

Tom V.
SVS

Hmmm.......Can you please give me your definition of 'clean output'?

Heres a quote from Tom Nousaine's Stereo Review of the CT-120 (which you all know is not quite as good as the CT-150).

"Interestingly, the CT-120 is one of the few subwoofers I've tested at any price that could produce clean output at 20 Hz at a listening distance of 2 metres. This sub cranked out 87dB sound-pressure (SPL) at 20 Hz with less than 10 percent distortion." - Tom Nousaine, Stereo Review June 1998

It appears in TN's review that the CT-120 can pump out 87dB of clean output at 20 Hz. Where as in your above quote, it states that the CT-150 (which has Current Sensing Servo) can only produce a mere 82dB of clean output (5dB less than the CT-120) at 20 Hz?

Somehow, something just doesn't quite add up:confused:
 
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Tom Vodhanel

Guest
>>>If anyone would like to tell me how to beat the distortion figures of the above subwoofers without using some kind of measurement-correction system I would love to know how to do it.<<<


Subwoofer distortion(let's just concentrate on Harmonics for this context) occurs when one aspect of the subwoofer is pushed beyond its linear operating limits. If the subwoofer is well designed, uses quality components,and kept within the intended operating range for the sub...THD should be quite low. By *low* I don't mean <1%(as none of the units here stay <1%...even the mighty HGS series will top out in the 3-5% range), I think anything <5% is quite low...and quite inaudible with actual source material.

If the driver begins to exceed its linear operating range, it will begin to produce harmonics. If the driver suffers any dynamic offset due to poor motor design or an enclosure issue, that will results in harmonics. If the port begins to compress(can't flow enough air in a completely linear fashion),an increase in THD happens. Is the enclosure isn't well build(panel flexing or doesn't keep the driver from moving due to reactive forces),THD can result. If the amp is pushing into clipping, THD can skyrocket.

So I believe it is very possible to design a subwoofer that doesn't use active servo feedback and still keeps THD low. In fact this has been documented over and over again by reviewers who use strict distortion limits in their test like Nousaine....or reviews use include high resolution distortion data in their reviews(like John Johnson---who was quoted ealier).

We can also break harmonics down to EVEN order and ODD order too, but I'm not sure if that would really push the discusion forward at this point.


Tom V.
SVS
 

tk2001

Active Member
Originally posted by Tom Vodhanel


even the mighty HGS series will top out in the 3-5% range), I think anything <5% is quite low...and quite inaudible with actual source material.

Tom V.
SVS

How would the HGS-15/18 obtain a THX Ultra II certification if it tops out in the 3-5% range?

Assuming velodyne's frequency-response and distortion figures are all measured in an Anechoic chamber, and when it states that both the HGS-15/18 will distort "Less than .5%", how do you conclude that they will "top out in the 3-5% range"?
 
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