• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

boXem ARTHUR 2408/N2 Review (Stereo Amplifier)

Rate this amplifier:

  • 1. Poor (headless panther)

    Votes: 1 0.5%
  • 2. Not terrible (postman panther)

    Votes: 9 4.1%
  • 3. Fine (happy panther)

    Votes: 131 59.5%
  • 4. Great (golfing panther)

    Votes: 79 35.9%

  • Total voters
    220

peniku8

Active Member
Joined
Dec 9, 2020
Messages
213
Likes
356
The length of a 8Hz sound wave is 42 meters. Even at quarter wavelength you need a room with 10m wide/deep. It’s not possible to create 8Hz in a standard residential listening room.
How can I have bass in headphones when the wavelength needs to 'fit' into the acoustic space?
 

sarumbear

Major Contributor
Forum Donor
Joined
Aug 15, 2020
Messages
3,261
Likes
2,934
Location
Southampton, UK
And the point being?

Amplifiers are measured across their rated bandwidth and in the case of the Hypex modules, they specify down to 0Hz.
I was mistaken, sorry. I mistakenly thought I was responding to a comment on a subwoofer. I do however think response at 8Hz is not a thing.
 

sarumbear

Major Contributor
Forum Donor
Joined
Aug 15, 2020
Messages
3,261
Likes
2,934
Location
Southampton, UK
How can I have bass in headphones when the wavelength needs to 'fit' into the acoustic space?
It’s sound pressure you hear not the pressure wave in open air.
 

peniku8

Active Member
Joined
Dec 9, 2020
Messages
213
Likes
356
It’s sound pressure you hear not the pressure wave in open air.
Sorry, I don't understand the difference between the two. People want infrasonics mostly for the tactile aspect they deliver and that seems to be working well enough for a crowd of people to drop large sums of money on large quantities of subwoofers and amps.
 

restorer-john

Master Contributor
Joined
Mar 1, 2018
Messages
8,735
Likes
24,258
Location
Gold Coast, Queensland, Australia
I do however think response at 8Hz is not a thing.

8Hz is definitely more trouble than it's worth. So many amplifiers back in the vinyl days would pump woofers to their stops with cart/arm resonances around there.

I have some music CDs with content you can see (the woofers slowly modulating) but not hear. Most likely ADC related DC issues in the recording/masterings. My amps and preamps/players are flat to 1Hz or so. The infrasonic filters gets used in those cases. It can be disconcerting to look at the woofer/s moving large slow excursions when the music is not all that loud. Hit the infrasonic filter and it stops dead. Then I go look at the spectrum of the music on the PC and see the problem.
 

sarumbear

Major Contributor
Forum Donor
Joined
Aug 15, 2020
Messages
3,261
Likes
2,934
Location
Southampton, UK
Sorry, I don't understand the difference between the two. People want infrasonics mostly for the tactile aspect they deliver and that seems to be working well enough for a crowd of people to drop large sums of money on large quantities of subwoofers and amps.
You may want to learn then
 

peniku8

Active Member
Joined
Dec 9, 2020
Messages
213
Likes
356
You may want to learn then
Any pointers on this? I'm on this forum to learn after all and I'd be very happy if you could supply me with something interesting to read!

I do however think response at 8Hz is not a thing.
You probably meant acoustic response by this, but if not, it sure is a thing, in tactile transducers. Look at Powersoft's Mover for example. It's a piston on a servo motor meant to be driven by speaker amps. Since they're a servo design they have no resonance frequency, so they can be driven at 10Hz, 1Hz or 1 oscillation per minute, they do not care. They can also just lift something when fed DC.
Coming back to acoustic response, have you ever tested this? Like in a small room with a bunch of heavy duty subwoofers? How does it manifest itself? I mean, you can measure the response, so why is it not 'proper' acoustic response then? I've seen this claim made by others who went as far as saying a subwoofer makes no sense since bass frequencies 'don't fit in your room' and even published a paper about this. They used full wavelength as a point of reference, you use quarter wave length. You said headphones are different, but what about cars? The largest dimension in my Focus is maybe 2.5m, which would equal to a low limit of 30Hz according to your claim, but I'm pretty sure the response at 20Hz is just as fine as anywhere else.
 

nagster

Active Member
Joined
Jan 24, 2021
Messages
175
Likes
234
Who cares.

boxem02.jpg

I'm inconvenienced if I can't use double banana plugs. At least + and-.
You may want to line up A- and B- for safety and internal wiring, but considering the bridge connection, the layout of the image below is perfect.
photoviewer_poweramp_p7000s_rear_4b5958f77bfae5436116d6ae33e4c613.jpg
 
Last edited:

rynberg

Member
Joined
Dec 30, 2020
Messages
66
Likes
81
Location
Bay Area, California
The length of a 8Hz sound wave is 42 meters. Even at quarter wavelength you need a room with 10m wide/deep. It’s not possible to create 8Hz in a standard residential listening room.
Sigh...if you are going to (condescendingly) criticize another user's understanding, you might want to be more precise with your wording. While an 8Hz wave won't propagate in a standard room, it changes to pressurization (or pulse if you want to think of it that way) -- what do you think "room gain" is? I think it should be patently obvious on the face of it that you can generate sound below the 1/4 wavelength of a space.
 

MaxBuck

Addicted to Fun and Learning
Forum Donor
Joined
May 22, 2021
Messages
917
Likes
1,171
Location
SoCal, Baby!
Yes you would

I don't understand your comment in your signature : addicted to fun and learning ..

DiY is about fun and learning
I don't need to assemble my own amplifiers to learn or have fun.

My Heathkit/Dynakit days are long behind me. And I'm glad of it.
 

pma

Major Contributor
Forum Donor
Joined
Feb 23, 2019
Messages
2,894
Likes
5,754
Location
Prague
Amplifiers are measured across their rated bandwidth and in the case of the Hypex modules, they specify down to 0Hz.
Hmmm ….
They specify direct coupling, quite a difference. It is an audio amplifier and has DC output protection, as every normal audio amplifier. DC at the output destroys speaker coil very quickly.
 

Larry B. Larabee

Senior Member
Joined
Nov 24, 2021
Messages
348
Likes
176
Hmmm ….
They specify direct coupling, quite a difference. It is an audio amplifier and has DC output protection, as every normal audio amplifier. DC at the output destroys speaker coil very quickly.
I doubt any company these days would make a direct coupled amp. You're just asking for problems.
 

restorer-john

Master Contributor
Joined
Mar 1, 2018
Messages
8,735
Likes
24,258
Location
Gold Coast, Queensland, Australia
Hmmm ….
They specify direct coupling, quite a difference. It is an audio amplifier and has DC output protection, as every normal audio amplifier. DC at the output destroys speaker coil very quickly.

Like I said, Pavel, Hypex specify down to 0Hz in some of their modules.

NC-500OEM:
1639803208949.png


NC-1200:
1639804016030.png


The NC-122MP is specified down to 10Hz:
1639803831215.png


Of course the DC protection will kick in and depending on the timing/fc of the filter or zero cross duration threshold detection, and overall level, it may be well above DC.

So why not inject some DC or extreme LF (<0.5Hz) into a module and see how quickly the protector trips at various levels and find out?

I have plenty of amps rated from DC up. And yes, they all have DC protection of some sort or another. A misnomer? Maybe.

No DC protection, just 100% [email protected] in the FB loop:
1639804263490.png

Denon power amp:
1639804401215.png


Kenwood LO7m power amp (monoblock):
1639804495278.png


Both the two power amps have DC protection...
 
Last edited:

pma

Major Contributor
Forum Donor
Joined
Feb 23, 2019
Messages
2,894
Likes
5,754
Location
Prague
Like I said, Pavel, Hypex specify down to 0Hz in some of their modules.

Please stick with the NC122MP which is the subject of this review, John.

1639810219977.png


1639810284639.png


So concerning your statement
Amplifiers are measured across their rated bandwidth
this one would start to be measured from 10 Hz.
 
Last edited:

sarumbear

Major Contributor
Forum Donor
Joined
Aug 15, 2020
Messages
3,261
Likes
2,934
Location
Southampton, UK
Any pointers on this? I'm on this forum to learn after all and I'd be very happy if you could supply me with something interesting to read!
It takes a large transducer (speaker cone) moving back and forth to create a low-frequency pressure wave with enough amplitude to move our eardrums. The larger the speaker, the better chance it has to create those big waves. That’s why PA systems at live events use large subwoofer speakers with extra large cones, 18″ is the standard as well as some form of horn loading to increase efficiency. Consider how much sound wave will be created by such a large cone, and you’ll understand why most small speakers operating in open air, like those on your phone or laptop, can’t put out a lot of bass.

Then how the headphones generate bass with their puny cones? That is because unlike loudspeakers, headphones aren’t operating in open air! Headphones, especially the in-ear types, create a closed “tunnel” between the speaker and your ear. Relatively little air can escape from this tunnel, so your headphones are basically directly coupled to your eardrums, making them very efficient. An in-ear monitor sealed into your ear canal couples very well with your eardrums, and produces plenty of bass despite its small size. Open-back headphones may not seal so tightly, but they’re typically loaded with larger headphone drivers (usually 40 or 50 mm) and are able to move plenty of air down the ear canal.

You probably meant acoustic response by this, but if not, it sure is a thing, in tactile transducers. Look at Powersoft's Mover for example. It's a piston on a servo motor meant to be driven by speaker amps. Since they're a servo design they have no resonance frequency, so they can be driven at 10Hz, 1Hz or 1 oscillation per minute, they do not care. They can also just lift something when fed DC.
First think first, LFE track is designed to be fed to a loudspeaker. It is an audio track. Secondly, it is monitored in a film post-production studio by ear, hence it should have the range of signal that can be heard in a 15m average room where response down to 8Hz was not available. Why do you want an octave lower response in your room then the makers of the sound track had?

Coming back to acoustic response, have you ever tested this? Like in a small room with a bunch of heavy duty subwoofers? How does it manifest itself? I mean, you can measure the response, so why is it not 'proper' acoustic response then? I've seen this claim made by others who went as far as saying a subwoofer makes no sense since bass frequencies 'don't fit in your room' and even published a paper about this. They used full wavelength as a point of reference, you use quarter wave length.
I am an electroacoustic engineer with a M.Sc. I have designed a commercial speaker. I worked in music and sound track production as a a recording engineer.

I have four identical 15" closed box subwoofer at each corners of my HT, which is 8m by 5m. Each measured to have their fc @ 22Hz. That means I should be able to reproduce below 20Hz with the help of the boundary boost. I can verify that with an SPL meter.

Hence, I can assure you that I know what I am talking about and I also have the set-up to test that on.

You said headphones are different, but what about cars? The largest dimension in my Focus is maybe 2.5m, which would equal to a low limit of 30Hz according to your claim, but I'm pretty sure the response at 20Hz is just as fine as anywhere else.
Like in a headphone, the sound in a car does not work like on open air. There is a lossy tunnel between the speakers and your ear. However, as the tunnel is lossy you need much larger low frequency energy on low frequencies. That is why you need disproportionally larger subwoofers in cars.
 

peniku8

Active Member
Joined
Dec 9, 2020
Messages
213
Likes
356
It takes a large transducer (speaker cone) moving back and forth to create a low-frequency pressure wave with enough amplitude to move our eardrums. The larger the speaker, the better chance it has to create those big waves. That’s why PA systems at live events use large subwoofer speakers with extra large cones, 18″ is the standard as well as some form of horn loading to increase efficiency. Consider how much sound wave will be created by such a large cone, and you’ll understand why most small speakers operating in open air, like those on your phone or laptop, can’t put out a lot of bass.

Then how the headphones generate bass with their puny cones? That is because unlike loudspeakers, headphones aren’t operating in open air! Headphones, especially the in-ear types, create a closed “tunnel” between the speaker and your ear. Relatively little air can escape from this tunnel, so your headphones are basically directly coupled to your eardrums, making them very efficient. An in-ear monitor sealed into your ear canal couples very well with your eardrums, and produces plenty of bass despite its small size. Open-back headphones may not seal so tightly, but they’re typically loaded with larger headphone drivers (usually 40 or 50 mm) and are able to move plenty of air down the ear canal.


First think first, LFE track is designed to be fed to a loudspeaker. It is an audio track. Secondly, it is monitored in a film post-production studio by ear, hence it should have the range of signal that can be heard in a 15m average room where response down to 8Hz was not available. Why do you want an octave lower response in your room then the makers of the sound track had?


I am an electroacoustic engineer with a M.Sc. I have designed a commercial speaker. I worked in music and sound track production as a a recording engineer.

I have four identical 15" closed box subwoofer at each corners of my HT, which is 8m by 5m. Each measured to have their fc @ 22Hz. That means I should be able to reproduce below 20Hz with the help of the boundary boost. I can verify that with an SPL meter.

Hence, I can assure you that I know what I am talking about and I also have the set-up to test that on.


Like in a headphone, the sound in a car does not work like on open air. There is a lossy tunnel between the speakers and your ear. However, as the tunnel is lossy you need much larger low frequency energy on low frequencies. That is why you need disproportionally larger subwoofers in cars.
I think we were not on the same page here, as your write up there had nothing to do with the initial discussion/my question, but I'm sure the info you presented will be useful to someone who comes across it, since it's good general info, so it was not in vain.

You stated 8Hz can't be reproduced inside a room with its largest dimension being smaller than a quarter of the wavelength of the frequency (physical relationship). That's what my question was directed to, because that statement doesn't make sense to me.
"Why does the wavelength need to fit inside the acoustic space?" would be my question. Not "Why is is harder to reproduce bass outside than it is to do so inside a closed headphone?".

Regarding the example of your listening room: You say your room is 8m wide/deep(?), so according to your previous claim, it's impossible to reproduce frequencies of a wavelength longer than 4*8m=32m, which equals to 9Hz and below. You say you "should" be able to reproduce below 20Hz, but 9Hz is a long shot from 20. Hearing threshold of 9Hz is ~99db, your setup is a good starting point to get there, depending on the drivers used, albeit probably not with low distortion. Typically you see those chasing sub 10Hz response with setups like 8 21" drivers or more. I've seen a "home" theater with 24 24" subs...

Lastly, to answer your question as to "why", there is an entire community around it and the main term would be "BEQ" or "Bass EQ".
1000+ pages and 1million+ views.
500 pages and 500k views.
They basically analyze the response of an entire movie and then EQ it to target.

Hundreds of people have built systems to either reproduce frequencies below 10Hz acoustically or mechanically (the latter mostly, as it's way easier to achieve and doesn't come with the penalty of sounds your neighbours will hear), to get the tactile aspect I was talking about. Why? Because it's awesome. I had my couch on a riser with tactile transducers taking care of frequencies between 10 and 25Hz (not lower because it wasn't capable enough; it does not produce sound, only vibrations). EQ'ing movies/games/"content" can be hit and miss, since these frequencies are typically not properly mixed/taken good care of like you pointed out, but most of the time it adds a to a great experience.
 

sarumbear

Major Contributor
Forum Donor
Joined
Aug 15, 2020
Messages
3,261
Likes
2,934
Location
Southampton, UK
You stated 8Hz can't be reproduced inside a room with its largest dimension being smaller than a quarter of the wavelength of the frequency (physical relationship). That's what my question was directed to, because that statement doesn't make sense to me.
"Why does the wavelength need to fit inside the acoustic space?" would be my question. Not "Why is is harder to reproduce bass outside than it is to do so inside a closed headphone?".

Regarding the example of your listening room: You say your room is 8m wide/deep(?), so according to your previous claim, it's impossible to reproduce frequencies of a wavelength longer than 4*8m=32m, which equals to 9Hz and below. You say you "should" be able to reproduce below 20Hz, but 9Hz is a long shot from 20.
Your calculation is for area. Wavelength is a single dimension, length. I can generate half of a 20Hz waveform in my room. That means anything below 20Hz will be reproduced in diminishingly lower level.

Hearing threshold of 9Hz is ~99db, your setup is a good starting point to get there, depending on the drivers used, albeit probably not with low distortion. Typically you see those chasing sub 10Hz response with setups like 8 21" drivers or more. I've seen a "home" theater with 24 24" subs...
There is no hearing at 9Hz and hence no threshold.

Hundreds of people have built systems to either reproduce frequencies below 10Hz acoustically or mechanically (the latter mostly, as it's way easier to achieve and doesn't come with the penalty of sounds your neighbours will hear), to get the tactile aspect I was talking about.
There are thousands of people who use speaker raisers, holly water to put next to their turntable, $10K+ mains cables, etc. I am an engineer and I work within physical laws. Those laws say 10Hz audio reproduction in a residential room is not possible. My music and soundtrack experience tells me that no LFE track will have any signal much below 20Hz.

You are perfectly entitled to join the millions you mention on the Internet that refutes me. With respect I will stop here as we have polluted this review post enough already.
 

peniku8

Active Member
Joined
Dec 9, 2020
Messages
213
Likes
356
Your calculation is for area. Wavelength is a single dimension, length. I can generate half of a 20Hz waveform in my room. That means anything below 20Hz will be reproduced in diminishingly lower level.
It it not for area, it's according to your own calculations (quarter wavelength, remember? Hence multiplying your room length by 4 to get the full wavelength). Now you mention half a wave length, before that it was a quarter. Also now you say 'lower levels', which is correct, but before you said 'impossible' which is incorrect.

There is no hearing at 9Hz and hence no threshold.
There are many studies on this subject and a bunch of white papers have been published, which I have read. Tonal hearing disappears below ~20Hz, but you can still very much hear those frequencies. Once you know what they sound like you'll be able to tell what frequency is playing, even if it's 10Hz. I know, because I do. You think you can't hear 9Hz because you've never heard it properly.
Similar studies have also been done about high frequencies, which show that we in fact can hear frequencies above 20khz. They just have to be loud enough.
One interesting paragraph from one of the papers hints at an actual low frequency limit for reproduction, but it is seems unrelated to wavelength and partially to size, which goes against your claims. It's related to construction of the room, aka how sturdy it is and how air tight it is.
The rigidity of the walls and the airtightness ofthe chamber are so good that the cham-
ber serves as a pressure chamber in the low and infrasonic frequency range. To check
the air tightness the time constant was measured. A rectangular signal was applied to
the loudspeakers and the sound pressure in the centre of the chamber was measured.
A time constant 't = 0.75 s was found and a lower limiting frequency can be estimated
as 0.2 Hz

You are perfectly entitled to join the millions you mention on the Internet that refutes me. With respect I will stop here as we have polluted this review post enough already.
I agree, you ignore my points and denounce them as snake oil. That's enough of a red flag for me that tells me our understandings are not compatible. It seems like you're not open to accept anything outside of the boudaries of your own knowledge.
Let's leave it at that and drop the topic then, I'll enjoy my music and you enjoy your music, as long as we're having fun in the end it doesn't matter ;)
 

Attachments

  • 1990WatanabeandMllerLFJournal.pdf
    729.6 KB · Views: 21
Top Bottom