Keith_W DSP system

[3ll3d00d]

issues below 100Hz may be because the microphone position picks up nulls,

you wouldn't expect a room issue to have a non linear response to volume changes

 

[OCA]

That is a very good point. Also, the subwoofers are located about 1.5m further away from the speakers. So to make "86dB" at the mic, they probably have to make closer to 90dB.



I am very skeptical that the tube amp is distorting at all. The horn has a quoted sensitivity of 98dB/W/m, and the tube amp puts out a nominal 110W. The amp would be barely chugging along at that volume.

BTW, I was surprised by how loud 76dB was. 86dB was intolerable, and 96dB had me plugging my ears. I normally listen at about 60-70dB. It is really quiet where I live. I find that when the noise floor is so low, music does not need to be turned up so loud. For example, I typically listen louder in the day and softer at night. I wonder if you guys have the same experience.

I am guessing something is wrong with your SPL meter. I doubt your woofers would start port chuffing at these levels. I measure not 76 but 75dB steady state almost daily and it's not really too loud, 86dB is loud but not ear plug loud. I can't comment on 96dB, too loud is too loud from some level onwards.

 

[Keith_W]

I am guessing something is wrong with your SPL meter. I doubt your woofers would start port chuffing at these levels. I measure not 76 but 75dB steady state almost daily and it's not really too loud, 86dB is loud but not ear plug loud. I can't comment on 96dB, too loud is too loud from some level onwards.

I have compared my SPL meter to another SPL meter. It reads the same Sadly I think the SPL I am measuring is accurate. If anything, it is likely that the speakers are producing less than the SPL meter indicates because of room gain.

 

[Mr. Widget]

I have compared my SPL meter to another SPL meter. It reads the same Sadly I think the SPL I am measuring is accurate. If anything, it is likely that the speakers are producing less than the SPL meter indicates because of room gain.

When you are talking about 76dB or 86dB, are you using dBA, dBC, or dBZ? If you are using a typical meter with dBA, you are really talking about ~1kHz to ~8kHz.

 

[Keith_W]

When you are talking about 76dB or 86dB, are you using dBA, dBC, or dBZ? If you are using a typical meter with dBA, you are really talking about ~1kHz to ~8kHz.

Thanks. Answered in this post. I am using dBC.

 

[MaxwellsEq]

BTW, I was surprised by how loud 76dB was. 86dB was intolerable, and 96dB had me plugging my ears. I normally listen at about 60-70dB. It is really quiet where I live. I find that when the noise floor is so low, music does not need to be turned up so loud. For example, I typically listen louder in the day and softer at night. I wonder if you guys have the same experience

I calibrated my setup at 78dB using Bob Katz' approach. On well recorded music, this sounds to me like a sweet spot between too quiet and too loud. Going up 10dB sounds very loud on compressed rock, and acceptable for quieter classical recordings. So I can understand why this sounds loud to you.

 

[Hayabusa]

I calibrated my setup at 78dB using Bob Katz' approach. On well recorded music, this sounds to me like a sweet spot between too quiet and too loud. Going up 10dB sounds very loud on compressed rock, and acceptable for quieter classical recordings. So I can understand why this sounds loud to you.

I think you better use white noise, it has peak to average ratio of around 6dB (this means the peaks have 4 times more power than average)
so if you have this level set, what level comes your sweep out?

 

[Hayabusa]

2. Output increased until SPL meter registered 76dB at mic position.
3. White noise played for 2 min.
4. Sweep done at 76dB.

So SPL 76dB registered with what signal ? white noise?
How did you verify your sweep was at 76?
You can do this by playing a 1000Hz with the same level setting as the sweep...

 

[3ll3d00d]

Better to use rew for this sort of thing, avoid having to translate dBFS to SPL manually and then you can easily see spl at every frequency with whatever smoothing you like rather than relying on any form on band limited pink noise to estimate level.

 

[Keith_W]

I calibrated my setup at 78dB using Bob Katz' approach. On well recorded music, this sounds to me like a sweet spot between too quiet and too loud. Going up 10dB sounds very loud on compressed rock, and acceptable for quieter classical recordings. So I can understand why this sounds loud to you.

What is Bob Katz's approach? Can I have a link please?

So SPL 76dB registered with what signal ? white noise?
How did you verify your sweep was at 76?
You can do this by playing a 1000Hz with the same level setting as the sweep...

1. SPL of 76dB registered with white noise.
2. I did not verify that my sweep was at 76dB. I ... umm ... sort of assumed that it would be

BTW a little anecdote. I showed this measurement to my friend, and he asked me "what are you going to do now?". My response: ignore it and pretend that all is well. Live in denial.

Jokes aside, there is more to say about this tweeter. Plasma tweeters wear down their electrodes and valves. Valves are used because of robustness and resistance to high voltage spikes. They are also user replaceable. A high voltage spark can easily kill a transistor so transistors are not used. In my speaker, I last changed the electrodes and PL519 valve about 6-7 years ago. They are supposed to have a 10,000 hour service life, but I haven't opened up the tweeter to inspect the electrode for years. Nor do I have any way to test the valve. This may be a reason why it is compressing and distorting so much. It might improve if I ordered another set of electrodes and valves from Acapella.

And another thing. This will make me sound like a total subjectivist, but this tweeter has an amazing ethereal sound. I have been chasing measurements looking to see why it does that. So far I haven't found very much. The impulse response is better than the average tweeter (no ringing!), but there is not much to find otherwise. You really have to hear it to understand. Under normal use, I listen very softly so the compression does not really bother me.

This speaker is the reason I am an objectivist. Before I bought this speaker, I owned the lot - audiophile speaker cables, SACD player, everything. I could hear issues with this speaker, which lead to purchase of a mic, which then lead to purchase of Acourate ... many years later, I junked all my old beliefs and here I am. It has been quite the journey.

 

[3ll3d00d]

SPL of 76dB registered with white noise.

band limited pink noise (500-2000Hz) is commonly used for this purpose so probably it's rather louder than you think then (another reason to use rew ....). A sweep with v coarse (eg octave) smoothing can also be useful.

 

[MaxwellsEq]

What is Bob Katz's approach? Can I have a link please?

if you search Bob Katz' K-System, you will find his AES paper. Gearspace has a good article as well.

 

[Hayabusa]

What is Bob Katz's approach? Can I have a link please?



1. SPL of 76dB registered with white noise.
2. I did not verify that my sweep was at 76dB. I ... umm ... sort of assumed that it would be

This definitely not the case!
Please do the 1000Hz sine wave test and set the level of the generator and the sweep the same

 

[Hayabusa]

This definitely not the case!
Please do the 1000Hz sine wave test and set the level of the generator and the sweep the same

Or better: use a calibrated mic like the minidsp UMIK

 

[gnarly]

I was genuinely displeased to see this. What I see:

- Subwoofer: behaves extremely poorly. As volume gets louder, severe dynamic compression occurs.
- Woofer: behaves as expected at 86dB. By 96dB it is showing slight dynamic compression. I am unsure of the cause of the dip at 210Hz, could be some kind of cabinet resonance causing cancellation?
- Horn: exhibits the opposite of compression. In fact it exaggerates loudness. This might be why the horn sounds so lively.
- tweeter: behaves extremely poorly. Dynamic compression sets in at 86dB, but it "only" loses up to 2.3dB in loudness. By 96dB it is all over the place, that huge peak >15kHz is probably

If i may suggest:
use pink noise instead of white. White noise is a brutal unrealistic test for HF/VHF imo. Without the -3dB per octave attenuation the pink noise has, I think white is bound to show serious compression. Yikes that must have been painful at 96dB !
and use z-weighting. A and C are just confusing bastards imnsoho lol

Was the sub signal white noise too? Just curious. And what amp was driving them? I agree with the person who said sub displacement should handle 96dB easy.
Something seems amiss.
I can't agree that rooms remain linear with SPL increase. Ime, rooms go very unilinear with major SPL increase....particularly from subs.
All you have to do to verify this, is play 'subs only' and listen as new rattles and resonances appear all over the place at higher and high SPL.
I'm also convinced room absorption can handle only so much energy. So RT60 curves go to hell past a certain SPL. Once a level is exceeded at whatever frequencies, those particular frequencies gain level, vs the rest of the unaffected, still absorbed spectrum.

If you really get into wanting to measure uncompressed, undistorted, and unlimited SPL, AES75 is a new spec for that.
I'm not an AES member and wont pay the $100 for the spec pdf. But I followed it's development when it was Meyer M-Noise. Stimulus signal is basically pink noise with an expanding crest factor as frequency goes higher.
Here's a free tool for implementing AES75. https://eclipseaudio.com/speakermeasure/

 

[3ll3d00d]

I can't agree that rooms remain linear with SPL increase. Ime, rooms go very unilinear with major SPL increase....particularly from subs.

It's certainly true that you can introduce new sources of distortion but that's a different situation, I was talking about modal response of the room.

 

[gnarly]

It's certainly true that you can introduce new sources of distortion but that's a different situation, I was talking about modal response of the room.

Gotcha, thx.
I do think modes moves some too. But, not as big an effect as room rattles and resonances.
I think the same "absorption capacity" for the higher end of the spectrum", needs a companion "rigidity capacity" for the lower and of the spectrum .
As walls, ceiling and floor loose their rigidity, and room barriers begin to flex, I think it probably reduces the room modes' Q's, and lowers their peak strength.

 

[3ll3d00d]

I guess it depends how loud you go and how the room is constructed, certainly I've gone v loud in my room (until the door frame groans ) without seeing any such effects but my room is solid brick walls so probably they are not going to flex so much.

 

[gnarly]

I guess it depends how loud you go and how the room is constructed, certainly I've gone v loud in my room (until the door frame groans ) without seeing any such effects but my room is solid brick walls so probably they are not going to flex so much.

Yes, i feel certain you are correct on both loud and construction.

All anecdotal here.. one pair of speakers has been with me for almost 50 years now, Acoustat-X electrostats.
They make very good bass for a 'stat', and I've set them up in about 15 rooms over the years..
In a small size Manhattan apartment where all walls, floors, and ceiling were poured concrete , bass including sub was all I wanted. Powerful, balanced low extension. Maybe some real cabin gain going on too, due to small size.
In another mid size apt that was also all poured concrete, bass was still very strong.
Later ...I had an old 1800's farmhouse whose outer walls were 3 courses thick of brick, with crazy strong interior walls......and some rooms with walls of normal framing construction.
Stiff small rooms were great, others could often use a sub. Great comparisons there. The rooms really made a difference for Martin-Logan CLS stats (which do lack bass)

Now at another place, with a large room and loose construction up top, and a similar sized room area-wise below it with stout construction.....bass is night and day different, upstairs vs down.
(As is outdoors....I play/experiment a lot with larger speaker and sub setups).

A really interesting phenom (to me at least) that I've never encountered before, is my latest subs need LESS drive level outdoors than in the large upstairs room.
Theory...
Every sub I've had before (many) has not gone below f-3 at 30Hz. That's been my design target until latest DIY subs that reach to 25Hz.
My theory is that the extra 5 Hz extension is loosening up the house to the point I'm loosing both modes and potential cabin gain.
Weird really....i don't yet know what to make of it, other than acknowledge the indoor vs out level disparity exists .......opposite all my prior experience.

 

[3ll3d00d]

I hadn't done anything like a compression sweep for ages so gave it a quick go today, can confirm 95dB sweeps are rather loud (fortunately I do still remember to wear my earplugs whenever I sit in the room when sweeping ) and that, in my room, 75-85-90 all stack on top as you'd expect with no variation, 95 also fine except some anomaly in the woofer (but not the sw or mid). On replaying with a slower sweep, 95dB provoked a burst of crackling from my woofer amp which is a) old (a cinepro 2k6), and b) the gain dials have been going on it for a while. I'd been dissuaded from taking it out investigate/clean/replace for a while cos the thing is so damn heavy but I guess I finally need to do it. Anyway, moral of the story is, giving your system a blast every now and again is a good idea!