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Old 7th January 2013, 09:48 PM   #11
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There's an error in my math; I used seconds for group delay but minutes for BPM. I'll fix that and post the results.
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Old 7th January 2013, 09:55 PM   #12
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Quote:
Originally Posted by weltersys View Post
Assuming both are time aligned at a crossover point of 125 Hz, that lag of 1000 ms /40Hz =25 ms per cycle, one half cycle (180 degrees) is 12.5 ms, one beat at 80 B.P.M.

Art
Sorry, shouldn't one beat at 80 BPM be [(60 sec/min)*(1000 ms/sec)/ (80/min)] = 750 ms?

There's no way in heck that 80 bpm is 12.5 ms per beat - I've been to enough clubs and studied enough stopwatches.
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Old 7th January 2013, 09:59 PM   #13
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Originally Posted by Patrick Bateman View Post
Can we perceive a difference of 0.758 milliseconds?
In adjusting time alignment in a full active car audio setup, I found that changes of .1ms were audible in the sound stage when tweaking the tweeter vs. mid. For the sub vs. mid, .1ms increments are VERY noticeable on how natural and integrated the bass sounds.

In running stereo subs, I have found that if they are too far ahead of the mains, even by an inch or so, the bass will sound unnaturally quick and ahead of the music.

I personally think low order crossovers and time alignment are the most important factors in getting natural sounding bass, assuming there is nothing else massively wrong.
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Old 7th January 2013, 10:10 PM   #14
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Do acoustical filters and electrical filters have the same effect on phase?
IE, I know that a passive or electronic filter will affect the phase of a loudspeaker.
And I understand that the phase shift that's present in single reflex bandpass is tied to the frequency response.

But what if you improved the frequency response? Do you improve the phase at the same time?

For instance, let's say I have a single reflex bandpass with a resonance of 60hz. It rolls off at 4th order, so there's 100dB of output at 60hz, 76db of output at 30hz, and 76db of output at 120hz.

If I EQ'd is so that the rolloff was 2nd order instead of 4th order, would the group delay go down as well?

With passive filters this is a bit impractical, but with mini DSP seems like you might be able to just 'dial it in.'
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Old 7th January 2013, 10:17 PM   #15
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Quote:
Originally Posted by Patrick Bateman View Post
Do acoustical filters and electrical filters have the same effect on phase?
IE, I know that a passive or electronic filter will affect the phase of a loudspeaker.
And I understand that the phase shift that's present in single reflex bandpass is tied to the frequency response.

But what if you improved the frequency response? Do you improve the phase at the same time?

For instance, let's say I have a single reflex bandpass with a resonance of 60hz. It rolls off at 4th order, so there's 100dB of output at 60hz, 76db of output at 30hz, and 76db of output at 120hz.

If I EQ'd is so that the rolloff was 2nd order instead of 4th order, would the group delay go down as well?

With passive filters this is a bit impractical, but with mini DSP seems like you might be able to just 'dial it in.'
I would call any sub tuned to 60 hz a poor design, and adding the eq would only increase delay. The key is to move the tuning to below 40hz or preferably far lower, into the 20hz's. Which keeps the group delay really down where it is fully masked by room gain/resonance.

Then crossover as high as is reasonable. If you are time aligned and use low phase crossovers, you can cross well above 100hz, where there is minimal group delay from the sub, and you are above the onset of group delay from the main's mid-woofer. Last thing you want to do is put a crossover point where there is major group delay on one of the drivers.

This also takes a huge bass load off your mains, resulting in cleaner midrange.

Last edited by turbodawg; 7th January 2013 at 10:20 PM.
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Old 7th January 2013, 11:57 PM   #16
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A couple of things that I have picked up generally over the years.

Bass wavelengths are huge and take sometime to propagate and produce a note to the ear but we can pick up the initial pressure quickly. We are much more sensitive to time related issues the higher in frequency they are though. Below 30Hz you can get away with a lot without much consequence. At 120Hz 2 octaves higher much much less. There can be delay, ringing, phase mismatch around the crossover region etc. delay can be compensated for and matched near the xover. Ringing on the other hand cannot be as easily fixed. However it takes a bit to be noticeable to me. The other big fly in the ointment is usually the room or space that the bass system ends up in will utterly dominate the resulting response and will play havoc in the time domain. Abrupt spikes in distortion around certain frequencies are more easily noticed to me than but still it takes quite a large amount of bass distortion to be audibly bad. Having very large amounts of headroom always sounds better to me. Also systems with smooth extended bandwidth on both ends usually sound better to me even after filtering is applied that rolls off the extra bandwidth.

Bass reflex sounds better the lower it is tuned. I'm talking at least 30hz or lower. Pushing the port ringing, high pass induced phase changes, etc. lower helps a lot. Below 30Hz the wavelengths are so long that any delay or ringing is doubtful to be audible unless truly bad. Again the higher in frequency the more sensitive we are to these issues. Also large ports that can prevent compression, tune shifting and air noise as much as possible are key. Watch out for the port resonances from a long pipe though. The worst bass reflex cabs I have heard were tuned 50Hz or higher.

Band pass typically is tuned higher in the 40-70 Hz range which puts the energy storage issues where it is more audible. BP usually has longer energy decay than BR also plus it is trickier to design well with many designs being cheap " thumper" units with limited bandwidth. Also the ports produce all of the output so they typically seem to have higher average airspeeds. On a positive note the natural acoustic filtering of harmonics can keep the distortion down.

Sealed or IB sound amazing and avoid many issues IF you can afford the required headroom needed for your app. Still the acoustic space largely dominates the result in the time domain.

Tapped horns in some ways are the opposite of bass reflex. The design results in large high q spikes in response which also have significant ringing associated with them. For example in the dts10 measurement posted the 54 Hz and 102hz ringing are clearly audible and give a boomy droning sound. There is tons of content in this region and if a kick drum fundamental is near the 54 Hz spike it is very noticeable. Also these spikes acoustically boost the harmonic distortion of lower frequencies that fall into the range of these spikes in response. This is not as noticeable to me as the ringing though which is clearly audible. Judging from a few other TH designs that I have seen measurements of it is a good guess that the lower the cabinet is tuned and the more undersized for the corner the worse these effects get. However the self damping in the design and driver play a role as well. So the dts10 which is tuned very low drags these issues down into the 50-100hz octave. IMHO it is best to keep TH's with an effective corner of 25Hz or higher to keep these issues above 100Hz and the xover for this reason. On the positive the efficiency, sensitivity and leveraging of the driver output are great. The distortion below the 5th horn harmonic (54Hz in the case of the dts10) is exceptionally low and coupled with the large amounts of deep bass headroom provide an effortless low bass presentation that is hard to match.

FLH's also have some ringing issues from the measurements I have seen especially when undersized as almost all are, but less than TH's. distortion performance is good but will also have some spikes if there are peaks in the response due to the horn loading. However the positives from a TH apply as well as the additional one of having a more extended and smoother useful bandwidth if designed well. A larger cabinet is required though.

I did do a comparison of the same TC sounds driver in a small sealed, small very low tuned bass reflex with passive radiators and the dts10 tapped horn and compared sensitivity, max output, impedance, etc. then I EQ'd each into the same base response as the sealed and compared output compression, distortion, etc...This was done to get a look at what the cab alignment is doing to the driver performance. I find it very interesting. The article is at my Data-Bass site.
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Old 8th January 2013, 12:19 AM   #17
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Originally Posted by weltersys
Assuming both are time aligned at a crossover point of 125 Hz, that lag of 1000 ms /40Hz =25 ms per cycle, one half cycle (180 degrees) is 12.5 ms, one beat at 80 B.P.M.

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Originally Posted by 454Casull View Post
Sorry, shouldn't one beat at 80 BPM be [(60 sec/min)*(1000 ms/sec)/ (80/min)] = 750 ms?

There's no way in heck that 80 bpm is 12.5 ms per beat - I've been to enough clubs and studied enough stopwatches.
You are correct, I followed Patrick's math error, though it is not the first time I made that error- a 25ms beat would be 2400 BPM, even faster than speed metal

Art
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Old 8th January 2013, 05:13 AM   #18
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Originally Posted by turbodawg View Post
In running stereo subs, I have found that if they are too far ahead of the mains, even by an inch or so, the bass will sound unnaturally quick and ahead of the music.
You can hear a delay of 0.07 ms with music?
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Old 8th January 2013, 01:21 PM   #19
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Originally Posted by 454Casull View Post
You can hear a delay of 0.07 ms with music?
My eclipse CD8053 adjusts in .1ms increments, which provide clearly audible changes to soundstage and bass timing. Yes, with music.

I just built and setup a pair of stereo subs, they are very audibly sensitive to alignment with the mains, moving an inch makes a difference between wrong and right sounding bass integration.

I'd say that cold (no A-B comparison, with music) I could probably detect a mis-timing between a sub and midbass of greater than +.2ms or -.5ms on the sub, given a 100 hz crossover and no weird distortion issues. Advancing the sub is much more audible for obvious reasons.

Last edited by turbodawg; 8th January 2013 at 01:29 PM.
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Old 8th January 2013, 01:42 PM   #20
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josh and turbo,
excellent posts. 27hz tuned sounded way better than 40hz. Sealing it off was not audibly faster, just less bass (like -6db on a 30hz slider on a 10 band eq).

Ported's less cone motion arounding tuning sounded better than 4 drivers sealed with eq (elf). Makes sence. The more cones move, the louder the harmonic distortion and higher junk too.

Danley uses 1/4 wave stubs is some of his tapped horns to lower the 1st 10db spike and lowering the ringing. Even then it probably is a bit audible.

I saw a post but can't remember where, thay said a push pull sounded better than a tapped horn.

454,
you'd be suprised what you can hear, like fractions of an inch using 24db LR crossover slopes. We can perceive a change due to the difference of integration with the highs, especially on transient percussive stuff. But an inch ? I'd say bs if i hadn't been moving around an 8" 2 way on the floor near a wall. inch made a decent difference.

Fast bass?
Slow bass?
Run a sub by itself, sealed vs ported. It all sounds like mud. if i remember, 18db 80hz low pass crossover had around 15ms of delay around 75hz and decreasing back to zero as you went lower towards dc. Nasty when you think about it, but the room will “ring down” slower than your sub at medium levels anyway.

Norman

Last edited by norman bates; 8th January 2013 at 01:47 PM.
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