Vented vs TH Sound Quality

[rafaro]

Realistic Subwoof Options for Quality PA use.

Better Late than never

Low 30 Hzs tuned vented large cabs

Tapped Horns ideally with larger volume mouth which will smooth freq response, increase SPL 3-5dB and reduce ringing. It can be designed so mouth can be enlarged with hinges and opened at showtime and closed for traveling

My 2 cents

Best Rafaro

 

[Octavia]

Patrick you mention Tapped Horn as sounding best versus several others even including Rythmic's servo subs (which I would imagine must be one of the most accurate and lowest distortion). I wonder if you have had the opportunity to hear any of the variations on H frame subwoofers? I suppose an H Frame subwoofer could be considered a variation on open baffle. Anyway just wondered if you have heard that as well.

 

[Scott L]

very informative

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.

Even though this is an older post, I just HAD to chime in and comment that this is the most informative post I had read in a VERY long time. Okay, now having stated that, let me go back and finish reading the entire thread.

 

[norman bates]

There is something else to consider.
The crossover point and it's changing delay.


with a 4th order x-over, about 1 octave on either side of the crossover point is off. Say at a 1khz crossover, the phase shoots toward positive infinity after about 500hz. Then just after the 1khz, the tweeter phase comes up from negative infinity towards zero.

An 18db crossover at 80hz causes the sub about 20ms delay then more as it gets closer to the crossover point. (can't remember where I got this)

from Roy Hall (Green Mountain Audio)
"If a speaker uses a 4th-order crossover at 3,000Hz (common for a 1" tweeter), what will we actually hear from this system?

*

Down at 1,500Hz, the tweeter isn't really contributing. Thus, the image is formed by the woofer. However, the woofer moves back by one inch because the circuit imposes 75 degrees of shift at 1,500Hz. But the dimensional shift is always relative to that 3,000Hz wavelength reference point, where (75 degrees/360) x (13,500ips/3000Hz) = 1 inch.
*

At 2,000Hz, the tweeter output is now audible (12dB softer then the woofer). We hear the image from the woofer move back by a little more, to 1.1" (90-degrees of 3,000Hz equals ¼ wavelength). Yet the tweeter is actually forward by 3/4ths of a wavelength of 3,000Hz, or 3.4". As a soprano's harmonics move through this region, we'll hear the image begin to split by 4.5" total. The image will begin to diffuse from front-to-rear, and harmonics structures will begin to fuzz over -- the sound will become grainy.
*

At 3,000Hz, the woofer and tweeter contribute equally. However, the woofer image has moved backwards by 2.25", for the same total split of 4.5". At this point, the image is very confusing and textures are at maximum graininess. The voice is split into two parts -- 'esses' and 'tees' from the tweeter arrive first, stretched out from the sound of the throat as delivered by the woofer -- an unnatural occurrence. The voice hisses and spits, and strings are edgy*. There'll be comments such as "the transients are etched..." "...detail thrust at the listener..." "...this speaker seems very fast..." "...analytical..." and "...very sensitive to electronics...." Of course, these comments would be expected because the tweeter arrived first!

* Not all higher-order designs sound like this, because there are ways to disguise the problem. Again, if the designer tunes the "Q" of the circuit (computer-optimized, or by ear), or otherwise misaligns the actual crossover point, the graininess will be reduced, along with transient response. The spatial distortion remains, however, and even a solo flute can be heard to wander.
*

At 5,100Hz, the woofer is now 12dB softer than the tweeter -- just audible. It's now 3.4" behind the tweeter's highest frequencies, and the tweeter is still 1.1" ahead -- a 4.5" total split.
*

At 12,000Hz, two octaves above the crossover point, the woofer output is non-existent, but the tweeter output will still arrive 30 degrees ahead (0.4 inches) of its very top end at 24,000Hz, where phase error returns to zero. This will disturb the timing of a wooden stick striking a bell, blurring its image. A musician striking the bell .4" late is definitely behind the beat as well."
Green Mountain Audio - Speaker-Time-Phase-Coherence - Loudspeaker Phase Accuracy and MusicalTiming

"Higher-order circuits, from 2nd on up, cannot be made time-coherent, because that Phase Difference each one exhibits at the crossover point does not remain a Constant Phase Difference when the tones move away from the crossover point. In other words, the drivers' Relative Phase Difference is always changing."
AudiogoN Forums: Phase Coherence or Time Alignment: Which More Imp?

Here on page 2 and 8 show the phase of a 24db crossover from eaw.
http://www.aalt.com.au/FAQ/DSP_setti...over_point.pdf

here is a picture of a 24db and its phase shift.



There's a reason I like large 2-way speakers, no phase angle / delay the bass region.

Norman

 

[CLS]

Ah, choosing xover points is like choosing poisons.

I myself like the sound very much from 15" playing up to 600Hz (2 x TAD in a huge box, that is). And this box might probably go down to 30Hz or so, I guess. Very deep already but not the deepest.

If the goal is down to the 20's, then, inevitable, bigger or heavier drivers are needed, which are not very good for midrange. Sigh~

 

[norman bates]

I know whatcha mean. I cross at 750hz................



But I prefer a much cleaner smaller horn.


That necessitates a smaller driver to get up to 2khz (nicely), then great, now I need a sub or make it a 3 way.

Oh well. sigh..........

Norman