Does the DTS-10 deserve new test charts & graphs to better represent what its owners actually hear at home?
I certainly think so.
I’ve always wondered why the existing frequency response, spectrogram, waterfall & distortion graphs are so awful, and so different from what I’m experiencing at home, but I finally realized that the DTS-10 was never designed to play outside in the anechoic space of an open field, it’s supposed to be played in the smaller acoustical space typically found within the average home.
I think the problem is that it’s become so widely accepted that the best place to measure a subwoofer or full range speaker is either in an anechoic room or in the great outdoors in order to prevent reflections from contaminating the measurements. This method works well for direct radiator designs (i.e. sealed, infinite baffle or vented designs) but it definitely does not work well for the DTS-10 because the acoustical transformer properties of a horn are greatly affected by the acoustical impedance of the air that they are designed to play in, whereas a direct radiators response is not appreciably affected at all.
Tom Danley has already explained this in post #430 of this thread. Tom answers multiple questions in that post, but in paragraphs 1, 2, 3 & 5 he explains to "bossobass" how the frequency response of the TH-115’s gets smoothed out when it's operated in a space with higher acoustical radiation resistance, which occurs when either multiple subwoofers are operated close to each other, or when a single sub is operating in a smaller fractional space. (like indoors or close to a wall or corner)
Tom makes it very clear that the DTS-10 was never designed to operate in a free space environment.
Tom’s attached picture at the end of the post (visible here) shows multiple characteristics affected when operating in a higher acoustical radiation resistance location, notably:
- a flattening the power response curve.
- extending the low frequency cut-off point.
- increasing efficiency/raising sensitivity.
I think the only fair way of assessing the DTS-10’s true capabilities are to measure them in a small acoustical space that is somehow devoid of reflections, but I don’t know how that can be done. I’d like to hear your opinions/suggestions on possible methods that can achieve that goal.
Previously, reviewers made use of the near-field measurement method when testing subwoofers indoors, where the microphone is placed as close to the sound source as possible in order to reduce room reflection contribution to a minimum. This is the only method I can think of that will provide measurements more closely resembling what I hear in my listening position.
Examples of outdoor versus near-field indoor measurements: (Note: no EQ is used on indoor signals)
Notice the typical peaky response with a major resonance at 55Hz.
My indoor near-field measurement, positioned in right front corner of room, sub is parallel to and approximately 6" from right wall, mouth is facing wall.
Notice how the peaky response is greatly reduced, and the 55Hz resonance has dropped to 51Hz.
Indoor near-field measurement, right front corner diagonal placement. (sub placed 45° against front and right wall with mouth facing corner)
Notice how the deep bass energy is higher than the upper bass energy now.
Indoor near-field measurement comparison, parallel to diagonal placement differences.
This graph shows just how much deep bass energy is gained without changing the input drive level just by placing the sub diagonally in the corner, also the 51Hz peak has now dropped to 46Hz!
Most of the energy is in the upper bass and isolated to two narrow frequency domains.
Indoor near-field spectrogram.
Notice how the bass energy is more evenly spread out and extends to <20Hz.
Outdoor waterfall display.
Notice the prominent ringing at 55Hz & 100Hz.
Indoor near-field waterfall display.
Notice how all frequencies take longer to decay in a non-anechoic environment.
The shape of the waterfall at 0mS is the DTS-10 frequency response, whereas the shape of the waterfall at 300mS is the rooms natural resonant frequency response.
Notice that most of the DTS-10 peaks in the response do not correlate to the rooms peaks. The 46Hz peak is actually notched out and the 100Hz peak has split to 96Hz and 102Hz.
Since those were all near-field measurements, you're probably wondering what the listening position measurements look like.
This is an average of six seating position measurements available in the room. (No EQ)
I think this is very different from the original outdoor measurement.
Anechoic measurements just don't reflect what you will get when an indoor horn/tapped horn speaker is listened to or measured indoors.
How much EQ is required to flatten the response of a DTS-10 indoors?
Notice that less than +/-5dB is required to flatten the listening position response to my liking, and even the 46Hz peak only needs a 2.5dB cut to remove any remnants of the peak from view.
The above settings were used to flatten the response in this central seating location.
(Please ignore the nasty notch at 68Hz. The microphone was sitting on the backrest for this sweep and the notch goes away if the mic is moved forward to where a head would be)
The point I'm trying to make here is that very little EQ is necessary to make a DTS-10 useful in an indoor location, compared to the misleading conclusions one could jump to based on outdoor anechoic measurements.
I think it's time we respond to any negative comments from other forum members about the DTS-10's abysmal measurements by stating that previous graphs were not taken in its designed environment.
(That's like stating Ferrari's don't have fast acceleration, when you're actually testing it on a gravel road)
When it comes to horns, the ones that are designed to play outdoors should be measured outdoors, but the ones that are designed to be played indoors should be measured either indoors or in a simulated indoor condition, whatever that may be.
I would really like to hear other peoples ideas on how to take better indoor measurements. Let us know what ideas work to reduce room induced aberrations while maintaining the high radiation resistance of a small acoustical space.