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Multi-Way Conventional loudspeakers with crossovers

Bass reflex not so good
Bass reflex not so good
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Old 30th June 2020, 03:17 AM   #21
ILikeFoodz is offline ILikeFoodz  United States
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Wow, thanks for all the info GM! Sounds like there's some interesting history behind that driver. Any thoughts on what particularly about its design helps so much with the IMD?
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Old 30th June 2020, 05:46 AM   #22
phase_accurate is offline phase_accurate
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The material and shape of the cone makes it suitable for being used higher up in frequency than straight-sided cones, due to less severe cone breakup which is also happening higher up in frequency compared to straight-sided cones.

The improved IMD performance simply comes form the fact that they are alsmost idling if used at home listening levels. A 8" Driver has to move four times as much for the same listening level as a 15".

Regards

Charles
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Old 30th June 2020, 10:24 PM   #23
francesco81rs is offline francesco81rs  Italy
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Quote:
Originally Posted by HumbleDeer View Post
It looks like first gen DATS software doesn't it? "DATS" in the title bar and not DATS v2 or v3.
Yes, the HW/SW is "DATS" V2

Quote:
Originally Posted by ScottG View Post
..is that 700 liters total per loudspeaker?

350 liters per driver is not so great as far as bass reflex is concerned (for this driver), unless you are "tailoring" the freq. response for a specific result (..boosted bass and truncated lower freq. (sub-bass) response relative to the average.) That amount of volume isn't bad for a sealed design though.
The box is about 350L and has 2 woofers.
I attach some photos to show you the construction.
as for the response of the system, I had already understood that the response curve would lower first as regards the lower frequencies.
Regarding the "boosted bass" I had seen through a simulation with the SW Hornresp that between 30-100hz a sort of "peak" was formed.
By tuning the box to 25hz this "peak" disappeared.
Clearly the F3 of the system is less good.
In any case, what I aim for is a correct sound, even at the expense of a less extensive response towards the lower notes.
I do not reject any hypothesis, from the closed case, to the reflex with the two woofers, until eventually switch to a single woofer.

Quote:
Originally Posted by ScottG View Post
-take out ALL of the fiber.

Then listen again and take another Impedance measurement.
I removed all the internal fiber (what a sweat I did!); attached you can see the log and linear impedance curve.
As soon as I can I will try to listen again but now I don't like that peak around 250hz.

Thanks everyone for the help
Attached Images
File Type: png bass-parallel-no-fill-lin.png (61.5 KB, 158 views)
File Type: png bass-parallel-no-fill-log.png (63.2 KB, 162 views)
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File Type: jpg photo_2020-07-01_00-12-38 (3).jpg (60.4 KB, 51 views)
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Old 2nd July 2020, 01:08 AM   #24
N101N is offline N101N
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phase_accurate,
that optimistically extended frequency range embracing several heavy octaves will be muddled by resonant low frequency cone vibrations. Efficient systems are generally less well controlled, to be used at low listening levels, and there is no way to overcome this circumstance. Also, paralleled devices do not play in unison.
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Old 2nd July 2020, 06:27 AM   #25
ScottG is offline ScottG  United States
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Quote:
Originally Posted by francesco81rs View Post

The box is about 350L and has 2 woofers.

By tuning the box to 25hz this "peak" disappeared.
IF the T/S parameters of each driver are close to GPA's product sheet then 25 Hz should be OK (..35 Hz isn't good). ..personally I'd like to see 600 liters and 20 Hz (assuming spec'ed T/S parameters).

How did it sound without the stuffing? (..the impedance is closer to what I'd expect without it, but still less in magnitude.)

Yes, the 250 Hz "bump" in impedance is worrying. With this design I'd be hanging (off of all interior surfaces) a 4 inch "sheet" of rockwool (mineral wool insulation) at about 3/4's of the way into the interior (from the drivers). The sheet at almost the same size of the rear cabinet panel. I'd also be thinking about a diagonal (relative to the side-panels) sheet of rockwool. (..and yes, I realize that it's more difficult to do so with the bracing.)

The foam you had wasn't particularly good for anything.
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Last edited by ScottG; 2nd July 2020 at 06:41 AM.
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Old 2nd July 2020, 06:45 AM   #26
ScottG is offline ScottG  United States
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I'd also have an "open-frame" stand that elevates the cabinet by at least 5 inches, probably another frame that lifts the horn about the same (and angled-down as needed relative to the listener).

Finally, I'd want a good area carpet with good padding in front of the cabinets.
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Old 2nd July 2020, 07:08 AM   #27
brig001 is online now brig001  United Kingdom
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Could your problem be down to the dimensions of the listening room?
Mine has a strong peak at 50Hz, so I have to notch that out on my large speakers (flat to 35Hz)

Brian
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Old 2nd July 2020, 07:46 AM   #28
giralfino is offline giralfino  Italy
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The 250Hz impedance bump was already present in the measure with the foam. The fact that in this way was minor suggests that the problem lies in the driver/enclosure/fastening. I'd like to see a free air impedance (without box), just to compare the results.

Ralf
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Old 2nd July 2020, 07:46 PM   #29
ScottG is offline ScottG  United States
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With regard to the impedance "bump" at about 250 Hz.

It's the driver. GPA's other drivers display similar problems (..the 12" 414 has it around 160 Hz), and yes it does generate higher levels of non-linear distortion.

Still, that shouldn't be a problem resulting in the subjective quality he's having problems with (..as others who have similar drivers would have noted).

Making sure the drivers are properly coupled to the cabinet with a good air-tight seal is of course a priority.
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Last edited by ScottG; 2nd July 2020 at 07:48 PM.
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Old 3rd July 2020, 07:10 AM   #30
markbakk is offline markbakk  Netherlands
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Quote:
Originally Posted by ScottG View Post
With this design I'd be hanging (off of all interior surfaces) a 4 inch "sheet" of rockwool (mineral wool insulation) at about 3/4's of the way into the interior (from the drivers).
Loose sheets of mineral wools (or other flexible absorption materials) are prone to nonlinear behavior. The sheets will resonate themselves at certain frequencies. Locating the stuff in the center of the enclosure is a good suggestion, but it has to be braced.
 

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