which subwoofer for 250W@4ohms class D amp ? - Page 4 - diyAudio
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Old 21st July 2012, 08:52 PM   #31
Djim is offline Djim  Netherlands
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Both 129 Litres loaded with Monacor SPH-390TC
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File Type: jpg TTQWT_SPH-390TC_Basreflex_01.jpg (165.8 KB, 91 views)
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Old 22nd July 2012, 11:03 AM   #32
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Thank you for the line charts
uhh... I am not sure... does it mean that for 130L, Bass reflex is MUCH better
for group delay, impulse response and even global frequency response for bass ?

By the way : 130L is not Bessel volume, isn't it ?
Would group delay and impulse response be even better with 150L ??

Last edited by FroggySeven; 22nd July 2012 at 11:05 AM.
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Old 22nd July 2012, 02:22 PM   #33
tb46 is offline tb46  United States
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Hi FroggySeven,

Post #32: "... does it mean that for 130L, Bass reflex is MUCH better for group delay, impulse response and even global frequency response for bass ?"

In Post #21 I tried to show, that in my opinion the enclosure size for bjorno's T-TQWT could be reduced.

Anyway, using Hornresp to model the T-TQWT family of enclosures is only a convenience, as it seems to give an adequate idea of the raw frequency response. The response, especially the pipe resonances changes drastically when the enclosure is properly treated with sound absorbing material. Bjorno models this with MJK's MathCad software (see: link in Post #25). The frequency response is smoothened, and the impulse response ends up to be closer to that of a closed box. The pipe resonances in a bass reflex will not be attenuated as effectively; the resonances of a 15cm diameter x 50cm long duct port will definitely be audible

Bjorno has shown a large number of examples here on diyaudio, and people who have build these enclosures have given very positive responses. The biggest difference seems to be an audible improvement in sound quality. Naturally, this is a somewhat subjective criterium. Here are two examples of threads on this subject:

Fiddling with Hornresp - Peerless 831759

Tang Band Tang Band W8Q-1071F 8 X 12 box reccomendation

Let me add, that I do not yet have personal experience in listening to T-TQWTs. I find them interesting, and I have been helping out with the folding and drawing of boxes. I don't have MathCad, nor do I have the obviously extensive experience with this type of box that bjorno brings to the table. My past experiments with transmission line enclosures (and numerous BRs) leads me to believe, that a properly treated transmission line (or any one of what we could now call the MJK mass-loaded family) is superior in sound quality to a bass reflex.

Hopefully borno will find the time to add his comments to this.

Regards,
__________________
Oliver

Last edited by tb46; 22nd July 2012 at 02:24 PM.
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Old 23rd July 2012, 02:43 AM   #34
Djim is offline Djim  Netherlands
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Hi FroggySeven,

Somehow I get the feeling my intentions are interpreted differently from what I meant. I showed the impulse response just to consider (like its phase behaviour) and not as a ‘battle’ argument; In reality the impulse responses are often more the result of the location within an acoustic space (room acoustics).

I do agree with Oliver that you should wait until Bjorno is back since he is the (only?) person here on DIY who can show you advanced modelling of T-TQWT type enclosures. I am not ‘battling’ over the qualities a proper worked out T-TQWT can offer. However, I think it is more than fair to show the disadvantages of a loss of 2dB to 3dB @ 1W/1m and 4dB to 6dB @ Xmax in relation to basreflex.

Which considerations you should make is a personal matter and probably comes down to dynamics versus overall quality. I don’t favour any design over another since I strongly believe that for each type there are advantages and disadvantage and limitations. Each should be judged by personal preference in a specific situation. Another design, like a Tapped Horn as suggested earlier by jwmbro is possible but would end in a much larger enclosure that doesn't seem to fit in your demands.

To answer your earlier question about PPSL, it’s nothing more than a special arrangement of two drivers in one enclosure that could be of almost any type. One driver should face the magnet of the other driver and preferable share the same acoustic volume to suppress non-linear movement of the cones. Whatever enclosure type you consider, I can recommend this configuration because of the reputation of your drivers. You can use the search button by entering 'PPSL' to find more information on DIY forum.

Last edited by Djim; 23rd July 2012 at 02:49 AM.
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Old 23rd July 2012, 03:15 AM   #35
Djim is offline Djim  Netherlands
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One small note: If you can bridge your two plate amplifiers (500W @ 8Ohms) you can consider an improvement over the excursion and the impulse behaviour by connecting the VC’s of each driver in series (16Ohms). Wire each driver independently to your amplifier and connect them in parallel to get 8 Ohms for your bridged plates. Of course, such arrangement should be decided before designing the final enclosure(s) because of the changing parameter inputs.
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Old 24th July 2012, 06:16 PM   #36
bjorno is offline bjorno  Sweden
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Hi,

I'm almost back again...50% ?.... Ive noticed that my T-TQWT suggestion had a Re = 4 Ohm but should be = 3Ohm = as a result = minor FR difference but more important is that the advertised T/S is not consistent.
A consistency check can be found in the first submitted picture.

I fully agree with tb46 in post# 33 as the comparison made with a BR at 1W only show the speaker sensitivity and empty box behavior differences.

A more useful comparison is shown in the second of pictures.

If comparing the impulse response (always above + 10 mS where it matters its clear that the BR more or less would have an easy heard 'signature' at higher amplitudes even if using a LPF at or above 80 Hz.

Note: The tb46/Djim ? T-TQWT compared with the BR is xmax limited whereas the BR is port noise limited at higher SPL.

The T-TQWT sub can at max be XO:d at 145 Hz using a 24 dB/octave LPF(= max if Hi-Fi where 250 Hz would be 20 dB down) but not the BR that for Hi-Fi use should IMO use a XO < = 120 Hz.

b
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Old 25th July 2012, 01:51 AM   #37
Djim is offline Djim  Netherlands
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Hi Bjorno,

Maybe I am wrong but why do you compare the outputs based on different excursion values or without notification? See picture with added possible(?) values.

If there are worries about port noises as result of the air velocity, you can always improve it by using internal damping and/or make the port area as big the mouth/port of the T-TQWT (length compensation and volume compensation needed). Internal damping would also improve impulse response of a basreflex.
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File Type: jpg Ports_SPH-390TC_03.jpg (204.1 KB, 49 views)
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Old 29th July 2012, 06:40 PM   #38
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lots lots of interesting informations... I need time to digest all of them

thanks !
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