Ideal Box size for Dynaudio 17W75EXT - diyAudio
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Old 1st August 2004, 09:58 PM   #1
Jozua is offline Jozua  South Africa
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Default Ideal Box size for Dynaudio 17W75EXT

Hi

I am keen to build a closed box using two of the Dynaudio 17W75EXT drivers per box I prefer to sound to be quick and dynamic hence the preference for a closed box. Low frequency extension is not a priority but a ultra clean midrange is.

Has anybody used these drivers and is there a preferred box size that people have buildt that works well with these drivers ? Any recommendations will be appreciated.

Thanks


Jozua
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Old 2nd August 2004, 06:34 AM   #2
Ap is offline Ap
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Not that particular one but the 20w75.
I initially went for a larger volume low Qtc <0.707, result no bass, so filled the box & aimed for a Qtc of 0.85 much better.
I think all Dynaudios I designed for higher >0.8 Qtc.
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Old 2nd August 2004, 07:46 AM   #3
Jozua is offline Jozua  South Africa
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Ap

I already have the Dynaudio 17W75EXT drivers, so my interest is in the 17W75EXT.

The problem is there are so many box permutations possible with these drivers hence my request for a possible working box design/volume that will sound good with these drivers.

Thanks


Jozua
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Old 2nd August 2004, 12:30 PM   #4
SY is offline SY  United States
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The EXTs start with an uncomfortably high Qts, so for any sort of tight bass, the box options are limited. Are you going to cross them over to subwoofers? If so, you can tune the system for a bit higher Qt than you want, then let the crossover knock it down. For example, if you use a box that will result in a Qtc of 1, then run a first order highpass at the resonant frequency, you'll end up with a third-order acoustic highpass at the resonance frequency and with a Q of 0.707. This is, of course, easiest to pull off by multiamping and using an electronic crossover.

If this isn't an option, then use about 30-40 liters per driver and use a Variovent.
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Old 2nd August 2004, 03:59 PM   #5
Jozua is offline Jozua  South Africa
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Hi

I used 18 liters with a single 17W85EXT but I found the extreme low end not tight enough for my liking. With a subwoofer the speaker is truly excellent but by itself the extreme low end bass distracts from what could be a very good speaker system.

A easy solution would be to cut the low frequency extention but if possible I would like to make use of the drivers dynamics at the lowest possible frequency. I am hoping that somebody in this forum has found a solution to this problem.


Jozua
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Old 2nd August 2004, 04:05 PM   #6
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What all your ppl are referring to as: "not tight enough" is simply the behaviour of the polyprop cone. This material isn't as rigid as for instance kevlar or aluminium.

The best solution is to add a stiff cone driver and make a 2.5 way speaker. Good candidates are the scanspeak 18w8546, the eton 7"Hex with heatpipe or a Focal with kevlar or W-membrame.
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Old 2nd August 2004, 06:02 PM   #7
SY is offline SY  United States
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It's not the cone, it's the motor. The cone has zip effect on Qes and that's where the issues are. If you want tight bass, this driver as a standalone is not a great choice. Dynaudio addressed this problem with later versions of the 17W series, but the EXT suffers from rather wimpy magnet/coil structure.

As it happens, the cone breakup on the EXTs is pretty high up into the midrange (over 3kHz), and is rather gentle; not as sharp and sudden as the normal 17W75 (which goes to pieces at 2kHz).
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Old 3rd August 2004, 05:42 AM   #8
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Your thin bass may be due to a lack of baffle-step compensation, rather than system Q. How much are you using?
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