Link to original post here: http://www.diyaudio.com/forums/mult...dipole-15-lo15-need-advice-3.html#post3730011
We are posting here in relation to a question surfaced by member JackG3, so this is his thread.
He asked about problems he is having with room modes and his woofer EMINENCE ALPHA 15 A in a dipole. He mentioned the room dimensions, in the same thread, with a waterfall attachment for the same driver.
After checking for bad modes and proportions of the listening room, nothing was found. This is, the modes are there but the room proportions can be classified as good room ratios (shadow Bolt-area) after Bolt. In this case this is the approximate dimensions ratio (#1 below):
1 : 1.57 : 1.95
But, the first length Modal resonance is ~43 Hz.
The first height Modal resonance is ~84 Hz, and the second length Modal resonance is ~86 Hz. So, very close but nothing very bad here for a home studio. We could check better with real dimensions for behind the drywall that is over the cinderblocks, but I think that's not necessary because might not be the culprit.
If we look at this woofer (pic of the linked post), ALPHA 15 A, the mounted resonance (Fsp) is 41Hz. So as a first guess I would say and concentrate in this problem. We have a speaker with 41Hz maximum impedance and a room length with a bad mode at the closest frequency of 43Hz. Usually in other cases a passive series RLC is used (#2) to attenuate the resonance of the driver.
We are posting here in relation to a question surfaced by member JackG3, so this is his thread.
He asked about problems he is having with room modes and his woofer EMINENCE ALPHA 15 A in a dipole. He mentioned the room dimensions, in the same thread, with a waterfall attachment for the same driver.
After checking for bad modes and proportions of the listening room, nothing was found. This is, the modes are there but the room proportions can be classified as good room ratios (shadow Bolt-area) after Bolt. In this case this is the approximate dimensions ratio (#1 below):
1 : 1.57 : 1.95
But, the first length Modal resonance is ~43 Hz.
The first height Modal resonance is ~84 Hz, and the second length Modal resonance is ~86 Hz. So, very close but nothing very bad here for a home studio. We could check better with real dimensions for behind the drywall that is over the cinderblocks, but I think that's not necessary because might not be the culprit.
If we look at this woofer (pic of the linked post), ALPHA 15 A, the mounted resonance (Fsp) is 41Hz. So as a first guess I would say and concentrate in this problem. We have a speaker with 41Hz maximum impedance and a room length with a bad mode at the closest frequency of 43Hz. Usually in other cases a passive series RLC is used (#2) to attenuate the resonance of the driver.
Attachments
Hi,
That RLC won't do anything unless the amplifier
has high output impedance. 36mH ? a bit big ....
If it has high impedance that will drive the woofer
Q up at Fs, a low output impedance would help.
rgds, sreten.
That RLC won't do anything unless the amplifier
has high output impedance. 36mH ? a bit big ....
If it has high impedance that will drive the woofer
Q up at Fs, a low output impedance would help.
rgds, sreten.
Actually, the loudspeaker is the problem
Of course here, in this case the loudspeaker has a resonance that is at the same frequency that one or more (modal R) of one of the dimensions of the room. 😀
Of course here, in this case the loudspeaker has a resonance that is at the same frequency that one or more (modal R) of one of the dimensions of the room. 😀
ABOUT JACKG3's MEASUREMENTS
I'm just going to pop in to all the threads where JackG3 posted about his wonderful dipole and remind everyone that it isn't a dipole from where he is seated. I am doing this to quell any confusion about the speaker and/or room response.
Since he is also measuring the speaker in the near field, the direct response from the front of the driver's cone is much higher in SPL that the room response. That is why his response plots don't show any room resonances. This has nothing to do with the attempt at using this speaker as a dipole. It could be used as a dipole if it was farther away from the listening position, but this is not the setup he has shown.
His setup likely provides the clean and visceral bass that he describes (at least down to 30-40Hz) but it's essentially the infinite baffle closed box response that he is getting from the driver. This explains not only the frequency response, but also the waterfall - the ringing at 40 Hz is caused by the somewhat high Qts of the driver.
There is no need to over analyze this situation. If you put your ears near the radiator (of sound) you will get these effects. If my wife would let me put a large speaker right behind my head in our living room, I would do it too!
I'm just going to pop in to all the threads where JackG3 posted about his wonderful dipole and remind everyone that it isn't a dipole from where he is seated. I am doing this to quell any confusion about the speaker and/or room response.
Since he is also measuring the speaker in the near field, the direct response from the front of the driver's cone is much higher in SPL that the room response. That is why his response plots don't show any room resonances. This has nothing to do with the attempt at using this speaker as a dipole. It could be used as a dipole if it was farther away from the listening position, but this is not the setup he has shown.
His setup likely provides the clean and visceral bass that he describes (at least down to 30-40Hz) but it's essentially the infinite baffle closed box response that he is getting from the driver. This explains not only the frequency response, but also the waterfall - the ringing at 40 Hz is caused by the somewhat high Qts of the driver.
There is no need to over analyze this situation. If you put your ears near the radiator (of sound) you will get these effects. If my wife would let me put a large speaker right behind my head in our living room, I would do it too!
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