I never really understood the Allison effect, despite reading your interview, Joachim. 
SpeakerBuilding.com - Interview with Joachim Gerhard of Audio Physic, Page 1
I remember the Roy Allison speakers though. Bass near the wall. Or the floor.
SpeakerBuilding.com - Interview with Joachim Gerhard of Audio Physic, Page 1
I remember the Roy Allison speakers though. Bass near the wall. Or the floor.
It is very simple. Imagine a typical 2 way monitor on a stand. The sound of the woofer will reach you direct and reflected from the floor.
That sound from the floor is delayed because the path : woofer - floor - ear is longer then woofer - ear. The result is a loss of energy in the region around 200Hz because of phase cancelation. That " hole " in the fundamental tone region can amount to up to 11dB, making the sound thin. In my box the woofer is close to the floor up to 300Hz avoiding this double path effect.
It could be argued that we are used to this because our head ( voice ) and other intruments are also off the floor. Problem is that with conventional speakers this effect is doubled. It is already on the recording plus the physical arangement of the speaker.
That sound from the floor is delayed because the path : woofer - floor - ear is longer then woofer - ear. The result is a loss of energy in the region around 200Hz because of phase cancelation. That " hole " in the fundamental tone region can amount to up to 11dB, making the sound thin. In my box the woofer is close to the floor up to 300Hz avoiding this double path effect.
It could be argued that we are used to this because our head ( voice ) and other intruments are also off the floor. Problem is that with conventional speakers this effect is doubled. It is already on the recording plus the physical arangement of the speaker.
The effect is real. For example Stereoplay sometimes measures speakers in room.
Here are 2 two way speakers on stands. They are typical british monitors.
You can see the loss of energy and bumpyness between ca. 150Hz and 400Hz.
It amounts to ca. 5dB but it can be worce when you do not average.
Here are 2 two way speakers on stands. They are typical british monitors.
You can see the loss of energy and bumpyness between ca. 150Hz and 400Hz.
It amounts to ca. 5dB but it can be worce when you do not average.
Attachments
Another posibility to improve the situation is listening to the speakers in the nearfield and sitting close to the backwall :http://suesskind.dinologic.net/wp-content/uploads/2013/10/Speaker-Set-Up.pdf
This is my loudspeaker setup guide edited by Allen Perkins.
This is my loudspeaker setup guide edited by Allen Perkins.
I meant the wall behind the listener. In your preferred setup the listening position is right up against the wall. In my experience a very early and strong rear wall reflection leads to degraded imaging, possibly some coloration and more listening fatigue at high sound levels. A wideband damping panel can eliminate those problems, yet it also makes the sound less spacious. Therefore I prefer to have some free space behind the listening position.
Joachim, I'm obviously being a bit dim here, but you say the Allison effect dip in power response occurs at a certain frequency depending how close the bass is to the nearest boundary. You cross over at 300Hz with your low placed woofer here. So if I follow, the Allison effect is occurring at a higher frequency, say 500Hz here. And you are avoiding it that way?
The speed of sound is 343 metres/second, so the wavelength at 343 Hz is one metre. AFAIK, the Allison effect occurs around 100Hz for a 1 metre boundary. Your 250mm bass's centre is about 200mm off the floor, so your Allison effect is around 500Hz?
Have I got it right?
The speed of sound is 343 metres/second, so the wavelength at 343 Hz is one metre. AFAIK, the Allison effect occurs around 100Hz for a 1 metre boundary. Your 250mm bass's centre is about 200mm off the floor, so your Allison effect is around 500Hz?
Have I got it right?
Yes, putting the woofer close to the floor shifts the Allison effect upwards.
The bass is rolled off at 300Hz so at 500Hz where the Allison effect would be is out of band.
Likewise the midranges are high up shifting the Allison effect downwards. So crossed over at 300Hz the allison effect is out of band too but this time shifted downwards.
I made some in room measurements of the German Speaker and they looked very well.
No succout in the fundamental tone range. It also sounds different then a two way on a stand.
Somewhoe more " complete ". Distortion, specially intermodulation, is low too.
The bass is rolled off at 300Hz so at 500Hz where the Allison effect would be is out of band.
Likewise the midranges are high up shifting the Allison effect downwards. So crossed over at 300Hz the allison effect is out of band too but this time shifted downwards.
I made some in room measurements of the German Speaker and they looked very well.
No succout in the fundamental tone range. It also sounds different then a two way on a stand.
Somewhoe more " complete ". Distortion, specially intermodulation, is low too.
Hi,
Search for 'flooder' here on diyaudio. Got plenty of discussion about floor coupling.
PS. Allison "invented" floor reflection ???
You don't know who you're talking to here, do you?
And you throw in a dig at Roy Allison too.
What is it they say? "Better to remain silent and be thought a fool, than to speak out and remove all doubt."
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Thanks, Joachim.
You don't know who you're talking to here, do you?
And you throw in a dig at Roy Allison too.
What is it they say? "Better to remain silent and be thought a fool, than to speak out and remove all doubt."
You are asking if I know who you are ? Now why that would be of any importance ?
I gave you a hint to diyaudio threads where you can learnd about floor efects, since you don't seem to know what a floor reflection does to sound. That's what you were asking earlier.
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ME? I'm of no importance at all. I didn't realise you were talking to ME. Just a toiler in the vinyard.
Without sounding too obsequious, I get a kick out of rubbing along with some top speaker designers like Joachim. And fair play to the man, he is quite open about his projects. Roy Allison is one of my heroes. He didn't just do room acoustics and speaker placement, he designed some unusual mid and treble drivers too.
At this point in the thread, we are talking about the effect of room acoustics on speaker performance. It's an interesting topic that Steen Duelund's work got me interested in:
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You have to add the reflections too, to make more sense of it. Steen came up with the interesting idea that cabinet damping can be inside or outside the speaker, and it amounts to the same thing. So somehow, the damping and placement rules inside speaker cabinets apply to the room too.
I think I've lost myself. Can someone else pick it up from there?
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Dr. Veronique Adam did a PHD thesis about that.
You can read this AES paper to see a refference to this work :http://www.swissaes.org/nl/aes_newsletter_114.pdf
I have a copy of her work she gave to me but now we go very deep.
It is posible to use a dynamic speaker as a microphone.
Baxandall also did work on this.
You can read this AES paper to see a refference to this work :http://www.swissaes.org/nl/aes_newsletter_114.pdf
I have a copy of her work she gave to me but now we go very deep.
It is posible to use a dynamic speaker as a microphone.
Baxandall also did work on this.
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