The manual actually says: "..adjusts the voltage to bias the amplifier for Class AB operation,.."
Well, eventually curiosity strikes again, so I have another question.
On the web there are calculators for ceiling and floor bounce cancellation calculations. The "best" (or most practical) solution seems to be designing a speaker system with the woofer at floor level, and have it handle frequencies up to about 400 cycles.
However .... almost NONE of the designs I see out there, DIY or otherwise, seem to take this problem seriously. In fact, almost none seem to even acknowledge the existence of floor bounce or ceiling bounce cancellation. Why is that? Is the effect inaudible, or is the principle spurious, or what?
Thank you for your time and consideration. jj
On the web there are calculators for ceiling and floor bounce cancellation calculations. The "best" (or most practical) solution seems to be designing a speaker system with the woofer at floor level, and have it handle frequencies up to about 400 cycles.
However .... almost NONE of the designs I see out there, DIY or otherwise, seem to take this problem seriously. In fact, almost none seem to even acknowledge the existence of floor bounce or ceiling bounce cancellation. Why is that? Is the effect inaudible, or is the principle spurious, or what?
Thank you for your time and consideration. jj
Not one of my (few) fields of expertise, but the principle certainly isn't spurious. Here are the fruits of my research. They may suffice until a real expert comes along! 
Floor bounce causes comb filtering effects which are unique to each seating position in the room. It's not so much a case of loudspeaker design as a consequence of direct and floor reflected sound interaction.
The audible consequences depend on the degree of reflectivity of the listener's floor which is not in the control of the speaker designer.
Digital signal processing can provide the equalisation to remove these effects, but only at, or around, one seating position.
It is especially difficult to maintain equalisation at high frequencies and that is where your 400Hz limit must come in.
Floor bounce causes comb filtering effects which are unique to each seating position in the room. It's not so much a case of loudspeaker design as a consequence of direct and floor reflected sound interaction.
The audible consequences depend on the degree of reflectivity of the listener's floor which is not in the control of the speaker designer.
Digital signal processing can provide the equalisation to remove these effects, but only at, or around, one seating position.
It is especially difficult to maintain equalisation at high frequencies and that is where your 400Hz limit must come in.
It's a mandatory consideration for me. Especially at certain frequencies.
Ie above 700Hz where the ear is sensitive to the reflection's properties.. and between 200-700Hz where an inadvertent null could be difficult to equalise (or to absorb). I've also suffered time based discrepancies in the 200-700Hz region.
At the other extreme there is the omni and similar style. I think you either go for lots of diverse reflections or as few as possible. When you get close it may seem to get worse before it gets better.
Ie above 700Hz where the ear is sensitive to the reflection's properties.. and between 200-700Hz where an inadvertent null could be difficult to equalise (or to absorb). I've also suffered time based discrepancies in the 200-700Hz region.
At the other extreme there is the omni and similar style. I think you either go for lots of diverse reflections or as few as possible. When you get close it may seem to get worse before it gets better.
Galu: As always, thank you!
AllenB: You used the phrase, "mandatory consideration", and you mentioned the 200-700 cycle region. May I assume that you therefore take this cancellation to be audible? jj
AllenB: You used the phrase, "mandatory consideration", and you mentioned the 200-700 cycle region. May I assume that you therefore take this cancellation to be audible? jj
If there is cancellation of sufficient proportions then why shouldn't it be audible. However when using box speakers there can be a lot of energy all around at these frequencies lower than the box is controlling.
Therefore the modal combination may be less distinct than a single reflection. Now in some cases at these frequencies you can try to equalise and the result will not sound right. Here you need to reconsider your acoustic situation. Other times you can equalise.
Therefore the modal combination may be less distinct than a single reflection. Now in some cases at these frequencies you can try to equalise and the result will not sound right. Here you need to reconsider your acoustic situation. Other times you can equalise.
" ... If there is cancellation of sufficient proportions then why shouldn't it be audible...."
True, true. But I was asking about your opinion fron your own experiences. I didn't make myself clear about that, as usual. jj
True, true. But I was asking about your opinion fron your own experiences. I didn't make myself clear about that, as usual. jj
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Yes, the floor bounce cancellation in particular, but I'd be interested in learning about any other cancellations about which you had concerns. jj
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In my room I have to sit close to the back wall. Being married this is one of the things I can't change. There is cancellation at around 40-50Hz, but with a peak at 30Hz. If I sit forward it all evens out.
Is that the kind of thing you want to know?
Is that the kind of thing you want to know?
Yes..... and you just told me. I think my hearing is less than perfect, so to speak. Now I just need to figure out what to do about it.
Thanks for the help. jj
Thanks for the help. jj
This is a room acoustics problem, Jim. Reflections from the floor, ceiling and walls all combine to give nulls and peaks at different frequencies and locations throughout the room.
If you have the freedom to choose your ideal listening position then you probably don't have a partner who shares the same space!
The closest reflecting surface to the speaker is usually the floor, so get yourself a thick woolen carpet and take it from there! 😉
If you have the freedom to choose your ideal listening position then you probably don't have a partner who shares the same space!
The closest reflecting surface to the speaker is usually the floor, so get yourself a thick woolen carpet and take it from there! 😉
Thanks, Galu. I have a lot of experimenting to do, it seems. Like ABD, I can detect some peaks and valleys in the response as I move. However, I thought there was a difference between room modes (reinforcement and cancellation) and floor (and ceiling) cancellation. I don't know exactly what to make of it all. In other words, I don't know how to identify whether a particular cancellation is due to floor cancellation or a room mode cancellation. I was under the impression that woofer floor cancellation could be reduced by placing the woofer as close as possible to the floor.
If, on the other hand, I need to treat my listening room, that will be a lot of money. Two different problems to try and identify. jj
If, on the other hand, I need to treat my listening room, that will be a lot of money. Two different problems to try and identify. jj
Sometimes eliminating one particular mode can make the result worse.
Eg a line array is one way to cut the floor reflection and potentially reduce the ceiling. After this though, the other reflections might be more exposed. There are further steps to take along this road.
A good speaker could be made either way, it's just a matter of how.
Eg a line array is one way to cut the floor reflection and potentially reduce the ceiling. After this though, the other reflections might be more exposed. There are further steps to take along this road.
A good speaker could be made either way, it's just a matter of how.
That depends, I guess the most important step would be getting a calibrated measurement microphone. A lot of different types pending on budget and whatnot, the Dayton IMM 6 starts around 16.50$, I really like the minidsp Umik 1 for about 90$ but you can get some cheaper or pricier ones for use with a computer.
Dayton Audio iMM-6 Calibrated Measurement Microphone for Tablets iPhone iPad and Android
miniDSP UMIK-1 Omni-directional USB Measurement Calibrated Microphone
Trusting your ears is not recommended practice, we can easily fool ourselves.
Dayton Audio iMM-6 Calibrated Measurement Microphone for Tablets iPhone iPad and Android
miniDSP UMIK-1 Omni-directional USB Measurement Calibrated Microphone
Trusting your ears is not recommended practice, we can easily fool ourselves.
" ... Trusting your ears is not recommended practice, we can easily fool ourselves. ..."
This is true. However, it works two ways; for us as well as against us. Every day we tolerate imperfections that we don't find especially bothersome. I'm not OCD enough to get all worked up about this. I think what I really need to do is find out how cheaply I can get room treatment. If I can get that done and still have questions, I'll get back to all of you.
Thank you! jj
This is true. However, it works two ways; for us as well as against us. Every day we tolerate imperfections that we don't find especially bothersome. I'm not OCD enough to get all worked up about this. I think what I really need to do is find out how cheaply I can get room treatment. If I can get that done and still have questions, I'll get back to all of you.
Thank you! jj
Yes, guess I'm just trying to say that some issues (not all) can be dealt with by DSP, much less physical labour and probably lower cost than more advanced room treatments.
No point in using DSP without a half decent measurement mic, best money I've ever spent.
No point in using DSP without a half decent measurement mic, best money I've ever spent.
Am I correct in thinking that DSP works for the mic position, but not necessarily anywhere else? I haven't use it, but I have used REW and a Umik mic for trying to tune loudspeaker construction, and moving the mic just a few inches can give very different results.