Double Bass Cabinet design, High pass filters & feedback

[macmrkt]

It's become apparent to me that some URB rigs feedback a lot more with the same bass in the same room, than others. While these are personal observations, as opposed to a scientific test, it does make me wonder what might be the possible explanation. Amps that I remember using that had more feedback issues were the AI Coda and recently, a Markacoustic 101. Rigs that had little feedback and could be set to play at higher perceived volumes are a Bergantino HT110 or a Wizzy-M driven by an iAMP800. I remember when using the AI Coda, I really needed the 'notch filter' that was included to minimize feedback. With the Wizzy-M, I don't seem to need it at all...

 

[Ric Vice]

It's become apparent to me that some URB rigs feedback a lot more with the same bass in the same room, than others. While these are personal observations, as opposed to a scientific test, it does make me wonder what might be the possible explanation. Amps that I remember using that had more feedback issues were the AI Coda and recently, a Markacoustic 101. Rigs that had little feedback and could be set to play at higher perceived volumes are a Bergantino HT110 or a Wizzy-M driven by an iAMP800. I remember when using the AI Coda, I really needed the 'notch filter' that was included to minimize feedback. With the Wizzy-M, I don't seem to need it at all...

I would agree with this and add that most amplifiers tend to use controls that only boost a particular frequency range, when what you really need in most situations with Acoustic Bass is the ability to cut frequencies. Walter Woods, Acoustic Image, and Euphonic Audio amps allow you to roll off the bad stuff for the most part.

Ric

 

[bolo]

Maybe the more efficient the speaker, the less likely it is to feedback at a given (perceived) volume in a given room if all the other variables (bass, p/u, amp) are the same?

I am not really a techie, and it wouldn't surprise me or hurt my feelings if this is dead wrong.

 

[drurb]

I would agree with this and add that most amplifiers tend to use controls that only boost a particular frequency range, when what you really need in most situations with Acoustic Bass is the ability to cut frequencies. Walter Woods, Acoustic Image, and Euphonic Audio amps allow you to roll off the bad stuff for the most part.

Ric

Virtually all of the amplifier circuits I have seen provide for both boost and cut. The centered positions of the controls usually provide neither with counterclockwise and clockwise rotation actually cutting and boosting, respectively. Much of the dissatisfaction with tone controls stems from poor choices (from the standpoint of DB amplification) of:

1) center frequency-- self explanatory
2) bandwidth (Q)-- the range of frequencies affected by the control
3) response-type (e.g., shelving, constant-Q, variable-Q, etc)-- how the range of frequencies affected by the control varies with the degree of boost and cut

Design of useful tone controls for DB amplification would, ideally, combine knowledge concerning circuit theory, physical acoustics, and psychoacoustics (the response properties of the ear, masking effects, loudness functions, and other factors that relate to human auditory perception).

 

[drurb]

Maybe the more efficient the speaker, the less likely it is to feedback at a given (perceived) volume in a given room if all the other variables (bass, p/u, amp) are the same?

I am not really a techie, and it wouldn't surprise me or hurt my feelings if this is dead wrong.

All other things being equal, this is not true. The design parameters typical of more efficient cabinets do not cause them to be any more or less susceptible to feedback.