Equalized Quasi-Sealed System

[bob]

For those interested, I've put a detailed description of my EQSS technique up on my web site at <A HREF="http://www.cordellaudio.com">www.cordellaudio.com</A>. This is the low-frequency technique used in the Athena active loudspeaker system, with four 5.25 inch drivers in each box, doen 3 dB at 35 Hz. It was also used in my EQSS subwoofer that I brought to a DIY gathering awhile back

Cheers,
Bob

[rory]

> For those interested, I've put a detailed
> description of my EQSS technique up on my
> web site at <A HREF="http://www.cordellaudio.com">www.cordellaudio.com</A> . This is
> the low-frequency technique used in the
> Athena active loudspeaker system, with four
> 5.25 inch drivers in each box, doen 3 dB at
> 35 Hz. It was also used in my EQSS subwoofer
> that I brought to a DIY gathering awhile
> back

> Cheers,
> Bob

I've had exactly this thought WRT using a driver in a smaller-than-optimum vented enclosure with equalization. I learned from a transducer engineer friend of mine that the reason I couldn't get a satisfactory LF response characteristic from a particular 8" midbass (the Audax HM210Z0) in a mini-monitor enclosure, or from a particular high-excursion subbass driver in a particular small box with a passive radiator was because of the fact that the driver's motor was not strong enough to work against the high acoustic impedance in the small enclosure. I also considered the use of a quarter-wave stub with a closed end (after Hegeman) to make sealed box performance acceptable, but never experimented with this.

It seems like there are two limitations here -- the driver's own excursion and the power handling of the voice coil. I also understand that one of the functions of the active equalization in the Bose 901 was to force the drivers to operate below their Fs in an enclosure whose resonator is tuned to support that particular frequency, and the equalizer only serving to compensate for the driver having to work against its own suspension compliance. In your configuration, however, it seems like the driver is equalized to work against the driver's insufficient motor structure.

[ajinfla]

> For those interested, I've put a detailed
> description of my EQSS technique up on my
> web site at <A HREF="http://www.cordellaudio.com">www.cordellaudio.com</A> . This is
> the low-frequency technique used in the
> Athena active loudspeaker system, with four
> 5.25 inch drivers in each box, doen 3 dB at
> 35 Hz. It was also used in my EQSS subwoofer
> that I brought to a DIY gathering awhile
> back

> Cheers,
> Bob

Thank you kindly for the information. Why didn't you include group delay for the three 5.25" driver systems in your comparison?

cheers,

AJ

[freddyi]

cool Bob - how much vent area might be needed with say 15" and 8mm xmax?

best,
Freddy

[bob]

Hi Rory,

Thanks for your interest in EQSS. The original BOSE 901 was not a ported system, so it was essentailly an example of an equalized sealed system. More recent 901's use a multi-chamber Acoustic Matrix enclosure (variation of Acousti-Mass, and they do not significantly equalize at the low end. The EQSS system is very different from anything Bose has done. Also, it is not the case that the equalization in EQSS is there to make up for an inadequate driver motor. You could employ drivers with much stronger motors in a conventional ported system and still not achieve the performance afforded by EQSS.

Bob

> I've had exactly this thought WRT using a
> driver in a smaller-than-optimum vented
> enclosure with equalization. I learned from
> a transducer engineer friend of mine that
> the reason I couldn't get a satisfactory LF
> response characteristic from a particular
> 8" midbass (the Audax HM210Z0) in a
> mini-monitor enclosure, or from a particular
> high-excursion subbass driver in a
> particular small box with a passive radiator
> was because of the fact that the driver's
> motor was not strong enough to work against
> the high acoustic impedance in the small
> enclosure. I also considered the use of a
> quarter-wave stub with a closed end (after
> Hegeman) to make sealed box performance
> acceptable, but never experimented with
> this.

> It seems like there are two limitations here
> -- the driver's own excursion and the power
> handling of the voice coil. I also
> understand that one of the functions of the
> active equalization in the Bose 901 was to
> force the drivers to operate below their Fs
> in an enclosure whose resonator is tuned to
> support that particular frequency, and the
> equalizer only serving to compensate for the
> driver having to work against its own
> suspension compliance. In your
> configuration, however, it seems like the
> driver is equalized to work against the
> driver's insufficient motor structure.

[bob]

> Thank you kindly for the information. Why
> didn't you include group delay for the three
> 5.25" driver systems in your
> comparison?

> cheers,

> AJ

Hi AJ,
Yes, that would have been a good idea. I should have done it.

Bob

[bob]

Hi Freddy,

Thanks. I'd recommend a 4-inch diameter flared port. That's what I use on the EQSS subwoofer, which employs two 10-inch Dayton II woofers.

Bob

> cool Bob - how much vent area might be
> needed with say 15" and 8mm xmax?

> best,
> Freddy

[ajinfla]

> Hi AJ,
> Yes, that would have been a good idea. I
> should have done it.

> Bob

I tried a few alignments in WinISD using your method and found that PR's were nearly a must for true subwoofers (unless I could figure out how to bend a 1m+ port :-) ). GD held up reasonably well down to maybe the 30's, but then skyrocketed below. How audible would this be, if at all?
Probably not very, but the alignments I tried would need 2 PR's per active driver. For about the same cost, I could add a 2nd sub, drive it off the same amp in a different location and possibly excite modes in a more evenly.
It seemed best used for extending the range of a monopole main speaker. Perhaps your subwoofer page may cause me to re-investigate when you post your results. Thanks again.

cheers,

AJ