HOSS question

[Pete Schumacher ®]

Dan Nuebecker posted plots of the HOSS RS150-4, and there was no indication of a baffle step. He's taking the measurements roughly 90 degrees off axis, explaining the reduction of the high frequencies, but I noticed that there was really no drop off below 800Hz, typical for a front-firing woofer on a small baffle.

I really wonder what's going on. Does being so far off-axis also reduce baffle step loss by causing the upper end to fall off?

Dan, did you notice the same thing with the Mentor Omni's?

[dlneubec]

Hi Pete,

Yes the same thing occurred with the Mentor omni's.

John K. explained to me that there was no need to worry about baffle step in this application. I believe he said it was due to the fact that the drivers, up and down firing at each other, are forced to play in 4pi space thoughout their operating range and never play in 2pi space.

Hopefully John will see this and chime in and correct my most likely erroneous recollection of his explanation. I'm certain he told me on several occations that I did not have to consider baffle step in this type of omni design and the measurements I have taken on these two omni projects seem to bear that assertion out.

Regards,

Dan

> Dan Nuebecker posted plots of the HOSS
> RS150-4, and there was no indication of a
> baffle step. He's taking the measurements
> roughly 90 degrees off axis, explaining the
> reduction of the high frequencies, but I
> noticed that there was really no drop off
> below 800Hz, typical for a front-firing
> woofer on a small baffle.

> I really wonder what's going on. Does being
> so far off-axis also reduce baffle step loss
> by causing the upper end to fall off?

> Dan, did you notice the same thing with the
> Mentor Omni's?

[Jeff B.]

> Hi Pete,

> Yes the same thing occurred with the Mentor
> omni's.

> John K. explained to me that there was no
> need to worry about baffle step in this
> application. I believe he said it was due to
> the fact that the drivers, up and down
> firing at each other, are forced to play in
> 4pi space thoughout their operating range
> and never play in 2pi space.

> Hopefully John will see this and chime in
> and correct my most likely erroneous
> recollection of his explanation. I'm certain
> he told me on several occations that I did
> not have to consider baffle step in this
> type of omni design and the measurements I
> have taken on these two omni projects seem
> to bear that assertion out.

> Regards,

> Dan

That sounds about right. Part of the key is the 90 degrees radiation. At 90 degrees off-axis you are seeing a roll-off of the frequencies that would have ordinarily received a gain from the baffle, hence the response more closely resembles that of a 4pi environment.

[Jeff B.]

> That sounds about right. Part of the key is
> the 90 degrees radiation. At 90 degrees
> off-axis you are seeing a roll-off of the
> frequencies that would have ordinarily
> received a gain from the baffle, hence the
> response more closely resembles that of a
> 4pi environment.

The way to think of this lies in the fact that baffle step is usally always discussed as a loss, but in reality it is actually an acosutic gain. You're losing that gain here, that's why you don't see it.

[Pete Schumacher ®]

> The way to think of this lies in the fact
> that baffle step is usally always discussed
> as a loss, but in reality it is actually an
> acosutic gain. You're losing that gain here,
> that's why you don't see it.

It's still a loss, just over the whole range.

The infinite baffle response would ideally be 6dB higher then, since it's a 2pi response.

Or am I missing something again?

Dan, are the RS150-4 measuring 6dB below their stated 91-92dB level?

[Jeff B.]

> It's still a loss, just over the whole
> range.

> The infinite baffle response would ideally
> be 6dB higher then, since it's a 2pi
> response.

> Or am I missing something again?

> Dan, are the RS150-4 measuring 6dB below
> their stated 91-92dB level?

Yes, your thinking is correct. If these are behaving as in 4pi space then they are 6 dB below their 2pi reference sensitivity.

[johnk]

> It's still a loss, just over the whole
> range.

> The infinite baffle response would ideally
> be 6dB higher then, since it's a 2pi
> response.

> Or am I missing something again?

> Dan, are the RS150-4 measuring 6dB below
> their stated 91-92dB level?

No, you aren't missing anything. When measured at 90 degrees you are looking pretty much at the frequency range where the driver is operating in omnidirectional mode. That is why the drivers are mounted vertically in an omni application. The caveat is, of course, if you move vertically there is a possibility of increasing high frequency response from the mids, depending on crossover point and configuration. You are working with 4Pi sensitivity levels. That is why an MTM format is advantageous.

[Pete Schumacher ®]

> No, you aren't missing anything. When
> measured at 90 degrees you are looking
> pretty much at the frequency range where the
> driver is operating in omnidirectional mode.
> That is why the drivers are mounted
> vertically in an omni application. The
> caveat is, of course, if you move vertically
> there is a possibility of increasing high
> frequency response from the mids, depending
> on crossover point and configuration. You
> are working with 4Pi sensitivity levels.
> That is why an MTM format is advantageous.

Also, room/wall treatment. Since the omni will be shooting in all directions, reflected sound is obviously part of why it has the sound it does. I'd expect that just like in conventional baffle speakers, you don't want to place them too close to a reflective surface, like a painted wall. At a minimum, you want a diffuser, or absorber. What kind of placement do you recommend to optimize the omni effect while maintaining smooth response and clear imaging?

[johnk]

While I helped Dan with his first design and helped him understand the the concept, I don't do omnis. Played with them 30 years ago. Even had a pair of Ohm F's that I quickly traded to a pair of DQ 10's.