Mark Audio CHR-70 Application Thread

[GM]

Sounds like the baffle loaded too low. You ideally only want to load the driver to its mass corner (2*Fs/effective Qts) otherwise a high Q driver will be under-damped and vice versa. Of course if the driver's low distortion excursion is too high for this point at peak SPL, then either a smaller baffle and/or higher XO point is required.

GM

[vaughn]

thanks for the responses


Is there any way to mount two drivers on an open baffle to help with
this problem without introducing weirdness?(not a technical term).

I am also wondering if having them on an L shaped open baffle positioned like they are
on the Lotus would work?

Or I guess I could try bipole?

[GM]

As long as one driver is low passed to keep them from audibly comb filtering, i.e. one is only a mid-bass system, then I see no reason why it can't be an 'L' shaped baffle.

GM

[vaughn]

OK, I guess I thought the comb filtering would be taken care of by having them positioned
at 90 degrees to each other...

I guess it starts to become complicated then as I would have to run them in parallel, lowering the impedance into the "dangerous" range so that I could run a low pass filter on one of the drivers...

I suppose in bipole configuration the comb filtering would be a non issue?

[gapmedia]

Could I ask what type of power/intergrated amps you guys are using with your CHR-70's? (D-Class/T-amps, Valve, transistor, Gainclones etc.)

Thanks.
Simon

[GM]

Originally posted by vaughn
OK, I guess I thought the comb filtering would be taken care of by having them positioned
at 90 degrees to each other...

I suppose in bipole configuration the comb filtering would be a non issue?

Hardly! Visualize the drivers emanating a ~infinite number of different size balls from room size large to the size of a BB. Now obviously at the large low frequencies they will sum, so no comb filtering, but as they get small enough to only partially combine at some frequencies and cancel at others (comb filtering) combined with arriving at your ears far enough apart in time to be audible and it's hopefully obvious that mounting one off axis increases the problem, not alleviate it, especially at higher frequencies where they are both beaming as discrete sources.

From this we see that the bipole is potentially the worst comb filtering scenario, making getting the speaker positioning and/or the room acoustically 'right' even more important than in a dipole or monopole if the rear driver isn't rolled off.

Being an 'acoustic solutions for acoustic problems' type, I'd damp both sides of the driver as required to cause the roll off rather than using an inductor.

GM

[planet10]

Originally posted by GM
Visualize the drivers....

Here is a diagram from Taylor's seminal paper on line arrays that illustrates the point (at one specific frequency):



Toole in his new book has something to say about comb filtering, which seems (i'm only half-way thru) to have research showing that the ear-brain expects comb filtering and that the theoretical issues with it are not as serious when it comes to listening. This has me wondering again about things like the Audience arrays using "big" drivers (ie 3").

dave

[GM]

Good one, thanks!

Well, comb filtering is what creates a stereo image, but when combined with a discrete stereo image the effect is magnified enough to be a major problem for folks like me that are fairly sensitive to phasing errors. Factor in the room and horns, focused arrays or large 'FR'/coincident drivers with their high directivity through our most acute hearing BW are pretty much my only high SQ options.

GM

[planet10]

Originally posted by GM
folks like me that are fairly sensitive to phasing errors.

According to the research Toole is going over, that is down to having been trained...

dave

[GM]

Well, if that means growing up with mass quantities of live un-amplified music, then I'm 'trained'.

GM