Sorry, I apparently directed my question to the wrong person. I should have asked HareBrained.
HairBrained, re my post above, I'd really like to better understand the pros and cons of your design vs a standard BR box. BTW, does your double chamber help with the small hump in LF response due the Hi Q of the CHR-70 or does that stay the same?
Thanks much,
Steve
HairBrained, re my post above, I'd really like to better understand the pros and cons of your design vs a standard BR box. BTW, does your double chamber help with the small hump in LF response due the Hi Q of the CHR-70 or does that stay the same?
Thanks much,
Steve
audiosteve said:
audiosteve said:
As you mentioned, all credits goes to HairBrained. I just hoped his calculations are right and wanted him to review the plan before implementing it.
The reason why I chose this design is they are just 5” deep and intended to stay close to the wall. That’s exactly what I need for my PC speakers.
Sorry for the delay in seeing the posts. I'm in the process of relocating to Portland for a contract and have been otherwise occupied.
Audiosteve, I have to question being able to get a lower F3 from the same driver in a smaller box. You may have an error somewhere. The F3 should be the same for a dual chamber as a single chamber for the same net volume. The benefit of a dual chamber reflex is excursion control. Any full range driver (that's run full range) will have excursion/power handling issues because of it trying to put out bass that it's not really capable of producing. Given the same net volume and power input, the DCR will have better excursion control then the BR.
I have my speakers against a wall, and I had to add more stuffing to the driver chamber to control the bump. If used further from the wall, I doubt it would be necessary. My modeling (Unibox) showed only 1db of ripple in the 8.1L box. And since I was able to tune it with the stuffing, you should see similar results.
Voldemar1, nice job on the sketch-up drawing. I thought you were interested in lowering the driver but it looks like you moved it up. Either way, shouldn't be a problem. That is one nice thing about the design, it can be tailored to suit the need. Please post your honest impressions of the design when you've had a chance to listen. I found it took only about 20 hours of playback before the output started to crystallize.
Audiosteve, I have to question being able to get a lower F3 from the same driver in a smaller box. You may have an error somewhere. The F3 should be the same for a dual chamber as a single chamber for the same net volume. The benefit of a dual chamber reflex is excursion control. Any full range driver (that's run full range) will have excursion/power handling issues because of it trying to put out bass that it's not really capable of producing. Given the same net volume and power input, the DCR will have better excursion control then the BR.
I have my speakers against a wall, and I had to add more stuffing to the driver chamber to control the bump. If used further from the wall, I doubt it would be necessary. My modeling (Unibox) showed only 1db of ripple in the 8.1L box. And since I was able to tune it with the stuffing, you should see similar results.
Voldemar1, nice job on the sketch-up drawing. I thought you were interested in lowering the driver but it looks like you moved it up. Either way, shouldn't be a problem. That is one nice thing about the design, it can be tailored to suit the need. Please post your honest impressions of the design when you've had a chance to listen. I found it took only about 20 hours of playback before the output started to crystallize.
HareBrained said:
Thank you,
I was unsure about driver position. Aesthetically I want driver to be on the same distances from the left and right sides of the front baffle. But at the end I decided to put it in the middle of the upper chamber. Talking about distance from the top, I think I’ll lower it a little bit, to put it closer to the ear level.
Right now I have small pile of plywood sitting in my garage. Taking to account Canadian Civic Holiday next Monday (which I usually spent outside the city) I’m not expecting any outcome in next couple of weeks.
So I’m going to fully enjoy building speakers first, and then will certainly post my impressions.
Vlad
Thanks for your reply Harebrained.
So the primary benefit is in reducing excursion and not in lowering F3. That is a useful benefit for a smaller driver and would make it wothwhile. I have since done some googling and found out quite a bit more about the dual chamber reflex (DCR) design. I may try one.
Incidentally, in looking at your plans I saw that the box was 21.5" by 8.5" and assumed it was much larger than the design of the simple BR that WinISD showed. I did not realize that the box was only 4" deep. In fact, the optimized WinISD alignment is in about 17.5 liters. So there is no size advantage. But you can jam it down to about 12 liters and still get a decent response.
Thanks for turning me on this design type. I see there is now another option available to me that could be beneficial in some circumstances.
Steve
So the primary benefit is in reducing excursion and not in lowering F3. That is a useful benefit for a smaller driver and would make it wothwhile. I have since done some googling and found out quite a bit more about the dual chamber reflex (DCR) design. I may try one.
Incidentally, in looking at your plans I saw that the box was 21.5" by 8.5" and assumed it was much larger than the design of the simple BR that WinISD showed. I did not realize that the box was only 4" deep. In fact, the optimized WinISD alignment is in about 17.5 liters. So there is no size advantage. But you can jam it down to about 12 liters and still get a decent response.
Thanks for turning me on this design type. I see there is now another option available to me that could be beneficial in some circumstances.
Steve
audiosteve said:
From my experience, you can jam it down to 8L and get very good response. My next project will be a FAST with the CHR. There are numerous woofers that would work well, it's really going to come down to how much I want to spend. But with me moving to Portland OR USA, it's all gonna have to wait.
My next 'real' project will also be a FAST once the CHR-70's are done. The CHr-70's shouldn't take much time. I am sure you have seen the 'Boominator' thread. My plan is to make the "Audinator', an audiophile quality boombox that can be closed up to be fully protected for travel so I can have good sound in hotels when on the road. I already have all the parts and have started building the amp. It is using a 41Hz Amp-9, the group buy active filter boards, a pair of Jordan J6's, a pair of 3 1/2" Peerless woofers, a 24V 10A universal switching supply and a small DC/DC converter to power the crossover boards. I'm not trying to hijack the thread with this. Just mentioning the project because you had also mentioned doing a FAST. I started planning this quite a while ago and am now dismayed to see that I could probably get similar performance out of just a pair of Alpair 6's. But I wasn't aware of them when I started down this road. 'nuff said about that. Back to the real thread.
I tried these little CHR-70 in an OB crossed at 200Hz and they didn't do too well. Seemed very sloppy and lost control around 7-10W. I tried crossing at 330Hz and they did behave better but they still didn't perform nearly as well as the same driver in a boxed varient. YMMV but I didn't like how they performed OB....
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
GM
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?
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?
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?
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?
vaughn said:
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
GM said:
Here is a diagram from Taylor's seminal paper on line arrays that illustrates the point (at one specific frequency):
An externally hosted image should be here but it was not working when we last tested it.
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
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
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
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