I started a new project Sunday. It began with opening a factory sealed box containing the first of a pair of Bohlender & Grabener RD75’s.
I’m looking for and easy way to mount them to get a sense of how they sound. I don’t have any woodworking tools (or skills LOL) so I’m thinking of using 15X15 extruded aluminum to make a frame and base.
Initially I’ll start with a simple crossover to a pair of JBL 128H-1s in a 2 CF ported box because I have them.
Suggestions welcome.
Long term I will pair them with the tweeter and woofer panel(s) from Magneplanar Tympani IVa’s.
I’m looking for and easy way to mount them to get a sense of how they sound. I don’t have any woodworking tools (or skills LOL) so I’m thinking of using 15X15 extruded aluminum to make a frame and base.
Initially I’ll start with a simple crossover to a pair of JBL 128H-1s in a 2 CF ported box because I have them.
Suggestions welcome.
Long term I will pair them with the tweeter and woofer panel(s) from Magneplanar Tympani IVa’s.
A week after I posted this I found a house I liked. Within the next six weeks I closed on the house, moved and got the Tympani IVa's set up.
Last weekend I swapped out the mid\tweeter panels for the RD75's.
Last weekend I swapped out the mid\tweeter panels for the RD75's.
An externally hosted image should be here but it was not working when we last tested it.
I have a set of RD48s and here are my experiences.
1) They sounded best when operated open baffle. I had a trapezoidal baffle similar to the Carver design.
2) Mine buzzed around 1kHz. You may want to run a sweep and see if you have any buzzing issues. I had to cross mine higher than I wanted because of this.
3) I paired mine with two double Dayton 8" Classic subs in vented boxes.
4) A notch filter may be needed due to cavity resonance. It is mentioned in the instruction manual, so you may want to check there. I personally didn't notice much of an issue without it.
1) They sounded best when operated open baffle. I had a trapezoidal baffle similar to the Carver design.
2) Mine buzzed around 1kHz. You may want to run a sweep and see if you have any buzzing issues. I had to cross mine higher than I wanted because of this.
3) I paired mine with two double Dayton 8" Classic subs in vented boxes.
4) A notch filter may be needed due to cavity resonance. It is mentioned in the instruction manual, so you may want to check there. I personally didn't notice much of an issue without it.
Finally making some progress. 🙂
I have found someone to help me with construction of a cabinet. We traded some electronic equipment he wanted for his help and use of his workshop.
I lined up a pair of Magneplanar ribbon tweeters, the 60.25" tweeters they us in their flagship 30.7 speakers and I bought a pair of Rythmik F8's to handle the bass.
I have been turning over various constructions of the cabinets in my head for months and it is starting to coalesce. A combination of 80/20 for the frame and MDF for the sides. I haven't worked out what material to use for the rear panel. Suggestions? MDF does not lend itself well to being removed and replaced. Not that I expect this to be a regular thing, I may need to do some tweaking and don't want to have an issue. A separate section at the bottom of the rear panel will be for access to the crossover.
RD75 and ribbon tweeter cabinet.jpg - Google Drive
The left speaker would be a mirror image version of the right. The wide black section is the B&G RD75. The narrow black section is the Maggie tweeter. The gray sections are 80/20 and the vertical tan represents MDF and will be one piece. The gray on the right is the frame with attachment points for the MDF sides. Still working on the base, might end up using legs made of 80/20 which would facilitate leveling feet and provide further attachment points for the MDF sides. All of the cabinet elements will be painted black.
Is there anything better than Rockwool for internal sound absorption?
I have found someone to help me with construction of a cabinet. We traded some electronic equipment he wanted for his help and use of his workshop.
I lined up a pair of Magneplanar ribbon tweeters, the 60.25" tweeters they us in their flagship 30.7 speakers and I bought a pair of Rythmik F8's to handle the bass.
I have been turning over various constructions of the cabinets in my head for months and it is starting to coalesce. A combination of 80/20 for the frame and MDF for the sides. I haven't worked out what material to use for the rear panel. Suggestions? MDF does not lend itself well to being removed and replaced. Not that I expect this to be a regular thing, I may need to do some tweaking and don't want to have an issue. A separate section at the bottom of the rear panel will be for access to the crossover.
RD75 and ribbon tweeter cabinet.jpg - Google Drive
The left speaker would be a mirror image version of the right. The wide black section is the B&G RD75. The narrow black section is the Maggie tweeter. The gray sections are 80/20 and the vertical tan represents MDF and will be one piece. The gray on the right is the frame with attachment points for the MDF sides. Still working on the base, might end up using legs made of 80/20 which would facilitate leveling feet and provide further attachment points for the MDF sides. All of the cabinet elements will be painted black.
Is there anything better than Rockwool for internal sound absorption?
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Where you are going to cross over will drive some of the absorption choice. How much absorption you want in the box, how close you want it to the driver, etc. will also influence the decision. Layered materials might have some advantages if you are trying to cross over low.
When it comes to absorption and things in close proximity to low-mass drivers, I typically mock them up before committing to a path. Better to find out early in the design phase.
There's a decent quick overview of some absorption materials about midway down this page:
Science of Absorption - Primacoustic
If you need a small driver to experiment with, the GRS planars are reasonably priced and would give you a feel for how the intended internal geometry/absorption affect the sound.
GRS - Parts Express
When it comes to absorption and things in close proximity to low-mass drivers, I typically mock them up before committing to a path. Better to find out early in the design phase.
There's a decent quick overview of some absorption materials about midway down this page:
Science of Absorption - Primacoustic
If you need a small driver to experiment with, the GRS planars are reasonably priced and would give you a feel for how the intended internal geometry/absorption affect the sound.
GRS - Parts Express
@mattstat, thanks for the reply and link, great info.
The RD75's should be good down to 150 Hz. The F8's are supposed to be good up to 250 Hz. I will shoot for the lowest frequency which has good integration.
The RD75's should be good down to 150 Hz. The F8's are supposed to be good up to 250 Hz. I will shoot for the lowest frequency which has good integration.
I worked at BG for 5 years and grew up around the development of that driver at my Dad's company. I personally wouldn't cross over the RD-75 that low. BG and Wisdom audio used to cross these over that low (trying to get them to mate directly to a subwoofer) but they are really much better at 300 hz and up.
Nowadays, I would probably use a DSP to do the notch filter (around 6khz) and EQ the top end above 8khz or so.
Nowadays, I would probably use a DSP to do the notch filter (around 6khz) and EQ the top end above 8khz or so.
My solution to the 5 - 6 kHz bump is to cross over to a ribbon tweeter low enough to miss that. The ribbon tweeters are good to 40 kHz.
At this point I am committed to trying. The woofers I have, Rythmik F8's are said to be good to 250 Hz. I'm going to try to stretch the RD75's down to where I can get a good transition to the F8's.
At this point I am committed to trying. The woofers I have, Rythmik F8's are said to be good to 250 Hz. I'm going to try to stretch the RD75's down to where I can get a good transition to the F8's.
Arraying ribbon tweeters is an option but, depending on the size of the mounting flanges and active area of the tweeters along the line, there can be issues with coupling and combing. Don Keele has some pretty good information on this in his CBT papers and studies.
I ordered a pair of ribbon tweeters used in Magnepan 30.7s for my project and have pretty much finalized the cabinet design.
The cabinet depth variance is a TBD while I evaluate dampening material. One or two 2" layers of Owens Corning 701 for the high freqs and two layers of 2" 8lb Rockwool for the low freqs.
Tan is MDF
Black is the tweeter and RD75
Brown is the base
Gray is a 2" X 2" piece of dampening material to space the first layer of 701 back from the transducers.
The cabinet depth variance is a TBD while I evaluate dampening material. One or two 2" layers of Owens Corning 701 for the high freqs and two layers of 2" 8lb Rockwool for the low freqs.
Tan is MDF
Black is the tweeter and RD75
Brown is the base
Gray is a 2" X 2" piece of dampening material to space the first layer of 701 back from the transducers.
Attachments
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Cabinets are helpful for keeping dust off the drivers. But aside from creating resonances (BR or TL) to meretriciously augment bass, there's nothing HiFi that boxes add. Let the drivers fill the room, the less box the better.
B.
The only cabinet that does add HiFi is a horn - but just not feasible for the frequencies where it is needed way down low
B.
The only cabinet that does add HiFi is a horn - but just not feasible for the frequencies where it is needed way down low
Agreed, the pair of RD75's/ribbon tweeters in my main system now are OB and they are spectacular.
This pair is for a smaller room where OB is not practical. The woofers are in a separate cabinet, Rythmik F8's.
This pair is for a smaller room where OB is not practical. The woofers are in a separate cabinet, Rythmik F8's.
Steve3J, my old RD75 project looks virtually identical to your drawing in post #4. This shape followed the Blondia/Whittaker gymnasium baffle study which is discussed elsewhere on diyAudio. I build my baffles from solid red oak. Lots of shaping because I decided to rollover the baffle edges! This project was circa 1998. Sound was excellent. I had some difficulties integrating my over the top Bass List Shiva reference subwoofers which displayed extremely impressive cabin gain necessitating 24dB/Oct active filtering. I archived RD-75s awaiting future development of reference low frequency modules (not subwoofers) as I was itching at the time to focus on full range horns. My view of these RD-75 was and still is to use them effectively as satellites. For example my now completed reference low frequency modules are currently crossed at 1khz with the Great Heil AMT's. I will near future substitute the BG RD-75's and lower the crossover point first with Rane 23B and then proceed to design and align a passive crossover after crossover points are optimized...unless more urgent project strikes my fancy. He, he, he...
In post #7, Crispy79 makes a very interesting point about crossing planers at higher frequencies than we might intuit from driver FR. I reference the work of Roger Sanders and Barry Waldron on ESL panels which they often crossed at around 500Hz to Dynaudio 12's. Barry said to me years ago that this applied equally well to planer magnetic drivers. I subsequently adopted 500Hz as my mid to bass horn crossover point and never looked back once smooth bass horn response to 500Hz was achieved. I will certainly look at 500Hz very carefully when I integrate my RD-75's to my reference low frequency drivers.
In post #7 crispy79 also suggests using a DSP to notch the ~6KHz resonance and provide EQ boost. What's current best practice for notch filtering the RD-75's? TIA
In post #7 crispy79 also suggests using a DSP to notch the ~6KHz resonance and provide EQ boost. What's current best practice for notch filtering the RD-75's? TIA
I have some good analysis equipment at work and the lead engineer for the project presently in my lab is an audiophile so we had alittle fun.
@lager_brewer
B&G published a recipie for a notch filter. The pic shows the response curve of the one I have.
Perhaps someone will share some more information.
B&G published a recipie for a notch filter. The pic shows the response curve of the one I have.
Perhaps someone will share some more information.