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Help w/ Bohlender Graebner 420 planar speaker
Help w/ Bohlender Graebner 420 planar speaker
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Old 28th January 2018, 05:05 PM   #1
Gwho is offline Gwho  United States
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Default Help w/ Bohlender Graebner 420 planar speaker

I just purchased a used pair of BG radia 420 speakers. I find that I can listen to them without fatigue. They definitely lack midbass and bass which is what I would like to cure (obviously a subwoofer is suggested) The BG 420 has a 40" planar array with two 6.5" woofers that are crossed to the planar array at 350hz. I have listened to the 420s on a carpeted floor as well as off the carpet about a foot. I thought they sounded much better off the carpet (could this be related to having the woofers closer to the listening height).

My questions are as follows:
1. How directional is the sound between 80hz and 350hz
2. I am thinking of adding a pair of Dayton RSS365HF 10" woofers to the system which can augment the 6.5" woofers or replace them (the speakers have bi-amp input)
3. Should I place the woofer underneath the 420 speakers (like a Martin-Logan?
4. Or would I be better off placing it behind the 420 raised in height to listening level where I can blend or eliminate the stock 6.5" woofers.
5. Or just use the 10" woofers as subs (below 70hz which is the low end spec for the 6.5" 420 woofers).

I would like to thank any of you who respond with your input.

Best Regards,
gwho
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Old 29th January 2018, 11:06 AM   #2
lowmass is offline lowmass  United States
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Directionality not an issue crossed over at 350 hz

I would go for replacing the 6.5 with the bigger woofer rather than use big woffer as a sub only. Yes as a sub you may get it al to blend BUT in my experience with larger ribbons is if you can cross below around 400 wich it looks like you can then its best to start looking at larger woofers that give a good response to well past 1 khz

That Parts express 10 inch woffer has a nasty spike in response at around 1khz. This will likley be heard with a crossover at 350 hz. I would be looking at the 8 inch version of that woofer. Its much better behaved above 1khz. Even a single 8 inch will be able to go lower than two 6.5s

Many of these subs however have a low sensativity so you will have to bi amp to match everything OR pad down the ribbon to match the woofer
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Old 29th January 2018, 02:30 PM   #3
Gwho is offline Gwho  United States
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Lowmass

Thank you for the reply. There is definitely something lacking with the 6.5" woofers that they use. I like the idea of having the woofer cover the frequency range of the 6.5s. I will look into the 8" woofers (I already have the 10s). My question on directionality @ 350hz and below relates to the woofer placement in relation to the 40" array. There is a company Newform Research that places woofers (albeit a line array of woofers) behind their ribbon. I was wondering if I would be better off placing the woofer behind the array at ear height (and perhaps delaying the line array). I will likely use a dsp crossover and bi-amping as I like the sound of the BG 40" and want to improve the sq if possible.

I assume that since you say it is non-directional, I have the option of placing the woofer (or woofers) below, on the side, or behind the array.

Regards,
gwho
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Old 29th January 2018, 05:47 PM   #4
lowmass is offline lowmass  United States
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Well Newform I believe is crossing over at around 1khz. At that high a freq it becomes much more important to put the woofers and ribbons acoustic centers close together at normal listening environments.. Their original systems did not do this and I bet over time they wanted to improve so made a "concentric" of sorts with the ribbon right in front of the woofers.Their ribbon is closed back so this is OK and it will work. Your BGs are open back? I assume?. Even if closed back , at 350 hz you would need far to big an enclosure to do same physical arraignment as Newform.

Apogee used to put the ribbon just to the side of the woofer but there too they are aligning acoustic centers wich was needed at the 6-700hz crossover.

I have built many protos of all these arraignments and the one i like best is cross over around 350 with woofer eather below the ribbon as you already have with the BG or at the side and centered with ribbon as in Apogee designs.Eather way that ribbon is wayyy more capable than two little 6.5s stuffed into a tiny box. Its not a good match IMO. You need a bigger piston down there to match the overall fidelity of that long ribbon

BTW if you already have the 10s I would experiment with them first. You have eq to taim the peak so may be fine.

I see Parts express also has an aluminum cone 12 inch woofer that has a very good response past your crossover.

Dayton Audio DSA315-8 12" Designer Series Aluminum Cone Woofer

This one would likley be a close match in sensativity BUT will need a bigger box
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Old 29th January 2018, 05:50 PM   #5
lowmass is offline lowmass  United States
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Well Newform I believe is crossing over at around 1khz. At that high a freq it becomes much more important to put the woofers and ribbons acoustic centers close together at normal listening environments.. Their original systems did not do this and I bet over time they wanted to improve so made a "concentric" of sorts with the ribbon right in front of the woofers.Their ribbon is closed back so this is OK and it will work. Your BGs are open back? I assume?. Even if closed back , at 350 hz you would need far to big an enclosure to do same physical arraignment as Newform.

Apogee used to put the ribbon just to the side of the woofer but there too they are aligning acoustic centers wich was needed at the 6-700hz crossover.

I have built many protos of all these arraignments and the one i like best is cross over around 350 with woofer below the ribbon as you already have with the BG. BUT that ribbon is wayyy more capable than two little 6.5s stuffed into a tiny box. Its not a good match IMO. You need a bigger piston down there to match the overall fidelity of that long ribbon

BTW if you already have the 10s I would experiment with them first. You have eq to taim the peak so may be fine.

I see Parts express also has an aluminum cone 12 inch woofer that has a very good response past your crossover.

Dayton Audio DSA315-8 12" Designer Series Aluminum Cone Woofer

This one would likley be a close match in sensativity BUT will need a bigger box
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Old 29th January 2018, 07:22 PM   #6
Gwho is offline Gwho  United States
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Lowmass,

Thanks for the answers! You explanations make sense. Yes my BGs are open backed. I did not think about that when asking my question. I will experiment with the 10s first (I wrote down the wrong number, they are RSS265HF speakers).

I will likely make a closed box for the woofers and eq the low frequency. I want to thank you again for the help. One last question. Did you ever add open baffle woofers to the array (since the array is open baffle). Is so, did they integrate better.

I appreciate the help and knowledge.
Best Regards,
Gary
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Old 29th January 2018, 07:25 PM   #7
Gwho is offline Gwho  United States
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Also, thanks for the head up on the 8" woofer and the 12" aluminum woofers.

gwho
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Old 30th January 2018, 03:00 AM   #8
lowmass is offline lowmass  United States
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I did do open and I highly recomend you try it if for no other reasion than its so cheap to try and so much is learned. Open baff bass is almost too easy to get good sound from and if you have a way to EQ then its even easyer. Fast bass and open mids, good match to the ribbon sonic imo.
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Old 30th January 2018, 07:18 PM   #9
Gwho is offline Gwho  United States
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Thank you lowmass!
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