B&G RD-75 dipole - baffle and or waveguide?

[maestrok1]

I was hoping a fellow member could help answer the few questions I posted. I would really like to order a pair of BG RD75 but it is important I know the answers to my previous questions. StigErik you have a lot of knowledge on these drivers and would really appreciate your help if you have the time. Thanks guys.

[StigErik]

Originally Posted by maestrok1

I have a few more questions if you don't mind answering me. By the way thanks for the reply Stig. I've been looking at the RD75 for a few years now but have been resistant to order because I like tube amps. I have a 15 watt transcendent sound otl amplifier that I really enjoy and was hoping maybe it would be enough to run the RD75's. Would 15 watts per channel be enough power. My room is 14 feet wide by 16 feet long. I have a active crossover with 48db slopes that I would use at 175hz to crossover with the woofers. I don't listen ridiculously loud. Usually around 95-98db peak and average of 90db. Also what is the lowest impedance the driver gets down to. Is it pretty much a flat 6 ohms across the frequency range?. Thanks for the help :-)

15 watts should be enough, but it all depends....

90 dB average is quite loud, and depending on the dynamic range of the music and your listening distance you might need up to 100 watts or more. The RD-75's are not very efficient speakers.

Impedance is 6 ohms flat from 20 to 20k.

[maestrok1]

Thanks for the help. I guess I'll just have to order them and see if I have enough power. I was mistaken when I said I listen at a average of 90db. I measured the volume at the listening chair and average is 84-86 with peaks of 93 sometimes but rarely. What width of baffle do you recommend if I want to crossover at 175hz without having to eq. I figured around 21 inches, does that sound correct?. Again thanks for all the help.

[CV]

Low Impedance of RD75 could be an issue with your OTL... power available will drop drastically....

[SpinMonster]

What kind of system SPL can be hit with the RD75 in ultimate terms with a 400-500hz LR4 crossover?

[StigErik]

Originally Posted by maestrok1

Thanks for the help. I guess I'll just have to order them and see if I have enough power. I was mistaken when I said I listen at a average of 90db. I measured the volume at the listening chair and average is 84-86 with peaks of 93 sometimes but rarely. What width of baffle do you recommend if I want to crossover at 175hz without having to eq. I figured around 21 inches, does that sound correct?. Again thanks for all the help.

What is your listening distance?

[maestrok1]

Listening distance would be 8 to 10 feet. Is that far enough or should I sit back further from these drivers.

[SpinMonster]

Originally Posted by StigErik

What is your listening distance?

I can do the math for the distance drop in SPL....1 meter.

[auplater]

Mine will do measured ~105 - 108 dBC (depending on crest factor) @ 12 - 14 feet in a 1000 ft^2 2 story space b4 audible distortion sets in...

John L.

[StigErik]

Originally Posted by maestrok1

Listening distance would be 8 to 10 feet. Is that far enough or should I sit back further from these drivers.

The point is that the frequency response changes with distance. Since the RD-75 is not a true line-source below 1 kHz, the level below 1 kHz or so will roll off slightly the farther from the driver you get.

With 10 feet distance, I recommend a fairly large baffle, around 50 cm (~20 inches) total width. This should make the FR fairly flat 10 feet away.