RD75s just arrived

[ryoshu]

So I bit the bullet and bought a pair. They are finally here (sort of, one was damaged in shipping) and I'm wondering what woofer to pair them up with. I was originally thinking of the M8a after seeing all the good things about it, but the Dayton aluminum 7" and the Dayton Reference Series 7" are looking quite good too. Darren just mentioned that the RS 7 is going on sale for their 12 Days of Xmax.

After reading about different integration problems people have had, I think I've settled on using a dipole array of 8 or 10 woofers. The 7s or 8s should get me low enough to integrate with the sub and both of the Daytons look primed for a 500 Hz crossover point (24 dB LR).

Does anyone have a recommendation or any experience with RD75s and any of the Dayton drivers?

thanks

[PMazz]

I have the RD50s paired with 6 of the Dayton alum 7"ers per side. They're good to ~50Hz in room in a dipole alignment. I may switch to the RS 7 or 8"ers to gain shielding and maybe lower distortion, although using a line of 6 drivers, distortion is probably a wash. I cross them over to my sub at 90Hz and they're fine. I use a 500Hz xover too.

Pete

[JonMarsh]

I'm doing something similar, but will be pushing the system a bit harder, to 107 dB, so will be going with Extremis 6. But the RS180 or RS225 could be a good choice. The advantages to the Extremis are very high Xmax for the type of driver, XBL2 motor, and very littel rear shadowing- (nedymium magnet). Disadvantage is cost- score a big one for Dayton RS on that factor.

I'm using the RS in some other more conventional projects, just not with my RD's.

[PMazz]

Jon, I don't think you'll achieve those SPLs with the RD50s.....They get a little nasty sounding pushed hard IMO.

Pete

[ThomasW]

Jon's room isn't all that big and he's only going to be running them as a true midrange about 500Hz-5kHz. They should be fine within those limits.

[ryoshu]

PE just put the RS180s on sale for $25 per, so I guess this issue is settled. The only thing left to decide is 8 or 10 per side. Time to pull out the pencil and calculator.

PMazz, how did the aluminum cones sound? I've always had a soft spot for aluminum cones and lows. The Reference Series is too good of a deal though.

JonMarsh, I built an array before using the (in)famous NSBs. Would pushing the system really be an issue for an array of 8-10 woofers? I never noticed the NSBs to distort, even when the volume was cranked.

thanks!

[ThomasW]

10 at the very least. Those aren't a very big driver, you might want to wait until the RS225 go on sale

[JonMarsh]

PE just put the RS180s on sale for $25 per, so I guess this issue is settled. The only thing left to decide is 8 or 10 per side. Time to pull out the pencil and calculator.

PMazz, how did the aluminum cones sound? I've always had a soft spot for aluminum cones and lows. The Reference Series is too good of a deal though.

JonMarsh, I built an array before using the (in)famous NSBs. Would pushing the system really be an issue for an array of 8-10 woofers? I never noticed the NSBs to distort, even when the volume was cranked.

thanks!

The big issue is required swept volume for a given SPL and low frequency cut off. You can use the nice Excel sheet which SL posted on his site to estimate your requirements. For example, my desire was for each dipole mid woofer array to be able to hit up to 107 dB clean at down to ~75 Hz. At the bottom end of a dipole system, it's the swept volume required for a given effective front to rear baffle distance which is critical. Sd X Xmax, and for a 7" driver, at 12 mm, the Extremis is the Xmax King. For my planned baffle dimensions, considering the Xmax and driver radiating size, it requires a minimum of 8 Extremis 6 in a line array. 10 would be a little better, giving more headroom, but I'm not certain I'm willing to build something that tall.

Similarly, since bass below ~ 75 Hz is usually mixed mono, I figured my woofer array will need to do a similar level down to 40 Hz or a little lower; can always fill in the very deepest bass with a monopole sub; the minimum with driver's I'm interested in and baffle size I'm considering worked out to 4 TC2+, two per size. Four per side would be better, but a tad difficult to deal with.

For the RD50's, I'm only looking for 30-60 watts of power handling in the range between 600 Hz and 4 kHz, with fairly steep crossover slopes. This would amount to a peak level of 107 dB.

For the range above 4 kHz, where the RD cavity resonance produces a peak in the resonse and narrowed dispersion, I've ordered 16 Fountek JP2. These don't have very high power handling (~ 17 watts each), but with their neodymium magnets and low mass ribbons they're frighteningly efficient ( ~ 98 dB/watt at 1 meter), so 8 watts gives about 107 dB. Line array improves the throw, of course, so they don't fall off with the normal square law rules.

Now, with real music, and a mix of frequencies (midbass, low bass, midrange, and treble), this should translate to a typical peak level capability in excess of 110 dB, with amplifier power around 200 watts per channel at 8 ohms. Since my Palladium monoblocks are 125 watt class A, and clip around 600 watts+ at 8 ohms, I'm sure they'll provide the sheer SPL. No, I don't plan on listening at these levels; this is more to assure low distortion at the levels I do like on a regular basis. :B

I've been working on some experimental designs for new channel modules for these, so it may be possible to upgrade the sonics further- a big part of the development incentive for both the Arvo Part and Saint-Saen was to have speakers that could give 100 to 500 watt per channel amps a good work out without "wimping out", and without being a PA system, per se.

Whether the Saint-Saen fully meet that requriement remains to be seen, but it's a lead pipe cinch they'll do it better than a 7" sealed box two way, MTM or not...


~Jon

[ryoshu]

ThomasW - why would more than 10 be required? They aren't a very big driver, but I plan on handling anything in the lowest few octaves with a sub. The current configuration is a ported Maelstrom, but that will soon change to a TL. Integration will be an issue I'm sure, but I'm only expecting the 7s to be usable to around 60 or so Hz.

JonMarsh - Thank you for the very detailed response. I looked at SL's (Siegfried Linkwitz?) site a number of times, but I didn't notice the spreadsheet. So much work to do and only hours left on the sale...

To both of you, thank you very much for the information you've provided on various sites. Your posts on the RDs are what pushed me in this direction in the first place.

Now if I can only explain to my wife why I need to order 20+ more speakers...

To share an anecdote that some of the married folk might appreciate: after our new furniture arrived, my wife asked me about the old NSB line arrays. I retired them months back, stored in another room, unattached to anything that would make them go. The crossovers had been long gutted and they became drivers in a box with no goal.

I explained to her my reasons for retiring the speakers and she asked me what I was going to do "next". Well, the PE catalog came out and the B&G RD75s were shown. I got the okay.

The tradeoff? I turn one of our closets into a cage for our water dragon. Some wives understand, some don't.

I love this hobby.

[ThomasW]

The T/S parameters speak for themselves. Particularily the Fs, Sd those are important for dipole use.


RS225 PARAMETERS

Re 6.40 [ê ]
Fs 26.35 [Hz]
F1 14.13 [Hz]
F2 47.32 [Hz]
Zm 26.01 [ê]
D 162.00 [mm]
Qms 1.55
Qes 0.50
Qts 0.38
Bl 7.60 [N/A]
L1K 0.79 [mH]
L10K 0.26 [mH]
Ms 27.52 [g]
Vas 78.64 [l]
dBSpl 87.48 [dB]
Cms 1.33 [mm/N]
Ma 84.00 [g]
FsMa 13.09 [Hz]


RS180 PARAMETERS

Re 6.30 [ê ]
Fs 40.26 [Hz]
F1 23.04 [Hz]
F2 72.86 [Hz]
Zm 27.05 [ê]
D 125.00 [mm]
Qms 1.62
Qes 0.49
Qts 0.38
Bl 6.62 [N/A]
L1K 0.75 [mH]
L10K 0.25 [mH]
Ms 13.50 [g]
Vas 24.35 [l]
dBSpl 88.09 [dB]
Cms 1.16 [mm/N]
Ma 18.00 [g]
FsMa 26.35 [Hz]

[ryoshu]

The T/S parameters speak for themselves. Particularily the Fs, Sd those are important for dipole use.

My knowledge in this area is certainly lacking, but I pulled the spreadsheet off of Linkwitz's site to do some rough estimates. Making the assumption that the Sd is the same as another 7" Dayton driver (127.5 cm^2), with a default path distance of 248mm, the dipole spl @ 100 Hz is 90 dB. This drops to 81 dB at 71 Hz.

These are worrisome figures, but these are only for a single driver. If I recall correctly, you get a 6 dB boost for every doubling of drivers. So using 8 drivers would provide an 18 dB boost, making the figures 108 dB and 98 dB respectively.

The latter figure is where the sub is going to be picking up anyway, so I'm not sure that those figures are too distressing. I already have to deal with the problem of the sensitivity discrepancy between the RD75 and the woofer array.

At the very least, this will be another fun experiment

-addendum, adding 100mm to the baffle bumps the output to 93 and 84 dB. There is alot of room to play around.