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Old 10th July 2014, 09:13 PM   #1
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Default Which fr driver for my 300b set?

Hi all,

No sooner have I finished my new Tubelab 300b amp and I'm looking for new speakers...

I have the dMar-Ken7.3's and they sound great however, their near 86db efficiency has put paid to any kind of serious volume. They were fine with my other amp, a Tubelab SSE with kt88's but the reduction in wattage with the 300b amp is an issue.

I've looked a lot at the alpair 10p which is nearly 90db efficient. My understanding of speaker efficiency is limited but is the difference between the two drivers likely to be the increase in volume I'm looking for?

Thanks in advance.

Last edited by mudchute; 10th July 2014 at 09:51 PM.
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Old 10th July 2014, 10:20 PM   #2
GM is offline GM  United States
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A lot depends on the amp's output impedance [series resistance] that effectively increases the driver's Qts, so what is yours [not the tap rating] or do you know its damping factor?

GM
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Old 11th July 2014, 12:42 PM   #3
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Ah, no idea for either. I'll give Google a bash and see what I come up with.
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Old 11th July 2014, 02:35 PM   #4
GM is offline GM  United States
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If not available for your amp, but component values are published or you can measure them, then it can be calculated close enough for speaker design: Amplifier Output Impedance

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Old 11th July 2014, 04:34 PM   #5
chrisb is offline chrisb  Canada
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The outcome of the calculation of your amp's damping factor and the 10Ps increased sensitivity is one thing, but being familiar with a most of the Alpair models, driven by both solid state and SE ( 6CA7) and P/P (EL84) tube amps, there is also a marked difference in the tonality / timbre of the paper and metal cones to consider.

I've made no bones in the past about preferring the sonics of the 10P to 10.3 on initial listening to each, and indeed recently jumped in the deep end and upgraded the front row of HT rig from 7.3s to 10Ps. However, after finally hearing a pair of 10.3s well broken in by a third party (Bernie), if I was inclined to second guess myself, I just might revisit that assessment.

If you're well acclimated to all the things the 7.3 does so well, you might prefer the 10.3 - noting that it doesn't offer the same degree of increased sensitivity as the paper, I think it is more "cut from the same cloth" in terms of detail and microdynamics.
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Old 11th July 2014, 04:47 PM   #6
Greg B is offline Greg B  United States
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The 10P could be a reasonable and good sounding choice, but it is somewhat on the low side of what will normally suffice with a 300B SET. It depends on your room, listening preferences, etc.

I run the 10.3M with roughly the same watts, but PP tubes. Less damping factor means less subjective 'loudness' effect, but it's my bedroom system, and it is more than sufficient SPL-wise for me.

If sticking with a full range driver, you're not going to do much better than 90db or so without going to horns or other relatively complex cabinets. Going to an 8" FR will IME provide a bit more subjective sense of realism and power, though there are tradeoffs.

For some alternatives, you could take look at the Fostex FF165WK, FF225WK + supertweeter, or F200A (if you have the budget). There's also the L. Cao FR, and various other Diatone inspired FR that are reported to sound good.
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Old 11th July 2014, 05:05 PM   #7
Retsel is offline Retsel  United States
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Default Lowthers are a good match for 300B amps

I have the 15 ohm DX4 Lowthers which work well for 300B amps. The 15 ohm version of the Lowther driver does not have the 2K hz spike that the 8 ohm version has. Probably the Alnico magnets are a little better than the neos (DX) series.

The best speaker layouts for Lowthers are front horns and open baffle. The next best speaker layout is in a back horn.

The stronger magnet Lowther drivers are over 95 db efficient (the horn version is likely around or above 100 db efficient).

To have the best dynamics, you want to be able to reproduce 10 db higher output than what you listen to (some say 20 db). Thus, if you listen at 90 db on average, your amp/speaker combination should be able to play at 100 db to get good dynamics.

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Old 11th July 2014, 05:50 PM   #8
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Thanks for the feedback guys. If I've worked it out correctly my amps output impedance is something like 0.56ohms.

I should add re driver choice my budegt is limited to about 200 which is the landed cost of x2 stock 10p's to my door. Lowthers may be beyond my price range and I'm limited to 8ohm drivers too as my output transformers are wound with 8ohm secondaries.

Thanks for the insight into the different alpair models Chris. I do love my 10.3's. crystal clear and a great range of frequencies but even flat out my 300b can't quite hit the desired volumes hence looking at the change. I've looked at the 10.3's but that extra db of sensitivity the 10p's have swayed me as I need all the help I can get. Our room isn't huge but its a new style build so brick/breeze block walls (or stud walls) with a lot of insulation which has dampened things down a bit compared to our previous place which was solid brick walls all round hence again, thinking the 10p's may be a better choice.

You're right though, I would feel a bit miffed if I lost a lot of the dynamics of the 7.3's. I do love them dearly.
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Old 11th July 2014, 06:56 PM   #9
chrisb is offline chrisb  Canada
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retsel - if I may be so bold - whatever the advantages of the Lowthers might be - sensitivity and personality among them - for someone as familiar with the sonics of the Alpairs as mudchute (& myself), the former might take quite some adjustment. Yes, I have heard several iterations of Lowthers in a range of enclosure designs, and it's probably safe to say that they're an acquired taste.

mudchute: I think the 10Ps would provide a much more familiar experience than the Lowther, or for that matter, AER or similar very high sensitivity makes, and with the flavoring by judicious selection of driver or output valves, the match with 300Bs could well be quite satisfactory. It's been several years since I owned a 300B amp - yes, a guy can have too many - and last listened to the A10Ps with 6CA7 SE pentode - more than plenty of power for upper 80s dB SPL my light damped, 320ft^2 room.

the 7.3 is a tough act to follow - fortunately Mark, et al are not sitting on their laurels
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Old 11th July 2014, 06:58 PM   #10
GM is offline GM  United States
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Hmm, 0.56 ohms is typically PP with lots of -fb, while SET typically have ~2-4 ohms, so I'm thinking you didn't do it right.

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