OB with Alpair 12P and Eminence Beta 15

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Max N
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#46 Re: OB with Alpair 12P and Eminence Beta 15

Post by Max N »

The only thing stopping me just pressing the buy button on a pair of Betas is the impedance. Two in parallel = low impedance, two in series = 6db less sensitivity and high impedance. I will ask the suppliers if other impedance versions can be custom ordered.

These look really nice:
http://www.faitalpro.com/en/products/LF ... =101060101
http://www.faitalpro.com/en/products/LF ... =101060101
Fs 35Hz, flat response out to 3K
2 of the 4ohm version in series could be good?
£150 each so I need to sell some stuff :)
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IslandPink
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#47 Re: OB with Alpair 12P and Eminence Beta 15

Post by IslandPink »

Qts looks rather low for OB, 0.32 ....

Max, can I ask a couple of starter questions about the project, in case I missed them in thread :
Is it going to be a passive crossover ( eg. like a Quasar ) ?
How loud do you want to go ( typical averaged SPL ) , how big is the room ?

You want tone and no trouble at 40Hz, I gleaned that from the intro :D
You seem set on the dual bass drivers, hence the second question.

ps. Fostex 405's get very good reviews from one or two reliable people ... at a cost. Good specs eg. Qts , low power handling, smooth response ....
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Max N
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#48 Re: OB with Alpair 12P and Eminence Beta 15

Post by Max N »

Yes, passive crossover.
I want to be able to drive them from a valve amp, say 300B SET or 45 PP. Would prefer 8 ohm-ish rather than 4 ohm-ish, but I guess I could live with 4. I have several OPTs that are 8-ohm only, but I guess I could always buy some 4-ohm
Room is 4.5m x 9m, angled ceiling 2.8m high
No idea what SPLs I want. I'll try to take some measurements at typical listening level.....

Please bear in mind WAF. I have approval for something looking like the Pure Audio Project Trio 15, but not for Quasar. No reflection on the Quasar, I like them a lot, but my wife doesn't. I'm not building these speakers so I can listen to them in the garage :) . The intention is that these speakers are the first part in a project of me 'sorting out' my whole system.

Thanks for taking an interest. :)
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#49 Re: OB with Alpair 12P and Eminence Beta 15

Post by steve s »

Max N wrote: Wed Jul 12, 2017 8:18 am The only thing stopping me just pressing the buy button on a pair of Betas is the impedance. Two in parallel = low impedance, two in series = 6db less sensitivity and high impedance. I will ask the suppliers if other impedance versions can be custom ordered.

These look really nice:
http://www.faitalpro.com/en/products/LF ... =101060101
http://www.faitalpro.com/en/products/LF ... =101060101
Fs 35Hz, flat response out to 3K
2 of the 4ohm version in series could be good?
£150 each so I need to sell some stuff :)
The speakers look sort of ok to me but i would be looking at using them in an H or U frame to help the low end as much as you can
I have tried a few speakers in series using one inductor, i found the sound a little muddy, it worked bettter for me with 2 x 16 ohm speakers each with their own inductor, i. Know that may sound daft but its what i found ... I'd use one up to around 300hz and the second one to in cut of lower say 100 Hz, i looked at the graphs,ten modified it with what the inductors effect should be, and move the value/ frequency point to align with the full range unit and give a reasonably flat sound

I have 4 x vintage wharfedale 15's with the red square magnet, they are not the best, but im sure they sound better than the cheap eminence drivers... But probably not super bassy
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#50 Re: OB with Alpair 12P and Eminence Beta 15

Post by steve s »

IslandPink wrote: Tue Jul 11, 2017 7:08 pm
steve s wrote: Tue Jul 11, 2017 8:25 am But it has a big magnet and double the bl which generally is a speaker that's faster with more life.
Weight and strength of the magnet usually relates to the cost of the speaker
Yes, but ....again ....
The speed and life bit is supposed to be being provided by the midrange driver.
If you want a driver that's going to be an OB bass driver it doesn't want a really bit magnet and a high BL. If you get one like that, it's more of a midrange driver when used on OB because it'll just have a rising response from the bass through to about 300Hz or more. Then you'll have more trouble crossing to eg. the Alpair, and need EQ from 150 down to 50Hz .
This sort of driver is more suited to ported box.
What you want is a driver with the RIGHT SIZED MAGNET to balance against the cone mass to give you a flat response in the upper bass and lower mids when used on a big baffle or infinite baffle as per the datasheet. Look at the datasheet FR of the Beta 15A - it's overall flat from 100Hz to 500Hz. When you use a bit choke as per the Quasar you pull the response down above 100Hz and all it sort-of pivots clockwise around 100Hz so you get relatively more bass below 100Hz than on the datasheet curve.

What you've had to do with your 18" unit on the latest build is load it with undersized ports, which is precisely because it's a large-magnet driver which is more suited to a ported box than OB use.
Thats all fair comment mark... And similar to what I have done to a lesser degree

I was at one point using a pair of 18's per side but i could not get on with a solid state amp driving them, and there was too much energy sapping going on for the px25 amp, so my goal has been to use just one large driver for the last few years
The ported idea came to me after trying various ways to increase the bass with out restricting or loading the bass driver, as i found that saps the quality, even in the bass, its critical to have drivers with the same transient capabilities through the range
Remember Collins electrstatics and cheap bass driver...was a good lesson for me.

The comprimises are that if you use the 'right' sized magnet to achieve a flat bass, the excelleration is less than what i use, and that directly comprimises the sound in my view...
Phils open baffles for example have some nice vintage 18" fane drivers, they are high bl/ low fs and worked very well, and on the lines of the drivers im using, but still retain a good balance

What i had to do with my speakers (you have made it sound like its another compromise) is actually genius.. The two main issues with open baffles, bass responce and placement, have been sorted,
I've retained the open baffle speed and tone, whilst using drivers that are more acurate with transients... And in a relatively small package considering whats inside them... I'm thrilled to bits


Max i also have a spare pair of the drivers phil uses too ?
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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#51 Re: OB with Alpair 12P and Eminence Beta 15

Post by IslandPink »

Ok but what do you do with the 18" , Steve, where it hands over - because you have something like a 12" alnico Goodmans doing the midrange, don't you ?
Do you low-pass the 18"-er ?
Agree that it's good to have a midrange-capable bass driver if you are going to use a low-order crossover , it will need to work Ok through to at least 500Hz, but it's the big magnet bit I don't agree with. James's Quasars are to me the best speakers I've heard in the upper bass and lower midrange , and they use a bass driver with a Q of 0.4 and a middling-sized magnet. They also have more low bass than yours.

Don't think I'm generally 'down' on your speaks though - I did comment to Nick after Owston that they could play vocals cleanly and with tone at levels where any other speaker would be harsh and breaking up - for instance on the Sunday session. This is a rare capability. I definitely think you've got the midrange and treble really sorted.
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chris661
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#52 Re: OB with Alpair 12P and Eminence Beta 15

Post by chris661 »

IIRC, Steve's OB bass loading is kind-of like a transmission line, but with loads of stuffing to gradually absorb most of the back wave. Should give something that heads towards an infinite-baffle (not sealed box) rolloff, which IIRC for those drivers would be very gently rolling off down to around 35Hz-ish, where it'll start rolling off a bit steeper. Should be a good complement to most rooms.

Since we didn't have the two sets of speakers in the same room, and no measurements have been taken, it's extremely difficult to say who had more low/mid/upper bass or whatever. Our auditory memory is pretty terrible, and our perception of sound changes so much during the course of a day that I think any attempt at comparison between the two would be guesswork at best.
Put them in the same room, with similar positioning, and play the same music and we can see what's what.

Chris
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#53 Re: OB with Alpair 12P and Eminence Beta 15

Post by steve s »

IslandPink wrote: Fri Jul 14, 2017 10:53 am Ok but what do you do with the 18" , Steve, where it hands over - because you have something like a 12" alnico Goodmans doing the midrange, don't you ?
Do you low-pass the 18"-er ?
Agree that it's good to have a midrange-capable bass driver if you are going to use a low-order crossover , it will need to work Ok through to at least 500Hz, but it's the big magnet bit I don't agree with. James's Quasars are to me the best speakers I've heard in the upper bass and lower midrange , and they use a bass driver with a Q of 0.4 and a middling-sized magnet. They also have more low bass than yours.

Don't think I'm generally 'down' on your speaks though - I did comment to Nick after Owston that they could play vocals cleanly and with tone at levels where any other speaker would be harsh and breaking up - for instance on the Sunday session. This is a rare capability. I definitely think you've got the midrange and treble really sorted.
I think Mark we will have agree to disagree with our views on the best type of drivers for ob bass
In my set up the 18 goes up to 250 ish, no 15 or 18 inch driver should be used too high
Supporting full range drivers it may be a little higher to fill in the lower mids. But it all depends on what's right for the bass speakers in question and to what they are being mated with
I'm surprised at you views on James' speakers, the main flaws in them was the bass, even James was aware they was not quite perfect... but they are still very nice speakers and I quite liked the level of bass achieved from a small driver
We all have different goals and ideals, its for Niel to decide which route he takes and which set of compromises he chooses if any... as I'm sure we are adding to his confusion

Chris is right .. once you get your set up sorted we can have a good session exploring the virtues of both of our systems at an Owston meet ?
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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Nick
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#54 Re: OB with Alpair 12P and Eminence Beta 15

Post by Nick »

In my set up the 18 goes up to 250 ish, no 15 or 18 inch driver should be used too high
Out of interest, is 250Hz the xover point? I think Marks point is that with a first order crossover, a -3dB point of 100Hz is still only -18 dB down at 800Hz, and even with a 2nd order xover -36dB will still be contributing more than 1% of the sound.
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Max N
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#55 Re: OB with Alpair 12P and Eminence Beta 15

Post by Max N »

Thanks again for everyone's input, it is very useful.
I have a couple of things on Ebay, so should have some funds in a week or so. I think I'm just going to have to buy something (probably Betas) and start experimenting for myself.
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#56 Re: OB with Alpair 12P and Eminence Beta 15

Post by IslandPink »

chris661 wrote: Fri Jul 14, 2017 6:59 pm Our auditory memory is pretty terrible, and our perception of sound changes so much during the course of a day that I think any attempt at comparison between the two would be guesswork at best.
Speak for yourself, Chris !
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#57 Re: OB with Alpair 12P and Eminence Beta 15

Post by steve s »

Nick wrote: Sat Jul 15, 2017 7:28 pm
In my set up the 18 goes up to 250 ish, no 15 or 18 inch driver should be used too high
Out of interest, is 250Hz the xover point? I think Marks point is that with a first order crossover, a -3dB point of 100Hz is still only -18 dB down at 800Hz, and even with a 2nd order xover -36dB will still be contributing more than 1% of the sound.
That's a fair point Nick, of course in 1st order at either side of the crossover point there's a lead driver and the rolled off one in the background, I don't see that as a negative
In my speakers the ports are well padded which also further damp the higher frequencies.
I'll do a response plot of just the bass driver this week
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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#58 Re: OB with Alpair 12P and Eminence Beta 15

Post by steve s »

IslandPink wrote: Sun Jul 16, 2017 7:21 pm
chris661 wrote: Fri Jul 14, 2017 6:59 pm Our auditory memory is pretty terrible, and our perception of sound changes so much during the course of a day that I think any attempt at comparison between the two would be guesswork at best.
Speak for yourself, Chris !
My experiences observing at many bake offs, meets and a/b comparisons seem in general to prove Chris's point
You must have exceptional auditory skills Mark
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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#59 Re: OB with Alpair 12P and Eminence Beta 15

Post by Ali Tait »

He does!
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Nick
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#60 Re: OB with Alpair 12P and Eminence Beta 15

Post by Nick »

That's a fair point Nick, of course in 1st order at either side of the crossover point there's a lead driver and the rolled off one in the background, I don't see that as a negative

I wasn’t suggesting it was a negative, just making Marks point about considering the HF response of LF drivers even though you may have a low xover frequency.
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