[Bumpy]

My OBs have Eminence Alpha drivers doing the work below 200Hz with their own dedicated amp, and sound fine.

Yesterday I was experimenting and played several pieces of music with the set up just below 200Hz. I have to admit is didn't sound great Hi-Fi and am wondering if this is typical.

Can anyone else with similar set up play music over this low frequency range (no midrange or tweeter) and describe what they hear

[FullRangeMan]

Sounds as you are missing the resonance and impact from a boxed woofer, you could add two active subs under 60Hz.

My Carver Amazing Silver have three 12'' woofers and the bass is open, wide and very musical with great image, but it dont can have the usual resonance from a box.

[Bumpy]

Thanks FRM

I do have a single big powered subwoofer that will underpin the entire system, but just wanted to get the 15" driver working optimally before I move on to integrate it.

I was just a bit surprised at how odd the 15" drivers sounded covering the range 200Hz and down and I was looking for a reality check.

[opnly bafld]

What is the x-o slope?    6, 12, 24?

Bass without the harmonics sounds pretty dreadful.

[DannyBadorine]

Only listening to 200Hz and down will sound terrible.  I've done it many times in order to work with designs.  No Matter how you work it, those frequencies are not fun by themselves.

[Bumpy]

What is the x-o slope?    6, 12, 24?

Bass without the harmonics sounds pretty dreadful.

The x-over slope is 24db. It needs an abrupt wall to stop the upper frequencies of the bass driver overlapping and spoiling the lower frequencies of the mid

[Bumpy]

Only listening to 200Hz and down will sound terrible.  I've done it many times in order to work with designs.  No Matter how you work it, those frequencies are not fun by themselves.

Thanks, that is EXACTLY what I wanted to hear.

Are there any elements of it that might help me optimise the choice of driver or amp.

[richidoo]

Eminence Alpha is a terible driver for hifi. It is popular because of the low price and the weak motor which allows the cone to flop around uncontrolled which allows exaggerated extension which gives the illusion of deep bass. There is no mechanical damping and no electrical damping so no detail. The signal cant stop and reverse the cone so it keeps sailing along and extending too far. This is why its so cheap.

I used 4 super high quality AE Dipole 12  drivers in a OB diy years ago. I did not cheap out as they cost $300 ea back then. They still had no detail becuase the q is too high. High Q means poor damping. If you want bass detail you need electrical damping. Which means low Q driver with applied EQ, or a servo system which applies feedback to control the motion of a loose and floppy high q driver. Both are complex and expensive compared to alpha. But thats where the pursuit of sound quality will take you if you stay in dipole camp.

[Bumpy]

Eminence Alpha is a terible driver for hifi. It is popular because of the low price and the weak motor which allows the cone to flop around uncontrolled which allows exaggerated extension which gives the illusion of deep bass. There is no mechanical damping and no electrical damping so no detail. The signal cant stop and reverse the cone so it keeps sailing along and extending too far. This is why its so cheap.

I used 4 super high quality AE Dipole 12  drivers in a OB diy years ago. I did not cheap out as they cost $300 ea back then. They still had no detail becuase the q is too high. High Q means poor damping. If you want bass detail you need electrical damping. Which means low Q driver with applied EQ, or a servo system which applies feedback to control the motion of a loose and floppy high q driver. Both are complex and expensive compared to alpha. But thats where the pursuit of sound quality will take you if you stay in dipole camp.

So I should look for a 15" driver with low Qts to be driven by a high current amp and perhaps the need for EQ. So plenty of information but specifically I need names of these drivers.??

[OCityruxer]

Assembling my Nx Studio. Have the enclosure 90+% complete and working my way through the wiring. Been a fun project with only a few self inflicted frustrations. Looking forward to hearing them

[richidoo]

So I should look for a 15" driver with low Qts to be driven by a high current amp and perhaps the need for EQ. So plenty of information but specifically I need names of these drivers.??

You seem like a competent DIYer asking the right questions, so I’m sure that you can find a 15” driver with lower Q than alpha. US Speakers has a good collection. A typical Q for multipurpose professional use is ~.45 and that is adequate. You dont need to use Q .20 extreme hifi subwoofer driver, nor does it need 2kW power handling for playing music inside your house.

EQ is always necessary for dipole bass. The EQ can be applied in different ways, like elecronically filtering the source signal or mechanically exaggerating cone excursion. But the diffraction and cancellation effects of dipole radiator always require more bass boost EQ to achieve flat, musically rewarding FR than any other type of speaker. High Q is the easiest and cheapest way but as you’re hearing it’s not the best sound quality.

Easiest “tell me what to do” solution is GR Research servo OB sub. It is proven solution for decent price with warranty and support. I know a couple experienced audiophiles who have and like them. But its built to a price and is not the only solution for excellent dipole bass. You can learn a lot about dipole bass and how to implement an audiophile worthy dipole bass system from Sigmund Linkwitz. linkwitzlab.com

[FullRangeMan]

So I should look for a 15" driver with low Qts to be driven by a high current amp and perhaps the need for EQ. So plenty of information but specifically I need names of these drivers.??

A part from OB if you want a driver for the usual BassReflex slam consider these Beyma 15'':

[Bumpy]

So now you have me confused.   

In my specific use (sub 200Hz, OB, dedicated amp) richido is weaning me off the normal drivers that everyone recommends such as Eminence, BUT FRM recommends the Beyma 15" if I want to use Bass Reflex and not OB

Correct me if I have misunderstood, but I am assuming that the Beyma is just the sort of driver that richido is hinting at, so you can see my confusion.

Why would the Beyma not work for me in OB?

[FullRangeMan]

Why would the Beyma not work for me in OB?

Richidoo post very instructive.
I have saw an expert rec Qts 0.8 or more for OB.
The Qts is too low on these Beyma drivers hence suited to BR or Sealed, what make sense to PA and reinforcement.

[Bumpy]

Richidoo post very instructive.
I have saw an expert rec Qts 0.8 or more for OB.
The Qts is too low on these Beyma drivers hence suited to BR or Sealed.
YMMV.

The more I read and investigate this topic I believe many have been brainwashed into thinking that high Qts is the governing parameter for OB drivers. Every time a question is asked in a forum, the perceived 'wisdom' trots out this response.

Certainly for a competitively priced system its good advice, with the ability to get enhanced 'bass' essentially from a driver having good but ultimately poorly controlled cone movement. Throw in high sensitivity and its an attractive package

When we move onto more ambitious projects involving a limited range of frequencies (say less than 200Hz), EQ and dedicated amps, then high Qts and even high sensitivity become almost irrelevant.

Having said that I have little knowledge of what parameters are important - I would suggest things like high magnet strength, well designed spiders, light cones, amps with good control of current, and high cone excursion all play a part.

I suppose a first question is "when a manufacturer sets out to design and build an OB 15" driver where do they place there efforts and please don't say high Qts

[FullRangeMan]

I suppose a first question is "when a manufacturer sets out to design and build an OB 15" driver where do they place there efforts and please don't say high Qts

Not sure never was a driver engineer, came to mind large Xmax, Mms and Xlim, low Le, hi Qts. The Beyma 15P80feN have low Qts 0.18 but hi Vas 305L what may be suited to your experiment, great driver to horn loading, 101dB.

[Bumpy]

I thought I would try and draw together what manufacturers say when they set out to design a 15" driver specifically for OB

I start with Acoustic Excellence


In open baffle applications, drivers are required to operate at much higher excursions than in typical boxed applications to compensate for the roll off of the baffle. In applications where woofers are continually called upon to operate at higher excursions, Bl and Le linearity are extremely critical. To achieve this linearity, the Dipole15 woofers were designed with a large underhung motor and Full Copper Faraday Sleeve covering the entire pole.   This combination utilizing the Faraday ring and underhung motor provides the most possible linearity and low distortion during high excursion use. The high Q and low Fs allow the Dipole15 woofers to be very efficient at low frequencies and have very good low end extension. While EQ is typically needed to correct for the baffle roll off itself, no additional EQ is required to flatten the response of the driver.

I have highlighted Bl and Le which say say are "extremely critical", but at present I have no idea what they are 

Dipole15-D8
Fs: 21.7Hz
Qms: 15.2
Vas: 623 L
Cms: 0.6 mm/N
Mms: 90 g
Rms: 0.81 kg/S
Xmax: 15 mm(peak)
Xmech: 18 mm(peak)
Sd: 855 sqcm
Vd: 2.06L (p-p)
Qes: 1.00
Re: 3.08 ohm (parallel)
Le: 0.04 mH (parallel)
Z: 4 ohm (parallel)
Bl: 6.1 T/m
Pe: 100W (cont.)
Qts: 0.94
1WSPL: 90 dB
2.83V: 94.2 dB
Weight 13.6Kg

[FullRangeMan]

I have highlighted Bl and Le which say say are "extremely critical", but at present I have no idea what they are 

BL or BxL is the motor force, B is a value related to the magnet assembly, or magnet flux density in gap say in Gauss or Tesla, L is a value related to the VC or length of the voice coil, so B x L= motor force say in N/A.

Le or Lces is the electrical inductance + airload from motor say in Henries(mH).

[Bumpy]

Excellent.

Its pretty obvious that a high BL is good, but do we want Le to be high or low?

[FullRangeMan]

Low is better.