4 15 INCHERS SOUND SLOOOOW

[tinitus]

This implies that the woofer doesn't come to a stop fast enough. There is some degree of ringing, hence the "slowness/ woolyness".

even if it illustrates very well what 'could' happen, I notice that it says box-port
some have even reported to have dips instead of peaks
anyway, in-room reality may be very different from the theoretical

another point
even if not considering the low Xmax, I dont think a woofer with such high Qts should move much
might work fine at low SPL, where the woofer isnt moving much
but looses control very fast at greater excursions
or might ok with classical music, but less good with modern pop, etc etc

 

[Michael Chua]

even if it illustrates very well what 'could' happen, I notice that it says box-port

Boxport is just a name. It models Sealed, Bass Reflex and Bandpass.

In OB, one can actually take the Qts. To have an idea of the shape of the Q, use Sealed Box and enter a very large volume. The System Q will equal the Qts, which is measured in Free Air.

One can use eq or a crossover slope to flatten the peak of the Alpha 15. This will only make the response flatter but the Qts remains unchanged. In other words, the ringing is still there.

The Beta 15A has much better damping (Qts=0.58). When loaded in a Sealed Box, System Q=0.887. This will result in a more defined bass compared to one with Q >1.2

I am not suggesting that Q>1.2 is inferior. It is a cheap way of getting bass. Let's say I am designing speakers and my target market is ordinary buyers, not audiophiles. I will seriously consider using High Q woofers. With it, I can get more bass in a small box. And since High Q woofers cost less, I can price the speakers lower. Big Bass, Small Box, Low Price = SALE

 

[tinitus]

In OB, one can actually take the Qts. To have an idea of the shape of the Q, use Sealed Box and enter a very large volume. The System Q will equal the Qts, which is measured in Free Air.

hmm, that would be IB, and not OB

forgetting 'dipole roll off' ?

it is true though that such peak like from a too small box in relation to Qts would cause slow uncontrolled bass

though different here , being OB, I do think you are right about the too high Qts
but probably SPL related
meaning at low SPL, no problem
still, who would use 4 woofers, and not play loud
so, I would say thats the issue here
not fit fore playing loud, thats all

 

[tinitus]

I wonder if clamshell mounting in pairs would help, giving more linear excursion

 

[tinitus]

maybe even mount them in a way that they are all 'connected'

 

[Blorgon]

PA amp probably doesn't have low frequency capability. This is important because the phase changes rapidly at the rolloff. High damping factor is essential to speed up your woofers.

Although a high power amp that is good to DC is preferred for me, you should have freq response to 10 Hz or below.

 

[Blorgon]

You didn't mention the style of open baffle. If the drivers are mnounted in a wall, you will have an open baffle - then these should sound good and the problem is in the amp. If you have an open baffle like a 4-ft sqare board, then you will have low frequency air flow from the front to the back and you will have loss of sensitivity or alteration of the frequency response and damping of the drivers depending on the room geometry and where your speakers are placed.

Also, we are all assuming that your phasing of the drivers is correct. If wired properly according to red dot or plus sign, you could check each driver with a 9v battery. With battery plus allied to the +terminal, they should all move in the same direction. If there is a problem with phase, this would "slow" the sound.

I would put my money on an amp with more power and a higher damping factor and consider something besides a open baffle design.

 

[Blorgon]

My subs are 2 - 15" Madisound Sledgehammer woofers in a 10 cu ft sealed box crossed over at 60-80 Hz. Very tight. I use a Hafler DH-500 for about 800W power. Sealed 2nd order enclosures provide less rolloff and more linear phase transition through the rolloff, without the resonance of the enclosure. Consider that the energy from the rear of the driver has to be dealt with and the OB has to reflect the energy and delay it - causing "slow bass". Bass transients may end up sounding like organ pipes.

 

[Dust]

Hi, Just wanted to say thanks to all you dudes that helped me out with my bass troubles. I am now the proud owner of 2 Kappa Pro 15Lf2's and wow what a difference!
Tight deep bass....just lovin it.

Dust

 

[skorpion]

Congratulations, Dust !

The bizarre story is that so few react to the lousy Alpha15 output.
I really don't know what they are listening to, but if anything like an acoustic instrument or a natural voice should be transferred the Alpha15 shortcomings should be immediately revealed.

But I myself didn't really react until I put up AE IB15 woofers beside. But a lot of my experienced Hi-Fi Forum friends in Sweden never showed entusiastic comment about the Alpha15 and that should have made me suspicious. They thought my 'Volks-OB' was the best original construction I contributed so far. And it probably is !

/Erling