A woofer question - Beyma 15G300

[Black Stuart]

Hi all,
These are s/hand and according to the vendor they are 110dB @ 8 Ohms. I forgot to ask what they go down to and did'nt notice last night that the auction ended at 12 last night. No one made an offer and the start price was only E45.

Now I was looking to buy 4 Ohm woofers to go with the 4 Ohms Heils, but if the quoted SPL is correct it is way above the Heils 96.5dB. As I don't want to lose any of the Heils sensitivity I need amps with o/put txs of 4 Ohms. As I also intend to use active x/overs - the question is, do I just need to use a series resistor to bring the woofer down to match the Heils.

Perhaps this is one for Petercom.

I am in touch with the vendor, so I can still buy if they are suitable for my project.

Black Stuart

Stewart, Attenuator here http://www.mhsoft.nl/spk_calc.asp
Will.

[Black Stuart]

Will that is brilliant,
the deal is still on but the vendor in Pais Vasco is really ****ed off with E-bay/PayPal.

I questioned whether the SPL was correct and I was right to do so - it's 101dB and that's fine (I think) as the woofers are 8 Ohm and the Heils 4 Ohms.

Now here's an interesting option to bi-amp, of course with an active x/over, using an 8 Ohm amp for the woofer and a 4 Ohm amp for the mid/high Heils. Would I still need to attenuate the woofer?

Black Stuart

I can't answer that but, I would go for something like the Behrringer s/p active crossover and go from there, http://cgi.ebay.co.uk/BEHRINGER-CROS...QQcmdZViewItem
Will.

Ho, euro sale http://cgi.ebay.co.uk/Behringer-SUPE...QQcmdZViewItem

[Black Stuart]

Will,
it looks very tempting, presumably it's a stand alone unit ie plug and play?
I shall have to check further - many thanks for the links.

Black Stuart

[petercom]

You can't attenuate bass speakers with resistors - the resistors tend to overheat and the amplifier loses control of the cone motion through loss of damping factor.

I shouldn't worry too much about sensitivity. I doubt the Beymas are 101dB sensitivity all the way down in the bass. Probably they hit this at 1kHz or somewhere higher up the audio band and are 6 - 9 dB down on this at the bass end. So by the time you've equalised them they'll be running at around the right level for the Heils.

Can't find exact specs on this unit but this link gives the TS parameters to help design a box

http://www.bandpass.de/thiele-small.html

[Black Stuart]

Hi Peter,
they don't go down so Low as I thought they would.

Black Stuart

[petercom]

you can't have it both ways - either high efficiency, high fs or low efficiency, los fs. Fs is governed by moving mass and suspension compliance. Increase the mass and the efficiency drops - increase the compliance and the cone becomes unstable.

[James D]

Well at 40Hz and 100dB we have the Supravox GMF285 and the BD-designs BD15 - so it can be done but it requires quite particular design and neither is cheap...

As always with engineering there are ways to minimise the restrictions that standard approaches lead too but ultimately Physics will prevail and the two above are the exceptions that prove the rule as they sit right on the cusp of what is possible and lose at least an octave off the bottom end - I want 20Hz at 100dBs but my wife has ruled all my designs out so far...

On a more practical note the Eminence 15" speakers will give you low to mid 90s efficency at 20-30Hz. Trouble is I need two of then each side minimum for my designs and really would like four each side...

James