Hi, thought I would share my latest build with you all. This is a small practice combo I have built for rehearsals and small acoustic/Jazz gigs.
It uses an Eminence Deltalite 2 speaker and I am using a GK MB200 amplifier in this combo (so it is providing around 140watts in to 8 ohms). at 97 dB/w this should give me 118 dB or so. Enough for a rehearsal.
Here are some pictures for you:
The speaker itself uses a long port in an adaption of my previous reflex/quarter wave hybrid. The design models suggest that I am getting around 45 Hz resonance from the reflex mode, which appears to model well if you consider only the 35mm straight section as the port. The rest of the tapered section appears to be partially "box volume" in the model. (Actual transition point is unknown at this time).
The line length is physically 650mm but this should also include up to 260mm to the top of the box behind the driver. This would suggest a resonance of around 115 Hz although by tapering the line and partly stuffing it, the resonance is just under 100 Hz. (The driver spreads its output across the length of the first 1/4 of the line helping reduce nulls. This section is stuffed right up to the 180 degree bend at the top of the box.
This means I can tune the system pretty low for a small box to prevent large cone movements at the low end and in a typical reflex box, this would mean I would breach the 4.2mm X max at 90 to 100 Hz. As it has this second resonance which controls the cone as well, this movement does not happen so I end up with a broader port output than a reflex and better cone control.
In fact I have run this on my 300W amp (reasonably carefully) but drove it harder than the MB200 could allow and it still seems to handle it (short term as it is a 250W speaker).
Will do an impedance plot next to confirm the resonances. It certainly sounds great (it also has a custom tweeter which I made 15 years ago.)
If my calculations are true, this means I am converting more of the cone movement to port movement (some mass loading effects going on too). With a large area port, this is not a problem as the maximum velocity is still below 17mm/s. I tend to slightly flare the terminus to improve flow here.
This also means that ultimate X max is less important in bass guitar speaker of this type than seems to be mentioned on this site for conventional speakers. If you model a sealed box, below resonance, there is lots of movement above the X max. For a high tuned reflex, even more at the low end. A low tuned reflex has more at 2 x the resonance. In my design, the entire low end is controlled and above resonances, the cone movement is never that large so up to 140W, no issues (in fact up to nearly 200W in this design).
Enjoy!
