Speaker Design

I've been working on a few designs but I seem to be afraid to commit to one. After many designs I've come to like this one:

The finish will be a high gloss white lacquer (think piano finish or electric guitar gloss)

I've tried to separate the power and signal inputs. There will also be a switch on the back for the power.

The heatsink is recessed into the back. Inside the enclosure you can see the bass port and the power transformer. I might move the heatsink slightly and mount the transformer on the back instead depending on how it looks once I've built it.

The drivers will also be recessed so they are flush against the baffle. The green thing is the amp PCB.

After the transformer, port and drivers are inside the enclosure it will be about 20L in volume.

I designed the response in WinISD alpha. I put the T/S paramters into the software then it allows you to change paramters like box volume, port tuning frequency, input power, EQ + filters. It then allows you to look at things like: cone excursion, max SPL, max power, SPL at a given input power, port gain, port air velocity at a given SPL. It's really very useful to help you optimise the performance to get a good balance of power handing, excursion and cutoff frequency. Here are the predicted results for this speaker:

I set the input power to 23Watts. This is the SPL achieved, it is about 103dB

This graphs shows the cone excursion of the woofer. the red line is the xmax (the point at which the woofers linearity deviates by 10%). The xmax of the woofer is 4.2mm, and with a 23W input the cone excursion is about 3.75mm so no problems at this power level. The maximum mechanical excursion (the absolute limit of travel) is 8mm.

This graph shows the group delay. As you can see the port and high pass filter (used to protect the driver from over excursion) have delayed the low frequencies. If possible FIR filters will be used to try to correct this although I'm not sure if they work as well at low frequencies.

This graph is the same shape as the SPL graph but this highlights the -3db point which is about 53Hz.