*May*

# Redcatt 81Find - The Saga continues

Now that we have tested our drivers parameters & the driver is loaded into Winisd, we cant start to work out our design.

## Design considerations

Now we know some basic parameters which are important to us which is:

- Xmax

calculated as: Voice coil winding height - Gap height / 2 which is, 12.5mm - 8mm = 4.5 & thus 4.5mm / 2 is 2.25mm. Though something to consider here is Redcatt quote 6mm peak to peak and I'm not sure but I would guess this is out to around 70% Bl means to peak. So we don't have much to work with here to help produce deep base, though we need to still look at the rest of the parameters!

- Power Handling

Redcatt has provided power handling ratings in Aes / Program / Peak, I only care about the Aes value mostly as I personally believe that a speaker should never be pushed into power compression, this also keeps Xmax lower & gives more range to work with on the lower frequency range. Remember the more something moves the more it distorts due to nonlinearity. Our supplied power ratings are 200 Watts Aes, 400 Program & 800 Peak.

- FS

Fs is a measure of a speakers resonance frequency, generally speakers with a low fs ranging between 30 to 50hz are indications they are potentially better at producing low deep bass. We can assume 50hz to 100Hz to be good woofer indicators that can play low but still generally might need a subwoofer, where compression drivers and dome tweeters might have an Fs between 800Hz to 3500hz which indicate ( Leave your answer in the comment section) Redcatt gave a quoted figure of 80Hz I measured after conditioning for several hours 96Hz which is 15Hz difference!

- Sensitivity

Redcatt defined the sensitivity being 94.68, Winisd give our values as USPL 98.16 & SPL which is 95.79, want to know the difference take our loudspeaker course here Crash course but im going to give it to you in any case lol

- 1 Watt/1 Meter Sensitivity: This is the SPL measured at a distance of 1 meter from the speaker when 1 watt of power is applied into nominal impedance.
- 2.83 Volts/1 Meter Sensitivity: This is the SPL measured at a distance of 1 meter from the speaker when 2.83 volts are applied which is is Z-min which is normally close to Re value.

An 8 ohm speaker nominal could have a Re value around 6 ohms and it can be higher or lower, we mostly care about the lesser impedance as this is what the amplifier could see and delivery some handsome extra watts that you never planned for.

To simplify this I'm going to round up to 95dB, this is much louder than you think for an example a vacuum is around 70 to 80dB, we are roughly 15 to 25dB louder. at this level of 95dB we have around 1 hour of listening and after this period we can start to suffer from hearing loss and fatigue. So please consider 1 watt is way louder than you think for the sake of your safety!

Winisd gives us a SPLmax value under the driver tab advance parameters of 115.80dB, lets compare. Using our log formula to derive how loud we can get with 200 watts Aes

Winisd SPL max 115.80dB

Sensitivity 1 watt 1 meter 118dB

Sensitivity 2.83 Volts 1 meter 121.17

Interesting we have 3dB increase to maximum spl using 200 watts as I giggle, I wonder if you find this to be interesting information in reference to 3 power ratings or am I just misguiding you lol.

Our sensitivity and loudness is looking great with our 200 watts but we don't have much in Xmax or a very deep fs, so its most likely best to keep away from tuning low I normally as a rule of thumb sit around 10Hz above the drivers Fs on tuning. In turn the lower we tune the quicker Xmax will peak. We could say that just by looking at these basic parameters we can see we not a sub woofer or a woofer and are hinting more at a mid range driver, this means we are most likely going to need a woofer that can handle below 150 to 100hz and deliver bass as deep as possible which for me if we can see 40hz we ok.

### Design limitations in Winisd

Winisd is but a basic tool which is easy to understand, we cant do so many critical things say as VituixCad which has a learning curve of 1 zillion to a novice, so no baffle step calculation and other key factors.

Here we are taking the shortest root to victory or something being a speaker in a box, though this is still good enough to make things happen.

The driver has a very high Ebp so a vented might be the best option or we could go fancy and design a horn but that is beyond the scope of this project, I always reference a midrange and sometimes other speakers against a closed box as a reference point. Good habit or not it is one that I am fond of doing as it is a point to work around. We are using a Q of 0.707 for a flat response in our closed box and a nice gradual roll off, which looks like this in Winisd.

Don't worry if your graphs look different I explain how to change this in our crash course.

Now I'm going to add 2 more designs that are vented which is our Qb3 alignment and our "Boom Box" & compare this to our closed box, Navy Blue is our closed, green is our QB3 with Red being our Boom Box

Both of our bass reflex or vented enclosure play louder from about 300hz lets compare the points of F3 & F6 which is -3dB from "flat" and -6dB from flat for each of these designs.

Closed Box is -3dB @146.60Hz & -6dB @ 113.85Hz

QB3 Box is -3dB @ 71.14Hz & -6dB @ 65.6Hz

Boom Box is -3dB @90Hz & -6dB @ 79.69Hz

Our vented enclosures intersect around 108.45Hz and at this frequency they are both 6.5dB louder compared to our closed box, our Qb3 only starts to roll off at 84Hz give or take and if bass was a priority we can deduce that it will score in this order 1 being the best and 3 being the worst.

- QB3 deepest bass
- Boom Box best of both worlds
- Closed box... not competing

Now I want to automatically jump onto Xmax + power handling, I will keep adding watts reading the graph from right to left when the peak hits displacement. I know we are going to use a high pass filter on the lows so for not I'm not super concerned about the second peak which is out of control and well above Xmax which just means distortion!!

Here is what the graphs look like after completing this with each enclosure:

#### Power handling to Xmax approximation

QB3 25 watt

Closed 25 watt

Boom Box 37 watt

This means on average at 100hz with these "watts" into our speaker we will have a loudness of:

QB3 100hz 110dB

Boom Box 100hz 110dB

Closed box 100hz 102dB

This gives us around 13.98dB increase in loudness with another 5dB to go according to winisd, why is this important simple...

We have not determined how far away the speakers are from us or we could say our listening position, which is IDK lol I have not considered the application yet which will influence the design choice and loudness required at distance.

Something to consider is Winisd is not considering crest factor its assuming everything is the same level like a sign wave which is -3dB to clipping or 0, popular or "pop music" music has around 6dB above and below in peaks.

our constant 25 watts will reach out to 100 watts of our 200 watts and if we listen to music with higher dynamic range of say 9dB we reach out to 200 watts on those peaks with our average Rms still floating around 25 watts.

So long term 25 watts is looking healthy and we have tons of dynamic range without worrying if we are going to break anything with and spl average of 110db to 116db, this is 1/4 of the Aes power handling keeping us out of power compression for the most part.

400 watt amplifier 2 channel amplifier would be ideal here including some dynamic range.

Group delay consideration

Lower is better, remember group delay will increase as you go down in frequency.