Peerless TC9FD18-08 3-1/2" box help!

[Johnybass]

I have two TC9FB18-08 3.5" full range drivers. I plan to run these full range with no midbass or tweeter. Just one of these little guys per box and then a separate powered subwoofer. It's for a bedroom.

I was originally under the impression that the right size box would be .2 ft and tuned to about 100hz but now I am second guessing if that will sound good or not. I have already built the boxes so I am stuck with .2ft or smaller. But the ports I have are 1.75" diameter and 4" long. What should I cut them down to? And should I add stuff to the box to make it smaller? Should I add polyfill at all?

They will be playing all sorts of music. Rarely movies. Thanks for the help.


Product Specifications

• Nominal Diameter3-1/2"
• Power Handling (RMS)30 Watts
• Power Handling (max)60 Watts
• Impedance8 ohms
• Frequency Response100 to 20,000 Hz
• Sensitivity83.5 dB 1W/1m
• Voice Coil Diameter0.75"

Thiele-Small Parameters

• Resonant Frequency (Fs)125 Hz
• DC Resistance (Re)6.3 ohms
• Voice Coil Inductance (Le)0.05 mH
• Mechanical Q (Qms)2.7
• Electromagnetic Q (Qes)1.33
• Total Q (Qts)0.89
• Compliance Equivalent Volume (Vas)0.04 ft.³
• Mechanical Compliance of Suspension (Cms)0.67 mm/N
• BL Product (BL)3.01 Tm
• Diaphragm Mass Inc. Airload (Mms)2.43g
• Maximum Linear Excursion (Xmax)2.55 mm
• Surface Area of Cone (Sd)36.3 cm²

 

[rojo]

Cutting a 1.75" dia vent down to 1 3/4" length should give you a tuning of just above 100Hz in a 0.2ft³ enclosure. One of the answers on this page claims the T/S parameters differ from the published specs. His unit had an Fs of 104.3Hz, which would make your intended tuning a good plan. Edit: See TLS Guy's observation below.

 

[Johnybass]

Do I need to do any baffle step compensation? My front panel is 5" wide and about 12" tall. What's the easiest way to compensate if so?

 

[rojo]

Do I need to do any baffle step compensation? My front panel is 5" wide and about 12" tall. What's the easiest way to compensate if so?

I doubt it. Baffle 0.75" on either side of the driver shouldn't cause any increased amplitude in any frequencies you'd care about. Wonder how flat the native response of the driver is? Prolly one of those things where you can't know until you get it assembled and measured.

Pretty sure bsc is usually handled with a clever crossover point and slope and a resistor to attenuate where one driver is more sensitive than the other; but I wouldn't know how to model such things without a physical unit to measure. Dennis Murphy wrote an informative intro to bsc and crossover design and posted it on the salksound blog if you want a bit more info. In any case, I don't think it's applicable to a speaker comprised of a single full range driver and no tweet.

 

[TLS Guy]

Do I need to do any baffle step compensation? My front panel is 5" wide and about 12" tall. What's the easiest way to compensate if so?

I think you need to worry about making this speaker mate with any sub. This driver is not suitable for vented alignment. The Qts is much too high. In addition the Fs is 125 Hz. That sets the lower limit of the frequency response however you load it. In fact it will be a bit above. It will sound best sealed and have an F3 around 150 Hz. So you need a sub that can be crossed at 150 Hz.

The literature that goes with that driver is fanciful.

 

[rojo]

This driver is not suitable for vented alignment. The Qts is much too high.

TLS Guy is right. This driver models with a 6dB hump at 100Hz in your intended config. It's going to sound bloated. A sealed box has an F3 of 110Hz, but a much flatter response.

If you intend to go forward with your vented box, you'll have to flatten that hump with some sort of EQ. My math might be off, but I think one of these on the + wire should tame the hump. I really hope someone with more experience can confirm.

There is an argument to be made for ported. Here's sealed (blue) vs. ported (green) at 10 watts showing the xmax limitation. The ported line is modeled with a 120Hz high pass filter with a Q of 0.5. (That's 1st order, isn't it?). And again, if my math is correct, the cap I linked above will accomplish such a filter.

Or a notch filter from 80 - 120Hz using a 300µF cap, 7.5mH choke, and a 13.25Ω resistor would be even better. But don't pull the trigger until someone more experienced confirms this! Seriously, I'm not convinced I haven't missed something important.

 

[TLS Guy]

TLS Guy is right. This driver models with a 6dB hump at 100Hz in your intended config. It's going to sound bloated. A sealed box has an F3 of 110Hz, but a much flatter response.

If you intend to go forward with your vented box, you'll have to flatten that hump with some sort of EQ. My math might be off, but I think one of these on the + wire should tame the hump. I really hope someone with more experience can confirm.

There is an argument to be made for ported. Here's sealed (blue) vs. ported (green) at 10 watts showing the xmax limitation. The ported line is modeled with a 120Hz high pass filter with a Q of 0.5. (That's 1st order, isn't it?). And again, if my math is correct, the cap I linked above will accomplish such a filter.

Or a notch filter from 80 - 120Hz using a 300µF cap, 7.5mH choke, and a 13.25Ω resistor would be even better. But don't pull the trigger until someone more experienced confirms this! Seriously, I'm not convinced I haven't missed something important.

There are two issues here. You really can not do a vented model on a driver with a Qts of 0.89! It is going to be garbage. The suspension is really floppy and the driver will destroy itself fast in a vented box. In practice I doubt the low end will be as good as modeled and the hump at tuning will be severe.

The next issue is that notching a 100 Hz hump is not like notching a 4 KHz peak. Those components are very likely to blow the output stage. The probability of instability is very high and not worth the risk.

That driver should be used sealed period.

This is not going to be a reference system. If he gets his sub up to at least 120 Hz, the gap is not going to be that noticeable. He should seal the port and put in heavy fill and call it a day.