Cab cutoff frequency

[girya32]

Quick question, [font=arial, helvetica, sans-serif]I was looking at an [/font][color=#323232][font=arial, helvetica, sans-serif]Ashdown MAG 115 Deep cab spec, and it says it cuts off at 2kHz[/font][/color]

[color=#323232][font=arial, helvetica, sans-serif]Why so low ? Is it all down to the driver or is there some other filter circuitry added ? [/font][/color]

[LewisK1975]

As far as I know frequency specs are based on the sound of the cabinet as a whole unit, not just the driver itself, but I could be wrong.

2khz is not low for a single 15 cab without tweeter IMHO.

Take a Barefaced super compact for instance, single 12, no tweeter, quoted cutoff frequency of 4khz.

[Bill Fitzmaurice]

It's a property of the driver. Some 15s do go higher, but only on-axis. Any fifteen is going to start beaming around 1.5kHz.

[girya32]

So after an hour or 2 on the barefaced website, and reading the Loudspeaker Cookbook, i'm not much the wiser... I was sort of hoping someone would say"ah yes I pulled one of those apart and the driver is a XYZ-123 subwoofer", but its not going to be that simple

[chris_b]

[quote name='girya32' timestamp='1491319839' post='3272086']
Quick question, [font=arial, helvetica, sans-serif]I was looking at an [/font][color=#323232][font=arial, helvetica, sans-serif]Ashdown MAG 115 Deep cab spec, and it says it cuts off at 2kHz[/font][/color]

[color=#323232][font=arial, helvetica, sans-serif]Why so low ? Is it all down to the driver or is there some other filter circuitry added ? [/font][/color]
[/quote]
What is the problem?

[Phil Starr]

As Bill said it is down to the driver. the 38-2000Hz isn't a cut off either. It is probably just where the speaker's response is down 10dB.

They've probably simply made a driver with better excursion and a heavier cone which has emphasised the bass but inevitably cut the top end as a consequence. I assume you chose it because of the sound so don't worry

[Dan Dare]

[quote name='Bill Fitzmaurice' timestamp='1491322118' post='3272114']
It's a property of the driver. Some 15s do go higher, but only on-axis. Any fifteen is going to start beaming around 1.5kHz.
[/quote]

Mr Bill, he correct. Large cones simply cannot move swiftly or accurately enough to produce high frequencies. Without a tweeter, few if any 15" cabs are going to produce appreciable output over 1.5kHz. Even the smaller (typically around 6") bass drivers in your hi-fi need tweeters to cover anything much over 3kHz (try covering your hi fi tweeters and listening to your speakers and you'll see what I mean).

[Bill Fitzmaurice]

[quote name='Dan Dare' timestamp='1491474273' post='3273282']
Large cones simply cannot move swiftly or accurately enough to produce high frequencies. [/quote]That's far less of a problem than the size of the cone relative to the wavelength being reproduced. As frequency goes up dispersion shrinks. To account for that the size of the cone must shrink as well. This shows how it works:
http://www.acoustics.salford.ac.uk/feschools/waves/flash/diffractionslider.swf

Axial high frequency limits are meaningless. What matters is 30 and 45 degrees off-axis.
Dispersion, not response, is why midranges are smaller than woofers, and tweeters are smaller than midranges.

[Phil Starr]

[quote name='Dan Dare' timestamp='1491474273' post='3273282'] Mr Bill, he correct. Large cones simply cannot move swiftly or accurately enough to produce high frequencies. Without a tweeter, few if any 15" cabs are going to produce appreciable output over 1.5kHz. Even the smaller (typically around 6") bass drivers in your hi-fi need tweeters to cover anything much over 3kHz (try covering your hi fi tweeters and listening to your speakers and you'll see what I mean). [/quote]

I'm fairly confident the OP didn't want this much detail but basically this is right, just not the whole story. Above certain frequencies the output from a speaker starts to fall at 6db/octave due to the mass elements. This is compensated for sometimes by a 6dB/octave rise in output due to the beaming Bill mentions, so both are important. This all assumes the cone acts as a perfect piston, it doesn't in real life of course. In reality all cones flex a little and some quite a lot. It may be that most of the output of a speaker at higher frequencies is actually being radiated from a relatively small central area of the cone. This may happen according to Colloms at around the frequency at which beaming starts. Above these frequencies you've pretty much got to measure each driver as the theory begins to break down.

[Dan Dare]

[quote name='Bill Fitzmaurice' timestamp='1491479621' post='3273355']
That's far less of a problem than the size of the cone relative to the wavelength being reproduced. As frequency goes up dispersion shrinks. To account for that the size of the cone must shrink as well. This shows how it works:
http://www.acoustics.salford.ac.uk/feschools/waves/flash/diffractionslider.swf

Axial high frequency limits are meaningless. What matters is 30 and 45 degrees off-axis.
Dispersion, not response, is why midranges are smaller than woofers, and tweeters are smaller than midranges.
[/quote]

Cheers Bill. Interesting. I'd assumed it was just the physical limitations of a large heavy cardboard or plastic cone that limited high frequencies.

[Bill Fitzmaurice]

[quote name='Dan Dare' timestamp='1491997273' post='3277030']
I'd assumed it was just the physical limitations of a large heavy cardboard or plastic cone that limited high frequencies.
[/quote]To some extent that's true, but you can make a fifteen with a low mass cone and low Qes that will extend the axial response to even 5kHz. The EVM15L is an example. It's of little benefit if the vast majority of the audience won't hear anything above 1.5kHz.