Speakers that measure well and work in small room

[b1daly]

In the case of a closed box, the air inside the box exerts pressure on the woofer which impedes its motion, raising the resonance frequency and creating a 12dB/octave high pass filter. The smaller the volume, the higher the resonance/cutoff.

In the case of a ported speaker, the port is a Helmholtz resonator: a region of air having lower acoustic impedance than the air from which the sound wave is propagated (in this case, the air behind the woofer inside the box). When sound is reflected through such a low-impedance region, its phase is reversed. Since the phase of the back wave of the woofer is already out of phase with the wave coming from the front of the woofer, when the back wave’s phase is reversed by the port it ends up exiting the port in-phase with the front wave (except below the frequency of the ported box's resonance frequency, where the port is ineffective). The result is that the outputs from the port and the front of the woofer add constructively from the resonance frequency up, which a sharper (24dB/octave) roll-off below the resonance frequency due to cancellation between the port's output and the output from the front of the woofer (due to their being out of phase below this frequency).

In reality, box materials are not infinitely rigid or reflective, and boxes are not infinitely tightly sealed, so there are losses and unintended resonances that contribute additionally to the output. By this I mean that:

• panels vibrate much like a speaker, especially at particular frequencies defined by cabinet geometry and materials
• sound passes through panels
• sound escapes through gaps in the panels or e.g. through the woofer’s cone or dustcap etc

This can of course be audible if it’s significant enough.

In most high quality speakers since the 80s, losses and resonances have been quite well suppressed. I believe Celestion is widely credited with making the first serious attempt to address this issue in the late 70s, but I’ve forgotten which model it was now. Even long before this though, it was understood that losses and resonances were theoretically undesirable, and some effort was made by various manufacturers to brace cabinets, use thicker ply or other materials, etc (to the best of my knowledge - I wasn’t actually around back then )

Thanks for the mini-lesson! I’ve always wondered about how ports (or passive radiators) could possibly work...

 

[FrantzM]

Thanks for the perspective on baffle width very interesting.

The issue I’m noticing with modern studio monitors is they are made of very dense materials, with rounded shapes. This trend started sometime in the last 15 years.

What I find disconcerting is that I don’t hear much cabinet resonance at all. I was attributing this to the inert materials and reduction of standing waves and rectangular panels.

But you’re right, the diffraction effects are reduced to.

This brings me to my limits of understanding of speaker design.

My vague concept was that the drivers have fundamental resonance, which you try to move out of the with the crossover frequency.

But there’s also a calculation for the volume of the cabinet. I’ve never been clear whether the physical structure and any resonance characteristics are part of the equation.

My perception has always been that more “traditional” wooden box designs are generating sound from the whole cabinet, in the way a violin would.

Speakers from the 60s were sometimes sealed empty plywood boxes. I have a pair of EV “The Layton” home speakers, and they sound crazy, the box is definitely part of the sound.

One issue I’m not grasping is how the cabinet enables such a louder and more “full” from the driver.

If you have a very dense, modern cabinet shape, presumably stuffed with absorption, how does whatever impact the cabinet air volume contribute to the sound?

The studio monitors I’ve been dissing are ported, so some sound must come out of the port. Does it actually change the movement of the driver.

As an extreme example I was trying to fix some JBL Duet computer style speakers recently. As far as such speakers go, these aren’t bad.

They have a bulbous plastic housing with a proportionate big port.

I pulled the driver out and it’s this tiny full range driver that when played out of the enclosure is just a tinny, fizzy. The difference the enclosure makes borders on magical.

Anyway, always more to learn!

Some modern speakers are made that flimsy too. Harbeth comes to mind ... they sound nice but not my cup of tea...

 

[Cortes]

Yeah, I second the Genelec One 8331. Nothing better at that price point or higher that I have heard. They will blow you away with their DSP room correction and precision.

How they perform at low SPL?. I'm looking for some monitors that are excellent at only ~50 db, 1.4m distance Monitors to Ear.