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Why Are Ported Speakers the Dominant Design?

Wombat

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Err.. That's written by Robert Harley.

But I'm familiar with the fundamentals. I asked because don't see an advantage from the design perspective given the difficulty of tuning and preventing leakage. Low bass extension is also better done with subwoofers. The only thing I can see tipping the scale is commercial considerations and the practicality of keeping it in one box.

Edit: To be clear, my post was in light of @KSTR's comments about the best designs.
Well; Harley did a good summary, there.

Considered attention to tuning can produce very good results. E.g. JBL M2s.
 

pozz

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Wombat

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One thing is certain: the infinite baffle can have its LF breakpoint lowered by EQ, within the rating limit of its LF driver/s.

The unloading of the driver below the port operating range in BR intrinsically limits this approach. So, design a BR system that covers the desired frequency range without the need for compensation.

My cabs are 13.75 cu.ft. BR tuned to 32Hz. LF driver is Altec 416-8B.

This driver in an optimal IB enclosure Qtc =0.7, gives 4.9 cu.ft and -3dB @ 65Hz. Increase the volume of the box and Qtc goes down and -3dB freq rises.

BR is a winner for this driver.
 

Juhazi

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Some historical remarks, of most popular domestic loudspeaker types (radios, record players, cabinets)
- First ones were cones, installed on record players where needle was directly coupled to tymphani. Response 300-2000Hz
- 1925 Rice & Kellog introduced dynamic drivers, radio loudspeakers were open baffles or installed in large leaky cabinets. Frequency response was like 100-3000Hz. PA speakers adopted horn loading.
- In 1954 Villchur introduced closed box (acoustic suspension) which gained popularity in slowly growing hifi market. Response 50-10 000Hz. This cult has revived best in Britain (BBC heritage).
- in '60 woofers & tweeters and crossover circuits gained popularity, basics laid by Thiele & Small Response 30-20 000Hz
- in '70s electrostatic panel speakers didn't get much popularity.
- Transmission line and bass-reflex porting gained popularity during '70s with the rapidly growing cheap stereo set business. Boxes were made by robots, of plastic instead of wood/laminates.

The continuing popularity of BR enclosures came from the typical boosted bass response around 100Hz, which gave "better" sound in typical environment of these cheap stereo sets with small lightweight speakers. Many hifi speakers adopted this, because loud bass sells! Soon people also started to want to see the port, it was no longer hidden by cloth or put on the backside.

In this millenium people started to buy HT set with separate subwoofers, but still most main speakers have BR loading, sadly. Simultaneously high-end hifi market started to have life of it's own with cults of open baffles, horns, TL omnis etc.
 

watchnerd

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Soon people also started to want to see the port, it was no longer hidden by cloth or put on the backside.
They did?

I don't recall hearing anyone say "oh, I wasn't sure between speaker A & B, but speaker A had those sexy ports on the front you could see.."

I thought the main argument for putting ports on the front was easier placement relative to a wall.
 

maty

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maty

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The excess of bass or the spectacularity we have to add via a good minimum phase PEQ and DSP. Now it is very simple because almost everything is digital from a computer; it is the more logic and... cheap.
 

watchnerd

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The excess of bass or the spectacularity we have to add via a good minimum phase PEQ and DSP. Now it is very simple because almost everything is digital from a computer; it is the more logic and... cheap.
I still don't get what you mean.

Does this song have an excess of bass? Or exactly as much bass as the creators intended?

 

maty

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The creator who does what he wants. But if the music has bass excesses and the speakers add even more we will probably have problems in the room.

It is like everything in life, continued excesses are harmful.
 

Wombat

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Like high DR? ;)
 

maty

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You know, English is not my first language. I meant:

A lot of bass -> bass boost. If you like it -> PEQ or DSP.

A lot of bass != not that the loudspeakers reproduce up to 20 Hz - 30 Hz.
 

KSTR

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True in the bass and for port contribution but a ported system has an inherent lack of back wave absorption due to its typically modest box stuffing.
True, and one of reasons why implementation matters. A two-way speaker with the woofer playing up to several kHz and havening front-firing ports is almost impossible design without noticable leakage and no pipe resonances exited by the front wave of the woofer, the "pan flute" effect. A three-way speaker (or subwoofer) with rear-firing ports does much better in this regard.
 

Cosmik

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Gradually homing in on this. I present to you three statements:
1. Linkwitz says: "Vented bass speakers are resonant structures and store energy which is released over time. For accuracy, bass must be reproduced from sealed or open baffle speakers that are non-resonant."
2. Some maths forum says: "The impulse response and frequency response are two attributes that are useful for characterizing linear time-invariant (LTI) systems. They provide two different ways of calculating what an LTI system's output will be for a given input signal."
3. Another university physics site says: "Circuits that have non-zero energy stored on capacitors or inductors at t = 0 are generally not time invariant."

I suggest the following statements may be true:

A ported speaker cannot be considered time invariant if you're in the middle of playing some music. What it does depends on the energy already stored in the resonator when you begin making your measurement. It doesn't have a single 'frequency response' or 'impulse response' because its behaviour is dependent on what's already stored in the resonator. It can't be corrected using time invariant-applicable techniques because it is not time invariant when playing real music. Any maths that assumes it is time invariant is not valid when the speaker is in the middle of playing real music.
 
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Ron Texas

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Thread Starter #116
I think using a sub and rolling off a ported speaker, say down 6 db @ 80 hz with a 24 db/octave filter should help as it reduces the output of the port. Measured FR in my room is the same for the port plugged and with -6db @ 90 hz unplugged.

A few have mentioned passive radiators are superior to ports. They are not expensive, but do cost more than a hole in a box. It appears those in the speaker business are fond of their margins. Manufacturers are selling $600 speakers built in China with a crossover consisting of a cap, inductor and resistor, but spending extra on a second set of binding posts. It's ludicrous.
 

watchnerd

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Manufacturers are selling $600 speakers built in China with a crossover consisting of a cap, inductor and resistor, but spending extra on a second set of binding posts. It's ludicrous.
If you're trying to make money and run a business, it's not ludicrous -- buyers see binding posts, not caps -- and if you, the manufacturer, believe it creates differentiated value and helps sales, bingo.

It's not really any more ludicrous than car makers charging thousands extra for walnut interior trim on a car.
 
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Ron Texas

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@watchnerd if cars were priced like audio gear they would cost twice as much. People pay what they do for audio gear because it becomes an obsession. I agree with you that some of the optional equipment in cars is pricey. In a 911 Porsche a different color of plastic trim on the dash is $900.
 

Trdat

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There are several aspects in play, it seems to me.
My question is: can the composite sum of the cone's front face and the output of the port be pre-corrected with DSP to provide the correct time domain behaviour with transients? Unlike a sealed box, we are hearing the output of two 'transducers', one of whose output is derived from the inverse of the other's.

By the way I am reading through your responses and I think this is the third time. Trying to get the jist of it, very interesting.

I am not an expert in DSP, but I know Audiolense does correct phase shifts regardless of sealed or ported. Mitcho might be able to give you more idea on how its executed.
 

watchnerd

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@watchnerd if cars were priced like audio gear they would cost twice as much. People pay what they do for audio gear because it becomes an obsession. I agree with you that some of the optional equipment in cars is pricey. In a 911 Porsche a different color of plastic trim on the dash is $900.
Right.

And there is at least a chunk of the industry that earns a living catering to that obsession.

I don't have a problem with people buying audio jewelry from McIntosh, any more than I have a problem buying real jewelry from Cartier.

They're both fashion purchases designed to display status.

Even "engineering oriented" speaker makers like Revel offer bi-wire posts:




I don't think it's ludicrous of them to offer that if they think it increases sales with their target market.

Even if they know it's no more useful than VU meters on a McIntosh amp.....it's fashion.
 
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