My apologies in advance if this question has been asked ad nauseam already, but forum searching got me nowhere, so I figured I'd just ask...
What is the optimum placement on the baffle for a full-range driver in a ported box? I.e. the height at which the driver is mounted relative to the total height of the enclosure.
My plan is to build a bass reflex speaker for the Tang-Band W5-1611SA that I picked up a while back. I think I'll use the same technique as This Guy for building a teardrop, Sonus Faber style enclosure.
Thanks,
~Tom
What is the optimum placement on the baffle for a full-range driver in a ported box? I.e. the height at which the driver is mounted relative to the total height of the enclosure.
My plan is to build a bass reflex speaker for the Tang-Band W5-1611SA that I picked up a while back. I think I'll use the same technique as This Guy for building a teardrop, Sonus Faber style enclosure.
Thanks,
~Tom
The average ear height of an adult seated listener is between 39" and 42". Many designers often put the center of a full range speaker close to ear height if the cabinet is tall enough to accomodate it.
If you have studied MLTL ported full range speakers (quarterwave.com) you have seen tall, narrow cabinets which locate the speaker at ear height and locate the port near the floor to both improve bass gain and also to minimize unwanted internal cabinet resonances.
Some designers would use large radius/bevel edges on the front cabinet edges to reduce diffraction.
If you have studied MLTL ported full range speakers (quarterwave.com) you have seen tall, narrow cabinets which locate the speaker at ear height and locate the port near the floor to both improve bass gain and also to minimize unwanted internal cabinet resonances.
Some designers would use large radius/bevel edges on the front cabinet edges to reduce diffraction.
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Esthetically, I think the driver position looks the best somewhere around the 0.62-0.667 range. So Golden Ratio to 2/3 up from the bottom of the baffle. Not sure how important it is to the sound of the box, maybe less so for a small ported box vs something bigger?
jeff
The actual height apart from aesthetics or ear height will have an important effect on back wall and floor bounce cancellation. I see this when modeling it in Akabak and can be a huge impact. 5 or 6 in can be critical. How far away from back wall do you intend to have cabinet and do you plan on front/back/down firing ports? They all affect the sound and placement of speakers relative to wall.
A full range will beam at high frequencies, and locating it at ear height with some box toe-in to aim the high frequency lob at the listener is common. This is why many full range designers start with ear level mounting.
Jeff Bagby has a free baffle/room simulator. Your W5-1611 may not have ideal T/S parameters for optimum MLTL bass gain, but applying the quarter wave design rules to a bass reflex will still reduce cabinet resonances and generate great bass.
I'm sure you have read about TL and horn cabinets for your W5.
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Acoustically, working with inside dimensions [i.d.], a speaker cab can be viewed as a small, well sealed room, so placing the driver and/or the vent at odd harmonics [3rds, 5ths are popular] same as seating in a listening/HT room will get you close enough to the smoothest practical response.
When planning a MLTL based on ear height, then the acoustical path-length is easily reverse engineered to account for it.
If you're willing, able to work through the higher math wave, etc. equations [or have someone that will do it for you], then you can fine tune it further [0.333 Vs 0.349 offset for instance], but in my limited comparisons, internal damping to 'taste' negates any subtle audible differences that one might hear in an undamped cab.
Note that if you also use a wide baffle, then the driver should ideally be offset in both planes.
GM
When planning a MLTL based on ear height, then the acoustical path-length is easily reverse engineered to account for it.
If you're willing, able to work through the higher math wave, etc. equations [or have someone that will do it for you], then you can fine tune it further [0.333 Vs 0.349 offset for instance], but in my limited comparisons, internal damping to 'taste' negates any subtle audible differences that one might hear in an undamped cab.
Note that if you also use a wide baffle, then the driver should ideally be offset in both planes.
GM
I've done the math (well, WinISD) on a ported box for the W5-1611SA. It should come in with an f3 of about 50 Hz. With a MLTL (see this thread) I might be able to get down to 40 Hz.
However, I am a bit concerned that with a MLTL, the radiating surface (i.e. the driver and the throat of the port) gets acoustically rather large as they're quite far apart. In the design linked to above, the driver and the port are about 90 cm apart. I'm a bit afraid that it'll have issues with directivity at the resonant frequency of the transmission line. However, I don't have the experience to judge whether this concern is valid. I'd be interested in the public opinion (preferably backed up by scientific arguments and/or measurements) on this.
With a ported box (not a quarter-wave TL design), the driver and the port can be close together. Hence, the radiating surface becomes acoustically small(er) and the directivity, at least as I understand it, should be better.
I do understand that the drivers should be at ear level (so 90ish cm off the floor). And if my speakers don't end up that tall, I'll put them on stands. That's not an issue.
The placement I'm talking about is that of the driver on the baffle. One post above suggested a golden mean ratio. That was my suspicion as well.
My listening room (aka living room) measures 4 x 4.5 meters. It has a hallway appendix that's probably 120 x 200 cm and a kitchen about 3 x 4 meters connecting to it through a roughly 2 m opening in the wall. The speakers are situated roughly 120 from the rear wall and about centered side-to-side in the room. The speakers are 150 cm apart and my listening position about 180 cm in front of the speakers (100-120 cm from the rear wall).
I am not locked into a cabinet. I would prefer a regular ported box or a MLTL. Those are both manageable in size and have relatively high WAF. I would like a speaker that has good directivity - both horizontally and vertically, though most importantly horizontally. I like the sweet spot to be reasonably large. I would like some precision in the bass and prefer it to be non-boomy if possible. I would like to try a full-range design and have the TB W5-1611SA (not SAF) on hand.
I'm curious about the MLTL and their directivity compared to a sealed and ported box speaker. Can anybody elaborate (and point me to data or simulation, please)? I'm also curious about the resonances and panel reflections in the MLTL compared with a ported box and how they color the sound.
~Tom
However, I am a bit concerned that with a MLTL, the radiating surface (i.e. the driver and the throat of the port) gets acoustically rather large as they're quite far apart. In the design linked to above, the driver and the port are about 90 cm apart. I'm a bit afraid that it'll have issues with directivity at the resonant frequency of the transmission line. However, I don't have the experience to judge whether this concern is valid. I'd be interested in the public opinion (preferably backed up by scientific arguments and/or measurements) on this.
With a ported box (not a quarter-wave TL design), the driver and the port can be close together. Hence, the radiating surface becomes acoustically small(er) and the directivity, at least as I understand it, should be better.
I do understand that the drivers should be at ear level (so 90ish cm off the floor). And if my speakers don't end up that tall, I'll put them on stands. That's not an issue.
The placement I'm talking about is that of the driver on the baffle. One post above suggested a golden mean ratio. That was my suspicion as well.
My listening room (aka living room) measures 4 x 4.5 meters. It has a hallway appendix that's probably 120 x 200 cm and a kitchen about 3 x 4 meters connecting to it through a roughly 2 m opening in the wall. The speakers are situated roughly 120 from the rear wall and about centered side-to-side in the room. The speakers are 150 cm apart and my listening position about 180 cm in front of the speakers (100-120 cm from the rear wall).
I am not locked into a cabinet. I would prefer a regular ported box or a MLTL. Those are both manageable in size and have relatively high WAF. I would like a speaker that has good directivity - both horizontally and vertically, though most importantly horizontally. I like the sweet spot to be reasonably large. I would like some precision in the bass and prefer it to be non-boomy if possible. I would like to try a full-range design and have the TB W5-1611SA (not SAF) on hand.
I'm curious about the MLTL and their directivity compared to a sealed and ported box speaker. Can anybody elaborate (and point me to data or simulation, please)? I'm also curious about the resonances and panel reflections in the MLTL compared with a ported box and how they color the sound.
~Tom
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If you've spent any time with MJKs worksheets you find out very quickly how driver placement can change drastically depending on your intended final result. Moving a the driver a few inches up or down can eliminate resonance bumps, odd freq spikes and tuning intensity. I'd start with Martin's ML TQWT worksheet and model your BR box in it. Then play with driver and port placement and you'll understand where I'm coming from. So short answer is it depends on what your end goals are.
Tom
Tom
For a quarter-wave TL, I fully understand that. The tuning of the TL relies on the driver placement. However, for a BR box, I don't believe it does. The BR does not rely on standing waves except in the port. That's why the port length matters.
At least that's how I understand it. I have lots of circuit design experience but practically no speaker building experience, so feel free to prove me wrong.
~Tom
Frankly, i'm not sure how I would prove you wrong as I have no written data to support my assertion but to think that driver placement has nothing to do with frequency response seems a mistake to me. All boxes function as though they were a TL to some degree. Placing a tuning device in a spot where frequencies reflect poorly or too intensely can make a difference in how effective said tuning device is. In other words, sound in a volume is not evenly distributed. Due to differing wavelengths of different frequencies transmitting from a point or close to a point source, predictable results can occur as to the location or thereabouts of those different frequencies. Therefore, a driver placed near or far from the port of a box, no matter it's dimension will produce different results. To look at it as you have stated seems to me to be treating sound like air. For example sound building up like air being pressurized results in a release of that air through a hole evenly. Sound simply doesn't function like this. Just my two cents! 🙂
Tom
Tom
A simple example of what I am referring to just occurred to me. It's a bit like setting up loudspeakers. Different frequencies are intensified depending on their distance from the source. If you stand in front of a corner placed loudspeaker and then move across the room, you can hear marked differences in how intense the bass tones are (all of them really but the bass is most noticeable). It's the same in the room that is your speaker box. There are ideal place,nets of both driver and port in a box. Finding those ideals is the tough parts!
Tom
Tom
Perhaps my choice of the word "prove" was poor. I didn't mean to be confrontational. But I am a stickler for data or explanations based in science.
In the equations and port calculators I've seen, all that was needed was the port area, enclosure volume, an tuning frequency. Then the length of the port could be calculated. This leads me to believe that placement isn't critical. That's not to say that it doesn't matter at all, it just doesn't factor into the tuning frequency of the port.
In TL designs, the driver placement is critical as it determines the length of the TL, hence, the tuning frequency.
Regardless... I think I'll try the TL design. Shred some plywood. See if I like it. 🙂
~Tom
In the equations and port calculators I've seen, all that was needed was the port area, enclosure volume, an tuning frequency. Then the length of the port could be calculated. This leads me to believe that placement isn't critical. That's not to say that it doesn't matter at all, it just doesn't factor into the tuning frequency of the port.
In TL designs, the driver placement is critical as it determines the length of the TL, hence, the tuning frequency.
Regardless... I think I'll try the TL design. Shred some plywood. See if I like it. 🙂
~Tom
This speaker has been around for a long time. IIRC the designer remains anonymous. For all of the technobabble, the cabinet itself is simply a end-loaded straight pipe stuffed until it acts like an infinite baffle.
Bob
Bob,
That was the conclusion I arrived at as well. It seems the mass loaded transmission line designs like the TABAQ and others, like the TLb, function as closed boxes (or infinite baffles?) above the quarter-wave frequency of the transmission line and get some help from the port to get low-frequency extension. Am I thinking about this the right way?
Now, is the LF extension caused by port emissions or is it due to the cabinet resonance increasing the response of the driver itself by allowing it to work more efficiently at the lower frequencies?
(Sorry if my questions are out in left field. I'm still trying to wrap my head fully around these transmission line speakers).
~Tom
That was the conclusion I arrived at as well. It seems the mass loaded transmission line designs like the TABAQ and others, like the TLb, function as closed boxes (or infinite baffles?) above the quarter-wave frequency of the transmission line and get some help from the port to get low-frequency extension. Am I thinking about this the right way?
Now, is the LF extension caused by port emissions or is it due to the cabinet resonance increasing the response of the driver itself by allowing it to work more efficiently at the lower frequencies?
(Sorry if my questions are out in left field. I'm still trying to wrap my head fully around these transmission line speakers).
~Tom
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I must apologize for seeming confrontational as well! That was not my intent. I understand your definition of a ported box but for whatever it's worth I believe that the placements for all elements in any speaker enclosure are important. I'd like to model your BR box design and see what happens when I move the elements around. Would you be interested in that experiment? If not I will pick a random design to work with. Thanks! 🙂
Hi,
Your'e almost right. The driver is loaded by the total volume below the quarter-wave frequency and as the box is longer than a quarter-wave for all frequencies above tuning: This is causing resonances seen in the output of the terminus or port together with eventual superimposed half wave port resonance if using a port with a low aspect ratio Diam/ Length <= ~0.3 b🙂
PS: The TABAQ Large ML-TL* is modeled in your room:
http://www.diyaudio.com/forums/full-range/237166-help-best-enclosure-2.html#post3522691
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