Hi there,
finally after a long, long time I'm able to toy around with audio!
I want to build a simple vented speaker design (17l enclosure, port tuned to 40 Hz) and adapt it to work as bookshelf speaker.
In the shelf, the speaker is about 1m from the floor, but integrated in the shelf it has no distance from the "rear" wall (as it is flush with the shelf). Also sidewalls/corners are within 0.5m or so, so there will be a strong bass boost (at least 6db) due to these conditions.
To put a speaker into a book shelf is a difficult and suboptimal location, but it certainly occurs very often in real life. Nevertheless I cannot find much design info about that online.
I thought of building the speaker as closed design to cope with this bass boost.
What are your thoughts about this?
How do you design speakers for use in book shelves?
finally after a long, long time I'm able to toy around with audio!
I want to build a simple vented speaker design (17l enclosure, port tuned to 40 Hz) and adapt it to work as bookshelf speaker.
In the shelf, the speaker is about 1m from the floor, but integrated in the shelf it has no distance from the "rear" wall (as it is flush with the shelf). Also sidewalls/corners are within 0.5m or so, so there will be a strong bass boost (at least 6db) due to these conditions.
To put a speaker into a book shelf is a difficult and suboptimal location, but it certainly occurs very often in real life. Nevertheless I cannot find much design info about that online.
I thought of building the speaker as closed design to cope with this bass boost.
What are your thoughts about this?
How do you design speakers for use in book shelves?
Why not front port it?
Bigger than you are looking at but give you some ideas.
Bookshelf-3WC
These are pretty close to your outline spec.
Studio-101-mkII
Note - these are closed designs but will give an idea as to what is possible.
Bigger than you are looking at but give you some ideas.
Bookshelf-3WC
These are pretty close to your outline spec.
Studio-101-mkII
Note - these are closed designs but will give an idea as to what is possible.
The problem is that what you consider bass boost is not what really happens. If the speaker is "buried" in the library, you are effectively approaching the infinite wall condition. In this case every speaker designed for free field will sound bass heavy because all frequencies below the transitions from 4pi to 2pi will be gradually incremented in SPL, no matter if the enclosure is vented or closed. In this case you should find a speaker designed for in wall mount. One example is here: Zaph|Audio - ZA5 Speaker Designs with ZA14W08 woofer and Vifa DQ25SC16-04 tweeter
The other alternative for a speaker explicitly designed for bookshelf use is the already mentioned one: Bookshelf-3WC
Modding a speaker for bookshelf use means coping with the primary coil in order to reduce the baffle step compensation that was chosen in the original design. Consequently you need to alter the tweeter output, something easier if there is an L-pad. All in all not an easy task.
Ralf
Ralf is completely right. The bass extension on behalf of the chosen resonant system (closed or BR or even TL) has nothing to do with the directivity of the speaker. In your case there will be (almost) no baffle step, other than some comb filtering due to phase differences between direct sound and reflected sound from the back wall. You can manage that by choosing a wide baffle design combined with a controlled dispersion of high frequencies (e.g, by using a waveguided tweeter). Anyhow, there are quite a few on-wall designs to be considered. Like the WaveWall from Heissmann.
Doesn't that depend on the size of the shelf?
Back in the day it was common for "Bookshelf" speakers to use 8inch woofers and a 200mm woofer can do 40Hz, perhaps not at high volumes but doable.
I used to own IMF Super compacts, and mine did indeed sit on our bookshelves and they did play bass reasonably in a small room. These days you could use a good 155mm woofer and exceed the spec of the small IMF
Super Compact - IMF electronics
17 litres is a bit small tho, get bigger books which need deeper shelves
Sorry, should have been clearer, by "closed designs" I meant that the crossover designs were not available publicly, you have to buy the kit from Jantzen, as opposed to a closed box vs. vented box.
The 3wc kit is designed for use in a bookcase with front vent and a crossover that is designed for 2pi space wrt baffle step. at 1045 euro for the kit (plus wood and time) it is fairly good value but is a little larger at around 25l.
Hi there,
many thanks for your replies...however, I'm a bit puzzled now.
I guess my original post was not really clear, sorry.
I want to use a simple ported design (it uses a full range transducer, no crossover) and close the port (or, in other words, do not install the originally intended port), but keep dimensions.
Without port, bass output of the speaker is reduced naturally and rolls off earlier.
And that was my intention to help with the bass boost due to the bookshelf radiation conditions.
Sorry for the confusion!
many thanks for your replies...however, I'm a bit puzzled now.
I guess my original post was not really clear, sorry.
I want to use a simple ported design (it uses a full range transducer, no crossover) and close the port (or, in other words, do not install the originally intended port), but keep dimensions.
Without port, bass output of the speaker is reduced naturally and rolls off earlier.
And that was my intention to help with the bass boost due to the bookshelf radiation conditions.
Sorry for the confusion!
Again many thanks for your kind replies!
I'm not looking for designs fitting the purpose, but to make the intended design a little bit better fitting to this originally not intended location.
The designs by Troels are excellent, though.
I'm not looking for designs fitting the purpose, but to make the intended design a little bit better fitting to this originally not intended location.
The designs by Troels are excellent, though.
The IMF you show is -6dB @ 40 Hz. Convention uses the -3dB as the cut off point.
The garage that maintains my car has a rack with shelves with motor blocks and gear boxes. Those shelves would be large enough, but again, as per convention ....
Again, it seems you don't know how the baffle step works. The baffle step effect works in the 100-1000 Hz range (exact numbers depend on the baffle width), and affect every speaker in free space, and for this reason a speaker needs a correction for the effect to work with a flat response in free space. If you intend to use a speaker in a bookshelf you will minimize the effect. OTOH a speaker with a driver only without a crossover will benefit from being in a infinite wall or like condition, as its output in the baffle step effect range will remain flat.
Having a port or not in an enclosure affect only the sub 100 Hz frequencies, so this choice has nothing to do with the placement.
The choice for a vent is dictated by the need of the bass extension and the roll-off desired. Moreover some drivers work best in a bass reflex enclosure, some other in a closed box, depending on their TS parameters. For a given driver the closed box is always smaller than the vented one, so simply building a closed box with the same volume as the optimal vented box is not the best you can do.
Can you share the design you want to adapt and the driver it uses?
Ralf
Hi Ralf,
many thanks for your kind post!
I fully agree with your comments on the baffle step.
Honestly I was not thinking at all about the baffle step as in this design the transducer is not corrected at all so it does whatever it wants.
I'm sorry I do not understand this.
The more distance a speaker has from walls/floor the more its output will become similar to free field conditions.
Put a speaker right into a corner (eigth space) and bass will increase largely (compared to infinite baffle response) as also the bass is forced to radiate "directionally" (for the lack of a better term). Putting a speaker into a book shelf with a close corner/side wall pretty much resembles this situation.
Of course! Many thanks for your interest!
It is this design:
http://wodendesign.com/downloads/simpleReflex-103-10p-plan-100214.pdf
with an Alpair 10.3 transducer.
I'm well aware that the T/S parameters indicate a vented box for this speaker.
Smaller is not better for my application as size is given by the book shelf.
Thank you!
many thanks for your kind post!
I fully agree with your comments on the baffle step.
Honestly I was not thinking at all about the baffle step as in this design the transducer is not corrected at all so it does whatever it wants.
I'm sorry I do not understand this.
The more distance a speaker has from walls/floor the more its output will become similar to free field conditions.
Put a speaker right into a corner (eigth space) and bass will increase largely (compared to infinite baffle response) as also the bass is forced to radiate "directionally" (for the lack of a better term). Putting a speaker into a book shelf with a close corner/side wall pretty much resembles this situation.
Of course! Many thanks for your interest!
It is this design:
http://wodendesign.com/downloads/simpleReflex-103-10p-plan-100214.pdf
with an Alpair 10.3 transducer.
I'm well aware that the T/S parameters indicate a vented box for this speaker.
Smaller is not better for my application as size is given by the book shelf.
Thank you!
You go wrong here in assuming it's only true for bass frequencies. It is essentially true for every frequency which has a wavelength that is bigger than (about) double the distance of the speaker cone to the wall. So if that would be -say- 20cm, the effect will be there up til approx 800Hz. That is not bass, play a b (the one above C) on a keyboard or listen to a tone generator.
I perfectly agree!
I'm sorry that my wording is not more accurate.
I do not claim that my suggestion is high-end nor that it is a clean and full solution to this issue.
It was just an idea I had to remedy this special situation with minimum effort - of course it should clearly be an improvement in comparison to building the vented box and put it into the shelf.
Of course I would love to hear any ideas that might give more improvement!
The Alpair will perform poorly in a closed box. The vented box is clearly the best option.
What you should do is to put books around the speaker, to minimize the infinite wall situation. And IMHO in this way the situation can be seen as an improvement of the original design, which doesn't address the baffle step effect and thus is bass (and midrange) thin.
Ralf
What you should do is to put books around the speaker, to minimize the infinite wall situation. And IMHO in this way the situation can be seen as an improvement of the original design, which doesn't address the baffle step effect and thus is bass (and midrange) thin.
Ralf
Thanks for your thoughts!
What is the reason for this? What does it mean technically (sorry I'm an engineer)?
I keep reading many times that Qts of 0.3 means best suited for a vented box. So far I haven't seen an explanation for that.
What is the reason for this? What does it mean technically (sorry I'm an engineer)?
I keep reading many times that Qts of 0.3 means best suited for a vented box. So far I haven't seen an explanation for that.
Download Unibox and simulate yourself what happens with the intended enclosure (vented and closed).
Ralf
Ralf
Doing a few calculations it appears to me that these general rules - use a driver with Qtc=0.3 in a vented box - might have a rather simple reason?
With qtc=0.3 there is simply enough distance to a target tuning of (usually) 0.71 left so that a vented box would work.
Otherwise I have not understood why a qtc=0.3 driver would not work in a sealed box.
With qtc=0.3 there is simply enough distance to a target tuning of (usually) 0.71 left so that a vented box would work.
Otherwise I have not understood why a qtc=0.3 driver would not work in a sealed box.
The TS parameters are a set of parameters aimed to simulate the low frequency performance of a driver. An explanation is out of question here.
Using Unibox to simulate the 17L vented cab you want to build yield this:
The same 17L but closed is this:
A better closed box is a 4L enclosure:
The summary: the Alpair driver with its Qts can't produce bass in a closed box of any volume. The best closed box of only 4L is useful for an integration with a sub, with a F6 point of roughly 75Hz, whereas the 17L closed box has a rolloff starting at 300+ Hz, and very poor handling as it will exceed xmax at 45Hz with 16W of applied power. The vented box of 17L tuned to 40Hz provides useful bass and good power handling as it will exceed xmax at 35Hz with 32W of applied power.
Ralf
Using Unibox to simulate the 17L vented cab you want to build yield this:
The same 17L but closed is this:
A better closed box is a 4L enclosure:
The summary: the Alpair driver with its Qts can't produce bass in a closed box of any volume. The best closed box of only 4L is useful for an integration with a sub, with a F6 point of roughly 75Hz, whereas the 17L closed box has a rolloff starting at 300+ Hz, and very poor handling as it will exceed xmax at 45Hz with 16W of applied power. The vented box of 17L tuned to 40Hz provides useful bass and good power handling as it will exceed xmax at 35Hz with 32W of applied power.
Ralf
