Importance of enclosure design / volume.

[pastedavid]

Hello.

I have a pair of Heybrook Prima loudspeakers which I have connected to my television - a good upgrade from the internal units.

I also had a pair of small (150mm x 90mm) Blaupunkt car speakers salvaged from a car going to scrap. I had various plans for them, but ultimately they ended up in sealed cabinets of approximately 100 litres which were made for something else but never used. This paring was more out of curiosity than anything else.

Now clearly there was no proper 'designing' of these cabinets for these speakers, so I wasn't expecting much, but they have surprised me. The bass qualities of these little speakers is, after a long time listening (greater than 4 months) very definitely better (to my ears, obviously - subjectivism and all that) than the Heybrook Primas, although they have a larger cone area & a properly designed enclosure.

My question is: If I had the relevant information (I have looked but cannot find it) what difference would there be in sound reproduction for these little Blaupunkt speakers if they were in more appropriately sized enclosures over the current sealed 100 litre ones?

As a follow on: What differences would you generally expect to hear if a good quality loudspeaker with known T/S parameters if it was put into an enclosure of a size significantly above or below it's optimum design volume or type (sealed / ported, etc).

Thanks in advance,

David.

[gedlee]

Originally Posted by pastedavid

What differences would you generally expect to hear if a good quality loudspeaker with known T/S parameters if it was put into an enclosure of a size significantly above or below it's optimum design volume or type (sealed / ported, etc).

Thanks in advance,

David.

I would say that in a real room the T/S frequency range and the enclosure design are going to be dominated by the room - that makes them relatively unimportant to irrelavent. I don;t even look at T/S values and cabinet size in any of my designs because the techniques that I use for sound in the "room modal region" makes these parameters completely irrelavent. In speaker design sound quality is all above a few hundered Hz, below that its all room design and speaker architecture.

[WithTarragon]

Well, not everyone will agree with the above statement, (even with the caveat about being above the cut off frequency).

Yes, I agree that the sound at the listener will be a convolution of the cabinet's response and the room's response.

I would abide by the recommended geometry especially if the design is a ported cabinet, horn loaded cabinet or a TL cabinet.

If there is a specific problem, there may be a way to "change" the specs on the driver or to effectively change (after the cabinet was built) the port length (via flaring) or its volume (with fiberglass stuffing) etc.

Where is the mis-match?

[leadbelly]

So because you put some car speakers which are typically designed for large Vas into some relatively large cabinets you had lying around and got good results, the whole field of speaker design is now in question?

[event horizon]

Originally Posted by pastedavid

My question is: If I had the relevant information (I have looked but cannot find it) what difference would there be in sound reproduction for these little Blaupunkt speakers if they were in more appropriately sized enclosures over the current sealed 100 litre ones?

As a follow on: What differences would you generally expect to hear if a good quality loudspeaker with known T/S parameters if it was put into an enclosure of a size significantly above or below it's optimum design volume or type (sealed / ported, etc).

I'm not familiar with your drivers but a 6" x 4" isn't going to require a large sealed enclosure that's for sure. A lot depends on the drivers Qts or total Q & as they are really just fairly cheap car speakers i'd guess & say that they'll likely be fairly high. When i say that i mean having a Qts of above 0.383.

Driver free air resonance is also likely to be fairly high as in a lot of car installations they are not used in any kind of sealed enclosure, so it'd need to be highish to avoid overload on deep bass.

You could probably drop them into 20L cabinets or less & not notice a difference in bass quality. Saying that there would be far less enclosure to excite so quality may well improve

On the subject of bass drivers generally.

In a sealed box if the enclosure is made to be much larger than needed the response in the bass region will roll off from a frequency that might approach 100Hz but it'll do so very gradually & Qcb (closed box Q) will likely be low. This will result in a rather lean bass response but very good transient response indeed. If placed in too small an enclosure there will be a peak in bass response at & around the resonance frequency & a rapid rolloff just below resonance & then below this it'll gradually revert to a 12Db/octave rolloff. Transient response will suffer & there will be some overhang or boominess to the bass. Simply put the driver can't stop & start as quickly when fed a signal.


In a reflex things get more problematic. It all depends on the frequency that the enclosure is tuned to in comparison to the drivers Qts. Assuming you know this & design an enclosure that approximates a flat response & then make the enclosure larger but keep the tuning frequency the same you'll get a big peak produced at the enclosure resonance frequency which is port output. Bad transient response

Too small & again there will be a peak but at the driver resonance frequency & the response will roll off similar to a sealed box with high Q until things go out of phase with the port. Interestingly the phase change that the port introduces is spread much wider when the driver is in a box that quite a bit too small. Port velocity is also lower. It won't go out of phase until it's quite a bit below the port tuning frequency.

Hope that helps, probably raised more questions than it has answered though

Bests, Mark.

[jonkun227]

Yes, that's exactly what he said. Man, I love it when someone, myself included, asks an intelligent question in an attempt to learn, and someone gives a condescending reply. I know it always makes me want to learn and ask more!

OP: in my experience, which largely consists of playing around with car speakers I pick up at amazing rates in home enclosures of my own design, you really have to be picky for the specs to make much difference. This is ENTIRELY my own subjective evaluation of my own creations.

I've found that driver and amp selection are an order of magnitude more important than the precise size and shape of the enclosure. Still, understanding the effects of basic geometry considerations are important, including perpendicular sides and parallel back and rounded versus square corners and all that.

I make a mockup out of fomecore or styrofoam and masking tape first. If I like the proportions I build it out of particleboard and install the drivers and see how it sounds. Sometimes I call it good and finish up the particleboard construction with sanding and painting. Other times I duplicate it in mdf for an even better finish. And sometimes I scrap the design altogether because it just didn't feel right.

Bottom line: unless you are trying to impress guys who get seriously turned in at the mention of the performance statistics, just make something that works for you. Don't be afraid to throw away a rough draft or two. My next door neighbor growing up, a woman in her 70s or 80s, taught me this. When she was first married she had her husband buy her hundreds of pounds of flour which she went through fairly quickly, throwing away much of what she made until she figured out the best way to make bread. If you asked her for her recipe she couldn't have told you to save your life. She just knew when it was right from all of that experience.

Hopefully this diatribe has helped?


- Jon

[jonkun227]

Sorry, Mark. Looks like you posted while I was still writing. That wasn't directed at you.

[event horizon]

Originally Posted by jonkun227

Sorry, Mark. Looks like you posted while I was still writing. That wasn't directed at you.

No worries, i already worked that one out

[gedlee]

Originally Posted by WithTarragon

Well, not everyone will agree with the above statement, (even with the caveat about being above the cut off frequency).

Yes, I agree that the sound at the listener will be a convolution of the cabinet's response and the room's response.

Thats fine. So you don't agree that in this "convolution" that the room will dominate the situation?

[limono]

Originally Posted by gedlee

Thats fine. So you don't agree that in this "convolution" that the room will dominate the situation?

Does this mean that you deliberatly design speakers without extended LF leaving final user choice of bass solution,because "it cannot be done" without given room in equasion? I really like that thinking.