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Emotiva Airmotiv B1+ Review (Bookshelf Speaker)

ROOSKIE

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It's been suggested that shoving the port round the back minimises interference from the direct sounds from the front, but it appears not to be the case if these upper midrange resonances are screwing with an otherwise well behaved driver. Short of blocking the port either completely or with dense foam, thereby creating a 'controlled leak,' any ideas as to how these comparatively nasty midrange resonances can be better tamed while keepngat least some of the benefit?
Dense foam will create a sealed box. If it is a good fit. It won't be a controlled leak. Same as a cork in a wine bottle or a foam plug in olive oil. Nothing leaks.
These resonances are in the nature of porting the box. Where they are strongest and how strong they are is related to port length, box size and placement on the box.
It might be possible to tame them by adding some material/stuffing to the box as they are high enough in frequency (greater than 900/1000hz) to be reduced this way. Even reducing them by 3-6db would be great and very possible. It is possible that being a budget speaker this cabinet has no or very little/ineffective stuffing. Stuffing/thick lining will lower the tuning to some degree as well. It might also reduce the bass if over used. Try not to block the port with stuffing/thick lining.
If the speaker was well away from the wall the port resonance will be "reduced/delayed psycoacoustically filtered" in its ultimate effect as well - however so will bass reinforcement.
I can see using room absorbtion behind them if they are close to the wall, 900-1300hz can be treated.
Sealing the box will likely lower power handling by significant amounts unless highpassed fairly high (guessing 100-120 or maybe higher to reduce distortion to the minimum). So if you need real loud, then keep that in mind. The box will very likely be larger than optimal for a sealed size (as it was desined for the ported alignment) and thus the woofer will be less controlled than it would be in a smaller box. Plus the port helps the woofer out and mitigates excursion down to and around the tuning frequency, there is even a point where the woofer essentually stops moving in and out (minimum motion). If sealing you can try to remove any stuffing as this makes the box appear larger and you dont want that here since you actually would want a smaller box.
In any case someone would be wise to play around here. Looks awesome with only this port issue.
 
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thewas

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These resonances are in the nature of porting the box.
Port resonances can be reduced a lot with intelligent engineering:

KEF LS50 Meta - Dr Sebastien Degraeve 21-51 screenshot.png KEF LS50 Meta - Dr Sebastien Degraeve 23-51 screenshot.png KEF LS50 Meta - Dr Sebastien Degraeve 24-34 screenshot.png

Source
 

sarumbear

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I cannot for the life of me understand why speaker manufacturers place the vents at the centre of the baffle and use straight ports. Their approach will almost always cause a pipe resonance that we discuss on this forum ad infinitum.

The first pipe resonance will occur at F1 = C / ( 2 * L + 0.8 * D )

C: speed of sound (m/s)
L: vent length (m)
D: vent dia. (m)

By using this formula and entering the size of a range of small size (bookshelf) speakers on the market to a spreadsheet you can see that almost all of them will have a port resonance around 500 - 1000 Hz. Why would you allow that to happen if it is that obvious?

My answer would be because they don't know or they don't care!

A little bit of ingenuity should have shown that they can utilise the resonances that naturally occur in a rectangular box to reduce that resonance?

It is perfectly possible to position the internal opening of the vent at a null point of a standing wave inside the box. This will make the first pipe resonance frequency equal to that standing wave. As there is not much sound level at that location due to the standing wave null, the vent will not get "excited" and hence no prominent port resonance will occur.

Speaker design is not rocket science, nor is modern. I wonder if the manufacturers have wondered why are they filling their boxes with sound absorbent materials or heard the great work of the 19th century Harvard professor, Wallace Clement Sabine?

I hope that through the good work of @amirm manufacturers will pay attention and start to realise that speakers are designed not by eye but by knowledge, a little bit of ingenuity, and lots of trial and error through measurement. A select few manufacturer do just that. However, when it comes to mass manufactured models even they ignore the basics. Otherwise how can anyone explain B&W who can design a method to manage the rear loading of the twitter for their top models would fill the world with a million speakers that has audible port resonance by design?
 
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Ron Texas

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Nice inexpensive speaker from a reputable manufacturer. Too bad it's not available anymore. Thank you @amirm .
 

ROOSKIE

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@thewas
Yes of course.
Now how to deal with them in the B1+.
Moving the port to a better location on the box where the port is in a null(place where the strong resonant requecy is being canceled inside the box), making a new port out of the material KEF is using. I don't see these as options for the Emotiva user.
Your point though that an engineer can fix this before manufacture is deff true.
For now appropriate material added in the box and/or behind the speaker in room or sealing are good options to try.
They might work very well.
 

Bear123

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It's been suggested that shoving the port round the back minimises interference from the direct sounds from the front, but it appears not to be the case if these upper midrange resonances are screwing with an otherwise well behaved driver. Short of blocking the port either completely or with dense foam, thereby creating a 'controlled leak,' any ideas as to how these comparatively nasty midrange resonances can be better tamed while keepngat least some of the benefit?
I wonder if crossing to subs at 80 Hz to drastically reduce port output would reduce the affects of this 900 Hz resonance, or does it exist independently of port output?

Edited to pose as a question rather than a factual statement.
 
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Rottmannash

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Wonder how the towers perform.

The T0+ is $400/pair and adds another woofer. Sensitivity is rated 1dB higher. Port is much larger so hopefully it isn’t as noisy.

The T1+ is $700/pair and is a 3-way with a 5.25” midrange with phase plug and dual 6” woofers. Directivity is great on this B1+ without a phase plug, but the T1+ crosses it over 300Hz higher at 2700Hz and midrange plays down to 275Hz. Sensitivity is rated 2dB higher than B1+ and FR spec is 11Hz lower. 1 giant port on the back.

The T2+ is $1000/pair and swaps the dual 6” for dual 8”. The tweeter crossover is bumped up to 3200Hz (probably the real reason for the phase plug on the midrange) and midrange plays down to 350Hz, Stereophile measured the original T2 and directivity was good. Sensitivity is rated 5dB higher than the B1+ and FR spec is 13Hz lower. Oddly, still a singular port and it looks the same size as the T1+.

__________

I may put money on the T1+ being a better performer in terms of directivity, with the T2+ of course winning in bass and probably overall distortion.
May I ask, what is a "phase plug"?
 

ROOSKIE

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Cross to subs at 80 Hz to drastically reduce port output.
That does nothing to reduce a resonance at 1000hz.
That will only help with chuffing or similar port issue.
 

Bear123

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Nice inexpensive speaker from a reputable manufacturer. Too bad it's not available anymore. Thank you @amirm .
I think they are only temporarily out of stock. Seems the pandemic is still causing widespread outages on many types of goods.

Edit: just poked around on Emotiva site, and it literally says "temporarily unavailable"
 
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richard12511

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Directivity is very good although flatter than one would want in a hi-fi speaker (could sound a bit bright).

Can you expand on this a bit more? I went back and checked the Revel M105 and F208 reviews, and both those speakers seem to have slightly more flat(ie slightly wider dispersion) directivity, and those are about as optimized as it gets (blind tested) for hifi. Also, many of the pro speakers tested (ex: KH310) seem to have more tilted directivity.
 

Bear123

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That does nothing to reduce a resonance at 1000hz.
That will only help with chuffing or similar port issue.
You may be right, as I'm certainly not speaking from a position of expertise. I probably should have stated it more like "I wonder if.....". I was basing the idea on this:
1618149526981.png

Are you saying the port will cause the same resonance even if port output is reduced/eliminated with a crossover?
 

MZKM

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May I ask, what is a "phase plug"?
The “plug” in the center of the woofer. No clue how it works, but as frequency goes up, the dispersion narrows, a phase plug helps increase high frequency performance just like how a waveguide helps increase low frequency performance. Usually it’s meant to have a smoother crossover transition.
 

Bear123

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I just helped a buddy with some of his first audio purchases, and budget was VERY low. I had him get the Emotiva C1+ center channel which is a 3 way.....perhaps the cheapest 3 way center channel available(other than RC263 on fire sale). If the B1+ is any indication, it seems as though the C1+ may be a fantastic value for small, inexpensive, good center channel. I'd love to see more Emotiva stuff measured since the are all very low in cost:

Emotiva C2+ center channel....dual 6.5", 3 way, dual midrange, 92 dB sensitivity.....$400!!
 

DSJR

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Thanks for replies to my question above. I just felt the frontal response from the bass driver was being messed with by the port at the back, so any reduction in port misbehaviour must help the driver response at and around the upper hundred Hz. Lord, I wish I really knew what I was on about here, but little bits do get absorbed and mulled over, the connections forming nicely when repeatable proof is shown, so many thanks for taking the trouble :)
 

respice finem

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I cannot for the life of me understand why speaker manufacturers place the vents at the centre of the baffle and use straight ports... ...because they don't know or they don't care! ...I hope that through the good work of @amirm manufacturers will pay attention and start to realise that speakers are designed not by eye but by knowledge, a little bit of ingenuity, and lots of trial and error through measurement. A select few manufacturer do just that. However, when it comes to mass manufacturing models even they ignore the basics. Otherwise how can anyone explain B&W who can design a method to manage the rear loading of the twitter for their top models would fill the world with a million speakers that has audible port resonance by design?
This is even more interesting, considering that probably every major manufacturer today uses advanced software for their designs and manufacturing. It's IMHO reasonable to expect that such software would warn of basic mistakes, and the design must pass an internal audit as well as prototyping before going into production. So It must be on purpose, especially from manufacturers who "knew earlier how to do it better". The question is, why, because a flawed design isn't necessarily much cheaper to manufacture than a good one (at least in aspects as port form and placement). The only reasonable answer I can think of: the "pennies" which it will make it cheaper are of more value for them than good design = plain old greed, oh sorry, today it's called "profit maximization". :rolleyes:

A similar question, why, in this day and age, there are relatively few non-ported designs combined with a matching sub. There were some in the 80s, and strangely died out... Maybe because 2.1 seemed more expensive to the customer than 2.0 and marketing told him 2.0 is as good?
 
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sarumbear

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respice finem

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They care - for their profit... Only a DIYer or small newcomer may not know IMHO.
 

ROOSKIE

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You may be right, as I'm certainly not speaking from a position of expertise. I probably should have stated it more like "I wonder if.....". I was basing the idea on this:
View attachment 123388
Are you saying the port will cause the same resonance even if port output is reduced/eliminated with a crossover?
Yes because the high pass is only cutting frequency responce around and below the HP frequency.
The driver is still playing 1000hz notes just as loudly.
The resonance is similar to a room mode. The speaker box is a tiny room and accentuates/reinforces certains frequency content.
3/4/5 way speakers or subwoofers where the resonance of the box is above the low pass cutt off for the ported bass unit will not have the same issues. This is a good reason for 3 ways. Although one can still have issues if the port resonances are low like 300/400hz and the woofer is still playing there. Especially as box stuffing/lining will not help with 300hz notes.
 
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