I am in the middle of modifying a W-King D8 portable boom box (I'm adding some jack connectors to be able to connect external speakers). The speaker has a stereo pair of woofers and tweeters, divided in the middle of the speakers into separate, unconnected sides. This is the D8: https://images-na.ssl-images-amazon.com/images/G/01/apparel/rcxgs/tile._CB483369110_.gif
The speaker has a bit of a frequency response spike around 57.5Hz and 115Hz (B-flat 1 and B-flat 2 are noticeably boomy indoors, but not so much outdoors). When reassembling it, I thought about removing the division and another internal divider separating the electronics, to see if it would make any difference to the resonant frequency of the woofers. Based on what theory I have read, I also figured though that there would be be more cancellation of any slightly out of phase left and right bass signal if the woofers share the same enclosure space (stereo bass signals and drum signals in music are often slightly out of phase).
However I've just seen a few speakers, including the newer version of this same speaker (W-King D9), which share the same passive radiator, and thus presumably the same enclosure space.
https://m.media-amazon.com/images/S...20f18a0a9.__CR0,0,300,300_PT0_SX300_V1___.jpg
https://m.media-amazon.com/images/S...fd119dfdd.__CR0,0,970,600_PT0_SX970_V1___.jpg
The D9 has a better bass response and power output than the D8, so now I'm wondering how much of a difference the existing division in my D8 is likely to make regarding avoiding phase cancellation inside the box. Can anyone share some wisdom on this?
The speaker has a bit of a frequency response spike around 57.5Hz and 115Hz (B-flat 1 and B-flat 2 are noticeably boomy indoors, but not so much outdoors). When reassembling it, I thought about removing the division and another internal divider separating the electronics, to see if it would make any difference to the resonant frequency of the woofers. Based on what theory I have read, I also figured though that there would be be more cancellation of any slightly out of phase left and right bass signal if the woofers share the same enclosure space (stereo bass signals and drum signals in music are often slightly out of phase).
However I've just seen a few speakers, including the newer version of this same speaker (W-King D9), which share the same passive radiator, and thus presumably the same enclosure space.
https://m.media-amazon.com/images/S...20f18a0a9.__CR0,0,300,300_PT0_SX300_V1___.jpg
https://m.media-amazon.com/images/S...fd119dfdd.__CR0,0,970,600_PT0_SX970_V1___.jpg
The D9 has a better bass response and power output than the D8, so now I'm wondering how much of a difference the existing division in my D8 is likely to make regarding avoiding phase cancellation inside the box. Can anyone share some wisdom on this?
Attachments
Last edited:
First picture is a 'tile' pattern.
LF standing waves are much too long to fit in such a small box, so just based on external dims to give an approximation: ~13543"_secs/2/12.5" = ~546 Hz and if divided in two, then ~1092 Hz, both in the midrange, and will be even higher in frequency since internal dims will be smaller.
In short, frequencies below these points will increasingly become just a pressure zone of increasingly uniform particle density, though hopefully the division is sufficient to keep these critical mids, HF from cross talking enough to audibly degrade speech intelligibility.
LF standing waves are much too long to fit in such a small box, so just based on external dims to give an approximation: ~13543"_secs/2/12.5" = ~546 Hz and if divided in two, then ~1092 Hz, both in the midrange, and will be even higher in frequency since internal dims will be smaller.
In short, frequencies below these points will increasingly become just a pressure zone of increasingly uniform particle density, though hopefully the division is sufficient to keep these critical mids, HF from cross talking enough to audibly degrade speech intelligibility.
THrough the middle of the speaker, separating the left and right speaker pairs. You can't see it in that photo becasue the divider is part of the other side of the box. When you glue it back together the divider goes in between the speakers you see in the photo there.
Are you saying that phase cancellation can only occur inside the enclosure if there are standing waves present inside it? Why would that be the case? If the two woofers are, for argument's sake, wired in opposite polarity, making them 180 out of phase, then my understanding was that their pressure waves (eg from a bass signal) destructively interfere inside the enclosure, regardless whether any standing waves are set up inside it.
Last edited:
So what's the deal with these boom boxes which don't separate the left and right channel woofers into separate compartments (eg. D9 above, Oontz Angle 3, etc?)
http://gadgetsin.com/uploads/2019/0...e_waterproof_portable_bluetooth_speaker_2.jpg
With these speakers is there just a recognition that some clarity will be lost as a result of some frequency ranges destructively interefering inside the enclosure? If this is the case why do thye not simply divide the enclosure?
http://gadgetsin.com/uploads/2019/0...e_waterproof_portable_bluetooth_speaker_2.jpg
With these speakers is there just a recognition that some clarity will be lost as a result of some frequency ranges destructively interefering inside the enclosure? If this is the case why do thye not simply divide the enclosure?
Which frequency ranges are you talking about? There is probably less interference than you are stating.
I made various different observations coinciding on B flat being the spike (or the most notable one at least). The one's I remember are below.
Firstly, I use the boom box as a portable amp for guitar and piano, or whatever instrument we have. I quicly noticed the boominess when b-flat (and to a lesser degree A natural and B natural) are played on the different instruments. I then micd up two rooms (to rule out room acoustics) and ran them through a spectrum analyser and got the spikes at A/B-flat (I did a frequency sweep if I remember correctly). Also found the same boominess in open spaces.
Also I checked for reviews of the speakers online with frequency response analyses and found a couple. They both have spikes around 110Hz, 220Hz, corresponding to fundamental and parcials of A/B-flat. Eg:
Last edited:
I was replying to GM's post where he/she said there will be some degree of critical mids and HF cross talking, but hopefully not enough to audibly degrade speech intelligibility.
I'd be finding the reason for the peaks. Try hitting it with an oscillator. Maybe the cabinet is vibrating.
What do you mean by hit it with an oscillator? Do you mean feed a sine tone into it and see how it sounds by sweeping ti through the frequency range? I've already done that. That's partly how I know about the spikes at b-flat.
Here's another speaker with stereo pair NOT separated into separate enclosures, and with a shared passive radiator.
http://gadgetsin.com/uploads/2019/0...e_waterproof_portable_bluetooth_speaker_2.jpg
Can anyone provide some insight into the second question and clarification of the first question? With a view to removing the divider in my D8, I'm wondering what the design rationale is with the speakers where the left and right woofers share the same single enclosure space, like the ones listed above. Is there an acceptance that some phase cancellation/destructive interference will occur inside the enclosure as a result of this? Is there some advantage conferred from only having one enclosure which compensates for this, perhaps lower resonant frequency of the drivers (due to larger enclosure volume), or something like this, perhaps giving a boost to bass signal at the expense of clarity?
http://gadgetsin.com/uploads/2019/0...e_waterproof_portable_bluetooth_speaker_2.jpg
Can anyone provide some insight into the second question and clarification of the first question? With a view to removing the divider in my D8, I'm wondering what the design rationale is with the speakers where the left and right woofers share the same single enclosure space, like the ones listed above. Is there an acceptance that some phase cancellation/destructive interference will occur inside the enclosure as a result of this? Is there some advantage conferred from only having one enclosure which compensates for this, perhaps lower resonant frequency of the drivers (due to larger enclosure volume), or something like this, perhaps giving a boost to bass signal at the expense of clarity?
I can't feel for anything now because it's disassembled, but it's not a rattling type spike sound. It's boomy. From handling it before I know it's not caused by loose panels. Perhaps the resonant frequency of one or more of the panels could be around 115Hz, or the resonant frequency of the drivers (this is one reason I thought removing the divide might reduce that 115Hz spike, given that the resonant frequency of the drivers will change as the enclusore volume changes).
Not per se, but unless times have changed; broadcast, recordings have historically been summed mono below ~120 Hz, so any minor phase changes to make a stereo recording will sum (comb filter) to a mean, ergo from a technical POV there will be some +/- phase cancellation, though offset with as much/more + summing that due to how we hear is what our brain will zero in on, rendering the -/nulls moot unless they're broadband enough to perceptibly alter the summed BW and even then normally only in our acute hearing BW:
https://alexiy.nl/eq_chart/ear_sensitivity.htm
So all things considered, in an acoustically small cab combined with driver closeness relative to our acute hearing BW this is 'much ado about nothing'. 😉
PS: Born n' bred in the USA and Southern by the Grace of God male in every way for better or worse depending on one's POV. 😉
Last edited:
Super interesting. I didn't know this. This applies to most commercially produced music?
NOt catching the idea here. I'm familiar with ear sensitivty curves but I'm not sure how what your saying here relates specifically to my question about volume lost as a result of phase cancellation of sound inside the enclosure.
Was baffled by this until I realized what confusion of mine it was a response to.😆
Don't know for sure if industry wide and why I said 'historically' since my 'insider' source went away when Altec was broken up, but see no reason to make it stereo except maybe for the bass/electronic music popular today, but your speaker can't reproduce it, so a moot point.
Frankly, your Q didn't make much sense to me since stereo only adds +3 dB, but summing can be up to +6 dB based on how close the drivers are relative to their 1/4 - 1 WL spacing in Hz.
As for hearing acuity, we only need a flat 250-2500 Hz BW for analog phones, public address systems (PA) and 300-3000 Hz for digital for high speech intelligibility with HF out 7-8 kHz for basic HiFi so above and particularly below, these just need to be reasonably flat with no deep broadband dips or big spikes to 'distract' us, though many like a bit of boost in the sibilant BW to help with 'clarity' and why so many drivers have it built in.
Frankly, your Q didn't make much sense to me since stereo only adds +3 dB, but summing can be up to +6 dB based on how close the drivers are relative to their 1/4 - 1 WL spacing in Hz.
As for hearing acuity, we only need a flat 250-2500 Hz BW for analog phones, public address systems (PA) and 300-3000 Hz for digital for high speech intelligibility with HF out 7-8 kHz for basic HiFi so above and particularly below, these just need to be reasonably flat with no deep broadband dips or big spikes to 'distract' us, though many like a bit of boost in the sibilant BW to help with 'clarity' and why so many drivers have it built in.
I'm not sure why you say this. The D8 has a left/right pair of tweeters and woofers and true stereo processing. Are you saying it can't produce stereo, or low bass, or something else? The low frequency response is listed as 50Hz.
Confused by this as well. What are you referring to here? I haven't indicated the Q of my system (?). Are you referring to the peaks I mentioned?
I'm familiar with sensitivity curves and speech frequency ranges but how does this relate to my issue? Are you saying the frequency response of the D8 (based on the links I have put up) is strange/uneven?
He's saying that the box is too little, the speakers are not spaced enough to appreciate a sensible difference if stereo program allows, and that after all those don't determine a really bad performance since speech & telephone band have their own BW (!?!)...